TLR4 Signaling Research Articles

Melissa officinalis Regulates Lipopolysaccharide-Induced BV2 Microglial Activation via MAPK and Nrf2 Signaling.

Neuroinflammation and microglial activation play critical roles in neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Modulating microglial activation may help prevent the progression of these disorders. This study aimed to investigate the effects and mechanisms of Melissa officinalis ethanol extract on lipopolysaccharide (LPS)-induced microglial activation in BV2 cells. Cell viability and nitric oxide (NO) production were assessed using MTT assay and Griess reagent, while inflammatory cytokine levels were measured by qPCR. Key inflammatory pathways, including MAPK, TLR4, and antioxidant biomarkers, were analyzed through western blot and immunofluorescence. Rosmarinic acid content in M. officinalis was determined using high-performance liquid chromatography (HPLC). The results demonstrated that M. officinalis ethanol extract significantly inhibited LPS-induced NO production and reduced inflammatory cytokine expression. Additionally, it downregulated inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), TLR4, NF-κB, and MAPK signaling pathways (p38, JNK, ERK), while increasing the expression of antioxidant markers, including Nrf2, HO-1, catalase, and SOD2. In conclusion, M. officinalis ethanol extract exerts neuroprotective effects by modulating inflammation and enhancing antioxidant defenses, suggesting its potential in the prevention and treatment of inflammation-related neurodegenerative diseases.

The Marginal Zone B Cell Compartment and T Cell-independent Antibody Responses Are Supported by B Cell Intrinsic Expression of IRF1.

The prototypic IFN-inducible transcription factor, IRF1, not only controls inflammatory gene expression but also regulates T cell and macrophage fate specification and function. Using bone marrow chimeras (80% B6.129S2-Ighmtm1Cgn/J [µMT] + 20% B6.129S2-Irf1tm1Mak/J [Irf1-/-]), we show that IRF1 expression in B cells is required for marginal zone B (MZB) cell development and T cell-independent Ab responses. Although IFNs can induce IRF1 expression in MZB precursors, deletion of the IFN-γR (C57BL/6J [B6], B6.129S7-Ifngr1tm1Agt/J) or IFN-αR (B6[Cg]-Ifnar1tm1Agt/J) did not affect MZB cell development. Instead, BCR and TLR signals promote IRF1 expression and nuclear translocation in MZB cell precursors. In turn, IRF1 is required for Notch2-dependent gene expression in BCR- and TLR-stimulated transitional B cells and development of the MZB cell compartment. Thus, IRF1 regulates MZB-driven T cell-independent Ab responses by regulating Notch programming in MZB precursors and facilitating commitment of these cells to the MZB lineage.

Morphine-induced intestinal microbial dysbiosis drives TLR-dependent IgA targeting of gram-positive bacteria and upregulation of CD11b and TLR2 on a sub-population of IgA+ B cells

ABSTRACT IgA binding dictates the composition of the intestinal microbiome and reflects dysbiotic states during chronic disease. Both pathogenic and commensal bacteria differentially bind to IgA with varying outcomes. Little is known regarding IgA dynamics immediately following microbial dysbiosis. Recent work shows that morphine treatment rapidly induces microbial dysbiosis within hours of administration. This microbial shift is characterized by the expansion of pathogenic bacteria with a concurrent decrease in commensal bacteria. Because of this rapid microbial shift, a murine model of chronic morphine treatment was used to gain insight on the host IgA response during early microbial disruption. Within 24 h, morphine treatment induces microbial dysbiosis which disrupts IgA-bacterial homeostasis, resulting in an increased concentration of unbound IgA with a corresponding decrease in the frequency of IgA-bound bacteria. Additionally, the increased concentration of unbound IgA is dependent on the microbiome, as microbial depletion abolishes the increase. At 48 h of morphine treatment, the frequency of IgA-bound bacteria increases and IgA-seq reveals increased IgA targeting of gram-positive bacteria. Both a whole-body TLR2 KO and treatment with the TLR inhibitor OxPAPC resulted in abrogation of IgA binding to bacteria, implicating modulation of IgA binding through TLR signaling. Finally, we identify that a sub-population of IgA+ B cells in the intestinal lamina propria has increased CD11b and TLR2 expression at 24 h of morphine treatment which could be a potential source of the observed IgA that targets gram-positive bacteria. Together, we demonstrate for the first time the role of TLR2 in IgA targeting of intestinal bacteria, and this study sheds light on the IgA dynamics during the initial hours of microbial dysbiosis.

