Elucidation of extracellular matrix mechanics from muscle fibers and fiber bundles.
TL;DR: A new method to quantify viscoelastic ECM modulus is presented by combining tests of single muscle fibers and fiber bundles, which demonstrate that ECM is a highly nonlinearly elastic material, while muscle fibers are linearly elastic.
About: This article is published in Journal of Biomechanics.The article was published on 2011-02-24 and is currently open access. It has received 156 citations till now. The article focuses on the topics: Skeletal muscle.
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TL;DR: The structure, composition, and mechanical properties of skeletal muscle ECM are reviewed; the cells that contribute to the maintenance of the ECMAreas for future study are proposed; and overview changes that occur with pathology are described.
Abstract: The skeletal muscle extracellular matrix (ECM) plays an important role in muscle fiber force transmission, maintenance, and repair. In both injured and diseased states, ECM adapts dramatically, a property thathas clinical manifestations and alters muscle function. Here, we review the structure, composition, and mechanical properties of skeletal muscle ECM, describe the cells that contribute to the maintenance of the ECM and, finally, overview changes that occur with pathology. New scanning electron micrographs of ECM structure are also presented with hypotheses about ECM structure-function relationships. Detailed structure-function relationships of the ECM have yet to be defined and, as a result, we propose areas for future studies.
737 citations
Cites methods from "Elucidation of extracellular matrix..."
...The ECM modulus can then be calculated using the rule of mixtures for composites after the load-bearing area of fiber and ECM are first defined.(79) Using this approach, isolated muscle fiber stress–strain behavior was shown to be linear, and muscle bundle stress–strain behavior...
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TL;DR: approaches used to study fibrosis in tissues, such as lung, kidney, and liver, need to be applied to studies of skeletal muscle to identify ways to prevent or even cure the devastating maladies of skeletal Muscle Fibrosis.
Abstract: Skeletal muscle fibrosis can be a devastating clinical problem that arises from many causes, including primary skeletal muscle tissue diseases, as seen in the muscular dystrophies, or it can be secondary to events that include trauma to muscle or brain injury The cellular source of activated fibroblasts (myofibroblasts) may include resident fibroblasts, adult muscle stem cells, or inflammatory or perivascular cells, depending on the model studied Even though it is likely that there is no single source for all myofibroblasts, a common mechanism for the production of fibrosis is via the transforming growth factor-β/phosphorylated Smad3 pathway This pathway and its downstream targets thus provide loci for antifibrotic therapies, as do methods for blocking the transdifferentiation of progenitors into activated fibroblasts A structural model for the extracellular collagen network of skeletal muscle is needed so that measurements of collagen content, morphology, and gene expression can be related to mechanical properties Approaches used to study fibrosis in tissues, such as lung, kidney, and liver, need to be applied to studies of skeletal muscle to identify ways to prevent or even cure the devastating maladies of skeletal muscle
231 citations
Cites background from "Elucidation of extracellular matrix..."
...Furthermore, the fiber groups bore the same stress (force/area), even though they were 10–20 times larger than the single fibers (86)....
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TL;DR: Findings indicate that theECM of tibialis anterior muscles from old mice has a higher modulus than the ECM of adult muscles, likely driven by an accumulation of densely packed extensively crosslinked collagen.
Abstract: Advanced age is associated with increases in muscle passive stiffness, but the contributors to the changes remain unclear. Our purpose was to determine the relative contributions of muscle fibers and extracellular matrix (ECM) to muscle passive stiffness in both adult and old animals. Passive mechanical properties were determined for isolated individual muscle fibers and bundles of muscle fibers that included their associated ECM, obtained from tibialis anterior muscles of adult (8–12 mo old) and old (28–30 mo old) mice. Maximum tangent moduli of individual muscle fibers from adult and old muscles were not different at any sarcomere length tested. In contrast, the moduli of bundles of fibers from old mice was more than twofold greater than that of fiber bundles from adult muscles at sarcomere lengths >2.5 μm. Because ECM mechanical behavior is determined by the composition and arrangement of its molecular constituents, we also examined the effect of aging on ECM collagen characteristics. With aging, muscle ECM hydroxyproline content increased twofold and advanced glycation end-product protein adducts increased threefold, whereas collagen fibril orientation and total ECM area were not different between muscles from adult and old mice. Taken together, these findings indicate that the ECM of tibialis anterior muscles from old mice has a higher modulus than the ECM of adult muscles, likely driven by an accumulation of densely packed extensively crosslinked collagen.
162 citations
Cites background or methods or result from "Elucidation of extracellular matrix..."
...Using the rule of mixtures (22), the corresponding contributions of ECM and muscle fibers to the passive stiffness of muscles of old mice is 73% ECM and 27% fibers....
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...Previous estimates of ECM stiffness for muscles of young adult mice have compared mechanical properties of single muscle fibers with those of muscle fiber bundles that include fibers and their surrounding ECM (22)....
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...Our data are in contrast to previous reports of a sixfold greater modulus of muscle fiber bundles compared with single fibers from adult mice as well as a linear stress-strain response of single fibers (22)....
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...In the present study, we report the tangent modulus at four different strains, with a maximum strain of 24%, whereas the previous study (22) reports quadratic modulus with maximum strains of 100%....
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...Given that the modulus of groups of fibers with their associated ECM removed is similar to that of single fibers (22), we are confident that this approach to determining the material properties of ECM is valid....
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TL;DR: It is concluded that muscle fibrosis does not lead to increased passive stiffness and that collagen content is not predictive of muscle stiffness.
