Efficacy of human muscle-stuffed vein seeded with neural-transdifferentiated human mesenchymal stem cells as a nerve conduit in rat sciatic nerve repair

Abstract

Peripheral nerve injuries are the most common injuries affecting a patient’s mobility and socio-psychology. The standard treatment – which uses autologous nerves – has a limited supply for clinical use. To address this, we investigated the efficacy of a human muscle-stuffed vein seeded with neural-transdifferentiated human mesenchymal stem cells (SMSV) as an alternative nerve conduit to repair sciatic nerve defect in athymic rats. With patient consent, mesenchymal stem cells were isolated from the bone marrows of the patients who were undergoing orthopaedic surgeries. The muscles and veins from the amputated limbs were decellularised and used in the fabrication of the MSV conduits. Quantitative RT-PCR and immunofluorescence analyses showed that human bone marrow-derived mesenchymal stem cells (MSCs) spontaneously expressed specific Schwann cell protein markers of MPZ, p75 NGFR, S100B, GFAP, at both gene and protein levels. Upon MSC neural-transdifferentiation, specific Schwann cell markers (i.e. MBP, p75 NGFR) and growth factors (i.e. NGF, GDNF) were upregulated for more than two folds at the transcript level while MPZ was consistently upregulated at the protein level. Collectively, these results showed that neural-transdifferentiated MSCs were likely to be feasible for seeding on MSV conduits to promote nerve regeneration. A 15-mm sciatic nerve defect was created in athymic rats. Each rat received either muscle-stuffed vein conduits alone (MSV), MSV seeded with neural transdifferentiated MSCs (SMSV), commercial polyglycolic acid conduits (Neurotube®; CC), reverse autografts (RA) or were left untreated (negative control; NC). Post-transplantation, functional assessments – including sciatic functional index (SFI; motor function), nerve conductivity (electrophysiological function), and withdrawal reflexes (sensory function) – were evaluated for 12 weeks, after which the grafts were harvested for histological analyses. All rats in the treated groups demonstrated a progressive increase in the mean SFI and nerve conduction amplitude; and showed positive withdrawal reflex by the 10th week of post-implantation. Histologically, harvested grafts from all except the NC groups exhibited axonal regeneration with the presence of mature myelinated axons. Autotomy, which is associated with neuropathic pain, was severe in all rats of the MSV group and one rat of the CC group; there was mild or no autotomy in the rats of other groups. In conclusion, treatment with muscle-stuffed vein conduit is comparable to that of the other treatment groups in supporting functional recovery following sciatic nerve injury. The addition of cells in the muscle-stuffed vein conduit alleviated neuropathic pain. Therefore, the efficacy of cell seeded-MSV conduits is comparable to that of the gold standard, so it can be explored as an alternative nerve conduit for peripheral nerve repairs in the future.