Pristane induces autophagy in macrophages, promoting a STAT1-IRF1-TLR3 pathway and arthritis

Targeting transcription factors for therapeutic benefit in rheumatoid arthritis

Rheumatoid arthritis (RA) is a destructive inflammatory autoimmune disease that causes pain and disability. Many of the currently available drugs for treating RA patients are aimed at halting the progression of the disease and alleviating inflammation. Further, some of these treatment options have drawbacks, including disease recurrence and adverse effects due to long-term use. These inefficiencies have created a need for a different approach to treating RA. Recently, the focus has shifted to direct targeting of transcription factors (TFs), as they play a vital role in the pathogenesis of RA, activating key cytokines, chemokines, adhesion molecules, and enzymes. In light of this, synthetic drugs and natural compounds are being explored to target key TFs or their signaling pathways in RA. This review discusses the role of four key TFs in inflammation, namely NF-κB, STATs, AP-1 and IRFs, and their potential for being targeted to treat RA.

lncRNAS56464.1 as a ceRNA promotes the proliferation of fibroblast‑like synoviocytes in experimental arthritis via the Wnt signaling pathway and sponges miR‑152‑3p

Rheumatoid arthritis (RA) is an autoimmune disease that occurs in approximately 1.0% of the general population. In RA patients, physical disability and joint damage are the major prognostic factors, which are associated with a reduction in the quality of life and early mortality. At present, the exact molecular mechanism of RA remains elusive. Long noncoding RNAs (lncRNAs) have been revealed to play a regulatory role in the pathogenesis of RA. To reveal the function of lncRNAs in rheumatoid arthritis, lncRNAS56464.1 was screened to verify its targeting of the microRNA (miR)-152-3p/Wnt pathway and its effect on the proliferation of fibroblast-like synoviocytes (FLS). In the present study, based on the competing endogenous RNA (ceRNA) theory, siRNA was designed for transfection into FLS to calculate the lncRNAS56464.1 interference efficiency and then the effect of lncRNAS56464.1 interference on FLS proliferation was detected by MTT assay. Then, lncRNAS56464.1 targeting of the miR-152-3p/Wnt pathway was detected by a dual-luciferase reporter assay. In addition, RT-qPCR, immunofluorescence and western blotting techniques were employed to detect the expression of lncRNAS56464.1, miR-152-3p and some key genes of the Wnt signaling pathway in FLS after lncRNAS56464.1 interference. The results revealed that lncRNAS56464.1 could combine with miR-152-3p and promoted the proliferation of FLS. In addition, lncRNAS56464.1 interference could not only decrease the proliferation of FLS and the expression of Wnt1, β-catenin, c-Myc, cyclin D1, and p-GSK-3β/GSK-3β, but it also increased the expression of SFRP4. The present data indicated that lncRNAS56464.1 could target the miR-152-3p/Wnt pathway to induce synovial cell proliferation and then participate in the pathogenesis of RA.

A new transcription factor ATG10S activates IFNL2 transcription by binding at an IRF1 site in HepG2 cells

IFNL2 is a potent antiviral interferon, but the regulation of its gene expression is not fully clear. Here, we report the regulation of ATG10S for IFNL2 transcription. Through sequential deletion of the IFNL2 promoter sequence, we found LP1-1, a fragment of the promoter responding to ATG10S activity. Subcellular localization and DNA immunoprecipitation assays showed ATG10S translocating into the nucleus and binding to LP1-1. Online prediction for transcription factor binding sites showed an IRF1 targeting locus in LP1-1. Luciferase assays, RT-PCR, and western blot analysis revealed a core motif (CAAGAC) existing in LP1-1, which determined ATG10S and IRF1 activity; individual nucleotide substitution showed that the functional nucleotides of ATG10S targeting were C1, A3, and C6, and the ones associated with IRF1 were A3 and G4 within the core motif. Co-immunoprecipitation assays revealed ATG10S combination with KPNA1/importin α, KPNB1/importin β, and IRF1. The knockdown of endogenous IRF1 increased ATG10S activity on IFNL2 transcription. These results indicate that ATG10S as a transcription factor competes with IRF1 for the same binding site to promote IFNL2 gene transcription. Abbreviations: ATG10: autophagy related 10; ATG10S: the shorter isoform of autophagy related 10; BD: binding domain; CM: core motif; co-IP: co-immunoprecipitation; GFP: green fluorescent protein; HCV: hepatitis C virus; IF: immunofluorescence; IFN: interferon; IRF: interferon regulatory factor; LP: lambda promoter; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; RLU: relative light unit; SQSTM1: sequestosome 1.

