Qiangrong Liang - Academia.edu (original) (raw)

Papers by Qiangrong Liang

Research paper thumbnail of Comprehensive lipidomic profiling in serum and multiple tissues from a mouse model of diabetes

Metabolomics, 2020

Introduction Diabetes mellitus is a serious metabolic disorder causing multiple organ damage in h... more Introduction Diabetes mellitus is a serious metabolic disorder causing multiple organ damage in human. However, the lipidomic profiles in different organs and their associations are rarely studied in either diabetic patients or animals. Objectives To evaluate and compare the characteristics of lipid species in serum and multiple tissues in a diabetic mouse model. Methods Semi-quantitative profiling analyses of intact and oxidized lipids were performed in serum and multiple tissues from a diabetic mouse model fed a high fat diet and treated with streptozotocin by using LC/HRMS and MS/MS. The total content of each lipid class, and the tissue-specific lipid species in all tissue samples were determined and compared by multivariate analyses. Results The diabetic mouse model displayed characteristic differences in serum and multiple organs: the brain and heart showed the largest reduction in cardiolipin, while the kidney had the most remarkable alterations in triacylglycerol. Interestingly, the lipidomic differences also existed between different regions of the same organ: triacylglycerol species with shorter fatty acyl chains decreased in renal medulla but increased in cortex; cardiolipin species with highly polyunsaturated fatty acyls decreased only in atrium but not in ventricle. Importantly, diabetes caused an accumulation of lipid hydroperoxides, suggesting that oxidative stress was induced in all organs except for the brain during the development of diabetes. Conclusion These findings provided novel insight into the organ-specific relationship between diabetes and lipid metabolism, which might be useful for evaluating not only diabetic tissue injury but also the effectiveness of diabetic treatments.

Research paper thumbnail of Mitochondrial quality control in the diabetic heart

Journal of Molecular and Cellular Cardiology, 2016

Diabetes is a well known risk factor for heart failure. Diabetic heart damage is closely related ... more Diabetes is a well known risk factor for heart failure. Diabetic heart damage is closely related to mitochondrial dysfunction and increased ROS generation. However, clinical trials have shown no effects of antioxidant therapies on heart failure in diabetic patients, suggesting that simply antagonizing existing ROS by antioxidants is not sufficient to reduce diabetic cardiac injury. A potentially more effective treatment strategy may be to enhance the overall capacity of mitochondrial quality control to maintain a pool of healthy mitochondria that are needed for supporting cardiac contractile function in diabetic patients. Mitochondrial quality is controlled by a number of coordinated mechanisms including mitochondrial fission and fusion, mitophagy and biogenesis. The mitochondrial damage consistently observed in the diabetic hearts indicates a failure of the mitochondrial quality control mechanisms. Recent studies have demonstrated a crucial role for each of these mechanisms in cardiac homeostasis and have begun to interrogate the relative contribution of insufficient mitochondrial quality control to diabetic cardiac injury. In this review, we will present currently available literature that links diabetic heart disease to the dysregulation of major mitochondrial quality control mechanisms. We will discuss the functional roles of these mechanisms in the pathogenesis of diabetic heart disease and their potentials for targeted therapeutical manipulation.

Research paper thumbnail of Autophagy and mitophagy in diabetic cardiomyopathy

Biochimica et biophysica acta, 2015

Diabetic cardiomyopathy is a heart muscle-specific disease that increases the risk of heart failu... more Diabetic cardiomyopathy is a heart muscle-specific disease that increases the risk of heart failure and mortality in diabetic patients independent of vascular pathology. Mitochondria are cellular power plants that generate energy for heart contraction and concurrently produce reactive oxygen species that, if unchecked, may damage the mitochondria and the heart. Elimination of damaged mitochondria by autophagy known as mitophagy is an essential process for maintaining normal cardiac function at baseline and in response to various stress and disease conditions. Mitochondrial structural injury and functional impairment have been shown to contribute to diabetic heart disease. Recent studies have demonstrated an inhibited autophagic flux in the hearts of diabetic animals. Surprisingly, the diminished autophagy appears to be an adaptive response that protects against cardiac injury in type 1 diabetes. This raises several questions regarding the relationship between general autophagy and s...

Research paper thumbnail of Cardiac expression of ms1/STARS, a novel gene involved in cardiac development and disease, is regulated by GATA4

Molecular and cellular biology, 2012

Ms1/STARS is a novel muscle-specific actin-binding protein that specifically modulates the myocar... more Ms1/STARS is a novel muscle-specific actin-binding protein that specifically modulates the myocardin-related transcription factor (MRTF)-serum response factor (SRF) regulatory axis within striated muscle. This ms1/STARS-dependent regulatory axis is of central importance within the cardiac gene regulatory network and has been implicated in cardiac development and postnatal cardiac function/homeostasis. The dysregulation of ms1/STARS is associated with and causative of pathological cardiac phenotypes, including cardiac hypertrophy and cardiomyopathy. In order to gain an understanding of the mechanisms governing ms1/STARS expression in the heart, we have coupled a comparative genomic in silico analysis with reporter, gain-of-function, and loss-of-function approaches. Through this integrated analysis, we have identified three evolutionarily conserved regions (ECRs), α, SINA, and DINA, that act as cis-regulatory modules and confer differential cardiac cell-specific activity. Two of these...

Research paper thumbnail of Targeted inhibition of calcineurin attenuates cardiac hypertrophy in vivo

Proceedings of the National Academy of Sciences, 2001

The Ca 2+ -calmodulin-activated Ser/Thr protein phosphatase calcineurin and the downstream transc... more The Ca 2+ -calmodulin-activated Ser/Thr protein phosphatase calcineurin and the downstream transcriptional effectors of calcineurin, nuclear factor of activated T cells, have been implicated in the hypertrophic response of the myocardium. Recently, the calcineurin inhibitory agents cyclosporine A and FK506 have been extensively used to evaluate the importance of this signaling pathway in rodent models of cardiac hypertrophy. However, pharmacologic approaches have rendered equivocal results necessitating more specific or genetic-based inhibitory strategies. In this regard, we have generated Tg mice expressing the calcineurin inhibitory domains of Cain/Cabin-1 and A-kinase anchoring protein 79 specifically in the heart. ΔCain and ΔA-kinase-anchoring protein Tg mice demonstrated reduced cardiac calcineurin activity and reduced hypertrophy in response to catecholamine infusion or pressure overload. In a second approach, adenoviral-mediated gene transfer of ΔCain was performed in the adu...

Research paper thumbnail of Thyroid Hormone Promotes Remodeling of Coronary Resistance Vessels

PLoS ONE, 2011

Low thyroid hormone (TH) function has been linked to impaired coronary blood flow, reduced densit... more Low thyroid hormone (TH) function has been linked to impaired coronary blood flow, reduced density of small arterioles, and heart failure. Nonetheless, little is known about the mechanisms by which THs regulate coronary microvascular remodeling. The current study examined the initial cellular events associated with coronary remodeling induced by triiodothyronine (T3) in hypothyroid rats. Rats with established hypothyroidism, eight weeks after surgical thyroidectomy (TX), were treated with T3 for 36 or 72 hours. The early effects of T3 treatment on coronary microvasculature were examined morphometrically. Gene expression changes in the heart were assessed by quantitative PCR Array. Hypothyroidism resulted in arteriolar atrophy in the left ventricle. T3 treatment rapidly induced small arteriolar muscularization and, within 72 hours, restored arteriolar density to control levels. Total length of the capillary network was not affected by TX or T3 treatment. T3 treatment resulted in the coordinate regulation of Angiopoietin 1 and 2 expression. The response of Angiopoietins was consistent with vessel enlargement. In addition to the well known effects of THs on vasoreactivity, these results suggest that THs may affect function of small resistance arteries by phenotypic remodeling of vascular smooth muscle cells (VSMC).

