Keloids are disfiguring, hypertrophic scars with yet poorly understood pathomechanisms, which could lead to severe functional impairments. Here we analyzed the characteristics of keloidal cells by single cell sequencing and discovered the presence of an abundant population of Schwann cells that persisted in the hypertrophic scar tissue after wound healing. In contrast to normal skin, keloidal Schwann cells show a unique, pro-fibrotic phenotype. Our data support the hypothesis that keloidal Schwann cells contribute to the formation of the extracellular matrix and are able to affect M2 polarization of macrophages. Indeed, we show that macrophages in keloids predominantly display a M2 polarization and produce factors that inhibit Schwann cell differentiation. This study suggests the contribution of a Schwann cell - macrophage cross-talk to the continuous expansion of keloids, and that targeting Schwann cells might represent an interesting novel treatment option for keloids.

Adult Schwann cells (SCs) possess an inherent plastic potential. This plasticity allows SCs to acquire repair-specific functions essential for peripheral nerve regeneration. Here, we investigate whether stromal SCs in benign-behaving peripheral neuroblastic tumors adopt a similar cellular state. We profile ganglioneuromas and neuroblastomas, rich and poor in SC stroma, respectively, and peripheral nerves after injury, rich in repair SCs. Indeed, stromal SCs in ganglioneuromas and repair SCs share the expression of nerve repair-associated genes. Neuroblastoma cells, derived from aggressive tumors, respond to primary repair-related SCs and their secretome with increased neuronal differentiation and reduced proliferation. Within the pool of secreted stromal and repair SC factors, we identify EGFL8, a matricellular protein with so far undescribed function, to act as neuritogen and to rewire cellular signaling by activating kinases involved in neurogenesis. In summary, we report that human SCs undergo a similar adaptive response in two patho-physiologically distinct situations, peripheral nerve injury and tumor development.

Surgical resection of the cancerous tissue represents one of the few curative treatment options for neoplastic liver disease. Such partial hepatectomy (PHx) induces hepatocyte hyperplasia, which restores liver function. PHx is associated with bacterial translocation, leading to an immediate immune response involving neutrophils and macrophages, which are indispensable for the priming phase of liver regeneration. Additionally, PHx induces longer-lasting intrahepatic apoptosis. Herein, we investigated the effect of apoptotic extracellular vesicles (aEVs) on neutrophil function and their role in this later phase of liver regeneration. A total of 124 patients undergoing PHx were included in this study. Blood levels of the apoptosis marker caspase-cleaved cytokeratin-18 (M30) and circulating aEVs were analyzed preoperatively and on the first and fifth postoperative days. Additionally, the in vitro effects of aEVs on the secretome, phenotype and functions of neutrophils were investigated. Circulating aEVs increased at the first postoperative day and were associated with higher concentrations of M30, which was only observed in patients with complete liver recovery. Efferocytosis of aEVs by neutrophils induced an activated phenotype (CD11b^highCD16^highCD66b^highCD62L^low); however, classical inflammatory responses such as NETosis, respiratory burst, degranulation, or secretion of pro-inflammatory cytokines were not observed. Instead, efferocytosing neutrophils released various growth factors including fibroblast growth factor-2 and hepatocyte growth factor (HGF). Accordingly, we observed an increase of HGF-positive neutrophils after PHx and a correlation of plasma HGF with M30 levels. These data suggest that the clearance of PHx-induced aEVs leads to a population of non-inflammatory but regenerative neutrophils, which may support human liver regeneration. In this study, we show that the surgical removal of a diseased part of the liver triggers a specific type of programmed cell death in the residual liver tissue. This results in the release of vesicles from dying cells into the blood, where they are cleared by circulating immune cells. These respond by secreting hepatocyte growth factors that could potentially support the regeneration of the liver remnant.

