Region-specific regulation of transforming growth factor alpha (TGF alpha) gene expression in astrocytes of the neuroendocrine brain.

Certain glial cells of the hypothalamus have been implicated in the neuroendocrine control of reproductive development. Hypothalamic astrocytes appear to exert this function via a cell-cell interactive mechanism that involves the production of transforming growth factor alpha (TGF alpha), a polypeptide able to affect both glial and neuronal functions in the CNS. In the hypothalamus, TGF alpha stimulates neuronal secretion of luteinizing hormone-releasing hormone (LHRH), the neuropeptide controlling sexual development, via activation of epidermal growth factor receptors (EGFR). Since astrocytes but not LHRH neurons express EGFR, it has been postulated that the stimulatory effect of TGF alpha on LHRH release is not exerted directly on LHRH neurons, but rather via glial intermediacy. The present experiments were undertaken to define whether TGF alpha is able to exert paracrine/autocrine effects on isolated hypothalamic astrocytes, and to determine if estradiol-previously shown to increase TGF alpha mRNA levels in the hypothalamus of immature animals--can act directly on hypothalamic astrocytes to upregulate TGF alpha gene expression. Treatment with either TGF alpha or its structural homolog, epidermal growth factor (EGF), increased TGF alpha mRNA levels within 8 hr of exposure; the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) was similarly effective. Blockade of EGFR with either tyrphostin RG-50864, an inhibitor of tyrosine kinase activity, or a monoclonal antibody that prevents ligand binding abolished the upregulatory effect of TGF alpha on TGF alpha mRNA levels. In contrast to hypothalamic astrocytes, cerebellar astrocytes did not respond to either TGF alpha or EGF with changes in TGF alpha mRNA abundance.(ABSTRACT TRUNCATED AT 250 WORDS)