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Toll-like receptors and their role in neuropathic pain and migraine


Migraine is a complex neurological disease of unknown etiology involving both genetic and environmental factors. It has previously been reported that persistent pain may be mediated by the immune and inflammatory systems. Toll-like receptors (TLRs) play a significant role in immune and inflammatory responses and are expressed by microglia and astrocytes. One of the fundamental mechanisms of the innate immune system in coordinating inflammatory signal transduction is through TLRs, which protect the host organism by initiating inflammatory signaling cascades in response to tissue damage or stress. TLRs reside at the neuroimmune interface, and accumulating evidence has suggested that the inflammatory consequences of TLR activation on glia (mainly microglia and astrocytes), sensory neurons, and other cell types can influence nociceptive processing and lead to pain. Several studies have shown that TLRs may play a key role in neuropathic pain and migraine etiology by activating the microglia. The pathogenesis of migraine may involve a TLR-mediated crosstalk between neurons and immune cells. Innate responses in the central nervous system (CNS) occur during neuroinflammatory phenomena, including migraine. Antigens found in the environment play a crucial role in the inflammatory response, causing a broad range of diseases, including migraines. These can be recognized by several innate immune cells, including macrophages, microglia, and dendritic cells, and can be activated through TLR signaling. Given the prevalence of migraine and the insufficient efficacy and safety of current treatment options, a deeper understanding of TLRs is expected to provide novel therapies for managing chronic migraine. This review aimed to justify the view that TLRs may be involved in migraine.



Migraine is a neurological disorder that manifests as a paroxysmal headache lasting approximately 4–72 h. This type of headache may be unilateral and is characterized by pulsating or throbbing. It is generally associated with nausea and/or vomiting and sensitivity to light and sound. It can be relieved after rest and aggravated after activity. If treated inactively or improperly, headache severity may progress throughout an attack and even develop into chronic migraine [1].

Migraine is divided into episodic (< 15 monthly headache days, MHDs) and chronic (≥ 15 MHDs, with migraine attacks occurring at least 8 days per month), according to the frequency of headache days per month [2]. In the 2016 Global Burden of Disease Study, migraine was a leading cause of disability among patients under 50 years of age worldwide, second only to lower back pain [1, 3].

However, the exact etiology and pathogenesis of migraine are still under discussion, resulting in limited treatment options. Recent studies have shown that Toll-like receptors (TLRs) are significantly associated with migraine. They mediate inflammatory pain and cause central sensitization by generating inflammatory mediators (e.g., TNF-α, IL-1β, and NO) [4].

Neuropathic pain

Neuropathic pain was redefined as pain caused by a lesion or disease of the somatosensory system [5, 6]. Its symptom severity and duration are often greater than those of other types of chronic pain [7], with 5% of patients debilitated despite the use of analgesics [8]. Therefore, in-depth study of the role of TLRs in neuropathic pain is conducive to better treatment. Several recent studies have demonstrated that TLRs are dramatically associated with neuropathic pain [4, 9,10,11,12,13,14,15,16,17]. Its pathogenesis may be that they induce the activation of microglia or astrocytes and the production of the proinflammatory cytokines in the spinal cord, resulting in the development and maintenance of inflammatory pain and neuropathic pain. In particular, primary sensory neurons express TLRs to sense exogenous PAMPs (pathogen-associated molecular patterns, PAMPs) and endogenous DAMPs  (damage-associated molecular patterns, DAMPs) released after tissue injury and/or cellular stress.

History of TLRs

TLRs have been characterized by their essential contribution to innate immune signaling [18, 19]. They were first discovered in the form of genes in Drosophila melanogaster that control the dorsal-ventral axis during embryonic development [20]. Toll was further identified as a transmembrane interleukin-1 receptor homolog that initiates immune responses in Drosophila in vitro [21, 22]. A human homolog of Drosophila Toll (Toll-like) was cloned and characterized as a transmembrane protein that can activate nuclear factor-κB (NF-κB), mediating transcription of the proinflammatory cytokines IL-1, IL-6, and IL-8 in human monocytes [23]. The discovery of this receptor provided preliminary evidence that TLRs are regulators of mammalian immunity [18, 24].

Structure and function of TLRs

All TLRs consist of an amino-terminal domain that has multiple leucine-rich repeats and a carboxy-terminal TIR domain that interacts with TIR-containing adaptors. Thirteen TLRs have been identified in humans and rodents. Humans functionally express TLR1 to TLR10, whereas rodents express TLR1 to TLR9 and TLR11 to TLR13 [18]. TLR10 is the latest to be discovered [25]. TLR2 likely forms heterodimers with TLR1 and TLR6, whereas other TLRs form homodimers. Nucleic acid–sensing TLRs (TLR3, TLR7, TLR8, and TLR9) are located within the endosomal compartments, while other TLRs (TLR1, TLR2, TLR4, TLR5, TLR6, TLR10, TLR11, TLR12) reside at the plasma membrane [26,27,28] (Fig. 1).

Fig. 1
figure 1

Location and structure of TLRs in cells. In human cells, TLR1, TLR2, TLR4, TLR5, TLR6, TLR10 reside at the plasma membrane, while the nucleic acid–sensing TLRs (TLR3, TLR7, TLR8, and TLR9) are localized within endosomal compartments

The TLR gene was discovered to be one of the key genes during development. TLRs are specific type-I transmembrane receptors and pathogen pattern recognition receptors in the innate immune system. These receptors initiate immediate innate immunity by recognizing pathogens and can initiate adaptive immunity via activating signaling pathways. However, they are also expressed in many non-immune tissues, both throughout development and in adulthood. Several studies have indicated that TLRs not only exert immune functions, but also have a wide range of functions in regulating cell fate, cell number, and cell shape [29,30,31,32,33]. These receptors also play a key role in regulating the survival of nerve and glial cells and regulating synaptic plasticity in the central nervous system (CNS) [34].

