Abstract 14536: 11,12-Epoxyeicsatrienoic Acid Reduces the Calpain-Induced Cardiac Dysfunction in ob-/ob- Rats
Background: Calpain induces the degradation of RXRα and prevents PPAR-α, a key regulator of CYP2J3, from heterodimer formation and gene transcription. Studies have shown that activation of calpain contributes to cardiomyocyte apoptosis induced by hyperglycemia. However, the relationship between calpain and CYP epoxygenase are not understood in diabetic hearts. Here, we investigate whether the calpain induces the cardiac dysfunction by reducing CYP2J expression and its metabolite 11,12-EET in ob-/ob- rats.
Methods: After 2 weeks of fenofibrate treatment, the expression of calpain, RXRα, PPAR-α and CYP2J3 were measured by western blotting and RT-PCR in ob-/ob- rat hearts and cardiomyocytes. PPAR-α agonist and 11,12-EET-induced cardioprotection was evaluated in H2O2-treated cardiomyocytes. Acetylcholine (ACh) and 11,12-EET-induced vascular relaxation was measured in ob-/ob- rat aortic ring. The level of 11,12-EET was measured by LC/MS.
Results: Calpain activity was upregulated in ob-/ob- rat hearts and H2O2- treated cardiomyocytes. Calpain induces RXRα, PPAR-α downregulation and leading to decrease of CYP2J3 expression and 11,12-EETs level in diabetic ob-/ob- rat hearts. Administration of PPAR-α agonist reduced the calpain activity (ob-/ob- vs. Feno, 102.7 ± 8.4% vs. 66.4 ± 10.4%, p<0.01) and restored the expression of RXRα, PPAR-α and CYP2J3 in diabetic ob-/ob- rat hearts. H2O2 provoked Ca2+ overload and increased calpain activity, followed by proteolysis of RXRα and decreases of PPAR-α and CYP2J3 in cardiomyocytes from ob-/ob- rats. Administration of calpastatin and 11,12-EET reduced myocardial apoptosis in ob-/ob- rats and cardiomyocytes leading to the improvement of myocardial function. ACh- and 11,12-EET-induced relaxation were also recovered by fenofibrate corresponding to the enhanced CYP2J3 expression and 11,12-EET level.
Conclusions: Calpain induces proteolysis of RXRα, thus inhibits RXRα and PPAR-α heterodimer formation resulting in the suppressed CYP2J3 expression. The increased activity of calpain and reduced synthesis of 11,12-EETs may contribute to cardiac dysfunction in diabetic ob-/ob- rats. Thus targeted inhibition of calpain may be a potential therapeutic target for reversing diabetic cardiomyopathy.
- © 2013 by American Heart Association, Inc.