Tremblay Marie-Eve, Zhang Issan, Bisht Kanchan, Savage Julie C, Lecours Cynthia, Parent Martin, Titorenko Vladimir, Maysinger Dusica
Department of Molecular Medicine, Faculty of Medicine, Université Laval, Axe Neurosciences, Centre de recherche du CHU de Québec, Québec, QC, Canada.
Department of Pharmacology and Therapeutics, McGill University, Montréal, QC, Canada.
J Neuroinflammation. 2016 May 24;13(1):116. doi: 10.1186/s12974-016-0580-0.
Organelle remodeling processes are evolutionarily conserved and involved in cell functions during development, aging, and cell death. Some endogenous and exogenous molecules can modulate these processes. Docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid, has mainly been considered as a modulator of plasma membrane fluidity in brain development and aging, while DHA's role in organelle remodeling in specific neural cell types at the ultrastructural level remains largely unexplored. DHA is notably incorporated into dynamic organelles named lipid bodies (LBs). We hypothesized that DHA could attenuate the inflammatory response in lipopolysaccharide (LPS)-activated microglia by remodeling LBs and altering their functional interplay with mitochondria and other associated organelles.
We used electron microscopy to analyze at high spatial resolution organelle changes in N9 microglial cells exposed to the proinflammogen LPS, with or without DHA supplementation. Our results revealed that DHA reverses several effects of LPS in organelles. In particular, a large number of very small and grouped LBs was exclusively found in microglial cells exposed to DHA. In contrast, LBs in LPS-stimulated cells in the absence of DHA were sparse and large. LBs formed in the presence of DHA were generally electron-dense, suggesting DHA incorporation into these organelles. The accumulation of LBs in microglial cells from mouse and human was confirmed in situ. In addition, DHA induced numerous contacts between LBs and mitochondria and reversed the frequent disruption of mitochondrial integrity observed upon LPS stimulation. Dilation of the endoplasmic reticulum lumen was also infrequent following DHA treatment, suggesting that DHA reduces oxidative stress and protein misfolding. Lipidomic analysis in N9 microglial cells treated with DHA revealed an increase in phosphatidylserine, indicating the role of this phospholipid in normalization and maintenance of physiological membrane functions. This finding was supported by a marked reduction of microglial filopodia and endosome number and significant reduction of LPS-induced phagocytosis.
DHA attenuates the inflammatory response in LPS-stimulated microglial cells by remodeling LBs and altering their interplay with mitochondria and other associated organelles. Our findings point towards a mechanism by which omega-3 DHA participates in organelle reorganization and contributes to the maintenance of neural cell homeostasis.
细胞器重塑过程在进化上是保守的，并且在发育、衰老和细胞死亡过程中参与细胞功能。一些内源性和外源性分子可以调节这些过程。二十二碳六烯酸（DHA），一种ω-3多不饱和脂肪酸，主要被认为是脑发育和衰老过程中质膜流动性的调节剂，而DHA在超微结构水平上对特定神经细胞类型的细胞器重塑中的作用仍 largely未被探索。DHA特别地被整合到称为脂质体（LBs）的动态细胞器中。我们假设DHA可以通过重塑脂质体并改变它们与线粒体和其他相关细胞器的功能相互作用来减轻脂多糖（LPS）激活的小胶质细胞中的炎症反应。
我们使用电子显微镜以高空间分辨率分析暴露于促炎原LPS的N9小胶质细胞中有无DHA补充时的细胞器变化。我们的结果显示DHA逆转了LPS在细胞器中的几种作用。特别地，大量非常小且聚集的脂质体仅在暴露于DHA的小胶质细胞中发现。相反，在没有DHA的情况下LPS刺激的细胞中的脂质体稀疏且大。在DHA存在下形成的脂质体通常电子密度高，表明DHA被整合到这些细胞器中。小鼠和人类小胶质细胞中脂质体的积累在原位得到证实。此外，DHA诱导脂质体与线粒体之间的大量接触，并逆转了LPS刺激时观察到的线粒体完整性的频繁破坏。DHA处理后内质网腔的扩张也不常见，表明DHA降低氧化应激和蛋白质错误折叠。对用DHA处理的N9小胶质细胞进行脂质组分析显示磷脂酰丝氨酸增加，表明这种磷脂在生理膜功能正常化和维持中的作用。小胶质细胞丝状伪足和内体数量的显著减少以及LPS诱导的吞噬作用的显著降低支持了这一发现。
DHA通过重塑脂质体并改变它们与线粒体和其他相关细胞器的相互作用来减轻LPS刺激的小胶质细胞中的炎症反应。我们的发现指向一种机制，通过该机制ω-3 DHA参与细胞器重组并有助于维持神经细胞内稳态。