The ameliorating effects of adipose-derived stromal vascular fraction cells on blue light-induced rat retinal injury via modulation of TLR4 signaling, apoptosis, and glial cell activity.

Blue light (BL)-induced retinal injury has become a very common problem due to over exposure to blue light-emitting sources. This study aimed to investigate the possible ameliorating impact of stromal vascular fraction cells (SVFCs) on BL-induced retinal injury. Forty male albino rats were randomly allocated into four groups. The control group rats were kept in 12-h light/12-h dark. Rats of SVFC-control as the control group, but rats were intravenously injected once by SVFCs. Rats of both the BL-group and BL-SVFC group were exposed to BL for 2 weeks; then rats of the BL-SVFC group were intravenously injected once by SVFCs. Following the BL exposure, rats were kept for 8 weeks. Physical and physiological studies were performed; then retinal tissues were collected for biochemical and histological studies. The BL-group showed physical and physiological changes indicating affection of the visual function. Biochemical marker assessment showed a significant increase in MDA, TLR4 and MYD88 tissue levels with a significant decrease in TAC levels. Histological and ultrastructural assessment showed disruption of the normal histological architecture with retinal pigment epithelium, photoreceptors, and ganglion cell deterioration. A significant increase in NF-κB, caspase-3, and GFAP immunoreactivity was also detected. BL-SVFC group showed a significant improvement in physical, physiological, and biochemical parameters. Retinal tissues revealed amelioration of retinal structural and ultrastructural deterioration and a significant decrease in NF-κB and caspase-3 immunoreactivity with a significant increase in GFAP immunoreaction. This study concluded that SVFCs could ameliorate the BL-induced retinal injury through TLR-4/MYD-88/NF-κB signaling inhibition, regenerative, anti-oxidative, and anti-apoptotic effects.

Blocking S100A9-signaling is detrimental to the initiation of anti-tumor immunity

S100A9, a multifunctional protein mainly expressed by neutrophils and monocytes, poses an immunological paradox. In virus infections or sterile inflammation, it functions as an alarmin attracting innate immune cells, as well as mediating proinflammatory effects through TLR4 signaling. However, in cancer, S100A9 levels have been shown to associate with poor prognosis and lack of response to immunotherapy. Its expression by myeloid cells has been related to an immune suppressive phenotype, the so-called myeloid derived suppressor cells (MDSCs). Targeting S100A9 in cancer has therefore been proposed as a potential way to relieve myeloid-mediated immune suppression. Surprisingly, we found that blocking the extracellular TLR4 signaling from S100A9 using the inhibitor Paquinimod, resulted in increased tumor growth and a detrimental effect on anti-PD-L1 efficacy in the CT26 tumor model. This effect was caused by a reduction in the tumor immune infiltration to about half of untreated controls, and the reduction was made up of a 5-fold decrease in Ly6Chigh monocytic cells. The suppressive Ly6G+ myeloid cells compartment was not reduced by Paquinimod treatment, suggesting alternative mechanisms by which S100A9 contributes to myeloid-mediated suppression. Intratumoral injection of recombinant S100A9 early after mice inoculation with CT26 cells had an anti-tumor effect. These findings indicate an important yet understudied role of S100A9 as an alarmin and immune stimulatory signal in cancer settings, and highlight the potential to exploit such signals to promote beneficial anti-tumor responses.

G-CSFR-induced leukocyte transendothelial migration during the inflammatory response is regulated by the ICAM1-PKCa axis: based on multiomics integration analysis

As an indispensable inflammatory mediator during sepsis, granulocyte colony-stimulating factor (G-CSF) facilitates neutrophil production by activating G-CSFR. However, little is known about the role of intracellular downstream signalling pathways in the induction of inflammation. To explore the functions of molecules in regulating G-CSFR signalling, RNA sequencing and integrated proteomic and phosphoproteomic analyses were conducted to predict the differentially expressed molecules in modulating the inflammatory response after G-CSFR expression was either up- or downregulated, in addition to the confirmation of their biological function by diverse experimental methods. In the integrated bioinformatic analysis, 3190 differentially expressed genes (DEGs) and 1559 differentially expressed proteins (DEPs) were identified in multiple-group comparisons (p < 0.05, FC > ± 1.5) using enrichment analyses, as well as those classic pathways such as the TNF, NFkappaB, IL-17, and TLR signalling pathways. Among them, 201 proteins, especillay intercellular cell adhesion molecule-1 (ICAM1) and PKCa, were identified as potential molecules involved in inflammation according to the protein–protein interaction (PPI) analysis, and the leukocyte transendothelial migration (TEM) pathway was attributed to the intervention of G-CSFR. Compared with the control and TNF-a treatment, the G-CSFR (G-CSFROE)-overexpressing led to an obvious increase in the number of leukocytes with the TEM phenotype. Mechanically, the expression of ICAM1 and PKCa was significantly up- and downregulated by G-CSFROE, which directly led to increased TEM; moreover, PKCa expression was negatively regulated by ICAM1 expression, leading to aberrant leukocyte TEM. Altogether, the ICAM1‒PKCa axis was found a meaningful target in the leukocyte TEM induced by G-CSFR upregulation.

