Expression of proteoglycan core proteins in human bone marrow stroma

Heparan sulphate proteoglycans (HSPGs) present on the surface of bone marro w stromal cells and in the extracellular matrix (ECM) have important roles in the control of adhesion and growth of haemopoietic stem and progenitor c ells. The two main groups of proteoglycans which contain heparan sulphate c hains are members of the syndecan and glypican families. In this study we h ave identified the main surface membrane and matrix-associated HSPGs presen t in normal human bone marrow stroma formed in long-term culture. Proteogly cans were extracted from the adherent stromal layers and treated with hepar itinase and chondroitinase ABC. The core proteins were detected by Western blotting using antibodies directed against syndecans-1-4, glypican-1 and th e ECM HSPG, perlecan. Stromal cell expression at the RNA level was detected by Northern blotting and by reverse transcription PCR. Glypican-1, syndeca n-3 and syndecan-4 were the major cell-membrane HSPG species and perlecan w as the major ECM proteoglycan. There was no evidence for expression of synd ecan-1 protein. Syndecan-3 was expressed mainly as a variant or processed 5 0-55 kDa core protein and in lower amounts as the characteristic 125 kDa co re protein. These results suggest that syndecan-3, syndecan-4 and glypican- 1 present on the surface of marrow stromal cells, together with perlecan in the ECM, may be responsible for creating the correct stromal 'niche' for t he maintenance and development of haemopoietic stem and progenitor cells. T he detection of a variant form of syndecan-3 as a major stromal HSPG sugges ts a specific role for this syndecan in haemopoiesis.