Podocyte injury enhances filtration of liver-derived angiotensinogen and renal angiotensin II generation

Abstract

Intrarenal angiotensin II is increased in kidney diseases independently of plasma angiotensin II and is thought to promote progressive deterioration of renal architecture. Here we investigated the mechanism of enhanced renal angiotensin II generation in kidney glomerular diseases. For this, kidney- or liver-specific angiotensinogen gene (Agt) knockout was superimposed on the mouse model of inducible podocyte injury (NEP25). Seven days after induction of podocyte injury, renal angiotensin II was increased ninefold in NEP25 mice with intact Agt, accompanied by increases in urinary albumin and angiotensinogen excretion, renal angiotensinogen protein, and its mRNA. Kidney Agt knockout attenuated renal Agt mRNA but not renal angiotensin II, renal, or urinary angiotensinogen protein. In contrast, liver Agt knockout markedly reduced renal angiotensin II to 18.7% of that of control NEP25 mice, renal and urinary angiotensinogen protein, but not renal Agt mRNA. Renal angiotensin II had no relationship with renal Agt mRNA, or with renal renin mRNA, which was elevated in liver Agt knockouts. Kidney and liver dual Agt knockout mice showed phenotypes comparable to those of liver Agt knockout mice. Thus, increased renal angiotensin II generation upon severe podocyte injury is attributed to increased filtered angiotensinogen of liver origin resulting from loss of macromolecular barrier function of the glomerular capillary wall that occurs upon severe podocyte injury.