Dual peroxisome-proliferator-activated-receptor-α/γ activation inhibits SIRT1-PGC1α axis and causes cardiac dysfunction

Dual peroxisome proliferator-activated receptor (PPAR)α/γ agonists that were developed to target hyperlipidemia and hyperglycemia in type 2 diabetes patients, caused cardiac dysfunction or other adverse effects. We studied the mechanisms that underlie the cardiotoxic effects of a dual PPARα/γ agonist, tesaglitazar, in wild type and diabetic (leptin receptor deficient - db/db) mice. Mice treated with tesaglitazar-containing chow or high fat diet developed cardiac dysfunction despite lower plasma triglycerides and glucose levels. Expression of cardiac peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α), which promotes mitochondrial biogenesis, had the most profound reduction among various fatty acid metabolism genes. Furthermore, we observed increased acetylation of PGC1α, which suggests PGC1α inhibition and lowered sirtuin 1 (SIRT1) expression. This change was associated with lower mitochondrial abundance. Combined pharmacological activation of PPARα and PPARγ in C57BL/6 mice reproduced the reduction of PGC1α expression and mitochondrial abundance. Resveratrol-mediated SIRT1 activation attenuated tesaglitazar-induced cardiac dysfunction and corrected myocardial mitochondrial respiration in C57BL/6 and diabetic mice but not in cardiomyocyte-specific Sirt1-/- mice. Our data shows that drugs, which activate both PPARα and PPARγ lead to cardiac dysfunction associated with PGC1α suppression and lower mitochondrial abundance likely due to competition between these two transcription factors.

Abstract 278: PGC1α Activation Corrects Cardiac Dysfunction Caused by Anti-diabetic Dual-PPARα/γ Therapy

Peroxisome proliferator-activated receptor (PPAR) agonists are used in metabolic diseases. PPARα agonists target hyperlipidemia and PPARγ agonists correct hyperglycemia. Dual PPARα/γ agonists were developed to combine the benefits in type 2 diabetes patients. Despite their beneficial effect, PPARα/γ agonists caused cardiac dysfunction. We studied the mechanisms that underlie this toxic effect aiming to improve a failed therapy.

Wild type mice were fed with chow and high fat diets containing Tesaglitazar (TESA) a dual PPARα/γ agonist for 6 weeks. Although, TESA lowered plasma triglyceride and glucose levels compared to controls, 2D-echo revealed severe cardiac dysfunction. Assessment of the expression of cardiac fatty acid metabolism genes that are regulated by PPARs showed that mRNA and protein levels of PPARγ-coactivator (PGC1α), a regulator of mitochondrial biogenesis, had the most profound reduction. Furthermore, we observed increased acetylation of PGC1α levels, which indicates lower activation and lower mitochondrial respiration.

We then examined the mechanisms that underlie lower expression of PGC1α upon activation of PPARα and PPARγ. Thus, we administered C57BL/6 mice with both single PPARα and PPARγ agonists (WY14643 and rosiglitazone). This treatment reproduced the reduction in PGC1α expression that we observed with TESA. Moreover, mitochondria abundance was lower. Luciferase promoter analysis in a human cardiomyocyte cell line showed that PPARα and PPARγ compete for binding on PPAR elements of the human Pgc1a promoter, as well as that PPARα binding compromises PPARγ-mediated activation of the Pgc1α promoter.

Aiming to decipher the mechanism via which dual PPARα/γ activation increases acetylation and thus inhibits PGC1α, we measured cardiac protein levels of the deacetylase sirtuin 1 (SIRT1), which were lower in primary cardiomyocytes from TESA-treated mice.

We then treated mice with diet containing TESA and Resveratrol (RSV), which stimulates SIRT1. RSV attenuated TESA-driven cardiac dysfunction and corrected mitochondrial respiratory rates in primary cardiomyocytes.

We propose that SIRT1-mediated activation of PGC1α blunts the cardiotoxic effect of dual PPARα/γ agonists and improves their therapeutic potential.