Angiotensin II stimulates extracellular matrix protein synthesis through induction of transforming growth factor-beta expression in rat glomerular mesangial cells.

TLDR

Angiotensin II is linked to progressive glomerulosclerosis, yet its precise mechanism remains unclear, while transforming‑growth‑factor β has been shown to drive extracellular‑matrix synthesis and remodeling in this disease. The study aimed to test whether Angiotensin II promotes glomerulosclerosis by inducing transforming‑growth‑factor β. Researchers treated cultured rat mesangial cells with Angiotensin II, measured TGF‑β and matrix proteins, and used the Angiotensin II antagonist saralasin, a neutralizing TGF‑β antibody, and in vivo Angiotensin II infusion to dissect the signaling pathway. Angiotensin II increased TGF‑β and biglycan, fibronectin, and collagen‑I expression in a dose‑ and time‑dependent manner, and these effects were blocked by saralasin or TGF‑β neutralization, with in vivo infusion also elevating glomerular TGF‑β and collagen‑I mRNA, confirming that Angiotensin II induces matrix synthesis through TGF‑β.

Abstract

Angiotensin II (Ang II) has been implicated in the development of progressive glomerulosclerosis, but the precise mechanism of this effect remains unclear. In an experimental model, we have shown previously that TGF-beta plays a key role in glomerulosclerosis by stimulating extracellular matrix protein synthesis, increasing matrix protein receptors, and altering protease/protease-inhibitor balance, thereby inhibiting matrix degradation. We hypothesized that Ang II contributes to glomerulosclerosis through induction of TGF-beta. Ang II treatment of rat mesangial cells in culture increased TGF-beta and matrix components biglycan, fibronectin, and collagen type I at both the mRNA and protein levels in a time- and dose-dependent manner. Saralasin, a competitive inhibitor of Ang II, prevented the stimulation. Ang II also promoted conversion of latent TGF-beta to the biologically active form. Coincubation of mesangial cells with Ang II and neutralizing antibody to TGF-beta blocked the Ang II-induced increases in matrix protein expression. Continuous in vivo administration of Ang II to normal rats for 7 d resulted in 70% increases in glomerular mRNA for both TGF-beta and collagen type I. These results indicate that Ang II induces mesangial cell synthesis of matrix proteins and show that these effects are mediated by Ang II induction of TGF-beta expression. This mechanism may well contribute to glomerulosclerosis in vivo.