Inhibition of TLR4 signaling protects mice from sensory and motor dysfunction in an animal model of autoimmune peripheral neuropathy

Short chain fatty acids mediates complement C1q pathway alleviation of perioperative neurocognitive disorders

Perioperative neurocognitive disorders (PND) is one of the most common postoperative complications, which can lead to a harmful impact on self-dependence, longer hospital stays, increased medical costs, morbidity, and mortality amongst older adults. Microglia can modulate synapse elimination involved in the complement component protein 1q (C1q) pathway to induce cognitive dysfunction, which is significantly improved by short chain fatty acids (SCFAs) treatment. Here we investigate the effects of SCFAs treatment on PND via mediating C1q complement pathway. High-throughput sequencing of 16S rDNA from fecal samples of male SD rats was applied to assess the changes in gut microbiota. Fecal microbiota transplantation (FMT) was performed to investigate whether gut microbiota from PND rats could alter cognitive impairment. The blood from the rat tail vein was collected to measure the SCFAs concentrations. Hippocampal and brain tissue samples were obtained to perform Western blots, Golgi and immunofluorescence staining. Primary microglia treated with SCFAs or Histone deacetylase inhibitor were cultured to measure microglial activation states and the expression of acetylated histone. The 16S rDNA sequencing results showed that PND rats had the significant changes in the species diversity of the gut microbiota and the metabolite of specifc species. Gut microbiota from PND rats could alter spatial learning and memory, and meanwhile, the changed SCFAs concentrations in plasma were involved. The synapse elimination in PND rats was strikingly reversed by SCFAs treatment involved in modulation complement C1q via suppressing neuroinflammation. This suggests that a link between gut microbiota dysbiosis and cognitive function impairment is involved in synapse elimination via mediating complement C1q pathway. SCFAs treatment can alleviate PND, the mechanisms of which may be associated with regulating complement C1q pathway.

Mitochondrial DAMPs: Key mediators in neuroinflammation and neurodegenerative disease pathogenesis

Neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) are increasingly linked to mitochondrial dysfunction and neuroinflammation. Central to this link are mitochondrial damage-associated molecular patterns (mtDAMPs), including mitochondrial DNA, ATP, and reactive oxygen species, released during mitochondrial stress or damage. These mtDAMPs activate inflammatory pathways, such as the NLRP3 inflammasome and cGAS-STING, contributing to the progression of neurodegenerative diseases. This review delves into the mechanisms by which mtDAMPs drive neuroinflammation and discusses potential therapeutic strategies targeting these pathways to mitigate neurodegeneration. Additionally, it explores the cross-talk between mitochondria and the immune system, highlighting the complex interplay that exacerbates neuronal damage. Understanding the role of mtDAMPs could pave the way for novel treatments aimed at modulating neuroinflammation and slowing disease progression, ultimately improving patient outcome.

Clavulanic acid prevents paclitaxel-induced neuropathic pain through a systemic and central anti-inflammatory effect in mice

Paclitaxel (PCX) based treatments, commonly used to treat breast, ovarian and lung cancers, have the highest incidence of chemotherapy-induced neuropathic pain, affecting from 38 to 94 ​% of patients. Unfortunately, analgesic treatments are not always effective for PCX-induced neuropathic pain (PINP). This study aimed to evaluate the antinociceptive effect of clavulanic acid (CLAV), a clinically used β-lactam molecule, in both therapeutic and preventive contexts in mice with PINP. A single dose of CLAV administered after the onset of PINP significantly reduced mechanical hyperalgesia. Interestingly, preventive administration of CLAV prevented PINP development. The effect of preventive CLAV on PINP was associated with increased levels of IL-10 and IFN-β in serum, and decreased levels of IL-1β and TNF-α in both the serum and CNS. Immunostaining experiments revelated that CLAV increased the levels of glutamate transporter type 1 (GLT-1) and toll-like receptor type 4 (TLR4) in the spinal cord, while reducing levels of the astrocytic marker the glial fibrillary acidic protein (GFAP). Notably, co-incubation with CLAV and PCX in triple-negative breast cancer cells did not interfere with PCX-induced cytotoxic effects. Hence, these findings suggest that CLAV could be employed as a clinical treatment aimed at preventing PINP without compromission the cytotoxic efficacy of PCX.

