scholarly journals Truncated dystrophins reduce muscle stiffness in the extensor digitorum longus muscle of mdx mice

2013 ◽  
Vol 114 (4) ◽  
pp. 482-489 ◽  
Author(s):  
Chady H. Hakim ◽  
Dongsheng Duan
Keyword(s):  
Extensor Digitorum Longus ◽  
Muscle Stiffness ◽  
Extensor Digitorum ◽  
Clinical Feature ◽  
Mdx Mice ◽  
Wild Type ◽  
Dmd Gene ◽  
Edl Muscle ◽  
Muscle Wasting Disease ◽  
Dystrophin Protein

Muscle stiffness is a major clinical feature in Duchenne muscular dystrophy (DMD). DMD is the most common lethal inherited muscle-wasting disease in boys, and it is caused by the lack of the dystrophin protein. We recently showed that the extensor digitorum longus (EDL) muscle of mdx mice (a DMD mouse model) exhibits disease-associated muscle stiffness. Truncated micro- and mini-dystrophins are the leading candidates for DMD gene therapy. Unfortunately, it has never been clear whether these truncated genes can mitigate muscle stiffness. To address this question, we examined the passive properties of the EDL muscle in transgenic mdx mice that expressed a representative mini- or micro-gene (ΔH2-R15, ΔR2-15/ΔR18-23/ΔC, or ΔR4-23/ΔC). The passive properties were measured at the ages of 6 and 20 mo and compared with those of age-matched wild-type and mdx mice. Despite significant truncation of the gene, surprisingly, the elastic and viscous properties were completely restored to the wild-type level in every transgenic strain we examined. Our results demonstrated for the first time that truncated dystrophin genes may effectively treat muscle stiffness in DMD.

scholarly journals S1P3 receptor influences key physiological properties of fast-twitch extensor digitorum longus muscle

2016 ◽  
Vol 120 (11) ◽  
pp. 1288-1300 ◽  
Author(s):  
Elena Germinario ◽  
Michela Bondì ◽  
Francesca Cencetti ◽  
Chiara Donati ◽  
Marta Nocella ◽  
...  
Keyword(s):  
Extensor Digitorum Longus ◽  
The Body ◽  
Extensor Digitorum ◽  
Disuse Atrophy ◽  
Wild Type ◽  
Muscle Properties ◽  
Fatigue Development ◽  
Physiological Properties ◽  
Edl Muscle ◽  
Fast Twitch

To examine the role of sphingosine 1-phosphate (S1P) receptor 3 (S1P3) in modulating muscle properties, we utilized transgenic mice depleted of the receptor. Morphological analyses of extensor digitorum longus (EDL) muscle did not show evident differences between wild-type and S1P3-null mice. The body weight of 3-mo-old S1P3-null mice and the mean cross-sectional area of transgenic EDL muscle fibers were similar to those of wild-type. S1P3 deficiency enhanced the expression level of S1P1 and S1P2 receptors mRNA in S1P3-null EDL muscle. The contractile properties of S1P3-null EDL diverge from those of wild-type, largely more fatigable and less able to recover. The absence of S1P3 appears responsible for a lower availability of calcium during fatigue. S1P supplementation, expected to stimulate residual S1P receptors and signaling, reduced fatigue development of S1P3-null muscle. Moreover, in the absence of S1P3, denervated EDL atrophies less than wild-type. The analysis of atrophy-related proteins in S1P3-null EDL evidences high levels of the endogenous regulator of mitochondria biogenesis peroxisome proliferative-activated receptor-γ coactivator 1α (PGC-1α); preserving mitochondria could protect the muscle from disuse atrophy. In conclusion, the absence of S1P3 makes the muscle more sensitive to fatigue and slows down atrophy development after denervation, indicating that S1P3 is involved in the modulation of key physiological properties of the fast-twitch EDL muscle.

scholarly journals The passive mechanical properties of the extensor digitorum longus muscle are compromised in 2- to 20-mo-old mdx mice

2011 ◽  
Vol 110 (6) ◽  
pp. 1656-1663 ◽  
Author(s):  
Chady H. Hakim ◽  
Robert W. Grange ◽  
Dongsheng Duan
Keyword(s):  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Muscle Pathology ◽  
Mdx Mice ◽  
Myotendinous Junction ◽  
Muscle Rigidity ◽  
Dependent Manner ◽  
Stress Strain ◽  
Longus Muscle ◽  
Edl Muscle