Research paper thumbnail of AMP Activated Protein Kinase Is Indispensable for Myocardial Adaptation to Caloric Restriction in Mice

PLoS ONE, 2013

Caloric restriction (CR) is a robust dietary intervention known to enhance cardiovascular health.... more Caloric restriction (CR) is a robust dietary intervention known to enhance cardiovascular health. AMP activated protein kinase (AMPK) has been suggested to mediate the cardioprotective effects of CR. However, this hypothesis remains to be tested by using definitive loss-of-function animal models. In the present study, we subjected AMPKa2 knockout (KO) mice and their wild type (WT) littermates to a CR regimen that reduces caloric intake by 20%-40% for 4 weeks. CR decreased body weight, heart weight and serum levels of insulin in both WT and KO mice to the same degree, indicating the effectiveness of the CR protocol. CR activated cardiac AMPK signaling in WT mice, but not in AMPKa2 KO mice. Correspondingly, AMPKa2 KO mice had markedly reduced cardiac function during CR as determined by echocardiography and hemodynamic measurements. The compromised cardiac function was associated with increased markers of oxidative stress, endoplasmic reticulum stress and myocyte apoptosis. Mechanistically, CR down-regulated the expression of ATP5g2, a subunit of mitochondrial ATP synthase, and reduced ATP content in AMPKa2 KO hearts, but not in WT hearts. In addition, CR accelerated cardiac autophagic flux in WT mice, but failed to do so in AMPKa2 KO mice. These results demonstrated that without AMPK, CR triggers adverse effects that can lead to cardiac dysfunction, suggesting that AMPK signaling pathway is indispensible for energy homeostasis and myocardial adaptation to CR, a dietary intervention that normally produces beneficial cardiac effects.

Research paper thumbnail of The Transcription Factor GATA4 Is Activated by Extracellular Signal-Regulated Kinase 1- and 2-Mediated Phosphorylation of Serine 105 in Cardiomyocytes

Molecular and Cellular Biology, 2001

The zinc finger-containing transcription factor GATA4 has been implicated as a critical regulator... more The zinc finger-containing transcription factor GATA4 has been implicated as a critical regulator of multiple cardiac-expressed genes as well as a regulator of inducible gene expression in response to hypertrophic stimulation. Here we demonstrate that GATA4 is itself regulated by the mitogen-activated protein kinase signaling cascade through direct phosphorylation. Site-directed mutagenesis and phospho-specific GATA4 antiserum revealed serine 105 as the primary site involved in agonist-induced phosphorylation of GATA4. Infection of cultured cardiomyocytes with an activated MEK1-expressing adenovirus induced robust phosphorylation of serine 105 in GATA4, while a dominant-negative MEK1-expressing adenovirus blocked agonist-induced phosphorylation of serine 105, implicating extracellular signal-regulated kinase (ERK) as a GATA4 kinase. Indeed, bacterially purified ERK2 protein directly phosphorylated purified GATA4 at serine 105 in vitro. Phosphorylation of serine 105 enhanced the tran...

Research paper thumbnail of Short term triiodo-l-thyronine treatment inhibits cardiac myocyte apoptosis in border area after myocardial infarction in rats

Journal of Molecular and Cellular Cardiology, 2008

Thyroid hormone (TH) levels decline after a myocardial infarction. Treatment with TH has been sho... more Thyroid hormone (TH) levels decline after a myocardial infarction. Treatment with TH has been shown to improve left ventricular (LV) function in myocardial infarction (MI) and other cardiovascular diseases, but the mechanisms are not clear. We have previously shown that TH can prevent myocyte apoptosis via Akt signaling in cultured neonatal rat cardiomyocytes. In this study, the effects of triiodo-L-thyronine (T3) on LV function and myocyte apoptosis after MI was examined in rats. After surgery, MI rats were treated with T3 for 3 days. Compared with sham-operated rats, MI rats showed significantly increased LV chamber dimension during systole and decreased LV function. T3 treatment increased LV ±dP/dt but did not change LV chamber dimensions. MI rats also showed significantly increased myocyte apoptosis in the border area as assessed by DNA laddering and TUNEL assay. T3 treatment decreased the amount of DNA laddering, and reduced TUNEL positive myocytes in the border area, which was associated with phosphorylation of Akt at serine 473. These results suggest that T3 can protect myocytes against ischemia induced apoptosis, which may be mediated by Akt signaling.

Research paper thumbnail of Regulation of Akt/PKB activity by P21-activated kinase in cardiomyocytes

Journal of Molecular and Cellular Cardiology, 2008

Akt/PKB is a critical regulator of cardiac function and morphology, and its activity is governed ... more Akt/PKB is a critical regulator of cardiac function and morphology, and its activity is governed by dual phosphorylation at active loop (Thr308) by phosphoinositide-dependent protein kinase-1 (PDK1) and at carboxyl-terminal hydrophobic motif (Ser473) by a putative PDK2. P21-activated kinase-1 (Pak1) is a serine/threonine protein kinase implicated in the regulation of cardiac hypertrophy and contractility, and was shown previously to activate Akt through an undefined mechanism. Here we report Pak1 as a potential PDK2 that is essential for Akt activity in cardiomyocytes. Both Pak1 and Akt can be activated by multiple hypertrophic stimuli or growth factors in a phosphatidylinositol-3-kinase (PI3K)-dependent manner. Pak1 overexpression induces Akt phosphorylation at both Ser473 and Thr308 in cardiomyocytes. Conversely, silencing or inactivating Pak1 gene diminishes Akt phosphorylation in vitro and in vivo. Purified Pak1 can directly phosphorylate Akt only at Ser473, suggesting that Pak1 may be a relevant PDK2 responsible for AKT Ser473 phosphorylation in cardiomyocytes. In addition, Pak1 protects cardiomyocytes from cell death, which is blocked by Akt inhibition. Our results connect two important regulators of cellular physiological functions and provide a potential mechanism for Pak1 signaling in cardiomyocytes.

