Protein phosphatases in TLR signaling

Molecular Role of Protein Phosphatases in Alzheimer's and Other Neurodegenerative Diseases

Alzheimer's disease (AD) is distinguished by the gradual loss of cognitive function, which is associated with neuronal loss and death. Accumulating evidence supports that protein phosphatases (PPs; PP1, PP2A, PP2B, PP4, PP5, PP6, and PP7) are directly linked with amyloid beta (Aβ) as well as the formation of the neurofibrillary tangles (NFTs) causing AD. Published data reported lower PP1 and PP2A activity in both gray and white matters in AD brains than in the controls, which clearly shows that dysfunctional phosphatases play a significant role in AD. Moreover, PP2A is also a major causing factor of AD through the deregulation of the tau protein. Here, we review recent advances on the role of protein phosphatases in the pathology of AD and other neurodegenerative diseases. A better understanding of this problem may lead to the development of phosphatase-targeted therapies for neurodegenerative disorders in the near future.

Insight into the role of IRF7 in skin and connective tissue diseases

Interferons (IFNs) are signalling proteins primarily involved in initiating innate immune responses against pathogens and promoting the maturation of immune cells. Interferon Regulatory Factor 7 (IRF7) plays a pivotal role in the IFNs signalling pathway. The activation process of IRF7 is incited by exogenous or abnormal nucleic acids, which is followed by the identification via pattern recognition receptors (PRRs) and the ensuing signalling cascades. Upon activation, IRF7 modulates the expression of both IFNs and inflammatory gene regulation. As a multifunctional transcription factor, IRF7 is mainly expressed in immune cells, yet its presence is also detected in keratinocytes, fibroblasts, and various dermal cell types. In these cells, IRF7 is critical for skin immunity, inflammation, and fibrosis. IRF7 dysregulation may lead to autoimmune and inflammatory skin conditions, including systemic scleroderma (SSc), systemic lupus erythematosus (SLE), Atopic dermatitis (AD) and Psoriasis. This comprehensive review aims to extensively elucidate the role of IRF7 and its signalling pathways in immune cells and keratinocytes, highlighting its significance in skin-related and connective tissue diseases.

Interferons in Viral Infections

Interferons (IFNs) are cytokines that inhibit viral replication in host cells by triggering innate immune responses through the transcriptional induction of various IFN-stimulated genes (ISGs) [...].

Evolution of the Major Components of Innate Immunity in Animals

Innate immunity is present in all animals. In this review, we explore the main conserved mechanisms of recognition and innate immune responses among animals. In this sense, we discuss the receptors, critical for binding to pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs); the downstream signaling proteins; and transcription factors that govern immune responses. We also highlight conserved inflammatory mediators that are induced after the recognition of DAMPs and PAMPs. At last, we discuss the mechanisms that are involved in the regulation and/or generation of reactive oxygen species (ROS), influencing immune responses, like heme-oxygenases (HOs).

Emerging roles of the Protein Phosphatase 1 (PP1) in the context of viral infections

Protein Phosphatase 1 (PP1) is a major serine/threonine phosphatase in eukaryotes, participating in several cellular processes and metabolic pathways. Due to their low substrate specificity, PP1's catalytic subunits do not exist as free entities but instead bind to Regulatory Interactors of Protein Phosphatase One (RIPPO), which regulate PP1's substrate specificity and subcellular localization. Most RIPPOs bind to PP1 through combinations of short linear motifs (4-12 residues), forming highly specific PP1 holoenzymes. These PP1-binding motifs may, hence, represent attractive targets for the development of specific drugs that interfere with a subset of PP1 holoenzymes. Several viruses exploit the host cell protein (de)phosphorylation machinery to ensure efficient virus particle formation and propagation. While the role of many host cell kinases in viral life cycles has been extensively studied, the targeting of phosphatases by viral proteins has been studied in less detail. Here, we compile and review what is known concerning the role of PP1 in the context of viral infections and discuss how it may constitute a putative host-based target for the development of novel antiviral strategies.

