Krox20 Expression Research Articles

BDNF and Krox20 as Indicators of Platelet-rich Plasma-Induced Nerve Regeneration in a Neuropathic Orofacial Pain Model.

Various growth factors contained in PRP can increase angiogenesis and cell proliferation, which plays an essential role in the process of neuroregeneration and peripheral nerve injury recovery. This study analyzed PRP effects in the neuro-regeneration of axonotmesis through brain-derived neurotrophic factor (BDNF) and Krox20 expressions. Freeze-dried allogeneic platelet-rich plasma (PRP) were prepared from allogeneic sources. Forty-two Rattus norvegicus were divided into three groups: negative control group, positive control group (crushing infraorbital nerve) and treatment group (crushing infraorbital nerve without PRP injection). Each group was observed for fourteen and twenty-one days after injury. Infraorbital nerve tissue is isolated for indirect immunohistochemistry examination with BDNF and Krox20 antibodies. Data analysis was performed using One-Way ANOVA and Mann-Whitney tests with significant value as p < 0.05. The PRP group showed BDNF expression significantly higher than control positive groups, both observation days (p = 0.00). A higher Korx20 expression showed by the PRP group after 21 days than in the control positive groups (p = 0.002). PRP can potentially improve neuroregeneration of axonotmesis through increased BDNF and Krox20 expression on the twenty-one days after injury.

Effects of Curcumin on Axon Growth and Myelin Sheath Formation in an In Vitro Model.

Although the beneficial effects of curcumin, extracted from rhizomes of the ginger family genus Curcuma, on the repair and regeneration of nerves have been evaluated in vitro, there are few studies concerning its effects on axon myelination. Here, we used pheochromocytoma cells as an in vitro model of peripheral nerves. Pheochromocytoma cells were cultured alone or cocultured with Schwann cells and treated with increasing concentrations of curcumin. Cell growth was observed, and the expression levels of growth-associated protein 43 (GAP-43), microtubule-associated protein 2 (MAP-2), myelin basic protein (MBP), myelin protein zero (MPZ), Krox-20, and octamer binding factor 6 (Oct-6) were quantified. We found a significant increase in expression of all six proteins following curcumin treatment, with a corresponding increase in the levels of MBP, MPZ, Krox-20, and Oct-6 mRNA. Upregulation was greater with increasing curcumin concentration, showing a concentration-dependent effect. The results suggested that curcumin can promote the growth of axons by upregulating the expression of GAP-43 and MAP-2, stimulate synthesis and secretion of myelin-related proteins, and facilitate formation of the myelin sheath in axons by upregulating the expression of Krox-20 and Oct-6. Therefore, curcumin could be widely applied in future strategies for the treatment of nerve injuries.

COUP-TFII plays a role in cAMP-induced Schwann cell differentiation and in vitro myelination by up-regulating Krox20.

Schwann cells (SCs) are known to produce myelin for saltatory nerve conduction in the peripheral nervous system (PNS). Schwann cell differentiation and myelination processes are controlled by several transcription factors including Sox10, Oct6/Pou3f1, and Krox20/Egr2. Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII/NR2F2) is an orphan receptor that plays a role in the development and differentiation. However, the role of COUP-TFII in the transcriptional regulatory network of SC differentiation has not been fully identified yet. Thus, the objective of this study was to investigate the role and molecular hierarchy of COUP-TFII during cAMP-induced SC differentiation. Our results showed that dibutyryl-cAMP (db-cAMP) increased expression levels of COUP-TFII along with the expressions of Oct6, Krox20, and myelin-related genes known to be related to SC differentiation. Our mechanistic studies showed that COUP-TFII acted downstream of Hsp90/ErbB2/Gab1/ERK-AKT pathway during db-cAMP-induced SC differentiation. In addition, we found that COUP-TFII induced Krox20 expression by directly binding to Krox20-MSE8 as revealed by chromatin immunoprecipitation assay and promoter activity assay. In line with this, the expression of COUP-TFII was increased before up-regulation of Oct6, Krox20, and myelin-related genes in the sciatic nerves during early postnatal myelination period. Finally, COUP-TFII knockdown by COUP-TFII siRNA or via AAV-COUP-TFII shRNA in SCs inhibited db-cAMP-induced SC differentiation and in vitro myelination of sensory axons, respectively. Taken together, these findings indicate that COUP-TFII might be involved in postnatal myelination through induction of Krox20 in SCs. Our results present a new insight into the transcriptional regulatory mechanism in SC differentiation and myelination.

