Abstract：
The growth hormone secretagogue receptor (GHSR), primarily known as the receptor for the hunger hormone ghrelin, potently controls food intake, yet the specific Ghsr-expressing cells mediating the orexigenic effects of this receptor remain incompletely characterized. Since Ghsr is expressed in gamma-aminobutyric acid (GABA)-producing neurons, we sought to investigate whether the selective expression of Ghsr in a subset of GABA neurons is sufficient to mediate GHSR\'s effects on feeding. First, we crossed mice that express a tamoxifen-dependent Cre recombinase in the subset of GABA neurons that express glutamic acid decarboxylase 2 (Gad2) enzyme (Gad2-CreER mice) with reporter mice, and found that ghrelin mainly targets a subset of Gad2-expressing neurons located in the hypothalamic arcuate nucleus (ARH) and that is predominantly segregated from Agouti-related protein (AgRP)-expressing neurons. Analysis of various single-cell RNA-sequencing datasets further corroborated that the primary subset of cells coexpressing Gad2 and Ghsr in the mouse brain are non-AgRP ARH neurons. Next, we crossed Gad2-CreER mice with reactivable GHSR-deficient mice to generate mice expressing Ghsr only in Gad2-expressing neurons (Gad2-GHSR mice). We found that ghrelin treatment induced the expression of the marker of transcriptional activation c-Fos in the ARH of Gad2-GHSR mice, yet failed to induce food intake. In contrast, food deprivation-induced refeeding was higher in Gad2-GHSR mice than in GHSR-deficient mice and similar to wild-type mice, suggesting that ghrelin-independent roles of GHSR in a subset of GABA neurons is sufficient for eliciting full compensatory hyperphagia in mice.
摘要：
生长激素促分泌素受体（GHSR），主要被称为饥饿激素ghrelin的受体，有效地控制食物摄入，然而，介导该受体促食欲作用的特异性Ghsr表达细胞仍未完全表征。由于Ghsr在产生γ-氨基丁酸的神经元（GABA神经元）中表达，我们试图研究Ghsr在GABA神经元亚群中的选择性表达是否足以介导GHSR对摄食的影响。首先,我们将表达谷氨酸脱羧酶2（Gad2）酶（Gad2-CreER小鼠）的GABA神经元亚群中表达他莫昔芬依赖性Cre重组酶的小鼠与报告小鼠交叉，并发现ghrelin主要靶向位于下丘脑弓状核（ARH）中的Gad2表达神经元的子集，并且主要与Agouti相关蛋白（AgRP）表达神经元分离。对各种单细胞RNA测序数据集的分析进一步证实，小鼠大脑中共表达Gad2和Ghsr的细胞的主要亚群是非AgRPARH神经元。接下来,我们将Gad2-CreER小鼠与可再激活的GHSR缺陷小鼠交叉,以产生仅在表达Gad2的神经元中表达Ghsr的小鼠(Gad2-GHSR小鼠).我们发现ghrelin处理诱导转录激活标记c-Fos在Gad2-GHSR小鼠ARH中的表达,但未能诱导食物摄入。相比之下,在Gad2-GHSR小鼠中，食物剥夺诱导的再摄食高于GHSR缺陷小鼠，与野生型小鼠相似，这表明GHSR在GABA神经元亚群中不依赖ghrelin的作用足以引起小鼠完全代偿性吞噬。