Signaling pathways of TLRs

The TLR ligands include exogenous pathogenic microorganisms and endogenous ligands released after tissue injury or damage. TLRs play an essential role in recognizing specific patterns of microbial components involved in the activation of innate immunity. Simultaneously, they can initiate a series of downstream reactions by binding to endogenous ligands during acquired immune activity. These noxious endogenous ligands are known as DAMPs (also known as alarmins).

TLRs signaling pathways arise from intracytoplasmic TIR domains, which are conserved among all TLRs [35]. Recent evidence has suggested that upon ligand binding, the cytoplasmic TIR domain of TLR recruits MyD88, TIRAP, TRAM, and TRIF (signal transduction connectors), which modulate TLR signaling pathways [26] (Fig. 1). In summary, different adaptors activate different kinases (IRAK4, IRAK1, IRAK2, TBK1, and IKKε) and ubiquitin ligases (TRAF6 and pellino 1), finally activating the NF-κB, type I interferon, p38 MAP kinase (MAPK), and JNK MAPK pathways [26, 36, 37] (Fig. 2).

Fig. 2
figure 2

TLRs signaling. TIR domain-containing adaptors and TLR signaling. MyD88 is an essential TIR domain-containing adaptor for the induction of inflammatory cytokines via all the TLRs. Upon stimulation, MyD88 recruits IL-1 receptor-associated kinase (IRAK) to TLRs. IRAK is activated by phosphorylation and then dimerizes with TRAF6, leading to the activation of two distinct signaling pathways, finally activating MAPK and NF-kB to elicit proinflammatory cytokines. TIRAP/Mal is a second TIR domain-containing adaptor that specifically mediates the MyD88-dependent pathway via TLR2 and TLR4, While TRIF specifically participates in the MyD88-independent pathway mediated by TLR3 and TLR4, TLR2 leads to the complexity of signal pathway by forming tlr2-tlr1 and tlr2-tlr6 heterodimers and starts intracellular signal transduction. Both homodimers (TLR10/TLR10) and heterodimers (TLR10/TLR2) can recruit MyD88. TLR10 can reduce the production of IL-1β by directly inhibiting MyD88 or MAPK. Although several studies have suggested its inflammatory properties, TLR10 has also been shown to increase the production of IL-1Ra (an anti-inflammatory factor), but the underlying mechanism is still unclear, as indicated by question marks. Nucleic acids in endolysosomes activate TLR3, TLR7 or TLR9 and initiate different and overlapping signal cascades

MyD88 is essential for the induction of inflammatory cytokines triggered by all TLRs. TIRAP is specifically involved in the MyD88-dependent pathway via TLR2 and TLR4, whereas TRIF is involved in the MyD88-independent pathway that is mediated by TLR3 and TLR4. Thus, the diversity of TIR domain-containing adapters provides the specificity and complexity of TLR signaling [35]. The TLR5, TLR7, TLR8, and TLR9 signaling pathways are MyD88-dependent.

Research on TLR10 signaling is currently inconclusive. To date, TLR10 is the only TLR known to exhibit anti-inflammatory properties. Previously, TLR10 was thought to be an “orphan receptor,“ but many recent studies have identified ligands of TLR10 [25, 38]. Some studies have suggested that TLR10 activation can promote inflammation by activating NF-κB, while others have shown that it suppresses inflammation by inhibiting NF-κB. However, the downstream signaling pathway remains to be elucidated. The complexity of TLR10 signaling may be related to its ability to form TLR2/TLR10 heterodimers or TLR10/TLR10 homodimers.

TLRs and migraine

TLRs are normally expressed in immune and glial cells of the CNS [39, 40]. In addition to pathogen recognition, TLRs also function to recognize the molecular patterns of ligands associated with cellular stress, tissue damage, or cell death [41,42,43].

Significant evidence has illustrated that innate immune signaling is the major mechanism responsible for persistent pain [18]. Previous studies have also suggested that TLRs (TLR2, TLR3, TLR4, TLR5, TLR7, TLR8, TLR9) are implicated in the pathogenesis of neuropathic pain models [4, 9,10,11,12,13,14,15,16,17]. However, the role of TLRs in migraines remains unclear. To date, several studies have shown that TLR2, TLR3, and TLR4 are associated with migraine [44,45,46,47,48].

The possible mechanisms by which TLRs cause migraine are as follows: activation of TLRs leads to the upregulation of NF-κB, while increasing the transcription of genes encoding IL-1 family cytokines and TNF [49, 50]. After activation, Th1, Th2, and Th17 effector cells express a series of cytokines that act on innate immune cells to fight infections and may cause migraine [51,52,53] (Fig. 3).

Fig. 3
figure 3

TLRs 2, 3, and 4 mediate migraine. Activation of TLRs (TLR2, TLR3, and TLR4) triggers upregulation of NF-κB and increases the transcription of genes encoding IL-1 family cytokines and TNF. Upon activation, a series of cytokines and inflammatory mediators are expressed that lead to central sensitization and possibly migraine



TLR2 signaling

Residing at the plasma membrane, TLR2 is characterized by an exceptional diversity of compatible exogenous and endogenous ligands [18, 54]. This is mainly because it can dimerize with TLR1 or TLR6, which increases the complexity of ligand specificity. Structural studies have confirmed that TLR2 can distinguish various lipopeptides by forming TLR2/TLR1 and TLR2/TLR6 heterodimers [18, 55, 56]. Ligand-induced heterodimerization of the TLR2 extracellular domain brings the cytoplasmic C-terminal TIR domain into proximity and then initiates intracellular signaling via the MyD88 -dependent pathway. This then leads to upregulation of NF-κB and increased transcription of genes encoding the IL-1 family cytokines and TNF by binding to the cofactor CD14, which induces the production of inflammatory cytokines, resulting in pain [18, 51, 57].

