Biomechanics show stem cell necessity for effective treatment of volumetric muscle loss using bioengineered constructs - PubMed (original) (raw)

Biomechanics show stem cell necessity for effective treatment of volumetric muscle loss using bioengineered constructs

Marco Quarta et al. NPJ Regen Med. 2018.

Abstract

Despite the regenerative capacity of muscle, tissue volume is not restored after volumetric muscle loss (VML), perhaps due to a loss-of-structural extracellular matrix. We recently demonstrated the structural and functional restoration of muscle tissue in a mouse model of VML using an engineered "bioconstruct," comprising an extracellular matrix scaffold (decellularized muscle), muscle stem cells (MuSCs), and muscle-resident cells (MRCs). To test the ability of the cell-based bioconstruct to restore whole-muscle biomechanics, we measured biomechanical parameters in uninjured muscles, muscles injured to produce VML lesions, and in muscles that were injured and then treated by implanting either the scaffolds alone or with bioconstructs containing the scaffolds, MuSCs, and MRCs. We measured the active and passive forces over a range of lengths, viscoelastic force relaxation, optimal length, and twitch dynamics. Injured muscles showed a narrowed length-tension curve or lower force over a narrower range of muscle lengths, and increased passive force. When treated with bioconstructs, but not with scaffolds alone, injured muscles showed active and passive length-tension relationships that were not different from uninjured muscles. Moreover, injured muscles treated with bioconstructs exhibited reduced fibrosis compared to injured muscles either untreated or treated with scaffolds alone. The cell-based bioconstruct is a promising treatment approach for future translational efforts to restore whole-muscle biomechanics in muscles with VML lesions.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1

Fig. 1

a Relationship between maximum isometric tetanic force measured ex vivo and muscle mass in mouse TAs. Control muscles are designated as “VML− Scaffold− Cells−”. In the VML injury groups, muscles were partially excised and left untreated (VML+ Scaffold− Cells−) or implanted with either a tissue-engineered bioconstruct comprising of scaffold alone (VML+ Scaffold+ Cells−) or with scaffold and muscle stem cells, and muscle-resident cells (VML+ Scaffold+ Cells+). “VML+ Scaffold+ Cells+” muscles showed proportionally increased mass and, statistically significant, force (Table 1), consistent with functional active stress generation in the newly formed tissue. b Active twitch force across a range of muscle lengths. (Left panel) In vivo measurements. (Right panel) Ex vivo measurements. The “VML+ Scaffold− Cells−” muscles have narrowed length-tension curves (comparisons between VML+ Scaffold+ Cells− group and VML+ Scaffold+ Cells+ or VML− Scaffold− Cells− groups; p < 0.0001). The length-tension curves of the “VML+ Scaffold+ Cells+” muscles were restored with treatment, meaning that a greater fraction of the maximum force was generated over a broader range of muscle lengths. No improvement was observed with “VML+ Scaffold+ Cells−” treatment. The curve from each muscle was normalized by its own maximum force and centered at optimal length. Symbols are the mean forces and error bars represent SEM (n = 6–9 muscles per group)

Fig. 2

Fig. 2

a Passive tension across a range of muscle lengths. Passive tension was measured at increasing lengths after 2 min of viscoelastic relaxation at each length. Horizontal axis was offset to the optimal length. Regression lines through each curve in the range Lo−0.5 to +0.5 were compared. The “VML+ Scaffold+ Cells+” group had lower passive tension than the “VML+ Scaffold− Cells−” group (p < 0.01). The treatment restored the low levels of passive tension observed in the “VML− Scaffold− Cells−” uninjured control group. Symbols are the means and error bars represent SEM (n = 8–11 muscles per group). b Representative immunofluorescence images of cross-sections of VML-injured TA muscles treated with cell-based tissue engineering compared to no-treatment and no-VML. The broken yellow line highlights the border between the regions of regenerative fibrosis below and the dense bioconstruct (BC) above. Collagen I (green); Laminin (white); DAPI (blue) (scale bar = 200 μm). c Quantification of immunofluorescence staining against Collagen I protein in regions not occupied by transplanted scaffolds in cross-sections of TA muscles (n = 4). d Force-relaxation test in response to stepwise increase in length and viscoelastic time constants. A stepwise length increase of 0.5 mm was applied, and the passive force recorded. e, f A two-exponential function was fit to the curve and the two resulting time constants reported. No difference was observed in viscoelastic relaxation time constants among the groups in either _τ_1 (p = 0.72) or _τ_2 (p = 0.68). Bars are the means and error bars represent ± SEM (n = 8–11 muscles per group)

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