Calcium homeostasis alterations in a mouse model of the Dynamin 2-related centronuclear myopathy

Abstract

Autosomal dominant centronuclear myopathy (CNM) is a rare congenital myopathy characterized by centrally located nuclei in muscle fibers. CNM results from mutations in the gene encoding dynamin 2 (DNM2), a large GTPase involved in endocytosis, intracellular membrane trafficking, and cytoskeleton regulation. We developed a knock-in mouse model expressing the most frequent DNM2-CNM mutation; i.e. the KI-Dnm2R465W model. Heterozygous (HTZ) KI-Dnm2 mice progressively develop muscle atrophy, impairment of contractile properties, histopathological abnormalities, and elevated cytosolic calcium concentration. Here, we aim at better characterizing the calcium homeostasis impairment in extensor digitorum longus (EDL) and soleus muscles from adult HTZ KI-Dnm2 mice. We demonstrate abnormal contractile properties and cytosolic Ca2+ concentration in EDL but not soleus muscles showing that calcium impairment is correlated with muscle weakness and might be a determinant factor of the spatial muscle involvement. In addition, the elevated cytosolic Ca2+ concentration in EDL muscles is associated with an increased sarcolemmal permeability to Ca2+ and releasable Ca2+ content from the sarcoplasmic reticulum. However, amplitude and kinetics characteristics of the calcium transient appear unchanged. This suggests that calcium defect is probably not a primary cause of decreased force generation by compromised sarcomere shortening but may be involved in long-term deleterious consequences on muscle physiology. Our results highlight the first pathomechanism which may explain the spatial muscle involvement occurring in DNM2-related CNM and open the way toward development of a therapeutic approach to normalize calcium content.

Impaired excitation–contraction coupling in muscle fibres from the dynamin2R465W mouse model of centronuclear myopathy

“…By contrast, Fraysse et al . () reported no difference in peak and time‐to‐peak Ca 2+ transients elicited by field stimulation between WT and KI‐ Dnm2 R465W fibres. The difference may result from their use of the high‐affinity indicator fura‐2, which is kinetically limited and easily saturated under non‐Ca 2+ ‐buffering conditions.…”

“…; Fraysse et al . ). Interestingly, defective intracellular Ca 2+ homeostasis and excitation–contraction (EC) coupling are hallmarks of the centronuclear myopathy resulting from MTM1 deficiency (Al Qusairi et al .…”

Correlative SICM‐FCM reveals changes in morphology and kinetics of endocytic pits induced by disease‐associated mutations in dynamin

“…A defect of clathrin-coated vesicles has been previously associated with several human diseases, including cancer, neurologic disorders, and myopathy (71, 72), and remains to be further investigated in centronuclear myopathies. In particular, CME defect may alter membrane content of ion channel, as suggested by alteration of the membrane permeability to calcium, leading to abnormal calcium homeostasis in a mouse model of the DNM2-linked CNM (73). A better knowledge of involvement of clathrin- and caveolin-dependent endocytosis in the pathomechanisms of the DNM2-linked CNM will be of particular interest for identification of specific targets for future development of therapeutic approaches.…”

Abnormal Excitation-Contraction Coupling and Calcium Homeostasis in Myopathies and Cardiomyopathies

“…Biochemical studies indicated that the DNM2 mutations increase dynamin 2 oligomer stability and GTPase activity [139,140], and in vivo investigations suggested that dynamin 2 is negatively regulated by myotubularin and amphiphysin 2 [141,142]. Knock-in mice harbouring the most common human mutation R465W manifested a mild myopathy with a structural disorganization of the muscle fibers, abnormal contractile properties, and elevated basal Ca 2+ concentrations in the cytosol [143,144]. AAV-mediated expression of the same mutation resulted in abnormal T-tubule structures and a swollen sarcoplasmic reticulum [145], and expression of the severe S619L mutation in zebrafish revealed defective excitation-contraction coupling [146].…”