Decoding Toll-like receptors: Recent insights and perspectives in innate immunity

Toll-like receptors (TLRs) are an evolutionarily conserved family in the innate immune system and are the first line of host defense against microbial pathogens by recognizing pathogen-associated molecular patterns (PAMPs). TLRs, categorized into cell surface and endosomal subfamilies, recognize diverse PAMPs, and structural elucidation of TLRs and PAMP complexes has revealed their intricate mechanisms. TLRs activate common and specific signaling pathways to shape immune responses. Recent studies have shown the importance of post-transcriptional regulation in TLR-mediated inflammatory responses. Despite their protective functions, aberrant responses of TLRs contribute to inflammatory and autoimmune disorders. Understanding the delicate balance between TLR activation and regulatory mechanisms is crucial for deciphering their dual role in immune defense and disease pathogenesis. This review provides an overview of recent insights into the history of TLR discovery, elucidation of TLR ligands and signaling pathways, and their relevance to various diseases.

Role of gut-derived bacterial lipopolysaccharide and peripheral TLR4 in immobilization stress-induced itch aggravation in a mouse model of atopic dermatitis

Psychological stress and intestinal leakage are key factors in atopic dermatitis (AD) recurrence and exacerbation. Here, we demonstrate the mechanism underlying bacterial translocation across intestinal epithelial barrier damaged due to stress and further aggravation of trimellitic anhydride (TMA)-induced itch, which remain unclear, in AD mice. Immobilization (IMO) stress exacerbated scratching bouts and colon histological damage, and increased serum corticosterone and lipopolysaccharide (LPS). Orally administered fluorescein isothiocyanate (FITC)-dextran and surgically injected (into the colon) Cy5.5-conjugated LPS were detected in the serum and skin after IMO stress, respectively. The relative abundance of aerobic or facultative anaerobic bacteria was increased in the colon mucus layer, and Lactobacillus murinus, E. coli, Staphylococcus nepalensis, and several strains of Bacillus sp. were isolated from the spleens and mesenteric lymph nodes. Oral antibiotics or intestinal permeability blockers, such as lubiprostone (Lu), 2,4,6-triaminopyrimidine (TAP) and ML-7, inhibited IMO stress-associated itch; however, it was reinduced through intradermal or i.p. injection of LPS without IMO stress. I.p. injection of TAK-242 (resatorvid), a TLR4 inhibitor, abrogated IMO stress-associated itch, which was also confirmed in TLR4-KO mice. IMO stress alone did not cause itch in naïve mice. IMO stress-induced itch aggravation in TMA-treated AD mice might be attributed to the translocation of gut-derived bacterial cells and LPS, which activates peripheral TLR4 signaling.

Fecal Microbiota Transplantation Alleviated Paclitaxel-Induced Peripheral Neuropathy by Interfering with Astrocytes and TLR4/p38MAPK Pathway in Rats

Purpose

Paclitaxel-induced peripheral neuropathy (PIPN) constitutes a refractory and progressive adverse consequence of paclitaxel treatment, causing pain and sensory anomalies in cancer survivors. Although the gut-brain axis is involved in multiple disorders including cancer, its impact on peripheral pain conditions remains elusive. Thus, we assessed the importance of gut microbiota and related mechanisms in PIPN.

Methods

By implementing fecal microbiota transplantation (FMT) in a rat PIPN model (ie, rats treated with paclitaxel; hereafter as PIPN rats), we explored the effect of gut microbiota on PIPN rats using multiple methods, including different behavioral tests, 16S ribosomal DNA (rDNA) sequencing, and biochemical techniques.

Results

Sequencing of 16S rDNA revealed that the abundance of genera Bacteroides and UCG-005 increased, while that of genera Turicibacter, Clostridium sensu stricto 1 and Corynebacterium decreased in the PIPN rats. However, when treated with FMT using fecal from normal rats, the mechanical allodynia and thermal hyperalgesia in PIPN rats were significantly alleviated. In addition, FMT treatment reduced the expression of toll-like receptor 4 (TLR4), phospho-p38 mitogen-activated protein kinase (p-p38MAPK), and the astrocytic marker glial fibrillary acidic protein in the colon and spinal dorsal horn. TAK242 (a TLR4 inhibitor) significantly alleviated the behavioral hypersensitivity of PIPN rats and inhibited the TLR4/p38MAPK pathway in astrocytes in these rats.

Conclusion

The gut microbiota played a critical role in PIPN. Future therapies treating PIPN should consider microbe-based treatment as an option.

The Effect of PD-1 Inhibitor Combined with Irradiation on HMGB1-Associated Inflammatory Cytokines and Myocardial Injury

PURPOSE

To explore the effect of PD-1 inhibitors combined with irradiation on myocardial injury and the changes of HMGB1-associated inflammatory markers.

