Cell surface heparan sulfate proteoglycans control the response of renal interstitial fibroblasts to fibroblast growth factor-2

Background. While the progression of renal disease to end stage is strongly correlated with tubulointerstitial changes, the control of the fibrotic pr ocess within the interstitium is poorly understood. Basic fibroblast growth factor (FGF-2) has been implicated as a major growth factor involved in fi broblast activation and extracellular matrix synthesis. Furthermore, in man y cells, the activity of FGF-2 is controlled by a low-affinity but high-cap acity interaction with heparan sulfate (HS) proteoglycans (PGs). such as me mbers of the syndecan family. These molecules are likely to be central to t he control of interstitial fibrosis, but as yet, there has been no characte rization of their synthesis by interstitial cells. Methods. The expression of HSPG on the surface of NRK 49F fibroblasts was d emonstrated by immunohistochemistry and by metabolic labeling with [S-35]-s ulfate. HSs were characterized by specific enzymatic digestion, size exclus ion chromatography, and anion exchange chromatography. The mRNA for syndeca n 1 through syndecan 4 in the fibroblasts was detected by semiquantitative reverse transcription-polymerase chain reaction. Fibroblast proliferation w as measured by the MTT assay. Results. Immunohistochemistry and [S-35]-sulfate-labeling demonstrated that renal fibroblasts expressed HSPGs on their surface. Furthermore, enzymatic removal of these HS (but not chondroitin sulfate) glycosaminoglycan (GAG) chains, or inhibition of GAG sulfation, abolished the proliferative respons e of both NRK cells and primary human cortical fibroblasts to FGF-2 but not to platelet-derived growth factor. The addition of conditioned medium, con taining MS-GAG fragments, restored the proliferative response to FGF-2, con firming the specificity of the interaction. Finally, the mRNA for all four syndecans was detected in the fibroblasts, and that for syndecan 1 in parti cular was up-regulated by FGF-2. Conclusions. The present study demonstrates that the expression of cell sur face HSPG was essential for the proliferation of renal fibroblasts in respo nse to FGF-2 and therefore may play a major role in the development and per sistence of a proliferating phenotype during interstitial nephritis.