Electroacupuncture alleviates neuropathic pain caused by SNL by promoting M2 microglia polarization through PD-L1

CD28 Superfamily Costimulatory Molecules in Chronic Pain: Focus on Immunomodulation

Chronic pain has substantial effects on patients' quality of life and psychological well-being. It does not respond satisfactorily to available medicinal therapeutics because its mechanism remains unclear. Recent studies have shown a strong relationship between chronic pain and immunomodulation. As important members of the immune response, CD28 superfamily costimulatory molecules were demonstrated to have an analgesic effect on chronic pain. Based on research on the role of these molecules in chronic pain, new and highly effective analgesic medicines are anticipated that could be used in combination with some previous analgesic medicines to reduce substance abuse and side effects. This review of the literature will examine the pain-regulating mechanisms of CD28 superfamily costimulatory molecules, focusing on immunomodulation. In addition, this review will discuss the potential and difficulties of developing novel analgesic medicines targeting CD28 superfamily costimulatory molecules.

GDF11 Mitigates Neuropathic Pain via Regulation of Microglial Polarization and Neuroinflammation through TGF-βR1/SMAD2/NF-κB Pathway in Male Mice

Spinal microglial activation and the polarization towards the M1 phenotype are implicated in the pathological process of neuropathic pain. Extensive research has elucidated that growth and differentiation factor 11 (GDF11), a constituent of the transforming growth factor-β (TGF-β) superfamily, exerts inhibitory effects on macrophage activation and mitigates inflammatory responses via the activation of TGF-β receptor type I (TGF-βR1). Nonetheless, the influence of GDF11 on spinal microglial polarization and its role in neuropathic pain remains to be ascertained. In the present investigation, a neuropathic pain model was induced via a spared nerve injury (SNI) procedure on the sciatic nerve in male mice. The impact of GDF11 on microglial polarization and neuropathic pain in SNI-subjected mice was evaluated through pain behavior assessments, WB, IF, qRT-PCR, and ELISA. Our findings revealed a significant downregulation of spinal GDF11 and TGF-βR1 expression levels in microglia of mice subjected to SNI. Furthermore, GDF11 treatment notably reversed the mechanical allodynia and thermal hyperalgesia, inhibited M1 microglial polarization, and attenuated neuroinflammatory processes by modulating the SMAD2/NF-κB in SNI mice. However, the analgesic effects of GDF11 on pain hypersensitivity and its modulatory influence on spinal microglial polarization were abrogated by the application of a specific antagonist of TGF-βR1, or the TGF-βR1 siRNA. In summary, GDF11 effectively ameliorated mechanical allodynia and thermal hyperalgesia, suppressed M1 microglial polarization, and alleviated neuroinflammation via the regulation of the TGF-βR1/SMAD2/NF-κB pathway in mice with SNI. These findings suggest that GDF11 holds promise as a therapeutic modality for the management of neuropathic pain.

Preclinical Insights into the Role of Kir4.1 in Chronic Pain and Depression: Mechanisms and Therapeutic Potential

Chronic pain and mental health disorders, such as depression and anxiety, frequently co-occur and share underlying mechanisms involving neuronal excitability and synaptic transmission. The inwardly rectifying potassium channel 4.1 (Kir4.1), predominantly expressed in glial cells, is crucial for maintaining extracellular potassium and glutamate homeostasis. Dysregulation of Kir4.1 leads to altered neuronal activity, contributing to both chronic pain and mental health disorders. In chronic pain, downregulation of Kir4.1 impairs potassium buffering and glutamate clearance, increasing neuronal excitability and enhancing pain signaling through peripheral and central sensitization. In mental health disorders, impaired Kir4.1 function disrupts neurotrophic factor secretion and neuroinflammatory pathways, leading to mood disturbances. This review primarily summarizes findings from preclinical studies to examine the relationship between Kir4.1 and the pathogenesis of chronic pain and mental health disorders, discussing its molecular structure, expression patterns, and functional roles. Furthermore, we explore therapeutic strategies targeting Kir4.1, including pharmacological modulators and gene therapy approaches, emphasizing its potential as a novel therapeutic target.

