622. Systemic β-Sarcoglycan Gene Therapy for Treatment of Cardiac and Skeletal Muscle Deficits in LGMD2E

Abstract

Limb-girdle muscular dystrophy type 2E (LGMD2E) results from mutations in the beta-sarcoglycan (SGCB) gene causing loss of a sarcolemmal structural protein component of the dystrophin-associated protein complex (DAPC). This leads to a progressive dystrophy with numerous histopathological features, resulting in deteriorating muscle function. This occurs not only in limb muscle but also in the diaphragm and the heart. Consequences include respiratory failure and cardiomyopathy in 50% or more of LGMD2E patients. SGCB knockout mice share many of the phenotypic deficiencies of LGMD2E patients. In this mouse model we quantified dystrophic histopathology, fibrosis, and functional outcomes in lower limb, upper limb, and torso skeletal muscles, as well as the diaphragm and cardiac muscles. Diaphragms of SGCB-/- mice demonstrated reduced specific force output (116.24 mN/mm2) compared to wild-type (WT) mice (236.67 mN/mm2), and hearts from SGCB-/- mice had lower ejection fraction (58.19%) compared to WT mice (75.04%) as determined by MRI. Additionally, radiographic imaging defined the degree of kyphoscoliosis in SGCB-/- mice. Laser monitoring of open-field cage activity showed a reduction of ~55% in both total ambulation as well as hindlimb vertical rearing in SGCB-/- mice compared to WT. For treatment, we designed a self-complementary AAVrh74 vector containing a codon optimized human SGCB transgene driven by a muscle specific promoter. We next demonstrated efficacy of vector delivery by intramuscular (IM) injection to the tibialis anterior muscle, as well as isolated-limb perfusion (ILP) to the lower limb muscles of SGCB-/- mice. Along with restoration of SGCB expression in treated muscle, we saw histological and functional improvements and a reduction in fibrosis as indicated by reduced collagen deposition. These regional gene delivery studies were followed by systemic delivery of scAAV.hSGCB through the tail vein of SGCB-/- mice to provide a potential rationale for gene delivery in clinical trial that would lead to clinically meaningful results. Tail vein injection of scAAV.hSGCB resulted in nearly 100% transgene expression in numerous muscles throughout the hindlimbs, forelimbs, torso, and the heart, that was accompanied by improvements in histopathology including reduction in central nucleation and increased fiber diameter. Kyphoscoliosis of the spine was also improved, and total ambulation increased in scAAV.hSGCB treated mice by ~22% while hindlimb vertical rearing increased by ~77% in treated mice compared to KO. We also saw complete restoration of diaphragm function following treatment with specific force output improved to 226.07 mN/mm2. In this well-defined mode of LGMD2E, we have demonstrated that systemic delivery of scAAV.hSGCB normalizes histologic and functional outcome measures in limb, diaphragm, and heart. These findings have established a path for AAV mediated gene therapy for LGMD2E that we are currently pursuing.