A new therapeutic approach for myotubular myopathy
Cross sections of muscles. Left the normal muscle fibers, in the middle those of a diseased mouse and on the right those of a diseased mouse overexpressing MTMR2.
Hum Mol Genet Oct. 1, 2017
July 19, 2017
Myotubular myopathy is a rare genetic disease characterized by muscle weakness which appears at birth or in the first few months. It is due to a defect in the MTM1 protein. Jocelyn Laporte’s team, in collaboration with Sylvie Friant’s team (CNRS – University of Strasbourg), compared the functions of this MTM1 protein with those of a similar protein MTMR2, involved in neuropathy. This allowed them to explain why these proteins are associated with different neuromuscular diseases, and to show that overexpression of a specific version of MTMR2 in myopathic mice due to lack of MTM1 prevents the progression of symptoms. This work was published in Human Molecular Genetics on 06 July 2017.
Myotubularins belong to a large proteins family involved in various neuromuscular diseases. Defects in the MTM1 protein are responsible for myotubular myopathy, while mutations in the gene coding for the MTMR2 protein cause a Charcot-Marie-Tooth neuropathy affecting the peripheral nerves. To understand why similar proteins are associated with different diseases, researchers aimed to determine the functions of these proteins, MTM1 and two versions of MTMR2 (short and long).
By analyzing various myotubularins functionand expression in yeast cells and in animals, they identified the N-terminal domain is responsible for functional differences between MTMR1 and MTMR2. An N-terminal extension observed in the long MTMR2 is absent in MTM1 and in the short MTMR2, suggesting that this short MTMR2 would have the same function as MTM1.
Using an adeno-associated virus (AAV), a small non-pathogenic DNA virus that easily penetrates cells, the researchers were able to introduce the gene encoding the short MTMR2 protein into myopathic mice no longer expressing MTM1. They observed that the expression of short MTMR2 prevents the myopathy progression in these mice.
In addition to showing that the involvement of similar proteins in different genetic diseases is due to functional and structural differences in these proteins, these results identify the short MTMR2 as a new therapeutic target for the myotubular myopathy treatment.
The study was funded by the French Agence nationale pour la recherche (ANR) and the AFM-Téléthon.