Pioglitazone limits myocardial infarct size, activates Akt, and upregulates cPLA2 and COX-2 in a PPAR-γ-independent manner

Pioglitazone (PIO), a PPAR-γ agonist, limits myocardial infarct size by activating Akt and upregulating cytosolic phospholipase A₂ (cPLA₂) and cyclooxygenase (COX)-2. However, PIO has several PPAR-γ-independent effects. We assessed whether PIO limits myocardial infarct size in PPAR-γ–knockout mice, attenuates hypoxia-reoxygenation injury and upregulates P-Akt, cPLA₂, and COX-2 expression in PPAR-γ–knockout cardiomyocytes. Cardiac-specific inducible PPAR-γ knockout mice were generated by crossing αMHC-Cre mice to PPAR-γ^loxp/loxp mice. PPAR-γ deletion was achieved after 7 days of intraperitoneal tamoxifen (20 mg/kg/day) administration. Mice received PIO (10 mg/kg/day), or vehicle, for 3 days and underwent coronary occlusion (30 min) followed by reperfusion (4 h). We assessed the area at risk by blue dye and infarct size by TTC. Cultured adult cardiomyocytes of PPAR-γ^{loxp/loxp/cre} mice without or with pretreatment with tamoxifen were incubated with or without PIO and subjected to 2 h hypoxia/2 h reoxygenation. Cardiac-specific PPAR-γ knockout significantly increased infarct size. PIO reduced infarct size by 51% in PPAR-γ knockout mice and by 55% in mice with intact PPAR-γ. Deleting the PPAR-γ gene increased cell death in vitro. PIO reduced cell death in cells with and without intact PPAR-γ. PIO similarly increased myocardial Ser-473 P-Akt, cPLA₂, and COX-2 levels after hypoxia/reoxygenation in cells with and without intact PPAR-γ. PIO limited infarct size in mice in a PPAR-γ-independent manner. PIO activated Akt, increased the expression of cPLA₂ and COX-2, and protected adult cardiomyocytes against the effects of hypoxia/reoxygenation independent of PPAR-γ activation.