Comparative sequence analysis of leucine-rich repeats (LRRs) within vertebrate toll-like receptors

RNA recognition in toll-like receptor signaling

RNA, either from invading pathogens or within the hosts, is one of the principal PAMPs (pathogen-associated molecular patterns). Toll-like receptors (TLRs) and other receptors of the innate immune system exist that detect immunostimulatory RNA including double and single stranded RNA, and then induce cytokine-mediated antiviral and proinflammatory responses. Recent years have seen remarkable progress in biochemical, immunological, and structural biological studies on TLRs, opening new avenues for TLR signaling. In this review, we highlight our current understanding of RNA- sensing TLRs and discuss the regulatory mechanisms that normally prevent inappropriate responses to self.

LRRC45 promotes lung cancer proliferation and progression by enhancing c-MYC, slug, MMP2, and MMP9 expression

BACKGROUND

The leucine-rich repeat-containing (LRRC) superfamily members are known for their significant roles in tumorigenesis and cellular proliferation. However, the specific regulatory role of LRRC45 in lung cancer remains unexplored. This study investigated the impact and underlying mechanisms of LRRC45 on the proliferative, migratory, and invasive capacities of lung adenocarcinoma (LUAD) cells, potentially identifying new targets for therapeutic intervention.

MATERIAL AND METHODS

The importance of LRRC45 in lung cancer was analyzed using the online databases of UCSC Xena, TCGA, TISIDB, and UALCAN, whereas to detect target gene expression, we used the qRT-PCR, Western blot, and immunofluorescence confocal. The cell growth was monitored by colony formation assay and migration was examined by cell migration assay. Finally, a xenograft mouse tumor model using A549 ​cells was used to explore the in vivo effect of LRRC45 in lung cancer.

RESULTS

Inhibition of LRRC45 expression led to a notable decrease in proliferation, migration, and invasion of A549 and H1299 ​cells. LRRC45 silencing significantly reduced the tumor volume and improved the mice's survival. Additionally, inhibition of LRRC45 expression dramatically suppressed c-MYC, Slug, MMP2, and MMP9 expression. Overexpression of c-MYC and/or Slug in the LRRC45-deficient cells can partially or totally restore the LRRC45 deficiency-suppressed growth. Moreover, the overexpression of MMP2 and/or MMP9 could partially or totally restore LRRC45 deficiency-reduced cell metastasis.

CONCLUSIONS

LRRC45 could promote the proliferative, migrative, and invasive capacities of lung cancer cells by increasing c-MYC, Slug, MMP2, and MMP9 expression, indicating the therapeutic implications and potential significance of these pathways in lung cancer.

The immune function of TLR4-1 gene in Octopus sinensis revealed by RNAi and RNA-seq

Toll-like receptors (TLRs) are a class of conserved pattern recognition receptors (PRRs) that are crucial for initiating the innate immune response and aiding in the clearance of pathogenic organisms. Many studies have identified TLR4 as a distinctive member of the TLR family, capable of activating both the Myeloid differentiation factor 88-dependent signaling pathway (MyD88-dependent) and the TIR-domain-containing adaptor inducing IFN-β dependent signaling pathway (TRIF-dependent). Nevertheless, the role of TLR4 in Cephalopoda is still largely unexplored. To elucidate the immune function of the OsTLR4-1 gene in Octopus sinensis, the OsTLR4-1 gene was first validated and analyzed in this study. The cDNA comprises a 2475 bp ORF region, encoding 824 amino acids. Evolutionary tree analysis indicated a high homology and a close phylogenetic relationship between the Octopus sinensis and other mollusks. RNA interference (RNAi) experiments demonstrated that the expression level of OsTLR4-1 gene and its protein in the lymphocytes of the RNAi group treated with OsTLR4-1 dsRNA was extremely significantly lower than that of the blank control group and negative control group (P < 0.01), and the expression of downstream genes of OsTLR4-1, including ligand MyD88, IRAK4, TRAF6, MKK6, Hsp90, COX2, TRAF3, and RIP1, were significantly down-regulated compared to the blank and negative control group (P < 0.01). Additionally, OsTLR4-1 expression in lymphocytes was highly significantly up-regulated in the LPS-treated group compared to the blank control group (P < 0.01), while its expression was extremely significantly lower in the LPS-treated group after OsTLR4-1 interference than in the blank control group (P < 0.01). The expression of its downstream effector genes Big Defensin (Big-Def) and histone H2A.V (H2A.V) was highly significantly up-regulated in lymphocytes in the LPS-treated group compared to the blank control group (P < 0.01), while their expression in the LPS-treated group after OsTLR4-1 interference was extremely significantly lower than that in the blank control group (P < 0.01). Through comparative transcriptome analysis of the RNAi group and the blank control group, it was found that differentially expressed genes were enriched in the Toll-like receptor signaling pathway, PI3K-AKT signaling pathway, P53 signaling pathway, MAPK signaling pathway, and NF-κB signaling pathway. qRT-PCR results of key genes in these pathways revealed a decrease in all genes except IκB and Jun2 genes. This study enhances our understanding of the immune function of the TLR gene family in O. sinensis and provides a foundation for further research into innate immune signaling pathways in cephalopods.

TLR10 (CD290) Is a Regulator of Immune Responses in Human Plasmacytoid Dendritic Cells

TLRs are the most thoroughly studied group of pattern-recognition receptors that play a central role in innate immunity. Among them, TLR10 (CD290) remains the only TLR family member without a known ligand and clearly defined functions. One major impediment to studying TLR10 is its absence in mice. A recent study on TLR10 knock-in mice demonstrated its intrinsic inhibitory role in B cells, indicating that TLR10 is a potential drug target in autoimmune diseases. In this study, we interrogated the expression and function of TLR10 in human plasmacytoid dendritic cells (pDCs). We have seen that primary human pDCs, B cells, and monocytes constitutively express TLR10. Upon preincubation with an anti-TLR10 Ab, production of cytokines in pDCs was downregulated in response to stimulation with DNA and RNA viruses. Upon further investigation into the possible mechanism, we documented phosphorylation of STAT3 upon Ab-mediated engagement of TLR10. This leads to the induction of inhibitory molecule suppressor of cytokine signaling 3 (SOCS3) expression. We have also documented the inhibition of nuclear translocation of transcription factor IFN regulatory factor 7 (IRF7) in pDCs following TLR10 engagement. Our data provide the (to our knowledge) first evidence that TLR10 is constitutively expressed on the surface of human pDCs and works as a regulator of their innate response. Our findings indicate the potential of harnessing the function of pDCs by Ab-mediated targeting of TLR10 that may open a new therapeutic avenue for autoimmune disorders.

Toll-like receptor signalling as a cannabinoid target

Toll-like receptors (TLRs) have become a focus in biomedicine and biomedical research given the roles of this unique family of innate immune proteins in immune activation, infection, and autoimmunity. It is evident that TLR dysregulation, and subsequent alterations in TLR-mediated inflammatory signalling, can contribute to disease pathogenesis, and TLR targeted therapies are in development. This review highlights evidence that cannabinoids are key regulators of TLR signalling. Cannabinoids include component of the plant Cannabis sativa L. (C. sativa), synthetic and endogenous ligands, and overall represent a class of compounds whose therapeutic potential and mechanism of action continues to be elucidated. Cannabinoid-based medicines are in the clinic, and are furthermore under intense investigation for broad clinical development to manage symptoms of a range of disorders. In this review, we present an overview of research evidence that signalling linked to a range of TLRs is targeted by cannabinoids, and such cannabinoid mediated effects represent therapeutic avenues for further investigation. First, we provide an overview of TLRs, adaptors and key signalling events, alongside a summary of evidence that TLRs are linked to disease pathologies. Next, we discuss the cannabinoids system and the development of cannabinoid-based therapeutics. Finally, for the bulk of this review, we systematically outline the evidence that cannabinoids (plant-derived cannabinoids, synthetic cannabinoids, and endogenous cannabinoid ligands) can cross-talk with innate immune signalling governed by TLRs, focusing specifically on each member of the TLR family. Cannabinoids should be considered as key regulators of signalling controlled by TLRs, and such regulation should be a major focus in terms of the anti-inflammatory propensity of the cannabinoid system.

TLR2 agonist prevents the progression of periapical lesions in mice by reducing osteoclast activity and regulating the frequency of Tregs

AIM

To evaluate the role of regulatory T lymphocytes (Tregs) in the presence or absence of the synthetic ligand Pam3Cys during the progression of periapical lesion in wild-type (WT) and toll-like receptor 2 knockout (TLR2KO) mice.

