Human brain glial cells synthesize thrombospondin.
Thrombospondin, a 450-kDa multinodular glycoprotein with lectin-type activity, is found in human platelets, endothelial cells, fibroblasts, smooth muscle cells, monocytes, and granular pneumocytes. Thrombospondin interacts with heparin, fibrinogen, fibronectin, collagen, histidine-rich glycoprotein, and plasminogen. Recently, thrombospondin synthesis by smooth muscle cells has been reported to be augmented by platelet-derived growth factor. We present evidence that thrombospondin is present within and synthesized by astrocytic neuroglial cells. Heparin-Sepharose affinity chromatography of material derived from a human brain homogenate yielded a protein that, when reduced, had an apparent size of 180 kDa and comigrated with reduced platelet thrombospondin on NaDodSO4/PAGE. Immunoblot analysis with monospecific anti-thrombospondin confirmed the presence of immunoreactive thrombospondin. Indirect immunofluorescence of cultured human glial cells indicated the presence of thrombospondin. Metabolic labeling of glial cell cultures with [35S]methionine followed by immunoprecipitation with monospecific anti-thrombospondin revealed synthesis of a 180-kDa polypeptide that comigrated with platelet thrombospondin on NaDodSO4/PAGE. Cultured human glial cells were incubated for 48 hr in serum-free medium with purified platelet-derived growth factor at concentrations up to 50 ng/ml. Aliquots taken at intervals were analyzed by a quantitative double-antibody ELISA. The growth factor stimulated the release of thrombospondin into the culture medium by as much as 10-fold over control cultures. The presence of thrombospondin within glial cells of the central nervous system and the augmentation of its synthesis by platelet-derived growth factor suggest that thrombospondin may play an important role in regulating cell-cell and cell-matrix interactions during periods of cell division and growth.
D001921:Brain / Q000378:metabolism*; D002448:Cell Adhesion; D002450:Cell Communication; D002478:Cells, Cultured; D005341:Fibrinolysin / Q000096:biosynthesis; D005455:Fluorescent Antibody Technique; D006023:Glycoproteins / Q000096:biosynthesis* / Q000276:immunology / Q000302:isolation & purification; D006801:Humans; D008715:Methionine / Q000378:metabolism; D009457:Neuroglia / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D019699:Thrombospondins
D006023:Glycoproteins; D010982:Platelet-Derived Growth Factor; D019699:Thrombospondins; D008715:Methionine; D005341:Fibrinolysin