Dihydromyricetin attenuates neuropathic pain via enhancing the transition from M1 to M2 phenotype polarization by potentially elevating ALDH2 activity in vitro and vivo

Transcriptome analysis unveils PLSCR1 associated with microglial polarization in neuropathic pain

Neuropathic pain (NP) continues to be a significant problem that lacks effective treatment. Our study sought to explore a new promising gene target for the treatment of NP. Differential and enrichment analyses were performed on 24,197 genes and 12,088 genes from the NP microglial microarray and sequencing dataset. Candidate differentially expressed genes (DEGs), functions, and signaling pathways that are closely related to NP were identified by analyzing the bioinformatic results. For in vivo experiments, mice were divided into the sham and NP groups. The expressions of DEGs were validated to screen out the NP hub genes. For in vitro experiments, the hub genes in resting M0-BV2 and polarized M1-BV2 microglia were examined by immunofluorescence, flow cytometry, and qRT-PCR. DEGs in the NP microarray and sequencing data shared five candidate genes, CD244, MEGF9, PCGF2, PLSCR1, and NECAB2. The results of the in vivo experiment showed that the NP model group exhibited higher expression of PLSCR1 and MEGF9 compared to the sham group. The enrichment results of the DEGs revealed the biological processes of "response to lipopolysaccharide". PLSCR1 was highly expressed in the lipopolysaccharide-induced M1-BV2 microglia. PLSCR1 is a potential gene associated with microglial polarization in NP. These findings provide a new view on understanding the pathogenesis mechanism of NP.

Amygdala-Targeted Relief of Neuropathic Pain: Efficacy of Repetitive Transcranial Magnetic Stimulation in NLRP3 Pathway Suppression

This study investigates the effectiveness of repetitive transcranial magnetic stimulation (rTMS) as a nonpharmacological approach to treating neuropathic pain (NP), a major challenge in clinical research. Conducted on male Sprague-Dawley rats with NP induced through chronic constriction injury of the sciatic nerve, the research assessed pain behaviors and the impact of rTMS on molecular interactions within the amygdala. Through a comprehensive analysis involving Mechanical Withdrawal Threshold (MWT), Thermal Withdrawal Latency (TWL), RNA transcriptome sequencing, RT-qPCR, Western blotting, immunofluorescence staining, and Co-Immunoprecipitation (Co-IP), the study focused on the expression and interaction of integrin αvβ3 and its receptor P2X7R. Findings reveal that rTMS significantly influences the expression of integrin αvβ3 in NP models, suggesting an inhibition of the NP-associated NLRP3 inflammatory pathway through the disruption of integrin αvβ3-P2X7R interactions. These outcomes highlight the potential of rTMS in alleviating NP by targeting molecular interactions within the amygdala, offering a promising therapeutic avenue for managing NP.

The role of ALDH2 rs671 polymorphism and C-reactive protein in the phenotypes of male ALS patients

Background

The aldehyde dehydrogenase 2 (ALDH2) rs671 (A) allele has been implicated in neurodegeneration, potentially through oxidative and inflammatory pathways. The study aims to investigate the effects of the ALDH2 rs671 (A) allele and high sensitivity C-reactive protein (hs-CRP) on the clinical phenotypes of amyotrophic lateral sclerosis (ALS) in male and female patients.

Methods

Clinical data and ALDH2 rs671 genotype of 143 ALS patients, including 85 males and 58 females, were collected from January 2018 to December 2022. All patients underwent assessment using the Chinese version of the Edinburgh Cognitive and Behavioral ALS Screen (ECAS). Complete blood count and metabolic profiles were measured. Clinical and laboratory parameters were compared between carriers and non-carriers of the rs671 (A) allele in males and females, respectively. The significant parameters and rs671 (A) Allele were included in multivariate linear regression models to identify potential contributors to motor and cognitive impairment. Mediation analysis was employed to evaluate any mediation effects.

Results

Male patients carrying rs671 (A) allele exhibited higher levels of hs-CRP than non-carriers (1.70 mg/L vs. 0.50 mg/L, p = 0.006). The rs671 (A) allele was identified as an independent risk factor for faster disease progression only in male patients (β = 0.274, 95% CI = 0.048-0.499, p = 0.018). The effect of the rs671 (A) allele on the executive function in male patients was fully mediated by hs-CRP (Indirect effect = -1.790, 95% CI = -4.555--0.225). No effects of the rs671 (A) allele or hs-CRP were observed in female ALS patients. The effects of the ALDH2 rs671 (A) allele and the mediating role of hs-CRP in male patients remained significant in the sensitivity analyses.

Conclusion

The ALDH2 rs671 (A) allele contributed to faster disease progression and hs-CRP mediated cognitive impairment in male ALS patients.

