Biology subjects

Dahir, N. S.

Publications and source records attributed to Dahir, N. S..

4 recordsLinked to original sources

bioRxiv2025

Estrogen Dependent Variation in the Contributions of TRPM4 and TRPM5 to Fat Taste

Sex differences in physiology have garnered significant interest of late; however, comparatively little is known about the effects of sex on the function of the peripheral taste system. Previously, we have shown that fat taste functions in a sexually dimorphic manner using molecular, cellular, and behavioral assays, and that a subtype of estrogen receptor (ER) proteins are highly expressed in Type II (receptor) cells. The underlying mechanisms of estrogens action, though, remain unknown. Here, we sought to better understand estrogens role in fat taste transduction at the molecular level by initially focusing on the transient receptor potential channels types M4 (Trpm4) and M5 (Trpm5), which we have shown to play roles in estrogen-sensitive fatty acid signaling in taste cells. That is, using Trpm5-deficient mice, both males and females in the estrus phase showed significantly reduced FA responses, whereas females in the proestrus phase did not, suggesting that there may be E2-dependent TRPM5-independent FA signaling in Type II cells. During periods of high levels of circulating estrogen, there was no significant difference in cellular responses to fatty acid (FA) stimuli between Trpm5-/- mice and their wild-type counterparts. Moreover, supplemental estradiol enhanced linoleic acid (LA)-induced TRPM5- mediated taste cell activation. Finally, while Type II cells depend on TRPM4 and TRPM5 for FA taste cell activation, proestrus (high estrogen) females showed a greater dependence on a TRPM5-independent pathway for fatty acid responsiveness. Together, these results underscore the substantial regulatory role of estrogen in the taste system, particularly for fatty acid signaling. Given that the taste system guides food preferences and intake, these findings may have important implications for understanding sex-specific differences in diet and, ultimately, metabolic health. SUMMARYThe current manuscript shows sex differences in fat taste signaling and identifies functional variations in specific transduction elements in taste cells that respond to sex hormones, such as estrogen, that may mediate differences in peripheral fat taste pathways.

neuroscience↗

bioRxiv2024

Functional coupling between MC4R and Kir7.1 contributes to clozapine-induced hyperphagia

Most antipsychotic drugs (APDs) induce hyperphagia and weight gain. However, the neural mechanisms are poorly understood, partly due to challenges replicating their metabolic effects in rodents. Here, we report a new mouse model that recapitulates overeating induced by clozapine, a widely prescribed APD. Our study shows that clozapine boosts food intake by inhibiting melanocortin 4 receptor (MC4R) expressing neurons in the paraventricular nucleus of the hypothalamus. Interestingly, neither clozapine nor risperidone, another commonly used APD, affects receptor-ligand binding or the canonical Gs signaling of MC4R. Instead, they inhibit neuronal activity by enhancing the coupling between MC4R and Kir7.1, leading to the open state of the inwardly rectifying potassium channel. Deletion of Kir7.1 in Mc4r-Cre neurons prevents clozapine-induced weight gain, while treatment with a selective Kir7.1 blocker mitigates overeating in clozapine-fed mice. Our findings unveil a molecular pathway underlying the effect of APDs on feeding behavior and suggest its potential as a therapeutic target.

neuroscience↗

bioRxiv2023

Inhibition of the melanocortin-3 receptor (MC3R) causes generalized sensitization to anorectic agents

The melanocortin-3 receptor (MC3R) acts presynaptically to regulate GABA release from agouti-related protein (AgRP) nerve terminals and thus may be a negative regulator of multiple circuits involved in feeding behavior and energy homeostasis. Here, we examined the role of MC3R in regulating the response to various anorexigenic agents. Our findings reveal that genetic deletion or pharmacological inhibition of MC3R improves the dose responsiveness to Glucagon-like peptide 1 (GLP1) agonists, as assayed by inhibition of food intake and weight loss. An enhanced anorectic response to other agents, including the acute satiety factors peptide YY (PYY3-36) and cholecystokinin (CCK) and the long-term adipostatic factor, leptin, demonstrated that increased sensitivity to anorectic agents is a generalized result of MC3R antagonism. Enhanced neuronal activation in multiple nuclei, including ARH, VMH, and DMH, was observed using Fos immunohistochemistry following low-dose liraglutide in MC3R knockout mice (Mc3r-/-), supporting the hypothesis that the MC3R is a negative regulator of circuits regulating multiple aspects of feeding behavior. The enhanced anorectic response in Mc3r -/- mice after administration of GLP1 analogs was also independent of the incretin effects and malaise induced by GLP1R analogs, suggesting that MC3R antagonists may have value in enhancing the dose-response range of obesity therapeutics.

neuroscience↗

bioRxiv2023

Cell autonomous regulation of the activation of AgRP neurons by the melanocortin-3 receptor

The melanocortin-3 receptor (MC3R) is a negative regulator of the central melanocortin circuitry via presynaptic expression on AgRP nerve terminals, from where it regulates GABA release onto secondary MC4R-expressing neurons. Hence, animals lacking MC3R (MC3R KO) exhibit hypersensitivity to MC4R agonists. However, MC3R KO mice also exhibit defective behavioral and neuroendocrine responses to fasting. Here, we demonstrate that MC3R KO mice exhibit defective activation of AgRP neurons in response to fasting and cold exposure, while exhibiting normal inhibition of AgRP neurons by sensory detection of food. Further, using an AgRP-specific MC3R knockout model, we show that the control of AgRP neuron activation by MC3R is cell-autonomous. One mechanism underlying this involves the response to ghrelin, which is also blunted in mice with AgRP-specific deletion of the MC3R. Thus, MC3R is a crucial player in the control of energy homeostasis by the central melanocortin system, not only acting presynaptically on AgRP neurons, but via AgRP cell-autonomous regulation of fasting- and cold-induced neuronal activation as well.

neuroscience↗