METHODOLOGY

A total of 130 C57BL/6 male WT and TLR2KO mice were allocated into control (n = 5) and experimental (periapical lesion induction) (n = 10) groups. In specific groups (WT+Pam3cys and TLR2KO+Pam3cys), the synthetic ligand Pam3cys was administered intraperitoneally every 7 days, according to the experimental period (14, 21 and 42 days). At the end of those periods, the animals were euthanized, and the mandible and the spleen were submitted to histotechnical processing. Mandible histological sections were analysed by haematoxylin and eosin, TRAP histoenzymology and immunohistochemistry (FOXP3, RANK, RANKL and OPG). Spleen sections were analysed by immunohistochemistry (FOXP3).

RESULTS

The inflammatory infiltrate and bone resorption were more intense in the TLR2KO group compared to the WT group. The animals that received the Pam3cys had smaller periapical lesions when compared to the animals that did not receive the ligand (p < .05). TLR2KO animals showed a significant increase in the number of osteoclasts when compared to TLR2KO+Pam3cys group (p < .05). At 21 days, the WT+Pam3cys group had a lower number of osteoclasts when compared to the WT animals (p = .02). FOXP3 expression was more intense in the WT+Pam3cys groups when compared to the WT animals in the 42 days (p = .03). In the spleen analysis, the WT+Pam3cys group also had a higher expression of FOXP3 when compared to the WT animals at 14 and 42 days (p = .02). Concerning RANKL, there was a reduction in staining in the KOTLR2+Pam3cys groups at 21 and 42 days (p = .03) and a higher binding ratio between RANK/RANKL in animals that did not receive the ligand.

CONCLUSION

Administration of the Pam3cys increased the proliferation of Tregs, showed by FOXP3 expression and prevented the progression of the periapical lesion in WT mice. On the other hand, in the TLR2KO animals, Treg expression was lower with larger areas of periapical lesions. Finally, systemic administration of the Pam3cys in KO animals was able to limit the deleterious effects of the absence of the TLR2 receptor.

The Role of the TLR4-MyD88 Signaling Pathway in the Immune Response of the Selected Scallop Strain "Hongmo No. 1" to Heat Stress

The innate immunity of marine bivalves is challenged upon exposure to heat stress, especially with increases in the frequency and intensity of heat waves. TLR4 serves a classical pattern recognition receptor in recognizing pathogenic microorganisms and activating immune responses. In this study, three genes, HMTLR4, HMMyD88 and HMTRAF6, were characterized as homologs of genes in the TLR4-MyD88 signaling pathway in the selected scallop strain "Hongmo No. 1". According to RT-PCR, acute heat stress (32 °C) inhibited genes in the TLR4-MyD88 signaling pathway, and LPS stimulation-induced activation of TLR4-MyD88 signal transduction was also negatively affected at 32 °C. ELISA showed LPS-induced tumor necrosis factor alpha (TNF-α) or lysozyme (LZM) activity, but this was independent of temperature. RNA interference (RNAi) confirmed that HMTLR4 silencing suppressed the expression of its downstream gene, whether at 24 °C or at 32 °C. The level of TNF-α and the activity of LZM also decreased after injection with dsRNA, indicating a negative effect on the innate immunity of scallops. Additionally, acute heat stress affected the suppression of downstream gene expression when compared with that at 24 °C, which led us to the hypothesis that heat stress directly influences the downstream targets of HMTLR4. These results enrich the knowledge of scallop immunity under heat stress and can be beneficial for the genetic improvement of new scallop strains with higher thermotolerance.

Application of LRG mechanism in normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH) is a prevalent type of hydrocephalus, including secondary normal pressure hydrocephalus (SNPH) and idiopathic normal pressure hydrocephalus (INPH). However, its clinical diagnosis and pathological mechanism are still unclear. Leucine-rich α-2 glycoprotein (LRG) is involved in various human diseases, including cancer, diabetes, cardiovascular disease, and nervous system diseases. Now the physiological mechanism of LRG is still being explored. According to the current research results on LRG, we found that the agency of LRG has much to do with the known pathological process of NPH. This review focuses on analyzing the LRG signaling pathways and the pathological mechanism of NPH. According to the collected literature evidence, we speculated that LRG probably be involved in the pathological process of NPH. Finally, based on the mechanism of LRG and NPH, we also summarized the evidence of molecular targeted therapies for future research and clinical application.

Evaluation of the TLR3 involvement during Schistosoma japonicum-induced pathology

BACKGROUND

Despite the functions of TLRs in the parasitic infections have been extensively reported, few studies have addressed the role of TLR3 in the immune response to Schistosoma japonicum infections. The aim of this study was to investigate the properties of TLR3 in the liver of C57BL/6 mice infected by S. japonicum.

METHODS

The production of TLR3+ cells in CD4+T cells (CD4+CD3+), CD8+T cells (CD8+CD3+), γδT cells (γδTCR+CD3+), NKT cells (NK1.1+CD3+), B cells (CD19+CD3-), NK (NK1.1-CD3+) cells, MDSC (CD11b+Gr1+), macrophages (CD11b+F4/80+), DCs (CD11c+CD11b+) and neutrophils (CD11b+ Ly6g+) were assessed by flow cytometry. Sections of the liver were examined by haematoxylin and eosin staining in order to measure the area of granulomas. Hematological parameters including white blood cell (WBC), red blood cell (RBC), platelet (PLT) and hemoglobin (HGB) were analyzed. The levels of ALT and AST in the serum were measured using biochemical kits. The relative titers of anti-SEA IgG and anti-SEA IgM in the serum were measured by enzyme-linked immunosorbent assay (ELISA). CD25, CD69, CD314 and CD94 molecules were detected by flow cytometry.

RESULTS

Flow cytometry results showed that the expression of TLR3 increased significantly after S. japonicum infection (P < 0.05). Hepatic myeloid and lymphoid cells could express TLR3, and the percentages of TLR3-expressing MDSC, macrophages and neutrophils were increased after infection. Knocking out TLR3 ameliorated the damage and decreased infiltration of inflammatory cells in infected C57BL/6 mouse livers.,The number of WBC was significantly reduced in TLR3 KO-infected mice compared to WT-infected mice (P < 0.01), but the levels of RBC, platelet and HGB were significantly increased in KO infected mice. Moreover, the relative titers of anti-SEA IgG and anti-SEA IgM in the serum of infected KO mice were statistically decreased compared with the infected WT mice. We also compared the activation-associated molecules expression between S.japonicum-infected WT and TLR3 KO mice.

CONCLUSIONS

Taken together, our data indicated that TLR3 played potential roles in the context of S. japonicum infection and it may accelerate the progression of S. japonicum-associated liver pathology.

Re-identification and characterization of grass carp Ctenopharyngodon idella TLR20

Toll-like receptors (TLRs) play a crucial role in the recognition of microbial-associated molecular patterns in the innate immune system. Fish TLRs have undergone significant gene expansion to adapt to complex aquatic environments. Among them, TLR20 from the TLR11 family actively responds to viral and bacterial invasions. Previous studies have reported two TLR20s in grass carp (Ctenopharyngodon idella), and in this study, we revised this conclusion. Based on the latest grass carp genome, we identified a new TLR20 member. These three TLR20s are arranged in tandem on chromosome 9, indicating that they are generated by gene duplication events. They were renamed CiTLR20.1 to CiTLR20.3 based on their chromosomal positions. The CiTLR20s in C. idella exhibit higher similarities with those in Danio rerio, Cyprinus carpio, and Megalobrama amblycephala, and lower similarities with those in other distantly related fish species. Selective pressure analysis revealed low conservation and negative evolution of TLR20s during evolution. The 3D structures of the three TLR20s showed significant differences, reflecting functional variations and different downstream adaptor molecule recruitment. Transcriptome data revealed tissue distribution differences of TLR20s, with TLR20.1 showing relatively low expression levels in all the tissues, while TLR20.2 and TLR20.3 showed higher expression in the head kidney, spleen, and gill. Additionally, TLR20.2 and TLR20.3 actively responded to GCRV-II infection, with higher upregulation of TLR20.2 in response to Aeromonas hydrophila challenge. In conclusion, this study corrected the number of grass carp TLR20 members and analyzed TLR20 from an evolutionary and structural perspective, exploring its role in antiviral and antibacterial defense. This study provides reference for future research on fish TLR20.

