Role of angiotensin II in glucose-induced inhibition of mesangial matrix degradation.

Abstract

Accumulation of mesangial matrix in diabetic nephropathy is caused by increased synthesis and decreased degradation. We have previously demonstrated that incubation in high-glucose medium decreases mesangial cell collagenase activity (Diabetes 44:929-935, 1995). Because angiotensin II (AII) is involved in the pathogenesis of diabetic nephropathy, the present studies were performed to determine if AII mediates glucose-induced 1) inhibition of mesangial collagenase activity, 2) mesangial matrix accumulation, and 3) in-crease in transforming growth factor (TGF)-beta1 secretion in mesangial cells. The direct effect of high glucose on AII generation in mesangial cells was also determined. Primary mesangial cells from normal Sprague-Dawley rats were used in all studies. Collagenase activity in cell medium was determined using three methods: 1) zymography; 2) quantitative assay using fluoresceinated gelatin as substrate; and 3) a new enzyme-linked immunosorbent assay (ELISA) that specifically measures 72-kDa collagenase (MMP-2), the principal collagenase synthesized by mesangial cells. Matrix accumulation was estimated by immunoperoxidase assay on cell layers using anti-glomerular basement membrane (GBM) antibodies. TGF-beta1 and AII levels were determined by ELISA. Exposure of mesangial cells to 30 mmol/l glucose (high glucose) vs. 5 mmol/glucose (normal glucose) for 5 days resulted in a significant decrease in collagenase activity (25%) that was normalized by 10(-4) mol/l losartan, a type 1 angiotensin II (AT1) receptor antagonist. High glucose increased anti-GBM binding compared with normal glucose; this effect of glucose was reversed by losartan. Incubation of cells with 30 mmol/l glucose increased total TGF-beta1 secretion, which was also normalized by losartan. Addition of AII (10(-6) mol/l) for 24 h to the culture medium inhibited collagenase activity by 33%; losartan (10(-4) mol/l) blocked this inhibition of enzyme activity. Also, AII decreased collagenase (MMP-2) levels but stimulated TGF-beta1 secretion in mesangial cells. Finally, glucose increased mesangial AII generation in a concentration-dependent manner, with incubation in 30 mmol/l glucose increasing AII by 25% compared with 5 mmol/l glucose. We conclude that glucose increases AII production by mesangial cells, which results in stimulation of TGF-beta1 secretion, decreased matrix degradation, and increased matrix accumulation. These effects of AII are mediated by the AT1 receptor.

Renoprotective effects of an angiotensin II receptor blocker in experimental model rats with hypertension and metabolic disorders

“…12,38 Previous reports of activated local RAS with an increased local production of Ang II and an expression of AT1 receptor in experimental rats modeling hypertension, diabetes mellitus and subtotal nephrectomy support this assertion. [41][42][43] Taken together, these results suggest that ARBs exhibit renoprotective effects by blocking local RAS in the kidney.…”

Angiotensin II induces human TGF-β1 promoter activation: similarity to hyperglycaemia

“…Our study which was focused on the ang II effect on TGF-β1 promoter activation (fragment -453/+11) in mesangial cells does not exclude that high glucose and ang II might have additive effects on other cellular functions. For example long-term incubation of mesangial cells with 30 mmol/l glucose (for 5 days) resulted in an ang II-dependent inhibition of mesangial matrix degradation suggested to be mediated by an increased ang II generation of the mesangial cells [40]. Furthermore, in vivo studies provide evidence for the activation of the renal renin-angiotensin system by hyperglycaemia, which might not occur in cultured mesangial cells [41].…”

Juxtaglomerular apparatus T-cell infiltration affects glomerular structure in Type 1 diabetic patients

“…Angiotensin II upregulates TGF-β receptor expression in cultured mesangial cells, thus stimulating ECM production [6]. Angiotensin II inhibits mesangial cell collagenase activity [7] and these effects can be blocked by Losartan [7], an angiotensin II receptor blocker. Angiotensin converting enzyme in-hibitors reduce fibronectin [8] and matrix metalloproteinase [9] production of mesangial cells exposed to high glucose.…”