CCL21 Induces Plasmacytoid Dendritic Cell Migration and Activation in a Mouse Model of Glioblastoma

Dendritic cells (DCs) are professional antigen-presenting cells that are traditionally divided into two distinct subsets: myeloid DCs (mDCs) and plasmacytoid DCs (pDCs). pDCs are known for their ability to secrete large amounts of cytokine type I interferons (IFN- α). In our previous work, we have demonstrated that pDC infiltration promotes glioblastoma (GBM) tumor immunosuppression through decreased IFN-α secretion via TLR-9 signaling and increased suppressive function of regulatory T cells (Tregs) via increased IL-10 secretion, resulting in poor overall outcomes in mouse models of GBM. Further dissecting the overall mechanism of pDC-mediated GBM immunosuppression, in this study, we identified CCL21 as highly upregulated by multiple GBM cell lines, which recruit pDCs to tumor sites via CCL21-CCR7 signaling. Furthermore, pDCs are activated by CCL21 in the GBM microenvironment through intracellular signaling of β-arrestin and CIITA. Finally, we found that CCL21-treated pDCs directly suppress CD8+ T cell proliferation without affecting regulatory T cells (Tregs) differentiation, which is considered the canonical pathway of immunotolerant regulation. Taken together, our results show that pDCs play a multifaced role in GBM immunosuppression, and CCL21 could be a novel therapeutic target in GBM to overcome pDC-mediated immunosuppression.

Mechanism research of Tollip negative feedback regulation in TLR4 signaling pathways based on spinal tuberculosis: Detection of Tollip and NF-κB expression levels

The emergence of drug-resistant mycobacterium tuberculosis (MTB, or TB) strains has led to an increasing incidence of TB. Spinal tuberculosis is the most common extrapulmonary tuberculosis. In the present study, tollip, a negative feedback regulatory factor in TLR4 signaling pathway was chosen based on previous studies on osteoarticular tuberculosis. U937 cells were transfected with recombinant lentivirus containing shRNA (RNA interference, RNAi) or overexpression vector containing Tollip gene and tested in vitro. The expression levels of Tollip and TLR4 were detected by Real-time PCR and immunofluorescence techniques, and the cell morphology and infection effect were observed by DAPI staining. The results suggested that Tollip gene could negatively inhibit the expression of related factors in TLR4 signaling pathway, and thus is a potential biomarker for early diagnosis.

Evaluation of immune sensor responses to a viral small noncoding RNA.

Gammaherpesviruses are widespread pathogens causing persistent infections linked to the development of numerous types of lymphomas in humans. During latency, most of the viral protein-coding genes are suppressed, facilitating evasion of adaptive immune recognition of protein antigens. In contrast, many noncoding RNA (ncRNA) molecules are expressed in infected cells and can regulate key cellular pathways while simultaneously evading adaptive immune recognition. To counteract this, many cells express internal pattern recognition receptors that can intrinsically sense ongoing infections and initiate cellular defenses. Murine gammaherpesvirus 68 (MHV68) is a valuable model to study in vivo aspects of gammaherpesvirus pathogenesis. The MHV68 ncRNA TMER4 (tRNA-miRNA-encoding RNA 4) promotes lymph node egress of infected B cells: in the absence of TMER4, MHV68-infected B cells accumulate in the lymph node in a manner similar to B cells activated through specific antigen encounter. We hypothesized that TMER4 may alter intrinsic immune activation. In research described here, we aimed to explore the immunomodulatory functions of TMER4 by evaluating its impact on signaling through the critical immune sensors Toll-like receptor 4 (TLR4), TLR3, TLR7, and retinoic acid-inducible gene I (RIG-I). To accomplish this, we developed a system to test noncoding RNAs using commercially available reporter cell lines. We optimized the experimental procedure to ensure ncRNA expression and to quantify immune sensory molecule induction or inhibition by the expressed ncRNA. Expression of TMER4 RNAs from plasmid constructs did not alter TLR or RIG-I signaling. This study provides a clear experimental framework that can be applied to test other small ncRNAs for their impact on various innate immune sensor proteins.

