Molecular mechanisms involved in CRH-induced morphological changes in hippocampal neurons

INDA, C.; BONFIGLIO, J.J.; MACCARRONE, G.; HOLSBOER, F.; ARZT, E.; SILBERSTEIN, S.

Bariloche, Río Negro

Congreso; The Second South American Spring Symposium in Signal Transduction and Molecular Medicine; 2012

Corticotropin-releasing hormone (CRH) and its type 1 receptor coordinate the neuroendocrine and behavioral adaptation to stress and are causally linked to affective disorders. In extra-hypothalamic circuits, CRH functions as a neuromodulator affecting neuronal architecture and the glutamatergic and dopaminergic transmission. We are exploring CRHR1 signaling network in order to identify mechanisms involved in CRH action in the brain. Given that our previous results show specific CRH actions in vivo in particular limbic structures such as hippocampus, we performed our studies in HT22 cells, a mouse hippocampal cell line widely used as a neuronal model. By image analysis and pharmacological tools, we demonstrated that CRH induces morphological changes in HT22 stably transfected with CRHR1 (HT22-CRHR1) that depend on CRHR1 and cAMP/PKA activation. Although we have shown that CRH triggers ERK1/2 activation in HT22-CRHR1 cells, activation of this MAPK was dispensable for CRH-neuritogenic effect, in contrast to previous reports. In most systems, activated-CRHR1 binds the Gαs protein, resulting in transmembrane adenylyl cyclase activation and cAMP increase. From proteomics studies, we detected the soluble isoform of adenylyl cyclase (sAC) as a partner of B-Raf, a MAPKKK predominantly expressed in the nervous system. This second source of cAMP has differential distribution and regulation that transmembrane isoforms. Interestingly, we identified for the first time that sAC is involved in CRHR1 signaling. Moreover, we found that the sAC-generated cAMP pool is the main responsible of the CRH-induced neurite outgrowth. The individual role and cross-talk between the different cAMP pools in CRH functions in hippocampus are currently being analyzed.