Abstract P184: Rescue of Reductive Stress by Nrf2 Deficiency in Protein Aggregation Cardiomyopathy Mice

Abstract

Background: We recently discovered that the overexpression of human mutant αB-crystallin (hR120GCryAB) in mouse resulted in protein aggregation cardiomyopathy (PAC) and reductive stress (RS) in the heart tissue (Rajasekaran et.al Cell, 2007). Further, we identified that sustained activation of Nrf2 (nuclear erythroid 2 related factor 2)/ARE signaling as a causal mechanism for RS in the MPAC mice. We hypothesize that abolishing Nrf2 could prevent RS in R120GTG mice and thereby rescue them from cardiomyopathy and heart failure. Methods: To elucidate loss-of-function mechanisms for Nrf2 on RS and MPAC, we produced (1) NTG/WT, (2) R120GTG/WT, (3) R120GTG/Nrf2+/- and (4) R120GTG/Nrf2-/- mice by intercrossing R120GTG X Nrf2-KO. Primarily, we determined the rate of survival and performed echocardiography to understand the degree of pathogenesis and cardiac function over time (n=6-10). Next, we analyzed the redox state and protein/mRNA expression for major antioxidants including enzymes that are involved in glutathione metabolism in the heart. Results: Disruption of Nrf2 prolonged the survival of MPAC mice along with no signs of cardiac dysfunction (by ECHO). The R120GTG mice with Nrf2 deficiency (either Nrf2+/- or Nrf2-/-; n=4) had significantly decreased glutathione (but equal to NTG) levels when compared with R120GTG/WT cohorts. Such a decline in GSH resulted in quenching of “reducing power” to prevent “reductive stress” and facilitated redox homeostasis in the myocardium. Interestingly, the intercross mice showed no cardiac hypertrophy even at 12 months while the R120GTG exhibited 90% mortality due to PAC/heart failure. Further, protein and mRNA levels for major antioxidants were found to be normal in the R120GTG/Nrf2+/- while there was significant down regulation of these parameters in the R120GTG/Nrf2-/- mice when compared to NTG/WT suggesting that Nrf2-independent pathways are inadequate to maintain the antioxidant capacity under stressed conditions. Conclusions: These results demonstrate a critical role for Nrf2 underlying antioxidant potential in the myocardium. Abrogating RS via Nrf2 might be highly relevant to cure the protein aggregation diseases that are coupled with elevated intracellular reducing potential.