Abstract: Many skeletal muscle diseases are associated with progressive fibrosis leading to impaired muscle function. Collagen within the extracellular matrix is the primary structural protein providing a me...
115 citations
Cites background from "Elucidation of extracellular matrix..."
...Passive stiffness in mammalian skeletal muscle is thought to be determined largely by ECM collagen, although intracellular elements are also known to contribute (13, 14, 30)....
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...Recent studies have suggested that the ECM is primarily responsible for passive stiffness in mammalian skeletal muscle (13, 14, 30); however, intracellular components may also contribute (37)....
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TL;DR: Findings provide novel evidence that the low regenerative potential of aged skeletal muscle is independent of intrinsic MPC properties but is related to the increase in the stiffness of the MPC microenvironment.
Abstract: Background
Skeletal muscle aging is associated with a decreased regenerative potential due to the loss of function of endogenous stem cells or myogenic progenitor cells (MPCs). Aged skeletal muscle is characterized by the deposition of extracellular matrix (ECM), which in turn influences the biomechanical properties of myofibers by increasing their stiffness. Since the stiffness of the MPC microenvironment directly impacts MPC function, we hypothesized that the increase in muscle stiffness that occurs with aging impairs the behavior of MPCs, ultimately leading to a decrease in regenerative potential.
Results
We showed that freshly isolated individual myofibers from aged mouse muscles contain fewer MPCs overall than myofibers from adult muscles, with fewer quiescent MPCs and more proliferative and differentiating MPCs. We observed alterations in cultured MPC behavior in aged animals, where the proliferation and differentiation of MPCs were lower and higher, respectively. These alterations were not linked to the intrinsic properties of aged myofibers, as shown by the similar values for the cumulative population-doubling values and fusion indexes. However, atomic force microscopy (AFM) indentation experiments revealed a nearly 4-fold increase in the stiffness of the MPC microenvironment. We further showed that the increase in stiffness is associated with alterations to muscle ECM, including the accumulation of collagen, which was correlated with higher hydroxyproline and advanced glycation end-product content. Lastly, we recapitulated the impaired MPC behavior observed in aging using a hydrogel substrate that mimics the stiffness of myofibers.
Conclusions
These findings provide novel evidence that the low regenerative potential of aged skeletal muscle is independent of intrinsic MPC properties but is related to the increase in the stiffness of the MPC microenvironment.
107 citations
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Journal Article•
TL;DR: Acellular matrix with intact ECM and complete removal of muscle fibers can be obtained by oscillatory treatment of rat skeletal muscle at 4 degrees C with 1% SDS for 72 hours.
Abstract: Objective To investigate an optimal method for SD rat skeletal muscle decellularization.Methods Sixteen SD rats(male and female) weighing 180-200 g were used.Thirty-six skeletal muscle bundles obtained from 10 rats were randomly divided into 3 groups:normal group(group A,n=4) received non-decellularization;time group(group T,n=16) and concentration group(group C,n=16) underwent decellularization using hypotonic-detergent method.Concentration of sodium dodecyl sulfate(SDS) was 1.0% for T group,which was subdivided into groups T1,T2,T3 and T4(n=4 per subgroup) according to different processing durations(24,48,72 and 96 hours).Group C was treated for 48 hours and subdivided into groups C1,C2,C3 and C4(n=4 per subgroup) according to different SDS concentrations(0.5%,1.0%,1.5% and 2.0%).The muscle bundles of each group underwent HE staining observation and hydroxyproline content detection in order to get the optimal decellularization condition.Seven of 14 complete skeletal muscle bundles obtained from 6 SD rats were treated with the optimal decellularization condition(experimental group),and the rest 7 muscle bundles served as normal control(control group).The muscle bundles of each group were evaluated with gross observation,Masson staining and biomechanical test.Results HE staining:there was no significant difference between groups T1,T2,C1,C2 and C3 and group A in terms of muscle fiber;portion of muscle fibers in group C4 were removed;muscle fibers in group T3 were fully removed with a complete basement membrane structure;muscle fibers of group T4 were fully removed,and the structure of basement membrane was partly damaged.Hydroxyproline content detection:there was no significant difference between group A and groups C1,C2,C3,T1 and T2(P 0.05);significant difference was evident between group A and groups C4,T3 and T4(P 0.05);the difference between group C4 and groups T3 and T4 was significant(P 0.05);no significant difference was evident between group T3 and group T4(P 0.05).The optimal decellularization condition was 4,1.0% SDS and 72 hours according to the results of HE staining and hydroxyproline content ℃ detection.Gross observation:the muscle bundles of the experimental group were pallid,half-transparent and fluffier comparing with the control group.Masson staining observation:the collagen fibers of the experimental group had a good continuity,and were fluffier comparing with control group.Biomechanics test:the maximum breaking load of the experimental group and the control group was(1.38 ± 0.35) N and(1.98 ± 0.77) N,respectively;the maximum extension displacement of the experimental group and the control group was(3.19 ± 3.23) mm and(3.56 ± 2.17) mm,respectively;there were no significant differences between two groups(P 0.05).Conclusion Acellular matrix with intact ECM and complete removal of muscle fibers can be obtained by oscillatory treatment of rat skeletal muscle at 4℃ with 1% SDS for 72 hours.
14 citations
Additional excerpts
...Attempts to remove muscle cells chemically from the ECM to test its properties directly have all met with some degradation or compromised mechanical properties (Borschel et al., 2004; Qing and Qin, 2009)....
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...Attempts to remove muscle cells chemically from the ECM to test its properties directly have all met with some degradation or compromised mechanical properties (Borschel et al., 2004; Qing and Qin, 2009)....
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