Anti-LGI4 Antibody Is a Novel Juxtaparanodal Autoantibody for Chronic Inflammatory Demyelinating Polyneuropathy.

The objective of this study was to discover novel nodal autoantibodies in chronic inflammatory demyelinating polyneuropathy (CIDP). We screened for autoantibodies that bind to mouse sciatic nerves and dorsal root ganglia (DRG) using indirect immunofluorescence (IFA) assays with sera from 113 patients with CIDP seronegative for anti-neurofascin 155 and anticontactin-1 antibodies and 127 controls. Western blotting, IFA assays using HEK293T cells transfected with relevant antigen expression plasmids, and cell-based RNA interference assays were used to identify target antigens. Krox20 and Periaxin expression, both of which independently control peripheral nerve myelination, was assessed by quantitative real-time PCR after application of patient and control sera to Schwann cells. Sera from 4 patients with CIDP, but not control sera, selectively bound to the nodal regions of sciatic nerves and DRG satellite glia (p = 0.048). The main immunoglobulin G (IgG) subtype was IgG4. IgG from these 4 patients stained a 60-kDa band on Western blots of mouse DRG and sciatic nerve lysates. These features indicated leucine-rich repeat LGI family member 4 (LGI4) as a candidate antigen. A commercial anti-LGI4 antibody and IgG from all 4 seropositive patients with CIDP showed the same immunostaining patterns of DRG and cultured rat Schwann cells and bound to the 60-kDa protein in Western blots of LGI4 overexpression lysates. IgG from 3 seropositive patients, but none from controls, bound to cells cotransfected with plasmids containing LGI4 and a disintegrin and metalloprotease domain-containing protein 22 (ADAM22), an LGI4 receptor. In cultured rat Schwann and human melanoma cells constitutively expressing LGI4, LGI4 siRNA effectively downregulated LGI4 and reduced patients' IgG binding compared with scrambled siRNA. Application of serum from a positive patient to Schwann cells expressing ADAM22 significantly reduced the expression of Krox20, but not Periaxin. Anti-LGI4 antibody-positive patients had a relatively old age at onset (mean age 58 years), motor weakness, deep and superficial sensory impairment with Romberg sign, and extremely high levels of CSF protein. Three patients showed subacute CIDP onset resembling Guillain-Barré syndrome. IgG4 anti-LGI4 antibodies are found in some elderly patients with CIDP who present subacute sensory impairment and motor weakness and are worth measuring, particularly in patients with symptoms resembling Guillain-Barré syndrome.

Expression of c-Jun and KROX-20 Following Facial Nerve Injury and Recovery in Rats.

Background:This study evaluated whether recovery from facial paralysis was associated with the expression of Krox-20 and c-Jun genes that are shown to be related to facial nerve regeneration after facial nerve compression and cutting.Methods:The left facial nerves of 24 male Sprague–Dawley rats aged 6 weeks were subjected to crushing or cutting injury. Whisker movements of the vibrissae muscle and blink reflexes of the eyelids were measured on days 4 and 14 after facial nerve injury. The facial nerves on both sides were removed, and the expression of c-Jun and Krox-20 proteins was evaluated by Western blotting.Results:The level of expression of Krox-20 on day 4 was lower in the crushing group, especially in the cutting group than in the control group (P < .05), but there was no statistically significant difference on day 14 (P > .05). The expression of c-Jun expression was significantly higher in the crushing and cutting groups than in the control group on days 4 and 14 (P < .05).Conclusion:The degree of facial paralysis was more severe and the recovery rate was lower in the cutting group than in the crushing group. The levels of expression of Krox-20 and c-Jun were associated with facial nerve regeneration after facial nerve injury.

