Specialized collagen mRNA and secreted collagens in human glomerular epithelial, mesangial, and tubular cells.

Abstract

Isolated glomeruli and cultured cells were examined under nonmitogenic conditions by Northern hybridization of steady-state mRNA levels for procollagens alpha 1(I), alpha 1(III), alpha 1(IV), alpha 2(IV), beta-actin, and fibronectin. Procollagens concurrently secreted from these cells were characterized after limited pepsin digestion. Poly(A)-mRNA from freshly isolated whole porcine glomeruli was primarily type IV. For cultured glomerular and tubular epithelial cells, the collagen mRNA species were almost exclusively alpha 1(IV) and alpha 2(IV). Correspondingly, the secreted collagen was almost entirely type IV. The mRNA signals for collagens in glomerular mesangial cells included alpha 1(I), alpha 1(IV), alpha 2(IV), and less alpha 1(III). The secreted collagens were also types I and IV, with less types III and V. There were similar patterns of mRNA signal levels for the two type IV collagens and similar patterns of expression of alpha 1(I) and alpha 1(III). In situ hybridization showed the fibroblast and epithelial cell populations homogeneous in expressing the same mRNA signals seen by Northern hybridization. These findings establish the correlation of collagen mRNA and protein expression of collagens in differentiated glomerular cells in culture, under resting nonmitotic conditions.