Recent studies showed a beneficial effect of adipose stem cell-derived extracellular vesicles (ADSC-EVs) on sciatic nerve repair, presumably through Schwann cell (SC) modulation. However, it has not yet been elucidated whether ADSC-EVs exert this supportive effect on SCs by extracellular receptor binding, fusion to the SC membrane, or endocytosis mediated internalization. ADSCs, ADSC-EVs, and SCs were isolated from rats and characterized according to associated marker expression and properties. The proliferation rate of SCs in response to ADSC-EVs was determined using a multicolor immunofluorescence staining panel followed by automated image analysis. SCs treated with ADSC-EVs and silica beads were further investigated by 3-D high resolution confocal microscopy and live cell imaging. Our findings demonstrated that ADSC-EVs significantly enhanced the proliferation of SCs in a time- and dose-dependent manner. 3-D image analysis revealed a perinuclear location of ADSC-EVs and their accumulation in vesicular-like structures within the SC cytoplasm. Upon comparing intracellular localization patterns of silica beads and ADSC-EVs in SCs, we found striking resemblance in size and distribution. Live cell imaging visualized that the uptake of ADSC-EVs preferentially took place at the SC processes from which the EVs were transported towards the nucleus. This study provided first evidence for an endocytosis mediated internalization of ADSC-EVs by SCs and underlines the therapeutic potential of ADSC-EVs in future approaches for nerve regeneration.

The search for a suitable material to promote regeneration after long‐distance peripheral nerve defects turned the spotlight on spider silk. Nerve conduits enriched with native spider silk fibers as internal guiding structures previously demonstrated a regenerative outcome similar to autologous nerve grafts in animal studies. Nevertheless, spider silk is a natural material with associated limitations for clinical use. A promising alternative is the production of recombinant silk fibers that should mimic the outstanding properties of their native counterpart. However, in vitro data on the regenerative features that native silk fibers provide for cells involved in nerve regeneration are scarce. Thus, there is a lack of reference parameters to evaluate whether recombinant silk fiber candidates will be eligible for nerve repair in vivo. To gain insight into the regenerative effect of native spider silk, our study aims to define the behavioral response of primary Schwann cells (SCs), nerve‐associated fibroblasts (FBs), and dorsal root ganglion (DRG) neurons cultured on native dragline silk from the genus Nephila and on laminin coated dishes. The established multi‐color immunostaining panels together with confocal microscopy and live cell imaging enabled the analysis of cell identity, morphology, proliferation, and migration on both substrates in detail. Our findings demonstrated that native spider silk rivals laminin coating as it allowed attachment and proliferation and supported the characteristic behavior of all tested cell types. Axonal out‐growth of DRG neurons occurred along longitudinally aligned SCs that formed sustained bundled structures resembling Bungner bands present in regenerating nerves. The migration of SCs along the silk fibers achieved the reported distance of regenerating axons of about 1 mm per day, but lacked directionality. Furthermore, rFBs significantly reduced the velocity of rSCs in co‐cultures on silk fibers. In summary, this study (a) reveals features recombinant silk must possess and what modifications or combinations could be useful for enhanced nerve repair and (b) provides assays to evaluate the regenerative performance of silk fibers in vitro before being applied as internal guiding structure in nerve conduits in vivo.

The successful reconstruction of supercritical peripheral nerve injuries remains a major challenge in modern medicine. Progress in tissue engineering has enabled the development of nerve guidance conduits as an alternative to autologous nerve transplantation and the enrichment of conduits with fibrous materials or hydrogels has shown great potential in bridging nerve defects. The application of the dragline silk of spider genus Nephila as a filament for nerve guidance conduits has led to promising results. However, the use of spider silk has been phenomenological so far and the reasons for its success are still not identified. This renders a targeted tuning of synthetic fibrous luminal fillings such as recombinant silk out of reach. In this work the existing research was extended and in addition to dragline, the cocoon silk of Nephila edulis, as well as the connecting and attaching silk of Avicularia avicularia were investigated. Scanning electron microscopy revealed a difference in size and morphology of the spider silks. However, in vitro experiments indicated that Schwann cells adhere to the four fibers, independent of these two attributes. Raman spectroscopy in native state and aqueous environment demonstrated similar secondary protein structures for dragline, cocoon, and connecting silk. In contrast, the attaching silk showed a significant lower conformation of β-sheets, crucial for the stiffness of the silk. This was in line with the in vitro experiments, where the flexible attaching silk fibers adhered to each other when placed in liquid. This resulted in their inability to guide Schwann cells, leading to the generation of cell agglomerations. This direct comparison demonstrated the crucial role of β-sheets conformation for the guidance properties of natural spider silk, providing essential insights into the necessary material properties for the integration of fibrous luminal fillings in nerve guidance conduits.