A dramatic increase of C1q protein in the CNS during normal aging.
The decline of cognitive function has emerged as one of the greatest health threats of old age. Age-related cognitive decline is caused by an impacted neuronal circuitry, yet the molecular mechanisms responsible are unknown. C1q, the initiating protein of the classical complement cascade and powerful effector of the peripheral immune response, mediates synapse elimination in the developing CNS. Here we show that C1q protein levels dramatically increase in the normal aging mouse and human brain, by as much as 300-fold. This increase was predominantly localized in close proximity to synapses and occurred earliest and most dramatically in certain regions of the brain, including some but not all regions known to be selectively vulnerable in neurodegenerative diseases, i.e., the hippocampus, substantia nigra, and piriform cortex. C1q-deficient mice exhibited enhanced synaptic plasticity in the adult and reorganization of the circuitry in the aging hippocampal dentate gyrus. Moreover, aged C1q-deficient mice exhibited significantly less cognitive and memory decline in certain hippocampus-dependent behavior tests compared with their wild-type littermates. Unlike in the developing CNS, the complement cascade effector C3 was only present at very low levels in the adult and aging brain. In addition, the aging-dependent effect of C1q on the hippocampal circuitry was independent of C3 and unaccompanied by detectable synapse loss, providing evidence for a novel, complement- and synapse elimination-independent role for C1q in CNS aging.
Stanford University School of Medicine, Department of Neurobiology, Stanford, California 94305-5345, USA. astephan@stanford.edu
Alexander H
AH
Stephan
Daniel V
DV
Madison
José María
JM
Mateos
Deborah A
DA
Fraser
Emilie A
EA
Lovelett
Laurence
L
Coutellier
Leo
L
Kim
Hui-Hsin
HH
Tsai
Eric J
EJ
Huang
David H
DH
Rowitch
Dominic S
DS
Berns
Andrea J
AJ
Tenner
Mehrdad
M
Shamloo
Ben A
BA
Barres
D000375:Aging / Q000378:metabolism*; D000818:Animals; D001522:Behavior, Animal; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism* / Q000502:physiology; D015922:Complement C1q / Q000096:biosynthesis*; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016253:Microscopy, Immunoelectron
D015922:Complement C1q