GPER1 stimulation alters posttranslational modification of RGSz1 and induces desensitization of 5-HT_1A receptor signaling in the rat hypothalamus

Hyperactivity of the hypothalamic-pituitary-adrenal axis is a consistent biological characteristic of depression, and response normalization coincides with clinical responsiveness to antidepressant medications. Desensitization of serotonin 1A receptor (5-HT_1AR) signaling in the hypothalamic paraventricular nucleus of the hypothalamus (PVN) follows selective serotonin reuptake inhibitor (SSRI) antidepressant treatment and contributes to the antidepressant response. Estradiol alone produces a partial desensitization of 5-HT_1AR signaling and synergizes with SSRIs to result in a complete and more rapid desensitization than with SSRIs alone as measured by a decrease in the oxytocin and adrenocorticotrophic hormone (ACTH) responses to 5-HT_1AR stimulation. G protein-coupled estrogen receptor 1 (GPER1) is necessary for estradiol-induced desensitization of 5-HT_1AR signaling, although the underlying mechanisms are still unclear. We now find that stimulation of GPER1 with the selective agonist G-1 and nonselective stimulation of estrogen receptors dramatically alter isoform expression of a key component of the 5-HT_1AR signaling pathway, RGSz1, a GTPase-activating protein selective for Gz, the G subunit necessary for 5-HT_1AR-mediated hormone release. RGSz1 isoforms are differentially glycosylated, SUMOylated, and phosphorylated, and differentially distributed in subcellular organelles. High-molecular-weight RGSz1 is SUMOylated and glycosylated, localized to the detergent-resistant microdomain (DRM) of the cell membrane, and increased by estradiol and G-1 treatment. Because activated Gz also localizes to the DRM, increased DRM-localized RGSz1 by estradiol and G-1 could reduce Gz activity, functionally uncoupling 5-HT_1AR signaling. Peripheral G-1 treatment produced a partial reduction in oxytocin and ACTH responses to 5-HT_1AR stimulation similar to direct injections into the PVN. Together, these results identify GPER1 and RGSz1 as novel targets for the treatment of depression.