The role of aldehyde dehydrogenase 2 in cardiovascular disease

Aldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme involved in the detoxification of alcohol-derived acetaldehyde and endogenous aldehydes. The inactivating ALDH2 rs671 polymorphism, present in up to 8% of the global population and in up to 50% of the East Asian population, is associated with increased risk of cardiovascular conditions such as coronary artery disease, alcohol-induced cardiac dysfunction, pulmonary arterial hypertension, heart failure and drug-induced cardiotoxicity. Although numerous studies have attributed an accumulation of aldehydes (secondary to alcohol consumption, ischaemia or elevated oxidative stress) to an increased risk of cardiovascular disease (CVD), this accumulation alone does not explain the emerging protective role of ALDH2 rs671 against ageing-related cardiac dysfunction and the development of aortic aneurysm or dissection. ALDH2 can also modulate risk factors associated with atherosclerosis, such as cholesterol biosynthesis and HDL biogenesis in hepatocytes and foam cell formation and efferocytosis in macrophages, via non-enzymatic pathways. In this Review, we summarize the basic biology and the clinical relevance of the enzymatic and non-enzymatic, tissue-specific roles of ALDH2 in CVD, and discuss the future directions in the research and development of therapeutic strategies targeting ALDH2. A thorough understanding of the complex roles of ALDH2 in CVD will improve the diagnosis, management and prognosis of patients with CVD who harbour the ALDH2 rs671 polymorphism.

Dihydromyricetin suppresses inflammatory injury in microglial cells to improve neurological behaviors of Alzheimer's disease mice via the TLR4/MD2 signal

AIM

We analyzed the role and mechanism of dihydromyricetin (DHM) in suppressing inflammatory injury in microglial cells via targeting MD2.

METHODS

In vitro, BV2 cells were used as the objects of study to induce inflammatory injury with LPS + ATP, then the cell apoptosis level was identified, inflammatory factor levels were measured by ELISA, TLR4 and MD2 were stained with fluorescence staining, and protein expression was determined using Western-blot (WB) assay. Afterwards, MD2 expression was knocked down n BV2 cells to construct the BV2-MD2^-/- cell line, so as to detect the role of DHM on BV2-MD2^-/-. Moreover, the binding of DHM to MD2 was analyzed via mall molecule-protein docking and pull-down assays. In-vivo, wild-type (WT) C67BL/6 mice and APP/PS1 (AD) mice were used as the objects of study, which were intervened with DHM to detect the changes in mouse cognition. In addition, the pathological changes of brain tissues were analyzed with H&E staining. In addition, the inflammatory factor and protein levels in brain tissues were also detected.

RESULTS

DHM suppressed inflammatory injury in BV2 cells, reduced the cell apoptosis rate and inflammatory factor levels, and suppressed the level of TLR4 and MD2. After MD2 knockdown, DHM was unable to further suppress BV2 cell injury. Results of small molecule-protein docking and pull-down assays suggested that DHM bound to MD2 to suppress the formation of TLR4 complex. In AD mice, DHM improved the cognitive disorder in mice, suppressed inflammatory injury in brain tissues and lowered the expression of TLR4 protein.

CONCLUSION

DHM targeted MD2 to suppress the formation of TLR4 protein complex, thereby suppressing inflammatory injury in microglial cells and improving the cognition in AD mice.

Novel Approach to the Treatment of Neuropathic Pain Using a Combination with Palmitoylethanolamide and Equisetum arvense L. in an In Vitro Study

Neuropathic pain is a typical patient disorder resulting from damage and dysfunction of the peripheral neuraxis. Injury to peripheral nerves in the upper extremities can result in a lifelong reduction in quality of life and a devastating loss of sensory and motor function. Since some standard pharmaceutical therapies can cause dependence or intolerance, nonpharmacological treatments have gained great interest in recent years. In this context, the beneficial effects of a new combination of palmitoylethanolamide and Equisetum arvense L. are evaluated in the present study. The bioavailability of the combination was initially analyzed in a 3D intestinal barrier simulating oral intake to analyze its absorption/biodistribution and exclude cytotoxicity. In a further step, a 3D nerve tissue model was performed to study the biological effects of the combination during the key mechanisms leading to peripheral neuropathy. Our results demonstrate that the combination successfully crossed the intestinal barrier and reached the target site, modulating the nerve recovery mechanism after Schwann cell injury and offering the initial response of relieving pain. This work supported the efficacy of palmitoylethanolamide and Equisetum arvense L. in reducing neuropathy and modifying the major pain mechanisms, outlining a possible alternative nutraceutical approach.