Photobiomodulation Combined With Human Umbilical Cord Mesenchymal Stem Cells Modulates the Polarization of Microglia

Neuroinflammation plays a key role in the development of neurodegenerative diseases, with microglia regulating this process through pro-inflammatory M1 and anti-inflammatory M2 phenotypes. Studies have shown that human umbilical cord mesenchymal stem cells (hUCMSCs) modulate neuroinflammation by secreting anti-inflammatory cytokines. Photobiomodulation (PBM), a non-invasive therapy, has demonstrated significant potential in alleviating neuroinflammation. This study examines the combined effects of PBM and hUCMSCs in an in vitro microglial inflammation model and an LPS-induced mouse model. The results show that PBM-pretreated hUCMSCs promoted M2 polarization and improved cognitive function in mice by downregulating the Notch signaling pathway, suggesting a promising new approach for treating neurodegenerative diseases.

Acupuncture in the treatment of chemotherapy-induced peripheral neuropathy: a meta-analysis and data mining

Background

The efficacy and acupoint selection of acupuncture in treating chemotherapy-induced peripheral neuropathy (CIPN) remain controversial. This study aims to explore the specific efficacy and acupoint selection of acupuncture in treating CIPN through a meta-analysis and data mining.

Methods

Searching for clinical trials on acupuncture treatment for CIPN in 8 databases, evaluating its efficacy and safety through a meta-analysis, and exploring its acupoint selection through data mining.

Results

The meta-analysis included 21 studies and 2,121 patients, showing that compared with the control group, the acupuncture group could significantly improve neuropathic pain intensity (SMD = -0.66, 95% CI [-1.07, -0.25], p = 0.002), significantly reduce the NCI-CTCAE (MD = -0.29, 95%CI [-0.50, -0.08], p < 0.01), significantly reduce the FACT-NXT score (MD = 2.09, 95% CI [0.73,3.45], p < 0.05), significantly increase the motor conduction velocities (MCV) of median nerve (MD = 2.38, 95% CI [2.10, 2.67], p < 0.001), the sensory conduction velocities (SCV) of the median nerve (MD = 0.56, 95 %CI [-1.45, 2.57], p = 0.58), the SCV of the tibial nerve (MD = 1.78, 95% CI [0.50, 3.05], p < 0.01), and the SCV of sural nerves (MD = 4.60, 95% CI [0.17, 9.02], p < 0.05), as well as improving the quality of life score (MD =7.35, 95% CI [1.53, 13.18], p = 0.01). Data mining showed that the core acupoints for acupuncture treatment of CIPN were LI4, ST36, LI11, LR3, and SP6.

Conclusion

Acupuncture can improve the neuropathic pain intensity, the intensity of the CIPN, MCV of the median nerve, SCV of the tibial nerve and peroneal nerve, quality of life, and has good safety in CIPN patients. LI4 (Hegu), ST36 (Zusanli), LI11 (Quchi), LR3 (Taichong), and SP6 (Sanyinjiao) are the core acupuncture points for treating CIPN, and this protocol has the potential to become a supplementary treatment for CIPN.

Systematic review registration

https://www.crd.york.ac.uk/prospero, identifier CRD42024551137.

CTRP9 attenuates peripheral nerve injury-induced mechanical allodynia and thermal hyperalgesia through regulating spinal microglial polarization and neuroinflammation mediated by AdipoR1 in male mice

Peripheral nerve injury triggers rapid microglial activation, promoting M1 polarization within the spinal cord, which exacerbates the progression of neuropathic pain. C1q/TNF-related protein 9 (CTRP9), an adiponectin homolog, is known to suppress macrophage activation and exhibit anti-inflammatory properties through the activation of adiponectin receptor 1 (AdipoR1) in various disease contexts. Nevertheless, the involvement of CTRP9 in microglial polarization in the context of neuropathic pain is still unclear. Our study aimed to how CTRP9 influences spinal microglial polarization, neuroinflammation, and pain hypersensitivity, as well as the underlying mechanism, using a neuropathic pain model in male mice with spared nerve injury (SNI) of sciatic nerve. Our findings revealed SNI elevated the spinal CTRP9 and AdipoR1 levels in microglia. Furthermore, intrathecal administration of recombinant CTRP9 (rCTRP9) substantially weakened mechanical hypersensitivity and heat-related pain response triggered by SNI. On the other hand, rCTRP9 mediated a phenotypic switch in microglia, from the pro-inflammatory M1 state to the anti-inflammatory M2 state, by influencing the spinal AMPK/NF-κB mechanism in SNI mice. Additionally, treatment with AdipoR1 siRNA or an AMPK-specific antagonist both reversed the effects of CTRP9 on the phenotypic switching of spinal microglia and pain hypersensitivity. Collectively, these results indicate that CTRP9 ameliorates mechanical hypersensitivity and heat-related pain response, shifted the balance of microglia towards the anti-inflammatory M2 state, and suppresses neuroinflammatory responses by modulating the AMPK/NF-κB pathway, mediated by AdipoR1 activation, in mice with SNI.