METHODS

Four groups of five mice were used, each groupformed by randomly dividing 20 mice (group A control; group B PD-1 inhibitors; group C Irradiation; group D PD-1 inhibitors+irradiation; n = 5 for each). The mice were treated with either PD-1 inhibitors or a 15 Gy dose of single heart irradiation, or both. Hematoxylin-eosin staining assessed the morphology and pathology of heart tissue; Masson staining assessed heart fibrosis; Tunel staining evaluated heart apoptosis; flow cytometry detected CD3+, CD4+, and CD8+ T lymphocytes in heart tissues; enzyme linked immunosorbent assay evaluated IL-1β, IL-6, and TNF-ɑ of heart tissue; Western blot and quantitative real-time PCR (qPCR) detected the expression of protein and mRNA of HMGB1, TLR-4, and NF-κB p65 respectively.

RESULTS

The degree of heart injury, collagen volume fraction (CVF) and apoptotic index (AI) in groups B, C, and D were higher than group A, but the differences between the CVF and AI of group A and group B were not statistical significance (P>0.05). Similarly, the absolute counts and relative percentage of CD3+ and CD8+ T lymphocytes and the concentrations of IL-1β, IL-6, and TNF-α in heart tissue with group D were significantly higher than the other groups (P<0.05). In addition, compared with group A, the expression of protein and mRNA of HMGB1 and NF-κB p65 in other groups were higher, and the differences between each group were statistically significant while TLR4 was not. In addition, interaction by PD-1 inhibitors and irradiation was found in inflammatory indicators, especially in the expression of the HMGB1 and CD8+ T lymphocytes.

CONCLUSION

PD-1 inhibitors can increase the expression of HMGB1-associated inflammatory cytokines and aggravate radiation-induced myocardial injury.

Remnant Cholesterol and Dyslipidemia Are Risk Factors for Guillain–Barré Syndrome and Severe Guillain–Barré Syndrome by Promoting Monocyte Activation

Background

Guillain–Barré syndrome (GBS) is the most common severe acute paralytic neuropathy, with a mortality rate of 5% and permanent sequelae rate of 10%. Currently, the cause of GBS remains unclear. Therefore, we sought to determine potential predictors for GBS and its severity.

Methods

A case–control study was performed at Tiantan Hospital in Beijing from January 2017 to December 2021. Laboratory and clinical characteristics were assessed in recruited GBS patients and healthy control individuals (matched by sex and age). The potential risk factors for GBS and severe GBS were assessed using a logistic regression analysis. The mRNA levels of toll-like receptor 4 (TLR4), toll-like receptor 2 (TLR2) and nuclear factor κB (NF-κB) in GBS patients and control PBMCs were detected by fluorescence quantitative PCR. THP-1 cells were costimulated with LPS and free cholesterol to demonstrate the effect of free cholesterol on monocyte activation.

Results

A total of 147 GBS patients and 153 healthy individuals were included in the study. Logistic regression analyses showed that preceding infection, alcohol consumption, remnant cholesterol, homocysteine and the dyslipidemia index were correlated with a higher risk of GBS. In contrast, increased HDL cholesterol was correlated with a lower risk of GBS. Moreover, remnant cholesterol and the dyslipidemia index were significantly correlated with severe GBS. The mRNA levels of TLR4, TLR2 and NF-κB in the PBMCs of GBS patients were significantly higher than those of healthy individuals. LPS activated THP-1 cells, and free cholesterol treatment increased the expression of TLR4, TLR2, NF-κB and IL-1β mRNA in LPS-activated THP-1 cells.

Conclusion

Dyslipidemia was correlated with the risk of GBS and severe GBS. Remnant cholesterol may promote the activation of monocytes in GBS patients. It may be valuable to control lipid levels in the prevention of GBS and severe GBS.

Monocyte Trafficking and Polarization Contribute to Sex Differences in Meta-Inflammation

Obesity is associated with systemic inflammation and immune cell recruitment to metabolic tissues. Sex differences have been observed where male mice challenged with high fat diet (HFD) exhibit greater adipose tissue inflammation than females demonstrating a role for sex hormones in differential inflammatory responses. Circulating monocytes that respond to dietary lipids and chemokines and produce cytokines are the primary source of recruited adipose tissue macrophages (ATMs). In this study, we investigated sexual dimorphism in biological pathways in HFD-fed ATMs from male and female mice by RNA-seq. We also conducted chemotaxis assays to investigate sex differences in the migration of monocytes isolated from bone marrow from male and female mice toward a dietary saturated lipid - palmitate (PA), and a chemokine - monocyte chemoattractant protein 1 (MCP1), factors known to stimulate myeloid cells in obesity. ATM RNA-Seq demonstrated sex differences of both metabolic and inflammatory activation, including pathways for chemokine signaling and leukocyte trans-endothelial migration. In vivo monocyte transfer studies demonstrated that male monocytes traffic to female adipose tissue to generate ATMs more readily. In chemotaxis assays, lean male monocytes migrated in greater numbers than females toward PA and MCP1. With short-term HFD, male and female monocytes migrated similarly, but in chronic HFD, male monocytes showed greater migration than females upon PA and MCP1 stimulation. Studies with monocytes from toll-like receptor 4 knockout mice (Tlr4^-/- ) demonstrated that both males and females showed decreased migration than WT in response to PA and MCP1 implying a role for TLR4 in monocyte influx in response to meta-inflammation. Overall, these data demonstrate the role of sexual dimorphism in monocyte recruitment and response to metabolic stimuli that may influence meta-inflammation in obesity.