Targeting Protein Phosphatases for the Treatment of Chronic Liver Disease

There exists a huge number of patients suffering from chronic liver disease worldwide. As a disease with high incidence and mortality worldwide, strengthening the research on the pathogenesis of chronic liver disease and the development of novel drugs is an important issue related to the health of all human beings. Phosphorylation modification of proteins plays a crucial role in cellular signal transduction, and phosphatases are involved in the development of liver diseases. Therefore, this article summarized the important role of protein phosphatases in chronic liver disease with the aim of facilitating the development of drugs targeting protein phosphatases for the treatment of chronic liver disease.

Tolerogenic dendritic cells and TLR4/IRAK4/NF-κB signaling pathway in allergic rhinitis

Dendritic cells (DCs), central participants in the allergic immune response, can capture and present allergens leading to allergic inflammation in the immunopathogenesis of allergic rhinitis (AR). In addition to initiating antigen-specific immune responses, DCs induce tolerance and modulate immune homeostasis. As a special type of DCs, tolerogenic DCs (tolDCs) achieve immune tolerance mainly by suppressing effector T cell responses and inducing regulatory T cells (Tregs). TolDCs suppress allergic inflammation by modulating immune tolerance, thereby reducing symptoms of AR. Activation of the TLR4/IRAK4/NF-κB signaling pathway contributes to the release of inflammatory cytokines, and inhibitors of this signaling pathway induce the production of tolDCs to alleviate allergic inflammatory responses. This review focuses on the relationship between tolDCs and TLR4/IRAK4/NF-κB signaling pathway with AR.

Toll-like receptors in cardiac hypertrophy

Toll-like receptors (TLRs) are a family of pattern recognition receptors (PRRs) that can identify pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). TLRs play an important role in the innate immune response, leading to acute and chronic inflammation. Cardiac hypertrophy, an important cardiac remodeling phenotype during cardiovascular disease, contributes to the development of heart failure. In previous decades, many studies have reported that TLR-mediated inflammation was involved in the induction of myocardium hypertrophic remodeling, suggesting that targeting TLR signaling might be an effective strategy against pathological cardiac hypertrophy. Thus, it is necessary to study the mechanisms underlying TLR functions in cardiac hypertrophy. In this review, we summarized key findings of TLR signaling in cardiac hypertrophy.

GADD34 Ablation Exacerbates Retinal Degeneration in P23H RHO Mice

The UPR is sustainably activated in degenerating retinas, leading to translational inhibition via p-eIF2α. Recent findings have demonstrated that ablation of growth arrest and DNA damage-inducible protein 34 (GADD34), a protein phosphatase 1 regulatory subunit permitting translational machinery operation through p-eIF2α elevation, does not impact the rate of translation in fast-degenerating rd16 mice. The current study aimed to validate whether P23H RHO mice degenerating at a slower pace manifest translational attenuation and whether GADD34 ablation impacts the rate of retinal degeneration via further suppression of retinal protein synthesis and apoptotic cell death. For this study, mice were examined with ERG and histological analyses. The molecular assessment was conducted in the naïve and LPS-challenged mice using Western blot and qRT-PCR analyses. Thus, this study demonstrates that the P23H RHO retinas manifest translational attenuation. However, GADD34 ablation resulted in a more prominent p-eIF2a increase without impacting the translation rate. GADD34 deficiency also led to a reduction in scotopic ERG amplitudes and an increased number of TUNEL-positive cells. Molecular analysis revealed that GADD34 deficiency reduces the expression of p-STAT3 and Il-6 while increasing the expression of Tnfa. Overall, the data indicate that GADD34 plays a multifunctional role. Under chronic UPR activation, GADD34 acts as a feedback player, dephosphorylating p-eIF2a, although this role does not seem to be critical. Additionally, GADD34 controls cytokine expression and STAT3 activation. Perhaps these molecular events are particularly important in controlling the pace of retinal degeneration.

[E.faecium QH06 alleviates TNBS-induced colonic mucosal injury in rats]

OBJECTIVE

To investigate the effect of Enterococcus faecium QH06 on TNBS-induced ulcerative colitis (UC) in rats and explore the mechanisms in light of intestinal flora and intestinal immunity.

