Leptin as a modulator of glial activity in inflammation

瘦素作为炎症中神经胶质活性的调节剂

• 批准号: RGPIN-2014-05553
• 负责人: Luheshi, Giamal
• 金额: $ 1.89万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=567237
• 关键词: Leptin; modulator; glial; activity; inflammation

The adipocyte derived circulating hormone leptin, acts on hypothalamic neurons to regulate energy balance by suppressing appetite and increasing energy expenditure. Recent discoveries have demonstrated that leptin also affects other biological systems including immunity. Several studies have now demonstrated complex and direct interactions between leptin and immune mediators, most notably cytokines such as interleukin (IL)-1, both in the periphery and the brain. Previously we demonstrated a functional link between leptin and brain IL-1ß by showing, that the appetite suppressing effects of this hormone were mediated via the induction of this cytokine. In addition we reported that leptin could trigger other brain-orchestrated responses synonymous with the host’s response to exogenous pathogenic exposure including fever, an effect that is also IL-1ß dependent. This was the first evidence directly linking leptin with ‘sickness’ type behaviours, which led to our original hypothesis that it could act as a classical peripheral inflammatory signal to the brain. We subsequently confirmed this by neutralizing endogenous leptin, in animals treated with the bacterial lipopolysaccharide (LPS), a potent activator of pro-inflammatory cytokines in the periphery and the brain. This led to a suppression of the LPS induced sickness responses, which were accompanied with the attenuation of hypothalamic IL-1ß expression. In subsequent in vitro studies we identified the cellular targets of leptin in the brain for the induction of IL-1 to be microglia, which we have shown to express the functional leptin receptor. In addition to the direct induction of IL-1 we discovered that pre-incubation of primary microglial cells in culture over 24h rendered the cells more reactive to secondary inflammatory stimuli such as LPS, which resulted in a several-fold increase in IL-1ß output in the culture medium. This effect was not limited to IL-1ß but was also true for other cytokines and chemokines. The role of leptin in potentiating the microglial response to LPS appeared to be linked to morphological changes involving the cytoskeletal component actin. In addition, using a time lapse study to monitor these morphological changes over an extended period of time we showed that the effects of leptin were long lasting (up to 96 h) with the microglia remaining fully viable compared to the untreated and LPS treated cells which had undergone cell death 72 h into the study. Other than its direct effect on microglia our most recent discoveries have linked this hormone with the modulation of IL-1ß expressing neutrophil trafficking into the brain to propagate the inflammatory response, a process that we believe involves chemokine production by microglia. Cumulatively these preliminary observations led us to hypothesize that the role of leptin in immunity is that of a modulator of immune cell activity in the brain, which may include the orchestration of the inflammatory response via the promotion of cell to cell interactions. Because circulating leptin levels fluctuate across a multitude of conditions (e.g. obesity, anorexia) a role for this hormone in modulating immune cell function in the brain could have wide-ranging implications for neuro-inflammatory responses. Thus to address this hypothesis we will conduct both in vivo and in vitro approaches in mice to investigate: 1. how leptin modulates microglial viability and survival, 2. if preconditioning by high or low levels of the hormone (as found in obese or food restricted animals respectively) affect the microglial responses to immunogenic stimuli, 3. whether neutrophil borne IL-ß activates microglial cells.

脂肪细胞来源的循环激素瘦素作用于下丘脑神经元，通过抑制食欲和增加能量消耗来调节能量平衡。最近的研究表明，瘦素还影响其他生物系统，包括免疫。一些研究已经证明了瘦素和免疫介质之间的复杂和直接的相互作用，最显着的细胞因子，如白细胞介素（IL）-1，在外周和大脑。以前，我们证明了瘦素和脑IL-1 β之间的功能联系，通过显示，这种激素的食欲抑制作用是通过诱导这种细胞因子介导的。此外，我们还报道了瘦素可以触发其他脑组织反应，这与宿主对外源性病原体暴露的反应同义，包括发热，这种效应也是IL-1 β依赖的。这是第一个直接将瘦素与“疾病”类型行为联系起来的证据，这导致了我们最初的假设，即它可以作为一种经典的外周炎症信号传递给大脑。随后，我们通过在接受细菌脂多糖（LPS）治疗的动物中中和内源性瘦素证实了这一点，细菌脂多糖是外周和大脑中促炎细胞因子的有效激活剂。这导致LPS诱导的疾病反应的抑制，其伴随着下丘脑IL-1 β表达的减弱。在随后的体外研究中，我们确定了瘦素在脑中诱导IL-1的细胞靶点是小胶质细胞，我们已经证明小胶质细胞表达功能性瘦素受体。除了直接诱导IL-1外，我们发现在培养物中预孵育原代小胶质细胞超过24小时使细胞对次级炎症刺激如LPS更具反应性，这导致培养基中IL-1 β输出增加数倍。这种作用不仅限于IL-1 β，对其他细胞因子和趋化因子也是如此。瘦素在增强小胶质细胞对LPS的反应中的作用似乎与涉及细胞骨架组分肌动蛋白的形态学变化有关。此外，使用时间推移研究来监测这些形态学变化在一段延长的时间内，我们表明，瘦素的影响是持久的（长达96小时），与未处理的和LPS处理的细胞相比，小胶质细胞保持完全存活，这些细胞在研究中经历了72小时的细胞死亡。除了对小胶质细胞的直接作用外，我们最近的发现将这种激素与调节表达IL-1 β的中性粒细胞运输到大脑中以传播炎症反应联系起来，我们认为这一过程涉及小胶质细胞产生趋化因子。累积这些初步观察使我们假设瘦素在免疫中的作用是脑中免疫细胞活性的调节剂，其可能包括通过促进细胞与细胞的相互作用来协调炎症反应。由于循环中的瘦素水平在多种情况下（例如肥胖，厌食症）波动，因此这种激素在调节大脑中免疫细胞功能中的作用可能对神经炎症反应具有广泛的影响。因此，为了解决这一假设，我们将在小鼠中进行体内和体外方法来研究：1。瘦素如何调节小胶质细胞的活力和存活，2.如果通过高或低水平的激素（如分别在肥胖或食物限制的动物中发现的）预处理影响小胶质细胞对免疫原性刺激的应答，3.中性粒细胞携带的IL-10是否激活小胶质细胞。