Krox20 expression in abnormal scars: An immunohistochemical study.

Scars are the end outcome of healing. They are grouped into several types, the common of which are keloids, hypertrophic, and atrophic scars. The role of Krox20 in skin and hair physiology and pathology had emerged. Overexpression of Krox20 was sufficient to stimulate collagen gene expression and myofibroblast differentiation and is necessary for transforming growth factor-β (TGF-β) induced profibrotic responses. To investigate the role of Krox20 in abnormal scar pathogenesis. Hopefully, this insight can set the route for newer therapeutic approaches. This study was carried out on 30 cases (10 cases of keloids, 10 cases of atrophic scars, and 10 cases with hypertrophic scars [HTS]) and 10 age and gender-matched apparently healthy subjects as a control group. Thirty biopsies were taken from perilesional areas. Evaluation of Krox20 expression was done using standard immunohistochemical technique. Krox20 was downregulated in epidermis of scar biopsies compared with perilesional and normal skin (p=0.02) while it was overexpressed in fibroblasts in lesional scar biopsies compared with perilesional and normal skin (p<0.001). Keloid cases have significantly higher Krox20 expression in fibroblasts compared with HTS cases (p<0.001). Krox20 had significantly nucleocytoplasmic pattern of staining in scar cases compared with normal skin (p<0.001). Krox20 overexpression may have a role in scar pathogenesis through upregulation of multiple genes associated with tissue remodeling and wound healing. This may open an avenue for research for new therapies based on Krox20 inhibition.

SGK1 in Schwann cells is a potential molecular switch involved in axonal and glial regeneration during peripheral nerve injury

Schwann cells play an important role in peripheral myelination, and dysfunction of these cells leads to axonal damage. Schwann cells degenerate following peripheral nerve injury. Immature Schwann cells proliferate, differentiate, and support axonal regeneration and extension during recovery. There are a lot of intracellular signals involved in the myelination process. Although serum- and glucocorticoid-inducible kinase (SGK1) in Schwann cells is supposedly involved in developmental myelination, its significance during peripheral nerve injury and repair remains unknown. In this study, we examined the dynamics of SGK1 during peripheral nerve repair and the potential role of SGK in the process. Axonal crush injury was first generated in the right sciatic nerve under anesthesia in mice, which exhibited apparent paralysis and subsequent recovery of the injured hindlimbs. Immunohistochemical analysis revealed the appearance of glial fibrillary acidic protein (GFAP)-positive immature Schwann cells around injured nerves, and SGK1 was present in these cells. Next, we employed S16 cells, a Schwann cell line, to explore the impact of SGK1 on Schwann cells. Administration of the SGK inhibitor gsk650394 decreased cell proliferation and increased cell size. SGK inhibition did not cause cellular injury, suggesting that it suppresses proliferation and enlarges Schwann cells without causing cell death. Furthermore, quantitative PCR and immunoblotting revealed that SGK inhibition upregulated the gene expression of BDNF, MBP, and Krox20, which are facilitating factors for myelination and neural regeneration, and downregulated that of Sox10. Taken together, these findings indicate that SGK1 inactivation in Schwann cells diverts cell fate from proliferation to differentiation.

Epithelial stem cell homeostasis in Meibomian gland development, dysfunction, and dry eye disease.

