Investigation of the effects of bioactive peptide nanofibers on acute muscle injury regeneration

Abstract

Skeletal muscle constitutes a large part of the human body. It is a hierarchically organized heterogeneous tissue and is composed of muscle fiber bundles, muscle fibers, myofibrils and myofilaments. Since muscle cells are terminally differentiated, they have limited capacity to renew themselves. Only new cells can fuse with muscle fibers and increase the size and volume of skeletal muscle. Myosatellite cells or satellite cells are small, mononuclear progenitor cells with virtually no cytoplasm. They are located in between the sarcolemma and basement membrane of terminally-differentiated muscle fibers. Satellite cells are precursors to skeletal muscle cells, and are able to give rise to satellite cells or differentiated skeletal muscle cells. They are normally found in silent state in adult muscle, but act as a reserve cell population that is able to proliferate in response to injury and give rise to regenerated muscle and to more satellite cells. Formation of the new muscular tissue is called myogenesis. During this event, satellite cells differentiate into myoblasts, and then myoblasts fuse with each other in order to form myofibers. There are many genes that regulate the myogenesis process and each of them is activated in a different step of myogenesis. Increased or decreased levels of gene expression determine the differentiation capacity. Peptide nanofibers are supramolecular structures formed via self-assembly and they are promising molecules in regenerative medicine and tissue engineering. Peptide-based molecules for tissue regeneration is a widely studied area and currently used in the treatment-investigation of many different tissues such as bone, cartilage, skin and nerve. Since laminin is one of the most abundant proteins found in the basal membrane of the skeletal muscle; in this thesis, we designed and synthesized a laminin-mimetic bioactive (LM/E-PA) molecule functionalized with bioactive groups for mimicking laminin activities and capable of accelerating satellite cell activation. Our research group had previously shown that LM/E-PA containing nanofibers can support muscle differentiation in vitro. In this thesis, the clinical relevance was demonstrated further by assessing laminin-mimetic bioactive scaffold in acute muscle injury in an in vivo rat model. Our findings revealed that this scaffold system significantly promotes satellite cell activation in skeletal muscle and accelerates regeneration following acute muscle injury. In addition, our findings show that the regeneration capacity of the skeletal muscle was increased and consequently regeneration time was reduced. This study is one of the first examples of molecular level and tissue level regeneration of skeletal muscle by using bioactive peptide nanofibers following acute muscle injury, and shows that laminin mimetic nanofiber system is a promising material for development of new therapeutic curatives for acute skeletal muscle injuries.