In addition to reacting with exogenous ligands, TLR2 is triggered by its binding to endogenous ligands when the body is damaged and stressed. Although endogenous DAMPs for TLR2 have not been definitively captured, a few studies have shown that TLR2 can bind to high-mobility group box 1 (HMGB1), Ganglioside GT1b, Heat Shock Protein 60 (HSP60), biglycan (a type of CSPG), and hyaluronan [18, 58,59,60,61,62].

The TLR2 signaling pathways are complex, not only because it is easy to form a heterodimer, but also because there seems to be a large overlap between some endogenous ligands and their effects on TLR2 and TLR4, creating crosstalk between TLR2 and its downstream targets. The ability to directly attribute to functional results to TLR2 depend on the method used [18].

TLR2 and neuropathic pain

TLR2 is found in many organisms, where it induces the generation of inflammatory cytokines, activating NF-kB, with consequent pain [51, 63]. Although low levels were detected in astrocytes, oligodendrocytes, Schwann cells, fibroblasts, endothelial cells, and neurons, they are predominantly expressed on microglia and other macrophages in the peripheral and central nervous system [49, 50, 64,65,66].

Several studies have shown that TLR2 activates microglia and astrocytes and produces proinflammatory cytokines in the spinal cord following tissue and nerve injury, leading to the development and maintenance of inflammatory and neuropathic pain [4]. Several researchers have also found that Tlr2 knockout partially alleviated mechanical allodynia and thermal hyperalgesia caused by nerve ligation [12, 18, 67].

TLR2 and migraine

RNA sequencing of the brain revealed that Tlr2 gene expression is highly enriched in microglia compared to other cell types, and has been identified as a reliable marker of activated microglia in vivo, but its detailed role in microgliosis is still unknown [18, 68, 69]. Previous studies have suggested that TLR2 is involved in the pathogenesis of neuropathic pain and trigeminal neuralgia. However, the mechanism of TLR2 pathway during migraine attacks remains unclear [40].

Evidence suggests that TLR are significantly associated with migraine. Transcriptomics has demonstrated that the expression of proinflammatory genes (e.g., TLR2, CCL8) in the calvarial periosteum is significantly increased in patients with CM [44]. In a study of migraine with aura, multiple cortical spreading depression (CSD) episodes induced significant HMGB1 release, and the HMGB1-TLR2/4 axis activated microglia [45]. Several studies have shown further evidence that both mast cells and T cells are activated and the expression of chemokine and TLR2 are increased in migraines [51, 70, 71].

An increase in inflammatory cytokines leads to increased cell adhesion, production of chemical inflammatory compounds, and NF-κB dysfunction (Fig. 3). Therefore, reducing inflammatory symptoms in migraine may affect innate immune response pathways by modulating the inflammatory cytokines, TLRs and NF-κB [44].

It is not difficult to see that research on TLR2 and migraine is still in its infancy. Further work is needed to elucidate the upstream and downstream molecular mechanisms of migraine.


TLR3 signaling

TLR3 is an intracellular receptor localized within the endosomal compartments. In addition to DRGs, TLR3 is thought to be expressed to varying degrees in microglia, astrocytes, oligodendrocytes, Schwann cells, fibroblasts, and endothelial cells [18].

Intracellular TLR3 is intrinsically capable of detecting nucleic acids. It acts within the endosomal compartment and can distinguish between host and foreign nucleic acids. This role is exerted at specific stages of endosomal maturation and acidification.

TLR3 recognizes double-stranded RNA (dsRNA) and is MyD88-independent [72]. TLR3 is specific to dsRNA, and in addition to ligand dsRNA, TLR3 is also able to recognize some ssRNA viruses [27]. It is unique among all TLRs, and it signals through the TRIF pathway, resulting in the release of type I interferons via IRF3 and/or inflammatory cytokines via NF-κB [18, 36].

TLR3 and neuropathic pain

Research on the mechanism of its involvement in pain is increasing [27], and there is some initial evidence suggesting that TLR3 modulates pain through both shared and distinct molecular mechanisms. This is indirectly supported by the observation that DRGs express TLR3 in culture. TLR3 specific agonist (poly I: C) can increase TRPV1 expression and the functional activity of these sensory neurons, along with triggering an increase in the release of pro-nociceptive prostaglandin E2 [18, 73]. However, few studies have investigated the relationship between TLR3 and neuropathic pain.

A recent investigation identified elevated TLR3 mRNA and protein levels in the rat spinal cord after nerve injury along with increased activation of microglial autophagy. Intrathecal injection of the TLR3 agonist poly (I: C) significantly increased the activation of microglial autophagy and promoted neuropathic pain, which was dramatically reversed by TLR3 knockout [11].

Several studies have shown that TLR3 plays a substantial role in the activation of spinal microglia and development of tactile allodynia after nerve injury [74]. TLR3 deficient mice exhibit moderately reduced allodynia in response to nerve injury, suggesting that activation of TLR3 can be used to regulate neuropathic pain [12]. Tong Liu demonstrated a critical role of TLR3 in regulating sensory neuronal excitability, spinal cord synaptic transmission, and central sensitization. Central sensitization-driven pain hypersensitivity, but not acute pain, is impaired in Tlr3(-/-) mice [10]. However, the specific endogenous ligands of TLR3 and mechanisms by which they induce neuropathic pain remain unclear.

TLR3 and migraine

Although little research has been conducted on the relationship between TLR3 and migraine, there is direct and indirect evidence to suggest that TLR3 is associated with migraine. Research has shown that TLR3 mediates inflammatory pain and causes central sensitization. The specific signaling pathways are as follows: activation of TLR3 in spinal cord microglia results in the activation of the nuclear factor κB (NF-κB), extracellular signal-regulated kinase (ERK), and p38 signaling pathways, leading to the production of inflammatory mediators, central sensitization, and chronic pain [4] (Fig. 3).

