Both intrinsic and extrinsic environmental stimuli influence neuronal and endocrine homeostasis. Perturbations in either of these systems can have profound effects on reproduction. Since luteinizing hormone-releasing hormone (LHRH) is the major neuropeptide regulating reproduction, we have used its gene expression, precursor biosynthesis. processing and secretion as a functional assay to assess environmental effects on reproductive and neuronal states. We have identified the LHRH precursor protein and all of the intermediate products in the pro-LHRH metabolic pathway. In addition, we have also identified each of the processing enzymes and have partially cloned the fourth and final enzyme in this pathway. In secretion studies, we have found that LHRH neurons secrete their peptides by two different pathways. Pro-LHRH is released through the constitutive pathway, while processed peptides are secreted through the regulated pathway. Since the pro-LHRH is devoid of biological activity the routing of this precursor for secretion can have important consequences on the preservation of the mammalian species. In regulation studies, we have shown that adenylyl cyclase activation has no effect on LHRH gene expression, but it can stimulate pro-LHRH processing and secretion. Chronic PKC activation, however, depresses LHRH gene expression while stimulating LHRH processing and secretion. Blockade of PKC activity also suppressed LHRH gene expression, suggesting that PKC is required to maintain LHRH expression levels. These data indicate that environmental stimuli which perturb adenylyl cyclase or PKC activity may have important consequences on neuronal functions. PKC can also exert effects on other hormonal systems. In osteoblasts, PKC can phosphorylate the estrogen receptor such that the receptor is unable to bind estradiol. Other steroid receptor systems may be similarly affected. Future studies will attempt to identify which environmental stimuli affect neuronal function through alterations both in PKC and expression of pro-LHRH and its processing enzymes, precursor biosynthesis, processing and secretion.
