Myeloid-Specific Gene Deletion of Protein Phosphatase 2A Magnifies MyD88- and TRIF-Dependent Inflammation following Endotoxin Challenge

A novel on-a-chip system with a 3D-bioinspired gut mucus suitable to investigate bacterial endotoxins dynamics

The possible pathogenic impact of pro-inflammatory molecules produced by the gut microbiota is one of the hypotheses considered at the basis of the biomolecular dialogue governing the microbiota-gut-brain axis. Among these molecules, lipopolysaccharides (LPS) produced by Gram-negative gut microbiota strains may have a potential key role due to their toxic effects in both the gut and the brain. In this work, we engineered a new dynamic fluidic system, the MINERVA device (MI-device), with the potential to advance the current knowledge of the biological mechanisms regulating the microbiota-gut molecular crosstalk. The MI-device supported the growth of bacteria that are part of the intestinal microbiota under dynamic conditions within a 3D moving mucus model, with features comparable to the physiological conditions (storage modulus of 80 ± 19 Pa, network mesh size of 41 ± 3 nm), without affecting their viability (∼ 109 bacteria/mL). The integration of a fluidically optimized and user-friendly design with a bioinspired microenvironment enabled the sterile extraction and quantification of the LPS produced within the mucus by bacteria (from 423 ± 34 ng/mL to 1785 ± 91 ng/mL). Compatibility with commercially available Transwell-like inserts allows the user to precisely control the transport phenomena that occur between the two chambers by selecting the pore density of the insert membrane without changing the design of the system. The MI-device is able to provide the flow of sterile medium enriched with LPS directly produced by bacteria, opening up the possibility of studying the effects of bacteria-derived molecules on cells in depth, as well as the assessment and characterization of their effects in a physiological or pathological scenario.

The oncogenic human B-cell lymphoma MYD88 L265P mutation genocopies activation by phosphorylation at the Toll/interleukin-1 receptor (TIR) domain

MYD88 is the key signaling adaptor-protein for Toll-like and interleukin-1 receptors. A somatic L265P mutation within the Toll/interleukin-1 receptor (TIR) domain of MYD88 is found in 90% of Waldenström macroglobulinemia cases and in a significant subset of diffuse large B-cell lymphomas. MYD88-L265P strongly promotes NF-κB pathway activation, JAK-STAT signaling and lymphoma cell survival. Previous studies have identified other residues of the TIR-domain crucially involved in NF-κB activation, including serine 257 (S257), indicating a potentially important physiological role in the regulation of MYD88 activation. Here, we demonstrate that MYD88 S257 is phosphorylated in B-cell lymphoma cells and that this phosphorylation is required for optimal TLR-induced NF-κB activation. Furthermore, we demonstrate that a phosphomimetic MYD88-S257D mutant promotes MYD88 aggregation, IRAK1 phosphorylation, NF-κB activation and cell growth to a similar extent as the oncogenic L265P mutant. Lastly, we show that expression of MYD88-S257D can rescue cell growth upon silencing of endogenous MYD88-L265P expression in lymphoma cells addicted to oncogenic MYD88 signaling. Our data suggest that the L265P mutation promotes TIR domain homodimerization and NF-κB activation by copying the effect of MY88 phosphorylation at S257, thus providing novel insights into the molecular mechanism underlying the oncogenic activity of MYD88-L265P in B-cell malignancies.

PP2Ac/STRN4 negatively regulates STING-type I IFN signaling in tumor-associated macrophages

