Effect of High Glucose on Type IV Collagen Production by Cultured Glomerular Epithelial, Endothelial, and Mesangial Cells

Immunochemical and metabolic radiolabeling procedures revealed that homogeneous cultures of calf glomerular epithelial, endothelial, and mesangial cells actively synthesize type IV collagen (primarily as α₁(Iv)₃) which is secreted into the medium and incorporated into the extracellular matrix. Exposure of confluent cultures of the three cell types to a high glucose concentration (30 mM) for 60 h resulted in a pronounced increase (two- to threefold) in type IV collagen production over that observed at a physiological level (5 mM) of this sugar, as determined by either immunoblotting or fluorography of electrophoretically separated media or cell-matrix components. The elevated glucose did not bring about a change in the rate of cell proliferation or fibronectin production. Moreover, studies with mannitol indicated that the stimulation of type IV collagen synthesis was not a function of hyperosmolarity. In contrast to the glomerular cells, glucose-induced enhancement of formation of this collagen was not observed in 3T3 cells despite a substantial acceleration in the consumption of this sugar. Time studies indicated that the response of the glomerular cells to high glucose occurs over an extended period (maximal at ∼78 h) and, furthermore, that the stimulatory effect on type IV collagen production is only slowly reversed after restoration of the glucose to a normal level. We believe that these findings are relevant to an understanding of the sequence of events that lead to the development of diabetic glomerular lesions.