Dysferlinopathies are a form of muscular dystrophy caused by gene mutations resulting in deficiency of the protein dysferlin. Symptoms manifest later in life in a muscle specific manner, although the pathomechanism is not well understood. This study compared the impact of dysferlin-deficiency on in vivo and ex vivo muscle function, and myofibre type composition in slow (soleus) and fast type (extensor digitorum longus; EDL) muscles using male dysferlin-deficient (dysf^-/-) BLAJ mice aged 10 months, compared with wild type (WT) C57Bl/6J mice. There was a striking increase in muscle mass of BLAJ soleus (+25%) (p<0.001), with no strain differences in EDL mass, compared with WT. In vivo measures of forelimb grip strength and wheel running capacity showed no strain differences. Ex vivo measures showed the BLAJ soleus had faster twitch contraction (-21%) and relaxation (-20%) times, and delayed post fatigue recovery (ps<0.05); whereas the BLAJ EDL had a slower relaxation time (+11%) and higher maximum rate of force production (+25%) (ps0.05); however, for the BLAJ EDL, there was an increased proportion of type IIx MHC isoform (+5.5%) and decreased type IIb isoform (-5.5%) (ps<0.01). This identification of novel differences in the impact of dysferlin-deficiency on slow and fast twitch muscles emphasises the importance of evaluating myofibre type specific effects to provide crucial insight into the mechanisms responsible for loss of function in dysferlinopathies; this is critical for the development of targeted future clinical therapies.

Dysferlinopathies are a clinically heterogeneous group of muscular dystrophies caused by a genetic deficiency of the membrane-associated protein dysferlin, which usually manifest post-growth in young adults. The disease is characterized by progressive skeletal muscle wasting in the limb-girdle and limbs, inflammation, accumulation of lipid droplets in slow-twitch myofibers and, in later stages, replacement of muscles by adipose tissue. Previously we reported myofiber-type specific differences in muscle contractile function of 10-month-old dysferlin-deficient BLAJ mice that could not be fully accounted for by altered myofiber-type composition. In order to further investigate these findings, we examined the impact of dysferlin deficiency on the abundance of calcium (Ca²⁺) handling and glucose/glycogen metabolism-related proteins in predominantly slow-twitch, oxidative soleus and fast-twitch, glycolytic extensor digitorum longus (EDL) muscles of 10-month-old wild-type (WT) C57BL/6J and dysferlin-deficient BLAJ male mice. Additionally, we compared the Ca²⁺ activation properties of isolated slow- and fast-twitch myofibers from 3-month-old WT and BLAJ male mice. Differences were observed for some Ca²⁺ handling and glucose/glycogen metabolism-related protein levels between BLAJ soleus and EDL muscles (compared with WT) that may contribute to the previously reported differences in function in these BLAJ muscles. Dysferlin deficiency did not impact glycogen content of whole muscles nor Ca²⁺ activation of the myofilaments, although soleus muscle from 10-month-old BLAJ mice had more glycogen than EDL muscles. These results demonstrate a further impact of dysferlin deficiency on proteins associated with excitation-contraction coupling and glycogen metabolism in skeletal muscles, potentially contributing to altered contractile function in dysferlinopathy.

Skeletal muscle function is governed by both the mechanical and structural properties of its constituent tissues, which are both modified by disease. Characterizing the mechanical properties of skeletal muscle tissue at an intermediate scale, i.e., between that of cells and organs, can provide insight into diseases such as muscular dystrophies. In this study, we use quantitative micro-elastography (QME) to characterize the micro-scale elasticity of ex vivo murine skeletal muscle in three-dimensions in whole muscles. To address the challenge of achieving high QME image quality with samples featuring uneven surfaces and geometry, we encapsulate the muscles in transparent hydrogels with flat surfaces. Using this method, we study aging and disease in quadriceps tissue by comparing normal wild-type (C57BL/6J) mice with dysferlin-deficient BLAJ mice, a model for the muscular dystrophy dysferlinopathy, at 3, 10, and 24 months of age (sample size of three per group). We observe a 77% decrease in elasticity at 24 months in dysferlin-deficient quadriceps compared to wild-type quadriceps.

Skeletal muscle tissue function is governed by the mechanical properties and organization of its components, including myofibers, extracellular matrix, and adipose tissue, which can be modified by the onset and progression of many disorders. This study used a novel combination of quantitative micro-elastography and clearing-enhanced three-dimensional (3D) microscopy to assess 3D micro-scale elasticity and micro-architecture of muscles from two muscular dystrophies: dysferlinopathy and Duchenne muscular dystrophy, using male BLA/J and mdx mice, respectively, and their wild-type (WT) controls. We examined three muscles with varying proportions of slow- and fast-twitch myofibers: the soleus (predominantly slow), extensor digitorum longus (EDL; fast), and quadriceps (mixed), from BLA/J and WT_BLA/J mice aged 3, 10, and 24 months, and mdx and WT_mdx mice aged 10 months. Both dysferlin deficiency and age reduced the elasticity and variability of elasticity of the soleus and quadriceps, but not EDL. Overall, the BLA/J soleus was 20% softer than WT and less mechanically heterogeneous (-14% in standard deviation of elasticity). The BLA/J quadriceps at 24 months was 72% softer than WT and less mechanically heterogeneous (-59% in standard deviation), with substantial adipose tissue accumulation. While mdx muscles did not differ quantitatively from WT, regional heterogeneity was evident in micro-scale elasticity and micro-architecture of quadriceps (e.g., 11.2 kPa in a region with marked pathology vs 3.8 kPa in a less affected area). These results demonstrate differing biomechanical changes in hind-limb muscles of two distinct muscular dystrophies, emphasizing the potential for this novel multimodal technique to identify important differences between various myopathies.

Exercise‐induced muscle damage (EIMD) can affect athlete performance and is a risk factor for major muscle injury. The temporal profile of thiol‐oxidized albumin, a marker of oxidative stress, has shown potential in assessing recovery from EIMD in non‐athletically trained participants but not yet in trained participants. Our primary aim was to assess whether there are changes in the level of thiol‐oxidized albumin after a marathon in athletically trained participants. Twenty participants completed a marathon and collected daily dried blood spots from 3 days prior to and 7 days after the marathon to measure thiol‐oxidized albumin using a novel methodology (OxiDx). Participants were also assessed for indirect markers of EIMD prior to and on days 2 and 5 post‐marathon. The level of thiol‐oxidized albumin peaked at 2 days and remained elevated until 5 days after the marathon and correlated with indirect measures of EIMD. Furthermore, time of recovery for thiol‐oxidized albumin varied between participants, some recovered at 3 days post‐marathon whereas others extended beyond 7 days post marathon. Tracking temporal changes in the level of thiol‐oxidized albumin has potential to be useful in managing recovery from EIMD in athletes, particularly considering the ease of the OxiDx methodology.

[This corrects the article DOI: 10.1371/journal.pone.0214908.].