Chang Philip K-Y, Khatchadourian Armen, McKinney Rebecca Anne, Maysinger Dusica
Department of Pharmacology and Therapeutics, McGill University, McIntyre Medical Building, Room 1314, 3655 Promenade Sir William Osler, Montreal, QC, H3G 1Y6, Canada.
Department of Pharmacology & Therapeutics, Bellini Life Science Complex, McGill University, Room 167, 3649 Promenade Sir-William-Osler, Montreal, QC, H3G 0B1, Canada.
J Neuroinflammation. 2015 Feb 22;12:34. doi: 10.1186/s12974-015-0244-5.
Recent studies have revealed that excessive activation of microglia and inflammation-mediated neurotoxicity are implicated in the progression of several neurological disorders. In particular, chronic inflammation in vivo and exposure of cultured brain cells to lipopolysaccharide (LPS) in vitro can adversely change microglial morphology and function. This can have both direct and indirect effects on synaptic structures and functions. The integrity of dendritic spines, the postsynaptic component of excitatory synapses, dictates synaptic efficacy. Interestingly, dysgenesis of dendritic spines has been found in many neurological diseases associated with ω-3 polyunsaturated fatty acid (PUFA) deficiency and cognitive decline. In contrast, supplemented ω-3 PUFAs, such as docosahexaenoic acid (DHA), can partly correct spine defects. Hence, we hypothesize that DHA directly affects synaptic integrity and indirectly through neuron-glia interaction. Strong activation of microglia by LPS is accompanied by marked release of nitric oxide and formation of lipid bodies (LBs), both dynamic biomarkers of inflammation. Here we investigated direct effects of DHA on synaptic integrity and its indirect effects via microglia in the hippocampal CA1 region.
Microglia (N9) and organotypic hippocampal slice cultures were exposed to the proinflammagen LPS (100 ng/ml) for 24 h. Biochemical and morphological markers of inflammation were investigated in microglia and CA1 regions of hippocampal slices. As biomarkers of hyperactive microglia, mitochondrial function, nitric oxide release and LBs (number, size, LB surface-associated proteins) were assessed. Changes in synaptic transmission of CA1 pyramidal cells were determined following LPS and DHA (25-50 μM) treatments by recording spontaneous AMPA-mediated miniature excitatory postsynaptic currents (mEPSCs).
Microglia responded to LPS stimulation with a significant decrease of mitochondrial function, increased nitric oxide production and an increase in the formation of large LBs. LPS treatment led to a significant reduction of dendritic spine densities and an increase in the AMPA-mediated mEPSC inter-event interval (IEI). DHA normalized the LPS-induced abnormalities in both neurons and microglia, as revealed by the restoration of synaptic structures and functions in hippocampal CA1 pyramidal neurons.
Our findings indicate that DHA can prevent LPS-induced abnormalities (neuroinflammation) by reducing inflammatory biomarkers, thereby normalizing microglia activity and their effect on synaptic function.
最近的研究表明，小胶质细胞的过度激活和炎症介导的神经毒性与几种神经系统疾病的进展有关。特别是，体内的慢性炎症以及体外培养的脑细胞暴露于脂多糖（LPS）会对小胶质细胞的形态和功能产生不利影响。这会对突触结构和功能产生直接和间接影响。树突棘是兴奋性突触的突触后成分，其完整性决定了突触效能。有趣的是，在许多与ω-3多不饱和脂肪酸（PUFA）缺乏和认知衰退相关的神经系统疾病中都发现了树突棘发育异常。相比之下，补充ω-3多不饱和脂肪酸，如二十二碳六烯酸（DHA），可以部分纠正脊柱缺陷。因此，我们假设DHA直接影响突触完整性，并通过神经元-胶质细胞相互作用间接影响。LPS对小胶质细胞的强烈激活伴随着一氧化氮的显著释放和脂滴（LB）形成，这两者都是炎症的动态生物标志物。在这里，我们研究了DHA对海马CA1区突触完整性的直接影响及其通过小胶质细胞的间接影响。
将小胶质细胞（N9）和海马脑片培养物暴露于促炎剂LPS（100 ng/ml）24小时。研究海马脑片小胶质细胞和CA1区炎症的生化和形态学标志物。作为过度活跃小胶质细胞的生物标志物，评估线粒体功能、一氧化氮释放和脂滴（数量、大小、脂滴表面相关蛋白）。通过记录自发的AMPA介导的微小兴奋性突触后电流（mEPSC），测定LPS和DHA（25-50 μM）处理后CA1锥体细胞的突触传递变化。
小胶质细胞对LPS刺激的反应是线粒体功能显著下降、一氧化氮产生增加以及大脂滴形成增加。LPS处理导致树突棘密度显著降低，AMPA介导的mEPSC事件间间隔（IEI）增加。DHA使LPS诱导的神经元和小胶质细胞异常恢复正常，海马CA1锥体细胞的突触结构和功能恢复表明了这一点。
我们的研究结果表明，DHA可以通过减少炎症生物标志物来预防LPS诱导的异常（神经炎症），从而使小胶质细胞活性及其对突触功能的影响正常化。
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