REGULATOR OF G-PROTEIN SIGNALING AS AN ENTEROENDOCRINE-SPECIFIC TARGET FOR OBESITY TREATMENT: ALTERED RGS9 IN ENTEROENDOCRINE CELLS IMPAIRS POSTPRANDIAL GLP-1 RESPONSE AND MODIFIES FOOD INTAKE IN MICE

Introduction: Enteroendocrine cells (EEC) secrete satiety hormones GLP-1 and PYY in response to luminal nutrients through nutrient-sensing GPCRs and are implicated in obesity (OB). We recently identified expression of regulator of G-protein signaling 9 (RGS9), a negative regulator of GPCR signaling, in human EECs and show that it may function to cease GLP-1 and PYY hormone secretion. Whether alterations to gut RGS can influence subsequent energy intake patterns is unknown. We aimed to investigate the role of gut RGS in GPCR-mediated hormone secretion with alterations to energy intake in mice with diet induced obesity (DIO) and transgenic mice overexpressing RGS9 (RGS9-KI).

Methods: Colon and terminal ileum tissue from euthanized mice (lean n=9; DIO n=9) were preserved in RNAlater and prepared for RT-qPCR. Overnight fasted DIO mice received rectal enemas of solutions containing water (Vehicle, n=3), 1,10-Phenanthroline [(1,10-PA), a GLP-1 secretagogue via T2R5 agonism, 5 mM, n=3], or 1,10-PA (5 mM) + CCG-50014 (non-selective RGS inhibitor, 1 mM)(n=4). Mice were placed in individual cages with premeasured food (~20 g) and food intake was measured at 2, 4, and 6 hours (h). In an additional cohort blood plasma was collected at fasting and 2h after food intake (0.8g chow) in WT and RGS9-KI mice. GLP-1 was measured by ELISA. The feeding paradigm test mentioned above was done in overnight fasted WT(n=8) and RGS9-KI mice(n=6).

Results: Compared to lean, DIO mice had elevated ileal mRNA expression of RGS9 (p<0.05)(1A). In DIO mice, 1,10-PA alone was sufficient to decrease energy intake at 2h compared to vehicle(p<0.05)(1B). At 4h, reduction in energy intake was only observed in mice treated with 1,10-PA+CCG-50014 (vs vehicle, p<0.001; vs 1,10-PA, p<0.001). In DIO mice, only treatment with 1,10-PA+CCG-50014 increased GLP-1 secretion (1C). At fasting and 2h post prandial, there was no difference in GLP-1 levels between WT and RGS9-KI mice(1D-E). WT mice displayed an increased trend in GLP-1 (pM) after 2h (p=0.06), whereas a decreased trend in GLP-1 was observed in RGS9-KI mice (p=0.07)(1F). ΔGLP1 levels were reduced in RGS9-KI mice compared to WT (p<0.05)(1G). Cumulative food intake was unchanged between WT and RGS9-KI mice during a 6h period, ΔFI in the 2-4 h time period was significantly increased in RGS9-KI mice compared to WT (P<0.05)(1H-J).

Conclusions: Similar to previous findings in humans, RGS9 is overexpressed in DIO intestine. Non-selective inhibition of RGS in mice, led to decrease food intake. Mice overexpressing RGS9 demonstrate an impaired GLP-1 secretion response to food intake and consume significantly more energy in the 2-4h postprandial time compared to controls. RGS9 inhibition may be a potential target for OB treatment.