Research paper thumbnail of Targeted inhibition of p38 MAPK promotes hypertrophic cardiomyopathy through upregulation of calcineurin-NFAT signaling

Journal of Clinical Investigation, 2003

The MAPKs are important transducers of growth and stress stimuli in virtually all eukaryotic cell... more The MAPKs are important transducers of growth and stress stimuli in virtually all eukaryotic cell types. In the mammalian heart, MAPK signaling pathways have been hypothesized to regulate myocyte growth in response to developmental signals or physiologic and pathologic stimuli. Here we generated cardiac-specific transgenic mice expressing dominant-negative mutants of p38α, MKK3, or MKK6. Remarkably, attenuation of cardiac p38 activity produced a progressive growth response and myopathy in the heart that correlated with the degree of enzymatic inhibition. Moreover, dominant-negative p38α, MKK3, and MKK6 transgenic mice each showed enhanced cardiac hypertrophy following aortic banding, Ang II infusion, isoproterenol infusion, or phenylephrine infusion for 14 days. A mechanism underlying this enhanced-growth profile was suggested by the observation that dominant-negative p38α directly augmented nuclear factor of activated T cells (NFAT) transcriptional activity and its nuclear translocation. In vivo, NFAT-dependent luciferase reporter transgenic mice showed enhanced activation in the presence of the dominant-negative p38α transgene before and after the onset of cardiac hypertrophy. More significantly, genetic disruption of the calcineurin Aβ gene rescued hypertrophic cardiomyopathy and depressed functional capacity observed in p38-inhibited mice. Collectively, these observations indicate that reduced p38 signaling in the heart promotes myocyte growth through a mechanism involving enhanced calcineurin-NFAT signaling.

Research paper thumbnail of Transcription Factor GATA4 Inhibits Doxorubicin-induced Autophagy and Cardiomyocyte Death

Journal of Biological Chemistry, 2009

Doxorubicin (DOX) is a potent anti-tumor drug known to cause heart failure. The transcription fac... more Doxorubicin (DOX) is a potent anti-tumor drug known to cause heart failure. The transcription factor GATA4 antagonizes DOX-induced cardiotoxicity. However, the protective mechanism remains obscure. Autophagy is the primary cellular pathway for lysosomal degradation of long-lived proteins and organelles, and its activation could be either protective or detrimental depending on specific pathophysiological conditions. Here we investigated the ability of GATA4 to inhibit autophagy as a potential mechanism underlying its protection against DOX toxicity in cultured neonatal rat cardiomyocytes. DOX markedly increased autophagic flux in cardiomyocytes as indicated by the difference in protein levels of LC3-II (microtubule-associated protein light chain 3 form 2) or numbers of autophagic vacuoles in the absence and presence of the lysosomal inhibitor bafilomycin A1. DOX-induced cardiomyocyte death determined by multiple assays was aggravated by a drug or genetic approach that activates autophagy, but it was attenuated by manipulations that inhibit autophagy, suggesting that autophagy contributes to DOX cardiotoxicity. DOX treatment depleted GATA4 protein levels, which predisposed cardiomyocytes to DOX toxicity. Indeed, GATA4 gene silencing triggered autophagy that rendered DOX more toxic, whereas GATA4 overexpression inhibited DOX-induced autophagy, reducing cardiomyocyte death. Mechanistically, GATA4 up-regulated gene expression of the survival factor Bcl2 and suppressed DOX-induced activation of autophagy-related genes, which may likely be responsible for the anti-apoptotic and anti-autophagic effects of GATA4. Together, these findings suggest that activation of autophagy mediates DOX cardiotoxicity, and preservation of GATA4 attenuates DOX cardiotoxicity by inhibiting autophagy through modulation of the expression of Bcl2 and autophagy-related genes. Doxorubicin (DOX) 4 is a very effective anti-cancer drug with cardiotoxicity that culminates in congestive heart failure (1-3).

Research paper thumbnail of The Transcription Factors GATA4 and GATA6 Regulate Cardiomyocyte Hypertrophy in Vitro and in Vivo

Journal of Biological Chemistry, 2001

Research paper thumbnail of Activation of GATA-4 by Serotonin in Pulmonary Artery Smooth Muscle Cells

Journal of Biological Chemistry, 2003

Serotonin (5-hydroxytryptamine (5-HT)) is a mitogen of pulmonary artery smooth muscle cells (PASM... more Serotonin (5-hydroxytryptamine (5-HT)) is a mitogen of pulmonary artery smooth muscle cells (PASMC) and plays an important role in the development of pulmonary hypertension. Signal transduction initiated by 5-HT involves serotonin transporter-dependent generation of reactive oxygen species and activation of the MEK-ERK pathway. However, the downstream transcriptional regulatory components have not been identified. In systemic smooth muscle cells, GATA-6 has been shown to regulate mitogenesis by driving cells into a quiescent state, and the down-regulation of GATA-6 induces mitogenesis. Thus, the present study tested the hypothesis that 5-HT induces mitogenesis of PASMC by down-regulating GATA-6. Quiescent bovine PASMC were treated with 5-HT, and the binding activity of nuclear extracts toward GATA DNA sequence was monitored. Surprisingly, PASMC express GATA-4, and 5-HT up-regulates the GATA DNA binding activity. Pretreatment of cells with inhibitors of serotonin transporter, reactive oxygen species, and MEK blocks GATA-4 activation by 5-HT. GATA-4 is not activated when the ERK phosphorylation site is mutated, indicating that 5-HT phosphorylates GATA-4 via the MEK/ERK pathway. GATA up-regulation is also induced by other mitogens of PASMC such as endothelin-1 and platelet-derived growth factor. Dominant negative mutants of GATA-4 suppress cyclin D2 expression and cell growth, indicating that GATA-4 activation regulates PASMC proliferation. Thus, GATA-4 mediates 5-HT-induced growth of PASMC and may be an important therapeutic target for the prevention of pulmonary hypertension.

Research paper thumbnail of Diminished GATA4 Protein Levels Contribute to Hyperglycemia-induced Cardiomyocyte Injury

Journal of Biological Chemistry, 2007

Hyperglycemia is an independent risk factor for diabetic heart failure. However, the mechanisms t... more Hyperglycemia is an independent risk factor for diabetic heart failure. However, the mechanisms that mediate hyperglycemiainduced cardiac damage remain poorly understood. The transcription factor GATA4 is essential for cardiac homeostasis, and its protein levels are dramatically reduced in the heart in response to diverse pathologic stresses. In this study, we investigated if hyperglycemia affects GATA4 expression in cardiomyocytes and if enhancing GATA4 signaling could attenuate hyperglycemia-induced cardiomyocyte injury. In cultured rat cardiomyocytes, high glucose (HG, 25 or 40 mM) markedly reduced GATA4 protein levels as compared with normal glucose (NG, 5.5 mM). Equal amount of mannitol did not affect GATA4 protein expression (NG, 100 ؎ 12%; mannitol, 97 ؎ 8%, versus HG, 43 ؎ 16%, p < 0.05). The GATA4 mRNA content, either steady-state or polysome-associated, remained unchanged. HG-induced GATA4 reduction was reversed by MG262, a specific proteasome inhibitor. HG did not activate the ubiquitin proteasome system (UPS) in cardiomyocytes as indicated by a UPS reporter, nor did it increase the peptidase activities or protein expression of the proteasomal subunits. However, the mRNA levels of ubiquitin-protein isopeptide ligase (E3) carboxyl terminus of Hsp70-interacting protein (CHIP) were markedly increased in HG-treated cardiomyocytes. CHIP overexpression promoted GATA4 protein degradation, whereas small interfering RNA-mediated CHIP knockdown prevented HG-induced GATA4 depletion. Moreover, overexpression of GATA4 blocked HG-induced cardiomyocyte death. Also, GATA4 protein levels were diminished in the hearts of streptozotocin and db/db diabetic mice (44 ؎ 7% and 67 ؎ 13% of control, p < 0.05), which correlated with increased CHIP mRNA abundance. In summary, increased GATA4 protein degradation may be an important mechanism that contributes to hyperglycemic cardiotoxicity.

