Background
Stress responses are believed to involve corticotropin releasing factor (CRF), its two cognate receptors (CRF1 and CRF2), and the CRF-binding protein (CRFBP). Whereas decades of research has focused on CRF1, the role of CRF2 in the central nervous system (CNS) has not been thoroughly investigated. We have previously reported that CRF2, interacting with a C terminal fragment of CRFBP, CRFBP(10kD), may have a role in the modulation of neuronal activity. However, the mechanism by which CRF interacts with CRFBP(10kD) and CRF2 has not been fully elucidated due to the lack of useful chemical tools to probe CRFBP.
Conclusion
These results provide the first evidence of specific roles for CRF2 and CRFBP(10kD) in the modulation of neuronal activity and suggest that CRFBP(10kD)-CRF2 NAMs can be further developed for the treatment of stress-related disorders including alcohol and substance use disorders.
Methods
We miniaturized a cell-based assay, where CRFBP(10kD) is fused as a chimera with CRF2, and performed a high-throughput screen (HTS) of 350,000 small molecules to find negative allosteric modulators (NAMs) of the CRFBP(10kD)-CRF2 complex. Hits were confirmed by evaluating activity toward parental HEK293 cells, toward CRF2 in the absence of CRFBP(10kD), and toward CRF1 in vitro. Hits were further characterized in ex vivo electrophysiology assays that target: 1) the CRF1+ neurons in the central nucleus of the amygdala (CeA) of CRF1:GFP mice that express GFP under the CRF1 promoter, and 2) the CRF-induced potentiation of N-methyl-D-aspartic acid receptor (NMDAR)-mediated synaptic transmission in dopamine neurons in the ventral tegmental area (VTA).
Results
We found that CRFBP(10kD) potentiates CRF-intracellular Ca2+ release specifically via CRF2, indicating that CRFBP may possess excitatory roles in addition to the inhibitory role established by the N-terminal fragment of CRFBP, CRFBP(27kD). We identified novel small molecule CRFBP-CRF2 NAMs that do not alter the CRF1-mediated effects of exogenous CRF but blunt CRF-induced potentiation of NMDAR-mediated synaptic transmission in dopamine neurons in the VTA, an effect mediated by CRF2 and CRFBP.