Mechanisms involved in CRH receptors signaling in hippocampal neurons.

INDA, C.; SENIN, S.; ARMANDO, N.G.; SILBERSTEIN, S.

Simposio; Fronteras en Biociencia 2; 2016

The corticotropin-releasing hormone (CRH) system orchestrates the response to stress, acting on the hypothalamic-pituitary-adrenal axis and on different brain regions. CRH and related peptides operate through G- protein-coupled receptors (GPCRs), CRHR1 and CRHR2, which display different localization and ligand affinity. Our goal is the identification of cellular mechanisms involved in CRH signaling downstream of its receptors which will be instrumental for understanding the physiological function of CRH and related peptides in physiologically relevant systems.The hippocampus is a brain structure related to behavioral response to stress in which the CRH system has been demonstrated to exert specific action. We are exploring signaling pathways activated by CRHRs in the mouse hippocampal neuronal HT22 cells as a model, stably expressing CRHRs (HT22-CRHR1 and HT22-CRHR2 cells). Cell lines are stimulated with CRH or urocortin 1 (UCN1) and signaling responses are analyzed to identify mechanisms ligand- and/or CRHRs- specific.As we previously reported, ERK1/2 activation by CRH-activated CRHR1 is biphasic. Remarkably, a similar pattern was observed with UCN1 as a CRHR1 ligand. However, the time course of ERK1/2 phosphorylation downstream of activated CRHR2 was different to the one from CRHR1 with CRH and UCN1 as well. We also compared the activation profiles of CREB and AKT activation and report here similarities and differences. Both receptors trigger a cAMP response as measured with FRET- based biosensors.Regulation of cAMP levels by activated GPCR modulate diverse cellular functions, being able to stimulate proliferation in some cell types, while it triggers cell differentiation in others. We found that CRH and UCN1 induce neurite outgrowth in HT22-CRHR1 cells, together with a decrease in cell proliferation. Moreover, these effects were mimicked by cAMP levels artificially increased. CRHR1- induced morphological changes were dependent on cAMP/PKA and independent of ERK1/2 activation. CREB activation was dependent on cAMP/PKA pathways whereas ERK1/2 activation was dispensable, although for c-fos expression in response to CRH both PKA and ERK1/2 pathways were involved. We recently demonstrated that CRHR1 activates two different sources of cAMP in HT22-CRHR1 cells. Both tmACs and sAC are involved in the activation of PKA, ERK1/2, CREB, and c-fos induction. However, only sAC-generated cAMP is critical for activated CRHR1 neuritogenic effect.