Multiple toll-like receptors (TLRs) display differential bacterial and ligand specificity in the earthworm, Eisenia andrei

Toll-like receptors (TLRs), an ancient and well-conserved group of pattern recognition receptors (PRRs), recognize conserved pathogen-associated molecular patterns. TLRs consist of three domains: the extracellular N-terminal domain, containing one or more leucine-rich repeats (LRRs), responsible for the recognizing and binding of antigens; the type-I transmembrane domain; and the intracellular domain known as the Toll/Interleukin-1 receptor (TIR) domain required for the downstream signaling pathway. We identified six new full-length complementary DNA (cDNA) sequences, Ean-TLR1/2/3/4/5/6. The deduced amino acid sequences indicate that Ean-TLRs consist of one signal peptide, one LRR N-terminal domain (Ean-TLR4/5), varying numbers of LRRs, one (Ean-TLR1/2/3/4/5) or two (Ean-TLR6) LRR C-terminal domains, one type-I transmembrane domain, and a TIR domain. In addition, a TIR domain alignment revealed that three conserved motifs, designated as Box 1, Box 2, and Box 3, contain essential amino acid residues for downstream signaling activity. Phylogenetic analysis of earthworm TLRs generated two separate evolutionary branches representing single (sccTLR) and multiple (mccTLR) cysteine cluster TLRs. Ean-TLR1/2/3/4 (sccTLR type) and Ean-TLR6 (mccTLR type) were clustered with corresponding types of previously reported earthworm TLRs as well as TLRs from Clitellata and Polychaete. As PRRs, earthworm TLRs should be capable of sensing a diverse range of pathogens. Except for Ean-TLR3, which was not responsive to any bacteria, earthworm TLR expression was significantly induced by Gram-positive but not Gram-negative bacteria. Moreover, it is likely that earthworms can differentiate between different species of Gram-positive bacteria via their TLR responses. The ligand specificity of earthworm TLRs suggests that their pathogenic ligand recognition is likely to be as specific and diverse as the mammalian TLR pathogen-sensing system.

Ancient fish lineages illuminate toll-like receptor diversification in early vertebrate evolution

Since its initial discovery over 50 years ago, understanding the evolution of the vertebrate RAG- mediated adaptive immune response has been a major area of research focus for comparative geneticists. However, how the evolutionary novelty of an adaptive immune response impacted the diversity of receptors associated with the innate immune response has received considerably less attention until recently. Here, we investigate the diversification of vertebrate toll-like receptors (TLRs), one of the most ancient and well conserved innate immune receptor families found across the Tree of Life, integrating genomic data that represent all major vertebrate lineages with new transcriptomic data from Polypteriformes, the earliest diverging ray-finned fish lineage. Our analyses reveal TLR sequences that reflect the 6 major TLR subfamilies, TLR1, TLR3, TLR4, TLR5, TLR7, and TLR11, and also currently unnamed, yet phylogenetically distinct TLR clades. We additionally recover evidence for a pulse of gene gain coincident with the rise of the RAG-mediated adaptive immune response in jawed vertebrates, followed by a period of rapid gene loss during the Cretaceous. These gene losses are primarily concentrated in marine teleost fish and synchronous with the mid Cretaceous anoxic event, a period of rapid extinction for marine species. Finally, we reveal a mismatch between phylogenetic placement and gene nomenclature for up to 50% of TLRs found in clades such as ray-finned fishes, cyclostomes, amphibians, and elasmobranchs. Collectively, these results provide an unparalleled perspective of TLR diversity and offer a ready framework for testing gene annotations in non-model species.

Toll-like receptor may be involved in acquired immune response in pearl oyster Pinctada fucata

The increasing experimental evidence suggests that there are some forms of specific acquired immunity in invertebrates, in which Toll-like receptors (TLRs) play vital roles in activating innate and adaptive immunity and have been comprehensively investigated in mammalian species. Yet, the immune mechanisms underlying TLR mediation in mollusks remain obscure. In this study, we identified a TLR13 gene in the pearl oyster Pinctada fucata for the first time and named it PfTLR13 which consists of a 5'-untranslated terminal region (5'-UTR) of 543 bp, an open reading frame (ORF) of 2667 bp, and a 3'-UTR of 729 bp. We found that PfTLR13 mRNA was expressed in all tissues examined, with the highest level in the gills. The expression of PfTLR13 in the gills of oysters exposed to Vibrio alginolyticus or pathogen-associated molecular patterns (PAMPs) (including LPS, PGN, and poly(I:C)) was significantly higher than in the control group. Interestingly, the immune response to the first stimulation was weaker than the response to the second stimulation, suggesting that the primary stimulation may lead to immune priming of TLR in pearl oysters, similar to acquired immunity in vertebrates. Furthermore, we found that PfTLR13 expression was differentially associated with allograft and xenograft in the pearl oyster P. fucata, with the highest expression levels observed at 12 h post-allograft and 24 h post-xenograft. Overall, our findings provide new insights into the immune mechanisms underlying TLR mediation in mollusks and suggest that PfTLR13 may play a crucial role in the specific acquired immunity of pearl oysters.

Surface decoration with leucine tetrapeptide: An antibacterial strategy against Gram-negative bacteria

Surface-associated microbe contamination by Gram-negative bacteria poses a serious problem in medical care. Cationic peptides or polymers are the main materials used for antibacterial surface coating, but the positive charge may lead to blood coagulation. Therefore, exploiting surface coating which is free of positive charge and is effective for Gram-negative bacteria inactivation is in urgent need. In this study, inspired by the affinity between lipopolysaccharides of Gram-negative bacteria and Toll-like receptors of immune cells, we develop a leucine-based tetrapeptide coating strategy for combating Gram-negative bacteria. The obtained surface has excellent bactericidal activity against Gram-negative bacteria like Pseudomonas aeruginosa and Escherichia coli. A 1 mm² coated glass surface could kill > 9.9 × 10⁴ CFU bacteria in 1 h and has nearly no damage to mammal cells. Moreover, this surface coating strategy could be applied on various surfaces like glass slices, glass capillary cavity and thermoplastic polyurethane slices. And the coated surface could largely mitigate the microbe contamination in an in vivo subcutaneous implantation. This work paves a new way for antibacterial surface-coating which is behaving no positive charge and is of great importance for biomedical devices.

TLR4 involved in immune response against Vibrio Parahaemolyticus by MyD88-dependent pathway in Crassostrea hongkongensis

Vibrio parahaemolyticus (V. parahaemolyticus) is a salt-loving gram-negative bacterium, and is the leading cause of mortality in cultured shellfish in recent years. Toll-like Receptor 4 (TLR4) is a classical pattern recognition receptor (PRRs) that recognizes pathogen-associated molecular patterns (PAMPs) of pathogenic microorganism and activates the immune response. However, the function and signal pathway of TLR4 in oyster are still unknown. In this study, a new TLR4 gene was identified from the Crassostrea hongkongensis (C. hongkongensis). The ChTLR4 contained an open reading frame of 2643 bp, encoding 880 amino acids with seven leucine-rich repeat (LRR) domains and a Toll/IL-1R (TIR) domain. The ChTLR4 shared the highest sequence identity (83.0%) with TLR4 of Crassostrea gigas. Tissue expression analysis revealed that ChTLR4 showed the highest constitutive expression in the gill and hepatopancreas, and was significantly upregulated in immune tissues post V. parahaemolyticus infection, especially in gill and hemocytes. Moreover, TLR4 silencing significantly inhibited the immune-enzyme activities, including SOD, CAT, ACP, AKP in gill and LZM in hemolymph supernatant, and increased MDA content in hemolymph supernatant. Meanwhile, the antimicrobial activities of the hemolymph supernatant were also significantly inhibited by TLR4 silencing. These data demonstrated that the ChTLR4 involved in innate immune response of C. hongkongensis against V. parahaemolyticus challenge. Finally, qRT-PCR analysis showed that ChTLR4 silencing clearly inhibited the expression of genes in TLR4-MyD88 pathway, indicating that MyD88-dependent pathway played a crucial role in ChTLR4-mediated immune response against V. parahaemolyticus.

