Abstract P3028: Conditional Knockout of Acid Ceramidase in Collecting Ducts Exacerbates Salt Sensitivity of Blood Pressure With High Fat Diet

Abstract

Ceramidase is the rate-limit step for the production of sphingosine-1-phosphate (S1P) by controlling the immediate substrate sphingosine for S1P generation. We have previously shown that S1P increases sodium excretion via S1P receptor 1, which is mainly localized in the collecting ducts. We have also shown that conditional deletion of acid ceramidase (AC), the major form of ceramidase in collecting duct, promotes sodium retention. It is well known that salt sensitivity of blood pressure is a characteristic in obesity-associated hypertension. The present study detected levels of renal medullary AC in male C57BL6J mice fed with a high fat (HF) diet (10 weeks) and/or 1% NaCl drinking water (2 weeks). Western blot analyses showed that there was no significant difference in AC levels among normal salt (NS)-, low fat (LF)- and HF-treated mice. However, the high salt (HS) intake increased the AC levels, whereas a HF diet blocked the high salt-induced increase of AC. The relative protein levels of AC were 1.0 ± 0.06, 1.4 ± 0.07, 0.99 ± 0.23, 1.1 ± 0.05, and 0.4 ± 0.06, in NS, HS, LF, HF, and HS+HF groups, respectively. Mice with collecting duct-specific AC knockout (CD-AC-KO) were generated by crossing AC floxed mice with Aquoporin 2-Cre mice. The specific knockout of AC in collecting ducts was confirmed by immunohistochemistry and western blot. The mean arterial pressure (MAP) was significantly increased in CD-AC-KO mice compared with AC floxed mice after fed with HS+HF diet. The delta MAP before and after 2 week HS intake were 3.45 ± 0.35 mmHg in control vs. 10.6 ± 1.04 mmHg in CD-AC-KO mice measured by a DSI telemetry system. These data indicate that collecting duct AC plays an important role in salt-sensitivity of blood pressure associated with a high fat diet and that modulation of AC function in the kidneys could be a therapeutic approach for salt-sensitive hypertension associated with obesity.