PD-1 mediates microglia polarization via the MAPK signaling pathway to protect blood-brain barrier function during cerebral ischemia/reperfusion

BACKGROUND

Cerebral ischemia is characterized by its rapid onset and high rates of recurrence, morbidity, and mortality, with blood-brain barrier (BBB) permeability playing a vital role in brain injury. Therefore, it is important to understand the molecular mechanism which regulates the BBB during cerebral ischemia.

MATERIALS AND METHODS

An in vitro model of oxygen-glucose deprivation (OGD) and an in vivo model of cerebral ischemia/reperfusion (I/R) were constructed. PD-1 overexpression vectors and vectors containing si-RNA were transfected and injected into in vitro and in vivo models. Western blotting, real-time quantitative PCR (qPCR), immunofluorescence (IF) analysis, and immunohistochemical staining were employed to evaluate the expression levels of programmed cell death-1 (PD-1), microglia M1 and M2 biomarkers, and tight junction proteins. Flow cytometry and ELISA were used to measure the levels of pro-inflammatory cytokines. The BBB permeability of brain tissues was evaluated by Evans blue dye (EBD) extravasation and transendothelial electrical resistance (TEER). Brain water content was measured to assess the extent of inflammatory exudation. The infarct volume and neurological severity score (NSS) were used to assess the severity of brain injury. Brain cell apoptosis was assessed by the TUNEL assay and hematoxylin-eosin (H&E) staining.

RESULTS

PD-1 helped to convert the microglia M1 phenotype to the M2 phenotype and to reduce BBB permeability both in vitro and in vivo. Overexpression of PD-1 promoted a shift of the M1 phenotype to the M2 phenotype and reduced BBB permeability via the ERK and p38 MAPK signaling pathways. PD-1 reduced inflammatory exudation, BBB permeability, cell apoptosis, and brain injury in vivo.

CONCLUSION

Our present study verified that PD-1 exerts an anti-inflammatory effect by converting the microglia M1 phenotype to the M2 phenotype, reducing BBB permeability, and thereby relieves brain injury caused by cerebral ischemia. PD-1 is potential therapeutic target for brain injury caused by cerebral ischemia.

MFG-E8 Ameliorates Nerve Injury-Induced Neuropathic Pain by Regulating Microglial Polarization and Neuroinflammation via Integrin β3/SOCS3/STAT3 Pathway in Mice

Spinal microglial polarization plays a crucial role in the pathological processes of neuropathic pain following peripheral nerve injury. Accumulating evidence suggests that milk fat globule epidermal growth factor-8 (MFG-E8) exhibits anti-inflammatory effect and regulates microglial polarization through the integrin β3 receptor. However, the impact of MFG-E8 on microglial polarization in the context of neuropathic pain has not yet been investigated. In this study, we evaluated the effect of MFG-E8 on pain hypersensitivity and spinal microglial polarization following spared nerve injury (SNI) of the sciatic nerve in mice. We determined the molecular mechanisms underlying the effects of MFG-E8 on pain hypersensitivity and spinal microglial polarization using pain behavior assessment, western blot (WB) analysis, immunofluorescence (IF) staining, quantitative polymerase chain reaction (qPCR), enzyme-linked immunosorbent assay (ELISA), and small interfering RNA (siRNA) transfection. Our findings indicate that SNI significantly increased the levels of MFG-E8 and integrin β3 expressed in microglia within the spinal cord of mice. Additionally, we observed that intrathecal injection of recombinant human MFG-E8 (rhMFG-E8) alleviated SNI induced-mechanical allodynia and thermal hyperalgesia. Furthermore, the results suggested that rhMFG-E8 facilitated M2 microglial polarization and ameliorated neuroinflammation via integrin β3/SOCS3/STAT3 pathway in the spinal cord of mice with SNI. Importantly, these effects were negated by integrin β3 siRNA, or SOCS3 siRNA. These results demonstrate that MFG-E8 ameliorates peripheral nerve injury induced-mechanical allodynia and thermal hyperalgesia by driving M2 microglial polarization and mitigating neuroinflammation mediated by integrin β3/SOCS3/STAT3 pathway in the spinal cord of mice. MFG-E8 may serve as a promising target for the treatment of neuropathic pain.