Chronic high-fat diet induces galectin-3 and TLR4 to activate NLRP3 inflammasome in NASH

NOD-like receptor protein 3 (NLRP3) inflammasome activation triggers inflammation progression in some metabolism disorders, frequently accompanying the up-regulation of galectin-3 (Gal-3). However, the precise mechanisms of Gal-3 activating NLRP3 inflammasome remain unclear in nonalcoholic steatohepatitis (NASH). Here, male C57BL/6J mice were fed by high-fat diet (HFD) for 32 weeks to induce NASH and then the hepatic damage, cytokines, Gal-3 and TLR4 expression, and NLRP3 inflammasome activation were examined. Such indicators were similarly determined when HepG2 cells were co-incubated with palmitic acid (PA, 200 μM), β-lactose, and TAK-242, or pre-transfected with TLR4. Immunofluorescence, immunohistochemistry, and co-immunoprecipitation were conducted to confirm the potential interaction between Gal-3 and TLR4. To further identify the inflammatory regulation roles of Gal-3 and its terminals in TLR4/NLRP3, HepG2 cells were transfected with Gal-3 and its variants. Chronic HFD induced sustained hepatic steatosis and inflammatory injury, with increased inflammatory cytokines, Gal-3 and TLR4 expression, and NLRP3 inflammasome activation. Similar changes were found in PA-dosed HepG2 cells, which were rescued by β-lactose but deteriorated with TLR4 overexpression. However, TAK-242 treatment decreased AST, ALT, cytokines, and normalized NLRP3, caspase-1, and ASC expression. Furthermore, TLR4 was pulled down when Gal-3 was enriched. Only full-length Gal-3 and its carbohydrate recognition domain (CRD) promoted cytokines, TLR4 expression, and NLRP3 inflammasome activation. Thus, gal-3 may induce chronic HFD-derived NASH progression by activating TLR4-mediating NLRP3 inflammasome via its CRD, which sheds new light on candidate target for the treatment and prevention of NASH inflammation despite further research for its precise roles in the future.

TLR3 forms a laterally aligned multimeric complex along double-stranded RNA for efficient signal transduction

Toll-like receptor 3 (TLR3) is a member of the TLR family, which plays an important role in the innate immune system and is responsible for recognizing viral double-stranded RNA (dsRNA). Previous biochemical and structural studies have revealed that a minimum length of approximately 40-50 base pairs of dsRNA is necessary for TLR3 binding and dimerization. However, efficient TLR3 activation requires longer dsRNA and the molecular mechanism underlying its dsRNA length-dependent activation remains unknown. Here, we report cryo-electron microscopy analyses of TLR3 complexed with longer dsRNA. TLR3 dimers laterally form a higher multimeric complex along dsRNA, providing the basis for cooperative binding and efficient signal transduction.

Identification and characterization of Toll-like receptor 14d in Northeast Chinese lamprey (Lethenteron morii)

Toll-like receptors (TLRs) play an important role in innate immunity of defense against bacterial or viral pathogens. To study the biological characteristics and functions of the TLR genes, TLR14d was identified from Northeast Chinese lamprey (Lethenteron morii) and named LmTLR14d. LmTLR14d coding sequence (cds) is 3285 bp in length and encodes 1094 amino acids (aa). The results showed that LmTLR14d has the typical structure of TLR molecule, which contains the extracellular domain of leucine-rich repeats (LRR), transmembrane domain, and intracellular domain of Toll/interleukin-1 receptor (TIR). The phylogenetic tree showed that LmTLR14d is a homologous gene of TLR14/18 in bony fish. Quantitative real-time PCR (qPCR) revealed that LmTLR14d was expressed in various healthy tissues, including immune and non-immune tissues. Pseudomonas aeruginosa infection up-regulated LmTLR14d in the supraneural body (SB), gill, and kidney tissues of infected Northeast Chinese lamprey. Immunofluorescence results showed that LmTLR14d was located in the cytoplasm of HEK 293T cells in clusters, and its subcellular localization was determined by the TIR domain. The immunoprecipitation results showed that LmTLR14d could recruit L.morii MyD88 (LmMyD88) but not L.morii TRIF (LmTRIF). Dual luciferase reporter results showed that LmTLR14d significantly enhanced the activity of L.morii NF-κβ (LmNF-κβ) promoter. Furthermore, co-transfection of LmTLR14d with MyD88 significantly enhanced the L.morii NF-κβ (LmNF-κβ) promoter activity. LmTLR14d can induce the expression of inflammatory cytokine genes il-6 and tnf-α downstream of NF-κB signal. This study suggested that LmTLR14d might play an important role in the innate immune signal transduction process of lamprey and revealed the origin and function of teleost-specific TLR14.

TIRAP, TRAM, and Toll-Like Receptors: The Untold Story

Toll-like receptors (TLRs) are the most studied receptors among the pattern recognition receptors (PRRs). They act as microbial sensors, playing major roles in the regulation of the innate immune system. TLRs mediate their cellular functions through the activation of MyD88-dependent or MyD88-independent signaling pathways. Myd88, or myeloid differentiation primary response 88, is a cytosolic adaptor protein essential for the induction of proinflammatory cytokines by all TLRs except TLR3. While the crucial role of Myd88 is well described, the contribution of other adaptors in mediating TLR signaling and function has been underestimated. In this review, we highlight important results demonstrating that TIRAP and TRAM adaptors are also required for full signaling activity and responses induced by most TLRs.

Genome-Wide Identification, Characterization and Expression Analysis of Toll-like Receptors in Marbled Rockfish (Sebastiscus marmoratus)

Toll-like receptor (TLR) is a cluster of type I transmembrane proteins that plays a role in innate immunity. Based on the marbled rockfish (Sebastiscus marmoratus) genome database, this study used bioinformatics methods to identify and analyze its TLR gene family members. The results showed that there were 11 TLR gene family members in Sebastiscus marmoratus (SmaTLR), which could be divided into five different subfamilies. The number of amino acids encoded by the Smatlr genes ranged from 637 to 1206. The physicochemical properties of the encoded proteins of different members were also computed. The results of protein structure prediction, phylogenetic relation, and motif analysis showed that the structure and function of the SmaTLRs were relatively conserved. Quantitative Real-Time PCR (qRT-PCR) analysis revealed the expression patterns of SmaTLRs in the gill, liver, spleen, head kidney, kidney, and intestine. SmaTLRs were widely detected in the tested tissues, and they tended to be expressed higher in immune-related tissues. After polyriboinosinic polyribocytidylic acid (poly(I:C)) challenge, SmaTLR14, SmaTLR3, SmaTLR5S, SmaTLR7, and SmaTLR22 were significantly upregulated in the spleen or liver. The results of this study will help to understand the status of TLR gene family members of marbled rockfish and provide a basis for further study of the functional analysis of this gene family.

Bifurcation of signalling in human innate immune pathways to NF-kB and IRF family activation

The human innate immune response can be activated through a wide range of stimuli. This multi-faceted system can be triggered by a range of immunostimulants including pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). These stimuli drive intracellular signalling pathways that branch off downstream to activate several distinct transcription factors. The two most impactful of which in innate immune outcomes are the NF-κB and the IRF family members. Both transcription factor families play defining roles in driving inflammation as well as the antiviral response. Pathways leading to their simultaneous activation share common upstream components but eventually distinct regulators which directly facilitate their activation. This review will discuss the current state of knowledge about what is known about how these pathways bifurcate to activate NF-κB and IRF family members.

Hepatitis C Virus Infection and Intrinsic Disorder in the Signaling Pathways Induced by Toll-Like Receptors

In this study, we examined the interplay between protein intrinsic disorder, hepatitis C virus (HCV) infection, and signaling pathways induced by Toll-like receptors (TLRs). To this end, 10 HCV proteins, 10 human TLRs, and 41 proteins from the TLR-induced downstream pathways were considered from the prevalence of intrinsic disorder. Mapping of the intrinsic disorder to the HCV-TLR interactome and to the TLR-based pathways of human innate immune response to the HCV infection demonstrates that substantial levels of intrinsic disorder are characteristic for proteins involved in the regulation and execution of these innate immunity pathways and in HCV-TLR interaction. Disordered regions, being commonly enriched in sites of various posttranslational modifications, may play important functional roles by promoting protein-protein interactions and support the binding of the analyzed proteins to other partners such as nucleic acids. It seems that this system represents an important illustration of the role of intrinsic disorder in virus-host warfare.

TLR23, a fish-specific TLR, recruits MyD88 and TRIF to activate expression of a range of effectors in melanomacrophages in Nile tilapia (Oreochromis niloticus)

Nile tilapia (Oreochromis niloticus) is an important food fish species that is mainly cultivated in tropical and subtropical countries. However, microbial diseases have created various difficulties for this industry. The fundamental prerequisite for tackling disease outbreak prevention and disease resistance is to know how hosts' immune responses against invading microbes are initiated. Toll-like receptors (TLRs) are vital pattern recognition receptors and play pivotal roles in the cellular innate immunity defense that is able to recognize pathogen-associated molecular patterns (PAMPs). In this study, Oreochromis niloticus TLR23 (OnTLR23) was cloned and bioinformatic analyses revealed that OnTLR23 is not an ortholog of mammalian TLR13 as previously suggested. The basal transcript level of OnTLR23 was found to be higher in the immune-related organs and was upregulated in the spleen and/or head kidney following Aeromonas hydrophila, Streptococcus agalactiae or poly I:C injections, and increased in the melanomacrophage-like tilapia head kidney (THK) cell line after LPS and zymosan stimulation. Furthermore, we demonstrated for the first time that OnTLR23 locates mainly in the intracellular region in fish cells and the constitutively active form of OnTLR23 promotes the expression of molecules related to antigen presentation, proinflammatory cytokines, antimicrobial peptides and type I interferon in THK cells. A co-immunoprecipitation assay revealed that OnTLR23 can interact with both OnMyD88 and OnTRIF, but not with OnTIRAP. A luciferase assay showed that the NF-κB activity was not elevated in the OnTLR23 overexpressed THK cells after treatment with ligand for TLR13 as well as other known purified bacterial-derived ligands of TLRs. Taken together, OnTLR23 is likely to recruit OnMyD88 and OnTRIF as adaptors to induce the expression of various effectors in melanomacrophages, but its corresponding ligand is an issue awaiting further investigation.

