Novel method for culturing Schwann cells from adult mouse sciatic nerve in vitro

Advantages of Adult Mouse Dorsal Root Ganglia Explant Culture in Investigating Myelination in an Inherited Neuropathic Mice Model

A co-culture of neurons and Schwann cells has frequently been used to investigate myelin sheath formation. However, this approach is restricted to myelin-related diseases of the peripheral nervous system. This study introduces and compares an ex vivo model of adult-mouse-derived dorsal root ganglia (DRG) explant, with an in vitro co-culture of dissociated neurons from mouse embryo DRG and Schwann cells from a mouse sciatic nerve. The 2D co-culture has disadvantages of different mouse isolation for neurons and Schwann cells, animal number, culture duration, and the identification of disease model. However, 3D DRG explant neurons and myelination cells in Matrigel-coated culture are obtained from the same mouse, the culture period is shorter than that of 2D co-culture, and fewer animals are needed. In addition, it has simpler and shorter experimental steps than 2D co-culture. This culture system may prove advantageous in studies of biological functions and pathophysiological mechanisms of disease models, since it can reflect disease characteristics as traditional co-culture does. Therefore, it is suggested that a DRG explant culture is a scientifically, ethically, and economically more practical option than a co-culture system for studying myelin dynamics, myelin sheath formation, and demyelinating disease.

Erythropoietin promotes M2 macrophage phagocytosis of Schwann cells in peripheral nerve injury

Following acute sciatic nerve crush injury (SNCI), inflammation and the improper phagocytic clearance of dying Schwann cells (SCs) has effects on remodeling that lead to morbidity and incomplete functional recovery. Therapeutic strategies like the use of erythropoietin (EPO) for peripheral nerve trauma may serve to bring immune cell phagocytotic clearance under control to support debris clearance. We evaluated EPO’s effect on SNCI and found EPO treatment increased myelination and sciatic functional index (SFI) and bolstered anti-apoptosis and phagocytosis of myelin debris via CD206⁺ macrophages when compared to saline treatment. EPO enhanced M2 phenotype activity, both in bone marrow-derived macrophages (BMMØs) and peritoneal-derived macrophages (PMØs) in vitro, as well as in PMØs in vivo. EPO increased efferocytosis of apoptotic sciatic nerve derived Schwann cells (SNSCs) in both settings as demonstrated using immunofluorescence (IF) and flow cytometry. EPO treatment significantly attenuated pro-inflammatory genes (IL1β, iNOS, and CD68) and augmented anti-inflammatory genes (IL10 and CD163) and the cell-surface marker CD206. EPO also increased anti-apoptotic (Annexin V/7AAD) effects after lipopolysaccharide (LPS) induction in macrophages. Our data demonstrate EPO promotes the M2 phenotype macrophages to ameliorate apoptosis and efferocytosis of dying SCs and myelin debris and improves SN functional recovery following SNCI.

Deletion of the Gene Encoding the NMDA Receptor GluN1 Subunit in Schwann Cells Causes Ultrastructural Changes in Remak Bundles and Hypersensitivity in Pain Processing

