Pharmacological Inhibition of Myostatin in a Mouse Model of Typical Nemaline Myopathy Increases Muscle Size and Force

Abstract

Nemaline myopathy is one of the most common non-dystrophic congenital myopathies. Individuals affected by this condition experience muscle weakness and muscle smallness, often requiring supportive measures like wheelchairs or respiratory support. A significant proportion of patients, approximately one-third, exhibit compound heterozygous nebulin mutations, which usually give rise to the typical form of the disease. Currently, there are no approved treatments available for nemaline myopathy. Our research explored the modulation of myostatin, a negative regulator of muscle mass, in combating the muscle smallness associated with the disease. To investigate the effect of myostatin inhibition, we employed a mouse model with compound heterozygous nebulin mutations that mimic the typical form of the disease. The mice were treated with mRK35, a myostatin antibody, through weekly intraperitoneal injections of 10 mg/kg mRK35, commencing at two weeks of age and continuing until the mice reached four months of age. The treatment resulted in an increase in body weight and an approximate 20% muscle weight gain across most skeletal muscles, without affecting the heart. The minimum Feret diameter of type IIA and IIB fibers exhibited an increase in compound heterozygous mice, while only type IIB fibers demonstrated an increase in wild-type mice. In vitro mechanical experiments conducted on intact extensor digitorum longus muscle revealed that mRK35 augmented the physiological cross-sectional area of muscle fibers and enhanced absolute tetanic force in both wild-type and compound heterozygous mice. Furthermore, mRK35 administration improved grip strength in treated mice. Collectively, these findings indicate that inhibiting myostatin can mitigate the muscle deficits in nebulin-based typical nemaline myopathy, potentially serving as a much-needed therapeutic option.

Characterization ofNEBmutations in patients reveals novel nemaline myopathy disease mechanisms and omecamtiv mecarbil force effects

“…[26][27][28][29][30][31] It has also been implicated in the regulation of thin filament length (TFL), as reduced levels of nebulin protein have been associated with shortened TFL in patients with NEB-related nemaline myopathy, as well as in nebulin-deficient mouse models, zebrafish, and chick skeletal myocytes. 30,[32][33][34][35][36][37][38][39] Despite investigating a number of therapeutic interventions including troponin activators such as Levosimendan, 40 CK-20066260, 30 dietary supplements 41 and myostatin inhibitors, 42,43 there are currently no effective therapies targeting the underlying pathological mechanisms for nebulinbased NEM (NEM2). It has been shown that Omecamtiv mecarbil (OM), a selective smallmolecule activator of cardiac myosin (MYH7) that was initially developed as a treatment for heart failure, 44,45 , increases submaximal force production in type I skeletal muscles of Neb cKO mouse model 46 and rat diaphragm.…”