Repair of traumatic skeletal muscle injury with bone-marrow-derived mesenchymal stem cells seeded on extracellular matrix

Further development of a tissue engineered muscle repair construct in vitro for enhanced functional recovery following implantation in vivo in a murine model of volumetric muscle loss injury

Volumetric muscle loss (VML) can result from trauma and surgery in civilian and military populations, resulting in irrecoverable functional and cosmetic deficits that cannot be effectively treated with current therapies. Previous work evaluated a bioreactor-based tissue engineering approach in which muscle derived cells (MDCs) were seeded onto bladder acellular matrices (BAM) and mechanically preconditioned. This first generation tissue engineered muscle repair (TEMR) construct exhibited a largely differentiated cellular morphology consisting primarily of myotubes, and moreover, significantly improved functional recovery within 2 months of implantation in a murine latissimus dorsi (LD) muscle with a surgically created VML injury. The present report extends these initial observations to further document the importance of the cellular phenotype and composition of the TEMR construct in vitro to the functional recovery observed following implantation in vivo. To this end, three distinct TEMR constructs were created by seeding MDCs onto BAM as follows: (1) a short-term cellular proliferation of MDCs to generate primarily myoblasts without bioreactor preconditioning (TEMR-1SP), (2) a prolonged cellular differentiation and maturation period that included bioreactor preconditioning (TEMR-1SPD; identical to the first generation TEMR construct), and (3) similar treatment as TEMR-1SPD but with a second application of MDCs during bioreactor preconditioning (TEMR-2SPD); simulating aspects of "exercise" in vitro. Assessment of maximal tetanic force generation on retrieved LD muscles in vitro revealed that TEMR-1SP and TEMR-1SPD constructs promoted either an accelerated (i.e., 1 month) or a prolonged (i.e., 2 month postinjury) functional recovery, respectively, of similar magnitude. Meanwhile, TEMR-2SPD constructs promoted both an accelerated and prolonged functional recovery, resulting in twice the magnitude of functional recovery of either TEMR-1SP or TEMR-1SPD constructs. Histological and molecular analyses indicated that TEMR constructs mediated functional recovery via regeneration of functional muscle fibers either at the interface of the construct and the native tissue or within the BAM scaffolding independent of the native tissue. Taken together these findings are encouraging for the further development and clinical application of TEMR constructs as a VML injury treatment.

Decellularized rabbit cricoarytenoid dorsalis muscle for laryngeal regeneration

OBJECTIVES

Although considerable progress has been made in regenerative medicine, a quantum step would be the replacement and/or regeneration of functional muscle tissue. For example, although patients' airways can now be successfully replaced with stem cell-based techniques, a much greater patient need would be addressed by regeneration of the muscles required for engineering a functional larynx, in which active movement is critical. The rabbit cricoarytenoid dorsalis muscle was chosen for the present study because it is equivalent to the posterior cricoarytenoid muscle, the only significant abductor muscle in human larynges.

METHODS

Rabbit cricoarytenoid dorsalis muscles were harvested, and different decellularization methods were compared by use of a combination of histologic, immunohistochemical, and molecular techniques. Decellularized scaffolds were implanted into Sprague-Dawley rats as part of a 2-week biocompatibility study to assess immunogenicity.

RESULTS

Decellularization with a combination of latrunculin B, potassium iodide, potassium chloride, and deoxyribonuclease resulted in total DNA clearance and reduced levels of major histocompatibility complex class II expression, with relative preservation of the scaffold's structural integrity (collagen, elastin, and glycosaminoglycan content). The scaffolds showed minimal signs of rejection at 2 weeks in a cross-species (xenotransplantation) study.

CONCLUSIONS

Decellularized laryngeal muscles, which are nonimmunogenic, may provide the optimal scaffold source for the generation of a fully functional tissue-engineered larynx.

Biologic scaffold composed of skeletal muscle extracellular matrix

Biologic scaffolds prepared from the extracellular matrix (ECM) of decellularized mammalian tissues have been shown to facilitate constructive remodeling in injured tissues such as skeletal muscle, the esophagus, and lower urinary tract, among others. The ECM of every tissue has a unique composition and structure that likely has direct effects on the host response and it is plausible that ECM harvested from a given tissue would provide distinct advantages over ECM harvested from nonhomologous tissues. For example, a tissue specific muscle ECM scaffold may be more suitable for constructive remodeling of skeletal muscle than non-homologous ECM tissue sources. The present study describes an enzymatic and chemical decellularization process for isolating skeletal muscle ECM scaffolds using established decellularization criteria and characterized the structure and chemical composition of the resulting ECM. The results were compared to those from a non-muscle ECM derived from small intestine (SIS). Muscle ECM was shown to contain growth factors, glycosaminoglycans, and basement membrane structural proteins which differed from those present in SIS. Myogenic cells survived and proliferated on muscle ECM scaffolds in vitro, and when implanted in a rat abdominal wall injury model in vivo was shown to induce a constructive remodeling response associated with scaffold degradation and myogenesis in the implant area; however, the remodeling outcome did not differ from that induced by SIS by 35 days post surgery. These results suggest that superior tissue remodeling outcomes are not universally dependent upon homologous tissue derived ECM scaffold materials.

