Further Development of a Tissue Engineered Muscle Repair ConstructIn Vitrofor Enhanced Functional Recovery Following ImplantationIn Vivoin a Murine Model of Volumetric Muscle Loss Injury

Abstract

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.

Evaluation of adipose-derived stem cells for tissue-engineered muscle repair construct-mediated repair of a murine model of volumetric muscle loss injury

“…Although the definitive mechanism for TEMR-ADSC construct-based VML repair is not yet clear, the apparent lack of equivalent regeneration in the NR and R-S groups (groups lacking donor cells), as was demonstrated from prior reports, 16,17 indicates the vital role played by ADSCs in this process. Scaffolds seeded with either MDCs or ADSCs displayed signs of scaffold remodeling and neotissue formation (Figures 2 and 3).…”

“…Approaches in this vein currently under development include those employing an acellular scaffold, 10,11 stem or progenitor cells, [12][13][14][15] or a combination of both. [16][17][18] Several groups have reported variable neotissue formation and functional recovery in skeletal muscle injuries by use of either satellite cell-derived muscle progenitor cells 19 or mesenchymal stem cells (MSCs). [20][21][22][23] In contrast to these approaches, recent reports 16,17 have focused on VML injury repair with tissueengineered muscle repair (TEMR) constructs generated by seeding muscle-derived progenitor cells (MDCs) on bladder acellular matrix (BAM) scaffolds and subjecting them to in vitro differentiation and maturation in a bioreactor.…”

“…[16][17][18] Several groups have reported variable neotissue formation and functional recovery in skeletal muscle injuries by use of either satellite cell-derived muscle progenitor cells 19 or mesenchymal stem cells (MSCs). [20][21][22][23] In contrast to these approaches, recent reports 16,17 have focused on VML injury repair with tissueengineered muscle repair (TEMR) constructs generated by seeding muscle-derived progenitor cells (MDCs) on bladder acellular matrix (BAM) scaffolds and subjecting them to in vitro differentiation and maturation in a bioreactor. Although these studies elegantly demonstrated the utility of TEMR for the treatment of VML injuries in flat sheet-based muscles such as latissimus dorsi (LD) in rodents, 16 several obstacles to scaling up the technology still remain for successful application of TEMR constructs to large injuries in humans, especially complex traumatic injuries sustained both on and off the battlefield.…”

“…Abbreviations: aDsc, adipose-derived stem cell; TeMr, tissue engineered muscle repair; BaM, bladder acellular matrix; TeMr-lenti-cherry-aDsc, tissue engineered muscle repair construct created with seeding aDscs that were labeled with lentivirally expressing cherry reporter; Ihc, immunohistochemistry. 16,17 whereas TEMR-ADSC constructs primarily displayed an undifferentiated phenotype. ADSCs on BAM scaffolds were left undifferentiated because prior reports suggested that ADSC differentiation best occurred only in the presence of cocultured muscle cells.…”

“…In this category, recent reports based on TEMR constructs for repair of VML injuries in murine LD model restored functional values to ~60%-70% of native uninjured muscle, 2 months postrepair. 16,17 While both studies utilized MDCs for the generation of TEMR constructs, this study differs from the previous studies in that it seeks to explore the potential of alternative cell source, namely, ADSCs for VML injury repair with TEMR-based approach.…”