Pristane promotes anaerobic glycolysis to facilitate proinflammatory activation of macrophages and development of arthritis

Pristane-induced arthritis (PIA) could be adoptively transferred by splenic T cells in rats, and innate immunity should play critical roles in T cell activation. However, in pre-clinical stage, the activation mechanism of innate cells like macrophages remains unclear. Here we found that PIA was dependent on macrophages since cell depletion alleviated disease severity. Splenic macrophages of PIA rats showed M1 phenotypic shifting. The quantitative proteomics analysis suggested that macrophages initiated metabolic reprogramming with the conversion of aerobic oxidation to glycolysis in response to pristane in vivo. Notably, macrophages treated with pristane showed mitochondrial dysregulation and increased glycolysis flux and enzyme activity. Additionally, TNFα production, strongly associating with the glycolysis enzyme Ldha/Ldhb, could be reduced as glycolysis was inhibited or be enhanced as citrate cycle was blocked. This work provides detailed insights into the molecular mechanisms of pristane-mediated metabolic reprogramming in macrophages and suggests a new therapeutic strategy for arthritic disorders.

Intervening upregulated SLC7A5 could mitigate inflammatory mediator by mTOR-P70S6K signal in rheumatoid arthritis synoviocytes

Objective

The disruption of metabolic events and changes to nutrient and oxygen availability due to sustained inflammation in RA increases the demand of bioenergetic and biosynthetic processes within the damaged tissue. The current study aimed to understand the molecular mechanisms of SLC7A5 (amino acid transporter) in synoviocytes of RA patients.

Methods

Synovial tissues were obtained from OA and RA patients. Fibroblast-like synoviocytes (FLS) were isolated, and SLC7A5 expression was examined by using RT-qPCR, immunofluorescence, and Western blotting. RNAi and antibody blocking treatments were used to knockdown SLC7A5 expression or to block its transporter activities. mTOR activity assay and MMP expression levels were monitored in RA FLS under amino acid deprivation or nutrient-rich conditions.

Results

RA FLS displayed significantly upregulated expression of SLC7A5 compared to OA FLS. Cytokine IL-1β was found to play a crucial role in upregulating SLC7A5 expression via the NF-κB pathway. Intervening SLC7A5 expression with RNAi or blocking its function by monoclonal antibody ameliorated MMP3 and MMP13 protein expression. Conversely, upregulation of SLC7A5 or tryptophan supplementation enhanced mTOR-P70S6K signals which promoted the protein translation of MMP3 and MMP13 in RA FLS.

Conclusion

Activated NF-κB pathway upregulates SLC7A5, which enhances the mTOR-P70S6K activity and MMP3 and MMP13 expression in RA FLS.

Xenophagy in innate immunity: A battle between host and pathogen

Autophagy is a fundamental bulk intracellular degradation and recycling process that directly eliminates intracellular microorganisms through "xenophagy" in various types of cells, especially in macrophages. Meanwhile, bacteria have evolved strategies and cellular self-defense mechanisms to prevent autophagosomal degradation and even attack the immune system of host. The lack of knowledge about the roles of autophagy in innate immunity severely limits our understanding of host defensive system and the development of farmed industry consisting of aquaculture. Increasing evidence in recent decades has shown the importance of autophagy. This review focuses on the triggering of xenophagy, targeting of invading pathogens to autophagosomes and elimination in the autophagolysosomes during pathogen infection. How the pathogen can escape from the xenophagy pathway was also discussed. Overall, we aim to reduce diseases and improve industrial production in aquaculture by providing theoretical and technical guidance on xenophagy.