Genetic, Cellular and Molecular Aspects involved in Apical Periodontitis

The development, establishment and repair of apical periodontitis (AP) is dependent of several factors, which include host susceptibility, microbial infection, immune response, quality of root canal treatment and organism's ability to repair. The understanding of genetic contributions to the risk of developing AP and presenting persistent AP has been extensively explored in modern Endodontics. Thus, this article aims to provide a review of the literature regarding the biochemical mediators involved in immune response signaling, osteoclastogenesis and bone neoformation, as the genetic components involved in the development and repair of AP. A narrative review of the literature was performed through a PUBMED/MEDLINE search and a hand search of the major AP textbooks. The knowledge regarding the cells, receptors and molecules involved in the host's immune-inflammatory response during the progression of AP added to the knowledge of bone biology allows the identification of factors inherent to the host that can interfere both in the progression and in the repair of these lesions. The main outcomes of studies evaluated in the review that investigated the correlation between genetic polymorphisms and AP in the last five years, demonstrate that genetic factors of the individual are involved in the success of root canal treatment. The discussion of this review gives subsides that may help to glimpse the development of new therapies based on the identification of therapeutic targets and the development of materials and techniques aimed at acting at the molecular level for clinical, radiographic and histological success of root canal treatment.

Numerous variants of leucine rich repeats in proteins from nucleo-cytoplasmic large DNA viruses

Leucine rich repeats (LRRs) occurring in tandem are 20-29 amino acids long. Eleven LRR types have been recognized. Sequence features of LRRs from viruses were investigated using over 600 LRR proteins from 89 species. Directly before, metagenome data of nucleo-cytoplasmic large dsDNA viruses (NCLDVs) have been published; the 2,074 NCLDVs encode 199,021 proteins. From the NCLDVs 547 LRR proteins were identified and 502 were used for analysis. Various variants of known LRR types were identified in viral LRRs. A comprehensive analysis of TpLRR and FNIP that belong to an LRR type was first performed. The repeating unit lengths (RULs) in five types are 19 residues which is the shortest among all LRRs. The RULs of eight LRR types including FNIP are one to five residues shorter than those of the known, corresponding LRR types. The conserved hydrophobic residues such as Leu, Val or Ile in the consensus sequences are frequently substituted by cysteine at one or two positions. Four unique LRR motifs that are different from those identified previously are observed. The present study enhances the previous result. An evolutionary scenario of short or unique LRR was discussed.

Toll-Like Receptors (TLRs) as Therapeutic Targets for Treating SARS-CoV-2: An Immunobiological Perspective

INTRODUCTION

Coronavirus disease-19 (COVID-19) caused by SARS-CoV-2 is presently the biggest threat to mankind throughout the globe. Increasing reports on deaths, cases of new infection, and socioeconomic losses are continuously coming from all parts of the world. Developing an efficacious drug and/or vaccine is currently the major goal to the scientific communities. In this context, toll-like receptors (TLRs) could be the useful targets in adopting effective therapeutic approaches.

METHODS

This chapter has been written by incorporating the findings on TLR-based therapies against SARS-CoV-2 demonstrated in the recently published research papers/reviews.

RESULTS

TLRs are the essential components of host immunity and play critical roles in deciding the fate of SARS-CoV-2 by influencing the immunoregulatory circuits governing human immune response to this pathogen. Hitherto, a number of multi-subunit peptide-based vaccines and pharmacological agents developed against SARS-CoV-2 have been found to manipulate TLR function. Therefore, circumventing overt immunopathology of COVID-19 applying TLR-antagonists can effectively reduce the morality caused from "cytokine storm"-induced multiorgan failure. Similarly, pre-administration of TLR- agonists may be used as a prophylaxis to sensitize the immune system of the individuals having risk of infection. A lot of collaborative efforts are required for bench-to-bench transformation of these knowledges.

CONCLUSION

This chapter enlightens the potentials and promises of TLR-guided therapeutic strategies against COVID-19 by reviewing the major findings and achievements depicted in the literatures published till date.

TLR1 in Nile tilapia: The conserved receptor cannot interact with MyD88 and TIRAP but can activate NF-κB in vitro

Toll-like receptors (TLRs) play a critical role in the innate immune response of fish. In this study, we isolated the cDNA sequence of Nile tilapia TLR1 (OnTLR1). The deduced OnTLR1 protein contains a signal peptide, 7 leucine-rich repeats (LRRs), a C-terminal LRR (LRR-CT), a transmembrane region and a highly conserved TIR domain. In healthy Nile tilapia, the OnTLR1 transcript was broadly expressed in all examined tissues, with the highest expression levels in the spleen. After infection with Streptococcus agalactiae, the OnTLR1 transcripts were upregulated in the gill and kidney. After stimulation with polyinosinic-polycytidylic acid (poly(I:C)), the expression levels of OnTLR1 were significantly downregulated in the intestine, whereas OnTLR1 transcripts were significantly upregulated in the kidney. After challenge with lipopolysaccharide (LPS), the expression levels of OnTLR1 were significantly upregulated in the spleen and kidney. The subcellular localization showed that OnTLR1 was expressed in the cytoplasm. TLR1 significantly increased MyD88-dependent NF-κB activity. However, the results of a pull-down assay showed that OnTLR1 did not interact with MyD88 or TIRAP. Binding assays revealed the specificity of OnTLR1 for pathogen-associated molecular patterns (PAMPs) and bacteria that included S. agalactiae, Aeromonas hydrophila and poly(I:C) and LPS. Taken together, these findings suggest that OnTLR1, as a pattern recognition receptor (PRR), might play an important role in the immune response to pathogen invasion.

Aeromonas hydrophila infection induces Toll-like receptor 2 (tlr2) and associated downstream signaling in Indian catfish, Clarias magur (Hamilton, 1822)

Motile Aeromonas septicaemia (MAS), caused by Aeromonas hydrophila, is one of the most significant bacterial disease responsible for mortality in Indian catfish, Clarias magur, a potential aquaculture species in the Indian subcontinent. In fish, innate immunity elicited by pathogen recognition receptors (PRRs) plays an important role in providing protection against bacterial infection. Information on PRRs including Toll-like receptors (tlrs) and their response to bacterial pathogens remains unexplored in magur. Toll-like receptor 2 (tlr2), a phylogenetically conserved germ-line encoded PRR recognizes specific microbial structure and trigger MyD88-dependent signaling pathway to induce release of various cytokines responsible for innate immune response. In the present study, tlr2 gene of magur was characterized and downstream signaling was studied following challenge with A. hydrophila. The full-length cDNA of magur tlr2 (mtlr2) comprised of 3,066 bp with a single open reading frame of 2,373 bp encoding 790 amino acids having a theoretical pI value of 6.11 and molecular weight of 90 kDa. Structurally, it comprised of signal peptide (1–42aa), one leucine-rich repeat region (LRR) at N-terminal (LRR1-NT: 50–73 aa) and C-terminal (LRR-CT: 588–608 aa), twenty LRRs in between, one trans-membrane (Tm) domain (609–631aa) followed by cytoplasmic TIR domain (670–783aa). Phylogenetically, mtlr2 is closely related to pangasius and channel catfish. Highest basal expression of mtlr2, myd88 and il-1β in spleen, nf-kb in anterior kidney was observed. Lowest basal expression of mtlr2 in skin and myd88, nf-kb and il-1β in muscle was detected. Significant up-regulation of mtlr2 and downstream expression occurred at 3, 8, 24 h post infection to A. hydrophila in important immune organs such as liver, spleen, intestine and kidney. These findings highlight the vital role of tlr2 in eliciting innate immune defence against A. hydrophila infection.

