Impact of Human Recombinant Irisin on Tissue-Engineered Skeletal Muscle Structure and Function.

Tissue engineering of exogenous skeletal muscle units (SMUs) through isolation of muscle satellite cells from muscle biopsies is a potential treatment method for acute volumetric muscle loss (VML). A current issue with this treatment process is the limited capacity for muscle stem cell (satellite cell) expansion in cell culture, resulting in a decreased ability to obtain enough cells to fabricate SMUs of appropriate size and structural quality and that produce native levels of contractile force. This study determined the impact of human recombinant irisin on the growth and development of three-dimensional (3D) engineered skeletal muscle. Muscle satellite cells were cultured without irisin (control) or with 50, 100, or 250 ng/mL of irisin supplementation. Light microscopy was used to analyze myotube formation with particular focus placed on the diameter and density of the monotubes during growth of the 3D SMU. Following the formation of 3D constructs, SMUs underwent measurement of maximum tetanic force to analyze contractile function, as well as immunohistochemical staining, to characterize muscle structure. The results indicate that irisin supplementation with 250 ng/mL significantly increased the average diameter of myotubes and increased the proliferation and differentiation of myoblasts in culture but did not have a consistent significant impact on force production. In conclusion, supplementation with 250 ng/mL of human recombinant irisin promotes the proliferation and differentiation of myotubes and has the potential for impacting contractile force production in scaffold-free tissue-engineered skeletal muscle.

Repairing Volumetric Muscle Loss with Commercially Available Hydrogels in an Ovine Model.

Volumetric muscle loss (VML) is the loss of skeletal muscle that exceeds the muscle's self-repair mechanism and leads to permanent functional deficits. In a previous study, we demonstrated the ability of our scaffold-free, multiphasic, tissue-engineered skeletal muscle units (SMUs) to restore muscle mass and force production. However, it was observed that the full recovery of muscle structure was inhibited due to increased fibrosis in the repair site. As such, novel biomaterials such as hydrogels (HGs) may have significant potential for decreasing the acute inflammation and subsequent fibrosis, as well as enhancing skeletal muscle regeneration following VML injury and repair. The goal of the current study was to assess the biocompatibility of commercially available poly(ethylene glycol), methacrylated gelatin, and hyaluronic acid (HA) HGs in combination with our SMUs to treat VML in a clinically relevant large animal model. An acute 30% VML injury created in the sheep peroneus tertius (PT) muscle was repaired with or without HGs and assessed for acute inflammation (incision swelling) and white blood cell counts in blood for 7 days. At the 7-day time point, HA was selected as the HG to use for the combined HG/SMU repair, as it exhibited a reduced inflammation response compared to the other HGs. Six weeks after implantation, all groups were assessed for gross and histological structural recovery. The results showed that the groups repaired with an SMU (SMU-Only and SMU+HA) restored muscle mass to greater degree than the groups with only HG and that the SMU groups had PT muscle masses that were statistically indistinguishable from its uninjured contralateral PT muscle. Furthermore, the HA HG, SMU-Only, and SMU+HA groups displayed notable efficacy in diminishing pro-inflammatory markers and showed an increased number of regenerating muscle fibers in the repair site. Taken together, the data demonstrates the efficacy of HA HG in decreasing acute inflammation and fibrotic response. The combination of HA and our SMUs also holds promise to decrease acute inflammation and fibrosis and increase muscle regeneration, advancing this combination therapy toward clinically relevant interventions for VML injuries in humans.