Molecular determinants of diaphragm muscle impairment in a mouse model of Spinal Muscular Atrophy and a possible nutraceutical intervention

Spinal muscular atrophy (SMA) is a genetic disorder characterized by the loss of spinal motor neurons leading to muscle weakness and respiratory failure. Energetic disturbances suggestive of underlying mitochondrial dysfunction are found in the skeletal muscle of patients with SMA. For obvious reasons, the diaphragm muscle is poorly studied, notwithstanding respiratory involvement plays a very important role in SMA mortality. The main goal of this study was to investigate diaphragm functionality and the underlying molecular adaptations in SMNΔ7 mice, a mice model that exhibits symptoms similar to that of patients with intermediate type II SMA. Functional, biochemical, and molecular analysis on isolated diaphragm was performed. The obtained results suggest the presence of an intrinsic energetic unbalance associated with mitochondrial dysfunction and a significant reactive oxygen radicals (ROS) accumulation. In turn, ROS accumulation can affect muscle fatigue, cause diaphragm wasting, and, in the long run, respiratory failure in SMNΔ7 mice. The exposure to the very potent antioxidant molecule Ergothioneine (ERGO) leads to the functional recovery of the diaphragm confirming the presence of mitochondrial impairment and redox imbalance. These findings foresee the possibility of carrying out a dietary supplementation in SMNΔ7 mice to preserve diaphragm function and increase the mice’s lifespan. ERGO was administered to SMNΔ7 mice during pregnancy and feeding time. Molecular analysis of the diaphragm showed a stimulation of mitophagy and the activation of the antioxidant system. The combination of these two actions could lead to the degradation of non-functional mitochondria and the scavenging of a good portion of ROS improving the diaphragm functionality. The lifespan and the quality of life of the treated mice were assessed. Treated mice mice have significantly greater survival and a significantly better quality of life. The in vivo results could be partly related to the molecular effect on the diaphragm but also to an effect on limb skeletal muscles and not to an effect on motorneurons (MNs) survival. Molecular and cellular analyses on Neural stem cells (NSCs) prepared from the subventricular zone of the brain of SMNΔ7 mice were performed. A significant difference in proliferation and differentiation of NSCs in comparison with control mice was found and, in treated mice, ERGO was able to increase the metabolic activity of NSCs suggesting that the observed in vivo effect of ERGO could be not only due to a peripheral action but can be achieved by a concomitant action at a central level.