Mini review: Biomaterials in repair and regeneration of nerve in a volumetric muscle loss

Abstract

Volumetric muscle loss (VML) following a severe trauma or injury is beyond the intrinsic regenerative capacity of muscle tissues, and hence interventional therapy is required. Extensive muscle loss concomitant with damage to neuromuscular components overwhelms the muscles' remarkable regenerative capacity. The loss of nervous and vascular tissue leads to further damage and atrophy, so a combined treatment for neuromuscular junction (NMJ) along with the volumetric muscle regeneration is important. There have been immense advances in the field of tissue engineering for skeletal muscle tissue and peripheral nerve regeneration, but very few address the interdependence of the tissues and the need for combined therapies to repair and regenerate fully functional muscle tissue. This review addresses the problem and presents an overview of the biomaterials that have been studied for tissue engineering of neuromuscular tissues associated with skeletal muscles.

Keywords: Muscle regeneration; Nerve regeneration; Neuromuscular junction; Tissue engineering.

Figure 1:

Illustration of the Neuromuscular Junction in Skeletal Muscle

Figure 2:

Debridement induces increase in compartment volume. Peroneus tertius muscles underwent volumetric muscle loss (VML) injury. (a & b) Twelve weeks after VML injury, fibrous tissue enveloped the anterior compartment (c & d) at which time the overlaying fibrous tissue was surgically debrided. (e) Lower limb anterior compartment volume was measured using computed tomography imaging at the times specified. Values are means ± SE. Image taken from Corona, B.T., J.C. Rivera, and S.M. Greising, Inflammatory and Physiological Consequences of Debridement of Fibrous Tissue after Volumetric Muscle Loss Injury. Clinical and translational science, 2018. 11(2): p. 208–217.

Figure 3:

Distribution of sympathetic neurons in skeletal muscle. (A) Diaphragm muscle of a DBH-Tomato mouse expressing Tomato protein in sympathetic neurons was co-stained with anti-TH antibody and BGT-AF647 (AChR). Signals from TH, Tomato, and BGT are depicted in the overlay in green, red, and blue, respectively. Three-dimensional maximum projection of a confocal z stack of a representative region is shown. All channels were brightness/contrast-enhanced. (B) Longitudinal sections of wild-type EDL muscles were labeled against VACHT, TH, and BGTAF647. Signals from these markers are depicted in the overlay in green, red, and blue, respectively. Three-dimensional maximum projection of a confocal z stack of a representative region is shown. All channels were brightness/contrast-enhanced. (C and D) EDL and soleus muscles were sectioned transversally, stained with BGT-AF555 (blue in overlay) and anti-TH antibody (red in overlay), and then imaged with confocal microscopy. (C) Representative confocal brightness/contrast-enhanced optical section from EDL. (D) Quantification of TH-positive NMJ regions from EDL and soleus (SOL) muscles. Mean ± SEM (n = 4 muscles each). Negative controls lacking primary antibodies showed 0.7 ± 0.7% (mean ± SEM, n = 4 muscles) in EDL and 0.0% (mean ± SEM, n = 4 muscles) in soleus of TH-positive NMJ regions. Image taken from Khan, M.M., et al., Sympathetic innervation controls homeostasis of neuromuscular junctions in health and disease. Proceedings of the National Academy of Sciences, 2016.

Figure 4

(Garg, 2015): Illustration of the TGF-β1 signaling pathways and the mechanism of therapeutics. ERK, Extracellular signal regulated kinase; JNK, c-Jun N-terminal kinase; LTBP, Latent transforming growth factor binding proteins; MAPKs, Mitogen-activated protein kinase; TSP-1, Thrombospondin-1. Image taken from K. Garg, B.T. Corona, T.J. Walters, Therapeutic strategies for preventing skeletal muscle fibrosis after injury, Front. Pharmacol. 6 (2015) 87. https://doi.org/10.3389/fphar.2015.00087.

Figure 5:

Supposed mechanism of PGC1-α/NRF1-NRF2 pathway anti-oxidative stress cellular defense in chronic kidney disease patients in peritoneal dialysis treatment. Oxidative stress alters the interaction of Kelch-like ECH-associated protein 1 (Keap1) and Nuclear factor erythroid-derived 2-like 2 (Nrf2), thereby liberating Nrf2 activity from repression by Keap1. NRF2 migrates into the nucleus where it activates the transcription of Superoxide dismutase 2, mitochondrial (SOD2). At the same time, oxidative stress causes the down-regulation of Peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1-α) and Nuclear respiratory factor-1 (NRF-1) with the consequent down-regulation of PGC-1α downstream target genes (TFAM, COX6C, COX7C, UQCRH and MCAD). The reduced TFAM expression causes a decrease in mitochondrial transcription and replication. The downregulation of all these factors suggests the decrease in mitochondrial OXPHOS activity to reduce ROS accumulation and creating an antioxidant feedback. Image taken from Zaza, G., et al., Downregulation of Nuclear-Encoded Genes of Oxidative Metabolism in Dialyzed Chronic Kidney Disease Patients. PLOS ONE, 2013. 8(10): p. e77847.

Figure 6:

Illustration of cell signaling cascades involved in Neuromuscular junction regeneration & remodeling

Figure 7:

Skeletal muscle cells and motor neurons were combined into a fabricated 3D co-culture system. C2C12 myoblasts were differentiated into multinucleated myotubes (a) and combined with extracellular matrix (ECM) proteins to create an engineered muscle ring tissue (b). In parallel, mouse embryonic stem cells (HBG3 mESCs) were differentiated into motor neurons (MNs) through the formation of embryoid bodies (EBs) (c and d) and then combined with the engineered muscle tissue and ECM proteins (e) on 3D-printed hydrogel devices (f and g). Once the multi-layered rings sequentially compacted and fused together, they were then placed on a stationary hydrogel skeleton (h). Scale bars, 50 μm (b and d), 500 μm (c), and 10 μm (d, inset)[1]. Image taken from Cvetkovic, C., et al., A 3D-printed platform for modular neuromuscular motor units. Microsystems & Nanoengineering, 2017. 3(1): p. 17015.