Lithium chloride corrects weakness and myopathology in a preclinical model of LGMD1D

Objective To understand DNAJB6's function in skeletal muscle and identify therapeutic targets for limb-girdle muscular dystrophy 1D (LGMD1D). Methods DNAJB6 knockout (KO) myoblasts were generated with Crispr/cas9 technology, and differentially accumulated proteins were identified using stable isotope labeling, followed by quantitative mass spectrometry. Cultured KO myotubes and mouse muscle from DNAJB6b-WT or DNAJB6b-F93L mice were analyzed using histochemistry, immunohistochemistry, and immunoblot. Mouse functional strength measures included forelimb grip strength and inverted wire hang. Results DNAJB6 inactivation leads to the accumulation of sarcomeric proteins and hypertrophic myotubes with an enhanced fusion index. The increased fusion in DNAJB6 KO myotubes correlates with diminished glycogen synthase kinase-beta (GSK3 beta) activity. In contrast, LGMD1D mutations in DNAJB6 enhance GSK3 beta activation and suppress beta-catenin and NFAT3c signaling. GSK3 beta inhibition with lithium chloride improves muscle size and strength in an LGMD1D preclinical mouse model. Conclusions Our results suggest that DNAJB6 facilitates protein quality control and negatively regulates myogenic signaling. In addition, LGMD1D-associated DNAJB6 mutations inhibit myogenic signaling through augmented GSK3 beta activity. GSK3 beta inhibition with lithium chloride may be a therapeutic option in LGMD1D.