Involvement of type VI collagen in interleukin-4-induced mineralization by human osteoblast-like cells in vitro

We recently showed that interleukin-4 (IL-4) enhanced collagen and osteocalcin accumulation and caused mineralization in human periosteal osteoblast-like (SaM-1) cells. At that time, the expression of alpha 1(VI) collagen mRNA was induced. In the present study, the possible role of IL-4-induced type VI collagen in the in vitro mineralization in osteoblasts was investigated. Addition of IL-4 in the early stage (for the first 10 days) was essential for the mineralization. The mRNA levels of alpha 1(VI) and alpha 2(VI) collagen and protein level of type VI collagen were transiently increased by IL-4 treatment up to day 5, whereas the alpha 1(I) procollagen mRNA level was greater at day 10 than at day 5. Addition of anti-type VT collagen antibody remarkably reduced the extracellular accumulations of calcium and hydroxyproline induced by IL-4. Furthermore, the transfection of antisense oligonucleotides of alpha 1(VI) to SaM-1 cells in the presence of IL-4 partially inhibited IL-4-induced type I collagen accumulation. These results demonstrated that type VI collagen played important roles for IL-4-induced mineralization and hydroxyproline accumulation, mostly type I collagen accumulation, in human periosteal osteoblast-like cells. (C) 1999 Elsevier Science B.V. All rights reserved.