Primary focal segmental glomerulosclerosis is associated with increased intraglomerular type IV collagen synthesis

Differential expression of parietal epithelial cell and podocyte extracellular matrix proteins in focal segmental glomerulosclerosis and diabetic nephropathy

In healthy glomeruli, parietal epithelial cell (PEC)-derived extracellular matrix (ECM) proteins include laminin-β1, perlecan, and collagen type IV-α2 and podocyte-specific ECM proteins include laminin-β2, agrin, and collagen type IV-α4. This study aimed to define individual ECM protein isoform expression by PECs in both experimental and human focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy (DN) and to determine if changes were CD44 dependent. In experimental FSGS induced with a cytotoxic podocyte antibody and in the BTBR ob/ob mouse model of DN, PEC-derived protein staining was significantly increased in PECs. Dual staining also showed de novo expression of the podocyte-specific ECM proteins laminin-β2 and agrin in PECs. Similar findings were observed in biopsies from patients with FSGS and DN. Increases in individual ECM proteins colocalized with CD44 in PECs in disease. To determine the role of CD44, FSGS was induced in CD44-/- and CD44+/+ mice. PEC staining for perlecan, collagen type IV-α2, laminin-β2, and agrin were significantly lower in diseased CD44-/- mice compared with diseased CD44+/+ mice. These results show that in experimental and human FSGS and DN, PECs typically in an activated state, produce both PEC-derived and podocyte-specific ECM protein isoforms, and that the majority of these changes were dependent on CD44.

Prostaglandin E2 stimulates expression of matrix metalloproteinase 2 in cultured rat mesangial cells

Prostaglandins of the E-series have been demonstrated to reduce extracellular accumulation of collagens in some models of glomerulonephritis. This effect is partially due to reduction of collagen formation by mesangial cells. The potential effects of prostaglandins on the expression of collagen degrading enzymes in mesangial cells are largely unknown. Since rat mesangial cells generate a matrix metalloproteinase 2 (MMP-2) that specifically degrades collagen type IV, the effects of prostaglandin E2 (PGE2) on transcription, steady-state mRNA levels, extracellular enzyme activity and protein concentration of this proteinase were evaluated. Mesangial cells (MC) were incubated with PGE2 (2 microM) for different time-periods (1 to 48 hr), and steady-state mRNA levels of MMP-2 were determined by Northern blotting. PGE2 increased MMP-2 mRNA levels beginning at one hour of incubation and remained elevated up to 24 hours. Nuclear run off experiments revealed that the PGE2-induced increase in mRNA expression for MMP-2 is due to stimulated gene transcription. Western blot analysis and zymography revealed that MMP-2 protein production and enzyme activity was also enhanced by PGE2. The cAMP analogue 8-bromo-cAMP increased MMP-2 mRNA levels, suggesting that PGE2-induced generation of intracellular cAMP plays a role in MMP-2 induction in MC. These studies demonstrate that PGE2 stimulates the transcription, protein formation and enzyme activity of MMP-2 in cultured rat MC. This effect may contribute to the prostaglandin mediated reduction of extracellular collagen deposition in glomerulonephritis.

Immunohistochemical analysis of type III and IV collagens in tubulointerstitial damage in human benign nephrosclerosis

Prolonged hypertension causes structural changes including glomerulosclerosis and tubulointerstitial damage of the kidney, termed benign nephrosclerosis. It is generally accepted that, in benign nephrosclerosis, increased accumulation of extracellular matrix in the glomeruli results in glomerulosclerosis. Little is known, however, about the possible role of the extracellular matrix in the tubulointerstitial damage in benign nephrosclerosis. In this study, the possible roles of type IV basement-membrane collagen and type III interstitial collagen in tubulointerstitial damage caused by hypertension were explored. Immunohistochemical techniques were used to investigate the distribution of type III and type IV collagens in the kidney sections of 15 patients with benign nephrosclerosis with tubulointerstitial damage and in 10 controls. In the control renal sections strong immunostaining for type III collagen was found in the interstitium and immunostaining for type IV collagen was present in the tubular basement membrane and weakly in the interstitium. In the patients with tubulointerstitial damage there was increased immunostaining for both type III and type IV collagens in the expanded interstitium and damaged tubules than was found in the control kidney sections. These findings indicate that increased accumulation of both type III and type IV collagens might play a significant role in the tubulointerstitial damage in benign nephrosclerosis.

Suppression of mesangial-cell proliferation by trapidil in glomerulonephritis induced by anti-thymocyte serum in rats

Trapadil (Mochida Pharmaceuticals, Japan), an antiplatelet drug, suppresses the growth of several cell types and is thought to antagonize platelet-derived growth factor. The effects of trapidil on mesangial-cell proliferation in glomerulonephritis induced by anti-thymocyte serum in Wistar rats were investigated. Control rats were treated with phosphate-buffered saline (group I); group II rats were injected with a single dose of anti-thymocyte serum (8 ml/kg body weight), and group III rats were treated with both a single dose of anti-thymocyte serum (8 ml/kg body weight) and with trapidil (5 mg/kg body weight/day). Three rats in each group were killed on day 3, and the other three on day 10. Control rats showed no significant histological changes on day 3 or day 10. In group II, on day 3, there was a marked decrease in glomerular cell numbers, with mesangiolysis. Histologically severe mesangial-cell proliferation with expansion of mesangial areas was noted on day 10. None of the rats in group III showed mesangial alterations, histologically, indicating that mesangial-cell proliferation was suppressed by trapidil. This suppression may result from antagonism of the binding of platelet-derived growth factor to the specific surface receptors in the mesangial cells. Trapidil may have clinical value in the treatment of mesangial-cell proliferative glomerular diseases.