Role of Toll-Like Receptors in Neuroimmune Diseases: Therapeutic Targets and Problems

Toll-like receptors (TLRs) are a class of proteins playing a key role in innate and adaptive immune responses. TLRs are involved in the development and progression of neuroimmune diseases via initiating inflammatory responses. Thus, targeting TLRs signaling pathway may be considered as a potential therapy for neuroimmune diseases. However, the role of TLRs is elusive and complex in neuroimmune diseases. In addition to the inadequate immune response of TLRs inhibitors in the experiments, the recent studies also demonstrated that partial activation of TLRs is conducive to the production of anti-inflammatory factors and nervous system repair. Exploring the mechanism of TLRs in neuroimmune diseases and combining with developing the emerging drug may conquer neuroimmune diseases in the future. Herein, we provide an overview of the role of TLRs in several neuroimmune diseases, including multiple sclerosis, neuromyelitis optica spectrum disorder, Guillain-Barré syndrome and myasthenia gravis. Emerging difficulties and potential solutions in clinical application of TLRs inhibitors will also be discussed.

Toll-like receptor 2 signaling in liver pathophysiology

Chronic liver diseases (CLD) are among the major cause of mortality and morbidity worldwide. Despite current achievements in the area of hepatitis virus, chronic alcohol abuse and high-fat diet are still fueling an epidemic of severe liver disease, for which, an effective therapy has yet not been discovered. In particular, the therapeutic regimens that could prevent the progression of fibrosis and, in turn, aid cirrhotic liver to develop a robust regenerative capability are intensively needed. To this context, a better understanding of the signaling pathways regulating hepatic disease development may be of critical value. In general, the liver responds to various insults with an orchestrated healing process involving variety of signaling pathways. One such pathway is the TLR2 signaling pathway, which essentially regulates adult liver pathogenesis and thus has emerged as an attractive target to treat liver disease. TLR2 is expressed by different liver cells, including Kupffer cells (KCs), hepatocytes, and hepatic stellate cells (HSCs). From a pathologic perspective, the crosstalk between antigens and TLR2 may preferentially trigger a distinctive set of signaling mechanisms in these liver cells and, thereby, induce the production of inflammatory and fibrogenic cytokines that can initiate and prolong liver inflammation, ultimately leading to fibrosis. In this review, we summarize the currently available evidence regarding the role of TLR2 signaling in hepatic disease progression. We first elaborate its pathological involvement in liver-disease states, such as inflammation, fibrosis, and cirrhosis. We then discuss how therapeutic targeting of this pathway may help to alleviate its disease-related functioning.

Toll-like receptors and toll-like receptor-targeted immunotherapy against glioma

Glioma represents a fast proliferating and highly invasive brain tumor which is resistant to current therapies and invariably recurs. Despite some advancements in anti-glioma therapies, patients’ prognosis remains poor. Toll-like receptors (TLRs) act as the first line of defense in the immune system being the detectors of those associated with bacteria, viruses, and danger signals. In the glioma microenvironment, TLRs are expressed on both immune and tumor cells, playing dual roles eliciting antitumoral (innate and adaptive immunity) and protumoral (cell proliferation, migration, invasion, and glioma stem cell maintenance) responses. Up to date, several TLR-targeting therapies have been developed aiming at glioma bulk and stem cells, infiltrating immune cells, the immune checkpoint axis, among others. While some TLR agonists exhibited survival benefit in clinical trials, it attracts more attention when they are involved in combinatorial treatment with radiation, chemotherapy, immune vaccination, and immune checkpoint inhibition in glioma treatment. TLR agonists can be used as immune modulators to enhance the efficacy of other treatment, to avoid dose accumulation, and what brings more interests is that they can potentiate immune checkpoint delayed resistance to PD-1/PD-L1 blockade by upregulating PD-1/PD-L1 overexpression, thus unleash powerful antitumor responses when combined with immune checkpoint inhibitors. Herein, we focus on recent developments and clinical trials exploring TLR-based treatment to provide a picture of the relationship between TLR and glioma and their implications for immunotherapy.

Role of nucleic acid sensing in the pathogenesis of type 1 diabetes

During infections, nucleic acids of pathogens are also engaged in recognition via several exogenous and cytosolic pattern recognition receptors, such as the toll-like receptors, retinoic acid inducible gene-I-like receptors, and nucleotide-binding and oligomerization domain-like receptors. The binding of the pathogen-derived nucleic acids to their corresponding sensors initiates certain downstream signaling cascades culminating in the release of type-I interferons (IFNs), especially IFN-α and other cytokines to induce proinflammatory responses towards invading pathogens leading to their clearance from the host. Although these sensors are hardwired to recognize pathogen associated molecular patterns, like viral and bacterial nucleic acids, under unusual physiological conditions, such as excessive cellular stress and increased apoptosis, endogenous self-nucleic acids like DNA, RNA, and mitochondrial DNA are also released. The presence of these self-nucleic acids in extranuclear compartments or extracellular spaces or their association with certain proteins sometimes leads to the failure of discriminating mechanisms of nucleic acid sensors leading to proinflammatory responses as seen in autoimmune disorders, like systemic lupus erythematosus, psoriasis and to some extent in type 1 diabetes (T1D). This review discusses the involvement of various nucleic acid sensors in autoimmunity and discusses how aberrant recognition of self-nucleic acids by their sensors activates the innate immune responses during the pathogenesis of T1D.

Toll-Like Receptors as a Therapeutic Target in the Era of Immunotherapies

Toll-like receptors (TLRs) are the pattern recognition receptors, which are activated by foreign and host molecules in order to initiate the immune response. They play a crucial role in the regulation of innate immunity, and several studies have shown their importance in bacterial, viral, and fungal infections, autoimmune diseases, and cancers. The consensus view from an immunological perspective is that TLR agonists can serve either as a possible therapeutic agent or as a vaccine adjuvant toward cancers or infectious diseases and that TLR inhibitors may be a promising approach to the treatment of autoimmune diseases, some cancers, bacterial, and viral infections. These notions are based on the fact that TLR agonists stimulate the secretion of proinflammatory cytokines and in general, the development of proinflammatory responses. Some of the TLR-based inhibitory agents have shown to be efficacious in preclinical models and have now entered clinical trials. Therefore, TLRs seem to hold the potential to serve as a perfect target in the era of immunotherapies. We offer a perspective on TLR-based therapeutics that sheds light on their usefulness and on combination therapies. We also highlight various therapeutics that are in the discovery phase or in clinical trials.

The fungivorous amoeba Protostelium aurantium targets redox homeostasis and cell wall integrity during intracellular killing of Candida parapsilosis

Predatory interactions among microbes are major evolutionary driving forces for biodiversity. The fungivorous amoeba Protostelium aurantium has a wide fungal food spectrum including foremost pathogenic members of the genus Candida. Here we show that upon phagocytic ingestion by the amoeba, Candida parapsilosis is confronted with an oxidative burst and undergoes lysis within minutes of processing in acidified phagolysosomes. On the fungal side, a functional genomic approach identified copper and redox homeostasis as primary targets of amoeba predation, with the highly expressed copper exporter gene CRP1 and the peroxiredoxin gene PRX1 contributing to survival when encountered with P. aurantium. The fungicidal activity was largely retained in intracellular vesicles of the amoebae. Following their isolation, the content of these vesicles induced immediate killing and lysis of C. parapsilosis in vitro. Proteomic analysis identified 56 vesicular proteins from P. aurantium. Although completely unknown proteins were dominant, many of them could be categorised as hydrolytic enzymes targeting the fungal cell wall, indicating that fungal cell wall structures are under selection pressure by predatory phagocytes in natural environments. TAKE AWAY: The amoeba Protostelium aurantium feeds on fungi, such as Candida parapsilosis. Ingested yeast cells are exposed to reactive oxygen species. A copper exporter and a peroxiredoxin contribute to fungal defence. Yeast cells undergo intracellular lysis. Lysis occurs via a cocktail of hydrolytic enzymes from intracellular vesicles.

Pattern recognition receptors in health and diseases

Pattern recognition receptors (PRRs) are a class of receptors that can directly recognize the specific molecular structures on the surface of pathogens, apoptotic host cells, and damaged senescent cells. PRRs bridge nonspecific immunity and specific immunity. Through the recognition and binding of ligands, PRRs can produce nonspecific anti-infection, antitumor, and other immunoprotective effects. Most PRRs in the innate immune system of vertebrates can be classified into the following five types based on protein domain homology: Toll-like receptors (TLRs), nucleotide oligomerization domain (NOD)-like receptors (NLRs), retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), C-type lectin receptors (CLRs), and absent in melanoma-2 (AIM2)-like receptors (ALRs). PRRs are basically composed of ligand recognition domains, intermediate domains, and effector domains. PRRs recognize and bind their respective ligands and recruit adaptor molecules with the same structure through their effector domains, initiating downstream signaling pathways to exert effects. In recent years, the increased researches on the recognition and binding of PRRs and their ligands have greatly promoted the understanding of different PRRs signaling pathways and provided ideas for the treatment of immune-related diseases and even tumors. This review describes in detail the history, the structural characteristics, ligand recognition mechanism, the signaling pathway, the related disease, new drugs in clinical trials and clinical therapy of different types of PRRs, and discusses the significance of the research on pattern recognition mechanism for the treatment of PRR-related diseases.

