Researchers at the University of Helsinki and Folkhälsan Research Center have, together with their collaborators, for the first time demonstrated in a mouse model that partial restoration of respiratory chain function in mitochondria, which serve as cellular power plants, may be sufficient to prevent symptoms of a severe mitochondrial disorder entirely.

Mitochondrial diseases are inherited disorders of energy metabolism. They can manifest at almost any age and in any tissue of the body. Modern molecular genetics often allow correct diagnosis at an early stage, but treatment options remain scarce. Diseases caused by a mutation affecting the third complex of the mitochondrial respiratory chain are sporadic. 

GRACILE syndrome

One of these, GRACILE syndrome, does however occur specifically in Finland, which makes it part of what is known as the Finnish disease heritage. The model employed in the study was based on the cross-breeding of two mouse strains: one developed by Professor Vineta Fellman's research group. 

Carrying the human GRACILE syndrome patient mutation, and mice expressing alternative oxidase (AOX), which was provided by Professor Howard Jacobs and Dr. Marten Szibor. The GRACILE syndrome is a currently untreatable mitochondrial disease belonging to the Finnish disease heritage.

Mammals do not usually have the AOX gene, but since mitochondria are so similar in all organisms, it maintains its function even after being transferred from a sea squirt (Ciona intestinalis) to mice. AOX is a mitochondrial enzyme that can improve electron flow in the respiratory chain when a part of the chain, complex III, in this case, becomes dysfunctional due to a disease-causing mutation.

In the recently published study, the research group headed by Professor Fellman and Docent Jukka Kallijärvi found out that a fatal cardiac disease did not develop at all in mice carrying the AOX transgene. Subsequently, the mice lived three times longer than the control group. Furthermore, AOX improved their kidney disease and brain cell changes.

"The AOX transgene extended the lifespan of the mice dramatically by enhancing respiration in the tissues that require the most energy, such as the heart. Of course, such a transgene cannot be used to treat humans, but our remarkable findings encourage further investigations in this and other mouse models for mitochondrial diseases. An interesting experiment would be, for example, to use a virus to express AOX in the infected tissues," Kallijärvi notes.