Verapamil mitigates chloride and calcium bi-channelopathy in a myotonic dystrophy mouse model

Abstract

Myotonic dystrophy type 1 (DM1) involves misregulated alternative splicing for specific genes. We used exon or nucleotide deletion to mimic altered splicing of genes central to muscle excitation-contraction coupling in mice. Mice with forced skipping of exon 29 in the Ca V 1.1 calcium channel combined with loss of ClC-1 chloride channel function displayed markedly reduced lifespan, whereas other combinations of splicing mimics did not affect survival. The Ca 2+ /Cl – bi-channelopathy mice exhibited myotonia, weakness, and impairment of mobility and respiration. Chronic administration of the calcium channel blocker verapamil rescued survival and improved force generation, myotonia, and respiratory function. These results suggest that Ca 2+ /Cl – bi-channelopathy contributes to muscle impairment in DM1 and is potentially mitigated by common clinically available calcium channel blockers.

Combinatorial effects of ion channel mis-splicing as a cause of myopathy in myotonic dystrophy

“…Importantly, pharmacologic blockade of the Ca v 1.1 channel by exposing the isolated muscle in the ex vivo bath to verapamil essentially eliminated both myotonia and transient weakness. These results demonstrated the synergistic effect of Cl – and Ca 2+ channels and the positive impact of blocking one of the contributing components ( 14 ) ( Figure 1 ).…”

“…In this issue of the JCI , Cisco and co-authors ( 14 ) used in vivo and ex vivo approaches to systematically test the combinatorial effects of four mis-spliced ion channels in a detailed analysis of skeletal muscle function. The postnatal splicing transitions of all four genes are conserved in humans and mice, all four are mis-spliced in DM1 skeletal muscle, and the DM1 splicing patterns of all four are reproduced by expression of CUG RNA repeats in skeletal muscle of an established DM1 mouse model ( 6 , 11 , 15 ).…”

“…What was unknown was the dramatic synergistic effect on muscle pathology of increased calcium flow combined with the loss of chloride conductance. Using detailed analysis of multiple muscle function parameters ex vivo, Cisco and co-authors showed that increased calcium conductance potentiated the transient muscle weakness caused by loss of chloride conductance ( 14 ). Transient weakness resulted from the loss of ClC-1 channel function due to the runs of action potentials that caused myotonia and created a state of depolarization and the loss of excitability.…”

Divergent Regulatory Roles of Transcriptional Variants of the Chicken LDB3 Gene in Muscle Shaping

“…Although extensive research on gene expression regulation in skeletal muscle development has been conducted in recent years, , the specific role of alternative splicing in the growth and development of skeletal muscles remains underexplored . Notably, skeletal muscles are among the tissues with the highest incidence of alternative splicing events. − In skeletal muscles, pre-mRNA transcripts are subject to diverse splicing patterns governed by the regulatory functions of RNA-binding proteins (RBPs) . Muscle-specific RBPs play a pivotal role in orchestrating and managing alternative splicing events during muscle differentiation.…”

Studying the Effect of MBNL1 and MBNL2 Loss in Skeletal Muscle Regeneration

“…In addition to their roles as splicing factors, these proteins have a myriad of functions in RNA processing and localization [ 11 ]. There is also experimental evidence for other mechanisms involving transcription factors, signaling such as the glycogen synthase kinase 3-beta (GSK-3β), AKT, AMPK, PKC, Tweak/Fn14, PI3K/AKT pathways, other RNA binding proteins (e.g., hnRNPA1 and MSI2), circular RNA generation, microRNAs, mitochondrial dysfunction, increased cellular senescence, and most recently, calcium channel dysfunction in conjunction with chloride channel dysfunction [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. However, the strongest evidence is for the loss of function of MBNL proteins due to binding to the mutant RNA and their sequestration in the RNA foci [ 35 ].…”