However, there seem to be opposing conclusions regarding the association between TLR3 and migraines. Significant evidence suggests that TLR3 activation is neuroprotective and anti-inflammatory in CSD-induced neuroinflammation. Targeting TLR3 may be a novel strategy for developing new treatments for CSD-related neurological disorders [46].

This contradictory conclusion provides research space and innovation for future research. Apparently, research on the relationship between TLR3 and migraine is insufficient, and more research is needed in the future.


TLR4 signaling

TLR4 is one of the most widely characterized TLRs owing to its fundamental role in bacterial perception and the resulting inflammatory response. The canonical ligand for TLR4 is lipopolysaccharide (LPS). The recognition of LPS by TLR4 is multifaceted, and requires the coordination of multiple accessory proteins and coreceptors [18].

Among the TLRs, TLR4 is unique in its capacity to signal through both MyD88-dependent and TRIF-dependent pathways [18]. Conformational changes in TLR4 after binding to ligands recruit adaptor proteins (MyD88 and TRIF) to initiate intracellular signaling cascades. Its recruitment can lead to activation of NF-κB, MAPKs, activator protein-1 (AP-1), and IFN regulatory factor 5 (IRF5), culminating in the transcription of cytokines, chemokines, and other immune mediators [18, 75,76,77,78].

TLR4 and neuropathic pain

A growing number of studies have shown that TLR4 is a key receptor associated with persistent pain [18, 79,80,81]. The participation of the sciatic nerve in neuropathic pain was confirmed by drug interventions in a chronic contraction injury model [82]. The TLR4 antagonist LPS-RS reversed mechanical hypersensitivity in a mouse model of arthritis pain [83]. While antagonism of TLR4 may help prevent dysregulated pain, the involvement of TLR4 may help orchestrate some aspects of tissue repair in the context of nerve injury [18, 84, 85]. Therefore, targeting TLR4 in the treatment of neuropathic pain needs to be cautiously confirmed through further in-depth research.

TLR4 and migraine

The findings of Rafiei et al. suggested that TLR-4 polymorphism is a genetic risk factor for migraine [86]. Other evidence has indicated that TLR4 is associated with hyperalgesia in migraines. The TLR4 signaling pathway promotes hyperalgesia induced by acute inflammatory soup delivery by stimulating the production of proinflammatory cytokines and activating microglia [87]. IL-18-mediated microglia/astrocyte interactions in the medullary dorsal horn likely contribute to the development of hyperpathia or allodynia induced by migraines [88]. In periorbital hypersensitivity of migraine, the TLR4 antagonist (+)-naltrexone blocked the development of facial allodynia after supradural inflammatory soup [89].

In addition, the relationship between the gut microbiota and migraine is currently a hot research topic. Significant research has shown that migraine is associated with functional gastrointestinal disorders (FGIDs), such as functional nausea, cyclic vomiting syndrome, and irritable bowel syndrome (IBS). Modulation of the Kynurenine (l-kyn) pathway (KP) may provide common triggers for migraine and FGIDs involving of TLR, aryl hydrocarbon receptor (AhR), and MyD88 activation; Meanwhile, TLR4 signaling was observed to initiate and maintain migraine-like behavior through mouse MyD88, and KP metabolites detected downstream of TLR activation may be a marker of IBS. Therefore, TLR4 may play a role in the mechanism of migraine induced by FGIDS [47, 48] (Fig. 3).

Although the relationship between TLR4 and migraine is more well-studied than that between TLR2 and TLR3, the related upstream and downstream mechanisms still require significant research.

Conclusions and perspectives

Decades of work have indicated that pain and inflammation are subtly entangled concepts. Here, we present evidence that TLRs are essential for migraine development. Research thus far has suggested that the TLR family members TLR2, TLR3, and TLR4 are associated with migraine, but the detailed underlying pathways and mechanisms remain unclear.

Since the effect of each TLR on pain varies widely due to its structure and cellular location, future studies should investigate the signaling properties of TLRs in migraine attacks at a deeper level, while seeking to translate preclinical insights into effective treatment. In the study of the relationship between TLR2, TLR3, TLR4, and migraine, more attention should be paid to the study of the detailed signaling pathways. We further dissected how each TLR affects nociception and how its expression in glial cells and neurons, or crosstalk between the two, differentially affects the processing of migraines. In addition to TLR2, TLR3, and TLR4, future research should also focus on the roles of TLR5, TLR7, TLR8, and TLR9 in the etiology of neuropathic pain in migraine. Despite these challenges, continuing to elucidate the role of each TLR in representing pain experience provides a very promising opportunity to improve pain in migraine sufferers.

Availability of data and materials

Not applicable.



Central nervous system


Pathogen-associated molecular pattern


Damage-associated molecular pattern


Double-stranded RNA


Extracellular signal-regulated kinase


High-mobility group box 1


Irritable bowel syndrome




MAP kinase


Monthly headache day


Nuclear factor-κB


Toll-like receptors


Cortical spreading depression


  1. Harris L, L’Italien G, O’Connell T, Hasan Z, Hutchinson S, Lucas S. A framework for estimating the eligible patient population for new migraine acute therapies in the United States. Adv Ther. 2021;38(10):5087–97.

    PubMed  PubMed Central  Article  Google Scholar 

  2. Edvinsson L, Haanes KA, Warfvinge K, Krause DN. CGRP as the target of new migraine therapies—successful translation from bench to clinic. Nat Rev Neurol. 2018;14(6):338–50.

