Inhibition of inflammation with celastrol fails to improve muscle function in dysferlin-deficient A/J mice

Abstract

The dysferlin-deficient A/J mouse strain represents a homologous model for limb-girdle muscular dystrophy 2B. We evaluated the disease phenotype in 10 month old A/J mice compared to two dysferlin-sufficient, C57BL/6 and A/JOlaHsd, mouse lines to determine which functional end-points are sufficiently sensitive to define the disease phenotype for use in preclinical studies in the A/J strain. A/J mice had significantly lower open field behavioral activity (horizontal activity, total distance, movement time and vertical activity) when compared to C57BL/6 and A/JoIaHsd mice. Both A/J and A/JOIaHsd mice showed decreases in latency to fall with rotarod compared to C57BL/6. No changes were detected in grip strength, force measurements or motor coordination between these three groups. Furthermore, we have found that A/J muscle shows significantly increased levels of the pro-inflammatory cytokine TNF-α when compared to C57BL/6 mice, indicating an activation of NF-κB signaling as part of the inflammatory response in dysferlin-deficient muscle. Therefore, we assessed the effect of celastrol (a potent NF-κB inhibitor) on the disease phenotype in female A/J mice. Celastrol treatment for four months significantly reduced the inflammation in A/J muscle; however, it had no beneficial effect in improving muscle function, as assessed by grip strength, open field activity, and in vitro force contraction. In fact, celastrol treated mice showed a decrease in body mass, hindlimb grip strength and maximal EDL force. These findings suggest that inhibition of inflammation alone may not be sufficient to improve the muscle disease phenotype in dysferlin-deficient mice and may require combination therapies that target membrane stability to achieve a functional improvement in skeletal muscle.

Dysferlin-deficiency has greater impact on function of slow muscles, compared with fast, in aged BLAJ mice

“…This study was particularly interested in the effect of dysferlin-deficiency on a wide range of measures of ex vivo muscle function. There were no differences in maximum tetanic force between WT and BLAJ soleus and EDL muscles, which is consistent with previous literature [25, 26, 32]. These findings indicate that higher stimulus frequencies do not produce observable differences in the force producing capacity of control and dysf -/- muscle.…”

“…Dysferlin-deficiency had no impact on body mass of the 10 month old male mice, which is consistent with findings in A/J mice aged 9 months [26]. For muscle mass, the BLAJ soleus was significantly heavier than normal WT soleus.…”

“…Normalised forelimb grip strength was unaffected in the 10 month old BLAJ (compared with WT) mice, a finding consistent with those in 9 month old A/J mice [26]. While increased forelimb grip strength (+63%) was reported in 2–6 month old dysf -/- SJL/J mice [30], this difference may be due to the choice of C57Bl/6J mice as a control strain for the SJL/J mice (since dysferlin positive control SJL/J mice were not available at the time of their experiments).…”

“…For example, swimming speeds of BLAJ mice were significantly slower than controls from 8 months of age [29]. Other studies have also shown significant reductions in voluntary wheel running distance [17] and open field behaviour [26, 27, 30] for dysf -/- mice, aged 14, 2–6, 3–4 and 9 months respectively, indicative of functional impairments even in the mild pathology of dysf -/- mice.…”

Deep phenotyping of an international series of patients with late‐onset dysferlinopathy

“…Indeed, LO patients showed lower degrees of necrosis and regeneration, as well as of inflammation. Previous evidence suggests that decreased myotube fusion in dysferlinopathy could be attributed to intrinsic inflammatory activation [30] although inhibition of inflammation with celastrol failed to improve muscle function in dysferlin‐deficient mice [31] The difference in inflammation levels and disease activity would need to be taken into account in future therapeutic choices and drug combinations.…”