Activation of phagocytic activity in astrocytes by reduced expression of the inflammasome component ASC and its implication in a mouse model of Alzheimer disease.
Activation of phagocytic activity in astrocytes by reduced expression of the inflammasome component ASC and its implication in a mouse model of Alzheimer disease.
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DOI：
10.1186/s12974-016-0477-y
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发表时间：
2016-01-27
影响因子：
9.3
通讯作者：
Octave JN
中科院分区：
文献类型：
--
作者：
Couturier J;Stancu IC;Schakman O;Pierrot N;Huaux F;Kienlen-Campard P;Dewachter I;Octave JN
促炎细胞因子白细胞介素-1β (IL-1β)在阿尔茨海默病（AD）中过度表达，是神经炎症的关键调节因子。淀粉样蛋白-β (Aβ)肽触发炎症小体的激活，炎症小体是小胶质细胞中负责IL-1β成熟的蛋白质复合物。在阿尔茨海默病小鼠模型中，下调NALP3 （NACHT、LRR和PYD结构域蛋白3）炎性体可减少淀粉样蛋白负荷并挽救认知缺陷。尽管炎性体在小胶质细胞中的活化在阿尔茨海默病中已被描述，但目前尚无关于星形胶质细胞中炎性体活化的数据，尽管它们参与炎症反应和吞噬作用。本研究以炎性小体适配蛋白ASC（含有CARD结构域的凋亡相关斑点样蛋白）为靶点，研究了炎性小体活化对星形胶质细胞吞噬活性的影响。我们使用ASC敲除小鼠模型，因为ASC是炎症小体中的中心蛋白，作为复合物的适配器和稳定剂，因此对其激活至关重要。利用脂多糖（LPS）诱导的新生小鼠星形胶质细胞原代培养物，通过电化学发光免疫分析法（ECLIA）测量IL-1β的释放来评估a β诱导的炎性体活化。通过生物颗粒的结合来测量吞噬效率，通过ECLIA来测量趋化因子CCL3 （C-C基序配体3）的释放。将ASC小鼠与5xFAD（家族性阿尔茨海默病）小鼠杂交，在7-8月龄时采用Morris水迷宫（MWM）测试其空间参考记忆。淀粉样蛋白载量和CCL3分别采用硫代黄酮S染色法和定量实时聚合酶链反应（qRT-PCR）法测定。LPS诱导培养的星形胶质细胞和Aβ处理的星形胶质细胞显示出asc依赖性的IL-1β产生，这是由Aβ吞噬和组织蛋白酶B酶活性介导的炎性体激活引起的。与ASC+/+和ASC - / -细胞相比，ASC+/ -星形胶质细胞表现出更高的吞噬活性，这是由于趋化因子CCL3的释放更高。携带ASC +/−基因型的7 - 8月龄5xFAD小鼠大脑中淀粉样蛋白负荷显著减少，与CCL3基因表达增加相关。此外，ASC +/−基因型修复了5xFAD小鼠的空间参考记忆缺陷。我们的研究结果表明，β能够激活星形细胞炎性体。由于CCL3的释放，炎性体活性的下调增加了星形胶质细胞的吞噬作用。这可以解释为什么炎性体活性的下调会减少淀粉样蛋白的负荷，并挽救AD小鼠模型中的记忆缺陷。本文的在线版本（doi:10.1186/s12974-016-0477-y）包含补充材料，可供授权用户使用。
The proinflammatory cytokine interleukin-1β (IL-1β) is overexpressed in Alzheimer disease (AD) as a key regulator of neuroinflammation. Amyloid-β (Aβ) peptide triggers activation of inflammasomes, protein complexes responsible for IL-1β maturation in microglial cells. Downregulation of NALP3 (NACHT, LRR, and PYD domains-containing protein 3) inflammasome has been shown to decrease amyloid load and rescue cognitive deficits in a mouse model of AD. Whereas activation of inflammasome in microglial cells has been described in AD, no data are currently available concerning activation of inflammasome in astrocytes, although they are involved in inflammatory response and phagocytosis. Here, by targeting the inflammasome adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD domain), we investigated the influence of activation of the inflammasome on the phagocytic activity of astrocytes. We used an ASC knockout mouse model, as ASC is a central protein in the inflammasome, acting as an adaptor and stabilizer of the complex and thus critical for its activation. Lipopolysaccharide (LPS)-primed primary cultures of astrocytes from newborn mice were utilized to evaluate Aβ-induced inflammasome activation by measuring IL-1β release by ECLIA (electro-chemiluminescence immunoassay). Phagocytosis efficiency was measured by incorporation of bioparticles, and the release of the chemokine CCL3 (C-C motif ligand 3) was measured by ECLIA. ASC mice were crossbred with 5xFAD (familial Alzheimer disease) mice and tested for spatial reference memory using the Morris water maze (MWM) at 7–8 months of age. Amyloid load and CCL3 were quantified by thioflavine S staining and quantitative real-time polymerase chain reaction (qRT-PCR), respectively. Cultured astrocytes primed with LPS and treated with Aβ showed an ASC-dependent production of IL-1β resulting from inflammasome activation mediated by Aβ phagocytosis and cathepsin B enzymatic activity. ASC+/− astrocytes displayed a higher phagocytic activity as compared to ASC+/+ and ASC −/− cells, resulting from a higher release of the chemokine CCL3. A significant decrease in amyloid load was measured in the brain of 7–8-month-old 5xFAD mice carrying the ASC +/− genotype, correlated with an increase in CCL3 gene expression. In addition, the ASC +/− genotype rescued spatial reference memory deficits observed in 5xFAD mice. Our results demonstrate that Aβ is able to activate astrocytic inflammasome. Downregulation of inflammasome activity increases phagocytosis in astrocytes due to the release of CCL3. This could explain why downregulation of inflammasome activity decreases amyloid load and rescues memory deficits in a mouse model of AD. The online version of this article (doi:10.1186/s12974-016-0477-y) contains supplementary material, which is available to authorized users.