目的:Proopiomelanocortin(POMC)神经元释放有效的厌食性神经肽,通过黑皮质素受体抑制食物摄入并增加能量消耗。尽管中枢黑皮质素在生理调节中的重要性已得到充分证实,定义黑皮质素神经元功能特性和维持下丘脑Pomc表达的潜在遗传机制仍有待完全确定。在这项研究中,我们研究了Six3的功能意义,Six3是一种在胚胎和成年小鼠POMC神经元中显著表达的转录调节因子,在调节下丘脑Pomc的表达和下游的生理后果。
方法:我们首先通过双荧光原位杂交评估了Six3在发育中和成年下丘脑中的表达。接下来,我们评估了从表达Pomc的神经元选择性缺乏Six3的突变小鼠的POMC免疫反应性,并在胚胎E9.5天激活的他莫昔芬诱导的Six3基因敲除小鼠模型中定量了PomcmRNA水平.我们还测定了葡萄糖和胰岛素的敏感性,每日食物摄入量,缺乏Six3特别是POMC神经元的成年雄性和雌性小鼠的身体组成和体重。最后,我们评估了从成年小鼠POMC神经元中消融Six3的生理后果。
结果:Six3和Pomc在小鼠下丘脑神经元发育和成年期共表达。Six3缺陷的小鼠胚胎在发育中的下丘脑中显示出Pomc表达降低。从POMC神经元靶向删除Six3导致下丘脑Pomc表达减少,增加每日食物摄入量,增强男性小鼠的葡萄糖敏感性和轻度肥胖,而不是雌性小鼠。最后,有条件地从成年小鼠的POMC神经元中去除Six3会导致下丘脑POMC免疫反应性降低,而对体重或食物摄入量没有显着影响。
结论:总而言之,我们的结果表明,Six3在POMC神经元身份的早期建立和下丘脑Pomc表达的生理水平的维持中起着至关重要的作用。此外,我们的研究表明,在POMC神经元中Six3表达的功能意义是性别二态和年龄依赖性的。
OBJECTIVE: Proopiomelanocortin (POMC) neurons release potent anorexigenic neuropeptides, which suppress food intake and enhance energy expenditure via melanocortin receptors. Although the importance of central melanocortin in physiological regulation is well established, the underlying genetic mechanisms that define the functional identity of melanocortin neurons and maintain hypothalamic Pomc expression remain to be fully determined. In this study, we investigate the functional significance of
Six3, a transcriptional regulator notably expressed in embryonic and adult mouse POMC neurons, in the regulation of hypothalamic Pomc expression and downstream physiological consequences.
METHODS: We first evaluated the expression of
Six3 in the developing and adult hypothalamus by double fluorescence in situ hybridization. Next, we assessed POMC immunoreactivity in mutant mice selectively lacking
Six3 from Pomc-expressing neurons and quantified Pomc mRNA levels in a tamoxifen-inducible
Six3 knockout mouse model activated at embryonic E9.5 days. We also determined glucose and insulin sensitivity, daily food intake, body composition and body weight in adult male and female mice lacking Six3 specifically from POMC neurons. Lastly, we assessed the physiological consequences of ablating Six3 from POMC neurons in adult mice.
RESULTS: Six3 and Pomc were co-expressed in mouse hypothalamic neurons during development and adulthood. Mouse embryos deficient in
Six3 showed reduced Pomc expression in the developing hypothalamus. Targeted deletion of Six3 specifically from POMC neurons resulted in decreased hypothalamic Pomc expression, increased daily food intake, enhanced glucose sensitivity and mild obesity in male but not in female mice. Finally, conditional removal of Six3 from POMC neurons in adult mice led to a reduction in hypothalamic POMC immunoreactivity with no significant effects in body weight or food intake.
CONCLUSIONS: Altogether, our results demonstrate that Six3 plays an essential role in the early establishment of POMC neuron identity and the maintenance of physiological levels of hypothalamic Pomc expression. In addition, our study demonstrates that the functional significance of Six3 expression in POMC neurons is sexually dimorphic and age-dependent.