Muscle weakness is a common symptom of both long-time alcoholics and patients with mitochondrial disease. Now researchers have found a common link: mitochondria that are unable to self-repair. The results will be published online April 21 in The Journal of Cell Biology. The link to self-repair provides researchers both a new way to diagnose mitochondrial disease, and a new drug target. Mitochondria -- organelles that produce the energy needed for muscle, brain, and every other cell in the body -- repair their broken components by fusing with other mitochondria and exchanging their contents. Damaged parts are segregated for recycling and replaced with properly functioning proteins donated from healthy mitochondria.
While fusion is one major method for mitochondrial quality control in many types of cells, researchers have puzzled over the repair mechanism in skeletal muscle -- a type of tissue that relies constantly on mitochondria for power, making repair a frequent necessity. However, mitochondria are squeezed so tightly in between the packed fibers of muscle cells, that most researchers assumed that fusion among mitochondria in this tissue type was impossible.
An inkling that fusion might be important for the normal muscle function came from research on two mitochondrial diseases: Autosomal Dominant Optical Atropy (ADOA) disease, and a type of Charcot-Marie-Tooth disease (CMT). A symptom of both disease is muscle weakness and patients with both these diseases carry a mutation in one of the three genes involved in mitochondrial fusion.