Limb-girdle muscular dystrophy type 2B causes HDL-C abnormalities in patients and statin-resistant muscle wasting in dysferlin-deficient mice

Abstract

Limb-girdle muscular dystrophy (MD) type 2B (LGMD2B) and Duchenne MD (DMD) are caused by mutations to the Dysferlin and Dystrophin genes, respectively. We have recently demonstrated in typically mild dysferlin- and dystrophin-deficient mouse models that increased plasma cholesterol levels severely exacerbate muscle wasting, and that DMD patients display primary dyslipidemia characterized by elevated plasma cholesterol and triglycerides. Herein, we investigate lipoprotein abnormalities in LGMD2B and if statin therapy protects dysferlin-deficient mice (Dysf) from muscle damage. Herein, lipoproteins and liver enzymes from LGMD2B patients and dysferlin-null (Dysf) mice were analyzed. Simvastatin, which exhibits anti-muscle wasting effects in mouse models of DMD and corrects aberrant expression of key markers of lipid metabolism and endogenous cholesterol synthesis, was tested in Dysf mice. Muscle damage and fibrosis were assessed by immunohistochemistry and cholesterol signalling pathways via Western blot. LGMD2B patients show reduced serum high-density lipoprotein cholesterol (HDL-C) levels compared to healthy controls and exhibit a greater prevalence of abnormal total cholesterol (CHOL)/HDL-C ratios despite an absence of liver dysfunction. While Dysf mice presented with reduced CHOL and associated HDL-C and LDL-C-associated fractions, simvastatin treatment did not prevent muscle wasting in quadriceps and triceps muscle groups or correct aberrant low-density lipoprotein receptor (LDLR) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) protein expression. LGMD2B patients present with reduced serum concentrations of HDL-C, a major metabolic comorbidity, and as a result, statin therapy is unlikely to prevent muscle wasting in this population. We propose that like DMD, LGMD2B should be considered as a new type of genetic dyslipidemia.

Psoas major muscle mass and upper limb muscle strength are the main factors influencing the rate of HDL-cholesterol within the target in T2DM patients

“…Skeletal muscle is an endocrine organ and is essential to lipid metabolism, including HDL-c adjustment [38]. When muscle atrophy occurs, HDL metabolism is impaired; for example, HDL-c is low in patients with limb-girdle muscular dystrophy type 2B, and the same results have been verified in dysferlin-deficient mice, suggesting that loss of dysferlin interferes with normal muscle expression of mevalonate/HMGCR and LDLR, two key regulators of cholesterol metabolism [39]. On the other hand, HDL-c maintains normal muscle metabolism and function by promoting glucose uptake by skeletal muscle through increasing plasma insulin and activating AMP-activated protein kinase in skeletal muscle and glycogen synthesis in muscle cells through promoting GSK3 phosphorylation [40].…”

Effects of HMGCR deficiency on skeletal muscle development

“…We did not examine this question directly in the current study, but it would merit examination in the future. Abnormal lipid profiles have been observed in humans with dystrophinopathy 38 and dysferlinopathy 39 . Statin therapy does not appear to be a viable primary or adjunctive therapy for muscular dystrophy, as confirmed in multiple mouse studies [39][40][41][42] .…”

Dyslipidemia in Muscular Dystrophy: A Systematic Review and Meta-Analysis

“…One of the limitations of our study is the low number of MD subtypes retained due to our inclusion and exclusion criteria that require lipid values from both MD patients and control subjects in the same study for our meta-analysis. Since performing this systematic review and meta-analysis, we have published on dyslipidemia in LGMD2B patients compared to healthy subject values [ 10 ], although this study was not included herein. In addition, we have identified 40 studies that also reported dyslipidemia in various types of MD but without analyzing control samples, instead using reference values for diagnosis of dyslipidemia, and these did not meet our inclusion criteria.…”

“…We have recently provided evidence that DMD, BMD and LGMD2B patients are afflicted by new forms of genetic dyslipidemia that affect normal lipoprotein-associated cholesterol and triglycerides (TG) levels [ 9 , 10 ]. This chronic dyslipidemic state is likely not secondary to muscle wasting or treatment as unmedicated, unaffected carrier females with only one dystrophin allele mutation and normal CK levels also showed elevated total cholesterol (TC) and low-density lipoprotein (LDL)-associated cholesterol, indicating a more primary dyslipidemic state intricately linked to abnormal dystrophin expression [ 9 ].…”

“…In vitro studies in primary human myotubes have revealed that cholesterol-induced insulin resistance could be rescued by co-treatment with HDL particles [ 21 ], which illustrates the complex interplay between documented regulators of whole-body metabolism and muscle homeostasis. While it is unknown whether MD-associated lipoprotein abnormalities play a causal role in muscle wasting typically observed in patients, reports documenting intra-myofiber free cholesterol accumulation in rodent and human DMD and LGMD2B biopsies [ 10 , 22 ] along with disease exacerbation in MD animals with blunted apolipoprotein E expression are supportive of this novel concept [ 23 , 24 ]. From a therapeutic perspective, treatment of severe DMD and LGMD2B mice with cholesterol absorption blocker ezetimibe drastically reduced muscle damage and prevented loss of ambulation, which combined with previous study of plasma miRNA in DMD patients, provided critical evidence of the significance of targeting cholesterol and lipoprotein metabolism as a cost-effective therapeutic option for patients [ 22 , 25 ].…”