Nebulin nemaline myopathy recapitulated in a compound heterozygous mouse model with both a missense and a nonsense mutation in Neb

Abstract

Nemaline myopathy (NM) caused by mutations in the gene encoding nebulin (NEB) accounts for at least 50% of all NM cases worldwide, representing a significant disease burden. Most NEB-NM patients have autosomal recessive disease due to a compound heterozygous genotype. Of the few murine models developed for NEB-NM, most are Neb knockout models rather than harbouring Neb mutations. Additionally, some models have a very severe phenotype that limits their application for evaluating disease progression and potential therapies. No existing murine models possess compound heterozygous Neb mutations that reflect the genotype and resulting phenotype present in most patients. We aimed to develop a murine model that more closely matched the underlying genetics of NEB-NM, which could assist elucidation of the pathogenetic mechanisms underlying the disease. Here, we have characterised a mouse strain with compound heterozygous Neb mutations; one missense (p.Tyr2303His), affecting a conserved actin-binding site and one nonsense mutation (p.Tyr935*), introducing a premature stop codon early in the protein. Our studies reveal that this compound heterozygous model, Neb Y2303H, Y935X , has striking skeletal muscle pathology including nemaline bodies. In vitro whole muscle and single myofibre physiology studies also demonstrate functional perturbations. However, no reduction in lifespan was noted. Therefore, Neb Y2303H,Y935X mice recapitulate human NEB-NM and are a much needed addition to the NEB-NM mouse model collection. The moderate phenotype also makes this an appropriate model for studying NEB-NM pathogenesis, and could potentially be suitable for testing therapeutic applications.

Recent advances in nemaline myopathy

“…In this model, the lower number of strongly bound cross-bridges was underlying the force depression observed [71] . The same mechanism was observed in the Neb Y2303H,Y935X model [67] , suggesting that a similar therapeutic modality might be functional in cases of different causative genes.…”

“…Modelling a milder, or typical NM phenotype has appeared difficult in the case of NEB . Two compound heterozygous mouse models were recently published, one with a combination of missense and nonsense mutations, Neb Y2303H,Y935X [67] , and another with a missense variant combined with the exon 55 deletion, Neb S6366I/ Exon55 [68] . Both did show some of the hallmark features of NM, but only the latter presented a detectable phenotype also in vivo , resembling typical NM in patients.…”

Removal of MuRF1 Increases Muscle Mass in Nemaline Myopathy Models, but Does Not Provide Functional Benefits

“…NM is characterized by muscle weakness and diminished muscle size due to muscle atrophy. Both of these characteristics have also been observed in animal models with mutations in NEB or ACTA1 (encodes skeletal muscle α-actin) [ 22 , 23 , 34 , 35 , 36 ]. The molecular mechanism underlying the muscle weakness is likely to include alterations in the contraction mechanism due to mutations in the sarcomeric proteins that disrupt the normal cross-bridge behavior [ 6 , 37 , 38 , 39 , 40 , 41 ].…”

Is Gene-Size an Issue for the Diagnosis of Skeletal Muscle Disorders?

“…Several RYR1 knock in mouse models have been generated to mimic the equivalent mutations identified in humans [96][97][98][99]. Recently, Laitila and colleagues have generated and characterized a mouse model with compound heterozygous Neb mutations (a missense p.Tyr2303His and a nonsense p.Tyr935*), matching the genotype observed in patients with a nemaline myopathy [100,101].…”