Extracellular vesicles in sepsis plasma mediate neuronal inflammation in the brain through miRNAs and innate immune signaling

BackgroundNeuroinflammation reportedly plays a critical role in the pathogenesis of sepsis-associated encephalopathy (SAE). We previously reported that circulating plasma extracellular vesicles (EVs) from septic mice are proinflammatory. In the current study, we tested the role of sepsis plasma EVs in neuroinflammation.MethodsTo track EVs in cells and tissues, HEK293T cell-derived EVs were labeled with the fluorescent dye PKH26. Cecal ligation and puncture (CLP) was conducted to model polymicrobial sepsis in mice. Plasma EVs were isolated by ultracentrifugation and their role in promoting neuronal inflammation was tested following intracerebroventricular (ICV) injection. miRNA inhibitors (anti-miR-146a, -122, -34a, and -145a) were applied to determine the effects of EV cargo miRNAs in the brain. A cytokine array was performed to profile microglia-released protein mediators. TLR7- or MyD88-knockout (KO) mice were utilized to determine the underlying mechanism of EVs-mediated neuroinflammation.ResultsWe observed the uptake of fluorescent PKH26-EVs inside the cell bodies of both microglia and neurons. Sepsis plasma EVs led to a dose-dependent cytokine release in cultured microglia, which was partially attenuated by miRNA inhibitors against the target miRNAs and in TLR7-KO cells. When administered via the ICV, sepsis plasma EVs resulted in a marked increase in the accumulation of innate immune cells, including monocyte and neutrophil and cytokine gene expression, in the brain. Although sepsis plasma EVs had no direct effect on cytokine production or neuronal injury in vitro, the conditioned media (CM) of microglia treated with sepsis plasma EVs induced neuronal cell death as evidenced by increased caspase-3 cleavage and Annexin-V staining. Cytokine arrays and bioinformatics analysis of the microglial CM revealed multiple cytokines/chemokines and other factors functionally linked to leukocyte chemotaxis and migration, TLR signaling, and neuronal death. Moreover, sepsis plasma EV-induced brain inflammation in vivo was significantly dependent on MyD88.ConclusionsCirculating plasma EVs in septic mice cause a microglial proinflammatory response in vitro and a brain innate immune response in vivo, some of which are in part mediated by TLR7 in vitro and MyD88 signaling in vivo. These findings highlight the importance of circulating EVs in brain inflammation during sepsis.

Discovery of pyrazolo[1,5-a]pyrimidine derivatives targeting TLR4−TLR4∗ homodimerization via AI-powered next-generation screening

TLR4 signaling is instrumental in orchestrating multiple aspects of innate immunity. Developing small molecule inhibitors targeting the TLR4 pathway holds potential therapeutic promise for TLR4-related disorders. Herein, an artificial intelligence (AI)-powered next-generation screening approach, employing HelixVS and HelixDock, was utilized to focus on the TLR4−TLR4∗ (a second copy of TLR4) homodimerization surface, leading to the identification of a potent pyrazolo[1,5-a]pyrimidine derivative, designated as compound 1. An extensive structure−activity relationship (SAR) exploration culminated in the discovery of the lead compound TH023, which effectively blocked the LPS-stimulated NF-κB activation and nitric oxide overproduction in HEK-Blue hTLR4 and RAW264.7 cells, with IC50 values of 0.354 and 1.61 μM, respectively. Molecular dynamic (MD) simulations indicated that TH023 stabilized TLR4−MD-2 and disrupted its association with TLR4∗. Moreover, TH023 alleviated the lung injury and decreased pro-inflammatory cytokine levels in LPS-induced septic mice. These findings not only illuminated the strategic advantage of HelixDock in advancing the frontiers of AI-driven drug discovery, but also provided valuable structural insights for the rational design of TLR4−TLR4∗ protein−protein interaction (PPI) inhibitors based on the pyrazolo[1,5-a]pyrimidine scaffold. Overall, this study validated a new strategy for TLR4 signaling regulation by targeting its dimerization, thereby underscoring the therapeutic promise of TH023 in treating TLR4-mediated inflammatory diseases.