Abnormalities in interactions between sensory neurons and Schwann cells (SCs) may result in heightened pain processing and chronic pain states. We previously reported that SCs express the NMDA receptor (NMDA-R), which activates cell signaling in response to glutamate and specific protein ligands, such as tissue-type plasminogen activator. Herein, we genetically targeted grin1 encoding the essential GluN1 NMDA-R subunit, conditionally in SCs, to create a novel mouse model in which SCs are NMDA-R-deficient (GluN1- mice). These mice demonstrated increased sensitivity to light touch, pinprick, and thermal hyperalgesia in the absence of injury, without associated changes in motor function. Ultrastructural analysis of adult sciatic nerve in GluN1- mice revealed increases in the density of Aδ fibers and Remak bundles and a decrease in the density of Aβ fibers, without altered g-ratios. Abnormalities in adult Remak bundle ultrastructure were also present including aberrant C-fiber ensheathment, distances between axons, and increased poly-axonal pockets. Developmental and post radial sorting defects contributed to altered nerve fiber densities in adult. Uninjured sciatic nerves in GluN1- mice did not demonstrate an increase in neuroinflammatory infiltrates. Transcriptome profiling of dorsal root ganglia (DRGs) revealed 138 differentially regulated genes in GluN1- mice. One third of the regulated genes are known to be involved in pain processing, including sprr1a, npy, fgf3, atf3, and cckbr, which were significantly increased. The intraepidermal nerve fiber density (IENFD) was significantly decreased in the skin of GluN1- mice. Collectively, these findings demonstrate that SC NMDA-R is essential for normal PNS development and for preventing development of pain states.SIGNIFICANCE STATEMENT Chronic unremitting pain is a prevalent medical condition; however, the molecular mechanisms that underlie heightened pain processing remain incompletely understood. Emerging data suggest that abnormalities in Schwann cells (SCs) may cause neuropathic pain. We established a novel mouse model for small fiber neuropathy (SFN) in which grin1, the gene that encodes the NMDA receptor (NMDA-R) GluN1 subunit, is deleted in SCs. These mice demonstrate hypersensitivity in pain processing in the absence of nerve injury. Changes in the density of intraepidermal small fibers, the ultrastructure of Remak bundles, and the transcriptome of dorsal root ganglia (DRGs) provide possible explanations for the increase in pain processing. Our results support the hypothesis that abnormalities in communication between sensory nerve fibers and SCs may result in pain states.

Performance of Schwann cell transplantation into extracted socket after inferior alveolar nerve injury in a novel rat model

An inferior alveolar nerve (IAN) injury is a common clinical problem that can affect a patients' quality of life. Cellular therapy has been proposed as a promising treatment for this injury. However, the current experimental models for IAN injury require surgery to create bone windows that expose the nerve, and these models do not accurately mimic human IAN injuries. Therefore, in this study, a novel experimental model for IAN injury has been established in rats. Using this model, the effects of Schwann cells and their role in the recovery from IAN injuries were investigated. Schwann cells were isolated from rat sciatic nerves and cultured. The first molar in the mandible was extracted and the IAN was immediately injured for 30 min by inserting an insect pin. Then, the Schwann cells or culture medium were transplanted into the extracted sockets of the cell and injury groups, respectively. After the surgery, the cell group displayed significantly increased sensory reflexes in response to mechanical stimulation, regenerated IAN width, and myelin basic protein-positive myelin sheaths when compared with the injury group. In conclusion, a novel animal experimental model for IAN injury has been developed that does not require the creation of a bone window to evaluate the impacts of cell transplantation and demonstrates that Schwann cell transplantation facilitates the regeneration of injured IANs.

Peripheral Nerve Regeneration Is Independent From Schwann Cell p75NTR Expression

Schwann cell reprogramming and differentiation are crucial prerequisites for neuronal regeneration and re-myelination to occur following injury to peripheral nerves. The neurotrophin receptor p75NTR has been identified as a positive modulator for Schwann cell myelination during development and implicated in promoting nerve regeneration after injury. However, most studies base this conclusion on results obtained from complete p75NTR knockout mouse models and cannot dissect the specific role of p75NTR expressed by Schwann cells. In this present study, a conditional knockout model selectively deleting p75NTR expression in Schwann cells was generated, where p75NTR expression is replaced with that of an mCherry reporter. Silencing of Schwann cell p75NTR expression was confirmed in the sciatic nerve in vivo and in vitro, without altering axonal expression of p75NTR. No difference in sciatic nerve myelination during development or following sciatic nerve crush injury was observed, as determined by quantification of both myelinated and unmyelinated nerve fiber densities, myelinated axonal diameter and myelin thickness. However, the absence of Schwann cell p75NTR reduced motor nerve conduction velocity after crush injury. Our data indicate that the absence of Schwann cell p75NTR expression in vivo is not critical for axonal regrowth or remyelination following sciatic nerve crush injury, but does play a key role in functional recovery. Overall, this represents the first step in redefining the role of p75NTR in the peripheral nervous system, suggesting that the Schwann cell-axon unit functions as a syncytium, with the previous published involvement of p75NTR in remyelination most likely depending on axonal/neuronal p75NTR and/or mutual glial-axonal interactions.

