Karolczak Eva O, Li Chia, Alcantara Ivan C, Cohen Isabel M, Gao Claire, Xiao Cuiying, Goldschmidt Abigail I, Pinkus Cynthia A, Li Junjie, Li Monica M, Esquejo Ryan M, Fortin Jean-Philippe, Bence Kendra K, Reitman Marc L, Krashes Michael J
Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA; NIH-Brown University Graduate Program in Neuroscience, Bethesda, MD, USA.
Mol Metab. 2025 May 29;98:102174. doi: 10.1016/j.molmet.2025.102174.
G protein-coupled receptors (GPCRs) are the most druggable targets in biology due to their cell-type specificity, ligand binding, and cell surface accessibility. Underscoring this, agonists for GPCRs have recently revolutionized the treatment of diabetes and obesity. The rampant success of these compounds has invigorated interest in identifying additional GPCRs that modulate appetite and body weight homeostasis. One such potential therapeutic target is G-protein couped receptor 45 (Gpr45), an orphan GPCR expressed both centrally and peripherally. We aimed to explore the role of Gpr45 as well as neurons expressing Gpr45 in energy balance.
Three novel transgenic mouse models were engineered to investigate the functional contribution of Gpr45 to body weight and appetite regulation: 1) a global Gpr45 knockout, 2) a conditional floxed Gpr45 allele, and 3) a Gpr45-CreERT2 knock-in. Metabolic profiling was performed in global Gpr45 knockout animals including body weight, food intake, body mass, energy expenditure, and body temperature measurements. Animals harboring a conditional floxed Gpr45 allele were bred to mice expressing Cre-recombinase in excitatory neurons labeled via Vesicular glutamate transporter 2 (Vglut2), inhibitory cells expressing Vesicular GABA transporter (Vgat), or neurons marked by the transcription factor Single-minded 1 (Sim1) and monitored for body weight and food consumption. Additionally, floxed Gpr45 mice were bilaterally injected with AAV-Cre targeting the paraventricular nucleus of the hypothalamus (PVH) and body weight and food intake were evaluated. The Gpr45-CreERT2 knock-in model was used to express chronic and acute actuators to the PVH to assess the role of PVH neurons in energy homeostasis.
Global Gpr45 disruption caused marked weight gain, increased food intake and fat mass, but no detectable alterations in core temperature or energy output. Selective deletion of Gpr45 from Sim1+ or excitatory Vglut2+ but not inhibitory Vgat+, neurons produced obesity and hyperphagia. Targeted deletion of Gpr45 from the PVH phenocopies these metabolic changes suggesting a major site of action of Gpr45 signaling is glutamatergic neurons residing in the PVH. Tetanus toxin light chain (TeNT) was used to permanently silence PVH neuronal activity in Gpr45-CreER mice leading to rapid weight accumulation and escalated food intake. These experiments highlight the critical role of both Gpr45 signaling and neural network activity in the regulation of body weight and appetite. A mutated version of the bacterial sodium channel, NaChBac, was used to constitutively activate PVH neuronal activity in Gpr45-CreER mice with limited to no effect on body weight and food consumption, implicating redundant circuitry acting in concert to bias weight loss protection. Acute chemogenetic stimulation of PVH neurons durably suppressed food intake regardless of caloric need state or food palatability demonstrating the capacity of these cells to curb appetite.
Gpr45 is a putative therapeutic candidate that could be targeted to combat obesity and overeating.
G蛋白偶联受体（GPCRs）因其细胞类型特异性、配体结合能力和细胞表面可及性，成为生物学中最具药物开发潜力的靶点。这一点的突出体现是，GPCRs激动剂最近彻底改变了糖尿病和肥胖症的治疗方式。这些化合物的巨大成功激发了人们对识别更多调节食欲和体重稳态的GPCRs的兴趣。一种这样的潜在治疗靶点是G蛋白偶联受体45（Gpr45），一种在中枢和外周均有表达的孤儿GPCR。我们旨在探究Gpr45以及表达Gpr45的神经元在能量平衡中的作用。
构建了三种新型转基因小鼠模型，以研究Gpr45对体重和食欲调节的功能贡献：1）全身性Gpr45基因敲除小鼠；2）条件性Gpr45基因 floxed 等位基因小鼠；3）Gpr45-CreERT2基因敲入小鼠。对全身性Gpr45基因敲除动物进行代谢分析，包括体重、食物摄入量、体重、能量消耗和体温测量。将携带条件性Gpr45基因 floxed 等位基因的动物与在通过囊泡谷氨酸转运体2（Vglut2）标记的兴奋性神经元、表达囊泡GABA转运体（Vgat）的抑制性细胞或由转录因子单 minded 1（Sim1）标记的神经元中表达Cre重组酶的小鼠进行杂交，并监测体重和食物消耗情况。此外，对 floxed Gpr45小鼠双侧注射靶向下丘脑室旁核（PVH）的腺相关病毒（AAV）-Cre，并评估体重和食物摄入量。利用Gpr45-CreERT2基因敲入模型对PVH表达慢性和急性激活剂，以评估PVH神经元在能量稳态中的作用。
全身性Gpr45缺失导致显著体重增加、食物摄入量增加和脂肪量增加，但核心体温或能量输出无明显变化。从Sim1+或兴奋性Vglut2+神经元而非抑制性Vgat+神经元中选择性删除Gpr45会导致肥胖和食欲亢进。从PVH中靶向删除Gpr45可模拟这些代谢变化，表明Gpr45信号传导的主要作用位点是位于PVH的谷氨酸能神经元。破伤风毒素轻链（TeNT）用于使Gpr45-CreER小鼠的PVH神经元活动永久沉默，导致体重迅速增加和食物摄入量增加。这些实验突出了Gpr45信号传导和神经网络活动在体重和食欲调节中的关键作用。使用细菌钠通道NaChBac的突变版本在Gpr45-CreER小鼠中组成性激活PVH神经元活动，对体重和食物消耗的影响有限或无影响，这意味着存在冗余回路协同作用以偏向体重减轻保护。无论热量需求状态或食物适口性如何，对PVH神经元进行急性化学遗传刺激均可持久抑制食物摄入量，表明这些细胞具有抑制食欲的能力。
Gpr45是一个有望成为治疗肥胖和暴饮暴食的候选靶点。