Screening the effective components of Lysionotus pauciflorus Maxim. on the treatment of LPS induced acute lung injury mice by integrated UHPLC-Q-TOF-MS/MS and network pharmacology

Ethnopharmacological relevanceAcute lung injury (ALI) is an inflammatory reaction produced through various injury-causing factors acting on the lungs in a direct or indirect way, with a high morbidity and mortality rate. A review of clinical experience has revealed that Lysionotus pauciflorus Maxim (LP) has a significant therapeutic effect on ALI. However, the comprehensive effective components of LP are uncertain, and the mechanisms, especially the potential therapeutic target for anti-ALI, are still unknown. Aims of the studyIn vitro and in vivo validation of the pharmacodynamics of LP in the treatment of ALI and exploration of its potential mechanism of action based on network pharmacology, molecular docking and experimental validation. Materials and methodsUltra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) was employed to identify the ingredients of LP extracts. The potential bioactive ingredients, key targets and signalling pathways were identified by network pharmacology, based on the results of the mass spectrometry analysis. Subsequently, molecular docking was performed on the screened core components and key targets to calculate their molecular binding energies and binding potentials, and to explore the mutual binding modes of small-molecule ligands and large-molecule proteins. Finally, lipopolysaccharide (LPS)-induced RAW264.7 cell model and ALI mice model were used to validate the therapeutic effects and potential mechanism of LP extract towards ALI. ResultsFrom the mass spectrometry results of LP extracts, a total of 89 chemical components were identified, including 46 phenylethanol glycosides, 26 flavonoids, 9 organic acids and their derivatives and 8 other compounds. And furthermore 39 core active components were screened by network pharmacology. The top 10 core components (4 phenylethanol glycosides, 6 flavonoids) have been screened in the composition -target-disease network, and 37 core targets related to LP efficacy were obtained by fitting PPI network analysis. 10 signalling pathways and their targets associated with LP treatment of ALI were obtained by GO/KEGG analysis, indicating that LP could regulate TLR4 and NF-κB signalling pathways through 4 key targets, namely NFKB1, RELA, TLR4 and TNF. The results of the molecular docking procedure indicated a strong affinity, with the binding energies between each component and the target site being less than −6 kcal/mol. The binding modes included Hydrogen Bonds, Pi-Pi interaction, Hydrophobic Interactions, Salt Bridges, Pi-cation interactions. These observations were subsequently validated in vitro and in vivo experiments. The outcomes of in vitro and in vivo experiments demonstrated that LP was effective in reducing the infiltration of inflammatory bacteria in lung tissues and attenuated the expression of pro-inflammatory cytokines in LPS-stimulated mice bronchoalveolar lavage fluid (BALF) and RAW264.7 cells. Furthermore, LP inhibited the expression and phosphorylation of TLR4 protein and NF-κB protein, thus playing a role in the prevention of ALI. ConclusionsIn this study, mass spectrometry analysis was combined with biomolecular networks to initially elucidate the potential of LP to treat ALI by modulating the TLR4/NF-κB pathway. This offers a definitive experimental basis for the development of new LP drugs.

STAT3 blockade ameliorates LPS-induced kidney injury through macrophage-driven inflammation

BackgroundSignal transducer and activator of transcription 3 (STAT3), a multifaceted transcription factor, modulates host immune responses by activating cellular response to signaling ligands. STAT3 has a pivotal role in the pathophysiology of kidney injury by counterbalancing resident macrophage phenotypes under inflammation conditions. However, STAT3’s role in acute kidney injury (AKI), particularly in macrophage migration, and in chronic kidney disease (CKD) through fibrosis development, remains unclear.MethodsStattic (a JAK2/STAT3 inhibitor, 5 mg/kg or 10 mg/kg) was administered to evaluate the therapeutic effect on LPS-induced AKI (L-AKI) and LPS-induced CKD (L-CKD), with animals sacrificed 6–24 h and 14 days post-LPS induction, respectively. The immune mechanisms of STAT3 blockade were determined by comparing the macrophage phenotypes and correlated with renal function parameters. Also, the transcriptomic analysis was used to confirm the anti-inflammatory effect of L-AKI, and the anti-fibrotic role was further evaluated in the L-CKD model.ResultsIn the L-AKI model, sequential increases in BUN and blood creatinine levels were time-dependent, with a marked elevation of 0–6 h after LPS injection. Notably, two newly identified macrophage subpopulations (CD11bhighF4/80low and CD11blowF4/80high), exhibited population changes, with an increase in the CD11bhighF4/80low population and a decrease in the CD11blowF4/80high macrophages. Corresponding to the FACS results, the tubular injury score, NGAL, F4/80, and p-STAT3 expression in the tubular regions were elevated. STAT3 inhibitor injection in L-AKI and L-CKD mice reduced renal injury and fibrosis. M2-type subpopulation with CD206 in CD11blowF4/80high population increased in the Stattic-treated group compared with that in the LPS-alone group in the L-AKI model. Additionally, STAT3 inhibitor reduced inflammation driven by LPS-stimulated macrophages and epithelial cells injury in the co-culture system. Transcriptomic profiling identified 3 common genes in the JAK-STAT, TLR, and TNF signaling pathways and 11 common genes in the LPS with macrophage response. The PI3K-AKT (IL-6, Akt3, and Pik3r1) and JAK-STAT pathways were determined as potential Stattic targets. Further confirmation through mRNA and protein expressions analyses showed that Stattic treatment reduced inflammation in the L-AKI and fibrosis in the L-CKD mice.ConclusionsSTAT3 blockade effectively mitigated inflammation by retrieving the CD11blowF4/80high population, further emphasizing the role of STAT3-associated macrophage-driven inflammation in kidney injury.