Schwann Cells Augment Cell Spreading and Metastasis of Lung Cancer

Although lungs are densely innervated by the peripheral nervous system (PNS), the role of the PNS in the progression of lung cancer is unknown. In this study, we report that mouse adult Schwann cells (SC), the principal glial cells of the PNS, can regulate the motility of lung cancer cells in vitro and the formation of metastases in vivo SCs promoted epithelial-to-mesenchymal transition (EMT) and the motility of two lung cancer cell lines by increasing expression of Snail and Twist in tumor cells; blocking of Snail and Twist expression abolished SC-induced motility of tumor cells. SC-derived CXCL5 was responsible for EMT in lung cancer cells, as the inhibition of CXCL5 or its receptor CXCR2 reduced SC-induced expression of Snail and Twist and reduced motility in tumor cells. CXCL5/CXCR2 binding activated the PI3K/AKT/GSK-3β/Snail-Twist signaling pathway in lung cancer cells, and the PI3K inhibitor blocked CXCL5-dependent phosphorylation of AKT and GSK-3β, reduced expression of Snail/Twist, and limited tumor cell invasiveness. SC conditioning of tumor cells prior to their injection into mice significantly increased the formation of metastases in the regional lymph nodes. In summary, SCs can regulate the CXCL5/CXCR2/PI3K/AKT/GSK-3β/Snail-Twist pathway to promote EMT, invasiveness, and metastatic potential of lung cancer cells. Our results reveal a new role of the PNS in the functional organization of the tumor microenvironment and tumor progression.Significance: This study increases our understanding of how nerves and, in particular, specific glial cells, Schwann cells, in the peripheral nervous system, may help promote tumor growth and metastasis. Cancer Res; 78(20); 5927-39. ©2018 AACR.

Magnetic-Activated Cell Sorting for the Fast and Efficient Separation of Human and Rodent Schwann Cells from Mixed Cell Populations

To date, magnetic-activated cell sorting (MACS) remains a powerful method to isolate distinct cell populations based on differential cell surface labeling. Optimized direct and indirect MACS protocols for cell immunolabeling are presented here as methods to divest Schwann cell (SC) cultures of contaminating cells (specifically, fibroblast cells) and isolate SC populations at different stages of differentiation. This chapter describes (1) the preparation of single-cell suspensions from established human and rat SC cultures, (2) the design and application of cell selection strategies using SC-specific (p75^NGFR, O4, and O1) and fibroblast-specific (Thy-1) markers, and (3) the characterization of both the pre- and post-sorting cell populations. A simple protocol for the growth of hybridoma cell cultures as a source of monoclonal antibodies for cell surface immunolabeling of SCs and fibroblasts is provided as a cost-effective alternative for commercially available products. These steps allow for the timely and efficient recovery of purified SC populations without compromising the viability and biological activity of the cells.

