ASTROCYTES SYNTHESIZE AND SECRETE PROSTAGLANDIN-D SYNTHETASE IN-VITRO

Prostaglandin D synthetase [PGD-S, prostaglandin-H, D-isomerase, (5Z, 13E)-(15S)-9 alpha, 11 alpha-epidioxy-15-hydroxyprosta-5, 13-dienoate D-isomerase, EC 5,3,99,2], an enzyme that catalyzes the formation of p rostaglandin D-2, was originally isolated from homogenates of rat brai n and spleen and is known to be a membrane-bound enzyme. Subsequent im munohistochemical studies have shown that PGD-S is associated with neu rons in the brain of immature rats, whereas in adult rats it is associ ated with oligodendrocytes. Several recent studies have shown that the beta-trace protein isolated from human cerebrospinal fluid (CSF), the second most abundant protein in human CSF after albumin, is equivalen t to PGD-S. In this paper, we report the preparation of a monospecific polyclonal antibody against purified PGD-S isolated from human CSF an d the establishment of a specific radioimmunoassay for this protein. U sing this radioimmunoassay in conjunction with immunoblot analysis, PG D-S was detected in various biological fluids including serum, aqueous humor, and rete testis fluid. In addition, an antibody prepared again st human PGD-S partially cross-reacted with the PGD-S in the rat and r am. Using a monospecific polyclonal antibody prepared against purified rat PGD-S isolated from rat CSF in conjunction with [S-35]methionine incorporation and immunoprecipitation techniques, it was shown for the first time that PGD-S is actively synthesized and secreted by astrocy tes cultured in vitro, suggesting the astrocyte is the cellular origin of PGD-S in the CSF. The identification of the astrocyte as the cellu lar origin of this unique enzyme will allow the use of an in vitro sys tem to study its regulation.