Microglia brain cells destroy healthy synapses
Thursday 24 May 2012
A study from Boston Children's Hospital shows that brain cells known as microglia specifically seek out and destroy unneeded synapses, the connections between neurons.
Microglia are the first and main form of active immune defence in the central nervous system. They operate inside the blood brain barrier and act as scavengers, ridding the body of damaged neurons, plaques and infectious agents. This study is the first to show that microglia also attack healthy synapses.
The study showed that microglia take their cues from neurons' activity patterns and from a set of signals called the complement cascade, used by the immune system to rid the body of unwanted pathogens and debris. When complement signaling was disrupted, pruning of synapses diminished.
Dr. Beth Stephens and Dr. Dori Schaffer, co-leaders of the study, demonstrated that microglia have receptors that recognize the complement protein C3 - the same protein found on synapses that are destined for elimination. Dr. Schaffer said: "We think that weaker synapses are being tagged with C3, and that microglia are eliminating them just as macrophages would eliminate bacteria. C3 is like an 'eat me' signal."
The findings may have implications for understanding neurodegenerative diseases in which synapses are lost, including Alzheimer's and Huntington's diseases and ALS.