House dust mite allergen directly activates ILC2 cells via the TLR4 signaling pathway in allergic airway diseases

BackgroundUnlike T cells and B cells, the activation process of group 2 innate lymphoid cells (ILC2s) is mainly driven by epithelial cell derived cytokines rather than specific antigen recognition. Whether antigens have a direct role in activating ILC2s remains poorly understood. MethodsFollowing stimulation, type 2 cytokine secretions and cell death were assessed in house dust mite (HDM)-stimulated ILC2s. To investigate the underlying mechanisms, RNA-sequencing (RNA-seq) was performed on HDM-stimulated ILC2s. The validation experiments were done through in vitro stimulation assays and an HDM-induced asthmatic murine model, using specific inhibitors targeting receptor and relevant proteins of signaling pathways. ResultsHDM stimulation increased the secretion of IL-5 and IL-13 cytokines from ILC2s, inhibited apoptosis of ILC2, and promoted the proliferation of ILC2s. As confirmed by RNA-seq, HDM stimulation upregulated genes in ILC2s, including those responsible for type 2 cytokines, ILC2s-specific transcriptional factors, and related receptors. Both toll-like receptor (TLR) 1 and TLR4 were constitutively expressed on ILC2s, however, only TLR4 was predominantly upregulated upon HDM stimulation. TAK242, a specific TLR4 inhibitor, significantly blocked the effect of HDM on ILC2s, in terms of type 2 cytokine secretions and cell death. Using specific inhibitors in pathways, we confirmed that HDM promoted ILC2s activation via TLR4-ERK, p38, and NF-κB signaling pathways. ConclusionsAllergen HDM directly activates ILC2s through TLR4 mediated-ERK/p38/NF-κB signaling pathway. These findings provide new insights into how antigens propagate type 2 immune response via ILC2s, contributing to chronic inflammations in allergic airway diseases.

TLR3/TRIF and MAVS Signaling Is Essential in Regulating Mucosal T Cell Responses during Rotavirus Infection.

The functions of the natural dsRNA sensors TLR3 (TRIF) and RIG-I (MAVS) are crucial during viral challenge and have not been accurately clarified in adaptive immune responses to rotavirus (RV) infection. In this study, we found that RV infection caused severe pathological damage to the small intestine of TLR3-/- and TRIF-/- mice. Our data found that dendritic cells from TLR3-/- and TRIF-/- mice had impaired Ag presentation to the RV and attenuated initiation of T cells upon viral infection. These attenuated functions resulted in impaired CD4+ T and CD8+ T function in mice lacking TLR3-TRIF signaling postinfection. Additionally, attenuated proliferative capacity of T cells from TLR3-/- and TRIF-/- mice was observed. Subsequently, we observed a significant reduction in the absolute number of memory T cells in the spleen and mesenteric lymph node (MLN) of TRIF-/- recipient mice following RV infection in a bone marrow chimeric model. Furthermore, there was reduced migration of type 2 classical dendritic cells from the intestine to MLNs after RV infection in TLR3-/- and TRIF-/- mice. Notably, RV infection resulted in attenuated killing of spleen and MLN tissues in TRIF-/- and MAVS-/- mice. Finally, we demonstrated that RV infection promoted apoptosis of CD8+ T cells in TRIF-/- and TLR3-/-MAVS-/- mice. Taken together, our findings highlight an important mechanism of TLR3 signaling through TRIF in mucosal T cell responses to RV and lay the foundation for the development of a novel vaccine.

