Muscle-specific expression of LARGE restores neuromuscular transmission deficits in dystrophic LARGE(myd) mice.

Mutations in several glycosyltransferases underlie a group of muscular dystrophies known as glycosylation-deficient muscular dystrophy. A common feature of these diseases is loss of glycosylation and consequent dystroglycan function that is correlated with severe pathology in muscle, brain and other tissues. Although glycosylation of dystroglycan is essential for function in skeletal muscle, whether glycosylation-dependent function of dystroglycan is sufficient to explain all complex pathological features associated with these diseases is less clear. Dystroglycan glycosylation is defective in LARGE(myd) (myd) mice as a result of a mutation in like-acetylglucosaminyltransferase (LARGE), a glycosyltransferase known to cause muscle disease in humans. We generated animals with restored dystroglycan function exclusively in skeletal muscle by crossing myd animals to a recently created transgenic line that expresses LARGE selectively in differentiated muscle. Transgenic myd mice were indistinguishable from wild-type littermates and demonstrated an amelioration of muscle disease as evidenced by an absence of muscle pathology, restored contractile function and a reduction in serum creatine kinase activity. Moreover, although deficits in nerve conduction and neuromuscular transmission were observed in myd animals, these deficits were fully rescued by muscle-specific expression of LARGE, which resulted in restored structure of the neuromuscular junction (NMJ). These data demonstrate that, in addition to muscle degeneration and dystrophy, impaired neuromuscular transmission contributes to muscle weakness in dystrophic myd mice and that the noted defects are primarily due to the effects of LARGE and glycosylated dystroglycan in stabilizing the endplate of the NMJ.

Soleus muscle in glycosylation-deficient muscular dystrophy is protected from contraction-induced injury.

The glycosylation of dystroglycan is required for its function as a high-affinity laminin receptor, and loss of dystroglycan glycosylation results in congenital muscular dystrophy. The purpose of this study was to investigate the functional defects in slow- and fast-twitch muscles of glycosylation-deficient Large(myd) mice. While a partial alteration in glycosylation of dystroglycan in heterozygous Large(myd/+) mice was not sufficient to alter muscle function, homozygous Large(myd/myd) mice demonstrated a marked reduction in specific force in both soleus and extensor digitorum longus (EDL) muscles. Although EDL muscles from Large(myd/myd) mice were highly susceptible to lengthening contraction-induced injury, Large(myd/myd) soleus muscles surprisingly showed no greater force deficit compared with wild-type soleus muscles even after five lengthening contractions. Despite no increased susceptibility to injury, Large(myd/myd) soleus muscles showed loss of dystroglycan glycosylation and laminin binding activity and dystrophic pathology. Interestingly, we show that soleus muscles have a markedly higher sarcolemma expression of ß(1)-containing integrins compared with EDL and gastrocnemius muscles. Therefore, we conclude that ß(1)-containing integrins play an important role as matrix receptors in protecting muscles containing slow-twitch fibers from contraction-induced injury in the absence of dystroglycan function, and that contraction-induced injury appears to be a separable phenotype from the dystrophic pathology of muscular dystrophy.

Systematic analysis of the regulatory and essential myosin light chain genes: genetic variants and mutations in hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) can be caused by mutations in genes encoding for the ventricular myosin essential and regulatory light chains. In contrast to other HCM disease genes, only a few studies describing disease-associated mutations in the myosin light chain genes have been published. Therefore, we aimed to conduct a systematic screening for mutations in the ventricular myosin light chain genes in a group of clinically well-characterised HCM patients. Further, we assessed whether the detected mutations are associated with malignant or benign phenotype in the respective families. We analysed 186 unrelated individuals with HCM for the human ventricular myosin regulatory (MYL2) and essential light chain genes (MYL3) using polymerase chain reaction, single strand conformation polymorphism analysis and automated sequencing. We found eight single nucleotide polymorphisms in exonic and adjacent intronic regions of MYL2 and MYL3. Two MYL2 missense mutations were identified in two Caucasian families while no mutation was found in MYL3. The mutation Glu22Lys was associated with moderate septal hypertrophy, a late onset of clinical manifestation, and benign disease course and prognosis. The mutation Arg58Gln showed also moderate septal hypertrophy, but, in contrast, it was associated with an early onset of clinical manifestation and premature sudden cardiac death. In conclusion, myosin light chain mutations are a very rare cause of HCM responsible for about 1% of cases. Mutations in MYL2 could be associated with both benign and malignant HCM phenotype.