Abstract 082: Histone Deacetylase 1 Activates Renal Inner-Medullary Nitric Oxide Production

Abstract

Fluid flow along the renal nephron, particularly within the inner-medullary collecting duct (IMCD), increases in response to high salt intake. We previously showed in a series of reports that high salt intake increases nitric oxide synthase 1 (NOS1) activity in the CD mediating inhibition of the epithelial sodium channel (ENaC) to promote natriuresis. However, the mechanism of how high salt increases NOS1 activity in the CD is not known. Histone deacetylase 1 (HDAC1) is known to mediate post-translational deacetylation in response to flow in other cell types. Hence, we hypothesized that HDAC1 activates renal medullary NOS1-dependent NO production in response to high salt intake. Renal medullas were isolated from C57bl/6J mice after one week of normal (NS, 0.4% NaCl) or high salt (HS, 4% NaCl) diet. Inner-medullary HDAC1 expression (NS: 1.00±0.1, HS: 1.61±0.1 RDU; n=5/group, p=0.001), but not activity (NS: 0.07±0.02, HS: 0.05±0.01μM/μg, n=5/group, p>0.05), was significantly elevated in mice on HS compared to NS. HDAC1-selective inhibitor, MS-275 (300 nM), was utilized in in vitro and ex vivo experiments to determine the contribution of HDAC1 to NOS activity. Nitrite production, analyzed by HPLC, increased >5-fold (static: 231±31.1, flow: 1291±183 pmol/mg pr/hr; n=7/group, p<0.001) in mouse IMCD cells in response to acute 10 dynes/cm 2 fluid-flow. MS-275 significantly blunted flow-responsive NO production (MS-275: 342±44.0 pmol/mg pr/hr; n=9/group, p<0.001). Likewise, ENaC activity, which is negatively regulated by NOS1, was significantly increased in isolated collecting ducts post ex vivo MS-275 treatment from mice on HS (HS: 0.34±0.11 NP o , HS+MS-275: 0.97±0.16 NP o ; n=22/group, p<0.05). Moreover, acute DETA-NONOate treatment, an NO donor, reversed this finding (HS+MS-275: 0.77±0.14 NP o , HS+MS-275+DETA: 0.46±0.14 NP o ; n=10/group, p<0.05). Lastly, acute MS-275 treatment in vitro did not increase NOS1 acetylation status as determined by co-immunoprecipitation, suggesting that HDAC1 may not directly deacetylate NOS1. Taken together, these data indicate that HS intake increases renal medullary HDAC1 to positively regulate NOS1-derived NO production.