Background: We have previously reported that Dysferlin-deficient mice, a notoriously mild model of limb-girdle muscular dystrophy type (LGMD) 2B/R2, show much exacerbated muscle wasting and early ambulatory dysfunction when bred to apolipoprotein E (ApoE) knockout (KO) mice, a model of elevated ‘bad’ cholesterol.
Objectives: Such an unexpected intolerance of Dysferlin KO muscles to circulating lipids led us to investigate the possibility that Dysferlinopathic patients and mice may be dyslipidemic and that their muscles may be affected by cholesterol metabolism anomalies. Blood samples from healthy controls and LGMD2B/R2 patients were obtained from the John Walton-Newcastle University Translational and Clinical Research Institute. Triceps muscles and plasma from asymptomatic Dysferlin KO and severe Dysferlin/ApoE double KO mice with ambulatory dysfunction were stained for basal membrane marker laminin and filipin, a marker of free cholesterol.
Results: We observed a 21% and 19% reduction in male and female ‘good’ high-density lipoprotein-associated cholesterol (HDLc) levels in LGMD2B/R2 serum (p < 0.01). 73% of male and 50% of female Dysferlinopathic patients had abnormal total cholesterol/HDLc ratios. Severe Dysferlin/ApoE DKO mouse triceps show 5.4-, 3.0- and 232.7-fold increases in sarcolemma, sarcoplasm and interstitial free cholesterol accumulation compared to mild Dysferlin KO mice. Areas of severe fibrofatty infiltration show large free cholesterol accumulation that colocalizes with 86% smaller (diameter) laminin-positive myofibers. We also detected a 2.9-fold increase in expression of cholesterol synthesis enzyme HMGCoA reductase in Dysferlin KO muscles, and similar HDLc abnormalities in Dysferlin KO plasma compared to WT controls. Conclusion: Dysferlinopathies cause circulating lipoprotein and intramuscular cholesterol anomalies, which likely exacerbate muscle wasting. As dystrophin deficiency also causes circulating and intramuscular cholesterol anomalies that exacerbate the mild mdx mouse phenotype, cholesterol may be a shared pathway by which multiple forms of MD cause muscle wasting as well as a universal therapeutic target.