Leptin as a modulator of glial function in inflammation

瘦素是脂肪细胞衍生的能量调节激素，现在被认为是生物体能量状态与其对入侵病原体建立*有效宿主防御反应能力之间的重要接口。这种作用与最近描述的这种荷尔蒙作为免疫调节器的功能有关，它是外周和大脑中免疫的重要调节器。我们是第一批描述瘦素和促炎细胞因子(如脑白介素1)之间的直接功能关系的人之一，因为我们证明了这种激素的食欲抑制效应是通过在大脑中诱导这种细胞因子来介导的。在随后的体外研究中，我们确定了大脑中瘦素的细胞靶点，以诱导IL-1成为小胶质细胞，我们已经证明，小胶质细胞表达功能性的瘦素受体。除了直接诱导IL-1外，我们还发现，在原代培养的小胶质细胞与瘦素预孵育后，细胞对细菌脂多糖(LPS)等次级免疫原性刺激的反应更强，从而使培养基中IL-1的产量增加了数倍。这种效应似乎与瘦素引起的形态变化有关。鉴于瘦素对小胶质细胞功能的明显调节作用，我们目前正在测试一种假设，即这些细胞长期暴露于高于正常浓度的这种激素，如长期食用高脂肪饮食(HFD)后发生的情况，将导致它们的正常活动和细胞周期发生根本且可能不可逆转的变化。在最近的实验中，我们已经证实，摄入1或3周的HFD会导致循环中瘦素水平升高，并导致小胶质细胞的显着激活。伴随着这种活动增加的是与小胶质细胞吞噬作用相关的蛋白质的表达上调，在已知有显著成人神经源性活动的区域，包括下丘脑和海马体，这种表达尤其强烈。此外，利用Nestin-GFP阳性小鼠，我们还观察到HFD诱导的Nestin(新生神经元标志物)阳性细胞在相同区域的表达显着增加。我们现在打算调查小胶质细胞的高活性是否在功能上与这些区域的新生细胞吞噬有关，以及这些事件的后果。为此，我们将使用多学科技术方法，包括尖端成像技术和一些转基因小鼠系，包括肥胖瘦素(ob/ob)缺陷小鼠。

The adipocyte derived energy regulating hormone, leptin is now established as an important interface between the energy status of an organism and its ability to mount an ***effective host defense response against invading pathogens. This role is linked to the recently described function of this hormone as an immune modulator and an important regulator of immunity both in the periphery and the brain. We were amongst the first to describe a direct functional relationship between leptin and pro-inflammatory cytokines such as brain interleukin (IL)- 1ß by showing, that the appetite suppressing effects of this hormone were mediated via the induction of this cytokine in the brain. 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 with leptin rendered the cells more reactive to secondary immunogenic stimuli such as bacterial lipopolysaccharide (LPS), which resulted in a several-fold increase in IL-1ß output in the culture medium. This effect appeared to be linked to morphological changes induced by leptin. Given this apparent modulatory effect of leptin on microglial function, we are currently testing the hypothesis that the prolonged exposure of these cells to higher than normal concentrations of this hormone, such as occurs following prolonged consumption of high fat diet (HFD), will results in a fundamental, and possibly irreversible, shift in their normal activity and cell cycle. In recent experiments we have confirmed that the consumption of HFD for 1 or 3 weeks induces higher circulating levels of leptin and results in significant activation of microglia. This increased activity, was accompanied by upregulations in the expression of proteins linked with microglial phagocytosis, was particularly intense in regions known for significant adult neurogenic activity, including the hypothalamus and hippocampus. Using Nestin-GFP positive mice we in addition observed a significant HFD induced increase in the expression of Nestin (marker for new born neurons) positive cells in the same regions. We now intend to investigate if the higher activity of microglia is functionally linked to phagocytosis of newborn cells in these regions and the consequences of these events. For this we will use a multidisciplinary technical approach including cutting edge imaging techniques and a number of transgenic mouse lines including the obese leptin (ob/ob) deficient mice.**