3D-bioprinted GelMA nerve guidance conduits promoted peripheral nerve regeneration by inducing trans-differentiation of MSCs into SCLCs via PIEZO1/YAP axis

Schwann cells (SCs)-based nerve guidance conduits (NGCs) is a promising strategy for repairing long-gap peripheral nerve injury (PNI). But the number of SCs is limited as terminally differentiated cells. Matrix stiffness is able to direct cell fate of stem cells. And nerve-special stiffness (NSS) may contribute to stem cells converting into SCs. However, the potential mechanisms remain uncertain. The present study aimed to elucidate whether the given NSS was able to promote mesenchymal stem cells (MSCs) trans-differentiating into Schwann cell-like cells (SCLCs), facilitating cell-based NGCs repairing PNI. Gelatin methacryloylate (GelMA) hydrogels with different stiffness were manufactured, and their roles in the trans-differentiation of MSCs into SCLCs were investigated in vitro study. The most favorable stiffness (0.9–2.9 kPa) for trans-differentiation and neurotrophic factors expression was confirmed by western blot and immunofluorescence assays. The reason might lie in softer stiffness stretched cell morphology, leading to up-regulation of PIEZO1 and then activating YAP nuclear translocation. As for in vivo study, multi-channel NGCs containing SCLCs were fabricated with extrusion-based bioprinting and then filled a 5 mm gap in sciatic nerve defect of SD rats. It turned out that GelMA-made NGCs with stiffness of 2.9 kPa achieved promising neurogenerative capacity, not only promoting recovering sensory and motor functions, but also improving myelinated nerve fiber regeneration. Our findings demonstrated that 0.9–2.9 kPa might be the desired mechanical strength inducing trans-differentiation into SCLCs via PIEZO1/YAP axis, and the 3D-printed GelMA NGCs combined with SCLCs could be a potential candidate for long-gap peripheral nerve injury.