Klotho Ameliorates Medullary Fibrosis and Pressure Natriuresis in Hypertensive Rat Kidneys

Renal expression of klotho is reduced in hypertension. Experiments were performed to examine whether exogenous klotho protein supplementation ameliorates pressure natriuresis in early phase of hypertension, using stroke-prone spontaneously hypertensive rats (sp-SHR). The interactions between klotho protein and renal renin-Ang (angiotensin) system were examined with immunoprecipitation and cell culture methods. Uninephrectomy was performed in sp-SHRs to induce nephrosclerosis, and they were treated with exogenous klotho protein or vehicle. Exogenous klotho protein supplementation to sp-SHR decreased blood pressure, renal Ang II levels, AGT (angiotensinogen) expression, HIF (hypoxia-inducible factor)-1α abundance, and medullary fibronectin levels, with increased renal klotho expression and serum and urine klotho levels. Klotho supplementation also reduced kidney weight, renal phosphorylated Akt, and mTOR (mammalian target of rapamycin) abundance. Furthermore, klotho supplementation restored renal autoregulation of glomerular filtration rate and enhanced pressure-induced natriuresis in sp-SHR. Klotho protein bound to AT1R (Ang II type-1 receptor) and decreased the presence of AT1R on HK-2 (human proximal tubular) cells, attenuating inositol triphosphate generation. Klotho protein suppressed Ang II–induced increments of AGT expression in HK-2 cells. Collectively, the present data demonstrate that klotho binds with the AT1R to suppress Ang signal transduction, participating in inactivating renal renin-Ang system. Our results also suggest that exogenous klotho supplementation represses Akt-mTOR signaling to reduce renal hypertrophy and restore the autoregulatory ability of glomerular filtration rate in uninephrectomized sp-SHRs. Finally, the present findings implicate that klotho supplementation inhibits HIF-1α pathway and medullary fibrosis, contributing to enhancements of pressure natriuresis and reduction in blood pressure.