A growing body of studies indicate that small noncoding RNAs, especially microRNAs (miRNA), play a crucial role in response to peripheral nerve injuries. During Wallerian degeneration and regeneration processes, they orchestrate several pathways, in particular the MAPK, AKT, and EGR2 (KROX20) pathways. Certain miRNAs show specific expression profiles upon a nerve lesion correlating with the subsequent nerve regeneration stages such as dedifferentiation and with migration of Schwann cells, uptake of debris, neurite outgrowth and finally remyelination of regenerated axons. This review highlights (a) the specific expression profiles of miRNAs upon a nerve lesion and (b) how miRNAs regulate nerve regeneration by acting on distinct pathways and linked proteins. Shedding light on the role of miRNAs associated with peripheral nerve regeneration will help researchers to better understand the molecular mechanisms and deliver targets for precision medicine.

Dragline silk of Trichonephila spiders has attracted attention in various applications. One of the most fascinating uses of dragline silk is in nerve regeneration as a luminal filling for nerve guidance conduits. In fact, conduits filled with spider silk can measure up to autologous nerve transplantation, but the reasons behind the success of silk fibers are not yet understood. In this study dragline fibers of Trichonephila edulis were sterilized with ethanol, UV radiation, and autoclaving and the resulting material properties were characterized with regard to the silk's suitability for nerve regeneration. Rat Schwann cells (rSCs) were seeded on these silks in vitro and their migration and proliferation were investigated as an indication for the fiber's ability to support the growth of nerves. It was found that rSCs migrate faster on ethanol treated fibers. To elucidate the reasons behind this behavior, the fiber's morphology, surface chemistry, secondary protein structure, crystallinity, and mechanical properties were studied. The results demonstrate that the synergy of dragline silk's stiffness and its composition has a crucial effect on the migration of rSCs. These findings pave the way towards understanding the response of SCs to silk fibers as well as the targeted production of synthetic alternatives for regenerative medicine applications.

Peripheral nerve reconstruction through the employment of nerve guidance conduits with Trichonephila dragline silk as a luminal filling has emerged as an outstanding preclinical alternative to avoid nerve autografts. Yet, it remains unknown whether the outcome is similar for silk fibers harvested from other spider species. This study compares the regenerative potential of dragline silk from two orb‐weaving spiders, Trichonephila inaurata and Nuctenea umbratica, as well as the silk of the jumping spider Phidippus regius. Proliferation, migration, and transcriptomic state of Schwann cells seeded on these silks are investigated. In addition, fiber morphology, primary protein structure, and mechanical properties are studied. The results demonstrate that the increased velocity of Schwann cells on Phidippus regius fibers can be primarily attributed to the interplay between the silk's primary protein structure and its mechanical properties. Furthermore, the capacity of silk fibers to trigger cells toward a gene expression profile of a myelinating Schwann cell phenotype is shown. The findings for the first time allow an in‐depth comparison of the specific cellular response to various native spider silks and a correlation with the fibers’ material properties. This knowledge is essential to open up possibilities for targeted manufacturing of synthetic nervous tissue replacement.

Reconstruction of long‐segment peripheral nerve gaps remains a clinical challenge, as neither autografts nor FDA‐approved nerve conduits achieve satisfactory functional recovery. Conduits filled with native Trichonephila dragline silk show promise for nerve defects exceeding the critical length, but translating natural silk to clinical use has limitations, necessitating research into recombinant silk replica. The search for optimal silk templates is ongoing, with numerous spider species still unexplored. This study aims to compare the ability of four native silk fibers from phylogenetically diverse spider families to support nerve regeneration. The influence of fiber morphology, primary and secondary protein structures, surface charge, chemical composition, and mechanical properties on the initial cell attachment is studied. Results demonstrate that silk collected from Peucetia lucasi do not adequately support Schwann cell adhesion, which is caused by the lack of a lipid layer and the limited fiber wettability. This reduced wettability, governed by the ratio of hydrophilic and hydrophobic amino acids of silk, is particularly relevant when considering the deployment of uncoated artificial silk fibers for neural tissue engineering. This knowledge is crucial for paving the way toward full functional recovery after peripheral nerve injury via implanting advanced synthetic nerve guidance conduits enhanced with luminal silk alternatives.

Peripheral nerve regeneration depends on close interaction between neurons and Schwann cells (SCs). After nerve injury, SCs produce growth factors and cytokines that are crucial for axon re-growth. Previous studies revealed the supernatant of SCs exposed to nuclear magnetic resonance therapy (NMRT) treatment to increase survival and neurite formation of rat dorsal root ganglion (DRG) neurons in vitro. The aim of this study was to identify factors involved in transferring the observed NMRT-induced effects to SCs and consequently to DRG neurons. Conditioned media of NMRT-treated (CM NMRT) and untreated SCs (CM CTRL) were tested by beta-nerve growth factor (ßNGF) ELISA and multiplex cytokine panels to profile secreted factors. The expression of nociceptive transient receptor potential vanilloid 1 (TRPV1) channels was assessed and the intracellular calcium response in DRG neurons to high-potassium solution, capsaicin or adenosine triphosphate was measured mimicking noxious stimuli. NMRT induced the secretion of ßNGF and pro-regenerative-signaling factors. Blocking antibody experiments confirmed ßNGF as the main factor responsible for neurotrophic/neuritogenic effects of CM NMRT. The TRPV1 expression or sensitivity to specific stimuli was not altered, whereas the viability of cultured DRG neurons was increased. Positive effects of CM NMRT supernatant on DRG neurons are primarily mediated by increased ßNGF levels.

Spider silk is an extraordinary natural material that combines strength, extensibility, and toughness in a lightweight, protein-based fiber. While the recombinant production of spidroins has advanced, the creation of silk fibers with additional intrinsic functionalities, such as color, remains a major challenge. Here, we report the rational design, expression, and spinning of intrinsically red-colored artificial silk fibers. A mini-spidroin variant was engineered as a fusion with the red fluorescent protein mCherry, expressed at high yields (20 g/L) in E. coli fed-batch fermentations, and purified under native conditions. Although the presence of the mCherry globular domain reduced spinnability when used alone, blending with wild-type mini-spidroins enabled continuous wet spinning into robust, fluorescent fibers. Our biomimetic spinning approach preserved the correct folding of the mCherry domain within the fiber, resulting in stable red coloration and fluorescence, while maintaining mechanical properties comparable to those of other recombinant silks. This work establishes a scalable, sustainable strategy for fabricating colored bio-based fibers, opening avenues for environmentally friendly textiles and functional biomaterials that may reduce reliance on synthetic and chemically dyed fibers.