Muscle rigidity and myotendinous junction (MTJ) deficiency contribute to immobilization in Duchenne muscular dystrophy (DMD), a lethal disease caused by the absence of dystrophin. However, little is known about the muscle passive properties and MTJ strength in a diseased muscle. Here, we hypothesize that dystrophin-deficient muscle pathology renders skeletal muscle stiffer and MTJ weaker. To test our hypothesis, we examined the passive properties of an intact noncontracting muscle-tendon unit in mdx mice, a mouse model for DMD. The extensor digitorum longus (EDL) muscle-tendon preparations of 2-, 6-, 14-, and 20-mo-old mdx and normal control mice were strained stepwisely from 110% to 160% of the muscle optimal length. The stress-strain response and failure position were analyzed. In support of our hypothesis, the mdx EDL preparation consistently developed higher stress before muscle failure. Postfailure stresses decreased dramatically in mdx but not normal preparations. Further, mdx showed a significantly faster stress relaxation rate. Consistent with stress-strain assay results, we observed significantly higher fibrosis in mdx muscle. In 2- and 6-mo-old mdx and 20-mo-old BL10 mice failure occurred within the muscle (2- to 14-mo-old BL10 preparations did not fail). Interestingly, in ≥14-mo-old mdx mice the failure site shifted toward the MTJ. Electron microscopy revealed substantial MTJ degeneration in aged but not young mdx mice. In summary, our results suggest that the passive properties of the EDL muscle and the strength of MTJ are compromised in mdx in an age-dependent manner. These findings offer new insights in studying DMD pathogenesis and developing novel therapies.

scholarly journals Autophagy in the heart is enhanced and independent of disease progression in mus musculus dystrophinopathy models

2019 ◽  
Vol 8 ◽  
pp. 204800401987958
Author(s):  
HR Spaulding ◽  
C Ballmann ◽  
JC Quindry ◽  
MB Hudson ◽  
JT Selsby
Keyword(s):  
Skeletal Muscle ◽  
Duchenne Muscular Dystrophy ◽  
Muscular Dystrophy ◽  
Disease Progression ◽  
Gene Mutations ◽  
Dystrophin Gene ◽  
Mdx Mice ◽  
Dystrophin Deficiency ◽  
Muscle Wasting Disease ◽  
Dystrophin Protein

Background Duchenne muscular dystrophy is a muscle wasting disease caused by dystrophin gene mutations resulting in dysfunctional dystrophin protein. Autophagy, a proteolytic process, is impaired in dystrophic skeletal muscle though little is known about the effect of dystrophin deficiency on autophagy in cardiac muscle. We hypothesized that with disease progression autophagy would become increasingly dysfunctional based upon indirect autophagic markers. Methods Markers of autophagy were measured by western blot in 7-week-old and 17-month-old control (C57) and dystrophic (mdx) hearts. Results Counter to our hypothesis, markers of autophagy were similar between groups. Given these surprising results, two independent experiments were conducted using 14-month-old mdx mice or 10-month-old mdx/Utrn± mice, a more severe model of Duchenne muscular dystrophy. Data from these animals suggest increased autophagosome degradation. Conclusion Together these data suggest that autophagy is not impaired in the dystrophic myocardium as it is in dystrophic skeletal muscle and that disease progression and related injury is independent of autophagic dysfunction.

scholarly journals Activity of mu- and m-calpain in regenerating fast and slow twitch skeletal muscles.

1996 ◽  
Vol 43 (4) ◽  
pp. 693-700 ◽  
Author(s):  
J Moraczewski ◽  
E Piekarska ◽  
M Zimowska ◽  
M Sobolewska
Keyword(s):  
Intracellular Calcium ◽  
Soleus Muscle ◽  
Muscle Regeneration ◽  
Skeletal Muscles ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Slow Twitch ◽  
Edl Muscle ◽  
Calpain Ii ◽  
Complete Regeneration

Calpains--non-lysosomal intracellular calcium-activated neutral proteinases, form a family consisting of several distinct members. Two of the isoenzymes: mu (calpain I) and m (calpain II) responded differently to the injury during complete regeneration of Extensor digitorum longus (EDL) muscle and partial regeneration of Soleus muscle. In the crushed EDL the level of m-calpain on the 3rd and 7th day of regeneration was higher than in non-operated muscles, whereas the activity of this calpain in injured Soleus decreased. The level of mu-calpain in EDL oscillated irregularly during regeneration whereas in Soleus of both injured and contralateral muscles its level rapidly rose. Our results support the hypothesis that m-calpain is involved in the process of fusion of myogenic cells whereas mu-calpain plays a significant but indirect role in muscle regeneration.