Sex differences in PD-L1-induced analgesia in paclitaxel-induced peripheral neuropathy mice depend on TRPV1-based inhibition of CGRP

AIMS

Paclitaxel (PTX) is extensively utilized in the management of diverse solid tumors, frequently resulting in paclitaxel-induced peripheral neuropathy (PIPN). The present study aimed to investigate sex differences in the behavioral manifestations and underlying pathogenesis of PIPN and search for clinically efficacious interventions.

METHODS

Male and female C57BL/6 mice (5-6 weeks and 12 months, weighing 18-30 g) were intraperitoneally (i.p.) administered paclitaxel diluted in saline (NaCl 0.9%) at a dose of 2 mg/kg every other day for a total of 4 injections. Von Frey and hot plate tests were performed before and after administration to confirm the successful establishment of the PIPN model and also to evaluate the pain of PIPN and the analgesic effect of PD-L1. On day 14 after PTX administration, PD-L1 protein (10 ng/pc) was injected into the PIPN via the intrathecal (i.t.) route. To knock down TRPV1 in the spinal cord, adeno-associated virus 9 (AAV9)-Trpv1-RNAi (5 μL, 1 × 1013 vg/mL) was slowly injected via the i.t. route. Four weeks after AAV9 delivery, the downregulation of TRPV1 expression was verified by immunofluorescence staining and Western blotting. The levels of PD-L1, TRPV1 and CGRP were measured via Western blotting, RT-PCR, and immunofluorescence staining. The levels of TNF-α and IL-1β were measured via RT-PCR.

RESULTS

TRPV1 and CGRP protein and mRNA levels were higher in the spinal cords of control female mice than in those of control male mice. PTX-induced nociceptive behaviors in female PIPN mice were greater than those in male PIPN mice, as indicated by increased expression of TRPV1 and CGRP. The analgesic effects of PD-L1 on mechanical hyperalgesia and thermal sensitivity were significantly greater in female mice than in male mice, with calculated relative therapeutic levels increasing by approximately 2.717-fold and 2.303-fold, respectively. PD-L1 and CGRP were partly co-localized with TRPV1 in the dorsal horn of the mouse spinal cord. The analgesic effect of PD-L1 in PIPN mice was observed to be mediated through the downregulation of TRPV1 and CGRP expression following AAV9-mediated spinal cord specific decreased TRPV1 expression.

CONCLUSIONS

PTX-induced nociceptive behaviors and the analgesic effect of PD-L1 in PIPN mice were sexually dimorphic, highlighting the significance of incorporating sex as a crucial biological factor in forthcoming mechanistic studies of PIPN and providing insights for potential sex-specific therapeutic approaches.

PD-L1/PD-1 pathway: a potential neuroimmune target for pain relief

Pain is a common symptom of many diseases with a high incidence rate. Clinically, drug treatment, as the main method to relieve pain at present, is often accompanied by different degrees of adverse reactions. Therefore, it is urgent to gain a profound understanding of the pain mechanisms in order to develop advantageous analgesic targets. The PD-L1/PD-1 pathway, an important inhibitory molecule in the immune system, has taken part in regulating neuroinflammation and immune response. Accumulating evidence indicates that the PD-L1/PD-1 pathway is aberrantly activated in various pain models. And blocking PD-L1/PD-1 pathway will aggravate pain behaviors. This review aims to summarize the emerging evidence on the role of the PD-L1/PD-1 pathway in alleviating pain and provide an overview of the mechanisms involved in pain resolution, including the regulation of macrophages, microglia, T cells, as well as nociceptor neurons. However, its underlying mechanism still needs to be further elucidated in the future. In conclusion, despite more deep researches are needed, these pioneering studies indicate that PD-L1/PD-1 may be a potential neuroimmune target for pain relief.

