PROLACTIN-INDUCED EXPRESSION OF INTERLEUKIN-1-ALPHA, TUMOR-NECROSIS-FACTOR-ALPHA, AND TRANSFORMING GROWTH-FACTOR-ALPHA IN CULTURED ASTROCYTES

Prolactin (PRL) is a potent mitogen in cultured astrocytes. Because one of the major effects of astrocyte proliferation is the expression of inflammatory cytokines, we examined the effect of PRL-induced mitogenesis on the expression of interleukin-1 (IL-1 alpha), tumor necrosis factor-alpha (TNF-alpha), and transforming growth factor-alpha (TGF-alpha) in cultured astrocytes. Astrocytes were stimulated with PRL or growth hormone (CH), and the expression of cytokines was determined by immunohistochemistry and Western blot analysis. Following incubation of astrocytes with 1 nM PRL for 6 h, strong positive staining of IL-1 alpha and TNF-alpha, but not TGF-alpha, was found. No detectable staining for the above cytokines was found in vehicle, or GH treated astrocytes. When astrocytes were incubated in the presence of 1 nM PRL for 18 h, strong positive staining for IL-1 alpha and TGF-alpha was found. Immunocytochemical analysis of the expression of TNF-alpha and IL-1 alpha in PRL stimulated astrocytes suggested that the expression of IL-1 alpha preceded the expression of TNF-alpha. To confirm this observation, Western blot analyses were performed on extracts from astrocytes incubated with 1 nM PRL. In unstimulated astrocytes, IL-1 alpha levels were not detectable. In astrocytes stimulated with 1 nM PRL, expression of IL-1 alpha was clearly detected after 1 h of incubation, and IL-1 alpha levels continued to increase during the course of the experiment (6 h). In contrast, in astrocytes stimulated with 1 nM PRL, an increase in the expression of TNF-alpha was first apparent after 2 h of incubation. TNF-alpha levels peaked 3 to 4 h after the addition of PRL, and returned to near control levels after 6 h. Finally, injection of PRL into a wound site in female rats increased the expression of glial fibrillary acid protein (GFAP), an astrocyte specific protein. These data suggest that PRL can stimulate astrogliosis at the wound site in vivo. These data clearly indicate that PRL can stimulate the expression of TNF-alpha and IL-1 alpha in cultured astrocytes and suggest that PRL may play a role in the regulation of the neuroimmune response in vivo. (C) 1995 Wiley-Liss, Inc.