Endoneurial extracellular matrix influences regeneration and maturation of motor nerve axons--a model of acellular nerve graft

Decellularized nerve matrix hydrogel scaffolds with longitudinally oriented and size-tunable microchannels for peripheral nerve regeneration

The scaffolding biomaterials and their internal structures are crucial in constructing growth-permissive microenvironment for tissue regeneration. A functional bioscaffold not only requires sufficient extracellular matrix components, but also provides topological guidance by mimicry of the ultrastructure of the native tissue. In our laboratory, a decellularized nerve matrix hydrogel derived from porcine sciatic nerve (pDNM-G) is successfully prepared, which shows great promise for peripheral nerve regeneration. Herein, longitudinally oriented microchannel structures were introduced into pDNM-G bioscaffolds (A-pDNM-G) through controlled unidirectional freeze-drying. The axially aligned microchannels effectively directed and significantly promoted neurite extension and Schwann cell migration, assessed by culturing dorsal root ganglion explants on the longitudinal sections of A-pDNM-G scaffolds. Such regenerative cellular responses can be further optimized by tuning the channel sizes. In vivo studies confirmed that the implanted nerve guidance conduits containing A-pDNM-G scaffolds significantly facilitated axonal extension, myelination, and reached considerable functional recovery in 15-mm rat sciatic nerve defects. The incorporation of nerve growth factor further improved the overall performance in the grafted nerve. The bioactive pDNM-G enables controlled release of neurotrophic factor and easy integration of topological cue provided by the axially aligned microchannels into implantable bioscaffolds, which may serve in future clinical treatments of peripheral nerve injury.

DPSCs seeded in acellular nerve grafts processed by Myroilysin improve nerve regeneration

Since synthetic nerve conduits do not exhibit ideal regeneration characteristics, they are generally inadequate substitutes for autologous nerve grafts in the repair of long peripheral nerve defects. To resolve this problem, in this study, a nerve regeneration acellular nerve graft (ANG) with homologous dental pulp stem cells (DPSCs) was constructed. Xenogeneic ANG was processed by Myroilysin to completely remove cells and myelin sheath, while preserving extracellular matrix (ECM) microstructure of the natural nerve. The study revealed that ANG could support cell attachment and proliferation and did not stimulate a vigorous host rejection response. After inoculation of rabbit DPSCs (r-DPSCs) onto ANG, cells were observed to align along the longitudinal axis of the acellular nerve matrix (ANM) and persistently express NGF and BDNF. Undifferentiated r-DPSCs also presented glial cell characteristics and promoted nerve regeneration after transplantation in vivo. We repaired 1 cm purebred New Zealand White Rabbits sciatic nerve defects using this nerve graft construction, and nerve gap regeneration was indicated by electrophysiological and histological analysis. Therefore, we conclude that the combination of an ANG processed by Myroilysin with DPSCs providing a microenvironment that increases nerve regeneration for repairing peripheral nerve defects.

Immunoregulation effects of bone marrow-derived mesenchymal stem cells in xenogeneic acellular nerve grafts transplant

This study evaluated whether bone marrow-derived mesenchymal stem cells (BM-MSCs) combined with xenogeneic acellular nerve grafts (xANGs) would reduce the inflammation reaction of xANGs transplantation. BM-MSCs were extracted, separated, purified, and cultured from the bone marrow of rats. Then BM-MSCs were seeded into 5 mm xANGs as experimental group, while xANGs group was chosen as control. Subcutaneous implantation and nerve grafts transplantation were done in this study. Walking-track tests, electrophysiological tests, H&E staining, and immunostaining of CD4, CD8, and CD68 of subcutaneous implantations, cytokine concentrations of IL-2, IL-10, IFN-γ and TNF-α in lymphocytes supernatants and serum of the two groups were evaluated. Walking-track tests and electrophysiological tests suggested the group of BM-MSCs with xANGs obtained better results than xANGs group (P < 0.05). H&E staining and immunostaining of CD4, CD8, and CD68 of subcutaneous implantations showed there were less inflammatory cells in the group of BM-MSCs when compared with the xANGs group. The cytokine concentrations of IL-2, IFN-γ, and TNF-α in BM-MSCs group were lower than xANGs group in lymphocytes supernatants and serum (P < 0.05). However, IL-10 concentrations in BM-MSCs group were higher than xANGs group (P < 0.05). xANG with BM-MSCs showed better nerve repair function when compared with xANG group. Furthermore, xANG with BM-MSCs showed less inflammatory reaction which might indicate the reason of its better nerve regeneration.

Schwann-like cells seeded in acellular nerve grafts improve nerve regeneration

BACKGROUND

This study evaluated whether Schwann-like cells (SLCs) induced from bone marrow-derived mesenchymal stem cells (BM-MSCs) transplanted into acellular nerve grafts (ANGs) could repair nerve defects compared with nerve isografts and ANGs with BM-MSCs.

METHODS

BM-MSCs extracted, separated and purified from the bone marrow of rats, and some of the BM-MSCs were cultured with mixed induction agents that could induce BM-MSCs into SLCs. Either SLCs or BM-MSCs were seeded onto 10-mm ANGs, and the isografts were chosen as the control. The walking-track test, tibialis anterior muscle weight measurement, electrophysiological examination, toluidine blue staining, transmission electron micrographs and immunostaining of S-100 and VEGF in these three groups were evaluated in a 10-mm rat sciatic injury-repair model.

RESULTS

The walking-track test, tibialis anterior muscle weight measurement and electrophysiological examination of the sciatic nerve suggested the groups of ANGs with SLCs and isografts obtained better results than the BM-MSC group (P<0.05). Meanwhile, the results of the SLCs and isograft groups were similar (P>0.05). All the histomorphometric analyses (toluidine blue staining, transmission electron micrographs and immunostaining of S-100 and VEGF) showed that there were more regenerating nerve fibers in the group of ANGs with SLCs than the BM-MSCs (P<0.05), but there was no significant difference between the SLC and isograft groups (P>0.05).

CONCLUSIONS

SLCs seeded in ANGs and isografts show better functional regeneration compared with BM-MSCs seeded in ANGs. Additionally, SLCs combined with ANGs present almost the same outcome as the isografts. Therefore, SLCs with ANGs can be a good choice in nerve defect repairs.