Tanaka J, Fujita H, Matsuda S, Toku K, Sakanaka M, Maeda N
Department of Physiology, School of Medicine, Ehime University, Japan.
Glia. 1997 May;20(1):23-37.
Effects of steroid hormones on the regulation of function and morphology of microglial cells were investigated using the cultured cells isolated from forebrain of newborn rats. Cortisol, corticosterone, and aldosterone at 100 nM caused a strong shrinkage of microglial cells cultured in a serum-supplemented medium. However, cholesterol, pregnenolone, testosterone, estradiol, and dehydroepiandrosterone did not exhibit any significant effects. The corticosteroids also inhibited the GM-CSF-mediated ramification of microglia in a serum-free medium. An anti-glucocorticoid agent RU38486 abolished the effects of corticosteroids on the microglial morphology, suggesting the presence of functional glucocorticoid receptor (GR) in microglial cells. The presence of GR was confirmed by immunoblotting with an antibody to the receptor. Cytokines GM-CSF and interleukin-3 altered the level of GR expression. Binding experiments with [3H]-corticosterone demonstrated the presence of not only GR but also mineralocorticoid receptor (MR): the dissociation constants (Kd) and the number of binding sites (Bmax) were 0.8 nM and 15 fmol/mg protein for MR and 5.0 nM and 73 fmol/mg protein for GR, respectively. The pure glucocorticoid RU28362 and dexamethasone at 20 nM (but not aldosterone and corticosterone at the same concentration) inhibited proliferation of microglial cells, as revealed by PCNA immunocytochemistry. RU28362 inhibited the activities of inducible nitric oxide synthase and acid phosphatase at concentrations higher than 1 nM. Aldosterone and corticosterone exhibited the similar inhibitory effect at 100 nM, and this inhibition was completely overcome by RU38486. On the other hand, corticosterone and aldosterone at concentrations lower than 1 nM enhanced the activities of both enzymes. The antimineralocorticoid agent spironolactone eliminated the stimulatory effects of corticosterone on the enzyme activities. In accordance with these biochemical results, electron microscopic observations revealed that glucocorticoids enhanced the formation of lysosomal vacuolation in microglial cells and aldosterone increased the number and size of lysosomes. In conclusion, it is suggested that GR and MR mediated the opposite effects of corticosterone on the functions of microglial cells; the hormone acted as an inhibitor through GR and as an stimulator through MR.
利用从新生大鼠前脑分离的培养细胞，研究了类固醇激素对小胶质细胞功能和形态调节的影响。100 nM的皮质醇、皮质酮和醛固酮可使在补充血清的培养基中培养的小胶质细胞强烈收缩。然而，胆固醇、孕烯醇酮、睾酮、雌二醇和脱氢表雄酮未表现出任何显著影响。皮质类固醇还抑制无血清培养基中GM-CSF介导的小胶质细胞分支形成。抗糖皮质激素药物RU38486消除了皮质类固醇对小胶质细胞形态的影响，表明小胶质细胞中存在功能性糖皮质激素受体（GR）。用该受体的抗体进行免疫印迹证实了GR的存在。细胞因子GM-CSF和白细胞介素-3改变了GR的表达水平。用[3H]-皮质酮进行的结合实验表明，不仅存在GR，还存在盐皮质激素受体（MR）：MR的解离常数（Kd）和结合位点数（Bmax）分别为0.8 nM和15 fmol/mg蛋白，GR分别为5.0 nM和73 fmol/mg蛋白。如PCNA免疫细胞化学所示，20 nM的纯糖皮质激素RU28362和地塞米松（但相同浓度的醛固酮和皮质酮则不然）抑制小胶质细胞的增殖。RU28362在高于1 nM的浓度下抑制诱导型一氧化氮合酶和酸性磷酸酶的活性。醛固酮和皮质酮在100 nM时表现出类似的抑制作用，而这种抑制作用被RU38486完全克服。另一方面，浓度低于1 nM的皮质酮和醛固酮增强了这两种酶的活性。抗盐皮质激素药物螺内酯消除了皮质酮对酶活性的刺激作用。根据这些生化结果，电子显微镜观察显示，糖皮质激素增强了小胶质细胞中溶酶体空泡化的形成，醛固酮增加了溶酶体的数量和大小。总之，提示GR和MR介导了皮质酮对小胶质细胞功能的相反作用；该激素通过GR起抑制剂作用，通过MR起刺激剂作用。
