Beyond the Capabilities of Mighty Mouse: Strengthening Muscle Mass in Monkeys
Patients who suffer from degenerative neuromuscular illnesses all share a sense of dread of the terrible handicap that lies in wait for them and from which there is little to no respite. A treatment that directly targets the severe muscular weakness that is the characteristic of these ailments would improve the lives of millions of people, despite the fact that this category of illnesses can have a number of different genetic and physiological causes. Now, in an expansion of their prior work in dystrophic mice, Kota et al. report such a treatment method in preclinical research carried out in nonhuman primates. These studies were carried out in order to prepare for human trials. This technique of treatment is applicable to a number of degenerative neuromuscular illnesses, regardless of whether or not researchers have determined the exact genetic abnormalities that cause these conditions.
Gene therapy was the method that the authors employed to insert a variant of the human gene that codes for follistatin into the muscles of the femurs of healthy cynomolgus macaques. Follistatin is a powerful inhibitor of the signalling protein known as myostatin, which controls the amount of skeletal muscle that is produced. Follistatin inhibits myostatin signalling and increases muscle growth and strength without adverse effects in mice; however, it has not been tried on primates up until this point. Researchers Kota et al. assessed gains in muscle mass and strength after injecting a follistatin-producing gene therapy vector into the leg muscles of monkeys and observing the results. The sustained production of follistatin did not result in any abnormalities in the architecture or functions of a number of different organs.
This encouraging improvement is accompanied by a few disclaimers. These findings are not indicative of what would happen in a clinical situation with people who suffer from muscular issues because the volunteers for this therapy procedure were healthy monkeys. The muscles go through a process of degeneration and regeneration on a continuous basis when affected by specific inherited neuromuscular illnesses. The vector that was utilised in this work does not integrate into the genome of the muscle cell, and as a result, it is possible for the vector to be eliminated from the cells during the cycles of degeneration and regeneration. However, the authors note out that the improvement in muscle size and strength that was shown in similarly treated dystrophic mice remained for more than a year even though there was notable muscle turnover. This was the case despite the fact that there was significant muscular growth. Before follistatin may be used in clinical settings, more research must be conducted. This may include a molecular analysis of gene and vector sequences in diverse tissues. Nevertheless, the research carried out by Kota and colleagues provides proof of principle for the utilisation of myostatin inhibitors in order to increase muscle mass in primates.
In studies conducted on rodents, antagonists of regulatory proteins, which is a blood-borne specific inhibitor of muscle building that is produced in muscle tissue, have already shown good prospects for enhancing muscle strength. These antagonists also have the potential to serve as part of treatment for human muscle illnesses. One of the most powerful of these medicines, follistatin, has been shown to be both safe and efficacious when tested on mice; however, comparable research on nonhuman primates has not been carried out. We investigated an alternatively spliced version of human follistatin to see whether or not it met this key condition for clinical translation. This form of human follistatin has an effect on skeletal muscle, but it has only a modest effect on nonmuscle cells. When injected into the thighs of cynomolgus chimps, a follistatin isoform produced from a corresponding author virus type 1 vector called AAV1-FS344 elicited substantial and sustained gains in muscle growth and strength. These effects lasted throughout the duration of the study. Gene delivery using intramuscular injection of an AAV1 vector was shown to be safe after long-term expression of the transgene did not induce any aberrant changes in the morphology or function of important organs, indicating that the gene delivery method was safe. Our findings, in conjunction with those obtained from studies conducted on mice, provide evidence to support the hypothesis that treatment with AAV1-FS344 may enhance muscle mass and function in individuals suffering from certain degenerative muscle illnesses.