STIMULATORY EFFECTS OF CARTILAGE-DERIVED MORPHOGENETIC PROTEINS 1 AND 2 ON OSTEOGENIC DIFFERENTIATION OF BONE MARROW STROMAL CELLS

Abstract

Cartilage-derived morphogenetic proteins 1 and 2 (CDMP-1 and CDMP-2) are members of the bone morphogenetic protein (BMP) family which play an important role in embryonic skeletal development. Throughout adult life, bone marrow-derived precursor cells maintain their ability to differentiate into osteoblasts in response to local growth factors. This study examines the osteogenic potential of CDMP-1, CDMP-2, BMP-6 and osteogenic protein 1 (OP-1) in bone marrow stromal cells (BMSC) and investigates the endogenous expression of CDMPs/BMPs and their respective activin receptor-like kinase (ALK) receptors. A 4-day exposure of BMSC to CDMP-1, CDMP-2, BMP-6, and OP-1 under serum-free conditions stimulated the progression of the osteogenic lineage in a dose-dependent manner as evaluated by alkaline phosphatase activity and osteocalcin synthesis. In contrast to the BMPs, CDMP-1 and especially CDMP-2 were significantly less osteogenic, as confirmed by Northern blot analysis. Moreover, BMSC were shown to express endogenously CDMP-2, BMP-2 to -6 and ALK-1, -2, -3, -5 and -6. Phenotypic characterization of BMSC by RT-PCR showed transcripts of the fat marker adipsin and the prechondrocytic marker procollagen type IIA; however, we were unable to detect the mature cartilage markers, procollagen type IIB and aggrecan, even after growth factor treatment. Our data indicate that CDMP-1, CDMP-2, BMP-6 and OP-1 enhance the osteogenic phenotype in BMSC, with CDMPs being clearly less osteogenic than BMPs. The endogenous expression of a variety of CDMPs/BMPs and their respective ALK receptors, suggests a possible involvement of these growth factors in the osteogenic differentiation of bone marrow progenitor cells.