The complement system: an unexpected role in synaptic pruning during development and disease.
An unexpected role for the classical complement cascade in the elimination of central nervous system (CNS) synapses has recently been discovered. Complement proteins are localized to developing CNS synapses during periods of active synapse elimination and are required for normal brain wiring. The function of complement proteins in the brain appears analogous to their function in the immune system: clearance of cellular material that has been tagged for elimination. Similarly, synapses tagged with complement proteins may be eliminated by microglial cells expressing complement receptors. In addition, developing astrocytes release signals that induce the expression of complement components in the CNS. In the mature brain, early synapse loss is a hallmark of several neurodegenerative diseases. Complement proteins are profoundly upregulated in many CNS diseases prior to signs of neuron loss, suggesting a reactivation of similar developmental mechanisms of complement-mediated synapse elimination potentially driving disease progression.
Department of Neurobiology, Stanford University School of Medicine, Stanford, California 94305-5125, USA. astephan@stanford.edu
Alexander H
AH
Stephan
Ben A
BA
Barres
Beth
B
Stevens
D000818:Animals; D001253:Astrocytes / Q000378:metabolism / Q000502:physiology; D001921:Brain / Q000254:growth & development* / Q000378:metabolism / Q000473:pathology*; D001930:Brain Injuries / Q000378:metabolism / Q000503:physiopathology*; D003165:Complement System Proteins / Q000096:biosynthesis / Q000502:physiology*; D006801:Humans; D017628:Microglia / Q000378:metabolism / Q000502:physiology; D018448:Models, Immunological; D008959:Models, Neurological; D009410:Nerve Degeneration / Q000473:pathology*; D009434:Neural Pathways / Q000254:growth & development; D019636:Neurodegenerative Diseases / Q000378:metabolism / Q000503:physiopathology*; D013569:Synapses / Q000473:pathology
D003165:Complement System Proteins