c-Jun N-terminal kinases mediate Fas-induced neurite regeneration in PC12 cells

Advances of Schwann cells in peripheral nerve regeneration: From mechanism to cell therapy

Peripheral nerve injuries (PNIs) frequently occur due to various factors, including mechanical trauma such as accidents or tool-related incidents, as well as complications arising from diseases like tumor resection. These injuries frequently result in persistent numbness, impaired motor and sensory functions, neuropathic pain, or even paralysis, which can impose a significant financial burden on patients due to outcomes that often fall short of expectations. The most frequently employed clinical treatment for PNIs involves either direct sutures of the severed ends or bridging the proximal and distal stumps using autologous nerve grafts. However, autologous nerve transplantation may result in sensory and motor functional loss at the donor site, as well as neuroma formation and scarring. Transplantation of Schwann cells/Schwann cell-like cells has emerged as a promising cellular therapy to reconstruct the microenvironment and facilitate peripheral nerve regeneration. In this review, we summarize the role of Schwann cells and recent advances in Schwann cell therapy in peripheral nerve regeneration. We summarize current techniques used in cell therapy, including cell injection, 3D-printed scaffolds for cell delivery, cell encapsulation techniques, as well as the cell types employed in experiments, experimental models, and research findings. At the end of the paper, we summarize the challenges and advantages of various cells (including ESCs, iPSCs, and BMSCs) in clinical cell therapy. Our goal is to provide the theoretical and experimental basis for future treatments targeting peripheral nerves, highlighting the potential of cell therapy and tissue engineering as invaluable resources for promoting nerve regeneration.

Ouabain and BDNF Crosstalk on Ganglion Cell Survival in Mixed Retinal Cell Cultures

Brain-derived neurotrophic factor (BDNF) is a well-known and well-studied neurotrophin. Most biological effects of BDNF are mediated by the activation of TrkB receptors. This neurotrophin regulates several neuronal functions as cell proliferation, viability, and differentiation. Ouabain is a steroid that binds to the Na(+)/K(+) ATPase, inducing the activation of several intracellular signaling pathways. Previous data from our group described that ouabain treatment increases retinal ganglion cells survival (RGC). The aim of the present study was to evaluate, if this cardiac glycoside can have a synergistic effect with BDNF, the classical trophic factor for retinal ganglion cells, as well as investigate the intracellular signaling pathways involved. Our work demonstrated that the activation of Src, PLC, and PKCδ participates in the signaling cascade mediated by 50 ng/mL BDNF, since their selective inhibitors completely blocked the trophic effect of BDNF. We also demonstrated a synergistic effect on RGC survival when we concomitantly used ouabain (0.75 nM) and BDNF (10 ng/mL). Moreover, the signaling pathways involved in this synergistic effect include Src, PLC, PKCδ, and JNK. Our results suggest that the synergism between ouabain and BDNF occurs through the activation of the Src pathway, JNK, PLC, and PKCδ.

Effect of CD95 on inflammatory response in rheumatoid arthritis fibroblast-like synoviocytes

OBJECTIVE

Many CD95-expressing cells don't always undergo apoptosis after stimulation with CD95 ligation. The purpose of this paper is to investigate the role of expression of CD95 (Fas/Apo1) on inflammatory response in fibroblast-like synoviocytes (FLS) obtained from rheumatoid arthritis (RA) and to evaluate the role of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB or Akt) pathways within this process.

METHODS

The expression levels of CD95 were monitored by immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR). Apoptotic cells were detected by in situ apoptosis detection (TUNEL) assay. The RA-FLS were treated with agonistic anti-CD95 antibody or CD95 siRNA. Then the proliferation was detected by CCK-8, and mRNA level of inflammatory cytokines was detected by RT-PCR. After the RA-FLS were treated with agonistic anti-CD95 antibody, the total Akt and pAkt protein expression was analyzed by Western blot, and the changes mentioned above were observed while pre-incubated with the PI3K inhibitor LY294002.

RESULTS

A significant increase of CD95 antigen was found in RA compared with osteoarthritis (OA) samples, while apoptosis in RA synovial tissue was not obvious. Low concentrations of agonistic anti-CD95 antibody could promote RA-FLS growth and interleukin-6 (IL-6) mRNA expression, while high concentrations could induce apoptosis. And both of these phenomena could be inhibited by CD95 siRNA. Agonistic anti-CD95 antibody could stimulate the expression of pAkt, and PI3K specific inhibitor LY294002 could induce opposite changes.

