Journal Article

Elevated glucose induction of thrombospondin-1 up-regulates fibronectin synthesis in proximal renal tubular epithelial cells through TGF-β1 dependent and TGF-β1 independent pathways

Susan Yung, Candice Y. Y. Lee, Qing Zhang, Shuk Kei Lau, Ryan C. W. Tsang and Tak Mao Chan

in Nephrology Dialysis Transplantation

Published on behalf of European Renal Association - European Dialysis and Transplant Assoc

Volume 21, issue 6, pages 1504-1513
Published in print June 2006 | ISSN: 0931-0509
Published online February 2006 | e-ISSN: 1460-2385 | DOI: http://dx.doi.org/10.1093/ndt/gfl017
Elevated glucose induction of thrombospondin-1 up-regulates fibronectin synthesis in proximal renal tubular epithelial cells through TGF-β1 dependent and TGF-β1 independent pathways

Show Summary Details

Preview

Background. TGF-β1 bioactivation, consequent to the interaction of latent TGF-β1 with thrombospondin-1 (TSP-1), correlates with matrix accumulation in mesangial cells. Tubulointerstitial damage predicts poor renal survival. There is little data on TGF-β1 bioactivation and matrix synthesis in human proximal renal tubular epithelial cells under the influence of high glucose concentrations. This study thus investigates the role of TSP-1 in mediating elevated glucose-induction of TGF-β1 bioactivation and fibronectin (FN) synthesis in human proximal tubular epithelial cells.

Methods. Human proximal renal tubular epithelial cells (HK-2 cells) were incubated with 5, 10, 20 or 30 mM d-glucose for up to 3 weeks either in the presence or absence of TSP-1 blocking peptide. In separate studies HK-2 cells were incubated with exogenous TSP-1 (0–10 ng/ml) or TGF-β1 (0–10 ng/ml) for 24 h. Cell proliferation was assessed by [3H]-thymidine incorporation. TGF-β1 transcript, secretion and bioactivity were investigated by quantitative real-time PCR, ELISA and the MLEC bioassay respectively. TSP-1 and FN synthesis were assessed by quantitative real-time PCR, ELISAs and Western blot analysis.

Results. Elevated glucose concentrations increased TSP-1 synthesis, which was associated with reduced cell proliferation, increased TGF-β1 bioactivity, and stimulation of FN synthesis. The inclusion of TSP-1 blocking peptide to cells stimulated with elevated glucose concentration abrogated activation of TGF-β1 and induction of FN secretion. Exogenous TSP-1 increased bioactive TGF-β1 in HK-2 cells to initiate FN accumulation. Of interest is our observation that TSP-1 also increased matrix synthesis through a mechanism independent of TGF-β1. TGF-β1 in turn modulated TSP-1 synthesis, indicative of an autocrine loop between TSP-1 and TGF-β1.

Conclusions. TSP-1 plays an important role in the induction of matrix synthesis by high glucose concentrations in human proximal renal tubular epithelial cells, through TGF-β1 dependent and TGF-β1 independent pathways. Pharmacological intervention targeting increased TSP-1 expression may interrupt the pathogenesis of diabetic nephropathy.

Keywords: fibronectin; glucose; proximal renal tubular epithelial cells; TGF-β1; thrombospondin-1

Journal Article.  5317 words.  Illustrated.

Subjects: Nephrology

Full text: subscription required

How to subscribe Recommend to my Librarian

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.