Glycated albumin stimulation of PKC-beta activity is linked to increased collagen IV in mesangial cells.

Abstract

Albumin modified by Amadori-glucose adducts induces coordinate increases in the expression of extracellular matrix proteins, transforming growth factor (TGF)-beta1, and the TGF-beta type II receptor in glomerular mesangial cells. Because activation of protein kinase C (PKC) accompanies the increased mesangial cell expression of matrix proteins and TGF-beta1 induced by high ambient glucose, we postulated that glycated albumin (GA) modulates PKC activity and that PKC participates in mediating the GA-induced stimulation of matrix production. To test this hypothesis, we examined the effects of PKC inhibitors on collagen type IV production by mouse or rat mesangial cells incubated with GA, and the influence of GA on PKC activity in these cells. Increased collagen type IV production evoked by GA in 5.5 and 25 mM glucose in mouse mesangial cells was prevented by both general (GF-109203X) and beta-specific (LY-379196) PKC inhibitors. Total PKC activity, measured by phosphorylation of a PKC-specific substrate, increased with time after exposure of rat mesangial cells to GA compared with the nonglycated, glucose-free counterpart. GA caused an increase in PKC-beta1 membrane-bound fraction and in total PKC activity in media containing physiological (5.5 mM) glucose concentrations in rat mesangial cells, confirming that the glucose-modified protein, and not a "hyperglycemic" milieu, was responsible. The findings indicate that Amadori-modified albumin stimulates mesangial cell PKC activity, and that activation of the PKC-beta isoform is linked to the stimulation of collagen type IV production.