Stimulator of IFN genes type I (STING-Type I) IFN signaling in myeloid cells plays a critical role in effective antitumor immune responses, but STING agonists as monotherapy have shown limited efficacy in clinical trials. The mechanisms that downregulate STING signaling are not fully understood. Here, we report that protein phosphatase 2A (PP2A), with its specific B regulatory subunit Striatin 4 (STRN4), negatively regulated STING-Type I IFN in macrophages. Mice with macrophage PP2A deficiency exhibited reduced tumor progression. The tumor microenvironment showed decreased immunosuppressive and increased IFN-activated macrophages and CD8+ T cells. Mechanistically, we demonstrated that Hippo kinase MST1/2 was required for STING activation. STING agonists induced dissociation of PP2A from MST1/2 in normal macrophages, but not in tumor conditioned macrophages. Furthermore, our data showed that STRN4 mediated PP2A binding to and dephosphorylation of Hippo kinase MST1/2, resulting in stabilization of YAP/TAZ to antagonize STING activation. In human patients with glioblastoma (GBM), YAP/TAZ was highly expressed in tumor-associated macrophages but not in nontumor macrophages. We also demonstrated that PP2A/STRN4 deficiency in macrophages reduced YAP/TAZ expression and sensitized tumor-conditioned macrophages to STING stimulation. In summary, we demonstrated that PP2A/STRN4-YAP/TAZ has, in our opinion, been an unappreciated mechanism that mediates immunosuppression in tumor-associated macrophages, and targeting the PP2A/STRN4-YAP/TAZ axis can sensitize tumors to immunotherapy.

Protein phosphatase 2A regulates xanthine oxidase-derived ROS production in macrophages and influx of inflammatory monocytes in a murine gout model

Background: Gout is a common arthritis, due to deposition of monosodium urate (MSU) crystals which results in IL-1β secretion by tissue-resident macrophages. Xanthine oxidase (XO) catalyzes uric acid (UA) production and in the process, reactive oxygen species (ROS) are generated which contributes to NLRP3 inflammasome activation. Protein phosphatase 2A (PP2A) may be involved in regulating inflammatory pathways in macrophages. The objective of this study was to investigate whether PP2A regulates gout inflammation, mediated by XO activity modulation. We studied UA and ROS generations in MSU stimulated murine bone marrow derived macrophages (BMDMs) in response to fingolimod phosphate, a PP2A activator, and compared its anti-inflammatory efficacy to that of an XO inhibitor, febuxostat. Methods: BMDMs were stimulated with MSU, GM-CSF/IL-1β or nigericin ± fingolimod (2.5 μM) or febuxostat (200 μM) and UA levels, ROS, XO, and PP2A activities, Xdh (XO) expression and secreted IL-1β levels were determined. PP2A activity and IL-1β in MSU stimulated BMDMs ± N-acetylcysteine (NAC) (10 μM) ± okadaic acid (a PP2A inhibitor) were also determined. M1 polarization of BMDMs in response to MSU ± fingolimod treatment was assessed by a combination of iNOS expression and multiplex cytokine assay. The in vivo efficacy of fingolimod was assessed in a murine peritoneal model of acute gout where peritoneal lavages were studied for pro-inflammatory classical monocytes (CMs), anti-inflammatory nonclassical monocytes (NCMs) and neutrophils by flow cytometry and IL-1β by ELISA. Results: Fingolimod reduced intracellular and secreted UA levels (p < 0.05), Xdh expression (p < 0.001), XO activity (p < 0.001), ROS generation (p < 0.0001) and IL-1β secretion (p < 0.0001), whereas febuxostat enhanced PP2A activity (p < 0.05). NAC treatment enhanced PP2A activity and reduced XO activity and PP2A restoration mediated NAC's efficacy as co-treatment with okadaic acid increased IL-1β secretion (p < 0.05). Nigericin activated caspase-1 and reduced PP2A activity (p < 0.001) and fingolimod reduced caspase-1 activity in BMDMs (p < 0.001). Fingolimod reduced iNOS expression (p < 0.0001) and secretion of IL-6 and TNF-α (p < 0.05). Fingolimod reduced CMs (p < 0.0001), neutrophil (p < 0.001) and IL-1β (p < 0.05) lavage levels while increasing NCMs (p < 0.001). Conclusion: Macrophage PP2A is inactivated in acute gout by ROS and a PP2A activator exhibited a broad anti-inflammatory effect in acute gout in vitro and in vivo.

