Influence of the fibroblast environment on the structure of mast cell proteoglycans.

The structure of the proteoglycan synthesized by rodent mast cells has been a useful biochemical marker of mast cell subpopulations, since mucosal mast cells synthesize predominantly oversulfated chondroitin sulfate proteoglycan and connective tissue mast cells synthesize heparin proteoglycan. Mast cells are intimately associated with fibroblasts in tissues and fibroblasts maintain the connective tissue type mast cell ex vivo. Whereas mouse IL-3-dependent, immature mast cells synthesize predominantly chondroitin sulfate E proteoglycan, after coculture with fibroblasts, the proliferating mast cells (cloned or uncloned) synthesize heparin proteoglycans, as well as change their phenotype to resemble connective tissue mast cells. Although there is a single peptide core for both heparin and chondroitin sulfate secretory granule proteoglycans, the relative predominance of a specific glycosaminoglycan is determined by the microenvironment in which the cell resides. This microenvironment can regulate the phenotypic properties of mast cells including the expression of their cationic constituents such as neutral proteases and the structure of their anionic proteoglycans.