Current Research Interests:
Stress is linked to a number of psychiatric disorders including major depression, anxiety, anorexia nervosa, and addiction. Studies in our laboratory have focused largely on a critical regulator of the mammalian stress response- corticotropin-releasing hormone (CRH). This 41 amino acid neuroendocrine peptide is the key hypothalamic releasing factor in the mammalian stress response. Hypothalamic CRH stimulates the synthesis and secretion of adrenocorticotropin (ACTH) from the anterior pituitary, which in turn stimulates the production and release of glucocorticoids from the adrenal cortex. Glucocorticoids then mediate the body's adaptive response to stress. CRH is also expressed in other regions of the brain and in the periphery where it mediates many of the endocrine, autonomic, and immunological effects of stress. A new family of CRH-like peptides, the urocortins (urocortin I, II and III), was recently identified in mammals. The role of this family of peptides in stress, anxiety, depression, and addiction is presently unclear, but is an area of current studies in the laboratory.
The biological effects of CRH and urocortin are, of course, dependent upon specific receptors on the post-synaptic or target cells. Both CRH and urocortin bind to the two classes of CRH receptors. In addition, they both bind to a high affinity CRH-binding protein (CRH-BP). This binding protein is distinct from the receptors, binds CRH and urocortin with an affinity equal to or greater than that of the receptors, and is expressed in the pituitary and CNS of rodents and primates. In vitro, this binding protein neutralizes the biological activity of CRH and urocortin I. These findings have led us to hypothesize that the CRH-BP may play an important physiological role by modulating the biological effects of CRH and urocortin in the pituitary and CNS. To begin to elucidate the functional role(s) of the CRH-BP, we examined the regulation of pituitary CRH-BP gene expression by stress and steroid hormones in vivo. Pituitary CRH-BP expression is significantly increased by restraint stress and glucocorticoids, suggesting that it may play a role in the termination of the stress response. Pituitary CRH-BP expression is also positively regulated by estrogen both in vivo and in vitro, suggesting sexually dimorphic roles for this binding protein. We have also created mouse models for CRH-BP overexpression or deficiency states. CRH-BP deficient mice, created by homologous recombination in embryonic stem cells, show increased anxiety-like behavior and decreased weight gain, consistent with elevated levels of "free" CRH and urocortin in the absence of CRH-BP. Recent studies have also suggested a role for central CRH-BP in stress-induced relapse to cocaine use and we have initiated a series of studies to elucidate the roles of CRH, CRH receptors, and CRH-BP in the stress-induced reinstatement of drug use. The results from additional in vivo and in vitro studies will allow us to better understand the role of the CRH-BP in modulating the actions of CRH and other CRH-like peptides in the pituitary and within the central nervous system and its potential links to depression, anxiety disorders, and substance abuse.
Finally, we have collaborated with the Akil/Watson laboratories to study the role of the corticosteroid receptors in modulation of the stress response and depressive- and anxiety-like behaviors. Together, we have created mouse models with increased forebrain glucocorticoid (GR) or mineralocorticoid (MR) receptor expression. Our laboratory is also studying the mechanisms of MR- and GR- mediated gene regulation in hippocampal cell lines at the transcriptome level using microarray and chromatin immuoprecipitation/deep sequencing methods. As we further characterize the mechanisms of gene regulation by GR and MR in hippocampal cells and the behavioral, endocrine, and molecular changes in the genetically modified mice, we will better understand the impact of altered GR/MR ratio in the negative feedback control of the stress response. As impaired negative corticosteroid feedback and dysregulated CRH activity within the HPA axis are two primary features of depression and anxiety-disorders, we believe that these studies will provide important information on the molecular changes in these disorders, with the potential for providing new therapeutic approaches.
Karolyi, I.J., Burrows, H.L., Nakajima, M., Ramesh, T., Camper, S.A., and Seasholtz, A.F. (1999) Altered anxiety and weight gain in CRH-binding protein deficient mice. Proc. Natl. Acad. Sci USA 96:11595-11600.
Speert, D.B., McClennen, S.J., and Seasholtz, A.F. (2002) Sexually dimorphic expression of CRH-binding protein in the mouse pituitary, Endocrinology 143:4730-4731.
Wei, Q., Lu, X.J., Liu, L., Schafer, G, Shieh, K.R., Burke, S, Robinson, T.E., Watson, S.J., Seasholtz, A.F, and Akil, H. (2004) Glucocorticoid receptor overexpression in forebrain: A mouse model of increased emotional lability. Proc. Natl. Acad. Sci USA 101:11851-11856.
van de Stolpe, A., Slycke, A.J., Reinders, M.O., Zomer, A.W.M., Goodenough, S., Behl, C., Seasholtz, A.F., van der Saag, P.T. (2004) Estrogen receptor (ER)-mediated transcriptional regulation of the human Corticotropin-Releasing Hormone-Binding Protein promoter: differential effects of ERalpha and ERbeta. Molecular Endocrinology 18:2908-2923.
Westphal, N.J., Seasholtz, A.F. (2006) CRH-BP: the regulation and function of a phylogenetically conserved binding protein. Front Biosci. 11:1878-91.
Rozeboom, A.M., Akil, H., and Seasholtz, A.F. (2007) Mineralocorticoid receptor overexpression in forebrain decreases anxiety-like behavior and alters the stress response in mice. Proc. Natl. Acad. Sci. USA 104:4688-4693.
Gammie, S.C., Seasholtz, A.F., Stevenson, S.A. (2008) Deletion of corticotropin-releasing factor binding protein selectively impairs maternal, but not intermale aggression. Neuroscience 157(3):502-12.
Westphal, N.J., Evans, R.T., and Seasholtz, A.F. (2009) Novel expression of type 1 CRH receptor in multiple endocrine cell types in the murine anterior pituitary. Endocrinology 150(1):260-7.
Seasholtz, A.F., Ohman, M., Wardani, A., Thompson, R.C. (2009) Corticotropin-releasing hormone receptor expression and functional signaling in murine gonadotrope-like cells. J Endocrinol. 200(2):223-32.
Evans, R.T., Seasholtz, A.F. (2009) Soluble corticotropin-releasing hormone receptor 2alpha splice variant is efficiently translated but not trafficked for secretion. Endocrinology 150(9):4191-202.