The MyoRobot technology discloses a premature biomechanical decay of skeletal muscle fiber bundles derived from R349P desminopathy mice

Figures

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  Figure 1. CAD design and photograph of the MyoRobot. Stepper motors drive the multi-well rack and lift or lower the muscle sample. The latter is mounted between force transducer and voice-coil pin (white box, enhanced to the right). The output current of the force-transducer is converted to a voltage signal and fed to a bridge amplifier prior to digitization. The voice-coil is an electro-magnetic length controller to stretch or relax the muscle fiber at μm resolution.

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  Figure 2. Ca2+ sensitivity of the contractile apparatus in small fiber bundles from (A) EDL and (B) SOL muscle of mice carrying the R349P desmin mutation during aging. Top row shows representative examples of force recordings during successive pCa steps in the adult age group (35–45 wks) for a small fiber bundle of each genotype alongside with the group analysis at this age and the mean reconstructed sigmoidal Hill fits. From Hill fits to each individual recording, the pCa50 values (middle row) and Hill coefficients (bottom row) were extracted and analyzed. Although not significant, there was a tendency for increased pCa50 values during aging across all genotypes. There were no significant differences in Ca2+-force sensor curve parameters by the presence of one or two R349P desmin alleles in the EDL bundles while in the SOL Ca2+-sensitivity was significantly lower in the mutation-carrying bundles from adult mice only. Numbers within or adjacent to the box plots indicate number of fiber bundles recorded. Box plots denominate lower and upper quartile and median value. Whiskers depict 5% and 95% percentile. Dots represent outliers. *P < 0.05; **P < 0.01; ***P < 0.001, Kruskal-Wallis with…

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  Figure 3. Passive elasticity and mechanical axial compliance of small fiber bundles from EDL and soleus (SOL) muscle of mice carrying the R349P desmin mutation during aging. (A) Examples of resting length-tension (RLT) curves from one fiber bundle per age group (young: 17–23 wks, adult: 35–45 wks, aged: 60–80 wks from each genotype wt, het hom). In the EDL (top) and SOL bundles (bottom), restoration forces increase with age with an emphasis on a pre-aged increase in the mutant bundles and generally larger forces in the SOL over EDL bundles (note the different scaling). (B) Statistical analysis shows complex significant changes in hom SOL bundles with age. (C) The larger restoration forces in hom and het bundles over the wt in EDL bundles are also reflected by the better survival of larger stretches in the wt. SOL bundles seem less fragile even in aged animals as compared to EDL bundles from even younger animals. (D) Axial absolute compliance values obtained from RLT curves for all bundles grouped by age and genotype indicate decreasing compliance with age in the EDL for wt mice, while for R349P desmin, the low compliance seen in older wt mice is already present in younger animals,…

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  Figure 4. Unloaded speed of shortening in a ‘slack-test’, configuration is increased with age in small muscle fiber bundles from EDL and SOL muscle carrying the R349P desmin mutation. (A) Example of a slack-test performed in a small fiber bundle from SOL muscle alongside with the corresponding dL-dt plots and biexponential fits from which the linear fast (v1) and slow (v2) shortening velocities were extrapolated. (B) Summary of all grouped dL-dt plots across ages and genotypes. (C) Comparison of the fast shortening velocities representing the unloaded shortening phase in EDL and SOL bundles. Although no genotype-related statistical significances were apparent, there is a trend towards larger shortening velocities in the mutants for older ages while at young age, the wt performs faster. Numbers within or adjacent to the box plots indicate number of fiber bundles recorded. Error bars: s.e.m.