Research paper thumbnail of Genetic Inhibition or Activation of JNK1/2 Protects the Myocardium from Ischemia-Reperfusion-induced Cell Death in Vivo

Journal of Biological Chemistry, 2005

The c-Jun NH 2-terminal kinase (JNK) branch of the mitogen-activated protein kinase signaling cas... more The c-Jun NH 2-terminal kinase (JNK) branch of the mitogen-activated protein kinase signaling cascade has been implicated in the regulation of apoptosis in a variety of mammalian cell types. In the heart, disagreement persists concerning the role that JNKs may play in regulating apoptosis, since both pro-and antiapoptotic regulatory functions have been reported in cultured cardiomyocytes. Here we report the first analysis of cardiomyocyte cell death due to JNK inhibition or activation in vivo using genetically modified mice. Three separate mouse models with selective JNK inhibition were assessed for ventricular damage and apoptosis levels following ischemia-reperfusion injury. jnk1؊/؊, jnk2؊/؊, and transgenic mice expressing dominant negative JNK1/2 within the heart were each shown to have less JNK activity in the heart and less injury and cellular apoptosis in vivo following ischemia-reperfusion injury. To potentially address the reciprocal gain-of-function phenotype associated with sustained JNK activation, transgenic mice were generated that express MKK7 in the heart. These transgenic mice displayed elevated cardiac c-Jun kinase activity but, ironically, were also significantly protected from ischemia-reperfusion. Mechanistically, JNK-inhibited mice showed increased phosphorylation of the proapoptotic factor Bad at position 112, whereas MKK7 transgenic mice showed decreased phosphorylation of this site. Collectively, these results underscore the complexity associated with JNK signaling in regulating apoptosis, such that sustained inhibition or activation both elicit cellular protection in vivo, although probably through different mechanisms.

Research paper thumbnail of Synapses of Amphids Defective (SAD-A) Kinase Promotes Glucose-stimulated Insulin Secretion through Activation of p21-activated Kinase (PAK1) in Pancreatic β-Cells

Journal of Biological Chemistry, 2012

Background: PAK1 is phosphorylated at Thr-423, which is required for glucose-stimulated insulin s... more Background: PAK1 is phosphorylated at Thr-423, which is required for glucose-stimulated insulin secretion, but the kinase regulator remains elusive. Results: We identified SAD-A as the kinase that phosphorylates PAK1 at Thr-423 in islet ␤-cells. Conclusion: SAD-A is required for insulin secretion through activation of PAK1. Significance: These data provide a key insight for biological function of SAD-A in islet ␤-cells.

Research paper thumbnail of Tissue-specific GATA factors are transcriptional effectors of the small GTPase RhoA

Genes & Development, 2001

Rho-like GTPases play a pivotal role in the orchestration of changes in the actin cytoskeleton in... more Rho-like GTPases play a pivotal role in the orchestration of changes in the actin cytoskeleton in response to receptor stimulation, and have been implicated in transcriptional activation, cell growth regulation, and oncogenic transformation. Recently, a role for RhoA in the regulation of cardiac contractility and hypertrophic cardiomyocyte growth has been suggested but the mechanisms underlying RhoA function in the heart remain undefined. We now report that transcription factor GATA-4, a key regulator of cardiac genes, is a nuclear mediator of RhoA signaling and is involved in the control of sarcomere assembly in cardiomyocytes. Both RhoA and GATA-4 are essential for sarcomeric reorganization in response to hypertrophic growth stimuli and overexpression of either protein is sufficient to induce sarcomeric reorganization. Consistent with convergence of RhoA and GATA signaling, RhoA potentiates the transcriptional activity of GATA-4 via a p38 MAPK-dependent pathway that phosphorylates...

Research paper thumbnail of An α1A-Adrenergic–Extracellular Signal-Regulated Kinase Survival Signaling Pathway in Cardiac Myocytes

Circulation, 2007

Background— In α1-AR knockout (α1ABKO) mice that lacked cardiac myocyte α1-adrenergic receptor (α... more Background— In α1-AR knockout (α1ABKO) mice that lacked cardiac myocyte α1-adrenergic receptor (α1-AR) binding, aortic constriction induced apoptosis, dilated cardiomyopathy, and death. However, it was unclear whether these effects were attributable to a lack of cardiac myocyte α1-ARs and whether the α1A, α1B, or both subtypes mediated protection. Therefore, we investigated α1A and α1B subtype–specific survival signaling in cultured cardiac myocytes to test for a direct protective effect of α1-ARs in cardiac myocytes. Methods and Results— We cultured α1ABKO myocytes and reconstituted α1-AR signaling with adenoviruses expressing α1-GFP fusion proteins. Myocyte death was induced by norepinephrine, doxorubicin, or H 2 O 2 and was measured by annexin V/propidium iodide staining. In α1ABKO myocytes, all 3 stimuli significantly increased apoptosis and necrosis. Reconstitution of the α1A subtype, but not the α1B, rescued α1ABKO myocytes from cell death induced by each stimulus. To address ...

Research paper thumbnail of Proteasome functional insufficiency activates the calcineurin–NFAT pathway in cardiomyocytes and promotes maladaptive remodelling of stressed mouse hearts

Cardiovascular Research, 2010

Time for primary review: 13 days Aims Proteasome functional insufficiency (PFI) may play an impor... more Time for primary review: 13 days Aims Proteasome functional insufficiency (PFI) may play an important role in the progression of congestive heart failure but the underlying molecular mechanism is poorly understood. Calcineurin and nuclear factor of activated T-cells (NFAT) are degraded by the proteasome, and the calcineurin-NFAT pathway mediates cardiac remodelling. The present study examined the hypothesis that PFI activates the calcineurin-NFAT pathway and promotes maladaptive remodelling of the heart. Methods and results Using a reporter gene assay, we found that pharmacological inhibition of 20S proteasomes stimulated NFAT transactivation in both mouse hearts and cultured adult mouse cardiomyocytes. Proteasome inhibition stimulated NFAT nuclear translocation in a calcineurin-dependent manner and led to a maladaptive cell shape change in cultured neonatal rat ventricular myocytes. Proteasome inhibition facilitated left ventricular dilatation and functional decompensation and increased fatality in mice with aortic constriction while causing cardiac hypertrophy in the sham surgery group. It was further revealed that both calcineurin protein levels and NFAT transactivation were markedly increased in the mouse hearts with desmin-related cardiomyopathy and severe PFI. Expression of an aggregation-prone mutant desmin also directly increased calcineurin protein levels in cultured cardiomyocytes. Conclusions The calcineurin-NFAT pathway in the heart can be activated by proteasome inhibition and is activated in the heart of a mouse model of desmin-related cardiomyopathy that is characterized by severe PFI. The interplay between PFI and the calcineurin-NFAT pathway may contribute to the pathological remodelling of cardiomyocytes characteristic of congestive heart failure.