Dry eye disease affects over 16 million adults in the US, and the majority of cases are due to Meibomian gland dysfunction. Unfortunately, the identity of the stem cells involved in Meibomian gland development and homeostasis is not well elucidated. Here, we report that loss of Krox20, a zinc finger transcription factor involved in the development of ectoderm-derived tissues, or deletion of KROX20-expressing epithelial cells disrupted Meibomian gland formation and homeostasis, leading to dry eye disease secondary to Meibomian gland dysfunction. Ablation of Krox20-lineage cells in adult mice also resulted in dry eye disease, implicating Krox20 in homeostasis of the mature Meibomian gland. Lineage-tracing and expression analyses revealed a restricted KROX20 expression pattern in the ductal areas of the Meibomian gland, although Krox20-lineage cells generate the full, mature Meibomian gland. This suggests that KROX20 marks a stem/progenitor cell population that differentiates to generate the entire Meibomian gland. Our Krox20 mouse models provide a powerful system that delineated the identity of stem cells required for Meibomian gland development and homeostasis and can be used to investigate the factors underlying these processes. They are also robust models of Meibomian gland dysfunction–related dry eye disease, with a potential for use in preclinical therapeutic screening.

Effects of Theranekron and alpha-lipoic acid combined treatment on GAP-43 and Krox-20 gene expressions and inflammation markers in peripheral nerve injury

ABSTRACT Peripheral nerve injury (PNI) is a major health problem that results in loss of motor and sensory functions. In treatment of PNI, various methods such as anastomosis, nerve grafts, nonneural tissue grafts, and nerve conduits are applied. In the present study, it was aimed to investigate the effects of Theranekron and Alpha-lipoic acid (ALA) combined treatment on nerve healing in experimental PNI by using histomorphometric, electron microscopic, immunohistochemical and molecular biological methods. Sixty-two Wistar rats were divided into six groups; the normal control group, sham operation group, experimental control group having a crush type injury with no treatment, Theranekron treatment group, ALA treatment group and Theranekron+ALA combined treatment group. Sciatic nerve tissue samples were obtained on days 1, 7 and 14 following injury in all groups. GAP-43 expression was upregulated in all PNI received groups compared to the control group. Krox-20 expression was downregulated in all groups that received PNI compared to the control group. While intensely positive TNF-α and IL-6 expressions were observed up to the 1st to the 14th day for the experimental control group, these expressions were seen as “weakly positive” in the treatment groups from the 1st day to the 14th day. The number of myelinated fibers was higher in the control and sham operation groups. Additionally, the number of myelinated nerve fibers increased in the combined treatment group. In conclusion, these findings suggest that combined therapy of Theranekron and ALA promotes structural recovery and it should be considered as an effective treatment protocol following PNI.

Gbx2 Is Required for the Migration and Survival of a Subpopulation of Trigeminal Cranial Neural Crest Cells.

The development of key structures within the mature vertebrate hindbrain requires the migration of neural crest (NC) cells and motor neurons to their appropriate target sites. Functional analyses in multiple species have revealed a requirement for the transcription factor gastrulation-brain-homeobox 2 (Gbx2) in NC cell migration and positioning of motor neurons in the developing hindbrain. In addition, loss of Gbx2 function studies in mutant mouse embryos, Gbx2neo, demonstrate a requirement for Gbx2 for the development of NC-derived sensory neurons and axons constituting the mandibular branch of the trigeminal nerve (CNV). Our recent GBX2 target gene identification study identified multiple genes required for the migration and survival of NC cells (e.g., Robo1, Slit3, Nrp1). In this report, we performed loss-of-function analyses using Gbx2neo mutant embryos, to improve our understanding of the molecular and genetic mechanisms regulated by Gbx2 during anterior hindbrain and CNV development. Analysis of Tbx20 expression in the hindbrain of Gbx2neo homozygotes revealed a severely truncated rhombomere (r)2. Our data also provide evidence demonstrating a requirement for Gbx2 in the temporal regulation of Krox20 expression in r3. Lastly, we show that Gbx2 is required for the expression of Nrp1 in a subpopulation of trigeminal NC cells, and correct migration and survival of cranial NC cells that populate the trigeminal ganglion. Taken together, these findings provide additional insight into molecular and genetic mechanisms regulated by Gbx2 that underlie NC migration, trigeminal ganglion assembly, and, more broadly, anterior hindbrain development.

