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

Abstract

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, β-, 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.

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

“…In our previous paper, incubation of cells, models of sarcoglycanopathy with a number of CFTR correctors, resulted in an increase of the mutated α-SG and the localization at the plasma membrane. Efficacy of one of these small molecules, C17, was subsequently confirmed in myogenic cells from a LGMD2D patient, where we also observed a reduction of the sarcolemma fragility [19]. Here, by using the human pathologic myotubes, we tested the efficacy of additional correctors belonging to the bithiazole family of C17, such as C13 [25], and of the quinoline family, such as C9 and C6 [25,26].…”

“…An interesting point is the possibility to rescue the defective sarcoglycan as well as the entire SG-complex, by preventing the degradation of the mutant, acting either at the initial [15,16], intermediate [17] or final step [14] of the pathway. On these premises and taking advantage from the tremendous work done on another genetic disease, cystic fibrosis, that shares with sarcoglycanopathy a similar pathogenic mechanism [18], we elaborated a novel strategy of therapeutic intervention [19]. Our approach is based on the use of small molecules known as CFTR correctors, which are effective in rescuing the type II mutants of the cystic fibrosis transmembrane regulator (CFTR) [20,21].…”

Functional and cellular localization diversity associated with Fukutin‐related protein patient genetic variants

“…Interestingly, despite the presence of the genetic variant, a certain degree of biological activity of the protein can still be preserved, suggesting that "rescue" of these proteins from the strict QC surveillance and degradation systems could ameliorate the related pathology. Indeed, pharmacological treatments proved successful in vitro for the rescue of FKTN (Tachikawa, Kanagawa, Yu, Kobayashi, & Toda, 2012) or of other mutated proteins of the DGC such as the sarcoglycans (Carotti et al, 2018;Soheili et al, 2012). Some of the most prevalent FKRP missense mutations have been described to be retained in the ER (Esapa et al, 2002;Esapa, McIlhinney, & Blake, 2005;Keramaris-Vrantsis et al, 2007;Matsumoto et al, 2004;Torelli et al, 2005), leading to loss of function though cellular mislocalization from the Golgi, the cellular compartment where FKRP exerts its function.…”

Identification of a novel SGCA missense mutation in a case of limb‐girdle muscular dystrophy 2D with the absence of four sarcoglycan proteins

“…Limb‐girdle muscular dystrophy 2D (LGMD2D) is a rare autosomal‐recessive myopathy, caused by mutations in the α‐sarcoglycan (SGCA) gene ( SGCA ). Nowadays more than 50 different SGCA missense mutations have been reported . LGMD2D has a significant clinical and genetic heterogeneity, with a broad spectrum of clinical symptoms, mainly characterized by weakness and atrophy of the limb muscles and pelvic muscles with variable age at onset and severity.…”

“…Nowadays more than 50 different SGCA missense mutations have been reported. 1 LGMD2D has a significant clinical and genetic heterogeneity, with a broad spectrum of clinical symptoms, mainly characterized by weakness and atrophy of the limb muscles and pelvic muscles with variable age at onset and severity. Even if the same gene mutation occurs in the same family, clinical symptoms range from mild to severe.…”