title: A novel size-based sorting mechanism of pinocytic luminal cargoes in microglia.
abstract: Microglia are the resident immune cells in the CNS and play diverse roles in the maintenance of CNS homeostasis. Recent studies have shown that microglia continually survey the CNS microenvironment and scavenge cell debris and aberrant proteins by phagocytosis and pinocytosis, and that reactive microglia are capable to present antigens to T cells and initiate immune responses. However, how microglia process the endocytosed contents and evoke an immune response remain unclear. Here we report that a size-dependent selective transport of small soluble contents from the pinosomal lumen into lysosomes is critical for the antigen processing in microglia. Using fluorescent probes and water-soluble magnetic nanobeads of defined sizes, we showed in cultured rodent microglia, and in a cell-free reconstructed system that pinocytosed proteins become degraded immediately following pinocytosis and the resulting peptides are selectively delivered to major histocompatibility complex class II (MHC-II) containing lysosomes, whereas undegraded proteins are retained in the pinosomal lumen. This early size-based sorting of pinosomal contents relied on the formation of transient tunnel between pinosomes and lysosomes in a Rab7- and dynamin II-dependent manner, which allowed the small contents to pass through but restricted large ones. Inhibition of the size-based sorting markedly reduced proliferation and cytokine release of cocultured CD4(+) T cells, indicating that the size-based sorting is required for efficient antigen presentation by microglial cells. Together, these findings reveal a novel early sorting mechanism for pinosomal luminal contents in microglial cells, which may explain how microglia efficiently process protein antigens and evoke an immune response.
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and.
authors: Cong
authors: C
authors: Chen
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and.
authors: Hui-Quan
authors: HQ
authors: Li
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and.
authors: Yi-Jun
authors: YJ
authors: Liu
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and.
authors: Zhi-Fei
authors: ZF
authors: Guo
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and.
authors: Hang-Jun
authors: HJ
authors: Wu
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and.
authors: Xia
authors: X
authors: Li
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and.
authors: Hui-Fang
authors: HF
authors: Lou
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and.
authors: Liya
authors: L
authors: Zhu
authors: Institute of Immunology, Zhejiang University School of Medicine, Hangzhou 310058, China.
authors: Di
authors: D
authors: Wang
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and.
authors: Xiao-Ming
authors: XM
authors: Li
authors: State Key Laboratory of Biomembrane and Membrane Biotechnology, Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China, and.
authors: Li
authors: L
authors: Yu
authors: Institute of Immunology, Zhejiang University School of Medicine, Hangzhou 310058, China, National Key Laboratory of Medical Immunology and Institute of Immunology, Second Military Medical University, Shanghai 200433, China.
authors: Xuetao
authors: X
authors: Cao
authors: Institute of Immunology, Zhejiang University School of Medicine, Hangzhou 310058, China.
authors: Linrong
authors: L
authors: Lu
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and duanshumin@zju.edu.cn zhihuagao@zju.edu.cn.
authors: Zhihua
authors: Z
authors: Gao
authors: Department of Neurobiology, Key Laboratory of Medical Neurobiology of The Ministry of Health of China, Key Laboratory of Neurobiology of Zhejiang Province, and duanshumin@zju.edu.cn zhihuagao@zju.edu.cn.
authors: Shu-Min
authors: SM
authors: Duan
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000648:ultrastructure; D000941:Antigens / Q000378:metabolism; D002459:Cell Fusion; D002469:Cell Separation; D048429:Cell Size; D005260:Female; D066298:In Vitro Techniques; D008247:Lysosomes / Q000378:metabolism; D008262:Macrophage Activation; D008297:Male; D051379:Mice; D017628:Microglia / Q000502:physiology* / Q000648:ultrastructure*; D010873:Pinocytosis / Q000502:physiology*; D061251:Primary Cell Culture; D051381:Rats; D017207:Rats, Sprague-Dawley; D023062:Receptors, Interleukin-8A / Q000235:genetics
chemical_list: D000941:Antigens; D023062:Receptors, Interleukin-8A
keywords: antigen presentation; endocytic trafficking; luminal contents; lysosome; microglia; size-based sorting