    CAS  PubMed  Article  Google Scholar 

  3. Global regional. and national incidence, prevalence, and years lived with disability for 328 diseases and injuries for 195 countries, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016. Lancet. 2017;390(10100):1211–59.

    Article  Google Scholar 

  4. Liu T, Gao YJ, Ji RR. Emerging role of toll-like receptors in the control of pain and itch. Neurosci Bull. 2012;28(2):131–44.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  5. Pereira EA, Aziz TZ. Neuropathic pain and deep brain stimulation. Neurotherapeutics. 2014;11(3):496–507.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  6. Jensen TS, Baron R, Haanpää M, Kalso E, Loeser JD, Rice ASC, et al. A new definition of neuropathic pain. Pain. 2011;152(10):2204–5.

    PubMed  Article  Google Scholar 

  7. Torrance N, Smith BH, Bennett MI, Lee AJ. The epidemiology of chronic pain of predominantly neuropathic origin. Results from a general population survey. J Pain. 2006;7(4):281–9.

    PubMed  Article  Google Scholar 

  8. Bouhassira D, Lantéri-Minet M, Attal N, Laurent B, Touboul C. Prevalence of chronic pain with neuropathic characteristics in the general population. Pain. 2008;136(3):380–7.

    PubMed  Article  Google Scholar 

  9. Yang H, Wu L, Deng H, Chen Y, Zhou H, Liu M, et al. Anti-inflammatory protein TSG-6 secreted by bone marrow mesenchymal stem cells attenuates neuropathic pain by inhibiting the TLR2/MyD88/NF-κB signaling pathway in spinal microglia. J Neuroinflamm. 2020;17(1):154.

    CAS  Article  Google Scholar 

  10. Liu T, Berta T, Xu ZZ, Park CK, Zhang L, Lü N, et al. TLR3 deficiency impairs spinal cord synaptic transmission, central sensitization, and pruritus in mice. J Clin Invest. 2012;122(6):2195–207.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  11. Chen W, Lu Z. Upregulated TLR3 promotes neuropathic pain by regulating autophagy in rat with L5 spinal nerve ligation model. Neurochem Res. 2017;42(2):634–43.

    CAS  PubMed  Article  Google Scholar 

  12. Stokes JA, Cheung J, Eddinger K, Corr M, Yaksh TL. Toll-like receptor signaling adapter proteins govern spread of neuropathic pain and recovery following nerve injury in male mice. J Neuroinflamm. 2013;10:148.

    Article  CAS  Google Scholar 

  13. Li Y, Yin C, Li X, Liu B, Wang J, Zheng X, et al. Electroacupuncture alleviates paclitaxel-induced peripheral neuropathic pain in rats via suppressing TLR4 signaling and TRPV1 upregulation in sensory neurons. Int J Mol Sci. 2019;20(23):5917.

    CAS  PubMed Central  Article  Google Scholar 

  14. Xu ZZ, Kim YH, Bang S, Zhang Y, Berta T, Wang F, et al. Inhibition of mechanical allodynia in neuropathic pain by TLR5-mediated A-fiber blockade. Nat Med. 2015;21(11):1326–31.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  15. He L, Han G, Wu S, Du S, Zhang Y, Liu W, et al. Toll-like receptor 7 contributes to neuropathic pain by activating NF-κB in primary sensory neurons. Brain Behav Immun. 2020;87:840–51.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  16. Zhang ZJ, Guo JS, Li SS, Wu XB, Cao DL, Jiang BC, et al. TLR8 and its endogenous ligand miR-21 contribute to neuropathic pain in murine DRG. J Exp Med. 2018;215(12):3019–37.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  17. Luo X, Huh Y, Bang S, He Q, Zhang L, Matsuda M, et al. Macrophage toll-like receptor 9 contributes to chemotherapy-induced neuropathic pain in male mice. J Neurosci. 2019;39(35):6848–64.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  18. Lacagnina MJ, Watkins LR, Grace PM. Toll-like receptors and their role in persistent pain. Pharmacol Ther. 2018;184:145–58.

    CAS  PubMed  Article  Google Scholar 

  19. Kawai T, Akira S. Toll-like receptors and their crosstalk with other innate receptors in infection and immunity. Immunity. 2011;34(5):637–50.

    CAS  PubMed  Article  Google Scholar 

  20. Anderson KV, Bokla L, Nüsslein-Volhard C. Establishment of dorsal-ventral polarity in the Drosophila embryo: the induction of polarity by the Toll gene product. Cell. 1985;42(3):791–8.

    CAS  PubMed  Article  Google Scholar 

  21. Gay NJ, Keith FJ. Drosophila Toll and IL-1 receptor. Nature. 1991;351(6325):355–6.

    CAS  PubMed  Article  Google Scholar 

  22. Rosetto M, Engström Y, Baldari CT, Telford JL, Hultmark D. Signals from the IL-1 receptor homolog, Toll, can activate an immune response in a Drosophila hemocyte cell line. Biochem Biophys Res Commun. 1995;209(1):111–6.

    CAS  PubMed  Article  Google Scholar 

  23. Medzhitov R, Preston-Hurlburt P, Janeway CA.Jr. A human homologue of the Drosophila Toll protein signals activation of adaptive immunity. Nature. 1997;388(6640):394–7.

    CAS  PubMed  Article  Google Scholar 

  24. O’Neill LA, Golenbock D, Bowie AG. The history of Toll-like receptors—redefining innate immunity. Nat Rev Immunol. 2013;13(6):453–60.

    PubMed  Article  CAS  Google Scholar 

  25. Fore F, Indriputri C, Mamutse J, Nugraha J. TLR10 and its unique anti-inflammatory properties and potential use as a target in therapeutics. Immune Netw. 2020;20(3):e21.