Toll protein family structure, evolution and response of the whiteleg shrimp (Litopenaeus vannamei) to exogenous iridescent virus

Whiteleg shrimp is a widely cultured crustacean, but frequent disease outbreaks have decreased production and caused significant losses. Toll-like receptors (TLRs) comprise a large innate immune family that is involved in the innate immune response. However, understanding of their regulatory mechanism is limited. In this study, PacBio sequencing and Illumina sequencing were applied to the gill and hepatopancreas tissues of whiteleg shrimp and an integrated transcript gene set was established. The upregulation of Toll1, Toll2 and Toll3 transcripts in the hepatopancreas tissue of whiteleg shrimp after iridescent virus infection implies that these proteins are involved in the immune response to the virus; simultaneously, the TRAF6 and relish transcripts in the Toll pathway were also upregulated, implying that the Toll pathway was activated. We predicted the three-dimensional structure of the five Toll proteins in whiteleg shrimp and humans and constructed a phylogenetic tree of the Toll protein family. In addition, there was a large discrepancy of Toll1 between invertebrates and vertebrates, presumably because of the loss of Toll1 protein sequence during the evolution process from invertebrates to vertebrates. Our research will improve the cognition of Toll protein family in invertebrates in terms of evolution, structure and function and provide theoretical guidance for researchers in this field.

TRAL 2.0: Tandem Repeat Detection With Circular Profile Hidden Markov Models and Evolutionary Aligner

The Tandem Repeat Annotation Library (TRAL) focuses on analyzing tandem repeat units in genomic sequences. TRAL can integrate and harmonize tandem repeat annotations from a large number of external tools, and provides a statistical model for evaluating and filtering the detected repeats. TRAL version 2.0 includes new features such as a module for identifying repeats from circular profile hidden Markov models, a new repeat alignment method based on the progressive Poisson Indel Process, an improved installation procedure and a docker container. TRAL is an open-source Python 3 library and is available, together with documentation and tutorials viavital-it.ch/software/tral.

Gene duplication and adaptive evolution of Toll-like receptor genes in birds

Toll-like receptors (TLRs) play an important role in innate immune through recognizes pathogens. In order to reveal the evolutionary patterns and adaptive evolution of avian TLRs, we examined 66 representative bird species in 26 orders. Phylogenetic results indicated that TLR1A and TLR1B may have differentiated functionally. Evolutionary analysis showed that the TLR genes in birds under strong Purification selection (0.165-0.4265). A total of 126 common positively selected codons were identified in 10 TLR genes of avian, and most sites were located in the extracellular leucine-rich repeat (LRR) functional domains, and both environment and feeding habits were external factors driving the evolution of avian TLR genes. Environmental pressures had a greater effect on TLR1B, TLR2B, TLR3 and TLR4, while feeding habits were active in affecting TLR2A, TLR2B, TLR15 and TLR21. Our data suggested that TLR genes have been subjected to different selective pressures in the diversification of birds and that these changes enabled them to respond differently to pathogens from diverse sources.

Toll-Like Receptors: General Molecular and Structural Biology

Background/Aim

Toll-like receptors (TLRs) are pivotal biomolecules in the immune system. Today, we are all aware of the importance of TLRs in bridging innate and adaptive immune system to each other. The TLRs are activated through binding to damage/danger-associated molecular patterns (DAMPs), microbial/microbe-associated molecular patterns (MAMPs), pathogen-associated molecular patterns (PAMPs), and xenobiotic-associated molecular patterns (XAMPs). The immunogenetic molecules of TLRs have their own functions, structures, coreceptors, and ligands which make them unique. These properties of TLRs give us an opportunity to find out how we can employ this knowledge for ligand-drug discovery strategies to control TLRs functions and contribution, signaling pathways, and indirect activities. Hence, the authors of this paper have a deep observation on the molecular and structural biology of human TLRs (hTLRs).

Methods and Materials

To prepare this paper and fulfill our goals, different search engines (e.g., GOOGLE SCHOLAR), Databases (e.g., MEDLINE), and websites (e.g., SCOPUS) were recruited to search and find effective papers and investigations. To reach this purpose, we tried with papers published in the English language with no limitation in time. The iCite bibliometrics was exploited to check the quality of the collected publications.

Results

Each TLR molecule has its own molecular and structural biology, coreceptor(s), and abilities which make them unique or a complementary portion of the others. These immunogenetic molecules have remarkable roles and are much more important in different sections of immune and nonimmune systems rather than that we understand to date.

Conclusion

TLRs are suitable targets for ligand-drug discovery strategies to establish new therapeutics in the fields of infectious and autoimmune diseases, cancers, and other inflammatory diseases and disorders.

Diurnal expression of CXC receptors 4 (CXCR4) and CXC chemokine ligand 12 (CXCL12) in Pelteobagrus vachellii

The CXC chemokine ligand 12/CXC receptor 4 ligand/receptor interaction is the most ancient chemokine system in vertebrates, and it plays a pivotal role in the immune system's response against bacterial infection. In the current study, 1211 bp CXCR4 and 937 bp CXCL12 genes, which encode 364 and 99 amino acids, respectively, were isolated. Within the 24-hour light/dark cycle, the maximum of CXCR4 in the intestine, spleen, and anterior kidney of Pelteobagrus vachellii occurs at 8:00, 16:00, and 16:00, respectively. The maximum of CXCL12 in the intestine, spleen, and anterior kidney of P. vachellii occurs at 20:00, 12:00, and 20:00, respectively. CXCR4 and CXCL12 expressions showed 24-hour variation, which contributed to understanding of the immune rhythm of the teleost.

Molecular cloning and functional studies on magang goose toll-like receptor 5

Disease outbreaks heavily impact the economic viability of animal industries. Little is known about the mechanisms of immune system-related diseases in geese. Toll-like receptors (TLRs) play a major role in the anti-inflammatory immunity process in most animal species, but they have not been studied in the Magang goose. To elucidate the role of TLRs, reverse transcription polymerase chain reaction (RT-PCR) and PCR amplification of cDNA ends (Smart RACE) were used to clone the Magang goose TLR5 gene (mgTLR5). The full-length cDNA of mgTLR5 was 2967 bp in length, including a 5'-terminal untranslated region (UTR) of 215 bp, a 3'-terminal UTR of 384 bp, and an open reading frame of 2583 bp that encodes a protein of 860 amino acids. Structurally, mgTLR5 has a toll/interleukin-receptor (TIR) domain, a transmembrane domain, and seven leucine-rich repeats (LRRs) domains. Homology alignment of TLR5 and its TIR domains with other species revealed that mgTLR5 shared 98 % and 81.3 % of sequence similarity with white goose TLR5 and chicken TLR5, respectively. Quantitative RT-PCR showed that the mgTLR5 gene of the goose is widely expressed in all tested tissues, with the highest expression in the kidney and spleen. The increase in NF-κB promoter activity stimulated by flagellin was dependent on mgTLR5 expression in 293 T cells. Salmonella pullorum and flagellin significantly upregulated the expression of TLR5, IL-8, and IL-1 mRNA in peripheral blood mononucleotide cells of Magang goose cultured in vitro. Stimulation by S. pullorum for 24 h upregulated mgTLR5 expression in the cecum and kidney. We conclude that Magang goose TLR5 is a functional TLR5 homologue of the protein in other species and plays an important role in bacterial recognition.

Mechanisms of Cisplatin-Induced Acute Kidney Injury: Pathological Mechanisms, Pharmacological Interventions, and Genetic Mitigations

Administration of the chemotherapeutic agent cisplatin leads to acute kidney injury (AKI). Cisplatin-induced AKI (CIAKI) has a complex pathophysiological map, which has been linked to cellular uptake and efflux, apoptosis, vascular injury, oxidative and endoplasmic reticulum stress, and inflammation. Despite research efforts, pharmaceutical interventions, and clinical trials spanning over several decades, a consistent and stable pharmacological treatment option to reduce AKI in patients receiving cisplatin remains unavailable. This has been predominately linked to the incomplete understanding of CIAKI pathophysiology and molecular mechanisms involved. Herein, we detail the extensively known pathophysiology of cisplatin-induced nephrotoxicity that manifests and the variety of pharmacological and genetic alteration studies that target them.

