The evolution of the metazoan Toll receptor family and its expression during protostome development

Background Toll-like receptors (TLRs) play a crucial role in immunity and development. They contain leucine-rich repeat domains, one transmembrane domain, and one Toll/IL-1 receptor domain. TLRs have been classified into V-type/scc and P-type/mcc TLRs, based on differences in the leucine-rich repeat domain region. Although TLRs are widespread in animals, detailed phylogenetic studies of this gene family are lacking. Here we aim to uncover TLR evolution by conducting a survey and a phylogenetic analysis in species across Bilateria. To discriminate between their role in development and immunity we furthermore analyzed stage-specific transcriptomes of the ecdysozoans Priapulus caudatus and Hypsibius exemplaris, and the spiralians Crassostrea gigas and Terebratalia transversa. Results We detected a low number of TLRs in ecdysozoan species, and multiple independent radiations within the Spiralia. V-type/scc and P-type/mcc type-receptors are present in cnidarians, protostomes and deuterostomes, and therefore they emerged early in TLR evolution, followed by a loss in xenacoelomorphs. Our phylogenetic analysis shows that TLRs cluster into three major clades: clade α is present in cnidarians, ecdysozoans, and spiralians; clade β in deuterostomes, ecdysozoans, and spiralians; and clade γ is only found in spiralians. Our stage-specific transcriptome and in situ hybridization analyses show that TLRs are expressed during development in all species analyzed, which indicates a broad role of TLRs during animal development. Conclusions Our findings suggest that a clade α TLR gene (TLR-Ca) and a clade β/γ TLR gene (TLR-Cβ/γ) were already present in the cnidarian-bilaterian common ancestor. However, although TLR-Ca was conserved in cnidarians, TLR-Cβ/γ was lost during the early evolution of these taxa. Moreover, TLR-Cβ/γ duplicated to generate TLR-Cβ and TLR-Cγ in the lineage to the last common protostome-deuterostome ancestor. TLR-Ca, TLR-Cβ and TLR-Cγ further expanded generating the three major TLR clades. While all three clades radiated in several spiralian lineages, specific TLRs clades have been presumably lost in other lineages. Furthermore, the expression of the majority of these genes during protostome ontogeny suggests a likely role in development.

Toll-like receptor signalling via IRAK4 confers epithelial integrity and tightness through regulation of junctional tension

Toll-like receptors (TLRs) in mammalian systems are well characterised for their role in innate immunity. In addition, TLRs also fulfil crucial functions outside immunity, including the dorso-ventral patterning function of the original Toll receptor in Drosophila and neurogenesis in mice. Recent discoveries in flies suggested key roles for TLRs in epithelial cells in patterning of cytoskeletal activity near epithelial junctions. Here we address the function of TLRs and the downstream key signal transduction component IRAK4 (interleukin-1 receptor associated kinase 4) in human epithelial cells. Using differentiated human Caco-2 cells as a model for the intestinal epithelium, we show that these cells exhibit baseline TLR signalling as revealed by p-IRAK4 and that blocking IRAK4 function leads to a loss of epithelial tightness involving key changes at tight junctions and adherens junctions. These changes correlate with a loss of epithelial tension and changes in junctional actomyosin. Knock-down of IRAK4 and certain TLRs phenocopies the inhibitor treatment. These data suggest a model whereby TLR receptors near epithelial junctions might be involved in a continuous sensing of the epithelial state to promote epithelial tightness and integrity.

A reaction-diffusion network model predicts a dual role of Cactus/IκB to regulate Dorsal/NFκB nuclear translocation in Drosophila

Dorsal-ventral patterning of the Drosophila embryo depends on the NFκB superfamily transcription factor Dorsal (Dl). Toll receptor activation signals for degradation of the IκB inhibitor Cactus (Cact), leading to a ventral-to-dorsal nuclear Dl gradient. Cact is critical for Dl nuclear import, as it binds to and prevents Dl from entering the nuclei. Quantitative analysis of cact mutants revealed an additional Cact function to promote Dl nuclear translocation in ventral regions of the embryo. To investigate this dual Cact role, we developed a predictive model based on a reaction-diffusion regulatory network. This network distinguishes non-uniform Toll-dependent Dl nuclear import and Cact degradation, from the Toll-independent processes of Cact degradation and reversible nuclear-cytoplasmic Dl flow. In addition, it incorporates translational control of Cact levels by Dl. Our model successfully reproduces wild-type data and emulates the Dl nuclear gradient in mutant dl and cact allelic combinations. Our results indicate that the dual role of Cact depends on the dynamics of Dl-Cact trimers along the dorsal-ventral axis: In the absence of Toll activation, free Dl-Cact trimers retain Dl in the cytoplasm, limiting the flow of Dl into the nucleus; in ventral-lateral regions, Dl-Cact trimers are recruited by Toll activation into predominant signaling complexes and promote Dl nuclear translocation. Simulations suggest that the balance between Toll-dependent and Toll-independent processes are key to this dynamics and reproduce the full assortment of Cact effects. Considering the high evolutionary conservation of these pathways, our analysis should contribute to understanding NFκB/c-Rel activation in other contexts such as in the vertebrate immune system and disease.