    PubMed  PubMed Central  Article  Google Scholar 

  26. Lim KH, Staudt LM. Toll-like receptor signaling. Cold Spring Harb Perspect Biol. 2013;5(1):a011247.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  27. Blasius AL, Beutler B. Intracellular toll-like receptors. Immunity. 2010;32(3):305–15.

    CAS  PubMed  Article  Google Scholar 

  28. McGettrick AF, O’Neill LA. Localisation and trafficking of Toll-like receptors: an important mode of regulation. Curr Opin Immunol. 2010;22(1):20–7.

    CAS  PubMed  Article  Google Scholar 

  29. Okun E, Griffioen KJ, Son TG, Lee JH, Roberts NJ, Mughal MR, et al. TLR2 activation inhibits embryonic neural progenitor cell proliferation. J Neurochem. 2010;114(2):462–74.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  30. Lathia JD, Okun E, Tang SC, Griffioen K, Cheng A, Mughal MR, et al. Toll-like receptor 3 is a negative regulator of embryonic neural progenitor cell proliferation. J Neurosci. 2008;28(51):13978–84.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  31. Rolls A, Shechter R, London A, Ziv Y, Ronen A, Levy R, et al. Toll-like receptors modulate adult hippocampal neurogenesis. Nat Cell Biol. 2007;9(9):1081–8.

    CAS  PubMed  Article  Google Scholar 

  32. Sloane JA, Batt C, Ma Y, Harris ZM, Trapp B, Vartanian T. Hyaluronan blocks oligodendrocyte progenitor maturation and remyelination through TLR2. Proc Natl Acad Sci U S A. 2010;107(25):11555–60.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  33. Zhu JW, Li YF, Wang ZT, Jia WQ, Xu RX. Toll-like receptor 4 deficiency impairs motor coordination. Front Neurosci. 2016;10:33.

    PubMed  PubMed Central  Google Scholar 

  34. Anthoney N, Foldi I, Hidalgo A. Toll and Toll-like receptor signalling in development. Development. 2018;145(9):dev156018.

    PubMed  Article  CAS  Google Scholar 

  35. Takeda K, Akira S. TLR signaling pathways. Semin Immunol. 2004;16(1):3–9.

    CAS  PubMed  Article  Google Scholar 

  36. Kawai T, Akira S. The role of pattern-recognition receptors in innate immunity: update on Toll-like receptors. Nat Immunol. 2010;11(5):373–84.

    CAS  PubMed  Article  Google Scholar 

  37. Morrison DK. MAP kinase pathways. Cold Spring Harb Perspect Biol. 2012;4(11):a011254.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  38. Jiang S, Li X, Hess NJ, Guan Y, Tapping RI. TLR10 is a negative regulator of both MyD88-dependent and -independent TLR signaling. J Immunol. 2016;196(9):3834–41.

    CAS  PubMed  Article  Google Scholar 

  39. Hayashi F, Smith KD, Ozinsky A, Hawn TR, Yi EC, Goodlett DR, et al. The innate immune response to bacterial flagellin is mediated by Toll-like receptor 5. Nature. 2001;410(6832):1099–103.

    CAS  PubMed  Article  Google Scholar 

  40. Chen WJ, Niu JQ, Chen YT, Deng WJ, Xu YY, Liu J, et al. Unilateral facial injection of Botulinum neurotoxin A attenuates bilateral trigeminal neuropathic pain and anxiety-like behaviors through inhibition of TLR2-mediated neuroinflammation in mice. J Headache Pain. 2021;22(1):38.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  41. Samir P, Place DE, Malireddi RKS, Kanneganti TD. TLR and IKK complex-mediated innate immune signaling inhibits stress granule assembly. J Immunol. 2021;207(1):115–24.

    CAS  PubMed  Article  Google Scholar 

  42. Foster SL, Hargreaves DC, Medzhitov R. Gene-specific control of inflammation by TLR-induced chromatin modifications. Nature. 2007;447(7147):972–8.

    CAS  PubMed  Article  Google Scholar 

  43. Brenner C, Galluzzi L, Kepp O, Kroemer G. Decoding cell death signals in liver inflammation. J Hepatol. 2013;59(3):583–94.

    CAS  PubMed  Article  Google Scholar 

  44. Perry CJ, Blake P, Buettner C, Papavassiliou E, Schain AJ, Bhasin MK, et al. Upregulation of inflammatory gene transcripts in periosteum of chronic migraineurs: implications for extracranial origin of headache. Ann Neurol. 2016;79(6):1000–13.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  45. Takizawa T, Shibata M, Kayama Y, Shimizu T, Toriumi H, Ebine T, et al. High-mobility group box 1 is an important mediator of microglial activation induced by cortical spreading depression. J Cereb Blood Flow Metab. 2017;37(3):890–901.

    CAS  PubMed  Article  Google Scholar 

  46. Ghaemi A, Sajadian A, Khodaie B, Lotfinia AA, Lotfinia M, Aghabarari A, et al. Immunomodulatory effect of toll-like receptor-3 ligand poly I:C on cortical spreading depression. Mol Neurobiol. 2016;53(1):143–54.

    CAS  PubMed  Article  Google Scholar 

  47. Fila M, Chojnacki J, Pawlowska E, Szczepanska J, Chojnacki C, Blasiak J. Kynurenine pathway of tryptophan metabolism in migraine and functional gastrointestinal disorders. Int J Mol Sci. 2021;22(18):10134.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  48. Ramachandran R, Wang Z, Saavedra C, DiNardo A, Corr M, Powell SB, et al. Role of Toll-like receptor 4 signaling in mast cell-mediated migraine pain pathway. Mol Pain. 2019;15:1744806919867842.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  49. Kursun O, Yemisci M, van den Maagdenberg A, Karatas H. Migraine and neuroinflammation: the inflammasome perspective. J Headache Pain. 2021;22(1):55.