METHODS

Thirty-six male Wistar rats were randomized equally into control group, UC model group, and E.faecium QH06 intervention group. The rats in the latter two groups were subjected to colonic enema with 5% TNBS/ethanol to induce UC, followed by treatment with intragastric administration of distilled water or E.faecium QH06 at the dose of 0.21 g/kg. After 14 days of treatment, the rats were examined for colon pathologies with HE staining. The mRNA and protein expression levels of IL-4, IL-10, IL-12, and IFN-γ in the colon tissues were detected using RT-qPCR and ELISA, and the expression of TLR2 protein was detected with immunohistochemistry and ELISA. Illumina Miseq platform was used for sequencing analysis of the intestinal flora of the rats with bioinformatics analysis. The correlations of the parameters of the intestinal flora with the expression levels of TLR2 and cytokines were analyzed.

RESULTS

The rats with TNBS- induced UC showed obvious weight loss (P < 0.01) and severe colon tissue injury with high pathological scores (P < 0.01). The protein expression levels of IFN-γ, IL-12, and TLR2 (P < 0.01) and the mRNA expression levels of IFN-γ, IL-12 and IL-10 (P < 0.05) were significantly increased in the colon tissues of the rats with UC. Illumina Miseq sequence analysis showed that in UC rats, the Shannon index (P < 0.05) ACE (P < 0.01)and Chao (P < 0.05) index for the diversity of intestinal flora both decreased with a significantly increased abundance of Enterobacteriaceae (P < 0.01) and a lowered abundance of Burkholderiaceae (P < 0.05). Compared with the UC rats, the rats treated with E. faecium QH06 showed obvious body weight gain (P < 0.05), lessened colon injuries, lowered pathological score of the colon tissue (P < 0.05), decreased protein expressions of IFN- γ, IL- 12, and TLR2 and mRNA expressions of IFN- γ and IL-12 (P < 0.01 or 0.05), and increased protein expressions of IL- 4 (P < 0.05). The Shannon index ACE (P < 0.05) and Chao (P < 0.05) index of intestinal microflora were significantly increased, the abundance of Enterobacteriaceae was lowered and that of Burkholderiaceae and Rikenellaceae was increased in E.faecium QH06- treated rats (P < 0.01 or 0.05). Correlation analysis showed that IFN-γ was positively correlated with the abundance of Enterobacteriaceae, and IFN-γ was negatively correlated with the abundance of Prevotellaceae, Desulfovibrionaceae, norank_o_Mollicutes_RF39 and Clostridiales_vadinBB60_group; TLR2 was negatively correlated with Clostridiales_vadinBB60_group, norank_o_Mollicutes_RF39 and Prevotellaceae.

CONCLUSION

E.faecium QH06 can alleviate TNBS-induced colonic mucosal injury in rats, and its effect is mediated possibly by increasing the abundance of SCFA-producing bacteria such as Prevotellaceae and inhibiting abnormal immune responses mediated by TLR2.

Targeting protein phosphatases for the treatment of inflammation-related diseases: From signaling to therapy

Inflammation is the common pathological basis of autoimmune diseases, metabolic diseases, malignant tumors, and other major chronic diseases. Inflammation plays an important role in tissue homeostasis. On one hand, inflammation can sense changes in the tissue environment, induce imbalance of tissue homeostasis, and cause tissue damage. On the other hand, inflammation can also initiate tissue damage repair and maintain normal tissue function by resolving injury and restoring homeostasis. These opposing functions emphasize the significance of accurate regulation of inflammatory homeostasis to ameliorate inflammation-related diseases. Potential mechanisms involve protein phosphorylation modifications by kinases and phosphatases, which have a crucial role in inflammatory homeostasis. The mechanisms by which many kinases resolve inflammation have been well reviewed, whereas a systematic summary of the functions of protein phosphatases in regulating inflammatory homeostasis is lacking. The molecular knowledge of protein phosphatases, and especially the unique biochemical traits of each family member, will be of critical importance for developing drugs that target phosphatases. Here, we provide a comprehensive summary of the structure, the "double-edged sword" function, and the extensive signaling pathways of all protein phosphatases in inflammation-related diseases, as well as their potential inhibitors or activators that can be used in therapeutic interventions in preclinical or clinical trials. We provide an integrated perspective on the current understanding of all the protein phosphatases associated with inflammation-related diseases, with the aim of facilitating the development of drugs that target protein phosphatases for the treatment of inflammation-related diseases.