Upregulated PKM2 in Macrophages Exacerbates Experimental Arthritis via STAT1 Signaling

Recent studies indicate that glucose metabolism is altered in rheumatoid arthritis. We hypothesize that Pkm2, as a key regulatory enzyme of glycolysis pathway, triggers the activation of macrophages (Mφ), which results in proinflammatory cytokine production during the arthritis progress. In this study, Pkm2 was found to be overexpressed in ED1-positive Mφ in spleens and synovial tissues from arthritic rats via immunofluorescence, Western blotting, and quantitative RT-PCR. To reveal the role of Pkm2, Dark Agouti rats were treated with either Pkm2 enzyme inhibitor shikonin or the RNA interference plasmids of Pkm2 and negative control plasmids, respectively, via i.p. injection. Pkm2 intervention could alleviate the severity of pristane-induced arthritis in aspects of the macroscopic arthritis score, perimeter changes of midpaw, and the synovitis and destruction of the bone and cartilage as well as reduce the ED1 and p-Stat1-positive cell population in rat synovial tissues. Silencing Pkm2 by RNA interference in classical activated rat and mouse Mφ resulted in less Tnf-α, Il-1β production via Stat1 signaling. Collectively, Pkm2 is highly expressed in ED1-positive Mφ of spleens and synovial tissues from arthritic rats and promotes Mφ activation via Stat1 signaling. Pkm2 might be a promising selective metabolic target molecule for rheumatoid arthritis treatment.

IRF1 up-regulates isg15 gene expression in dsRNA stimulation or CSFV infection by targeting nucleotides -487 to -325 in the 5' flanking region

Interferon (IFN)-stimulated gene 15 (ISG15) encodes a ubiquitin-like protein that is heavily involved in immune response elicitation. As an important member of interferon regulatory factor (IRF) family, IRF1 can activate the expression of multiple genes, including the human optineurin gene (Sudhakar et al., 2013). In this study, a sequence in the promoter region of the optineurin gene was compared to the 5' flanking region of the porcine isg15 gene. Porcine IRF1 also possesses antiviral activity against several swine viruses (Li et al., 2015), but the mechanism is not well understood. Herein, we report that porcine IRF1 and ISG15 were up-regulated in porcine kidney (PK-15) cells following stimulation with double-stranded RNA (dsRNA) or classical swine fever virus (CSFV) infection. We also found that siRNA-mediated knockdown of IRF1 expression resulted in lower ISG15 expression in response to polyinosinic:polycytidylic acid [poly(I:C)] or CSFV infection. The overexpression of IRF1 resulted in ISG15 up-regulation. IRF1 was shown to translocate to the nucleus in response to dsRNA stimulation. To further identify the functional domain of the isg15 gene that promotes IRF1 transcriptional activity, firefly luciferase and ISG15 reporter systems were constructed. The results of the firefly luciferase and ISG15 reporter assay suggested that IRF1 mediates the up-regulation of ISG15. Nucleotides -487 to -325, located in the 5' flanking region of the isg15 gene, constituted the promoter region of IRF1. ChIP assay indicated that IRF1 protein was able to interact with the DNA in the 5'fr of isg15 gene in cells. As an innate immune response protein with broad-spectrum antiviral activity, the up-regulation of ISG15 mediated by IRF1 in porcine cells is reported for the first time. These results warrant further investigation into the antiviral activity of porcine IRF1 against reported swine viruses.

Increased expression of Th17 cytokines and interleukin-22 correlates with disease activity in pristane-induced arthritis in rats

The objective of this study was to identify the key changed subtype of T helper cells (Th cells) and their cytokines in pristane-induced arthritis (PIA) in rats. The severity of arthritis was evaluated by body weight, clinical score, the perimeter of ankle and mid-paw and histological assessment of ankle joints. Cytokines of Th1, Th2 and Th17 were determined in the spleen and inguinal lymph nodes at 28 days after pristane injection by real-time qPCR. The mRNA levels of IL-22 receptors, IL-22R1 and IL-22BP, in the spleen were quantified by real-time qPCR. Additionally, IL-22 expression in synovial membrane was detected by Western blotting, and serum IL-22 concentration was determined by ELISA. Correlation between IL-22 concentration and clinical score was analyzed. By screening the cytokines of Th1, Th2 and Th17 expression profile, we found that the mRNA levels of Th17 cytokines were significantly increased in PIA rats. Particularly, a significant increase in the protein expression of IL-22 was determined in synovial membrane and serum from PIA rats, and correlated with clinical score. We conclude that IL-22 expression level was increased and correlated with disease severity, which indicated that IL-22 may play an important role in development of PIA, and was helpful to explorer the pathogenesis of rheumatoid arthritis.