Abstract 3945: Metabolic Coupling to Function is Restored in Reperfused Myocardium Overexpressing SERCA1 Without Compromising Energy Potential (PCr/ATP)
Recent studies find that increased expression of the sarcoplasmic reticulum Ca2+-ATPase (SERCA) improves contractility and reduces calcium overload in myocardial ischemia-reperfusion. However, whether metabolic uncoupling from contractile function, which underlies reperfusion injury, is also restored or if metabolic inefficiency remains is unknown. Therefore, we examined metabolic activity, substrate selection, and energetic potential (PCr/ATP) in reperfused hearts overexpressing SERCA1. Adv.cmv.SERCA1 (SR1) or PBS (control) was delivered via coronary perfusion to Sprague-Dawley rat hearts in vivo. Three days following gene transfer, isolated hearts were perfused with 0.4 mM 13C-palmitate + 5 mM glucose. 13C or 31P NMR signals were acquired throughout 15 min ischemia and 40 min reperfusion.
Results: Consistent with myocardial stunning, LVDP (63±15 mmHg) was depressed 40% vs preischemic LVDP (103±8) in the PBS group. SERCA1 expression ameliorated stunning as LVDP (104±9) recovered to preischemic values and contractility accelerated (±dP/dt: SR1 7330±260 mmHg/s, PBS 4710±620, p<0.05). PCr/ATP recovery was improved with SERCA1. In both groups, palmitate accounted for 73% of fuels oxidized for pre-ischemic ATP production and 63% after 50 min reperfusion, demonstrating that SERCA1 did not influence substrate use. More importantly, 13C NMR revealed similar Krebs cycle flux between groups during reperfusion (SR1 12.6±2.7 umol/m/gdw; PBS 13.2±3.4;), despite the lack of stunning with SR1. Therefore, coupling between cardiac work and Krebs cycle flux was restored with SR1 treatment. Furthermore, SERCA1 countered over-activation of Ca2+ sensitive mitochondrial dehydrogenases at reperfusion, restoring intermediate transfer of cytosolic NADH into the mitochondria (SR1 2.11±0.42 umol/m/gdw; PBS 1.35±0.47, p<0.05) and thereby, increasing oxidative efficiency and cytosolic redox regulation.
Conclusion: These data demonstrate improved metabolic efficiency and NADH handling with SERCA1 expression, despite persistent reductions in fat oxidation. This study finds the cardioprotective and metabolic effects of SERCA overexpresssion support the increasing potential of its therapeutic utility.