Lineage-dependent collagen expression and assembly during osteogenic or chondrogenic differentiation of a mesoblastic cell line

The mesoblastic clone, C1, behaves as a tripotential progenitor able to sel f-renew and to differentiate toward osteogenesis, chondrogenesis, or adipog enesis in response to specific inducers. In this study, expression and depo sition by the C1 cells of essential components of the extracellular matrix, collagens type I, II, III, V, XI, VI, IX, and X were followed along the os teogenic and chondrogenic pathways, through biochemical, immunochemical, an d electron microscopy analyses. Implementation of each program involves pro files of collagen synthesis and matrix assembly close to those documented i n vivo. Depending on the applied inducers, cells adopt a defined identity a nd, controls acting at transcriptional and posttranslational levels adapt t he set of deposited collagens to one particular cell fate. Osteogenic C1 ce lls selectively build a type I collagen matrix also containing type III, V, and XI collagens but selectively exclude type II collagen. Chondrogenic C1 cells first elaborate a type II collagen network and then acquire hypertro phic chondrocyte properties while assembling a type X collagen matrix as in the growth plate. This study provides an example of how a mesoblastic cell line can develop, in vitro, each of its genetic programs up to terminal di fferentiation. Intrinsic factors and time-dependent cell-matrix interaction s might, as in vivo underline the implementation of an entire differentiati on program. (C) 1999 Academic Press.