DEVELOPMENTAL AND CELL-TYPE-SPECIFIC EXPRESSION OF CELL-SURFACE HEPARAN-SULFATE PROTEOGLYCANS IN THE RAT-HEART

The expression of cell surface heparan sulfate proteoglycans in rat he art was investigated by Northern blot analysis with specific cDNA prob es. In adult heart syndecan-3 and glypican mRNAs were abundantly expre ssed. Lower levels of syndecan-2 mRNA and very low levels of syndecan- 1 mRNA were also detected. Analysis of RNA isolated from hearts of rat s of various ages revealed that syndecan-3 and glypican mRNAs levels i ncreased dramatically at birth, and continued to be expressed at high levels in adult animals. To determine which of these proteoglycans was expressed in cardiomyocytes, primary cultures of cardiomyocytes and n onmyocytes isolated from neonatal rat hearts were analyzed for proteog lycan expression. Glypican mRNA was localized almost exclusively to ca rdiomyocytes. Syndecan-3 mRNA was not detected in myocytes, but was de tected in the nonmyocyte cells. Biochemical characterization of cardio myocyte glypican revealed that it was a phosphatidylinositol-anchored heparan sulfate proteoglycan. Results of immunofluorescent staining of rat hearts with anti-glypican antibodies were consistent with the Nor thern blot data, and localized glypican to the lateral regions of myoc yte plasma membrane that contact the basement membrane, as well as sit es of myocyte adhesion junctions. At the latter site glypican colocali zed with vinculin. Visualization of basic fibroblast growth factor bin ding sites by means of a tissue slice overlay assay also revealed colo calization with glypican. These results demonstrate developmental and cell-type-specific expression of membrane heparan sulfate proteoglycan s in the heart. They also show that glypican is a major heparan sulfat e proteoglycan expressed on the cardiomyocyte plasma membrane. (C) 199 7 Academic Press