CONCLUSION

Stimulation of CD95 could promote RA-FLS proliferation and inflammation, and activation of the PI3K/Akt signaling pathway might be the possible mechanism.

Modulation of Fas-Fas Ligand Interaction Rehabilitates Hypoxia-Induced Apoptosis of Mesenchymal Stem Cells in Ischemic Myocardium Niche

Mesenchymal stem cells (MSCs) have the potential to repair and regenerate ischemic heart tissue; however, the poor viability of transplanted MSCs in the ischemic region is a major obstacle to their therapeutic use. This cell death is caused by Fas and Fas ligand (FasL) interactions under harsh conditions. To investigate improving the survival and therapeutic effects of MSCs, we focused our research on Fas-FasL-mediated cell death. In this study, we found that the poor viability of transplanted MSCs was caused by Fas-FasL interactions between host ischemic myocardial cells and implanted MSCs. In addition, we found that increased Fas expression and the corresponding decrease of cell survival were in close relation to hypoxic MSCs treated with FasL and H2O2. When MSCs were treated with a recombinant Fas/Fc chimera (Fas/Fc) inhibiting Fas-FasL interactions, the expressions of proapoptotic proteins including caspase-8, caspase-3, Bax, and cytochrome-c were attenuated, and the survival of MSCs was recovered. In ischemia-reperfusion injury models, the interaction between FasL in ischemic heart and Fas in implanted MSCs caused a loss of transplanted MSCs, whereas the inhibition of this interaction by Fas/Fc treatment improved cell survival and restored heart function. Thus, our study suggests that Fas-FasL interactions are responsible for activating cell death signaling in implanted stem cells and could be a potential target for improving therapeutic efficacy of stem cells in treating ischemic heart diseases.

Levetiracetam Differentially Alters CD95 Expression of Neuronal Cells and the Mitochondrial Membrane Potential of Immune and Neuronal Cells in vitro

Epilepsy is a neurological seizure disorder that affects over 100 million people worldwide. Levetiracetam, either alone, as monotherapy, or as adjunctive treatment, is widely used to control certain types of seizures. Despite its increasing popularity as a relatively safe and effective anti-convulsive treatment option, its mechanism(s) of action are poorly understood. Studies have suggested neuronal, glial, and immune mechanisms of action. Understanding the precise mechanisms of action of levetiracetam would be extremely beneficial in helping to understand the processes involved in seizure generation and epilepsy. Moreover, a full understanding of these mechanisms would help to create more efficacious treatments while minimizing side-effects. The current study examined the effects of levetiracetam on the mitochondrial membrane potential of neuronal and non-neuronal cells, in vitro, in order to determine if levetiracetam influences metabolic processes in these cell types. In addition, this study sought to address possible immune-mediated mechanisms by determining if levetiracetam alters the expression of immune receptor–ligand pairs. The results show that levetiracetam induces expression of CD95 and CD178 on NGF-treated C17.2 neuronal cells. The results also show that levetiracetam increases mitochondrial membrane potential on C17.2 neuronal cells in the presence of nerve growth factor. In contrast, levetiracetam decreases the mitochondrial membrane potential of splenocytes and this effect was dependent on intact invariant chain, thus implicating immune cell interactions. These results suggest that both neuronal and non-neuronal anti-epileptic activities of levetiracetam involve control over energy metabolism, more specifically, mΔΨ. Future studies are needed to further investigate this potential mechanism of action.

Role of JNK isoforms in the development of neuropathic pain following sciatic nerve transection in the mouse

Background

Current tools for analgesia are often only partially successful, thus investigations of new targets for pain therapy stimulate great interest. Consequent to peripheral nerve injury, c-Jun N-terminal kinase (JNK) activity in cells of the dorsal root ganglia (DRGs) and spinal cord is involved in triggering neuropathic pain. However, the relative contribution of distinct JNK isoforms is unclear. Using knockout mice for single isoforms, and blockade of JNK activity by a peptide inhibitor, we have used behavioral tests to analyze the contribution of JNK in the development of neuropathic pain after unilateral sciatic nerve transection. In addition, immunohistochemical labelling for the growth associated protein (GAP)-43 and Calcitonin Gene Related Peptide (CGRP) in DRGs was used to relate injury related compensatory growth to altered sensory function.

Results

Peripheral nerve injury produced pain–related behavior on the ipsilateral hindpaw, accompanied by an increase in the percentage of GAP43-immunoreactive (IR) neurons and a decrease in the percentage of CGRP-IR neurons in the lumbar DRGs. The JNK inhibitor, D-JNKI-1, successfully modulated the effects of the sciatic nerve transection. The onset of neuropathic pain was not prevented by the deletion of a single JNK isoform, leading us to conclude that all JNK isoforms collectively contribute to maintain neuropathy. Autotomy behavior, typically induced by sciatic nerve axotomy, was absent in both the JNK1 and JNK3 knockout mice.

