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Osteoarthritis (OA) is a common degenerative joint disease; however, its underlying pathogenesis remains to be elucidated. Previous studies have demonstrated that the transforming growth factor‑β (TGF‑β) signaling pathway has a role in the initiation and development of OA. Additionally, latent TGF‑β‑binding protein‑1 (LTBP‑1) modulates the activity of the TGF‑β‑mothers against decapentaplegic (Smad) signaling pathway in numerous diseases, including malignant glioma. The present study demonstrated that expression of LTBP‑1 is increased in OA synovial tissues compared with normal synovial tissues. The effect of TGF‑β was identified to be mediated by phosphorylated(p)‑(Smad)2/3, which may activate activin‑like kinase (ALK)5 receptor, and by p‑Smad1/5/8, which may induce ALK1, thereby stimulating expression of matrix metalloproteinase‑(MMP)‑13 in OA fibroblast‑like synoviocytes (FLS). Compared with normal FLS, OA FLS demonstrated an increased p‑Smad1/5/8:p‑Smad2 ratio, which led to elevated MMP‑13 expression and aggravation of OA. Furthermore, knockdown of the LTBP‑1 gene by siRNA transfection in OA FLS reduced p‑Smad1/5/8 expression without affecting TGF‑β mRNA levels, although p‑Smad2 expression increased. It was also demonstrated that OA FLS exhibited increased proliferation compared with normal FLS in vitro. Furthermore, siRNA‑mediated downregulation of LTBP‑1 reduced proliferation of OA FLS. In conclusion, the present study demonstrated that an alteration in the p‑Smad1/5/8:p‑Smad2 ratio as well as association between p‑Smad1/5/8 and MMP‑13 expression in human OA FLS, may contribute to the development of OA. The results of the present study suggested that LTBP‑1 is a modulator of the TGF‑β signaling pathway in human OA FLS, which may aid in elucidating the mechanism underlying the pathology of OA.
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