Targeting exosomal double-stranded RNA-TLR3 signaling pathway attenuates morphine tolerance and hyperalgesia

Long-term morphine use leads to tolerance and hyperalgesia in patients with chronic pain, with neuroinflammation playing a key role, but its underlying mechanisms remain elusive. This study determines that repeated intrathecal morphine injections increase double-stranded RNA (dsRNA) production in spinal neurons, due to downregulated adenosine deaminase RNA specific 1 (ADAR1) expression. Lentivirus-induced ADAR1 elevation decreases the high levels of intracellular dsRNA and attenuates morphine tolerance and hyperalgesia. dsRNA is released into cerebrospinal fluid via exosomes (Exos) after repeated morphine injections and is taken up by microglia for TLR3-TRIF-IL-6 signaling activation. Blocking Exos release with GW4869 or inhibition of TLR3 signaling mitigates neuroinflammation, preventing the development of morphine tolerance and hyperalgesia. Intrathecal injection of TLR3 inhibitor alone shows analgesic effects in neuropathic pain, and co-administration with morphine amplifies the analgesic efficacy of morphine. These findings demonstrate that targeting dsRNA-TLR3 signaling to mitigate neuroinflammation could be a promising treatment for morphine tolerance.

TLR3 activation mediates partial epithelial-to-mesenchymal transition in human keratinocytes.

TLR3 is expressed in human skin and keratinocytes, and given its varied role in skin inflammation, development, and regeneration, we sought to determine the cellular response in normal human keratinocytes to TLR3 activation. We investigated this mechanism by treating primary human keratinocytes with both UVB, an endogenous and physiologic TLR3 activator, and poly(I:C), a synthetic and selective TLR3 ligand. TLR3 activation with either UVB or poly(I:C) altered keratinocyte morphology, coinciding with the key features of epithelial-to-mesenchymal transition: increased epithelial-to-mesenchymal transition gene expression, enhanced migration, and increased invasion properties. These results confirm and extend previous studies demonstrating that in addition to its classical role in the innate immune response, TLR3 signaling also regulates stem cell-like properties and developmental programs.

Allocryptopine Attenuates Inflammatory Responses in Microglial Cells Via TLR4-Dependent NF-κB and p38 MAPK Pathways.

Studies in the existing literature propose that allocryptopine possesses both antioxidant and anti-inflammatory properties, showcasing its neuroprotective effects by potentially mitigating oxidative stress and inflammation. This study aims to investigate the antioxidant and anti-inflammatory effects of allocryptopine on various targets and potential mechanisms that have not been previously explored in the literature. Initially, we used MTT and LDH methods to evaluate the effects of allocryptopine on cell viability in BV-2 cells exposed to LPS-induced damage. Subsequently, we evaluated the impact of allocryptopine on pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), other inflammatory mediators (Cox-2 and iNOS), and p38 MAPK genes and proteins through qRT-PCR and Western blot analyses. Also, we evaluated the impact of allocryptopine on NF-κB proteins (TLR4, MyD88, IκBα, p-p50, and p-p65) through ELISA assay. Molecular docking analyses were performed to investigate the potential binding of allocryptopine to target proteins (TLR4, MyD88, IκBα, p50, p65, MKK3, MKK4, MKK6, p38, AP-1 (c-Jun and ATF2), IL-1β, IL-6, TNF-α, Cox-2, and iNOS) associated with the TLR4, NF-κB, and p38 MAPK pathways. Our results indicate that allocryptopine exerts a comprehensive influence on pro-inflammatory cytokines and other inflammatory mediators by inhibiting TLR4 signaling and modulating the NF-κB and p38 MAPK pathways. The outcomes of our study suggest that the antioxidant and anti-inflammatory efficacy of allocryptopine is intricately linked to the modulation of key molecular pathways associated with oxidative stress and inflammation. These findings highlight the potential of allocryptopine as a therapeutic agent for addressing neurodegenerative diseases by safeguarding neuronal health.

Activation of the NLRP1B inflammasome by caspase-8

Cleavage of the innate immune receptor NLRP1B by various microbial proteases causes the proteasomal degradation of its N-terminal fragment and the subsequent release of a C-terminal fragment that forms an inflammasome. We reported previously that metabolic stress caused by intracellular bacteria triggers NLRP1B activation, but the mechanism by which this occurs was not elucidated. Here we demonstrate that TLR4 signaling in metabolically stressed macrophages promotes the formation of a TRIF/RIPK1/caspase-8 complex. Caspase-8 activity, induced downstream of this TLR4 pathway or through a distinct TNF receptor pathway, causes cleavage and activation of NLRP1B, which facilitates the maturation of both pro-caspase-1 and pro-caspase-8. Thus, our findings indicate that caspase-8 and NLRP1B generate a positive feedback loop that amplifies cell death processes and promotes a pro-inflammatory response through caspase-1. The ability of NLRP1B to detect caspase-8 activity suggests that this pattern recognition receptor may play a role in the defense against a variety of pathogens that induce apoptosis.