Research paper thumbnail of Comprehensive lipidomic profiling in serum and multiple tissues from a mouse model of diabetes

Metabolomics, 2020

Introduction Diabetes mellitus is a serious metabolic disorder causing multiple organ damage in h... more Introduction Diabetes mellitus is a serious metabolic disorder causing multiple organ damage in human. However, the lipidomic profiles in different organs and their associations are rarely studied in either diabetic patients or animals. Objectives To evaluate and compare the characteristics of lipid species in serum and multiple tissues in a diabetic mouse model. Methods Semi-quantitative profiling analyses of intact and oxidized lipids were performed in serum and multiple tissues from a diabetic mouse model fed a high fat diet and treated with streptozotocin by using LC/HRMS and MS/MS. The total content of each lipid class, and the tissue-specific lipid species in all tissue samples were determined and compared by multivariate analyses. Results The diabetic mouse model displayed characteristic differences in serum and multiple organs: the brain and heart showed the largest reduction in cardiolipin, while the kidney had the most remarkable alterations in triacylglycerol. Interestingly, the lipidomic differences also existed between different regions of the same organ: triacylglycerol species with shorter fatty acyl chains decreased in renal medulla but increased in cortex; cardiolipin species with highly polyunsaturated fatty acyls decreased only in atrium but not in ventricle. Importantly, diabetes caused an accumulation of lipid hydroperoxides, suggesting that oxidative stress was induced in all organs except for the brain during the development of diabetes. Conclusion These findings provided novel insight into the organ-specific relationship between diabetes and lipid metabolism, which might be useful for evaluating not only diabetic tissue injury but also the effectiveness of diabetic treatments.

Research paper thumbnail of Mitochondrial quality control in the diabetic heart

Journal of Molecular and Cellular Cardiology, 2016

Diabetes is a well known risk factor for heart failure. Diabetic heart damage is closely related ... more Diabetes is a well known risk factor for heart failure. Diabetic heart damage is closely related to mitochondrial dysfunction and increased ROS generation. However, clinical trials have shown no effects of antioxidant therapies on heart failure in diabetic patients, suggesting that simply antagonizing existing ROS by antioxidants is not sufficient to reduce diabetic cardiac injury. A potentially more effective treatment strategy may be to enhance the overall capacity of mitochondrial quality control to maintain a pool of healthy mitochondria that are needed for supporting cardiac contractile function in diabetic patients. Mitochondrial quality is controlled by a number of coordinated mechanisms including mitochondrial fission and fusion, mitophagy and biogenesis. The mitochondrial damage consistently observed in the diabetic hearts indicates a failure of the mitochondrial quality control mechanisms. Recent studies have demonstrated a crucial role for each of these mechanisms in cardiac homeostasis and have begun to interrogate the relative contribution of insufficient mitochondrial quality control to diabetic cardiac injury. In this review, we will present currently available literature that links diabetic heart disease to the dysregulation of major mitochondrial quality control mechanisms. We will discuss the functional roles of these mechanisms in the pathogenesis of diabetic heart disease and their potentials for targeted therapeutical manipulation.

Research paper thumbnail of Autophagy and mitophagy in diabetic cardiomyopathy

Biochimica et biophysica acta, 2015

Diabetic cardiomyopathy is a heart muscle-specific disease that increases the risk of heart failu... more Diabetic cardiomyopathy is a heart muscle-specific disease that increases the risk of heart failure and mortality in diabetic patients independent of vascular pathology. Mitochondria are cellular power plants that generate energy for heart contraction and concurrently produce reactive oxygen species that, if unchecked, may damage the mitochondria and the heart. Elimination of damaged mitochondria by autophagy known as mitophagy is an essential process for maintaining normal cardiac function at baseline and in response to various stress and disease conditions. Mitochondrial structural injury and functional impairment have been shown to contribute to diabetic heart disease. Recent studies have demonstrated an inhibited autophagic flux in the hearts of diabetic animals. Surprisingly, the diminished autophagy appears to be an adaptive response that protects against cardiac injury in type 1 diabetes. This raises several questions regarding the relationship between general autophagy and s...

Research paper thumbnail of Cardiac expression of ms1/STARS, a novel gene involved in cardiac development and disease, is regulated by GATA4

Molecular and cellular biology, 2012

Ms1/STARS is a novel muscle-specific actin-binding protein that specifically modulates the myocar... more Ms1/STARS is a novel muscle-specific actin-binding protein that specifically modulates the myocardin-related transcription factor (MRTF)-serum response factor (SRF) regulatory axis within striated muscle. This ms1/STARS-dependent regulatory axis is of central importance within the cardiac gene regulatory network and has been implicated in cardiac development and postnatal cardiac function/homeostasis. The dysregulation of ms1/STARS is associated with and causative of pathological cardiac phenotypes, including cardiac hypertrophy and cardiomyopathy. In order to gain an understanding of the mechanisms governing ms1/STARS expression in the heart, we have coupled a comparative genomic in silico analysis with reporter, gain-of-function, and loss-of-function approaches. Through this integrated analysis, we have identified three evolutionarily conserved regions (ECRs), α, SINA, and DINA, that act as cis-regulatory modules and confer differential cardiac cell-specific activity. Two of these...

Research paper thumbnail of Targeted inhibition of calcineurin attenuates cardiac hypertrophy in vivo

Proceedings of the National Academy of Sciences, 2001

The Ca 2+ -calmodulin-activated Ser/Thr protein phosphatase calcineurin and the downstream transc... more The Ca 2+ -calmodulin-activated Ser/Thr protein phosphatase calcineurin and the downstream transcriptional effectors of calcineurin, nuclear factor of activated T cells, have been implicated in the hypertrophic response of the myocardium. Recently, the calcineurin inhibitory agents cyclosporine A and FK506 have been extensively used to evaluate the importance of this signaling pathway in rodent models of cardiac hypertrophy. However, pharmacologic approaches have rendered equivocal results necessitating more specific or genetic-based inhibitory strategies. In this regard, we have generated Tg mice expressing the calcineurin inhibitory domains of Cain/Cabin-1 and A-kinase anchoring protein 79 specifically in the heart. ΔCain and ΔA-kinase-anchoring protein Tg mice demonstrated reduced cardiac calcineurin activity and reduced hypertrophy in response to catecholamine infusion or pressure overload. In a second approach, adenoviral-mediated gene transfer of ΔCain was performed in the adu...

Research paper thumbnail of Thyroid Hormone Promotes Remodeling of Coronary Resistance Vessels

PLoS ONE, 2011

Low thyroid hormone (TH) function has been linked to impaired coronary blood flow, reduced densit... more Low thyroid hormone (TH) function has been linked to impaired coronary blood flow, reduced density of small arterioles, and heart failure. Nonetheless, little is known about the mechanisms by which THs regulate coronary microvascular remodeling. The current study examined the initial cellular events associated with coronary remodeling induced by triiodothyronine (T3) in hypothyroid rats. Rats with established hypothyroidism, eight weeks after surgical thyroidectomy (TX), were treated with T3 for 36 or 72 hours. The early effects of T3 treatment on coronary microvasculature were examined morphometrically. Gene expression changes in the heart were assessed by quantitative PCR Array. Hypothyroidism resulted in arteriolar atrophy in the left ventricle. T3 treatment rapidly induced small arteriolar muscularization and, within 72 hours, restored arteriolar density to control levels. Total length of the capillary network was not affected by TX or T3 treatment. T3 treatment resulted in the coordinate regulation of Angiopoietin 1 and 2 expression. The response of Angiopoietins was consistent with vessel enlargement. In addition to the well known effects of THs on vasoreactivity, these results suggest that THs may affect function of small resistance arteries by phenotypic remodeling of vascular smooth muscle cells (VSMC).