In Vitro Differentiation of Human Placenta-Derived Multipotent Cells into Schwann-Like Cells.

Human placenta-derived multipotent stem cells (PDMCs) resembling embryonic stem cells can differentiate into three germ layer cells, including ectodermal lineage cells, such as neurons, astrocytes, and oligodendrocytes. The favorable characteristics of noninvasive cell harvesting include fewer ethical, religious, and legal considerations as well as accessible and limitless supply. Thus, PDMCs are attractive for cell-based therapy. The Schwann cell (SC) is the most common cell type used for tissue engineering such as nerve regeneration. However, the differentiation potential of human PDMCs into SCs has not been demonstrated until now. In this study, we evaluated the potential of PDMCs to differentiate into SC-like cells in a differentiation medium. After induction, PDMCs not only exhibited typical SC spindle-shaped morphology but also expressed SC markers, including S100, GFAP, p75, MBP, and Sox 10, as revealed by immunocytochemistry. Moreover, a reverse transcription-quantitative polymerase chain reaction analysis revealed the elevated gene expression of S100, GFAP, p75, MBP, Sox-10, and Krox-20 after SC induction. A neuroblastoma cell line, SH-SY5Y, was cultured in the conditioned medium (CM) collected from PDMC-differentiated SCs. The growth rate of the SH-SY5Y increased in the CM, indicating the function of PDMC-induced SCs. In conclusion, human PDMCs can be differentiated into SC-like cells and thus are an attractive alternative to SCs for cell-based therapy in the future.

Deletion of Calcineurin in Schwann Cells Does Not Affect Developmental Myelination, But Reduces Autophagy and Delays Myelin Clearance after Peripheral Nerve Injury.

In the PNS, myelination occurs postnatally when Schwann cells (SCs) contact axons. Axonal factors, such as Neuregulin-1 Type III, trigger promyelinating signals that upregulate myelin genes. Neuregulin-1 Type III has been proposed to activate calcineurin signaling in immature SCs to initiate differentiation and myelination. However, little is known about the role of calcineurin in promyelinating SCs after birth. By creating a SC conditional KO of calcineurin B (CnBscko), we assessed the effects of CnB ablation on peripheral myelination after birth in both male and female mice. Surprisingly, CnBscko mice have minimal myelination defects, no alteration of myelin thickness, and normal KROX20 expression. In contrast, we did find a unique role for calcineurin in SCs after nerve injury. Following nerve crush, CnBscko mice have slower degeneration of myelin compared with WT mice. Furthermore, absence of CnB in primary SCs delays clearance of myelin debris. SCs clear myelin via autophagy and recent literature has demonstrated that calcineurin can regulate autophagy via dephosphorylation of transcription factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy. We demonstrate that loss of CnB reduces autophagic flux in primary SCs, indicating a possible mechanism for impaired myelin clearance. In addition, ablation of CnB impairs TFEB translocation to the nucleus 3 d after crush, suggesting that calcineurin may regulate autophagy in SCs via TFEB activation. Together, our data indicate that calcineurin is not essential for myelination but has a novel role in myelin clearance after injury.SIGNIFICANCE STATEMENT Our data offer a novel mechanism for activation of autophagy after peripheral nerve injury. Efficient clearance of myelin after injury by Schwann cells is important for axonal regrowth and remyelination, which is one reason why the PNS is significantly better at recovery compared with the CNS. Improved understanding of myelin clearance allows for the identification of pathways that are potentially accessible to increase myelin clearance and improve remyelination and recovery. Finally, this paper clarifies the role of calcineurin in Schwann cells and myelination.

