Myocardial lysyl oxidase regulation of cardiac remodeling in a murine model of diet-induced metabolic syndrome - PubMed (original) (raw)

Myocardial lysyl oxidase regulation of cardiac remodeling in a murine model of diet-induced metabolic syndrome

Sherma Zibadi et al. Am J Physiol Heart Circ Physiol. 2009 Sep.

Abstract

Metabolic syndrome (MetS) represents an increased risk of cardiovascular disease. Although its individual components adversely affect cardiac structure and function, the extent to which multiple components of MetS affect the cardiac extracellular matrix (ECM) has not been well characterized. Lysyl oxidase (LOX) is one of the cardiac ECM-modifying enzymes that catalyze the formation of collagen cross-linking. Our objective was to define the effect of diet-induced MetS on the LOX enzyme. MetS was induced in male C57BL/6 mice by administrating a high-fat, high-simple carbohydrate diet for 6 mo. Gene expression was determined by real-time PCR. The cardiac protein expression and enzymatic activity of LOX were measured. The severity of fibrosis was assessed by histology and hydroxylproline assay. Cardiac diastolic function was assessed by in vivo analysis of the pressure-volume relationship. LOX, matrix metalloproteinases, and their tissue inhibitors were analyzed, and of these three, LOX was most significantly changed in the MetS mice. Despite the blunted gene expression of LOX isoforms, MetS mice demonstrated a significant upregulation of bone morphogenetic protein-1. Correspondingly, there was an increase in the ratio of protein expression of mature to proenzyme LOX by 25.9%, enhanced LOX activity by 50.0%, and increased cardiac cross-linked collagen compared with the controls. This fibrotic response coincided with a marked increase in end-diastolic pressure, increased left ventricular stiffness, and impaired diastolic filling pattern. Our data signify that diet-induced MetS alters the remodeling enzymes, mainly LOX, thereby altering ECM structure by increasing the amount of cross-linking and inducing diastolic dysfunction.

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Figures

Fig. 1.

Fig. 1.

In vivo analysis of diastolic function. Data represent diastolic functional parameters obtained from in vivo pressure-volume (P-V) loop analysis. High-fat, high-simple carbohydrate (HFHSC) diet was associated with a significant decrease in end-diastolic volume (A), an increase in end-diastolic pressure (B), an increase in the slope of end-diastolic P-V relationship (β; C), and a reduction of left ventricular (LV) filling rate (D). There was also an upward and leftward shift of LV P-V loop (E). Values are presented as means ± SE; n = 4–8 mice/group. *P <0.05 and †P <0.05 compared with controls.

Fig. 2.

Fig. 2.

Cardiac lysyl oxidase (LOX) gene and protein expression and activity. A: relative mRNA expression of LOX, LOXL-3, and bone morphogenetic protein-1 (BMP-1) as determined by real-time PCR. BMP-1 gene expression was upregulated 1.8-fold after 6 mo of treatment with HFHSC diet. B: Western blot analysis of immunoreactive LOX protein representing the proenzyme (50 kDa) and the mature (30 kDa) forms. C: LOX activity represented by the production of H2O2 and detected by Amplex red oxidation. D: the correlation between cardiac LOX enzymatic activity and LV stiffness (β). Values are presented as means ± SE; n = 3 to 4 mice/group. *P <0.05 compared with controls.

Fig. 3.

Fig. 3.

Cardiac matrix metalloproteinase (MMP) gene expression and activity. A: relative mRNA expression of pro-MMP-2 and -9, tissue inhibitor of MMP (TIMP)-2 and -4 as determined by real-time PCR. B: representative gelatin zymogram showing changes in MMP-9, pro-MMP-2, and MMP-2 activities. C: the corresponding densitometric analyses of lytic bands. OD, optical density. Values are presented as means ± SE; n = 3 to 4 mice/group. *P <0.01 compared with controls.

Fig. 4.

Fig. 4.

Myocardial collagen characteristics. A: Picosirius red image of cardiac tissue. B: myocardial total and cross-linked collagen as determined by hydroxylproline and cyanogen bromide digestion assays. Data are expressed as micrograms of collagen per milligram dry heart weight, assuming that collagen contains an average of 13.5% hydroxyproline. Values are means ± SE; n = 4 mice/group. *P <0.05 compared with controls.

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