Post-Translational Modification of HMGB1 Disulfide Bonds in Stimulating and Inhibiting Inflammation

High mobility group box 1 protein (HMGB1), a highly conserved nuclear DNA-binding protein, is a “damage-associated molecular pattern” molecule (DAMP) implicated in both stimulating and inhibiting innate immunity. As reviewed here, HMGB1 is an oxidation-reduction sensitive DAMP bearing three cysteines, and the post-translational modification of these residues establishes its proinflammatory and anti-inflammatory activities by binding to different extracellular cell surface receptors. The redox-sensitive signaling mechanisms of HMGB1 also occupy an important niche in innate immunity because HMGB1 may carry other DAMPs and pathogen-associated molecular pattern molecules (PAMPs). HMGB1 with DAMP/PAMP cofactors bind to the receptor for advanced glycation end products (RAGE) which internalizes the HMGB1 complexes by endocytosis for incorporation in lysosomal compartments. Intra-lysosomal HMGB1 disrupts lysosomal membranes thereby releasing the HMGB1-transported molecules to stimulate cytosolic sensors that mediate inflammation. This HMGB1-DAMP/PAMP cofactor pathway slowed the development of HMGB1-binding antagonists for diagnostic or therapeutic use. However, recent discoveries that HMGB1 released from neurons mediates inflammation via the TLR4 receptor system, and that cancer cells express fully oxidized HMGB1 as an immunosuppressive mechanism, offer new paths to targeting HMGB1 for inflammation, pain, and cancer.

Novel Immunological and Therapeutic Insights in Guillain-Barré Syndrome and CIDP

Inflammatory neuropathies are a heterogeneous group of rare diseases of the peripheral nervous system that include acute and chronic diseases, such as Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). The etiology and pathophysiological mechanisms of inflammatory neuropathies are only partly known, but are considered autoimmune disorders in which an aberrant immune response, including cellular and humoral components, is directed towards components of the peripheral nerve causing demyelination and axonal damage. Therapy of these disorders includes broad-spectrum immunomodulatory and immunosuppressive treatments, such as intravenous immunoglobulin, corticosteroids, or plasma exchange. However, a significant proportion of patients do not respond to any of these therapies, and treatment selection is not optimized according to disease pathophysiology. Therefore, research on disease pathophysiology aiming to reveal clinically and functionally relevant disease mechanisms and the development of new treatment approaches are needed to optimize disease outcomes in CIDP and GBS. This topical review describes immunological progress that may help guide therapeutic strategies in the future in these two disorders.

CX3CR1 But Not CCR2 Expression Is Required for the Development of Autoimmune Peripheral Neuropathy in Mice

One hallmark of Guillain-Barre syndrome (GBS), a prototypic autoimmune peripheral neuropathy (APN) is infiltration of leukocytes (macrophages and T cells) into peripheral nerves, where chemokines and their receptors play major roles. In this study, we aimed to understand the potential contribution of chemokine receptors CCR2 and CX3CR1 in APN by using a well-established mouse model, B7.2 transgenic (L31) mice, which possesses a predisposed inflammatory background. We crossbred respectively CCR2KO and CX3CR1KO mice with L31 mice. The disease was initiated by partial ligation on one of the sciatic nerves. APN pathology and neurological function were evaluated on the other non-ligated sciatic nerve/limb. Our results revealed that L31/CX3CR1KO but not L31/CCR2KO mice were resistant to APN. CX3CR1 is needed for maintaining circulating monocyte and CD8⁺ T cell survival. While migration of a significant number of activated CD8⁺ T cells to peripheral nerves is essential in autoimmune response in nerve, recruitment of monocytes into PNS seems optional. Disease onset is independent of CCR2 mediated blood-derived macrophage recruitment, which can be replaced by compensatory proliferation of resident macrophages in peripheral nerve. CX3CR1 could also contribute to APN via its critical involvement in maintaining nerve macrophage phagocytic ability. We conclude that blockade of CX3CR1 signaling may represent an interesting anti-inflammatory strategy to improve therapeutic management for GBS patients.