Hormone-Independent Sexual Dimorphism in the Regulation of Bone Resorption by Krox20.

Krox20/EGR2 is a zinc finger transcription factor, implicated in the development of the hindbrain, nerve myelination, and tumor suppression. In skeletal biology, we have demonstrated that Krox20 also regulates adult bone metabolism. We and others have characterized several functions of Krox20 in the osteoclast lineage, namely, preosteoclast proliferation and differentiation, and mature osteoclast apoptosis. We have previously reported that systemically Krox20-haploinsufficient mice have a low bone mass with increased bone resorption. However, new data have now revealed that this phenotype is restricted to females. In addition, we discovered that conditional knockout of Krox20 (cKO) restricted to osteoclast progenitors is sufficient to induce the same female-specific bone loss observed in systemic mutants. To test whether this sexual dimorphism results from an interaction between Krox20 and sex hormones, we examined the sex- and hormone-dependent role of Krox20 deficiency on proliferation and apoptosis in osteoclastic cells. Our results indicate that male and female sex hormones (dihydrotestosterone [DHT] and estradiol [E2], respectively) as well as Krox20 inhibit preosteoclast proliferation and augment osteoclast apoptosis. The observation that Krox20 expression is inhibited by DHT and E2 negates the hypothesis that the effect of sex hormones is mediated by an increase in Krox20 expression. Interestingly, the effect of Krox20 deficiency was observed only with cells derived from female animals, regardless of any sex hormones added in vitro. In addition, we have identified sexual dimorphism in the expression of several Krox20-related genes, including NAB2. This sex-specific epigenetic profile was established at puberty, maintained in the absence of sex hormones, and explains the female-specific skeletal importance of Krox20. The findings described in this study emphasize the medical importance of sex differences, which may be determined at the epigenetic level. © 2019 American Society for Bone and Mineral Research.

Myelination key factor krox-20 is downregulated in Schwann cells and murine sciatic nerves infected by Mycobacterium leprae.

Schwann cells (SCs) critically maintain the plasticity of the peripheral nervous system. Peripheral nerve injuries and infections stimulate SCs in order to retrieve homeostasis in neural tissues. Previous studies indicate that Mycobacterium leprae (ML) regulates the expression of key factors related to SC identity, suggesting that alterations in cell phenotype may be involved in the pathogenesis of neural damage in leprosy. To better understand whether ML restricts the plasticity of peripheral nerves, the present study sought to determine the expression of Krox-20, Sox-10, c-Jun and p75NTR in SC culture and mice sciatic nerves, both infected by ML Thai-53 strain. Primary SC cultures were stimulated with two different multiplicities of infection (MOI 100:1; MOI 50:1) and assessed after 7 and 14days. Sciatic nerves of nude mice (NU-Foxn1nu ) infected with ML were evaluated after 6 and 9months. In vitro results demonstrate downregulation of Krox-20 and Sox-10 along with the increase in p75NTR-immunolabelled cells. Concurrently, sciatic nerves of infected mice showed a significant decrease in Krox-20 and increase in p75NTR. Our results corroborate previous findings on the interference of ML in the expression of factors involved in cell maturation, favouring the maintenance of a non-myelinating phenotype in SCs, with possible implications for the repair of adult peripheral nerves.

Optogenetic stimulation promotes Schwann cell proliferation, differentiation, and myelination in vitro