Skeletal muscle fibers play a functional role in host defense during sepsis in mice

Skeletal muscles secrete a wide variety of immunologically active cytokines, but the functional significance of this response to in vivo innate immunity is not understood. We addressed this by knocking out the toll receptor adapter protein, Myd88, only in skeletal muscle fibers (skmMyd88KO), and followed male and female mice at 6 and 12 h after peritoneal injection of cecal slurry (CS), a model of polymicrobial sepsis. Because of a previously identified increase in mortality to CS injection, males received ~ 30% lower dose. At 12 h, skmMyd88KO caused significant reductions in a wide variety of pro- and anti-inflammatory plasma cytokines, e.g. TNFα, IL-1β and IL-10, compared to strain-matched controls in both males and females. Similar reductions were observed at 6 h in females. SkmMyd88KO led to ~ 40–50% elevations in peritoneal neutrophils at 6 and 12 h post CS in females. At 12 h post CS, skmMyd88KO increased peritoneal monocytes/macrophages and decreased %eosinophils and %basophils in females. SkmMyd88KO also led to significantly higher rates of mortality in female mice but not in males. In conclusion, the results suggest that skeletal muscle Myd88-dependent signal transduction can play functionally important role in normal whole body, innate immune inflammatory responses to peritoneal sepsis.

Diabetes potentiates ROS production in granulocytes from patients with chronic kidney disease

Background: Type 2 diabetes (DM2) and chronic kidney disease (CKD) are inflammatory pathologies. Diabetes is characterized by hyperglycemia and CKD by the gradual and irreversible loss of kidney function. Both diseases develop oxidative stress, and reactive oxygen species (ROS) play a pivotal role in the pathogenesis. This study aimed to determine ROS production by granulocytes from renal patients (CKD) with or without diabetes. Methods: Granulocytes from patients with DM2, CKD, CKD-DM2, and healthy controls were purified using the Ficoll-Hypaque gradient method. Granulocyte ROS generation in the absence or the presence of PDB (an activator of NADPH-oxidase) or Concanavalin A (Toll- receptor 3,9 activator) was evaluated in a luminol-dependent chemiluminescence method. The cell-free DNA in the serum of DM2, CKD, and CKD-DM2 patients was measured by the fluorescence method before and after hemodialysis. Results: Our results show a significant increase in ROS production by granulocytes from patients with CKD, DM2, and CKD-DM2 compared to healthy control (p<0.05). CKD-DM2 group produced the most significant ROS levels with or without NADPH-oxidase activation. ROS production showed a significant increase in the presence of ConA. In contrast, mitochondrial (internal) ROS showed a different ROS response. DNA extrusion was higher in the CKD-DM2 group after hemodialysis suggesting cell death. Conclusion: The results demonstrated that CKD-DM2 patients produced high ROS generation levels and increased DNA extrusion after hemodialysis. It may suggest that CKD-DM2 disease is more severe and has a worse clinical prognosis.

The evolution of the metazoan Toll receptor family and its expression during protostome development

Background: Toll-like receptors (TLRs) play a crucial role in immunity and development. They contain leucine-rich repeat domains, one transmembrane domain, and one Toll/IL-1 receptor domain. TLRs have been classified into V-type/scc and P-type/mcc TLRs, based on differences in the leucine-rich repeat domain region. Although TLRs are widespread in animals, detailed phylogenetic studies of this gene family are lacking. Here we aim to uncover TLR evolution by conducting a survey and a phylogenetic analysis in species across Bilateria. To discriminate between their role in development and immunity we furthermore analyzed stage-specific transcriptomes of the ecdysozoans Priapulus caudatus and Hypsibius exemplaris, and the spiralians Crassostrea gigas and Terebratalia transversa.Results: We detected a low number of TLRs in ecdysozoan species, and multiple independent radiations within the Spiralia. V-type/scc and P-type/mcc type-receptors are present in cnidarians, protostomes and deuterostomes, and therefore they emerged early in TLR evolution, followed by a loss in xenacoelomorphs. Our phylogenetic analysis shows that TLRs cluster into three major clades: clade α is present in cnidarians, ecdysozoans, and spiralians; clade β in deuterostomes, ecdysozoans, and spiralians; and clade γ is only found in spiralians. Our stage-specific transcriptome and in situ hybridization analyses show that TLRs are expressed during development in all species analyzed, which indicates a broad role of TLRs during animal development.Conclusions: Our findings suggest that the bilaterian TLRs likely emerged by duplication from a single TLR encoding gene (proto-TLR) present in the last common cnidarian-bilaterian ancestor. This proto-TLR gene duplicated before the split of protostomes and deuterostomes; a second duplication occurred in the lineage to the Trochozoa. While all three clades further radiated in several spiralian lineages, specific TLRs clades have been presumably lost in others. Furthermore, the expression of the majority of these genes during protostome ontogeny suggests their involvement in immunity and development.

