Glucose Restriction Promotes Osteocyte Specification by Activating a PGC-1α-Dependent Transcriptional Program (original) (raw)
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Diabetes, 2015
Type 2 diabetes is associated with increased fracture risk and delayed facture healing; the underlying mechanism, however, remains poorly understood. We systematically investigated skeletal pathology in leptin receptor–deficient diabetic mice on a C57BLKS background (db). Compared with wild type (wt), db mice displayed reduced peak bone mass and age-related trabecular and cortical bone loss. Poor skeletal outcome in db mice contributed high-glucose– and nonesterified fatty acid–induced osteoblast apoptosis that was associated with peroxisome proliferator–activated receptor γ coactivator 1-α (PGC-1α) downregulation and upregulation of skeletal muscle atrogenes in osteoblasts. Osteoblast depletion of the atrogene muscle ring finger protein-1 (MuRF1) protected against gluco- and lipotoxicity-induced apoptosis. Osteoblast-specific PGC-1α upregulation by 6-C-β-d-glucopyranosyl-(2S,3S)-(+)-5,7,3′,4′-tetrahydroxydihydroflavonol (GTDF), an adiponectin receptor 1 (AdipoR1) agonist, as well a...
Deletion of the Transcription Factor PGC-1α in Mice Negatively Regulates Bone Mass
Calcified Tissue International, 2018
Peroxisome proliferator-activated receptor-gamma coactivator (PGC1α) is a transcription coactivator that interacts with a broad range of transcription factors involved in several biological responses. Here, we show that PGC1α plays a role in skeletal homeostasis since aged PGC1α-deficient mice (PGC1α−/−) display impaired bone structure. Micro-CT of the tibial mid-shaft showed a marked decrease of cortical thickness in PGC1α−/− (− 11.9%, p < 0.05) mice compared to wild-type littermate. Trabecular bone was also impaired in knock out mice which displayed lower trabecular thickness (Tb.Th) (− 5.9% vs PGC1α+/+, p < 0.05), whereas trabecular number (Tb.N) was higher than wild-type mice (+ 72% vs PGC1α+/+, p < 0.05), thus resulting in increased (+ 31.7% vs PGC1α+/+, p < 0.05) degree of anisotropy (DA), despite unchanged bone volume fraction (BV/TV). Notably, these impairments of cortical and trabecular bone led to a dramatic ~ 48.4% decrease in bending strength (p < 0.01). These changes in PGC1α−/− mice were paralleled by a significant increase in osteoclast number at the cortical bone surface and in serum level of the bone resorption marker, namely, C-terminal cross-linked telopeptides of type I collagen (CTX-I). We also found that in cortical bone, there was lower expression of mRNA codifying for the key bonebuilding protein Osteocalcin (Ocn). Interestingly, Collagen I mRNA expression was reduced in mesenchymal stem cells from bone marrow of PGC1α−/−, thus indicating that differentiation of osteoblast lineage is downregulated. Overall, results presented herein suggest that PGC1α may play a key role in bone metabolism.
PGC1β Organizes the Osteoclast Cytoskeleton by Mitochondrial Biogenesis and Activation
Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research, 2018
Osteoclasts are mitochondria-rich cells, but the role of these energy-producing organelles in bone resorption is poorly defined. To this end, we conditionally deleted the mitochondria-inducing co-activator, PGC1β, in myeloid lineage cells to generate PGC1βmice. In contrast to previous reports, PGC1β-deficient macrophages differentiate normally into osteoclasts albeit with impaired resorptive function due to cytoskeletal disorganization. Consequently, bone mass of PGC1βmice is double that of wild type. Mitochondrial biogenesis and function are diminished in PGC1βosteoclasts. All abnormalities are normalized by PGC1β transduction. Furthermore, OXPHOS inhibitors reproduce the phenotype of PGC1β deletion. PGC1β's organization of the osteoclast cytoskeleton is mediated by expression of GIT1, which also promotes mitochondrial biogenesis. Thus, osteoclast mitochondria regulate the cell's resorptive activity by promoting cytoskeletal organization. © 2018 American Society for Bone an...
