title: LRP1 modulates the microglial immune response via regulation of JNK and NF-κB signaling pathways.
abstract: Neuroinflammation is characterized by microglial activation and the increased levels of cytokines and chemokines in the central nervous system (CNS). Recent evidence has implicated both beneficial and toxic roles of microglia when over-activated upon nerve injury or in neurodegenerative diseases, including Alzheimer's disease (AD). The low-density lipoprotein receptor-related protein 1 (LRP1) is a major receptor for apolipoprotein E (apoE) and amyloid-β (Aβ), which play critical roles in AD pathogenesis. LRP1 regulates inflammatory responses in peripheral tissues by modulating the release of inflammatory cytokines and phagocytosis. However, the roles of LRP1 in brain innate immunity and neuroinflammation remain unclear.
  
  
  
  In this study, we determined whether LRP1 modulates microglial activation by knocking down Lrp1 in mouse primary microglia. LRP1-related functions in microglia were also assessed in the presence of LRP1 antagonist, the receptor-associated protein (RAP). The effects on the production of inflammatory cytokines were measured by quantitative real-time PCR (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA). Potential involvement of specific signaling pathways in LRP1-regulated functions including mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB) were assessed using specific inhibitors.
  
  
  
  We found that knocking down of Lrp1 in mouse primary microglia led to the activation of both c-Jun N-terminal kinase (JNK) and NF-κB pathways with corresponding enhanced sensitivity to lipopolysaccharide (LPS) in the production of pro-inflammatory cytokines. Similar effects were observed when microglia were treated with LRP1 antagonist RAP. In addition, treatment with pro-inflammatory stimuli suppressed Lrp1 expression in microglia. Interestingly, NF-κB inhibitor not only suppressed the production of cytokines induced by the knockdown of Lrp1 but also restored the down-regulated expression of Lrp1 by LPS.
  
  
  
  Our study uncovers that LRP1 suppresses microglial activation by modulating JNK and NF-κB signaling pathways. Given that dysregulation of LRP1 has been associated with AD pathogenesis, our work reveals a critical regulatory mechanism of microglial activation by LRP1 that could be associated with other AD-related pathways thus further nominating LRP1 as a potential disease-modifying target for the treatment of AD.
authors.affiliation: Institute of Neuroscience, Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Medical College, Xiamen University, Xiamen, 361102, China.
authors.forename: Longyu
authors.initials: L
authors.lastname: Yang
authors.affiliation: Department of Neuroscience, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL32224, USA.
authors.forename: Chia-Chen
authors.initials: CC
authors.lastname: Liu
authors.affiliation: Institute of Neuroscience, Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Medical College, Xiamen University, Xiamen, 361102, China.
authors.forename: Honghua
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Department of Neuroscience, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL32224, USA.
authors.forename: Takahisa
authors.initials: T
authors.lastname: Kanekiyo
authors.affiliation: Department of Neuroscience, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL32224, USA.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Atagi
authors.affiliation: Institute of Neuroscience, Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Medical College, Xiamen University, Xiamen, 361102, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Jia
authors.affiliation: Institute of Neuroscience, Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Medical College, Xiamen University, Xiamen, 361102, China.
authors.forename: Daxin
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Neuroscience, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL32224, USA.
authors.forename: Aurelie
authors.initials: A
authors.lastname: N'songo
authors.affiliation: Institute of Neuroscience, Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Medical College, Xiamen University, Xiamen, 361102, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Can
authors.affiliation: Institute of Neuroscience, Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Medical College, Xiamen University, Xiamen, 361102, China.
authors.forename: Huaxi
authors.initials: H
authors.lastname: Xu
authors.affiliation: Institute of Neuroscience, Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Medical College, Xiamen University, Xiamen, 361102, China. chenxf@xmu.edu.cn.|Shenzhen Research Institute of Xiamen University, Shenzhen, 518063, China. chenxf@xmu.edu.cn.
authors.forename: Xiao-Fen
authors.initials: XF
authors.lastname: Chen
authors.affiliation: Institute of Neuroscience, Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Medical College, Xiamen University, Xiamen, 361102, China. bu.guojun@mayo.edu.|Department of Neuroscience, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL32224, USA. bu.guojun@mayo.edu.
authors.forename: Guojun
authors.initials: G
authors.lastname: Bu
mesh_terms: D016229:Amyloid beta-Peptides / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D026563:LDL-Receptor Related Protein-Associated Protein / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D048670:MAP Kinase Kinase 4 / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000187:drug effects / Q000276:immunology*; D016328:NF-kappa B / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D016229:Amyloid beta-Peptides; D016207:Cytokines; D004791:Enzyme Inhibitors; D026563:LDL-Receptor Related Protein-Associated Protein; D008070:Lipopolysaccharides; D026503:Low Density Lipoprotein Receptor-Related Protein-1; C486645:Lrp1 protein, mouse; D016328:NF-kappa B; D010446:Peptide Fragments; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011973:Receptors, LDL; D025521:Tumor Suppressor Proteins; C075222:amyloid beta-protein (1-42); D048670:MAP Kinase Kinase 4
keywords: AD; Inflammation; JNK; LRP1; Microglia; NF-κB; RAP