Long non-coding RNA NONMMUG014387 promotes Schwann cell proliferation after peripheral nerve injury

Schwann cells play a critical role in peripheral nerve regeneration through dedifferentiation and proliferation. In a previous study, we performed microarray analysis of the sciatic nerve after injury. Accordingly, we predicted that long non-coding RNA NONMMUG014387 may promote Schwann cell proliferation after peripheral nerve injury, as bioinformatic analysis revealed that the target gene of NONMMUG014387 was collagen triple helix repeat containing 1 (Cthrc1). Cthrc1 may promote cell proliferation in a variety of cells by activating Wnt/PCP signaling. Nonetheless, bioinformatic analysis still needs to be verified by biological experiment. In this study, the candidate long non-coding RNA, NONMMUG014387, was overexpressed in mouse Schwann cells by recombinant adenovirus transfection. Plasmid pHBAd-MCMV-GFP-NONMMUG014387 and pHBAd-MCMV-GFP were transfected into Schwann cells. Schwann cells were divided into three groups: control (Schwann cells without intervention), Ad-GFP (Schwann cells with GFP overexpression), and Ad-NONMMUGO148387 (Schwann cells with GFP and NONMMUGO148387 overexpression). Cell Counting Kit-8 assay was used to evaluate proliferative capability of mouse Schwann cells after NONMMUG014387 overexpression. Polymerase chain reaction and western blot assay were performed to investigate target genes and downstream pathways of NONMMUG014387. Cell proliferation was significantly increased in Schwann cells overexpressing lncRNA NONMMUG014387 compared with the other two groups. Further, compared with the control group, mRNA and protein levels of Cthrc1, Wnt5a, ROR2, RhoA, Rac1, JNK, and ROCK were visibly up-regulated in the Ad-NONMMUGO148387 group. Our findings confirm that long non-coding RNA NONMMUG014387 can promote proliferation of Schwann cells surrounding the injury site through targeting Cthrc1 and activating the Wnt/PCP pathway.

A rapid and versatile method for the isolation, purification and cryogenic storage of Schwann cells from adult rodent nerves

We herein developed a protocol for the rapid procurement of adult nerve-derived Schwann cells (SCs) that was optimized to implement an immediate enzymatic dissociation of fresh nerve tissue while maintaining high cell viability, improving yields and minimizing fibroblast and myelin contamination. This protocol introduces: (1) an efficient method for enzymatic cell release immediately after removal of the epineurium and extensive teasing of the nerve fibers; (2) an adaptable drop-plating method for selective cell attachment, removal of myelin debris, and expansion of the initial SC population in chemically defined medium; (3) a magnetic-activated cell sorting purification protocol for rapid and effective fibroblast elimination; and (4) an optional step of cryopreservation for the storage of the excess of cells. Highly proliferative SC cultures devoid of myelin and fibroblast growth were obtained within three days of nerve processing. Characterization of the initial, expanded, and cryopreserved cell products confirmed maintenance of SC identity, viability and growth rates throughout the process. Most importantly, SCs retained their sensitivity to mitogens and potential for differentiation even after cryopreservation. To conclude, this easy-to-implement and clinically relevant protocol allows for the preparation of expandable homogeneous SC cultures while minimizing time, manipulation of the cells, and exposure to culture variables.

A new protocol for cultivation of predegenerated adult rat Schwann cells

The purpose of this study was to optimize the methodology of cultivation of predegenerated Schwann cells (SCs). SCs were isolated from 7-day-predegenerated sciatic nerves of adult rats. We applied commercially available culture medium for cultivation of endothelial cells endothelial cell culture medium (EBM-2) instead of Dulbecco's Modified Eagle's Medium commonly used to culture adult Schwann cells. Additionally, cell culture medium was supplemented with factors specifically supporting SCs growth as: bovine pituitary extract (5 μg/ml), heregulin (40 ng/ml) and insulin (2.5 ng/ml). Similarly to the reports of others authors, we did not observe any beneficial effects of Forskolin application, so we didn't supplement our medium with it. Cell culture purity was determined by counting the ratio of GFAP, N-Cadherin and NGFR p75-positive cells to total number of cells. About 94-97 % of cells were confirmed as Schwann cells. As a result, we obtained sufficient number and purity of Schwann cells to be applied in different experimental models in rats. EBM-2 medium coated with fibronectin was the best for cultivation of adult rat Schwann cells.