Hyperhomocysteinemia Impairs Agonist‐Induced eNOS Phosphorylation on S1179

Abstract

Previously, our group found that hyperhomocysteinemia (HHcy) impairs endothelium‐dependent vasodilation in mouse mesenteric arteries, which was attributed to attenuated nitric oxide (NO)‐dependent dilation, and coincident with decreased eNOS expression and decreased basal eNOS phosphorylation of serine 1179 (S1179) (Ashley et al., FASEB J 21:A910, 2007). Phosphorylation of eNOS of S1179 is necessary for NO‐dependent vasodilation in response to acetylcholine (Ach) stimulation. Thus, we hypothesized that HHcy impairs Ach‐induced eNOS phosphorylation at S1179. To test this hypothesis, we stimulated mesenteric arteries, ex vivo, with Ach (10−4 M) for 5 min and compared the ratio of phosphorylated eNOS at S1179 to total eNOS protein in diet‐induced HHcy mice (Hcy: 89.2 ± 49.0 μM) and their age‐matched controls (Hcy: 6.6 ± 1.9 μM). Densitometric quantification of protein immunoblots indicated robust S1179 phosphorylation in response to Ach in control arteries (% increase ± SD: 59.4% ± 18.5%), but not in HHcy arteries (4.8% ± 18.0%), a response that was significantly less in HHcy arteries (P<0.05). We conclude that attenuation of agonist‐induced NO‐dependent vasodilation in mesenteric arteries from mice with chronic HHcy, is at least partially caused by impaired S1179 phosphorylation of eNOS, and therefore reduced activation of eNOS. Supported by the American Heart Association and the American Physiological Society Undergraduate Summer Research Fellowship.