Spinal cannabinoid receptor 2 activation alleviates neuropathic pain by regulating microglia and suppressing P2X7 receptor

Neuropathic pain (NP) is the chronic pain in patients resulting from injuries or diseases in the somatosensory nervous system. However, effective treatment remains limited to opioids. Currently, there is an urgent need to develop new specific pharmaceuticals with low abuse potentiality. Cannabinoid receptor 2 (CB2R) is one of the significant receptors in the endocannabinoid system. It is widely expressed in the central nervous system, especially enriched in glial cells, and plays an important role in the occurrence and development of inflammation in the nervous system. CB2R activation has a neuroprotective effect on nerve injury. In this study, we report increased and more reactive microglia (with larger cell body, shorter processes, and fewer endpoints) observed in the spinal dorsal horn of spared nerve injury (SNI) rats. Continuous intrathecal administration of CB2R agonist PM226 attenuated mechanical and cold hyperalgesia in rats and prevented the transition of microglia to the proinflammatory stage. Thus, microglia transitioned into the neuroprotective stage. Meanwhile, the proinflammatory factors TNF-α and iNOS decreased, and the levels of anti-inflammatory factors Arg-1 and IL-10 increased. The content of P2X7 receptors in the spinal dorsal horn of rats increases with time after SNI. After continuous intrathecal administration of PM226, the content of P2X7 protein decreases significantly. The administration of P2X7 inhibitor A-438079 alleviated the mechanical hyperalgesia of rats, reduced the number of microglia, and decreased the content of P2X7. These results indicate that P2X7 is involved in the neuroprotective effect caused by CB2R activation. In conclusion, this study provides new insights into the neuroprotective mechanism of CB2R activation.

RNA interference-mediated silencing of DNA methyltransferase 1 attenuates neuropathic pain by accelerating microglia M2 polarization

Background

DNA methyltransferase 1 (DNMT1) exerts imperative functions in neuropathic pain (NP). This study explored the action of RNA interference-mediated DNMT1 silencing in NP by regulating microglial M2 polarization.

Methods

NP rat models were established using chronic constriction injury (CCI) and highly aggressive proliferating immortalized (HAPI) microglia were treated with lipopolysaccharide (LPS) to induce microglia M1 polarization, followed by treatment of DNMT1 siRNA or si-DNMT1/oe-DNMT1, respectively. The pain threshold of CCI rats was assessed by determining mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL). Levels of inflammatory factors (TNF-α/IL-1β/IL-6/IL-10) and DNMT1 in rat L4-L6 spinal cord samples and HAPI cells were measured using ELISA, RT-qPCR, and Western blot. iNOS and Arg-1 mRNA levels were measured via RT-qPCR. DNMT1, M1 marker (iNOS), and M2 marker (Arg-1) levels in microglia of CCI rats were detected by immunofluorescence. Percentages of M1 microglia phenotype (CD16) and M2 microglia phenotype (CD206) were detected by flow cytometry. The phosphorylation of PI3K/Akt pathway-related proteins was determined by Western blot.

Results

CCI rats exhibited diminished MWT and TWL values, increased pro-inflammatory cytokines, and decreased anti-inflammatory cytokine IL-10. Additionally, DNMT1 was upregulated in CCI rat microglia. DNMT1 siRNA alleviated CCI-induced NP and facilitated M2 polarization of microglia in CCI rats. DNMT1 knockdown inhibited LPS-induced M1 polarization of HAPI cells and promoted M2 polarization by blocking the PI3K/Akt pathway, but DNMT1 overexpression inhibited the M1-to-M2 polarization of microglia.

Conclusion

RNA interference-mediated DNMT1 silencing accelerates microglia M2 polarization by impeding the PI3K/Akt pathway, thereby alleviating CCI-induced NP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02860-6.

Crotalphine Modulates Microglia M1/M2 Phenotypes and Induces Spinal Analgesia Mediated by Opioid-Cannabinoid Systems