Conclusions

JNK signaling plays an important role in regulating pain threshold: the inhibition of all of the JNK isoforms prevents the onset of neuropathic pain, while the deletion of a single splice JNK isoform mitigates established sensory abnormalities. JNK inactivation also has an effect on axonal sprouting following peripheral nerve injury.

MKK7γ1 reverses nerve growth factor signals: proliferation and cell death instead of neuritogenesis and protection

c-Jun N-terminal kinases (JNKs) are the exclusive downstream substrates of mitogen-activated protein kinase kinase 7 (MKK7). Recently, we have shown that a single MKK7 splice variant, MKK7γ1, substantially changes the functions of JNKs in naïve PC12 cells. Here we provide evidence that MKK7γ1 blocks NGF-mediated differentiation and sustains proliferation by interfering with the NGF-triggered differentiation programme at several levels: (i) down-regulation of the NGF receptors TrkA and p75; (ii) attenuation of the differentiation-promoting pathways ERK1/2 and AKT; (iii) increase of JNK1 and JNK2, especially the JNK2 54kDa splice variants; (iv) repression of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1), which normally supports NGF-mediated cell cycle arrest; (v) strong induction of the cell cycle promoter CyclinD1, and (vi) profound changes of p53 functions. Moreover, MKK7γ1 substantially changes the responsiveness to stress. Whereas NGF differentiation protects PC12 cells against taxol-induced apoptosis, MKK7γ1 triggers an escape from cell cycle arrest and renders transfected cells sensitive to taxol-induced death. This stress response completely differs from naïve PC12 cells, where MKK7γ1 protects against taxol-induced cell death. These novel aspects on the regulation of JNK signalling emphasise the importance of MKK7γ1 in its ability to reverse basic cellular programmes by simply using JNKs as effectors. Furthermore, our results highlight the necessity for the cells to balance the expression of JNK activators to ensure precise intracellular processes.

Control of TrkA-induced cell death by JNK activation and differential expression of TrkA upon DNA damage

TrkA, a receptor for nerve growth factor, plays a crucial role in neuronal cell growth and differentiation. However, overactivation of TrkA signaling leads to cell death in various cell types. TrkA-mediated cell death shows some similarities to DNA damage-induced cell death. In this study, we examined how TrkA-induced cell death is regulated upon DNA damage. Cytoplasmic expression of TrkA protein was differentially modulated during the camptothecin-induced DNA damage response in TrkA-expressing U2OS cells. TrkA-induced cell death was synergistically increased by DNA damage, but it was blocked in the presence of the JNK inhibitor SP600125. Overexpression of a 54-kDa JNK isoform (JNK1alpha2) aggravated TrkA-induced cell death and was associated with TrkA functional activation. These results suggest that TrkA shares a functional connection with other mediators in the DNA damage response via JNK signaling.

Non-apoptotic Fas signaling regulates invasiveness of glioma cells and modulates MMP-2 activity via NFkappaB-TIMP-2 pathway

Fas (CD95/APO-1) is a cell surface "death receptor" that mediates apoptosis upon engagement by its ligand, FasL. Paradoxically, Fas/FasL can also promote cell invasion among non-apoptotic cells; here, we show that Fas/FasL signaling can promote tumor invasion when apoptosis is compromised. We have developed a recombinant FasL Interfering Protein (FIP) to interfere with Fas signaling in C6 glioma cells expressing both Fas receptor and its ligand. FIP administration did not affect cell viability but impaired cell motility and invasiveness of glioma cells. Blockade of Fas signaling reduced MMP-2 activity in glioma cells, that was associated with down-regulation of MAPK signaling, and AP-1 and NFkappaB-driven transcription. FIP treatment did not affect mmp-2 and mt1-mmp expression but significantly attenuated timp-2 expression and TIMP-2 amount in the culture medium. Studies with pharmacological inhibitors of JNK/c-Jun (SP600125) and NFkappaB (BAY11-7082) signaling pathways demonstrated that timp-2 expression is regulated by NFkappaB transcription factor. Our findings show that non-apoptotic Fas signaling activated in the autocrine manner or through microenvironment derived factors can regulate invasiveness of glioma cells via modulation of MMP-2 activation, likely by controlling TIMP-2 expression.