The desmin mutation R349P increases contractility and fragility of stem cell‐generated muscle micro‐tissues

Abstract

Aims Desminopathies comprise hereditary myopathies and cardiomyopathies caused by mutations in the intermediate filament protein desmin that lead to severe and often lethal degeneration of striated muscle tissue. Animal and single cell studies hinted that this degeneration process is associated with massive ultrastructural defects correlating with increased susceptibility of the muscle to acute mechanical stress. The underlying mechanism of mechanical susceptibility, and how muscle degeneration develops over time, however, has remained elusive. Methods Here, we investigated the effect of a desmin mutation on the formation, differentiation, and contractile function of in vitro‐engineered three‐dimensional micro‐tissues grown from muscle stem cells (satellite cells) isolated from heterozygous R349P desmin knock‐in mice. Results Micro‐tissues grown from desmin‐mutated cells exhibited spontaneous unsynchronised contractions, higher contractile forces in response to electrical stimulation, and faster force recovery compared with tissues grown from wild‐type cells. Within 1 week of culture, the majority of R349P desmin‐mutated tissues disintegrated, whereas wild‐type tissues remained intact over at least three weeks. Moreover, under tetanic stimulation lasting less than 5 s, desmin‐mutated tissues partially or completely ruptured, whereas wild‐type tissues did not display signs of damage. Conclusions Our results demonstrate that the progressive degeneration of desmin‐mutated micro‐tissues is closely linked to extracellular matrix fibre breakage associated with increased contractile forces and unevenly distributed tensile stress. This suggests that the age‐related degeneration of skeletal and cardiac muscle in patients suffering from desminopathies may be similarly exacerbated by mechanical damage from high‐intensity muscle contractions. We conclude that micro‐tissues may provide a valuable tool for studying the organization of myocytes and the pathogenic mechanisms of myopathies.

Analytical method for reconstructing the stress on a spherical particle from its surface deformation

“…We now analyze the properties of the resulting stress tensor (12). In order to better understand the result, we consider some basic limiting cases.…”

“…So far, we have discussed very simple shapes where only a small number of spherical harmonics is required to describe the shape of the deformed bead. The stress tensor (12) derived here is, however, applicable to arbitrary radial bead deformations. To test the result (12) for more complicated cases, experimental data is obtained and analyzed.…”

“…The stress tensor (12) derived here is, however, applicable to arbitrary radial bead deformations. To test the result (12) for more complicated cases, experimental data is obtained and analyzed.…”

“…The development of cells is influenced by the extracellular matrix (ECM), which is a three-dimensional network of macromolecules surrounding the cells. Biochemical and mechanical properties [7,8] of the ECM alter the shape and activity of the cells [9][10][11][12][13], while the macromolecules making up the ECM are produced by the cells themselves. This leads to a feedback loop between the ECM and the cells that usually results in homeostasis.…”

Dystrophin is a mechanical tension modulator

“…For this reason, numerous in vitro strategies have emerged in recent years for cultivating self-organizing, human multinucleated myotubes within 3D extracellular matrix (ECM) scaffolds [31,2,1,22] . Based on this, the first 3D bioengineered human skeletal muscle disease models were reported only recently, and offer great opportunities to further fundamental research and drug development [32,44,42,17,55,51] . By contrast to 2D myotube culture, these approaches support studies of the force generating capacity of normal and DMD muscle tissue upon stimulating a contraction.…”