Reviewed by New Harvest Journal Club’s Mark Middleton and John Nahay.
Abstract: Skeletal muscle tissue engineering is a promising interdisciplinary specialty which aims at the reconstruction of skeletal muscle loss caused by traumatic injury, congenital defects, or tumor ablations. Due to the difficulty in procuring donor tissue, the possibilities for alternative treatment like autologous grafting (e.g. muscle flaps) are limited. This process also presents consistent problems with donor-site morbidity. Skeletal muscle tissue engineering tries to overcome this problem by generating new, functional muscle tissue from autologous precursor cells (stem cells). Multiple stem cells from different sources can be utilized for restoration of differentiated skeletal muscle tissue using tissue engineering principles. After 15 years of intensive research in this emerging field, for the first time, solutions using different strategies (e.g. embryonic stem cells, arterio-venous (AV) loop models, etc.) are being presented to resolve problems like vascularisation of tissue-engineered constructs. This article reviews recent findings in skeletal muscle tissue engineering and outlines its relevance to clinical applications in reconstructive surgery.
Overview: This paper focuses on skeletal muscle tissue engineering for clinical uses, and describes advances in both in vitro and in vivo methods, including stimulating myoblasts to differentiate into myofibers, the use of scaffolds, and vascularization of tissue in vitro.
Key Points:
- Natural process of skeletal muscle renewal occurs by satellite myoblasts differentiating into multinucleated myotubes.
- In the case of muscle injury, local myoblasts are activated to start regenerating tissue, but scar tissue with reduced regenerative capacity forms as well.
- Muscle satellite cells can also give rise to bone and fat tissue after treatment with biochemical signals.
- An extracellular matrix (ECM) scaffold is not necessary, but effective, in creating 3D skeletal muscle tissue.
- An ideal ECM would have an optimal surface for cell proliferation and differentiation, be resorbable, and have a high affinity for biological surfaces. Other characteristics that may not be a concern for meat production are biocompatibility and nonimmunogenicity.
- Scaffold materials that have been used successfully are polyglycolic acid meshes, alginate, hyaluronic acid-hydrogels, Matrigel®, and fibrin.
- In vitro, there must be stimulating factors to initiate fusion of myosatellite cells into myofibers, such as co-cultivating neuronal tissue, adding growth factors, mechanical stimulation, or electrical stimulation.
- Electrical stimulation can increase cell proliferation, but in a 3D environment does not induce differentiation of myoblasts into myofibers.
- Vascularization is a fundamental concern in skeletal muscle tissue engineering, because skeletal muscle is a complex tissue with high energy and oxygen demand, and without vascularization to deliver nutrients and oxygen, tissue will not grow thicker than a distance through which nutrients and oxygen can diffuse.
- Experiments have been done with in vitro vascularization using mouse myoblasts, human embryonic or umbilical vein endothelial cells on a scaffold, and found that the myoblasts differentiated into muscle fibers, and the endothelial cells formed a vessel system. Then, mouse embryonic fibroblasts (a type of cell that synthesizes extracellular matrix and collagen) were added, which supported and stabilized the vessel system.
- This pre-vascularization was found to improve cell survival rates and blood perfusion when tissues were implanted back into mice.
Notable Statistics:
- A biopsy of 0.1 cubic cm of muscle tissue can give rise to 5000 proliferating cells
Glossary:
- autologous cells – cells which were taken from the same patient we want to heal (will not cause autoimmune response)
- differentiating – cell which change their role to a more specific type of cells
- in vitro – literally, “in glass”: experiments that are not done inside an animal (like in petri dish)
- in vivo – experiments that are done in/inside a (living) animal
- immunogenicity – something that can cause an immune response
- loop models – loop refers to a chemical molecule which runs outside then back inside a cell membrane and acts as a signal, or, as wikipedia puts it
- loop modeling is a problem in protein structure prediction requiring the prediction of the conformations of loop regions in proteins with or without the use of a structural template.
- myo – things that are related to muscles
- myoblasts – a single nucleus muscle cell that can become a mature muscle cell once it is merged with other myoblasts
- myosatellite – cells that can split many times and later differentiate (=turn into) myoblasts
- myotubes – (“muscle tubes”) the mature muscle. after myoblasts merge they turn into a myotube – an elongated cell with lots of nuclei
