TLR4

Overview

toll-like receptor 4 (TLR4) is a pattern recognition receptor belonging to the toll-like receptor (TLR) family, encoded by the TLR4 gene. It is a transmembrane glycoprotein constitutively expressed on the surface of innate immune cells — including monocytes, macrophages, dendritic cells, neutrophils, and microglia — as well as on a variety of non-immune cell types such as hepatic stellate cells and neurons. TLR4 is best characterized as the primary sensor for lipopolysaccharide (LPS), a structural component of gram-negative bacterial cell walls, but it also recognizes endogenous danger signals (damage-associated molecular patterns, or DAMPs) such as high-mobility group box 1 protein (HMGB1) and lumican. Upon ligand binding, TLR4 recruits the adapter protein myeloid differentiation primary response 88 (MyD88), initiating downstream signaling cascades that culminate in the activation of nuclear factor kappa B (NF-κB) and the production of proinflammatory cytokines including interleukin-1 beta (IL-1β) and interleukin-6 (IL-6).

Beyond its canonical role in host defense against bacterial infection, TLR4 is increasingly recognized as a central mediator of sterile inflammation across a broad spectrum of pathological conditions. Its activation drives tissue-damaging neuroinflammation in neurodegenerative and neuropathic pain states, promotes fibrosis, facilitates tumor progression and metastasis, and modulates immunophenotypic changes in circulating leukocytes exposed to environmental or pharmacological stressors. This dual role — protective in acute infection yet injurious in chronic or dysregulated contexts — makes TLR4 a high-priority research target for therapeutic intervention in inflammation-driven diseases, ranging from metabolic dysfunction–associated steatotic liver disease (MAFLD/NAFLD) to Parkinson's disease and cancer.

Focus of Latest Publications

Recent publications continue to position TLR4 as a central mediator of inflammatory signaling across diverse disease models, with many studies examining whether natural products or biomaterials can blunt TLR4-driven responses. In a rat model of desert dry-heat-induced exertional heat stroke, nanocurcumin was reported to reduce brain injury, neuroendocrine dysfunction, and systemic inflammation, with network pharmacology, molecular docking, histology, ELISA, biochemical assays, and western blotting all supporting suppression of the TLR4/MyD88/NF-κB axis. Similarly, astaxanthin was shown in a middle cerebral artery occlusion model to improve neurological deficits, reduce edema, infarct volume, and apoptosis, and lower TLR4, MyD88, NF-κB, IL-1β, IL-6, Cyt C, and caspase-3 expression; the protective effect was weakened by the TLR4 agonist RS 09, reinforcing TLR4 pathway involvement.

Several recent studies also linked TLR4 inhibition to protection in metabolic and hepatic inflammation. rutin was reported to alleviate hepatic steatosis, oxidative stress, mitochondrial dysfunction, and liver injury in high-fat diet-fed ApoE-/- mice and free fatty acid-exposed HepG2 cells, while suppressing IL-1β, IL-6, and TNF-α through direct binding to RUNX1 and downstream inhibition of TLR4/NF-κB signaling. In rheumatoid arthritis-related work, phenylpropanoids from Dendropanax proteus were identified by affinity ultrafiltration, SPR, UHPLC-MS/MS, network pharmacology, CETSA, ITDR, and DARTS as TLR4-COX-2 axis inhibitors; these compounds reduced TLR4 and COX-2/PGE2 expression in TNF-α-stimulated MH7A cells. Another liver-focused study reported that lumican-TLR4 interaction accelerates hepatic fibrosis by activating hepatic stellate cells, highlighting TLR4 as part of a profibrotic signaling interface.

TLR4 was also studied in neuroinflammatory and neurodegenerative contexts. Astragaloside IV was shown to directly bind TLR4 and inhibit TLR4/NF-κB signaling in microglia in an MPTP-induced Parkinson’s disease mouse model, improving motor and anxiety-like behaviors and preserving dopaminergic and hippocampal neurons; notably, these effects were abolished in TLR4-deficient mice. Liquiritin was investigated in trigeminal neuropathic pain, where network pharmacology suggested modulation of TLR4/MyD88-dependent microglial M1-like polarization. In microglia, another study examined charge-dependent dendrimeric polyglycerols and verified binding of HMGB1 and IL-33 to ST2, RAGE, and TLR4, showing that different dendrimer formulations altered alarmin-receptor interactions in lipopolysaccharide-activated human microglia.

