Disruption of calcium homeostasis by cardiac-specific over-expression of PPAR-γ in mice: A role in ventricular arrhythmia.

Aims: Adverse cardiovascular effects induced by peroxisome proliferator activator receptor-γ (PPAR-γ) activation were observed in clinical setting. But the underlying mechanism is unclear. Now, transgenic mice with cardiac specific peroxisome proliferator activator receptor-γ overexpression (TG-PPAR-γ) were used to explore the possible mechanisms.
Materials and Methods: Cardiac tissues from TG-PPAR-γ mice, a PPAR-γ over-expressing human cardiomyocyte line AC16 cell, and PPAR-γ agonist-treated primary cardiomyocytes were used to evaluate the expression of cardiac calcium regulatory proteins as sarcoplasmic reticulum Ca ²⁺ ATPase, Na ⁺ /Ca ²⁺ exchanger 1, ryanodine receptor 2 and phospholamban. Intracellular Ca ²⁺ levels were also examined by flow cytometry and confocal microscopy with Fluo-4/AM in these cells.
Key Findings: In this study, frequent ventricular premature contraction and polymorphic ventricular tachycardia were observed in TG-PPAR-γ but not in wild-type mice. Besides, we found the calcium regulatory proteins expression were higher in the TG-PPAR-γ mice, PPAR-γ overexpressing human cardiomyocyte line AC16 cell and PPAR-γ agonist-treated primary cardiomyocytes than the control group respectively. In addition, an increase of intracellular calcium levels and CaMKII δ expression in PPAR-γ overexpression and PPAR-γ activation group. Moreover, Inhibition of CaMKII δ could improve the intracellular calcium levels and reduce the occurrence of ventricular arrhythmia.
Significance: PPAR-γ over-expression perturbs the intracellular calcium homeostasis in cardiomyocytes which contribute to the ventricular arrhythmias and cardiac sudden death in TG-PPAR-γ mice.
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