Combined Use of CFTR Correctors in LGMD2D Myotubes Improves Sarcoglycan Complex Recovery.

Sarcoglycanopathies are rare limb girdle muscular dystrophies, still incurable, even though symptomatic treatments may slow down the disease progression. Most of the disease-causing defects are missense mutations leading to a folding defective protein, promptly removed by the cell's quality control, even if possibly functional. Recently, we repurposed small molecules screened for cystic fibrosis as potential therapeutics in sarcoglycanopathy. Indeed, cystic fibrosis transmembrane regulator (CFTR) correctors successfully recovered the defective sarcoglycan-complex in vitro. Our aim was to test the combined administration of some CFTR correctors with C17, the most effective on sarcoglycans identified so far, and evaluate the stability of the rescued sarcoglycan-complex. We treated differentiated myogenic cells from both sarcoglycanopathy and healthy donors, evaluating the global rescue and the sarcolemma localization of the mutated protein, by biotinylation assays and western blot analyses. We observed the additive/synergistic action of some compounds, gathering the first ideas on possible mechanism/s of action. Our data also suggest that a defective α-sarcoglycan is competent for assembly into the complex that, if helped in cell traffic, can successfully reach the sarcolemma. In conclusion, our results strengthen the idea that CFTR correctors, acting probably as proteostasis modulators, have the potential to progress as therapeutics for sarcoglycanopathies caused by missense mutations.

Repairing folding-defective α-sarcoglycan mutants by CFTR correctors, a potential therapy for limb-girdle muscular dystrophy 2D.

Limb-girdle muscular dystrophy type 2D (LGMD2D) is a rare autosomal-recessive disease, affecting striated muscle, due to mutation of SGCA, the gene coding for α-sarcoglycan. Nowadays, more than 50 different SGCA missense mutations have been reported. They are supposed to impact folding and trafficking of α-sarcoglycan because the defective polypeptide, although potentially functional, is recognized and disposed of by the quality control of the cell. The secondary reduction of α-sarcoglycan partners, ß-, γ- and δ-sarcoglycan, disrupts a key membrane complex that, associated to dystrophin, contributes to assure sarcolemma stability during muscle contraction. The complex deficiency is responsible for muscle wasting and the development of a severe form of dystrophy. Here, we show that the application of small molecules developed to rescue ΔF508-CFTR trafficking, and known as CFTR correctors, also improved the maturation of several α-sarcoglycan mutants that were consequently rescued at the plasma membrane. Remarkably, in myotubes from a patient with LGMD2D, treatment with CFTR correctors induced the proper re-localization of the whole sarcoglycan complex, with a consequent reduction of sarcolemma fragility. Although the mechanism of action of CFTR correctors on defective α-sarcoglycan needs further investigation, this is the first report showing a quantitative and functional recovery of the sarcoglycan-complex in human pathologic samples, upon small molecule treatment. It represents the proof of principle of a pharmacological strategy that acts on the sarcoglycan maturation process and we believe it has a great potential to develop as a cure for most of the patients with LGMD2D.

Severe murine limb-girdle muscular dystrophy type 2C pathology is diminished by FTY720 treatment.

INTRODUCTION: Limb-girdle muscular dystrophy type 2C (LGMD-2C) is caused by mutations in γ-sarcoglycan and is a devastating, progressive, and fully lethal human muscle-wasting disease that has no effective treatment. This study examined the efficacy of the sphingosine-1-phosphate receptor modulator FTY720 in treating Sgcg-/- DBA2/J, a severe mouse model of LGMD-2C. FTY720 treatment was expected to target LGMD-2C disease progression at 2 key positions by reducing chronic inflammation and fibrosis. METHODS: The treatment protocol was initiated at age 3 weeks and was continued with alternate-day injections for 3 weeks. RESULTS: The treatment produced significant functional benefit by plethysmography and significant reductions of membrane permeability and fibrosis. Furthermore, the protocol elevated protein levels of δ-sarcoglycan, a dystrophin-glycoprotein family member. CONCLUSION: This study showed that FTY720 is an effective muscular dystrophy treatment when therapy is initiated early in the disease progression. Muscle Nerve 56: 486-494, 2017.

Clinical aspects of patients with sarcoglycanopathies under steroids therapy.

UNLABELLED: Patients with sarcoglycanopathies, which comprise four subtypes of autosomal recessive limb-girdle muscular dystrophies, usually present with progressive weakness leading to early loss of ambulation and premature death, and no effective treatment is currently available. OBJECTIVE: To present clinical aspects and outcomes of six children with sarcoglycanopathies treated with steroids for at least one year. METHOD: Patient files were retrospectively analyzed for steroid use. RESULTS: Stabilization of muscle strength was noted in one patient, a slight improvement in two, and a slight worsening in three. In addition, variable responses of forced vital capacity and cardiac function were observed. CONCLUSIONS: No overt clinical improvement was observed in patients with sarcoglycanopathies under steroid therapy. Prospective controlled studies including a larger number of patients are necessary to determine the effects of steroids for sarcoglycanopathies.

Clinical aspects of patients with sarcoglycanopathies under steroids therapy / Aspectos clínicos de pacientes com sarcoglicanopatias sob efeito de corticoterapia

Patients with sarcoglycanopathies, which comprise four subtypes of autosomal recessive limb-girdle muscular dystrophies, usually present with progressive weakness leading to early loss of ambulation and premature death, and no effective treatment is currently available. Objective To present clinical aspects and outcomes of six children with sarcoglycanopathies treated with steroids for at least one year. Method Patient files were retrospectively analyzed for steroid use. Results Stabilization of muscle strength was noted in one patient, a slight improvement in two, and a slight worsening in three. In addition, variable responses of forced vital capacity and cardiac function were observed. Conclusions No overt clinical improvement was observed in patients with sarcoglycanopathies under steroid therapy. Prospective controlled studies including a larger number of patients are necessary to determine the effects of steroids for sarcoglycanopathies. .

Pacientes com sarcoglicanopatias, que compreendem quatro subtipos de distrofias musculares de cinturas autossômicas recessivas, geralmente apresentam fraqueza progressiva, levando à perda precoce da deambulação e morte prematura, e não há tratamento eficaz disponível até o momento. Objetivo Descrever os aspectos clínicos e a evolução de seis crianças com sarcoglicanopatias tratados com corticosteróides por pelo menos um ano. Método Prontuários dos pacientes foram analisados retrospectivamente. Resultados Estabilização da força muscular foi observada em um paciente, uma ligeira melhora em dois, e um ligeiro agravamento em três. Além disso, foram observadas respostas variáveis de capacidade vital forçada e da função cardíaca. Conclusões Não houve melhora clínica evidente em pacientes com sarcoglicanopatias sob terapia com corticosteróides. Estudos prospectivos controlados incluindo maior número de pacientes são necessários para determinar os efeitos dos corticosteróides para sarcoglicanopatias. .