Abstract P419: Klotho Ameliorate Medullary Fibrosis and Pressure Natriuresis in Hypertensive Rat Kidneys

Abstract

Recent data indicate that klotho interacts with the renin-angiotensin system (RAS). However, the effects of klotho protein supplementation on hypertensive renal injury have not been examined yet. First, the in vivo experiments were performed using spontaneously hypertensive rats (SHR). To elucidate in vivo observations, the in vitro studies were carried out to examine the interactions between klotho protein and angiotensin type-1 (AT1) receptor with immunoprecipitation and cell culture (HK-2 cell) methods. Uninephrectomized SHRs were treated with exogenous klotho protein or vehicle. Exogenous klotho protein supplementation to uninephrectomized SHRs decreased blood pressure, renal angiotensin II levels, angiotensinogen expression, HIF-1α abundance, and medullary fibronectin with increased renal klotho expression and serum and urine klotho levels. Klotho supplementation also reduced kidney weight, renal phosphorylated Akt and mTOR abundance. Furthermore, klotho supplementation restored renal autoregulation of glomerular filtration rate and renal plasma flow, and improved pressure-induced natriuresis in SHR. Klotho protein bound to AT1 receptors without affecting the bindings of angiotensin II to AT1 receptor. Klotho decreased the presence of AT1 receptors on HK-2 cells, attenuating inositol triphosphate generation. Angiotensin II elevated angiotensinogen expression in HK-2 cells, and klotho protein suppressed angiotensin II-induced increases in angiotensinogen expression. Of note, although angiotensin II improves glomerular autoregulatory ability especially at lower pressure range, angiotensin II impairs pressure-induced natriuresis. Collectively, the present data demonstrate that klotho binds with the AT1 receptors to suppress angiotensin signal transduction and inactivate the renal RAS. In addition, our results suggest that exogenous klotho supplementation suppresses Akt-mTOR signaling to decline renal hypertrophy and restores renal autoregulatory ability in uninephrectomized SHRs. Finally, the present findings implicate that klotho supplementation inhibits HIF-1α pathway to suppress medullary fibrosis, presumably involved in improvements of pressure-natriuresis and reduction in blood pressure.