Elimination of negative feedback in TLR signalling allows rapid and hypersensitive detection of microbial contaminants

The exquisite specificity of Toll-like receptors (TLRs) to sense microbial molecular signatures is used as a powerful tool to pinpoint microbial contaminants. Various cellular systems, from native human blood cells to transfected cell lines exploit TLRs as pyrogen detectors in biological preparations. However, slow cellular responses and limited sensitivity have hampered the replacement of animal-based tests such as the rabbit pyrogen test or lipopolysaccharide detection by Limulus amoebocyte lysate. Here, we report a novel human cell-based approach to boost detection of microbial contaminants by TLR-expressing cells. By genetic and pharmacologic elimination of negative control circuits, TLR-initiated cellular responses to bacterial molecular patterns were accelerated and significantly elevated. Combining depletion of protein phosphatase PP2ACA and pharmacological inhibition of PP1 in the optimized reporter cells further enhanced the sensitivity to allow detection of bacterial lipoprotein at 30 picogram/ml. Such next-generation cellular monitoring is poised to replace animal-based testing for microbial contaminants.

Detecting Critical Functional Ingredients Group and Mechanism of Xuebijing Injection in Treating Sepsis

Sepsis is a systemic inflammatory reaction caused by various infectious or noninfectious factors, which can lead to shock, multiple organ dysfunction syndrome, and death. It is one of the common complications and a main cause of death in critically ill patients. At present, the treatments of sepsis are mainly focused on the controlling of inflammatory response and reduction of various organ function damage, including anti-infection, hormones, mechanical ventilation, nutritional support, and traditional Chinese medicine (TCM). Among them, Xuebijing injection (XBJI) is an important derivative of TCM, which is widely used in clinical research. However, the molecular mechanism of XBJI on sepsis is still not clear. The mechanism of treatment of "bacteria, poison and inflammation" and the effects of multi-ingredient, multi-target, and multi-pathway have still not been clarified. For solving this issue, we designed a new systems pharmacology strategy which combines target genes of XBJI and the pathogenetic genes of sepsis to construct functional response space (FRS). The key response proteins in the FRS were determined by using a novel node importance calculation method and were condensed by a dynamic programming strategy to conduct the critical functional ingredients group (CFIG). The results showed that enriched pathways of key response proteins selected from FRS could cover 95.83% of the enriched pathways of reference targets, which were defined as the intersections of ingredient targets and pathogenetic genes. The targets of the optimized CFIG with 60 ingredients could be enriched into 182 pathways which covered 81.58% of 152 pathways of 1,606 pathogenetic genes. The prediction of CFIG targets showed that the CFIG of XBJI could affect sepsis synergistically through genes such as TAK1, TNF-α, IL-1β, and MEK1 in the pathways of MAPK, NF-κB, PI3K-AKT, Toll-like receptor, and tumor necrosis factor signaling. Finally, the effects of apigenin, baicalein, and luteolin were evaluated by in vitro experiments and were proved to be effective in reducing the production of intracellular reactive oxygen species in lipopolysaccharide-stimulated RAW264.7 cells, significantly. These results indicate that the novel integrative model can promote reliability and accuracy on depicting the CFIGs in XBJI and figure out a methodological coordinate for simplicity, mechanism analysis, and secondary development of formulas in TCM.

Role of active site arginine residues in substrate recognition by PPM1A

Reversible protein phosphorylation is a key mechanism for regulating numerous cellular events. The metal-dependent protein phosphatases (PPM) are a family of Ser/Thr phosphatases, which uniquely recognize their substrate as a monomeric enzyme. In the case of PPM1A, it has the capacity to dephosphorylate a variety of substrates containing different sequences, but it is not yet fully understood how it recognizes its substrates. Here we analyzed the role of Arg33 and Arg186, two residues near the active site, on the dephosphorylation activity of PPM1A. The results showed that both Arg residues were critical for enzymatic activity and docking-model analysis revealed that Arg186 is positioned to interact with the substrate phosphate group. In addition, our results suggest that which Arg residue plays a more significant role in the catalysis depends directly on the substrate.