Structural and functional understanding of the toll-like receptors

Recognition of invading pathogens by the innate immune system is essential to initiate antimicrobial responses and trigger adaptive immunity. This is largely mediated by an array of pattern-recognition receptor families that are essential for recognizing conserved molecular motifs characteristic of pathogenic microbes. One such family is the Toll-like receptors (TLRs). Activation of TLRs induces production of pro-inflammatory cytokines and type I interferons: the former triggers the synthesis of inflammatory mediators which cause fever, pain and other inflammation, and the latter mediates antiviral responses. Over the past decade, significant progress has been made in structural elucidation of TLRs in higher eukaryotes. The TLR structures with and without agonist and antagonist have been revealed by X-ray crystallography and cryo-electron microscopy studies, demonstrating the activated dimer formation induced by the agonistic ligand and the inhibition mechanism of the antagonistic ligand. Intracellular assembled structures and the TLR-chaperone complex are also reported. As the structural understanding of TLRs becomes better integrated with biochemical and immunological studies, a more comprehensive picture of their architectural and functional properties will emerge. This review summarizes recent advances in structural biological and mechanistic studies on TLRs.

Structurally diverse genes encode TLR13 in Nile tilapia: The two receptors can recognize Streptococcus 23S RNA and conduct signal transduction through MyD88

Toll-like receptors (TLRs) play a crucial role in the innate immune system, which is the first line of defence against pathogens and pathogenic products in fish. In the present study, we cloned the full-length cDNA and genome sequences of two TLR13 s (OnTLR13a, OnTLR13b) from Nile tilapia (Oreochromis niloticus). TLR family motifs, i.e., the leucine-rich repeat (LRR) domains and Toll/interleukin (IL)-1 receptor (TIR) domains, were conserved in the putative proteins OnTLR13a and OnTLR13b, with fifteen LRR domains and one TIR domain. Four exons and three introns were identified in the OnTLR13a genome sequence, and three exons and two introns were identified in the OnTLR13b genome sequence. In healthy Nile tilapia tissues, OnTLR13a and OnTLR13b were ubiquitously expressed in all 11 tested tissues/organs. The highest expression levels were observed in the spleen (OnTLR13a) and blood (OnTLR13b), and the lowest expression levels were observed in the liver (OnTLR13a) and stomach (OnTLR13b). The expression level of OnTLR13b at 5.5 days postfertilization (dpf) was significantly higher than that at the other 8 time points (2.5, 3.5, 4.5, 5, 6, 6.5, 7.5 and 8.5 dpf). Upon stimulation with an intraperitoneal injection of 200 μL (10⁷ CFU/mL) Streptococcus agalactiae, the expression levels of OnTLR13a and OnTLR13b were significantly upregulated in the intestine and gill. After cotransfection with MyD88, OnTLR13a significantly increased MyD88-dependent NF-κB activation in 293 T cells. However, OnTLR13b significantly impaired MyD88-dependent NF-κB activation. In addition, TLR13a slightly increased MyD88-dependent AP-1 activation, and TLR13b significantly increased MyD88-dependent AP-1 activation. TLR13a significantly increased MyD88-dependent interferon-β (IFN-β) activation, and TLR13b had no effect on MyD88-dependent IFN-β activation. These findings suggest that although the deduced protein structure of OnTLR13 is evolutionarily conserved between OnTLR13 and other TLR members, its signal transduction function is markedly different. Co-immunoprecipitation (Co-IP) assays showed that both OnTLR13a and OnTLR13b could interact with OnMyD88. RNA pulldown assays showed that TLR13a and TLR13b could combine with the 23S rRNA of S. agalactiae. These results indicate that TLR13a and TLR13b play important roles in the innate immune response against bacterial infection in Nile tilapia.

Identification and characterization of the LRR repeats in plant LRR-RLKs

Background

Leucine-rich-repeat receptor-like kinases (LRR-RLKs) play central roles in sensing various signals to regulate plant development and environmental responses. The extracellular domains (ECDs) of plant LRR-RLKs contain LRR motifs, consisting of highly conserved residues and variable residues, and are responsible for ligand perception as a receptor or co-receptor. However, there are few comprehensive studies on the ECDs of LRR-RLKs due to the difficulty in effectively identifying the divergent LRR repeats.

Results

In the current study, an efficient LRR motif prediction program, the “Phyto-LRR prediction” program, was developed based on the position-specific scoring matrix algorithm (PSSM) with some optimizations. This program was trained by 16-residue plant-specific LRR-highly conserved segments (HCS) from LRR-RLKs of 17 represented land plant species and a database containing more than 55,000 predicted LRRs based on this program was constructed. Both the prediction tool and database are freely available at http://phytolrr.com/ for website usage and at http://github.com/phytolrr for local usage. The LRR-RLKs were classified into 18 subgroups (SGs) according to the maximum-likelihood phylogenetic analysis of kinase domains (KDs) of the sequences. Based on the database and the SGs, the characteristics of the LRR motifs in the ECDs of the LRR-RLKs were examined, such as the arrangement of the LRRs, the solvent accessibility, the variable residues, and the N-glycosylation sites, revealing a comprehensive profile of the plant LRR-RLK ectodomains.

Conclusion

The “Phyto-LRR prediction” program is effective in predicting the LRR segments in plant LRR-RLKs, which, together with the database, will facilitate the exploration of plant LRR-RLKs functions. Based on the database, comprehensive sequential characteristics of the plant LRR-RLK ectodomains were profiled and analyzed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12860-021-00344-y.

Phosphatases in toll-like receptors signaling: the unfairly-forgotten

Over the past 2 decades, pattern recognition receptors (PRRs) have been shown to be on the front line of many illnesses such as autoimmune, inflammatory, and neurodegenerative diseases as well as allergies and cancer. Among PRRs, toll-like receptors (TLRs) are the most studied family. Dissecting TLRs signaling turned out to be advantageous to elaborate efficient treatments to cure autoimmune and chronic inflammatory disorders. However, a broad understanding of TLR effectors is required to propose a better range of cures. In addition to kinases and E3 ubiquitin ligases, phosphatases emerge as important regulators of TLRs signaling mediated by NF-κB, type I interferons (IFN I) and Mitogen-Activated Protein Kinases signaling pathways. Here, we review recent knowledge on TLRs signaling modulation by different classes and subclasses of phosphatases. Thus, it becomes more and more evident that phosphatases could represent novel therapeutic targets to control pathogenic TLRs signaling. Video Abstract.

Attenuation of the Induction of TLRs 2 and 4 Mitigates Inflammation and Promotes Neurological Recovery After Focal Cerebral Ischemia

The intense inflammatory response triggered in the brain after focal cerebral ischemia is detrimental. Recently, we showed that the suppression of toll-like receptors (TLRs) 2 and 4 attenuates infarct size and reduces the expression of pro-inflammatory cytokines in the ischemic brain. In this study, we further examined the effect of unsuppressed induction of TLRs 2 and 4 on the expression of its downstream signaling molecules and pro-inflammatory cytokines 1 week after reperfusion. The primary purpose of this study was to investigate the effect of simultaneous knockdown of TLRs 2 and 4 on M1/M2 microglial polarization dynamics and post-stroke neurological deficits and the recovery. Transient focal cerebral ischemia was induced in young adult male Sprague-Dawley rats by the middle cerebral artery occlusion (MCAO) procedure using a monofilament suture. Appropriate cohorts of rats were treated with a nanoparticle formulation of TLR2shRNA and TLR4shRNA (T2sh+T4sh) expressing plasmids (1 mg/kg each of T2sh and T4sh) or scrambled sequence inserted vector (vehicle control) expressing plasmids (2 mg/kg) intravenously via tail vein immediately after reperfusion. Animals from various cohorts were euthanized during reperfusion, and the ischemic brain tissue was isolated and utilized for PCR followed by agarose gel electrophoresis, real-time PCR, immunoblot, and immunofluorescence analysis. Appropriate groups were subjected to a battery of standard neurological tests at regular intervals until 14 days after reperfusion. The increased expression of both TLRs 2 and 4 and their downstream signaling molecules including the pro-inflammatory cytokines was observed even at 1-week after reperfusion. T2sh+T4sh treatment immediately after reperfusion attenuated the post-ischemic inflammation, preserved the motor function, and promoted recovery of the sensory and motor functions. We conclude that the post-ischemic induction of TLRs 2 and 4 persists for at least 7 days after reperfusion, contributes to the severity of acute inflammation, and impedes neurological recovery. Unlike previous studies in TLRs 2 or 4 knockout models, results of this study in a pharmacologically relevant preclinical rodent stroke model have translational significance.