Glomerular cells, extracellular matrix accumulation, and the development of glomerulosclerosis in the remnant kidney...

Expansion of the mesangial extracellular matrix (ECM) with subsequent glomerular sclerosis is a prominent finding in most progressive renal diseases. To investigate the chronology of accumulation of ECM components as it relates to previously described cellular events, biopsies were obtained from rats at various times following 5/6-nephrectomy as well as from sham-operated controls. The biopsies were stained with PAS as well as immunostained for PCNA (a cell proliferation marker), monocytes/macrophages, types I and IV collagen, laminin, s-laminin, fibronectin, heparan sulfate proteoglycan and entactin/nidogen. Immunostaining of biopsies obtained from 5/6 nephrectomized rats demonstrated an early glomerular cell proliferation, peaking at week 2. Expansion of the glomerular tuft area with rare glomeruli demonstrating focal sclerosis were also seen at week 2. Glomerular macrophage influx correlated with later ECM expansion and glomerulosclerosis. A progressive accumulation of all ECM proteins investigated was noted in the pathological mesangial matrix at week 2 and later time points. Northern analysis of total glomerular RNA at weeks 2 and 6 after 5/6 nephrectomy showed de novo expression type I collagen mRNA as well as small increases of glomerular mRNA levels for type IV collagen (1.2- and 1.4-fold over control RNA) and laminin (1.3- and 1.5-fold) but not s-laminin (1.1- and 0.9-fold). We conclude that cellular events including glomerular cell proliferation and macrophage influx are associated with increased gene and protein expression by ECM proteins in the remnant kidney model and may contribute to the development of sclerosis.