Type IV collagen, which is encoded by six genetically distinct alpha-chains (alpha
1-alpha 6), is a major component of the kidney glomerulus. The alpha 1(IV) and alpha
2(IV) chains are present predominantly in the mesangial matrix, whereas the alpha
3(IV), alpha 4(IV), and alpha 5(IV) chains are localized almost exclusively to the
glomerular basement membrane (GBM). Thickening of the GBM and expansion of the mesangial
matrix are believed to contribute to the pathogenesis of diabetic nephropathy. In
the present study, we evaluated the expression of alpha 1(IV), alpha 3(IV), and alpha
5(IV) chains in rat glomerular endothelial (GEndC) and mesangial cells (GMC). Under
physiological concentrations of glucose (5 mM), alpha 1(IV) and alpha 5(IV) chains
were detectable in GMCs, with an obvious absence of alpha 3(IV) chain. All three isoforms
tested were present in GEndCs. At diabetic concentrations of glucose (25 mM), alpha
1(IV) was up-regulated in GMCs, whereas expression level of alpha 1(IV) remained unaltered
in GEndCs. The alpha 3(IV) and alpha 5(IV) chains were up-regulated in GEndCs, but
remained unchanged in GMCs under diabetic glucose concentrations (25 mM). Collectively,
our results demonstrate that GMC might contribute to mesangial matrix expansion, mediated
by alpha 1(IV) collagen, while GEndC might contribute to thickening of GBM, mediated
by alpha 3(IV) collagen, in patients with diabetic nephropathy.