UPR attenuates the proinflammatory effect of HPDLF on macrophage polarization

Human periodontal ligament fibroblast (HPDLF) is a major component of the resident cells in the periodontal microenvironment, and plays important roles in periodontitis through multiple mechanisms. Although lipopolysaccharide (LPS) has been shown to cause endoplasmic reticulum (ER) stress and activate the unfolded protein response (UPR) in HPDLF, the mechanisms governing HPDLF function in periodontitis are unclear. In this study, we tested the ability of unfolded protein response (UPR) to regulate HPDLF in vitro and examined the underlying mechanisms. We found LPS-pretreated HPDLF induced macrophage polarization toward M1 phenotype. UPR activation reduced the inflammatory cytokine production and downregulated the expression of TLR4 in HPDLF. The phosphorylation of NF-κB p65 and I-κB was also inhibited by UPR activation. Our findings demonstrate that the connection of LPS, UPR, and HPDLF may represent a new concrete theory of innate immunity regulation in periodontal diseases, and suggest that targeting of UPR in HPDLF may be developed as a potent therapy for periodontitis.

Achyranthes bidentata Polysaccharide Activates Nuclear Factor-Kappa B and Promotes Cytokine Production in J774A.1 Cells Through TLR4/MyD88 Signaling Pathway

Achyranthes bidentata Blume, a traditional Chinese medicine, is widely acknowledged for its function of invigorating the liver and kidneys and as a stranguria-relieving diuretic and used in the treatment of edema, gonorrhea, and other diseases. Polysaccharide (ABPS), isolated from Achyranthes bidentata Blume, has been demonstrated to have multiple biological activities including immunomodulatory effects. However, the mechanisms underlying the effects of ABPS have not been fully investigated. The present study is conducted to explore the underlying mechanism of immunomodulatory activities of ABPS. Results showed that ABPS significantly increased the secretion of IL-1β and TNF-α in J744 A.1 cells. Nitric oxide (NO) also significantly increased after ABPS treatment. The special antibodies (Toll-like receptor 4 (TLR4) antibody and CD14/TLR4 antibody) significantly decreased the activation, while the Toll-like receptor 2 (TLR2) antibody could not abolish this activation. Meanwhile, pyrrolidine dithiocarbamate (PDTC), a specific inhibitor of NF-κB, remarkably inhibited the secretion of IL-1β and TNF-α induced by ABPS in J744 A.1 cells. Western blotting (WB) and confocal laser scanning microscopy (CLSM) showed that ABPS promoted NF-κB translocation into the nucleus. Furthermore, the mRNA and protein expression of TLR4 and MyD88 were significantly increased after ABPS treatment. Taken together, these findings suggested that the immunomodulatory mechanism of ABPS was associated with the secretion of cytokines by stimulating the NF-κB pathway through TLR4/MyD88 signaling.

USP18 negatively regulates and inhibits lipopolysaccharides-induced sepsis by targeting TAK1 activity

Sepsis is an inflammatory disease with exacerbated inflammation at early stage. Inflammatory cytokines play critical roles in the pathophysiology of sepsis. Ubiquitin specific peptidase 18 (USP18), a deubiquitinating enzyme, has been shown to modulate transforming growth factor-β-activated kinase 1 (TAK1) activity. However, it is not clear about the precise role of USP18 in sepsis. Here we investigated the potential effect of USP18 on inflammation in sepsis. We generated mice with USP18 or/and TAK1 deficiency in macrophages (USP18 MKO mice, TAK1 MKO mice and USP18 MKO TAK1 MKO mice) and established lipopolysaccharides (LPS)-induced septic mice model. Bone marrow derived macrophages were isolated from wild type (WT), USP18 MKO or TAK1 MKO mice and treated with LPS or CpG, the expressions of cytokines including IL-6, IL-10, IL-1β, and TNF-α were measured. The activation of NF-κB, ERK, p38 signaling pathways and ubiquitination of TAK1 were detected. We induced sepsis in WT, USP18 MKO, TAK1 MKO or USP18 MKO TAK1 MKO mice and evaluated the survival rate, lung pathology and inflammation cytokine level in serum. Macrophages deficient in USP18 produced significantly increased IL-6, IL-1β and TNF-α post LPS or CpG stimulation. Macrophages deficient in USP18 had promoted activation of NF-κB, p38 and ERK, and increased ubiquitination of TAK1. Mice with TAK1 deficiency in macrophages had increased survival rates, decreased immune cell infiltration in lung, and decreased pro-inflammatory cytokines in serum. In contrast, mice with USP18 deficiency in macrophages had decreased survival rates, increased cell infiltration in lung and increased pro-inflammatory cytokines in serum. USP18 alleviated LPS-induced sepsis by inhibiting TAK1 activity.