Abstract B050: Convergent signaling via C/EBPβ regulates MDSC-intrinsic NLRP3 inflammasomes to drive inflammatory CAF polarization

Abstract OBJECTIVE: Pivotal contributors to therapeutic resistance in pancreatic ductal adenocarcinoma (PDAC) are myeloid cell infiltration and signaling, and interleukin-1 (IL1)-mediated inflammatory polarization of cancer-associated fibroblasts (iCAF). We have shown that granulocytic myeloid- derived suppressor cell (gMDSC) promote iCAF polarization via NLRP3 inflammasome-derived IL-1β. Here, we sought to dissect the mechanisms regulating NLRP3 inflammasome induction in gMDSCs that drive iCAF polarization in PDAC. METHODS: Single-cell RNA sequencing (scRNA-seq) was performed in PKT mice treated with NLRP3i SB-NL02 vs vehicle. Single-Cell rEgulatory Network Inference and Clustering (SCENIC) analysis identified putative regulons binding upstream to Nlrp3 Transcription Start Site (TSS) in gMDSC subclusters in scRNA-seq data. CRISPR/cas9 silencing of Nlrp3 and Cebpb was performed in gMDSC-like J774M cells in vitro. These edited gMDSCs and J774M cells treated with/without SB-NL02 were co-cultured with Il6/Acta2 dual-reporter CAFs to examine iCAF polarization. RESULTS: PKT mice treated with NLRP3i SB-NL02 showed reduced tumor burden, gMDSC-intrinsic ASC oligomerization, and iCAF polarization in vivo. In silico analysis of intercellular single-cell communication showed striking attenuation in gMDSC-Nlrp3/Il1b:CAF-Il1r1 ligand-receptor crosstalk following NLRP3i treatment. To dissect mechanisms underlying NLRP3 regulation in gMDSCs that drive iCAF skewness, lineage trajectory inference revealed strong co-expression of Tlr4, Cxcr2, Nlrp3 and Il1b genes. Mechanistic studies in J774M gMDSCs showed activation of NLRP3 inflammasomes and IL-1βsecretion not only via canonical TLR4-MyD88 signaling, but also via CXCR2-mediated p38 MAPK induction. This was corroborated in vivo where ASC speck formation in intratumoral Ly6G+ gMDSCs was diminished in mice treated with CXCR2i AZD5069 and p38i peximetinib. To dissect how TLR4 and CXCR2-p38 signaling converge to regulate NLRP3, SCENIC analysis in single-cell gMDSCs transcriptomes revealed Cebpb as the top predicted regulon at the Nlrp3 TSS. In vitro studies using peximetinib and TLR4i (and combinations) revealed that p38 MAPK and TLR4-Myd88 signaling cooperatively regulate C/EBPβ, which in turn dictates Nlrp3 transcription. Cebpb silencing in J774M gMDSCs abolished Nlrp3 transcription, ASC assembly, and IL-1β secretion. ChIP-seq analysis showed strong occupancy of Cebpb on promoter regions of Nlrp3 upon inflammasome induction in gMDSCs. Finally, gMDSC-mediated CAF-Il6 induction in dual-reporter CAFs was significantly disrupted by co-culture with J774M-Cebpb KO cells, recapitulating the effect on iCAF mitigation demonstrated by co-cultures with J774M-Nlrp3 KO or gMDSCs pre-treated with SB-NL02. CONCLUSIONS: CXCR2-p38 and TLR4 signaling converge on C/EBPβ to regulate gMDSC-intrinsic NLRP3 inflammasomes, which drives iCAF polarization in PDAC. The role of C/EBPβ activation as a central node in imparting myeloid checkpoint function in gMDSCs warrants further exploration. Citation Format: Karthik Rajkumar, Andrew Adams, Haleh Amirian, Manan Patel, Erin Dickey, Harper Margaret Marsh, Siddharth Mehra, Nagaraj Nagathihalli, Nipun Merchant, Anna Bianchi, Jashodeep Datta. Convergent signaling via C/EBPβ regulates MDSC-intrinsic NLRP3 inflammasomes to drive inflammatory CAF polarization [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B050.