Protein Phosphatase 2A Improves Cardiac Functional Response to Ischemia and Sepsis

Reversible protein phosphorylation is a posttranslational modification of regulatory proteins involved in cardiac signaling pathways. Here, we focus on the role of protein phosphatase 2A (PP2A) for cardiac gene expression and stress response using a transgenic mouse model with cardiac myocyte-specific overexpression of the catalytic subunit of PP2A (PP2A-TG). Gene and protein expression were assessed under basal conditions by gene chip analysis and Western blotting. Some cardiac genes related to the cell metabolism and to protein phosphorylation such as kinases and phosphatases were altered in PP2A-TG compared to wild type mice (WT). As cardiac stressors, a lipopolysaccharide (LPS)-induced sepsis in vivo and a global cardiac ischemia in vitro (stop-flow isolated perfused heart model) were examined. Whereas the basal cardiac function was reduced in PP2A-TG as studied by echocardiography or as studied in the isolated work-performing heart, the acute LPS- or ischemia-induced cardiac dysfunction deteriorated less in PP2A-TG compared to WT. From the data, we conclude that increased PP2A activity may influence the acute stress tolerance of cardiac myocytes.

Recombinant Human Proteoglycan 4 Regulates Phagocytic Activation of Monocytes and Reduces IL-1β Secretion by Urate Crystal Stimulated Gout PBMCs

Objectives

To compare phagocytic activities of monocytes in peripheral blood mononuclear cells (PBMCs) from acute gout patients and normal subjects, examine monosodium urate monohydrate (MSU) crystal-induced IL-1β secretion ± recombinant human proteoglycan 4 (rhPRG4) or interleukin-1 receptor antagonist (IL-1RA), and study the anti-inflammatory mechanism of rhPRG4 in MSU stimulated monocytes.

Methods

Acute gout PBMCs were collected from patients in the Emergency Department and normal PBMCs were obtained from a commercial source. Monocytes in PBMCs were identified by flow cytometry. PBMCs were primed with Pam3CSK4 (1μg/mL) for 24h and phagocytic activation of monocytes was determined using fluorescently labeled latex beads. MSU (200μg/mL) stimulated IL-1β secretion was determined by ELISA. Reactive oxygen species (ROS) generation in monocytes was determined fluorometrically. PBMCs were incubated with IL-1RA (250ng/mL) or rhPRG4 (200μg/mL) and bead phagocytosis by monocytes was determined. THP-1 monocytes were treated with MSU crystals ± rhPRG4 and cellular levels of NLRP3 protein, pro-IL-1β, secreted IL-1β, and activities of caspase-1 and protein phosphatase-2A (PP2A) were quantified. The peritoneal influx of inflammatory and anti-inflammatory monocytes and neutrophils in Prg4 deficient mice was studied and the impact of rhPRG4 on immune cell trafficking was assessed.

Results

Enhanced phagocytic activation of gout monocytes under basal conditions (p<0.001) was associated with ROS generation and MSU stimulated IL-1β secretion (p<0.05). rhPRG4 reduced bead phagocytosis by normal and gout monocytes compared to IL-1RA and both treatments were efficacious in reducing IL-1β secretion (p<0.05). rhPRG4 reduced pro-IL-1β content, caspase-1 activity, conversion of pro-IL-1β to mature IL-1β and restored PP2A activity in monocytes (p<0.05). PP2A inhibition reversed rhPRG4’s effects on pro-IL-1β and mature IL-1β in MSU stimulated monocytes. Neutrophils accumulated in peritoneal cavities of Prg4 deficient mice (p<0.01) and rhPRG4 treatment reduced neutrophil accumulation and enhanced anti-inflammatory monocyte influx (p<0.05).

Conclusions

MSU phagocytosis was higher in gout monocytes resulting in higher ROS and IL-1β secretion. rhPRG4 reduced monocyte phagocytic activation to a greater extent than IL-1RA and reduced IL-1β secretion. The anti-inflammatory activity of rhPRG4 in monocytes is partially mediated by PP2A, and in vivo, PRG4 plays a role in regulating the trafficking of immune cells into the site of a gout flare.

