Anxiety, Recruited from Within

Science Signaling  04 May 2010:
Vol. 3, Issue 120, pp. ec128
DOI: 10.1126/scisignal.3120ec128

Signaling through both 5-HT2AR, a receptor for serotonin, and CRFR1, a receptor for corticotrophin-releasing factor (CRF), which acts as a neuromodulator in addition to regulating pituitary secretion of corticotrophin in response to stress, has been linked to anxiety (see González-Maeso). Noting that CRF can potentiate serotonin’s effects, Magalhaes et al. investigated signaling interactions between 5-HT2AR and CRFR1. 5-HT2AR and CRFR1 are G protein–coupled receptors (GPCRs) that link to distinct pathways, with 5-HT2AR signaling through Gαq/11 to stimulate inositol trisphosphate (IP3) production and CRFR1 signaling through Gαs to stimulate production of adenosine 3′,5′-monophosphate (cAMP). Experiments in human embryonic kidney (HEK) 293 cells heterologously expressing 5-HT2AR or 5-HT2CR with or without CRFR1 revealed that CRFR1 activation by CRF increased 5-HT2AR– and 5-HT2CR–mediated inositol phosphate (presumably IP3) production. Other Gαs-coupled GPCRs failed to enhance 5-HT2R signaling, and serotonin did not affect CRFR1-mediated cAMP production. Immunofluorescence analysis revealed that a subpopulation of neurons in mouse prefrontal cortex contained both CRFR1 and 5-HT2AR, and, as in HEK293 cells, pretreatment of neuronal cultures with CRF enhanced serotonin-mediated inositol phosphate production. Confocal analysis of tagged receptors revealed that 5-HT2AR underwent constitutive endocytosis (in both HEK293 cells and rat cortical neurons), whereas CRFR1 did not. CRF stimulated CRFR1 endocytosis, leading to its endosomal colocalization with 5-HT2AR; blocking endocytosis prevented CRF-dependent potentiation of 5-HT2AR signaling. CRF also increased cell surface abundance of 5-HT2AR, and inhibiting receptor recycling to the cell surface with monensin or with a dominant-negative form of Rab4 also inhibited the CRF-dependent increase in 5-HT2AR signaling. Deletion of PDZ domain-binding motifs on the C-terminal tails of 5-HT2AR or CRFR1 blocked the CRF-dependent increase in cell surface 5-HT2AR; similarly, their deletion blocked CRF-dependent increases in 5-HT2R–mediated inositol phosphate production, as did expression of a Tat-fusion peptide containing the last 10 amino acids of the CRFR1 C-terminal tail. In vivo analyses indicated that combined stimulation of CRFR1 and 5-HT2R had synergistic effects on anxiety-related behaviors in mice. Thus, the authors conclude that CRF signaling through CRFR1 leads to increased abundance of 5-HT2R at the cell surface, thereby enhancing anxiety.

A. C. Magalhaes, K. D. Holmes, L. B. Dale, L. Comps-Agrar, D. Lee, P. N. Yadav, L. Drysdale, M. O. Poulter, B. L. Roth, J.-P. Pin, H. Anisman, S. S. G. Ferguson, CRF receptor 1 regulates anxiety behavior via sensitization of 5-HT2 receptor signaling. Nat. Neurosci. 13, 622–629 (2010). [PubMed]

J. González-Maeso, Anxious interactions. Nat. Neurosci. 13, 524–526 (2010). [PubMed]