Schwann cells (SCs) constitute a crucial element of the peripheral nervous system, by structurally supporting the formation of myelin and conveying vital trophic factors to the nervous system. However, the functions of SCs in developmental and regenerative stages remain unclear. Here, we investigated how optogenetic stimulation (OS) of SCs regulates their development. In SC monoculture, OS substantially enhanced SC proliferation and the number of BrdU+-S100ß+-SCs over time. In addition, OS also markedly promoted the expression of both Krox20 and myelin basic protein (MBP) in SC culture medium containing dBcAMP/NRG1, which induced differentiation. We found that the effects of OS are dependent on the intracellular Ca2+ level. OS induces elevated intracellular Ca2+ levels through the T-type voltage-gated calcium channel (VGCC) and mobilization of Ca2+ from both inositol 1,4,5-trisphosphate (IP3)-sensitive stores and caffeine/ryanodine-sensitive stores. Furthermore, we confirmed that OS significantly increased expression levels of both Krox20 and MBP in SC-motor neuron (MN) coculture, which was notably prevented by pharmacological intervention with Ca2+. Taken together, our results demonstrate that OS of SCs increases the intracellular Ca2+ level and can regulate proliferation, differentiation, and myelination, suggesting that OS of SCs may offer a new approach to the treatment of neurodegenerative disorders.

Neural crest stem cells protect spinal cord neurons from excitotoxic damage and inhibit glial activation by secretion of brain-derived neurotrophic factor

The acute phase of spinal cord injury is characterized by excitotoxic and inflammatory events that mediate extensive neuronal loss in the gray matter. Neural crest stem cells (NCSCs) can exert neuroprotective and anti-inflammatory effects that may be mediated by soluble factors. We therefore hypothesize that transplantation of NCSCs to acutely injured spinal cord slice cultures (SCSCs) can prevent neuronal loss after excitotoxic injury. NCSCs were applied onto SCSCs previously subjected to N-methyl-d-aspartate (NMDA)-induced injury. Immunohistochemistry and TUNEL staining were used to quantitatively study cell populations and apoptosis. Concentrations of neurotrophic factors were measured by ELISA. Migration and differentiation properties of NCSCs on SCSCs, laminin, or hyaluronic acid hydrogel were separately studied. NCSCs counteracted the loss of NeuN-positive neurons that was otherwise observed after NMDA-induced excitotoxicity, partly by inhibiting neuronal apoptosis. They also reduced activation of both microglial cells and astrocytes. The concentration of brain-derived neurotrophic factor (BDNF) was increased in supernatants from SCSCs cultured with NCSCs compared to SCSCs alone and BDNF alone mimicked the effects of NCSC application on SCSCs. NCSCs migrated superficially across the surface of SCSCs and showed no signs of neuronal or glial differentiation but preserved their expression of SOX2 and Krox20. In conclusion, NCSCs exert neuroprotective, anti-apoptotic and glia-inhibitory effects on excitotoxically injured spinal cord tissue, some of these effects mediated by secretion of BDNF. However, the investigated NCSCs seem not to undergo neuronal or glial differentiation in the short term since markers indicative of an undifferentiated state were expressed during the entire observation period.

Class IIa histone deacetylases link cAMP signaling to the myelin transcriptional program of Schwann cells.

Schwann cells respond to cyclic adenosine monophosphate (cAMP) halting proliferation and expressing myelin proteins. Here we show that cAMP signaling induces the nuclear shuttling of the class IIa histone deacetylase (HDAC)-4 in these cells, where it binds to the promoter and blocks the expression of c-Jun, a negative regulator of myelination. To do it, HDAC4 does not interfere with the transcriptional activity of MEF2. Instead, by interacting with NCoR1, it recruits HDAC3 and deacetylates histone 3 in the promoter of c-Jun, blocking gene expression. Importantly, this is enough to up-regulate Krox20 and start Schwann cell differentiation program-inducing myelin gene expression. Using conditional knockout mice, we also show that HDAC4 together with HDAC5 redundantly contribute to activate the myelin transcriptional program and the development of myelin sheath in vivo. We propose a model in which cAMP signaling shuttles class IIa HDACs into the nucleus of Schwann cells to regulate the initial steps of myelination in the peripheral nervous system.

The Role of Wnt/β-Catenin Signaling Pathway in the Transdifferentiation from Periodontal Ligament Stem Cells to Schwann Cells.

