We seek to advance the understanding of the physiology and pathophysiology of the hypothalamic-pituitary-adrenal (HPA) and -gonadal (HPG) axes. The roles of the stress-related hormones corticotropin-releasing hormone (CRH) and glucocorticoids in normal and disease states are being examined, and clinical applications for these hormones and their antagonists are sought. We have demonstrated that several human states are characterized by hyperactivity or hypoactivity of the central stress system, which explains not only mood changes but also the propensity of patients with such disorders to develop developmental, metabolic, cardiovascular or autoimmune complications. We are currently performing preclinical studies with the newly discovered nonpeptide, oral, CRH type 1 receptor antagonist, antalarmin, which show that such an antagonist may be useful in a large number of states characterized by hyperactivity of the stress system, such as depression, anorexia nervosa and idiopathic insomnia. At the level of the stress system target tissues, we have elucidated the molecular pathophysiology of sporadic and familial glucocorticoid resistance by defining novel mutations and/or deletions of the glucocorticoid receptor gene leading to abnormally functioning or decreased receptors. In the same area, we have described inflammation-induced glucocorticoid resistance and glucocorticoid secretion insufficiency in the acute respiratory distress syndrome. We have also found that CLOCK/BMAL1, the self-oscillating transcription factors that generate circadian rhythms in both the central nervous system and periphery, rhythmically repressed GR-induced transcriptional activity, indicating that CLOCK/BMAL1 functions as a reverse phase negative regulator of glucocorticoid action in target tissues, possibly by antagonizing the biologic actions of diurnally fluctuating circulating glucocorticoids. Furthermore, the noncoding (nc) RNA Gas5, which accumulates in growth-arrested cells, but whose physiologic roles are not known as yet, and the adenosine 5 monophosphate-activated protein kinase (AMPK), a master regulator of energy homeostasis, sensing energy depletion inside the body and stimulating pathways that increase fuel uptake and save on peripheral supplies, regulated GR-induced transcriptional activity. The former accomplished this by acting as a decoy RNA GRE, the latter by phosphorylating the GR. These results indicate that the biologic actions of the HPA axis are regulated at the level of the target tissues by the nutritional state and availability of energy resources. In the brain, which consists of central component of the HPA and HPG axis, we found that the cyclin-dependent kinase 5, which plays important roles in the morphogenesis and functions of CNS, and whose aberrant activation is associated with development of neurodegenerative disorders, interacted with both GR and the mineralocorticoid receptor (MR) through its activators p35/p25 and differentially regulated the transcriptional activity of these steroid receptors. Endogenous glucocorticoids, cortisol and corticosterone, bind these receptors and cause receptor-specific biologic actions in CNS, while one of their target molecules, the brain-derived growth factor (BDNF) plays a critical roles in the neurobiability, synaptic plasticity, consolidation of memory and emotional changes. Therefore, aberrant activation of CDK5 may in part regulates neuronal activity through corticosteroid receptors/BDNF, further influencing the activity of the HPA, and possibly, the HPG axis. Extracellular hyperosmolarity or osmotic stress is a major threat for land organisms, and thus strongly stimulates HPA axis through secretion of ariginine vasopression from the hypothalamus/posterior lobe of the pituitary gland. In addition to this systemic response, it also activates a cellular cascade of adaptive response to extracellular hyperosmolarity. Extracellular hyperosmolarity or osmotic stress induces and activates a Rel-homology domain-containing transcription factor, the nuclear factor of activated T-cells 5 (NFAT5), which subsequently stimulates transcription of osmotic stress-responsive genes and causes intracellular accumulation of small organic osmolytes to maintain isotonicity between the inside and outside of the cells. We recently evaluated an intracellular signaling cascade responsive to osmotic stress in lymphocytes as a model tissue, and found that a Rho-type guanine nucleotide exchange factor (GEF) Brx or AKAP13 is essential for the osmotic stress-stimulated expression of NFAT5, and is a key component of the intracellular signaling cascade transmitting the extracellular hyperosmolarity signal to the nucleus. Osmotic stress-mediated induction of NFAT5 requires the Brx GEF domain and p38 mitogen-activated kinase (MAPK), while Brx in response to osmotic stress attracts through its C-terminal domain the cJun kinase (JNK)-interacting protein (JIP) 4, a scaffold specific to activation of the p38 MAPK cascade and NFAT5, coupling activated Rho-type small G proteins to components of the p38 MAPK signaling pathway. Importantly, this signaling system plays a critical role in the lymphocyte differentiation in the spleen, while it is a general mechanism for most of the organs and tissues to protect them from extracellular hyperosmolarity and to maintain their functions.
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