Complement C3 deficiency leads to accelerated amyloid beta plaque deposition and neurodegeneration and modulation of the microglia/macrophage phenotype in amyloid precursor protein transgenic mice.
Complement factor C3 is the central component of the complement system and a key inflammatory protein activated in Alzheimer's disease (AD). Previous studies demonstrated that inhibition of C3 by overexpression of soluble complement receptor-related protein y in an AD mouse model led to reduced microgliosis, increased amyloid beta (Abeta) plaque burden, and neurodegeneration. To further address the role of C3 in AD pathology, we generated a complement C3-deficient amyloid precursor protein (APP) transgenic AD mouse model (APP;C3(-/-)). Brains were analyzed at 8, 12, and 17 months of age by immunohistochemical and biochemical methods and compared with age-matched APP transgenic mice. At younger ages (8-12 months), no significant neuropathological differences were observed between the two transgenic lines. In contrast, at 17 months of age, APP;C3(-/-) mice showed significant changes of up to twofold increased total Abeta and fibrillar amyloid plaque burden in midfrontal cortex and hippocampus, which correlated with (1) significantly increased Tris-buffered saline (TBS)-insoluble Abeta(42) levels and reduced TBS-soluble Abeta(42) and Abeta(40) levels in brain homogenates, (2) a trend for increased Abeta levels in the plasma, (3) a significant loss of neuronal-specific nuclear protein-positive neurons in the hippocampus, and (4) differential activation of microglia toward a more alternative phenotype (e.g., significantly increased CD45-positive microglia, increased brain levels of interleukins 4 and 10, and reduced levels of CD68, F4/80, inducible nitric oxide synthase, and tumor necrosis factor). Our results suggest a beneficial role for complement C3 in plaque clearance and neuronal health as well as in modulation of the microglia phenotype.
Center for Neurologic Diseases, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Marcel
M
Maier
Ying
Y
Peng
Liying
L
Jiang
Timothy J
TJ
Seabrook
Michael C
MC
Carroll
Cynthia A
CA
Lemere
D000544:Alzheimer Disease / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D016229:Amyloid beta-Peptides / Q000235:genetics / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D003176:Complement C3 / Q000172:deficiency* / Q000235:genetics; D006801:Humans; D008264:Macrophages / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017628:Microglia / Q000378:metabolism* / Q000473:pathology; D009410:Nerve Degeneration / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D010641:Phenotype; D058225:Plaque, Amyloid / Q000235:genetics / Q000378:metabolism* / Q000473:pathology
D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D003176:Complement C3