free-floating-immunostaining-of-mouse-brains

Free-floating Immunostaining of Mouse Brains

Immunohistochemical staining of mouse brains is a routine technique commonly used in neuroscience to investigate central mechanisms underlying the ...

Baylor College of Medicine

AbstractCentral 5-hydroxytryptamine (5-HT), which is primarily synthesized by tryptophan hydroxylase 2 (TPH2) in the dorsal Raphe nuclei (DRN), plays a pivotal role in the regulation of food intake and body weight. However, the physiological functions of TPH2 on energy balance have not been consistently demonstrated. Here we systematically investigated the effects of TPH2 on energy homeostasis in adult male and female mice. We found that the DRN harbors a similar amount of TPH2+ cells in control male and female mice. Adult-onset TPH2 deletion in the DRN promotes hyperphagia and body weight gain only in male mice, but not in female mice. Ablation of TPH2 reduces hypothalamic pro-opiomelanocortin (POMC) neuronal activity robustly in males, but only to a modest degree in females. Deprivation of estrogen by ovariectomy (OVX) causes comparable food intake and weight gain in female control and DRN-specific TPH2 knockout mice. Nevertheless, disruption of TPH2 blunts the anorexigenic effects of exogenous estradiol (E2) and abolishes E2-induced activation of POMC neurons in OVX female mice, indicating that TPH2 is indispensable for E2 to activate POMC neurons and to suppress appetite. Together, our study revealed that TPH2 in the DRN contributes to energy balance regulation in a sexually dimorphic manner.

TPH2 in the Dorsal Raphe Nuclei Regulates Energy Balance in a Sex-Dependent Manner.

Obesity is a serious global health problem because of its increasing prevalence and comorbidities, but its treatments are limited. The serotonin 2C receptor (5-HTR), a G-protein-coupled receptor, activates proopiomelanocortin (POMC) neurons in the arcuate nucleus of hypothalamus (ARH) to reduce appetite and weight gain. However, several 5-HT analogs targeting this receptor, e.g., lorcaserin (Lor), suffer from diminished efficacy to reduce weight after prolonged administration. Here, we show that barbadin (Bar), a novel β-arrestin/β2-adaptin inhibitor, can prevent 5-HTR internalization in cells and potentiate long-term effects of Lor to reduce appetite and body weight in male mice. Mechanistically, we demonstrate that Bar co-treatment can effectively maintain the sensitivity of the 5-HTR in POMC neurons, despite prolonged Lor exposure, thereby allowing these neurons to be activated through opening the transient receptor potential cation (TRPC) channels. Thus, our results prove the concept that inhibition of 5-HTR desensitization can be a valid strategy to improve the long-term weight loss effects of Lor or other 5-HTR agonists, and also provide an intellectual framework to develop effective long-term management of weight by targeting 5-HTR desensitization. By demonstrating that the combination of barbadin (Bar) with a G-protein-coupled receptor (GPCR) agonist can provide prolonged weight-lowering benefits in a preclinical setting, our work should call for additional efforts to validate Bar as a safe and effective medicine or to use Bar as a lead compound to develop more suitable compounds for obesity treatment. These results prove the concept that inhibition of serotonin 2C receptor (5-HTR) desensitization can be a valid strategy to improve the long-term weight loss effects of lorcaserin (Lor) or other 5-HTR agonists. Since GPCRs represent a major category as therapeutic targets for various human diseases and desensitization of GPCRs is a common issue, our work may provide a conceptual framework to enhance effects of a broad range of GPCR medicines.

Barbadin Potentiates Long-Term Effects of Lorcaserin on POMC Neurons and Weight Loss.

Perineuronal nets (PNNs) are widely present in the hypothalamus, and are thought to provide physical protection and ion buffering for neurons and regulate their synaptic plasticity and intracellular signaling. Recent evidence indicates that PNNs in the mediobasal hypothalamus play an important role in the regulation of glucose homeostasis. However, whether and how hypothalamic PNNs are regulated are not fully understood. In the present study, we examined whether PNNs in various hypothalamic regions in mice can be regulated by sex, gonadal hormones, dietary interventions, or their interactions. We demonstrated that gonadal hormones are required to maintain normal PNNs in the arcuate nucleus of hypothalamus in both male and female mice. In addition, PNNs in the terete hypothalamic nucleus display a sexual dimorphism with females higher than males, and high-fat diet feeding increases terete PNNs only in female mice but not in male mice. On the other hand, PNNs in other hypothalamic regions are not influenced by sex, gonadal hormones or dietary interventions. In summary, we demonstrated that hypothalamic PNNs are regulated in a region-specific manner and these results provide a framework to further investigate the potential functions of PNNs in regulating energy/glucose homeostasis at the interplay of sex, gonadal hormones and diets.

Article	Year
TPH2 in the Dorsal Raphe Nuclei Regulates Energy Balance in a Sex-Dependent Manner. Endocrinology\| PubMed ID: 33034617	2021
Barbadin Potentiates Long-Term Effects of Lorcaserin on POMC Neurons and Weight Loss. The Journal of neuroscience : the official journal of the Society for Neuroscience\| PubMed ID: 34031163	2021
Hypothalamic Perineuronal Nets Are Regulated by Sex and Dietary Interventions. Frontiers in physiology\| PubMed ID: 34393830	2021

Longlong Tu

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