Type III collagen regulates growth of human osteoblastic cells

Objectives: Collagen has been reported to be essential for the proliferation and differentiation of various kinds of cells including human osteoblastic cells (Maehata et al., Matrix Biol. 2006), but the type(s) of collagen responsible for growth regulation is not known. Thus, we examined the molecular species of the collagen involved in the regulation of the growth of the human osteoblastic cells.

Methods: Human osteoblast-like MG 63 cells, normal human osteoblasts and human bone marrow mesenchymal stem cells were cultured in the presence or absence of ascorbic acid 2-phosphate (Asc 2-P), a long-acting vitamin C derivative, and cell growth and collagen synthetic activity were then determined. The levels of mRNA were analyzed by the cDNA microarray method, northern blotting and/or PT-PCR. The production of collagen proteins was determined by gel electrophoresis followed by fluorography.

Results: Asc 2-P stimulated both cell growth and the expression of mRNA for type III collagen in human osteoblast-like MG 63 cells and in normal human osteoblasts, as well as in human bone marrow mesenchymal stem cells, but not the expression of type I collagen in these cells. Among MG-63 cell clones, their growth rates correlated significantly with their COL3A1 messenger RNA levels but not with their COL1A1 or COL1A2 messenger RNA levels. Transfection of MG 63 cells with siRNA for COL3A1 but not with that for COL1A1 decreased the growth rates of the transfected cells concomitant with a drop in the level of COL3A1 mRNA. Furthermore, cell proliferation as observed by thymidine incorporation into DNA and cell number was increased when MG-63 cells were cultured on type III collagen-coated dishes.

Conclusion: Our results indicate that type III collagen is the collagen component responsible for the growth stimulation of human osteoblastic cells.