This study was aimed to investigate the role of Wnt/β-catenin signaling pathway in the differentiation from periodontal ligament stem cells (PDLSCs) to Schwann cells (SCs) and the possible mechanisms. FzB was applied to inhibit the Wnt/β-catenin signaling pathway of differentiated PDLSCs (dPDLSCs), and then immunofluorescence, polymerase chain reaction (PCR), and Western blotting analysis were performed to detect SC marker genes and proteins such as S100, glial fibrillary acidic protein (GFAP), and P75NTR. Results showed that when the Wnt/β-catenin signaling pathway was inhibited, the expression of S100, GFAP, and P75NTR protein significantly decreased in dPDLSCs, p < 0.05, whereas PCR results showed that expression of SC myelinogenesis-related genes krox-20, Oct-6, P0, and PMP-22 was significantly downregulated at the same time, p < 0.05. These results showed that Wnt/β-catenin signaling pathway participated in the differentiation from PDLSCs to SCs, and inhibiting it could inhibit the differentiation process.

Tissue Inhibitor of Metalloproteinase-3 Promotes Schwann Cell Myelination.

Tissue inhibitor of metalloproteinase-3 (TIMP-3) inhibits the activities of various metalloproteinases including matrix metalloproteinases and ADAM family proteins. In the peripheral nervous system, ADAM17, also known as TNF-α converting enzyme (TACE), cleaves the extracellular domain of Nrg1 type III, an axonal growth factor that is essential for Schwann cell myelination. The processing by ADAM17 attenuates Nrg1 signaling and inhibits Schwann cell myelination. TIMP-3 targets ADAM17, suggesting a possibility that TIMP-3 may elicit a promyelinating function in Schwann cells by relieving ADAM17-induced myelination block. To investigate this, we used a myelinating coculture system to determine the effect of TIMP-3 on Schwann cell myelination. Treatment with TIMP-3 enhanced myelin formation in cocultures, evident by an increase in the number of myelin segments and upregulated expression of Krox20 and myelin protein. The effect of TIMP-3 was accompanied by the inhibition of ADAM17 activity and an increase in Nrg1 type III signaling in cocultures. Accordingly, the N-terminus fragment of TIMP-3, which exhibits a selective inhibitory function toward ADAM17, elicited a similar myelination-promoting effect and increased Nrg1 type III activity. TIMP-3 also enhanced laminin production in cocultures, which is likely to aid Schwann cell myelination.

Age-Dependent Schwann Cell Phenotype Regulation Following Peripheral Nerve Injury.

Schwann cells are integral to the regenerative capacity of the peripheral nervous system, which declines after adolescence. The mechanisms underlying this decline are poorly understood. This study sought to compare the protein expression of Notch, c-Jun, and Krox-20 after nerve crush injury in adolescent and young adult rats. We hypothesized that these Schwann cell myelinating regulatory factors are down-regulated after nerve injury in an age-dependent fashion. Adolescent (2 months old) and young adult (12 months old) rats (n = 48) underwent sciatic nerve crush injury. Protein expression of Notch, c-Jun, and Krox-20 was quantified by Western blot analysis at 1, 3, and 7 days post-injury. Functional recovery was assessed in a separate group of animals (n = 8) by gait analysis (sciatic functional index) and electromyography (compound motor action potential) over an 8-week post-injury period. Young adult rats demonstrated a trend of delayed onset of the dedifferentiating regulatory factors, Notch and c-Jun, corresponding to the delayed functional recovery observed in young adult rats compared to adolescent rats. Compound motor action potential area was significantly greater in adolescent rats relative to young adult rats, while amplitude and velocity trended toward statistical significance. The process of Schwann cell dedifferentiation following peripheral nerve injury shows different trends with age. These trends of delayed onset of key regulatory factors responsible for Schwann cell myelination may be one of many possible factors mediating the significant differences in functional recovery between adolescent and young adult rats following peripheral nerve injury.