Research paper thumbnail of AMP Activated Protein Kinase Is Indispensable for Myocardial Adaptation to Caloric Restriction in Mice

PLoS ONE, 2013

Caloric restriction (CR) is a robust dietary intervention known to enhance cardiovascular health.... more Caloric restriction (CR) is a robust dietary intervention known to enhance cardiovascular health. AMP activated protein kinase (AMPK) has been suggested to mediate the cardioprotective effects of CR. However, this hypothesis remains to be tested by using definitive loss-of-function animal models. In the present study, we subjected AMPKa2 knockout (KO) mice and their wild type (WT) littermates to a CR regimen that reduces caloric intake by 20%-40% for 4 weeks. CR decreased body weight, heart weight and serum levels of insulin in both WT and KO mice to the same degree, indicating the effectiveness of the CR protocol. CR activated cardiac AMPK signaling in WT mice, but not in AMPKa2 KO mice. Correspondingly, AMPKa2 KO mice had markedly reduced cardiac function during CR as determined by echocardiography and hemodynamic measurements. The compromised cardiac function was associated with increased markers of oxidative stress, endoplasmic reticulum stress and myocyte apoptosis. Mechanistically, CR down-regulated the expression of ATP5g2, a subunit of mitochondrial ATP synthase, and reduced ATP content in AMPKa2 KO hearts, but not in WT hearts. In addition, CR accelerated cardiac autophagic flux in WT mice, but failed to do so in AMPKa2 KO mice. These results demonstrated that without AMPK, CR triggers adverse effects that can lead to cardiac dysfunction, suggesting that AMPK signaling pathway is indispensible for energy homeostasis and myocardial adaptation to CR, a dietary intervention that normally produces beneficial cardiac effects.

Research paper thumbnail of The Transcription Factor GATA4 Is Activated by Extracellular Signal-Regulated Kinase 1- and 2-Mediated Phosphorylation of Serine 105 in Cardiomyocytes

Molecular and Cellular Biology, 2001

The zinc finger-containing transcription factor GATA4 has been implicated as a critical regulator... more The zinc finger-containing transcription factor GATA4 has been implicated as a critical regulator of multiple cardiac-expressed genes as well as a regulator of inducible gene expression in response to hypertrophic stimulation. Here we demonstrate that GATA4 is itself regulated by the mitogen-activated protein kinase signaling cascade through direct phosphorylation. Site-directed mutagenesis and phospho-specific GATA4 antiserum revealed serine 105 as the primary site involved in agonist-induced phosphorylation of GATA4. Infection of cultured cardiomyocytes with an activated MEK1-expressing adenovirus induced robust phosphorylation of serine 105 in GATA4, while a dominant-negative MEK1-expressing adenovirus blocked agonist-induced phosphorylation of serine 105, implicating extracellular signal-regulated kinase (ERK) as a GATA4 kinase. Indeed, bacterially purified ERK2 protein directly phosphorylated purified GATA4 at serine 105 in vitro. Phosphorylation of serine 105 enhanced the tran...

Research paper thumbnail of Short term triiodo-l-thyronine treatment inhibits cardiac myocyte apoptosis in border area after myocardial infarction in rats

Journal of Molecular and Cellular Cardiology, 2008

Thyroid hormone (TH) levels decline after a myocardial infarction. Treatment with TH has been sho... more Thyroid hormone (TH) levels decline after a myocardial infarction. Treatment with TH has been shown to improve left ventricular (LV) function in myocardial infarction (MI) and other cardiovascular diseases, but the mechanisms are not clear. We have previously shown that TH can prevent myocyte apoptosis via Akt signaling in cultured neonatal rat cardiomyocytes. In this study, the effects of triiodo-L-thyronine (T3) on LV function and myocyte apoptosis after MI was examined in rats. After surgery, MI rats were treated with T3 for 3 days. Compared with sham-operated rats, MI rats showed significantly increased LV chamber dimension during systole and decreased LV function. T3 treatment increased LV ±dP/dt but did not change LV chamber dimensions. MI rats also showed significantly increased myocyte apoptosis in the border area as assessed by DNA laddering and TUNEL assay. T3 treatment decreased the amount of DNA laddering, and reduced TUNEL positive myocytes in the border area, which was associated with phosphorylation of Akt at serine 473. These results suggest that T3 can protect myocytes against ischemia induced apoptosis, which may be mediated by Akt signaling.

Research paper thumbnail of Regulation of Akt/PKB activity by P21-activated kinase in cardiomyocytes

Journal of Molecular and Cellular Cardiology, 2008

Akt/PKB is a critical regulator of cardiac function and morphology, and its activity is governed ... more Akt/PKB is a critical regulator of cardiac function and morphology, and its activity is governed by dual phosphorylation at active loop (Thr308) by phosphoinositide-dependent protein kinase-1 (PDK1) and at carboxyl-terminal hydrophobic motif (Ser473) by a putative PDK2. P21-activated kinase-1 (Pak1) is a serine/threonine protein kinase implicated in the regulation of cardiac hypertrophy and contractility, and was shown previously to activate Akt through an undefined mechanism. Here we report Pak1 as a potential PDK2 that is essential for Akt activity in cardiomyocytes. Both Pak1 and Akt can be activated by multiple hypertrophic stimuli or growth factors in a phosphatidylinositol-3-kinase (PI3K)-dependent manner. Pak1 overexpression induces Akt phosphorylation at both Ser473 and Thr308 in cardiomyocytes. Conversely, silencing or inactivating Pak1 gene diminishes Akt phosphorylation in vitro and in vivo. Purified Pak1 can directly phosphorylate Akt only at Ser473, suggesting that Pak1 may be a relevant PDK2 responsible for AKT Ser473 phosphorylation in cardiomyocytes. In addition, Pak1 protects cardiomyocytes from cell death, which is blocked by Akt inhibition. Our results connect two important regulators of cellular physiological functions and provide a potential mechanism for Pak1 signaling in cardiomyocytes.