Pain is a worldwide public health problem and its treatment is still a challenge since clinically available drugs do not completely reverse chronic painful states or induce undesirable effects. Crotalphine is a 14 amino acids synthetic peptide that induces a potent and long-lasting analgesic effect on acute and chronic pain models, peripherally mediated by the endogenous release of dynorphin A and the desensitization of the transient receptor potential ankyrin 1 (TRPA1) receptor. However, the effects of crotalphine on the central nervous system (CNS) and the signaling pathway have not been investigated. Thus, the central effect of crotalphine was evaluated on the partial sciatic nerve ligation (PSNL)-induced chronic neuropathic pain model. Crotalphine (100 µg/kg, p.o.)-induced analgesia on the 14th day after surgery lasting up to 24 h after administration. This effect was prevented by intrathecal administration of CB1 (AM251) or CB2 (AM630) cannabinoid receptor antagonists. Besides that, crotalphine-induced analgesia was reversed by CTOP, nor-BNI, and naltrindole, antagonists of mu, kappa, and delta-opioid receptors, respectively, and also by the specific antibodies for β-endorphin, dynorphin-A, and met-enkephalin. Likewise, the analgesic effect of crotalphine was blocked by the intrathecal administration of minocycline, an inhibitor of microglial activation and proliferation. Additionally, crotalphine decreased the PSNL-induced IL-6 release in the spinal cord. Importantly, in vitro, crotalphine inhibited LPS-induced CD86 expression and upregulated CD206 expression in BV-2 cells, demonstrating a polarization of microglial cells towards the M2 phenotype. These results demonstrated that crotalphine, besides activating opioid and cannabinoid analgesic systems, impairs central neuroinflammation, confirming the neuromodulatory mechanism involved in the crotalphine analgesic effect.

Lidocaine ameliorates chronic constriction injury-induced neuropathic pain through regulating M1/M2 microglia polarization

This study is intended to explore the mechanism that lidocaine ameliorates chronic constriction injury (CCI)-induced neuropathic pain (NP) related to the polarization of M1 and M2 microglia. CCI rats were established by surgery to induce NP. The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) of rats were determined. Microglial line HAPI cells were polarized into M1 or M2 cells using lipopolysaccharide (LPS) or interleukin (IL)-4, respectively. Immunofluorescence staining was performed to determine the Iba1/CD86- and Iba1/CD206-positive cells. Markers of M1 and M2 microglia were assessed using flow cytometry. Real-time polymerase chain reaction and enzyme-linked immunosorbent assay were performed to detect the level of mRNA and inflammatory factors. Lidocaine ameliorates CCI-induced NP, evidenced by the markedly increased values of MWT and TWL in NP rats. Lidocaine inhibited M1 microglia polarization but promoted M2 microglia polarization in a rat model of CCI-induced NP. Besides, in the in vitro experiment, lidocaine regulated M1/M2 polarization in LPS- or IL-4-treated HAPI microglia. Lidocaine ameliorates CCI-induced NP by regulating M1/M2 microglia polarization. This study investigated the biological role of lidocaine in regulating NP in rats, which may be helpful for revealing the pathogenic mechanisms of NP and provide a potential therapeutic factor.

Astrocyte-microglia interaction through C3/C3aR pathway modulates neuropathic pain in rats model of chronic constriction injury

Neuropathic pain (NP) is the cardinal symptom of neural injury, and its underlying molecular mechanism needs further investigation. Complements, especially complement 3 (C3), are involved in the pathophysiology of many neurological disorders, while the specific role of C3 in NP is still obscure. In this study, we found that both C3 and its receptor C3aR were upregulated in the spinal dorsal horn in a rat chronic constriction injury (CCI) model. In addition, C3 was mainly detected in astrocytes, while C3aR was expressed in microglia and neuron. Intrathecal injection of C3 antibody and C3aR antagonist alleviated NP in CCI model together with reduced M1 polarization of microglia. Our finding suggested that blockade of the C3/C3aR pathway might be a novel strategy for NP.

Circular RNA SMEK1 promotes neuropathic pain in rats through targeting microRNA-216a-5p to mediate Thioredoxin Interacting Protein (TXNIP) expression

Neuropathic pain (NP) is a disease induced by damage to the nervous system. A large number of studies have manifested that circular RNAs (circRNAs) are key in the development of neurological diseases. However, the role of circRNA in NP remains ambiguous. In this study, the biological function and molecular mechanism of circSMEK1 were investigated in NP. NP rat and cell models were established by chronic contractile injury (CCI) surgery and lipopolysaccharide (LPS) treatment, separately. The results exposed that circSMEK1 and TXNIP were up-regulated in NP, while miR-216a-5p was down-regulated. The claw retraction threshold and claw retraction latency in rats were elevated and reduced separately via knockdown circSMEK1 and miR-216a-5p. Meanwhile, knockout circSMEK1 or elevated miR-216a-5p declined inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL6 in spinal cord, and the activation of microglia, but promoted the polarization of microglia into anti-inflammatory type, while up-regulation of circSMEK1 or knockdown of miR-216a-5p was opposite. Mechanism studies demonstrated that circSMEK1 mediated TXNIP expression through competitive adsorption of miR-216a-5p. Functional rescue experiments manifested that the suppressive effect of circSMEK1 knockdown on NP was reversed by declined miR-216a-5p simultaneously. In conclusion, the results of this study affirmed that circSMEK1 facilitates NP inflammation and microglia M1 polarization by modulating miR-216a-5p/TXNIP axis, providing a new molecular target for the future treatment of NP.