Self-destructing mitochondria can leave some brain cells vulnerable.

A recently discovered type of mitochondrial self-destruction may make some brain cells vulnerable to ALS, also known as Lou Gehrig’s disease. In mice genetically engineered to develop some forms of a degenerative nerve disease similar to amyotrophic lateral sclerosis, power-generating organelles called mitochondria seem to dismantle without the help of the usual cell-wrecking kits.

This type of self-destruction was detected in upper motor neurons, the nerve cells in the brain that help initiate and control movement, but not in neighboring cells, the researchers report. The death of those upper motor neurons is a hallmark of ALS, and the self-destruction of mitochondria may be an early step that causes those cells to die later; it’s a separate process from mitophagy, the usual way that cell structures called autophagosomes and lysosomes remove damaged mitochondria from the cell.

Cleaning out old or damaged mitochondria is usually important for cells to stay healthy, when mitochondria suffer too much damage it can trigger the programmed death of the entire cell, known as apoptosis. ALS usually doesn’t strike until people are between the ages of 40 and 70, but by the time symptoms appear, motor neurons are already damaged.

Mitochondria feeding themselves can make upper motor neurons more vulnerable to ALS later in life. The details of that vulnerability have not yet been worked out.

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