scholarly journals Interrogation of Dystrophin and Dystroglycan Complex Protein Turnover After Exon Skipping Therapy

2021 ◽  
pp. 1-20
Author(s):  
James S. Novak ◽  
Rita Spathis ◽  
Utkarsh J. Dang ◽  
Alyson A. Fiorillo ◽  
Ravi Hindupur ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Protein Expression ◽  
Protein Turnover ◽  
Isotope Labeling ◽  
Exon Skipping ◽  
Mdx Mice ◽  
Wild Type ◽  
Gene Correction ◽  
Dystrophin Protein

Recently, the Food and Drug Administration granted accelerated approvals for four exon skipping therapies –Eteplirsen, Golodirsen, Viltolarsen, and Casimersen –for Duchenne Muscular Dystrophy (DMD). However, these treatments have only demonstrated variable and largely sub-therapeutic levels of restored dystrophin protein in DMD patients, limiting their clinical impact. To better understand variable protein expression and the behavior of truncated dystrophin protein in vivo, we assessed turnover dynamics of restored dystrophin and dystroglycan complex (DGC) proteins in mdx mice after exon skipping therapy, compared to those dynamics in wild type mice, using a targeted, highly-reproducible and sensitive, in vivo stable isotope labeling mass spectrometry approach in multiple muscle tissues. Through statistical modeling, we found that restored dystrophin protein exhibited altered stability and slower turnover in treated mdx muscle compared with that in wild type muscle (∼44 d vs. ∼24 d, respectively). Assessment of mRNA transcript stability (quantitative real-time PCR, droplet digital PCR) and dystrophin protein expression (capillary gel electrophoresis, immunofluorescence) support our dystrophin protein turnover measurements and modeling. Further, we assessed pathology-induced muscle fiber turnover through bromodeoxyuridine (BrdU) labeling to model dystrophin and DGC protein turnover in the context persistent fiber degeneration. Our findings reveal sequestration of restored dystrophin protein after exon skipping therapy in mdx muscle leading to a significant extension of its half-life compared to the dynamics of full-length dystrophin in normal muscle. In contrast, DGC proteins show constant turnover attributable to myofiber degeneration and dysregulation of the extracellular matrix (ECM) in dystrophic muscle. Based on our results, we demonstrate the use of targeted mass spectrometry to evaluate the suitability and functionality of restored dystrophin isoforms in the context of disease and propose its use to optimize alternative gene correction strategies in development for DMD.

Contraction-induced injury to single permeabilized muscle fibers from mdx, transgenic mdx, and control mice

2000 ◽  
Vol 279 (4) ◽  
pp. C1290-C1294 ◽  
Author(s):  
Gordon S. Lynch ◽  
Jill A. Rafael ◽  
Jeffrey S. Chamberlain ◽  
John A. Faulkner
Keyword(s):  
Null Hypothesis ◽  
Fiber Length ◽  
Extensor Digitorum Longus ◽  
Muscle Fibers ◽  
Extensor Digitorum ◽  
Mdx Mice ◽  
And Control ◽  
Permeabilized Fibers ◽  
Permeabilized Muscle ◽  
Sarcolemmal Integrity

Muscle fibers of mdx mice that lack dystrophin are more susceptible to contraction-induced injury, particularly when stretched. In contrast, transgenic mdx (tg -mdx) mice, which overexpress dystrophin, show no morphological or functional signs of dystrophy. Permeabilization disrupts the sarcolemma of fibers from muscles of mdx, tg- mdx, and control mice. We tested the null hypothesis stating that, after single stretches of maximally activated single permeabilized fibers, force deficits do not differ among fibers from extensor digitorum longus muscles of mdx, tg -mdx, or control mice. Fibers were maximally activated by Ca2+ (pCa 4.5) and then stretched through strains of 10%, 20%, or 30% of fiber length ( L f) at a velocity of 0.5 L f/s. Immediately after each strain, the force deficits were not different for fibers from each of the three groups of mice. When collated with studies of membrane-intact fibers in whole muscles of mdx, tg -mdx, and control mice, these results indicate that dystrophic symptoms do not arise from factors within myofibrils but, rather, from disruption of the sarcolemmal integrity that normally provides protection from contraction-induced injury.

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