Abstract P205: The Role of Nuclear Nox4 in Mediating Oxidation of HDAC4 in Response to Phenylephrine Stimulation

Abstract

Reduction and oxidation (Redox) stress is involved in the pathogenesis of cardiac hypertrophy and heart failure. We have shown previously that oxidation of conserved cysteine residues in histone deacetylase 4 (HDAC4) induces nuclear-to-cytoplasmic translocation of HDAC4, thereby mediating phenylephrine (PE)-induced cardiac hypertrophy. NAD(P)H oxidase 4 (Nox4) is a major source of oxidative stress in cardiomyocytes (CMs) in response to pressure overload. We hypothesized that Nox4 plays an essential role in mediating cardiac hypertrophy by regulating the redox state of HDAC4. Nox4 exists on intracellular membranes, including the mitochondria and nucleus in CMs. A subpressor dose of phenylephrine (PE, 20 mg/kg per day) or saline alone (control) was continuously infused into wild type (WT) and cardiac specific Nox4 knockout (Nox4-/-) mice subcutaneously via an osmotic minipumps. After 14 days, mean aortic pressure was similar between WT and Nox4-/- mice. Left ventricular (LV) wall thickness (1.04±0.03 vs. 1.27±0.06 mm, p<0.05) and LV weight/ tibial length (LVW/TL 5.7±0.14 vs. 6.4±0.05 mg/mm, p<0.05) were significantly lower in Nox4-/- than in WT mice. CM cross sectional area (MCA: 223±13 vs. 258±12 μm 2 , p<0.05) was significantly smaller in Nox4-/- than in WT mice. Superoxide production from the nuclear membrane, as evaluated by lucigenin chemiluminescent assays, was also significantly lower in Nox4-/- than in WT mice (4116±314 vs. 7057±1710 RLU, p<0.05). On the other hand, PE infusion induced significantly greater cardiac hypertrophy in transgenic mice with cardiac specific overexpression of Nox4 than in control mice. In cultured neonatal rat CMs, PE (100μM) treatment induced upregulation of Nox4 (2.8 fold vs. control, p<0.05) within 5 min, which was accompanied by increases in superoxide production (6 fold, p<0.01) and rapid (< 5min) nuclear export of HDAC4. Knockdown of Nox4 with shRNA-Nox4, but not Nox2 knockdown, attenuated superoxide production in the nucleus and prevented PE-induced nuclear export of HDAC4. These results suggest that Nox4 plays an essential role in mediating PE-induced cardiac hypertrophy. Nox4 mediates PE-induced superoxide production in the nucleus and nuclear export of HDAC4, possibly through cysteine oxidation.