Research paper thumbnail of Targeted inhibition of p38 MAPK promotes hypertrophic cardiomyopathy through upregulation of calcineurin-NFAT signaling

Journal of Clinical Investigation, 2003

The MAPKs are important transducers of growth and stress stimuli in virtually all eukaryotic cell... more The MAPKs are important transducers of growth and stress stimuli in virtually all eukaryotic cell types. In the mammalian heart, MAPK signaling pathways have been hypothesized to regulate myocyte growth in response to developmental signals or physiologic and pathologic stimuli. Here we generated cardiac-specific transgenic mice expressing dominant-negative mutants of p38α, MKK3, or MKK6. Remarkably, attenuation of cardiac p38 activity produced a progressive growth response and myopathy in the heart that correlated with the degree of enzymatic inhibition. Moreover, dominant-negative p38α, MKK3, and MKK6 transgenic mice each showed enhanced cardiac hypertrophy following aortic banding, Ang II infusion, isoproterenol infusion, or phenylephrine infusion for 14 days. A mechanism underlying this enhanced-growth profile was suggested by the observation that dominant-negative p38α directly augmented nuclear factor of activated T cells (NFAT) transcriptional activity and its nuclear translocation. In vivo, NFAT-dependent luciferase reporter transgenic mice showed enhanced activation in the presence of the dominant-negative p38α transgene before and after the onset of cardiac hypertrophy. More significantly, genetic disruption of the calcineurin Aβ gene rescued hypertrophic cardiomyopathy and depressed functional capacity observed in p38-inhibited mice. Collectively, these observations indicate that reduced p38 signaling in the heart promotes myocyte growth through a mechanism involving enhanced calcineurin-NFAT signaling.

Research paper thumbnail of Transcription Factor GATA4 Inhibits Doxorubicin-induced Autophagy and Cardiomyocyte Death

Journal of Biological Chemistry, 2009

Doxorubicin (DOX) is a potent anti-tumor drug known to cause heart failure. The transcription fac... more Doxorubicin (DOX) is a potent anti-tumor drug known to cause heart failure. The transcription factor GATA4 antagonizes DOX-induced cardiotoxicity. However, the protective mechanism remains obscure. Autophagy is the primary cellular pathway for lysosomal degradation of long-lived proteins and organelles, and its activation could be either protective or detrimental depending on specific pathophysiological conditions. Here we investigated the ability of GATA4 to inhibit autophagy as a potential mechanism underlying its protection against DOX toxicity in cultured neonatal rat cardiomyocytes. DOX markedly increased autophagic flux in cardiomyocytes as indicated by the difference in protein levels of LC3-II (microtubule-associated protein light chain 3 form 2) or numbers of autophagic vacuoles in the absence and presence of the lysosomal inhibitor bafilomycin A1. DOX-induced cardiomyocyte death determined by multiple assays was aggravated by a drug or genetic approach that activates autophagy, but it was attenuated by manipulations that inhibit autophagy, suggesting that autophagy contributes to DOX cardiotoxicity. DOX treatment depleted GATA4 protein levels, which predisposed cardiomyocytes to DOX toxicity. Indeed, GATA4 gene silencing triggered autophagy that rendered DOX more toxic, whereas GATA4 overexpression inhibited DOX-induced autophagy, reducing cardiomyocyte death. Mechanistically, GATA4 up-regulated gene expression of the survival factor Bcl2 and suppressed DOX-induced activation of autophagy-related genes, which may likely be responsible for the anti-apoptotic and anti-autophagic effects of GATA4. Together, these findings suggest that activation of autophagy mediates DOX cardiotoxicity, and preservation of GATA4 attenuates DOX cardiotoxicity by inhibiting autophagy through modulation of the expression of Bcl2 and autophagy-related genes. Doxorubicin (DOX) 4 is a very effective anti-cancer drug with cardiotoxicity that culminates in congestive heart failure (1-3).

Research paper thumbnail of The Transcription Factors GATA4 and GATA6 Regulate Cardiomyocyte Hypertrophy in Vitro and in Vivo

Journal of Biological Chemistry, 2001

Research paper thumbnail of Activation of GATA-4 by Serotonin in Pulmonary Artery Smooth Muscle Cells

Journal of Biological Chemistry, 2003

Serotonin (5-hydroxytryptamine (5-HT)) is a mitogen of pulmonary artery smooth muscle cells (PASM... more Serotonin (5-hydroxytryptamine (5-HT)) is a mitogen of pulmonary artery smooth muscle cells (PASMC) and plays an important role in the development of pulmonary hypertension. Signal transduction initiated by 5-HT involves serotonin transporter-dependent generation of reactive oxygen species and activation of the MEK-ERK pathway. However, the downstream transcriptional regulatory components have not been identified. In systemic smooth muscle cells, GATA-6 has been shown to regulate mitogenesis by driving cells into a quiescent state, and the down-regulation of GATA-6 induces mitogenesis. Thus, the present study tested the hypothesis that 5-HT induces mitogenesis of PASMC by down-regulating GATA-6. Quiescent bovine PASMC were treated with 5-HT, and the binding activity of nuclear extracts toward GATA DNA sequence was monitored. Surprisingly, PASMC express GATA-4, and 5-HT up-regulates the GATA DNA binding activity. Pretreatment of cells with inhibitors of serotonin transporter, reactive oxygen species, and MEK blocks GATA-4 activation by 5-HT. GATA-4 is not activated when the ERK phosphorylation site is mutated, indicating that 5-HT phosphorylates GATA-4 via the MEK/ERK pathway. GATA up-regulation is also induced by other mitogens of PASMC such as endothelin-1 and platelet-derived growth factor. Dominant negative mutants of GATA-4 suppress cyclin D2 expression and cell growth, indicating that GATA-4 activation regulates PASMC proliferation. Thus, GATA-4 mediates 5-HT-induced growth of PASMC and may be an important therapeutic target for the prevention of pulmonary hypertension.

Research paper thumbnail of Diminished GATA4 Protein Levels Contribute to Hyperglycemia-induced Cardiomyocyte Injury

Journal of Biological Chemistry, 2007

Hyperglycemia is an independent risk factor for diabetic heart failure. However, the mechanisms t... more Hyperglycemia is an independent risk factor for diabetic heart failure. However, the mechanisms that mediate hyperglycemiainduced cardiac damage remain poorly understood. The transcription factor GATA4 is essential for cardiac homeostasis, and its protein levels are dramatically reduced in the heart in response to diverse pathologic stresses. In this study, we investigated if hyperglycemia affects GATA4 expression in cardiomyocytes and if enhancing GATA4 signaling could attenuate hyperglycemia-induced cardiomyocyte injury. In cultured rat cardiomyocytes, high glucose (HG, 25 or 40 mM) markedly reduced GATA4 protein levels as compared with normal glucose (NG, 5.5 mM). Equal amount of mannitol did not affect GATA4 protein expression (NG, 100 ؎ 12%; mannitol, 97 ؎ 8%, versus HG, 43 ؎ 16%, p < 0.05). The GATA4 mRNA content, either steady-state or polysome-associated, remained unchanged. HG-induced GATA4 reduction was reversed by MG262, a specific proteasome inhibitor. HG did not activate the ubiquitin proteasome system (UPS) in cardiomyocytes as indicated by a UPS reporter, nor did it increase the peptidase activities or protein expression of the proteasomal subunits. However, the mRNA levels of ubiquitin-protein isopeptide ligase (E3) carboxyl terminus of Hsp70-interacting protein (CHIP) were markedly increased in HG-treated cardiomyocytes. CHIP overexpression promoted GATA4 protein degradation, whereas small interfering RNA-mediated CHIP knockdown prevented HG-induced GATA4 depletion. Moreover, overexpression of GATA4 blocked HG-induced cardiomyocyte death. Also, GATA4 protein levels were diminished in the hearts of streptozotocin and db/db diabetic mice (44 ؎ 7% and 67 ؎ 13% of control, p < 0.05), which correlated with increased CHIP mRNA abundance. In summary, increased GATA4 protein degradation may be an important mechanism that contributes to hyperglycemic cardiotoxicity.

