Star-shaped astrocytes (green) may donate mitochondria to nerve cells in distress, helping the brain escape damage from stroke and possibly other maladies, a new study suggests.It was known that astrocytes — star-shaped glial cells that, among other jobs, support neurons — take in and dispose of neurons’ discarded mitochondria. Now it turns out that mitochondria can move the other way, too. This astrocyte-to-neuron transfer is surprising, says neuroscientist Jarek Aronowski of the University of Texas Health Science Center at Houston. “Bottom line: It’s sort of shocking.” Study coauthor Eng Lo of Massachusetts General Hospital and Harvard Medical School cautions that the work is at a very early stage. But he hopes that a deeper understanding of this process might ultimately point out new ways to protect the brain from damage. Mitochondria produce the energy that powers cells in the body. Scientists have spotted the organelles moving into damaged cells in other parts of the body, including the lungs, heart and liver. The new study turns up signs of this mitochondrial generosity in the brain.
Mitochondria from astrocytes (red) make their way into a nerve cell’s main body (box 1) and its message-sending axon (box 2). Some astrocyte-made mitochondria seem to fuse with the neuron’s own mitochondria (yellow, box 3).Astrocytes produce mitochondria and shunt them out into the soup that surrounds cells, Lo and colleagues found. The researchers then put neurons into this mitochondria-rich broth. When starved of glucose and oxygen — a situation that approximates a stroke — the neurons took in the astrocyte-made organelles. Not only did the mitochondria make it into neurons, they actually helped, though the researchers don’t yet understand how. Neurons with donated mitochondria better survived their starvation diet. When grown in dishes without extra mitochondria floating around, neurons were less able to weather the poor conditions, the researchers found.
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