Abstract 4910: Forkhead Transcription Factor 3a (FOXO3a) is Involved in the Regulation of Functional Response to Aging and Stress in Murine Cardiomyocytes
Aging is a complicated but regulated process. Forkhead transcription factors (FOXO), the major substrates for the protein kinase Akt and AMP-activated protein kinase, play an important role in longevity. Our earlier studies suggested that deficiency in insulin-growth factor I (IGF-1) contribute to cardiomyocyte dysfunction but prolongs lifespan possibly through downregulation of FOXO3a signaling. Given that lifespan extension is closely associated with stress tolerance, our present study was set to examine the effect of FOXO3a inhibition on aging-/stress-induced cardiomyocyte contractility and survival. The dominant negative FOXO3a-GFP adenovirus was injected into adult and aged C57BL/6J murine hearts. Five days later, GFP positive cardiomyocytes (denoting successful Foxo3a transfection) isolated from in adult and old C57BL/6J mice were identified for assessment of contractile properties including peak shortening (PS), time-to-PS (TPS), time-to-relengthening (TR90), and maximal velocity of shortening/relengthening (+/−dL/dt). Dominant negative FOXO3a (FDN) transfection significantly reduced PS in adult group although it restored aging-induced dysfunction in PS, +/−dL/dt and TR90. Further study on MTT assay and western blot revealed that transfection of FDN in H9c2 myoblasts exhibited higher survival rate in response to paraquat and H2O2 compared to control group. Inhibition of FOXO3a expression enhanced phosphorylation of Akt and AMPK in both normal and paraquat-treated conditions. Paraquat downregulated the “aging” protein-klotho, the effect of which was restored by FDN transfection. These data suggested that FOXO3a plays an important role in regulation of cardiomyocyte contractility and stress resistance under aging or oxidative stress.