Diabetes, 2015
Type 2 diabetes is associated with increased fracture risk and delayed facture healing; the underlying mechanism however remains poorly understood. Here we made a systematic investigation of skeletal pathology in leptin receptor-deficient diabetic mouse in C57/BLKS background (db). Compared with wild-type (wt), db mice displayed reduced peak bone mass and age-related trabecular and cortical bone loss. Poor skeletal outcome in db was contributed by high glucose and non-esterified fatty acid (NEFA)-induced osteoblast apoptosis that was associated with PPARγ coactivator 1-α (PGC-1α) downregulation and upregulation of skeletal muscle atrogenes in osteoblasts. Osteoblast depletion of the atrogene, muscle ring finger protein-1 (MuRF1) protected against gluco-and lipotoxicity-induced apoptosis. Osteoblast-specific PGC-1α upregulation by 6-C-β-d-glucopyranosyl-(2S,3S)-(+)-5,7,3',4'tetrahydroxydihydroflavonol (GTDF), an adiponectin receptor 1 (AdipoR1) agonist as well as metformin in db mice that lacked AdipoR1 expression in muscle but not bone, restored osteopenia to wt levels without improving diabetes. Both GTDF and metformin protected against gluco-and lipotoxicity-induced osteoblast apoptosis and depletion of PGC-1α abolished this protection. While AdipoR1 but not AdipoR2-depletion abolished protection by GTDF, metformin action was not blocked by AdipoR-depletion. We conclude that PGC-1α upregulation in osteoblasts could reverse type 2 diabetes-associated deterioration in skeletal health.
Tsc2 is a molecular checkpoint controlling osteoblast development and glucose homeostasis
Molecular and cellular biology, 2014
Insulin signaling in osteoblasts regulates global energy balance by stimulating the production of osteocalcin, a bone-derived protein that promotes insulin production and action. To identify the signaling pathways in osteoblasts that mediate insulin's effects on bone and energy metabolism, we examined the function of the tuberous sclerosis 2 (Tsc2) protein, a key target important in coordinating nutrient signaling. Here, we show that loss of Tsc2 in osteoblasts constitutively activates mTOR and destabilizes Irs1, causing osteoblasts to differentiate poorly and become resistant to insulin. Young Tsc2 mutant mice demonstrate hypoglycemia with increased levels of insulin and undercarboxylated osteocalcin. However, with age, Tsc2 mutants develop metabolic features similar to mice lacking the insulin receptor in the osteoblast, including peripheral adiposity, hyperglycemia, and decreased pancreatic  cell mass. These metabolic abnormalities appear to result from chronic elevations in undercarboxylated osteocalcin that lead to downregulation of the osteocalcin receptor and desensitization of the  cell to this hormone. Removal of a single mTOR allele from the Tsc2 mutant mice largely normalizes the bone and metabolic abnormalities. Together, these findings suggest that Tsc2 serves as a key checkpoint in the osteoblast that is required for proper insulin signaling and acts to ensure normal bone acquisition and energy homeostasis.