    PubMed  PubMed Central  Article  Google Scholar 

  50. Karatas H, Erdener SE, Gursoy-Ozdemir Y, Lule S, Eren-Koçak E, Sen ZD, et al. Spreading depression triggers headache by activating neuronal Panx1 channels. Science. 2013;339(6123):1092–5.

    CAS  PubMed  Article  Google Scholar 

  51. Conti P, D’Ovidio C, Conti C, Gallenga CE, Lauritano D, Caraffa A, et al. Progression in migraine: role of mast cells and pro-inflammatory and anti-inflammatory cytokines. Eur J Pharmacol. 2019;844:87–94.

    CAS  PubMed  Article  Google Scholar 

  52. Supajatura V, Ushio H, Nakao A, Okumura K, Ra C, Ogawa H. Protective roles of mast cells against enterobacterial infection are mediated by Toll-like receptor 4. J Immunol. 2001;167(4):2250–6.

    CAS  PubMed  Article  Google Scholar 

  53. Cseh A, Farkas KM, Derzbach L, Muller K, Vasarhelyi B, Szalay B, et al. Lymphocyte subsets in pediatric migraine. Neurol Sci. 2013;34(7):1151–5.

    PubMed  Article  Google Scholar 

  54. Aliprantis AO, Yang RB, Mark MR, Suggett S, Devaux B, Radolf JD, et al. Cell activation and apoptosis by bacterial lipoproteins through toll-like receptor-2. Science. 1999;285(5428):736–9.

    CAS  PubMed  Article  Google Scholar 

  55. Jin MS, Kim SE, Heo JY, Lee ME, Kim HM, Paik SG, et al. Crystal structure of the TLR1-TLR2 heterodimer induced by binding of a tri-acylated lipopeptide. Cell. 2007;130(6):1071–82.

    CAS  PubMed  Article  Google Scholar 

  56. Kang JY, Nan X, Jin MS, Youn SJ, Ryu YH, Mah S, et al. Recognition of lipopeptide patterns by Toll-like receptor 2-Toll-like receptor 6 heterodimer. Immunity. 2009;31(6):873–84.

    CAS  PubMed  Article  Google Scholar 

  57. Lee CC, Avalos AM, Ploegh HL. Accessory molecules for Toll-like receptors and their function. Nat Rev Immunol. 2012;12(3):168–79.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  58. Jiang D, Liang J, Fan J, Yu S, Chen S, Luo Y, et al. Regulation of lung injury and repair by Toll-like receptors and hyaluronan. Nat Med. 2005;11(11):1173–9.

    CAS  PubMed  Article  Google Scholar 

  59. Lim H, Lee J, You B, Oh JH, Mok HJ, Kim YS, et al. GT1b functions as a novel endogenous agonist of toll-like receptor 2 inducing neuropathic pain. EMBO J. 2020;39(6):e102214.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  60. Park JS, Svetkauskaite D, He Q, Kim JY, Strassheim D, Ishizaka A, et al. Involvement of toll-like receptors 2 and 4 in cellular activation by high mobility group box 1 protein. J Biol Chem. 2004;279(9):7370–7.

    CAS  PubMed  Article  Google Scholar 

  61. Schaefer L, Babelova A, Kiss E, Hausser HJ, Baliova M, Krzyzankova M, et al. The matrix component biglycan is proinflammatory and signals through Toll-like receptors 4 and 2 in macrophages. J Clin Invest. 2005;115(8):2223–33.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  62. Vabulas RM, Ahmad-Nejad P, da Costa C, Miethke T, Kirschning CJ, Häcker H, et al. Endocytosed HSP60s use toll-like receptor 2 (TLR2) and TLR4 to activate the toll/interleukin-1 receptor signaling pathway in innate immune cells. J Biol Chem. 2001;276(33):31332–9.

    CAS  PubMed  Article  Google Scholar 

  63. Barua RS, Sharma M, Dileepan KN. Cigarette smoke amplifies inflammatory response and atherosclerosis progression through activation of the H1R-TLR2/4-COX2 axis. Front Immunol. 2015;6:572.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  64. Bsibsi M, Ravid R, Gveric D, van Noort JM. Broad expression of Toll-like receptors in the human central nervous system. J Neuropathol Exp Neurol. 2002;61(11):1013–21.

    CAS  PubMed  Article  Google Scholar 

  65. Fan J, Frey RS, Malik AB. TLR4 signaling induces TLR2 expression in endothelial cells via neutrophil NADPH oxidase. J Clin Invest. 2003;112(8):1234–43.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  66. Olson JK, Miller SD. Microglia initiate central nervous system innate and adaptive immune responses through multiple TLRs. J Immunol. 2004;173(6):3916–24.

    CAS  PubMed  Article  Google Scholar 

  67. Shi XQ, Zekki H, Zhang J. The role of TLR2 in nerve injury-induced neuropathic pain is essentially mediated through macrophages in peripheral inflammatory response. Glia. 2011;59(2):231–41.

    PubMed  Article  Google Scholar 

  68. Zhang Y, Chen K, Sloan SA, Bennett ML, Scholze AR, O’Keeffe S, et al. An RNA-sequencing transcriptome and splicing database of glia, neurons, and vascular cells of the cerebral cortex. J Neurosci. 2014;34(36):11929–47.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  69. Naert G, Laflamme N, Rivest S. Toll-like receptor 2-independent and MyD88-dependent gene expression in the mouse brain. J Innate Immun. 2009;1(5):480–93.

    CAS  PubMed  Article  Google Scholar 

  70. Marshall JS, McCurdy JD, Olynych T. Toll-like receptor-mediated activation of mast cells: implications for allergic disease? Int Arch Allergy Immunol. 2003;132(2):87–97.

