CXCL1-CXCR2 axis mediates inflammatory response after sciatic nerve injury by regulating macrophage infiltration

ARA290, an alternative of erythropoietin, inhibits activation of NLRP3 inflammasome in schwann cells after sciatic nerve injury

The challenge of repairing peripheral nerve injury is a critical issue that needs to be addressed urgently. Previous research has shown that erythropoietin (EPO) and its prolonged peptides exhibit beneficial effects in neurological disorders. In our study, we demonstrated that both EPO and pyroglutamic acid helix B surface peptide (pHBSP, also known as ARA290) inhibit the early inflammatory response and promote functional recovery after sciatic nerve crush injury in rat models. Our experimental results demonstrate that significant inflammatory response occurred in Schwann cells after sciatic nerve injury, and that the activation of NLRP3 inflammasome in Schwann cells is inhibited after EPO and ARA290 treatment. Our study further demonstrated that EPO and ARA290 inhibit the activation of NLRP3 inflammasome in Schwann cells by inhibiting NF-κB phosphorylation and reducing reactive oxygen species (ROS) production. In summary, EPO and ARA290 promote repair and regeneration by inhibiting the activation of NLRP3 inflammasome after sciatic nerve injury.

Mendelian randomization combined with single-cell sequencing data analysis of chemokines and chemokine receptors and key genes and molecular mechanisms associated with epilepsy

OBJECTIVE

To explore the functions and potential regulatory mechanisms of chemokine and chemokine receptor (CCR)-related genes in epilepsy.

METHODS

CCRs were identified as candidate genes and their causal relationship with epilepsy was rigorously evaluated via Mendelian randomization analysis. Subsequently, single-cell RNA sequencing (scRNA-seq) data were analyzed to identify and classify cell clusters into distinct types based on cellular annotation. Differential expression analysis was conducted to pinpoint key genes by overlapping the candidate gene set with differentially expressed genes (DEGs). Furthermore, potential therapeutic drugs for epilepsy were predicted, offering novel avenues for disease management and treatment.

RESULTS

In total, 6395 DEGs were identified across the six cell clusters. After their intersection, CCRL2, XCL2, CXCR5, CXCL1, and CX3CR1 were pinpointed as key genes. Microglia, T cells, B cells, and macrophages have been emerged as critical cells. Furthermore, CXCL1 was regulated by hsa-miR-570-3p and hsa-miR-532-5p. Notably, CXCR5, CXCL1, and CX3CR1 were associated with 27 drug compounds. This comprehensive study leveraged scRNA-seq and transcriptomic data to elucidate the roles of CCR-related genes in epilepsy. Notably, CCRL2, XCL2, CXCR5, CXCL1,and CX3CR1 were identified as key genes implicated in epilepsy, whereas microglia, T cells, B cells, and macrophages were recognized as critical contributors to the development of epilepsy.

CONCLUSIONS

Regulating the expression of CCRL2, XCL2, CXCR5, CXCL1, and CX3CR1, along with the activity of these immune cells may offer therapeutic potential for the alleviation of epilepsy.

Immune characteristics of olfactory ensheathing cells and repair of nerve injury

The process of nerve injury is accompanied by the change of inflammatory microenvironment, which is not conducive to axonal regeneration and hinders the repair of injured nerve. Therefore, looking for a way to improve the inflammatory attack and immune state around the injured nerve is beneficial to the progress of nerve injury repair. In recent years, cell transplantation strategy has played a foreground role in the repair of nerve injury. Olfactory ensheathing cells (OECs) are a special kind of glial cells, which have the characteristics of continuous renewal and survival, antigenic characteristics, variability and promoting the repair of nerve injury. OECs have been recognized in different injury models, including clinical trials, which has become a dominant cell in cell replacement therapy. An important feature of OECs lies in their anti-inflammatory and immunomodulatory functions. They are transplanted into the host to improve the catastrophic inflammatory microenvironment caused by injured nerves, thus promoting the repair and regeneration of injured nerves. The transplantation of OECs into the host can provide good groundwork and support for the repair and regeneration of nerve injury by regulating the activity and infiltration of immune cells, the secretion of inflammatory cytokines and phagocytosis. Therefore, this paper discusses the anti-inflammatory and immunomodulatory mechanisms of OECs transplantation in the repair of nerve injury and the functional role of OECs as an ideal substitute in the treatment of nerve injury.

The dual roles of chemokines in peripheral nerve injury and repair

Peripheral nerve injuries (PNI) occur in approximately 13-23 per 100,000 individuals, predominantly affecting young and middle-aged adults. These injuries often require a lengthy recovery period, placing substantial burdens on healthcare systems and national economies. Current treatment strategies have not significantly shortened this lengthy regenerative process, highlighting the urgent need for innovative therapeutic interventions. Chemokines were originally noted for their powerful ability to recruit immune cells; however, as research has advanced, it has become increasingly evident that their role in peripheral nerve repair has been underestimated. In this review, we provide the first comprehensive overview of chemokine expression and activity during peripheral nerve injury and regeneration. We summarize the existing literature on chemokine family members, detailing their expression patterns and localization in injured nerves to facilitate further mechanistic investigations. For chemokines that remain controversial, such as CXCL1 and CCL2, we critically examine experimental methodologies and discuss factors underlying conflicting results, ultimately affirming their contributions to promoting nerve repair. Importantly, we highlight the dual nature of chemokines: in the early stages of injury, they initiate reparative responses, activate Schwann cells, regulate Wallerian degeneration, and support nerve recovery; but when the axons are connected and the repair enters the later stages, their persistent proinflammatory effects during later stages may impede the healing process. Additionally, we emphasize that certain chemokines, including CXCL5, CXCL12, and CCL2, can act directly on neurons/axons, thereby accelerating axonal regeneration. Future research should focus on precisely mapping the localization and temporal expression profiles of these chemokines and exploring therapeutic approaches.

CXCR2 mediated trafficking of neutrophils and neutrophil extracellular traps are required for myelin clearance after a peripheral nerve injury

Neutrophils are a vital part of the innate immune system. Many of their functions eliminate bacteria & viruses, like neutrophil extracellular traps (NETs), which trap bacteria, enhancing macrophage phagocytosis. It was surprising when it was demonstrated that neutrophils are a part of Wallerian degeneration, a process that is essential for nerve regeneration after a nerve injury. It is not known what signals attract neutrophils into the nerve and how they aid Wallerian degeneration. Neutrophils accumulate in the distal nerve within one day after an injury and are found in the nerve from one to three days. We demonstrate that CXCR2 mediates the trafficking of neutrophils into the distal nerve, and without CXCR2 Wallerian degeneration, as indicated by luxol fast blue staining, was reduced seven days after a sciatic nerve crush or transection injury. NETs were detected in the distal nerve after a sciatic nerve transection. NET formation has been shown to require protein arginine deiminase 4 (PAD4), which citrullinates histone 3. Inhibiting PAD4 reduced NET formation significantly in the distal nerve at two days and myelin clearance at seven days indicating that NETs aid myelin clearance. These results demonstrate another function for NETs other than clearing pathogens. Neutrophils have been detected after injuries to the central nervous system and diseases in humans and animal models. Our results demonstrate neutrophils aid myelin clearance, suggesting a role for their presence in central nervous system injuries and diseases.