Research paper thumbnail of Genetic Inhibition or Activation of JNK1/2 Protects the Myocardium from Ischemia-Reperfusion-induced Cell Death in Vivo

Journal of Biological Chemistry, 2005

The c-Jun NH 2-terminal kinase (JNK) branch of the mitogen-activated protein kinase signaling cas... more The c-Jun NH 2-terminal kinase (JNK) branch of the mitogen-activated protein kinase signaling cascade has been implicated in the regulation of apoptosis in a variety of mammalian cell types. In the heart, disagreement persists concerning the role that JNKs may play in regulating apoptosis, since both pro-and antiapoptotic regulatory functions have been reported in cultured cardiomyocytes. Here we report the first analysis of cardiomyocyte cell death due to JNK inhibition or activation in vivo using genetically modified mice. Three separate mouse models with selective JNK inhibition were assessed for ventricular damage and apoptosis levels following ischemia-reperfusion injury. jnk1؊/؊, jnk2؊/؊, and transgenic mice expressing dominant negative JNK1/2 within the heart were each shown to have less JNK activity in the heart and less injury and cellular apoptosis in vivo following ischemia-reperfusion injury. To potentially address the reciprocal gain-of-function phenotype associated with sustained JNK activation, transgenic mice were generated that express MKK7 in the heart. These transgenic mice displayed elevated cardiac c-Jun kinase activity but, ironically, were also significantly protected from ischemia-reperfusion. Mechanistically, JNK-inhibited mice showed increased phosphorylation of the proapoptotic factor Bad at position 112, whereas MKK7 transgenic mice showed decreased phosphorylation of this site. Collectively, these results underscore the complexity associated with JNK signaling in regulating apoptosis, such that sustained inhibition or activation both elicit cellular protection in vivo, although probably through different mechanisms.

Research paper thumbnail of Synapses of Amphids Defective (SAD-A) Kinase Promotes Glucose-stimulated Insulin Secretion through Activation of p21-activated Kinase (PAK1) in Pancreatic β-Cells

Journal of Biological Chemistry, 2012

Background: PAK1 is phosphorylated at Thr-423, which is required for glucose-stimulated insulin s... more Background: PAK1 is phosphorylated at Thr-423, which is required for glucose-stimulated insulin secretion, but the kinase regulator remains elusive. Results: We identified SAD-A as the kinase that phosphorylates PAK1 at Thr-423 in islet ␤-cells. Conclusion: SAD-A is required for insulin secretion through activation of PAK1. Significance: These data provide a key insight for biological function of SAD-A in islet ␤-cells.

Research paper thumbnail of Tissue-specific GATA factors are transcriptional effectors of the small GTPase RhoA

Genes & Development, 2001

Rho-like GTPases play a pivotal role in the orchestration of changes in the actin cytoskeleton in... more Rho-like GTPases play a pivotal role in the orchestration of changes in the actin cytoskeleton in response to receptor stimulation, and have been implicated in transcriptional activation, cell growth regulation, and oncogenic transformation. Recently, a role for RhoA in the regulation of cardiac contractility and hypertrophic cardiomyocyte growth has been suggested but the mechanisms underlying RhoA function in the heart remain undefined. We now report that transcription factor GATA-4, a key regulator of cardiac genes, is a nuclear mediator of RhoA signaling and is involved in the control of sarcomere assembly in cardiomyocytes. Both RhoA and GATA-4 are essential for sarcomeric reorganization in response to hypertrophic growth stimuli and overexpression of either protein is sufficient to induce sarcomeric reorganization. Consistent with convergence of RhoA and GATA signaling, RhoA potentiates the transcriptional activity of GATA-4 via a p38 MAPK-dependent pathway that phosphorylates...

Research paper thumbnail of An α1A-Adrenergic–Extracellular Signal-Regulated Kinase Survival Signaling Pathway in Cardiac Myocytes

Circulation, 2007

Background— In α1-AR knockout (α1ABKO) mice that lacked cardiac myocyte α1-adrenergic receptor (α... more Background— In α1-AR knockout (α1ABKO) mice that lacked cardiac myocyte α1-adrenergic receptor (α1-AR) binding, aortic constriction induced apoptosis, dilated cardiomyopathy, and death. However, it was unclear whether these effects were attributable to a lack of cardiac myocyte α1-ARs and whether the α1A, α1B, or both subtypes mediated protection. Therefore, we investigated α1A and α1B subtype–specific survival signaling in cultured cardiac myocytes to test for a direct protective effect of α1-ARs in cardiac myocytes. Methods and Results— We cultured α1ABKO myocytes and reconstituted α1-AR signaling with adenoviruses expressing α1-GFP fusion proteins. Myocyte death was induced by norepinephrine, doxorubicin, or H 2 O 2 and was measured by annexin V/propidium iodide staining. In α1ABKO myocytes, all 3 stimuli significantly increased apoptosis and necrosis. Reconstitution of the α1A subtype, but not the α1B, rescued α1ABKO myocytes from cell death induced by each stimulus. To address ...

Research paper thumbnail of Proteasome functional insufficiency activates the calcineurin–NFAT pathway in cardiomyocytes and promotes maladaptive remodelling of stressed mouse hearts

Cardiovascular Research, 2010

Time for primary review: 13 days Aims Proteasome functional insufficiency (PFI) may play an impor... more Time for primary review: 13 days Aims Proteasome functional insufficiency (PFI) may play an important role in the progression of congestive heart failure but the underlying molecular mechanism is poorly understood. Calcineurin and nuclear factor of activated T-cells (NFAT) are degraded by the proteasome, and the calcineurin-NFAT pathway mediates cardiac remodelling. The present study examined the hypothesis that PFI activates the calcineurin-NFAT pathway and promotes maladaptive remodelling of the heart. Methods and results Using a reporter gene assay, we found that pharmacological inhibition of 20S proteasomes stimulated NFAT transactivation in both mouse hearts and cultured adult mouse cardiomyocytes. Proteasome inhibition stimulated NFAT nuclear translocation in a calcineurin-dependent manner and led to a maladaptive cell shape change in cultured neonatal rat ventricular myocytes. Proteasome inhibition facilitated left ventricular dilatation and functional decompensation and increased fatality in mice with aortic constriction while causing cardiac hypertrophy in the sham surgery group. It was further revealed that both calcineurin protein levels and NFAT transactivation were markedly increased in the mouse hearts with desmin-related cardiomyopathy and severe PFI. Expression of an aggregation-prone mutant desmin also directly increased calcineurin protein levels in cultured cardiomyocytes. Conclusions The calcineurin-NFAT pathway in the heart can be activated by proteasome inhibition and is activated in the heart of a mouse model of desmin-related cardiomyopathy that is characterized by severe PFI. The interplay between PFI and the calcineurin-NFAT pathway may contribute to the pathological remodelling of cardiomyocytes characteristic of congestive heart failure.