Abstract 16826: Reversal of TSPO Upregulation in the Diabetic Heart by Chronic TSPO Gene Silencing Causes Metabolic Sink via an Increase in ROMK Expression

Introduction: The mitochondrial translocator protein (TSPO) is an integral component of a macromolecular complex that regulates cell death & survival pathways. Myocardial TSPO levels are markedly increased in diabetes. Objectives: We sought to investigate the electrophysiological effects of TSPO in diabetes using a cardiotropic TSPO gene silencing approach that avoids off-target effects of TSPO ligands. Methods: In a standard model of diabetes mellitus consisting of Zucker Obese rats, AAV9.shTSPO (5E11 gc/mL) was delivered by tail vein injection (N=5). Non-diabetic lean (N=4) and spontaneously hypertensive (N=16) rats served as treatment controls. Untreated diabetic (N=6) and non-diabetic (N=6) hearts were also studied. The TSPO ligand DZP (64μμ) was perfused in additional diabetic hearts to contrast its effects with those of chronic TSPO knockdown. Optical action potential (AP) mapping was performed 2 wks following gene transfer. Hearts were challenged with 12 min ischemia followed by reperfusion. Results: Myocardial TSPO knockdown by AAV9.shTSPO promoted metabolic sink in diabetic hearts. This manifested as rapid and spatially heterogeneous loss of AP amplitude and upstroke velocity in response to ischemia (Figure). Areas of early loss of excitability remained inexcitable upon reperfusion resulting in wide regions of conduction block that supported VT. These findings were specific to diabetes as AAV9.shTSPO did not alter the response of non-diabetic hearts to ischemia. Loss of excitability was not related to irreversible cell death by TUNEL staining. Analysis of the expression of ATP-sensitive channel subunits revealed marked upregulation of ROMK in response to TSPO knockdown exclusively in the diabetic heart. Unlike TSPO knockdown, DZP did not promote metabolic sink but rather prevented post-ischemic VT. Conclusions: Chronic gene silencing of TSPO promotes VT via a metabolic sink mechanism likely arising from compensatory upregulation of ROMK.