Beyond disease treatment studies, TLR4 also appeared in broader immunology and cancer-related analyses. In lung adenocarcinoma, multi-omics and machine learning identified TLR4 among core PANoptosis-related genes, with enrichment in M2 macrophages and association with NF-κB and NOD-like receptor signaling; ginsenosides were reported to affect a TLR4/NLRP3 survival axis in vitro. A mucosal vaccination study used an intranasal liposomal formulation containing TLR4 and TLR7/8 ligands with ovalbumin and found broad protection in mice against respiratory threats including SARS-CoV-2 and Staphylococcus aureus, mediated by durable memory T-cell responses and alveolar macrophage imprinting. Together, these publications underscore TLR4 as a recurring target in inflammatory, neuroimmune, fibrotic, and vaccine-adjuvant research.

Key Publications

• NEWJul Nanocurcumin attenuates brain injury in rats with desert dry‑heat‑induced exertional heat stroke by suppressing TLR4/MyD88/NF‑κB signaling. (Molecular medicine reports, 2026, PMID 42396648): "Excessive activation of inflammatory signaling pathways, notably the Toll-like receptor (TLR)4/myeloid differentiation factor 88 (MyD88)/NF-κB axis, critically contributes to brain damage and neuroendocrine dysfunction in EHS."
• May Dually Charged Dendrimeric Polyglycerol Modulates Interleukin-33 at Alarmin Receptors in Microglia. (ACS chemical neuroscience, 2026, PMID 42081615): "...the binding of HMGB1 and IL-33 to ST2, RAGE and Toll-like receptor 4."
• Apr Transcriptomics and Experiments Verified that Astaxanthin Reduces the Apoptosis of Nerve Cells in Ischemic Stroke by Inhibiting the Toll-like Receptor Signaling Pathway. (Molecular neurobiology, 2026, PMID 42050264): "Also, ATX has reduced inflammation and apoptosis-related proteins such as TLR4, MyD88, NFκB, IL-1β, IL-6, Cyt C, and Caspase-3."
• May Lumican-TLR4 interaction accelerates hepatic fibrosis by activating hepatic stellate cells. (Hepatology communications, 2026, PMID 42043860): "Lumican-TLR4 interaction accelerates hepatic fibrosis by activating hepatic stellate cells."
• May Multi-omics reveals rutin directly targets RUNX1 to disrupt the RUNX1/TET2 complex and alleviate NAFLD via TLR4/NF-κB inhibition. (European journal of pharmacology, 2026, PMID 41997405): "...and thereby inhibits the downstream Toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) signaling pathway."
• May Lipid emulsion modulates myogenic and collagen-related gene expression in skeletal muscle of preterm fetal sheep. (Experimental physiology, 2026, PMID 41955312): "Similarly, genes related to inflammation, such as Tnfa (tumour necrosis factor α), Il-6 (interleukin 6), Tlr4 (Toll-like receptor 4) and Tlr2 (Toll-like receptor 2), were unaffected."
• Apr Integration of multi-omics and machine learning to identify core genes in PANoptosisof lung adenocarcinoma and their mechanisms in the tumor microenvironment and therapeutic potential. (Naunyn-Schmiedeberg's archives of pharmacology, 2026, PMID 41935997): "Six core genes of LUAD PANoptosis, including IRF1, NLRP3, CASP1, TIMP1, S100A8, and TLR4, were identified in the study."
• Mar Targeted screening of phenylpropanoids from Dendropanax proteus for rheumatoid arthritis therapy and mechanistic insights. (Bioorganic chemistry, 2026, PMID 41924844): "Toll-like receptor 4 (TLR4) and cyclooxygenase-2 (COX-2) are key mediators in its pathogenesis."
• May Liquiritin attenuates IONI-induced trigeminal neuropathic pain via TLR4/MyD88-dependent modulation of microglial M1-like polarization. (International immunopharmacology, 2026, PMID 41880679): "Microglia-driven neuroinflammation in the trigeminal system, particularly Toll-like receptor 4 (TLR4)/myeloid differentiation primary response 88 (MyD88) signaling, is increasingly recognized as a key driver of neuropathic pain."
• May Astragaloside IV alleviates motor and anxiety deficits in Parkinson's disease mice by targeting TLR4. (International immunopharmacology, 2026, PMID 41846059): "Mechanistically, AS-IV directly bound to TLR4, inhibiting the TLR4/NF-κB signaling pathway in microglia within the substantia nigra pars compacta (SNpc), ventral tegmental area (VTA), and hippocampus."