Objective Spinal muscular atrophy (SMA) is the number 1 genetic killer of young children. It is caused by mutation or deletion of the survival motor neuron 1 (SMN1) gene. Although SMA is primarily a motor neuron disease, metabolism abnormalities such as metabolic acidosis, abnormal fatty acid metabolism, hyperlipidemia, and hyperglycemia have been reported in SMA patients. We thus initiated an in-depth analysis of glucose metabolism in SMA. Methods Glucose metabolism and pancreas development were investigated in the Smn2B/− intermediate SMA mouse model and type I SMA patients. Results Here, we demonstrate in an SMA mouse model a dramatic cell fate imbalance within pancreatic islets, with a predominance of glucagon-producing α cells at the expense of insulin-producing β cells. These SMA mice display fasting hyperglycemia, hyperglucagonemia, and glucose resistance. We demonstrate similar abnormalities in pancreatic islets from deceased children with the severe infantile form of SMA in association with supportive evidence of glucose intolerance in at least a subset of such children. Interpretation Our results indicate that defects in glucose metabolism may play an important contributory role in SMA pathogenesis.

No abstract

Spinal muscular atrophy (SMA) is an inherited disease resulting in the highest mortality of children under the age of two. SMA is caused by mutations or deletions in the survival motor neuron 1 (SMN1) gene, leading to aberrant neuromuscular junction (NMJ) development and the loss of spinal cord alpha-motor neurons. Here, we show that Smn depletion leads to increased activation of RhoA, a major regulator of actin dynamics, in the spinal cord of an intermediate SMA mouse model. Treating these mice with Y-27632, which inhibits ROCK, a direct downstream effector of RhoA, dramatically improves their survival. This lifespan rescue is independent of Smn expression and is accompanied by an improvement in the maturation of the NMJs and an increase in muscle fiber size in the SMA mice. Our study presents evidence linking disruption of actin cytoskeletal dynamics to SMA pathogenesis and, for the first time, identifies RhoA effectors as viable targets for therapeutic intervention in the disease.

Objective Spinal muscular atrophy (SMA) is an inherited neuromuscular disorder leading to paralysis and subsequent death in young children. Initially considered a motor neuron disease, extra‐neuronal involvement is increasingly recognized. The primary goal of this study was to investigate alterations in lipid metabolism in SMA patients and mouse models of the disease. Methods We analyzed clinical data collected from a large cohort of pediatric SMA type I–III patients as well as SMA type I liver necropsy data. In parallel, we performed histology, lipid analysis, and transcript profiling in mouse models of SMA. Results We identify an increased susceptibility to developing dyslipidemia in a cohort of 72 SMA patients and liver steatosis in pathological samples. Similarly, fatty acid metabolic abnormalities were present in all SMA mouse models studied. Specifically, Smn2B/‐ mice displayed elevated hepatic triglycerides and dyslipidemia, resembling non‐alcoholic fatty liver disease (NAFLD). Interestingly, this phenotype appeared prior to denervation. Interpretation This work highlights metabolic abnormalities as an important feature of SMA, suggesting implementation of nutritional and screening guidelines in patients, as such defects are likely to increase metabolic distress and cardiovascular risk. This study emphasizes the need for a systemic therapeutic approach to ensure maximal benefits for all SMA patients throughout their life.