title: Cell-specific deletion of C1qa identifies microglia as the dominant source of C1q in mouse brain.
abstract: The complement cascade not only provides protection from infection but can also mediate destructive inflammation. Complement is also involved in elimination of neuronal synapses which is essential for proper development, but can be detrimental during aging and disease. C1q, required for several of these complement-mediated activities, is present in the neuropil, microglia, and a subset of interneurons in the brain.
  
  
  
  To identify the source(s) of C1q in the brain, the C1qa gene was selectively inactivated in the microglia or Thy-1+neurons in both wild type mice and a mouse model of Alzheimer's disease (AD), and C1q synthesis assessed by immunohistochemistry, QPCR, and western blot analysis.
  
  
  
  While C1q expression in the brain was unaffected after inactivation of C1qa in Thy-1+neurons, the brains of C1qaFL/FL:Cx3cr1CreERT2mice in which C1qa was ablated in microglia were devoid of C1q with the exception of limited C1q in subsets of interneurons. Surprisingly, this loss of C1q occurred even in the absence of tamoxifen by 1 month of age, demonstrating that Cre activity is tamoxifen-independent in microglia in Cx3cr1CreERT2/WganJmice. C1q expression in C1qaFL/FL: Cx3cr1CreERT2/WganJmice continued to decline and remained almost completely absent through aging and in AD model mice. No difference in C1q was detected in the liver or kidney from C1qaFL/FL: Cx3cr1CreERT2/WganJmice relative to controls, and C1qaFL/FL: Cx3cr1CreERT2/WganJmice had minimal, if any, reduction in plasma C1q.
  
  
  
  Thus, microglia, but not neurons or peripheral sources, are the dominant source of C1q in the brain. While demonstrating that the Cx3cr1CreERT2/WganJdeleter cannot be used for adult-induced deletion of genes in microglia, the model described here enables further investigation of physiological roles of C1q in the brain and identification of therapeutic targets for the selective control of complement-mediated activities contributing to neurodegenerative disorders.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697, USA.
authors.forename: Maria I
authors.initials: MI
authors.lastname: Fonseca
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697, USA.
authors.forename: Shu-Hui
authors.initials: SH
authors.lastname: Chu
authors.affiliation: Department of Pathology and Laboratory Medicine, University of California, Irvine School of Medicine, Irvine, CA, 92697, USA.
authors.forename: Michael X
authors.initials: MX
authors.lastname: Hernandez
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697, USA.
authors.forename: Melody J
authors.initials: MJ
authors.lastname: Fang
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697, USA.
authors.forename: Lila
authors.initials: L
authors.lastname: Modarresi
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697, USA.
authors.forename: Pooja
authors.initials: P
authors.lastname: Selvan
authors.affiliation: Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, 92697, USA.
authors.forename: Grant R
authors.initials: GR
authors.lastname: MacGregor
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697, USA. atenner@uci.edu.|Department of Pathology and Laboratory Medicine, University of California, Irvine School of Medicine, Irvine, CA, 92697, USA. atenner@uci.edu.|Department of Neurobiology and Behavior, University of California, Irvine, Irvine, CA, 92697, USA. atenner@uci.edu.
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Tenner
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000166:cytology*; D039481:CD11b Antigen / Q000235:genetics / Q000378:metabolism; D000073883:CX3C Chemokine Receptor 1; D015922:Complement C1q / Q000172:deficiency* / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017628:Microglia / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D019581:Neuropil / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D019707:Receptors, Chemokine / Q000235:genetics / Q000378:metabolism; D018800:Thy-1 Antigens / Q000235:genetics / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D039481:CD11b Antigen; D000073883:CX3C Chemokine Receptor 1; C471885:Cx3cr1 protein, mouse; D008164:Luminescent Proteins; D012333:RNA, Messenger; D019707:Receptors, Chemokine; D018800:Thy-1 Antigens; D015922:Complement C1q; D001616:beta-Galactosidase
keywords: Alzheimer’s; C1q; Complement; Conditional knockout; Expression; Microglia; Mouse model