Degradation of nNOS in the PVN of Rats With Heart Failure: Role of CHIP

One salient feature of congestive heart failure (CHF) is the exaggerated sympathetic drive. Reduced nNOS (neuronal nitric oxide synthase) within the paraventricular nucleus (PVN) is primarily responsible for the enhanced sympathetic tone in CHF. Here, we examined the role of CHIP (C-terminus of heat shock cognate protein 70-interacting protein) as a key regulator of nNOS in the PVN.

CHF in rats was induced by left coronary artery ligation. Alterations in the expression of nNOS, CHIP, HSP70 (heat shock protein 70), and HSP90 (heat shock protein 90) in the PVN of CHF rats were evaluated by Western blot and immunofluorescence techniques. Neuronal NG108-15 cells were used to analyze the effect of CHIP overexpression (using the pCMV3-CHIP-GFP spark plasmid) on nNOS expression in vitro. CHIP overexpression was achieved by viral injections in the PVN of normal rats.

CHIP (50%) and HSP70 (33%) were significantly upregulated in the PVN of rats with CHF. Overexpression of CHIP in neuronal NG108-15 cells showed an ≈74% increase in CHIP with a concomitant decrease in nNOS expression (≈49%). Overexpression of CHIP significantly increased ubiquitination of nNOS (46%) in NG108-15 cells. Overexpression of CHIP in the PVN of normal control rats significantly reduced NO-mediated inhibition of renal sympathetic nerve activity, blood pressure, and heart rate.

Overall, these studies identify overexpression of CHIP, which triggers ubiquitination and proteasomal degradation of nNOS in the PVN results in reduced inhibitory sympathetic tone in CHF.