Characterisation of the role of NG2-glia and microglia in hypothalamo-pituitary axis coupling.

由于更早的诊断和更好的治疗，80%受癌症影响的儿童现在存活下来，这要归功于发现这种疾病的5年后。这是一个很大的进步。然而，这些儿童需要额外的监测和护理，因为他们可能会受到抗癌治疗的后遗症的影响。特别是，脑放射治疗与患脑下垂体激素缺乏症的终身风险有关。这种风险很高，因为多达50%的幸存者存在这些缺陷。脑下垂体是位于大脑底部的一个小腺体。它与下丘脑相连，下丘脑控制着脑下垂体合成的六种激素的分泌：生长所必需的生长激素、诱导乳汁产生的催乳素、诱导甲状腺激素水平增加的促甲状腺激素、调节应激激素皮质醇分泌的促肾上腺皮质激素、调节青春期和生殖的黄体生成素和卵泡刺激素。由于垂体激素的不同作用，缺陷与显著的不良反应有关，包括甲状腺激素和皮质醇缺乏、青春期缺陷、生长迟缓和认知障碍。在成人中，脑肿瘤放射治疗后也会观察到脑垂体缺陷，尽管临床效果不是很明显。我们知道，辐射主要影响分裂细胞，这就是为什么它们被用于抗癌治疗；然而，我们不知道它们是如何导致脑下垂体激素水平下降的。了解这是如何发生的，将有助于找到预防措施或治疗方法，以避免儿科癌症幸存者的这些缺陷。在大鼠等动物模型中，颅脑照射也与垂体激素缺乏有关，因此啮齿类动物是研究这一现象的很好模型。在老鼠身上，就像在人类身上一样，放射治疗也与患肥胖症的风险有关。最近，科学家在老鼠身上证明，如果辐射集中在连接脑下垂体和下丘脑的区域，就会出现肥胖症。他们发现，在这个小区域，调节食欲的下丘脑神经不再感知肠道信号。这是因为保护它们的细胞，称为NG2胶质细胞，经常分裂，并被辐射摧毁。在我们的实验室，我们发现SOX3基因被移除的小鼠会出现垂体激素缺乏症，因为人类患者携带SOX3突变。引人注目的是，我们观察到，在SOX3突变体中，NG2-神经胶质细胞受到影响，位于连接下丘脑和垂体的同一区域。免疫系统可能会发挥作用，因为当我们服用阿司匹林时，可能会在这种情况下影响炎症反应，SOX3突变体中的正常激素水平会恢复。我们不知道阿司匹林对携带SOX3突变的患者是否有类似的效果。我们的目标是研究NG2胶质细胞和脑免疫细胞在下丘脑和垂体之间的通讯中所起的作用。我们想要研究辐射对这些细胞的破坏是否解释了受辐射的癌症患者发展为脑下垂体功能缺陷的风险。为了验证我们的假设，我们将使用一种新的方法专门消除老鼠体内的NG2胶质细胞，并测量脑下垂体激素。对该区域的NG2胶质细胞知之甚少：因此，我们将详细检查NG2胶质细胞与哪些细胞接触，以更好地了解其可能的功能。同时，我们将测试大脑免疫细胞的潜在参与，方法是在辐射后用一种已知的有效和选择性药物来消融它们，并在SOX3突变体中测试，以检查在没有它们的情况下是否仍然会出现荷尔蒙缺陷。最后，我们将研究阿司匹林对小鼠的影响，以了解它如何治愈携带SOX3突变的小鼠。我们希望，我们的结果最终将有助于预防癌症幸存者的脑下垂体功能缺陷。

80% of children affected by cancer now survive, 5 years after detection of the disease, thanks to earlier diagnoses and better treatments. This is a great improvement. However, these children require extra levels of monitoring and care because they can be affected by sequelae of anti-cancer treatments. In particular, brain radiation therapies are associated with a lifelong risk to develop pituitary hormone deficiencies. This risk is high, as up to 50% of survivors present these deficiencies. The pituitary is a small gland located at the base of the brain. It is attached to the hypothalamus, the region in the brain that controls the secretion in the blood of the six hormones the pituitary synthetizes: Growth Hormone, necessary for growth, Prolactin that induces milk production, Thyroid Stimulating Hormone inducing thyroid hormones levels to increase, Adrenocorticotropic Hormone that regulates secretion of the stress hormone cortisol, Luteinizing and Follicle-stimulating hormones both regulating puberty and reproduction. Because of the diverse roles of the pituitary hormones, deficits are associated with significant adverse effects including thyroid hormone and cortisol deficiencies, puberty defects, growth delay and cognitive impairments. In adults, pituitary deficits are also observed after treatment by radiotherapy for brain tumours, although the clinical effects are less profound. We know that radiation mostly affect the dividing cells, which is why they are used in anti-cancer therapy; however, we do not know how they induce a decrease in pituitary hormone levels. Understanding how this happens would help finding preventive measures or cures to avoid these deficits in paediatric cancer survivors. In animal models such as rats, cranial irradiation is also associated with pituitary hormones deficits, so rodents are a good model to study this phenomenon. In mice, as in humans, radiation therapies are also linked with a risk to develop obesity. Recently, scientists have demonstrated in mice that if radiations are focalised to the region that links the pituitary to the hypothalamus, obesity develops. They found that, in this small domain, hypothalamic nerves that regulate appetite are not sensing gut signals anymore. This is because the cells that protect them, called NG2 glia, divide frequently and are destroyed by radiations. In our lab, we have discovered that mice in which the Sox3 gene has been removed develop pituitary hormone deficits, as human patients carrying mutations in SOX3. Strikingly, we observe that NG2-glia is affected in Sox3 mutants, in this same region that links the hypothalamus and pituitary. The immune system may play a role, because when we give aspirin, likely to affect the inflammatory response in this context, normal hormone levels are restored in Sox3 mutants. We do not know whether aspirin has a similar effect in patients carrying SOX3 mutations. The goal of our project is to investigate the role of NG2 glia and brain immune cells in the communication between the hypothalamus and pituitary. We want to investigate if destruction of these cells by radiations explain the risk of irradiated cancer patients to develop pituitary deficiencies. To test our hypotheses, we will specifically eliminate the NG2 glia in mice using a novel approach and measure pituitary hormones. Little is known about the NG2 glia in this region: we will therefore examine in details which cells the NG2 glia is in contact with to understand better what its function could be. In parallel, we will test the potential involvement of brain immune cells by ablating them with a known efficient and selective drug after irradiation, and in Sox3 mutants, to examine whether hormonal deficits still develop in their absence. Finally, we will investigate the effects of aspirin in mice to understand how it can cure mice carrying Sox3 mutations. We hope that ultimately our results will help preventing pituitary deficits in cancer survivors.