Obacunone Alleviates Inflammatory Pain by Promoting M2 Microglial Polarization and by Activating Nrf2/HO-1 Signaling Pathway

Background

Treating inflammatory pain (IP) continues to pose clinical challenge, because of the lack of effective pharmacological interventions. Microglial polarization serves as pivotal determinant in IP progress. Obacunone (OB), a low-molecular-weight compound with a diverse array of biological functions, having reported as an activator of nuclear factor E2-related factor 2 (Nrf2), exhibits anti-inflammatory property. However, it remains uncertain whether OB can alleviate IP by facilitating the transition of microglial polarization from the M1 to M2 state through modulating Nrf2/ heme oxygenase-1 (HO-1) pathway.

Methods

We induced an mice IP model by subcutaneously administering Complete Freund's Adjuvant (CFA) into the hind paw. Paw withdrawal latency (PWL) in seconds (s) and paw withdrawal frequency (PWF) were employed to evaluate the establishment of the IP model, while a caliper was used to measure the maximal dorsoventral thickness of the mice paw. Nerve injury was assessed by Hematoxylin-Eosin (HE) Staining. Western blot and got conducted for detection of M1/M2 microglial polarization markers, Nrf2 and HO-1 in spinal cord tissues respectively.

Results

In comparison to the control cohort, PWF, M1 phenotype marker iNOS, CD86, paw thickness increased significantly within CFA cohort, while PWL, M2 phenotype marker Arg-1, interleukin-10 (IL-10) decreased in the CFA group. In comparison to model cohort, OB treatment decreased PWF, paw thickness, M1 phenotype marker iNOS, CD86 significantly, while PWL, M2 phenotype marker Arg-1, IL-10, Nrf2, HO-1 increased significantly. The morphological injuries of sciatic nerve in CFA mice were obviously improved by OB treatment. OB inhibited the release of M1-related IL-1β, CXCL1 but promoted M2-related TGF-β, IL-10 in serum in CFA mice. The intervention of the Nrf2 inhibitor ML385 mitigated analgesic effect of OB.

Conclusion

We demonstrate that OB is able to attenuate inflammatory pain via promoting microglia polarization from M1 to M2 and enhancing Nrf2/HO-1 signal. OB treatment may be a potential alternative agent in the treatment of IP.

Combination of Anti-PD-1 and Electroacupuncture Induces a Potent Antitumor Immune Response in Microsatellite-Stable Colorectal Cancer

Programmed death receptor-1 (PD-1) inhibitors are ineffective against microsatellite-stable (MSS) colorectal cancer. Electroacupuncture (EA) has oncosuppressive and immunomodulatory properties. Here, we investigated the antitumor effects of EA and explored the feasibility of EA combined with anti-PD-1 in MSS colorectal cancer. Results showed that EA exerted its antitumor effect in an intensity-specific manner, and moderate-intensity EA (1.0 mA) induced maximal tumor inhibition. EA enhanced antitumor immune responses by increasing lymphocytes and granzyme B (GzmB) levels, as well as activating the stimulator of IFN genes (STING) pathway. EA combined with anti-PD-1 showed superior efficacy compared with either monotherapy in multiple MSS colorectal cancer mouse models. Single-cell RNA sequencing revealed that cotreatment reprogrammed the tumor immune microenvironment (TIME), as characterized by enhancement of cytotoxic functions. Mechanically, we found that the potentiated effect of EA was dependent upon the STING pathway. Collectively, EA reshapes the TIME of MSS colorectal cancer and sensitizes tumors to anti-PD-1 in a STING pathway-dependent manner. These results provide a mechanistic rationale for using EA as an immunomodulatory strategy to improve the clinical efficacy of anti-PD-1 in MSS colorectal cancer. EA is safe, well-tolerated, and feasible for clinical translation as a promising strategy for treating MSS colorectal cancer.