The evolution of the metazoan Toll receptor family and its expression during protostome development

BackgroundToll-like receptors (TLRs) play a crucial role in immunity and development. They contain leucine-rich repeat domains, one transmembrane domain, and one Toll/IL-1 receptor domain. TLRs have been classified into V-type/scc and P-type/mcc TLRs, based on differences in the leucine-rich repeat domain region. Although TLRs are widespread in animals, detailed phylogenetic studies of this gene family are lacking. Here we aim to uncover TLR evolution by conducting a survey and a phylogenetic analysis in species across Bilateria. To discriminate between their role in development and immunity we furthermore analyzed stage-specific transcriptomes of the ecdysozoans Priapulus caudatus and Hypsibius exemplaris, and the spiralians Crassostrea gigas and Terebratalia transversa.ResultsWe detected a low number of TLRs in ecdysozoan species, and multiple independent radiations within the Spiralia. V-type/scc and P-type/mcc type-receptors are present in cnidarians, protostomes and deuterostomes, and therefore they emerged early in TLR evolution, followed by a loss in xenacoelomorphs. Our phylogenetic analysis shows that TLRs cluster into three major clades: clade α is present in cnidarians, ecdysozoans, and spiralians; clade β in deuterostomes, ecdysozoans, and spiralians; and clade γ is only found in spiralians. Our stage-specific transcriptome and in situ hybridization analyses show that TLRs are expressed during development in all species analyzed, which indicates a broad role of TLRs during animal development.ConclusionsOur findings suggest that the bilaterian TLRs likely emerged by duplication from a single TLR encoding gene (proto-TLR) present in the last common cnidarian-bilaterian ancestor. This proto-TLR gene duplicated before the split of protostomes and deuterostomes; a second duplication occurred in the lineage to the Trochozoa. While all three clades further radiated in several spiralian lineages, specific TLRs clades have been presumably lost in others. Furthermore, the expression of the majority of these genes during protostome ontogeny suggests their involvement in immunity and development.

Activation of Toll Immune Pathway in an Insect Vector Induced by a Plant Virus

The Toll pathway plays an important role in defense against infection of various pathogenic microorganisms, including viruses. However, current understanding of Toll pathway was mainly restricted in mammal and some model insects such as Drosophila and mosquitoes. Whether plant viruses can also activate the Toll signaling pathway in vector insects is still unknown. In this study, using rice stripe virus (RSV) and its insect vector (small brown planthopper, Laodelphax striatellus) as a model, we found that the Toll pathway was activated upon RSV infection. In comparison of viruliferous and non-viruliferous planthoppers, we found that four Toll pathway core genes (Toll, Tube, MyD88, and Dorsal) were upregulated in viruliferous planthoppers. When the planthoppers infected with RSV, the expressions of Toll and MyD88 were rapidly upregulated at the early stage (1 and 3 days post-infection), whereas Dorsal was upregulated at the late stage (9 days post-infection). Furthermore, induction of Toll pathway was initiated by interaction between a Toll receptor and RSV nucleocapsid protein (NP). Knockdown of Toll increased the proliferation of RSV in vector insect, and the dsToll-treated insects exhibited higher mortality than that of dsGFP-treated ones. Our results provide the first evidence that the Toll signaling pathway of an insect vector is potentially activated through the direct interaction between Toll receptor and a protein encoded by a plant virus, indicating that Toll immune pathway is an important strategy against plant virus infection in an insect vector.

Treatable metabolic and inflammatory abnormalities in Post COVID Syndrome (PCS) define the transcriptomic basis for persistent symptoms: Lessons from CIRS

Within three months of the onset of acute SARS-CoV-2 (COVID-19) infections, new and persistent symptoms were noted in survivors. While the world’s medical and research communities focus on saving lives following COVID-19 infection, a relentless march of new cases of Post-COVID Syndrome (PCS) continues to spread around the globe as a second COVID-related pandemic. Efforts to define the physiology of PCS, a multisystem, multi-symptom illness, continue without success, in part due to the markedly different case presentations. Using a transcriptomic assessment of persistently ill cases of PCS, we show the presence of (i) molecular hypometabolism (MHM) and proliferative physiology; (ii) elevated levels of ribosomal stress responses and a concomitant increase in gene activation of TGFBR; and (iii) common co-expression of CD14 and Toll Receptor 4, correlated to exposure of amplified microbial growth in a water-damaged environment, specifically Actinobacteria and endotoxin, respectively, compared to recovered PCS cases. Total symptom scores and visual contrast sensitivity (VCS) results showed statistically significant differences. The data reported here supports the concept that PCS occurs in patients with additional environmental exposures and enhanced TGF signaling. In a strikingly similar condition called Chronic Inflammatory Response Syndrome (CIRS), named in 2010, the transcriptomic abnormalities were identified to respond to treatment with FDA-cleared medications, with salutary benefits for affected cases. Though sparsely reported, PCS cases share proteomic findings with CIRS. While additional studies are indicated, a new approach to the treatment of PCS is suggested.