    CAS  PubMed  Article  Google Scholar 

  71. Kilinc E, Dagistan Y, Kotan B, Cetinkaya A. Effects of Nigella sativa seeds and certain species of fungi extracts on number and activation of dural mast cells in rats. Physiol Int. 2017;104(1):15–24.

    CAS  PubMed  Article  Google Scholar 

  72. Alexopoulou L, Holt AC, Medzhitov R, Flavell RA. Recognition of double-stranded RNA and activation of NF-kappaB by Toll-like receptor 3. Nature. 2001;413(6857):732–8.

    CAS  PubMed  Article  Google Scholar 

  73. Qi J, Buzas K, Fan H, Cohen JI, Wang K, Mont E, et al. Painful pathways induced by TLR stimulation of dorsal root ganglion neurons. J Immunol. 2011;186(11):6417–26.

    CAS  PubMed  Article  Google Scholar 

  74. Mei XP, Zhou Y, Wang W, Tang J, Wang W, Zhang H, et al. Ketamine depresses toll-like receptor 3 signaling in spinal microglia in a rat model of neuropathic pain. Neurosignals. 2011;19(1):44–53.

    CAS  PubMed  Article  Google Scholar 

  75. Arthur JS, Ley SC. Mitogen-activated protein kinases in innate immunity. Nat Rev Immunol. 2013;13(9):679–92.

    CAS  PubMed  Article  Google Scholar 

  76. Medzhitov R, Preston-Hurlburt P, Kopp E, Stadlen A, Chen C, Ghosh S, et al. MyD88 is an adaptor protein in the hToll/IL-1 receptor family signaling pathways. Mol Cell. 1998;2(2):253–8.

    CAS  PubMed  Article  Google Scholar 

  77. Takaoka A, Yanai H, Kondo S, Duncan G, Negishi H, Mizutani T, et al. Integral role of IRF-5 in the gene induction programme activated by Toll-like receptors. Nature. 2005;434(7030):243–9.

    CAS  PubMed  Article  Google Scholar 

  78. Strain SM, Fesik SW, Armitage IM. Characterization of lipopolysaccharide from a heptoseless mutant of Escherichia coli by carbon 13 nuclear magnetic resonance. J Biol Chem. 1983;258(5):2906–10.

    CAS  PubMed  Article  Google Scholar 

  79. Buchanan MM, Hutchinson M, Watkins LR, Yin H. Toll-like receptor 4 in CNS pathologies. J Neurochem. 2010;114(1):13–27.

    CAS  PubMed  PubMed Central  Google Scholar 

  80. Heiman A, Pallottie A, Heary RF, Elkabes S. Toll-like receptors in central nervous system injury and disease: a focus on the spinal cord. Brain Behav Immun. 2014;42:232–45.

    CAS  PubMed  Article  Google Scholar 

  81. Nicotra L, Loram LC, Watkins LR, Hutchinson MR. Toll-like receptors in chronic pain. Exp Neurol. 2012;234(2):316–29.

    CAS  PubMed  Article  Google Scholar 

  82. Hutchinson MR, Zhang Y, Brown K, Coats BD, Shridhar M, Sholar PW, et al. Non-stereoselective reversal of neuropathic pain by naloxone and naltrexone: involvement of toll-like receptor 4 (TLR4). Eur J Neurosci. 2008;28(1):20–9.

    PubMed  PubMed Central  Article  Google Scholar 

  83. Christianson CA, Dumlao DS, Stokes JA, Dennis EA, Svensson CI, Corr M, et al. Spinal TLR4 mediates the transition to a persistent mechanical hypersensitivity after the resolution of inflammation in serum-transferred arthritis. Pain. 2011;152(12):2881–91.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  84. Boivin A, Pineau I, Barrette B, Filali M, Vallières N, Rivest S, et al. Toll-like receptor signaling is critical for Wallerian degeneration and functional recovery after peripheral nerve injury. J Neurosci. 2007;27(46):12565–76.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  85. Church JS, Milich LM, Lerch JK, Popovich PG, McTigue DM. E6020, a synthetic TLR4 agonist, accelerates myelin debris clearance, Schwann cell infiltration, and remyelination in the rat spinal cord. Glia. 2017;65(6):883–99.

    PubMed  PubMed Central  Article  Google Scholar 

  86. Rafiei A, Abedini M, Hosseini SH, Hosseini-Khah Z, Bazrafshan B, Tehrani M. Toll like receptor-4 896A/G gene variation, a risk factor for migraine headaches. Iran J Immunol. 2012;9(3):159–67.

    CAS  PubMed  Google Scholar 

  87. Su M, Ran Y, He Z, Zhang M, Hu G, Tang W, et al. Inhibition of toll-like receptor 4 alleviates hyperalgesia induced by acute dural inflammation in experimental migraine. Mol Pain. 2018;14:1744806918754612.

    CAS  PubMed  PubMed Central  Google Scholar 

  88. Gong Q, Lin Y, Lu Z, Xiao Z. Microglia-astrocyte cross talk through IL-18/IL-18R signaling modulates migraine-like behavior in experimental models of migraine. Neuroscience. 2020;451:207–15.

    CAS  PubMed  Article  Google Scholar 

  89. Wieseler J, Ellis A, McFadden A, Stone K, Brown K, Cady S, et al. Supradural inflammatory soup in awake and freely moving rats induces facial allodynia that is blocked by putative immune modulators. Brain Res. 2017;1664:87–94.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

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This work was supported by the expert workstation of academician, Longde Wang, whom we would like to thank for his technical guidance in this study. In addition, we would like to thank Mr. Cheng Xiangyu, a special lecturer of New Oriental, for his English corrections.


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Liu, X., Yang, W., Zhu, C. et al. Toll-like receptors and their role in neuropathic pain and migraine. Mol Brain 15, 73 (2022).

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  • Migraine
  • TLRs
  • Microglia
  • Inflammatory response