Abstract 19066: D-Dopachrome Tautomerase Provides a Novel Cardioprotective Mechanism Through its Modulation on AMPK Activation in Heart During Ischemia-reperfusion

Abstract

Endogenously released cardiac proteins or cardiokines regulate intracelluar signaling pathway and cardiac injury in response to stress. Macrophage migration inhibitory factor (MIF) modulates AMP-activated protein kinase (AMPK) activation and limits cardiac injury during ischemia-reperfusion. Genetic deletion of the MIF receptor, CD74, has more profound effects on ischemic tolerance and AMPK activation, than deletion of MIF alone, suggesting the possibility of a second receptor ligand. We recently identified D-dopachrome tautomerase (DDT) as a homolog of MIF, and the purpose of this study was to determine the actions of DDT in the heart. DDT perfusion in mouse heart increased AMPK in a dose-dependent manner (from 10 to 50ng/ml) without alterations in LV contractile function. Immunohistochemistry showed that DDT was highly expressed in cardiomyocytes in the mouse heart. DDT release from perfused mouse hearts (baseline: 2 ± 0.5 ng/min; post-ischemia: 4.5 ± 0.7 ng/min, p<0.05) was triggered by brief episodes (15 min) of ischemia and the inhibition of DDT actions by perfusion with neutralizing antibody (anti-DDT vs. non-immune IgG) significantly attenuated AMPK activation during ischemia. Anti-DDT (100µg/ml) also resulted in more pronounced cardiac injury following ischemia-reperfusion. Parallel effects were observed in isolated rat heart papillary muscles: recombinant DDT treatment had a similar pharmacologic effect to induce AMPK activation in a dose-dependent manner. Hypoxia (15 min) also stimulated DDT release from rat papillary muscles and inhibition of extracellular DDT by DDT neutralizing antibodies impaired AMPK activation. These pharmacologic and physiologic effects of DDT were also observed in isolated rat cardiomyocytes, indicating that DDT has specific autocrine effects. DDT treatment (400ng/ml) increased intracellular calcium in cardiomyocytes and STO-609 (2µM), a calmodulin-dependent protein kinase kinase (CaMKK) inhibitor attenuated DDT induced AMPK phosphorylation, suggesting that DDT induced AMPK activation is mediated by calcium-CaMKK pathway. Thus, DDT is a novel endogenous cardiac protein that modulates cardiac stress response pathways and protects against injury during ischemia.