Muscle repair and regeneration: stem cells, scaffolds, and the contributions of skeletal muscle to amphibian limb regeneration

Skeletal muscle possesses a robust innate capability for repair of tissue damage. Natural repair of muscle damage is a stepwise process that requires the coordinated activity of a number of cell types, including infiltrating macrophages, resident myogenic and non-myogenic stem cells, and connective tissue fibroblasts. Despite the proficiency of this intrinsic repair capability, severe injuries that result in significant loss of muscle tissue overwhelm the innate repair process and require intervention if muscle function is to be restored. Recent advances in stem cell biology, regenerative medicine, and materials science have led to attempts at developing tissue engineering-based methods for repairing severe muscle defects. Muscle tissue also plays a role in the ability of tailed amphibians to regenerate amputated limbs through epimorphic regeneration. Muscle contributes adult stem cells to the amphibian regeneration blastema, but it can also contribute blastemal cells through the dedifferentiation of multinucleate myofibers into mononuclear precursors. This fascinating plasticity and its contributions to limb regeneration have prompted researchers to investigate the potential for mammalian muscle to undergo dedifferentiation. Several works have shown that mammalian myotubes can be fragmented into mononuclear cells and induced to re-enter the cell cycle, but mature myofibers are resistant to fragmentation. However, recent works suggest that there may be a path to inducing fragmentation of mature myofibers into proliferative multipotent cells with the potential for use in muscle tissue engineering and regenerative therapies.

The potential of stem cells in the treatment of skeletal muscle injury and disease

Tissue engineering is a pioneering field with huge advances in recent times. These advances are not only in the understanding of how cells can be manipulated but also in potential clinical applications. Thus, tissue engineering, when applied to skeletal muscle cells, is an area of huge prospective benefit to patients with muscle disease/damage. This could include damage to muscle from trauma and include genetic abnormalities, for example, muscular dystrophies. Much of this research thus far has been focused on satellite cells, however, mesenchymal stem cells have more recently come to the fore. In particular, results of trials and further research into their use in heart failure, stress incontinence, and muscular dystrophies are eagerly awaited. Although no doubt, stem cells will have much to offer in the future, the results of further research still limit their use.

Biologic scaffold remodeling in a dog model of complex musculoskeletal injury

BACKGROUND

Current treatment principles for muscle injuries with volumetric loss have been largely derived from empirical observations. Differences in severity or anatomic location have determinant effects on the tissue remodeling outcome. Biologic scaffolds composed of extracellular matrix (ECM) have been successfully used to restore vascularized, innervated, and contractile skeletal muscle in animal models but limited anatomic locations have been evaluated. The aim of this study was to determine the ability of a xenogeneic ECM scaffold to restore functional skeletal muscle in a canine model of a complex quadriceps injury involving bone, tendon, and muscle.

MATERIALS AND METHODS

Sixteen dogs were subjected to unilateral resection of the distal third of the vastus lateralis and medial half of the distal third of the vastus medialis muscles including the proximal half of their associated quadriceps tendon. This defect was replaced with a biologic scaffold composed of small intestinal submucosa extracellular matrix (SIS-ECM) and the remodeling response was evaluated at 1, 2, 3, and 6 mo (N = 4 per group).

RESULTS

The initial remodeling process followed a similar pattern to other studies of ECM-mediated muscle repair with rapid vascularization and migration of myoblasts into the defect site. However, over time the remodeling response resulted in the formation of dense collagenous tissue with islands of muscle in the segments of the scaffold not in contact with bone, and foci of bone and cartilage in the segments that were adjacent to the underlying bone.

CONCLUSIONS

SIS-ECM was not successful at restoring functional muscle tissue in this model. However, the results also suggest that SIS-ECM may have potential to promote integration of soft and boney tissues when implanted in close apposition to bone.

A tissue-engineered muscle repair construct for functional restoration of an irrecoverable muscle injury in a murine model

There are no effective clinical treatments for volumetric muscle loss (VML) resulting from traumatic injury, tumor excision, or other degenerative diseases of skeletal muscle. The goal of this study was to develop and characterize a more clinically relevant tissue-engineered muscle repair (TE-MR) construct for functional restoration of a VML injury in the mouse lattissimus dorsi (LD) muscle. To this end, TE-MR constructs developed by seeding rat myoblasts on porcine bladder acellular matrix were preconditioned in a bioreactor for 1 week and implanted in nude mice at the site of a VML injury created by excising 50% of the native LD. Two months postinjury and implantation of TE-MR, maximal tetanic force was ∼72% of that observed in native LD muscle. In contrast, injured LD muscles that were not repaired, or were repaired with scaffold alone, produced only ∼50% of native LD muscle force after 2 months. Histological analyses of LD tissue retrieved 2 months after implantation demonstrated remodeling of the TE-MR construct as well as the presence of desmin-positive myofibers, blood vessels, and neurovascular bundles within the TE-MR construct. Overall, these encouraging initial observations document significant functional recovery within 2 months of implantation of TE-MR constructs and provide clear proof of concept for the applicability of this technology in a murine VML injury model.

Regeneration of skeletal muscle

Skeletal muscle has a robust capacity for regeneration following injury. However, few if any effective therapeutic options for volumetric muscle loss are available. Autologous muscle grafts or muscle transposition represent possible salvage procedures for the restoration of mass and function but these approaches have limited success and are plagued by associated donor site morbidity. Cell-based therapies are in their infancy and, to date, have largely focused on hereditary disorders such as Duchenne muscular dystrophy. An unequivocal need exists for regenerative medicine strategies that can enhance or induce de novo formation of functional skeletal muscle as a treatment for congenital absence or traumatic loss of tissue. In this review, the three stages of skeletal muscle regeneration and the potential pitfalls in the development of regenerative medicine strategies for the restoration of functional skeletal muscle in situ are discussed.