HIF‐1α increases sympathoexcitation via upregulation of NMDA receptors in the PVN during heart failure (1130.16)

Abstract

Increased sympathetic outflow is a prominent feature of chronic heart failure (HF) associated with higher mortality. Multiple studies from our lab have reported that higher glutamatergic tone (increase in N‐methyl‐D‐aspartate (NMDA)‐type 1 (NR1) receptors expression) within the paraventricular nucleus (PVN) increase the sympathetic drive in HF. Further, HF (coronary artery ligation‐induced) augmented the expression of hypoxia‐inducible‐factor (HIF)‐1α both at mRNA (9 fold) and protein (2.5 fold) levels in the PVN which, led us to hypothesized that increased levels of HIF‐1α may contribute to exaggerated sympathetic drive via increasing NR1 expression in the PVN of rats with HF. Neuronal cell line (NG108‐15) exposed to hypoxia (2% O₂, 5% CO₂, 93% N₂) showed 2‐fold increase in HIF‐1α (12h) expression with concomitant increases in NR1 at transcription and protein levels after 4h (6.5 fold) and 12h (40%) respectively. Live cell imaging also showed marked increase in intracellular calcium in response to glutamate under hypoxic conditions. Mechanistically, hypoxia promotes the direct binding of HIF‐1α (3.2 fold) at NR1 promoter in neurons exposed to hypoxia as demonstrated by chromatin immunoprecipitation analysis. Furthermore, silencing of HIF‐1α by using HIF‐1α ‐targeted small interfering RNA in neurons led to 2.9 fold decrease in the expression of NR1. Validating our in vitro data, HIF‐1α knockdown by HIF‐1α‐siRNA in the PVN of rats with HF ameliorated the increased sympathoexcitation to NMDA (57±5% vs. 27±1% of basal value). Taken together, our study suggests a contribution of HIF‐1α in the regulation of NR1 expression within the PVN in HF, and provides a novel mechanism for the modulation of sympathoexcitation in HF. Supported by NIH HL62222. Grant Funding Source: NIH HL62222.