Albumin modified by Amadori-glucose adducts induces coordinate increases in the expression of extracellular matrix proteins, transforming growth factor (TGF)-β1, and the TGF-β 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-β1 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 β-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-β1 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-β isoform is linked to the stimulation of collagen type IV production.
Isolation and sequencing of cDNAs and genomic DNAs encoding the alpha 4 chain of basement membrane collagen type IV and assignment of the gene to the distal long arm of human chromosome 2.