Journal of Cellular Physiology, 2017
Diabetes mellitus (DM) induces bone deterioration, while mechanical stimulation promotes osteocyte-driven bone formation. We aimed to evaluate the interaction of acute exposure (24 h) to high glucose (HG) with both the pro-survival effect conferred to osteocytic MLO-Y4 cells and osteoblastic MC3T3-E1 cells by mechanical stimulation and the interaction of these cells with osteoclast precursor RAW264.7 cells. We found that 24 h of HG (25 mM) pre-exposure prevented both cell survival and ERK and β-catenin nuclear translocation upon mechanical stimulation by fluid flow (FF) (10 min) in both MLO-Y4 and MC3T3-E1 cells. However, migration of RAW 264.7 cells was inhibited by MLO-Y4 cell-conditioned medium (CM), but not by MC3T3-E1 cell-CM, with HG or FF. This inhibitory effect was associated with consistent changes in VEGF, RANTES, MIP-1α, MIP-1β MCP-1, and GM-CSF in MLO-Y4 cell-CM. RAW264.7 proliferation was inhibited by MLO-Y4 CM under static or HG conditions, but it increased by FF-CM with or without HG. In addition, both FF and HG abrogated the capacity of RAW 264.7 cells to differentiate into osteoclasts, but in a different manner. Thus, HG-CM in static condition allowed formation of osteoclast-like cells, which were unable to resorb hydroxyapatite. In contrast, FF-CM prevented osteoclastogenesis even in HG condition. Moreover, HG did not affect basal RANKL or IL-6 secretion or their inhibition induced by FF in MLO-Y4 cells. In conclusion, this in vitro study demonstrates that HG exerts disparate effects on osteocyte mechanotransduction, and provides a novel mechanism by which DM disturbs skeletal metabolism through altered osteocyte-osteoclast communication. K E Y W O R D S diabetes mellitus, mechanotransduction, osteoclast migration, osteoclastogenesis, osteocyte
Developmental Cell, 2008
It is intuitive to speculate that nutrient availability may influence differentiation of mammalian cells. Nonetheless, a comprehensive complement of the molecular determinants involved in this process has not been elucidated yet. Here, we have investigated how nutrients (glucose) affect skeletal myogenesis. Glucose restriction (GR) impaired differentiation of skeletal myoblasts and was associated with activation of the AMP-activated protein kinase (AMPK). Activated AMPK was required to promote GR-induced transcription of the NAD + biosynthetic enzyme Nampt. Indeed, GR augmented the Nampt activity, which consequently modified the intracellular [NAD + ]/[NADH] ratio and nicotinamide levels, and mediated inhibition of skeletal myogenesis. Skeletal myoblasts derived from SIRT1 +/− heterozygous mice were resistant to the effects of either GR or AMPK activation. These experiments reveal that AMPK, Nampt, and SIRT1 are the molecular components of a functional signaling pathway that allows skeletal muscle cells to sense and react to nutrient availability.
Research Square (Research Square), 2023
Enhanced osteoclastogenesis and osteoclast activity contribute to the development of osteoporosis, which is characterized by increased bone resorption and inadequate bone formation. As novel antiosteoporotic therapeutics are needed, understanding the genetic regulation of human osteoclastogenesis could help identify potential treatment targets. This study aimed to provide an overview of the transcriptional reprogramming during human osteoclast differentiation. Osteoclasts were differentiated from CD14 +-monocytes from eight female donors. RNA-sequencing during differentiation demonstrated 8446 differentially expressed genes grouped into eight temporal patterns conserved across donors. These patterns showed distinct molecular functions, associated with postmenopausal osteoporosis susceptibility genes based on RNA from iliac crest biopsies, and bone mineral density SNPs. Network analyses showed mutual dependencies between the expression patterns and detected subspeci c transcriptional networks. Differentially expressed G-protein coupled receptors showed strong expression during osteoclast differentiation and associated with bone mineral density SNPs, implying a pivotal role in osteoclast differentiation and activity. The regulatory effects of three differentially expressed G-protein coupled receptors were exempli ed by in vitro pharmacological modulation of complement 5A receptor 1 (C5AR1), somatostatin receptor 2 (SSTR2), and free fatty acid receptor 4 (FFAR4/GPR120). Activating C5AR1 enhanced osteoclast formation, while activating SSTR2 decreased resorptive activity of mature osteoclasts, and activating FFAR4 decreased both number and resorptive activity of mature osteoclasts. In conclusion, we report the transcriptional reprogramming during human osteoclast differentiation and identi ed SSTR2 and FFAR4 as anti-resorptive G-protein coupled receptors. These data can help future investigations to identify molecular regulators of osteoclast differentiation and activity and provide the basis for novel anti-osteoporotic targets.
Biochemistry and Cell Biology, 2006
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