PP2A-mTOR-p70S6K/4E-BP1 axis regulates M1 polarization of pulmonary macrophages and promotes ambient particulate matter induced mouse lung injury

To identify key signaling pathways involved in ambient particulate matter (PM)-induced pulmonary injury, we generated a mouse model with myeloid-specific deletion of Ppp2r1a gene (encoding protein phosphatase 2 A (PP2A) A subunit), and conducted experiments in a real-ambient PM exposure system. PP2A Aα^-/- homozygote (Aα HO) mice and matched wild-type (WT) littermates were exposed to PM over 3-week and 6-week. The effects of PM exposure on pulmonary inflammation, oxidative stress, and apoptosis were significantly enhanced in Aα HO compared to WT mice. The number of pulmonary macrophages increased by 74.8~88.0% and enhanced M1 polarization appeared in Aα HO mice upon PM exposure. Secretion of M1 macrophage-related inflammatory cytokines was significantly increased in Aα HO vs. WT mice following PM exposure. Moreover, we demonstrated that PP2A-B56α holoenzyme regulated M1 polarization and that the mTOR signaling pathway mediated the persistent M1 polarization upon PM2.5 exposure. Importantly, PP2A-B56α holoenzyme was shown to complex with mTOR/p70S6K/4E-BP1, and suppression of B56α led to enhanced phosphorylation of mTOR, p70S6K, and 4E-BP1. These observations demonstrate that the PP2A-mTOR-p70S6K/4E-BP1 signaling is a critical pathway in mediating macrophage M1 polarization, which contributes to PM-induced pulmonary injury.

Increased Ingestion of Hydroxy-Methionine by Both Sows and Piglets Improves the Ability of the Progeny to Counteract LPS-Induced Hepatic and Splenic Injury with Potential Regulation of TLR4 and NOD Signaling

Methionine, as an essential amino acid, play roles in antioxidant defense and the regulation of immune responses. This study was designed to determine the effects and mechanisms of increased consumption of methionine by sows and piglets on the capacity of the progeny to counteract lipopolysaccharide (LPS) challenge-induced injury in the liver and spleen of piglets. Primiparous sows (n = 10/diet) and their progeny were fed a diet that was adequate in sulfur amino acids (CON) or CON + 25% total sulfur amino acids as methionine from gestation day 85 to postnatal day 35. A total of ten male piglets were selected from each treatment and divided into 2 groups (n = 5/treatment) for a 2 × 2 factorial design [diets (CON, Methionine) and challenge (saline or LPS)] at 35 d old. After 24 h challenge, the piglets were euthanized to collect the liver and spleen for the histopathology, redox status, and gene expression analysis. The histopathological results showed that LPS challenge induced liver and spleen injury, while dietary methionine supplementation alleviated these damages that were induced by the LPS challenge. Furthermore, the LPS challenge also decreased the activities of GPX, SOD, and CAT and upregulated the mRNA and(or) protein expression of TLR4, MyD88, TRAF6, NOD1, NOD2, NF-kB, TNF-α, IL-8, p53, BCL2, and COX2 in the liver and (or) spleen. The alterations of GPX and SOD activities and the former nine genes were prevented or alleviated by the methionine supplementation. In conclusion, the maternal and neonatal dietary supplementation of methionine improved the ability of piglets to resist LPS challenge-induced liver and spleen injury, potentially through the increased antioxidant capacity and inhibition of TLR4 and NOD signaling pathway.

Cytoplasmic zinc promotes IL-1β production by monocytes and macrophages through mTORC1-induced glycolysis in rheumatoid arthritis

[Figure: see text].

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.

Protein phosphatases in TLR signaling

Toll-like receptors (TLRs) are critical sensors for the detection of potentially harmful microbes. They are instrumental in initiating innate and adaptive immune responses against pathogenic organisms. However, exaggerated activation of TLR receptor signaling can also be responsible for the onset of autoimmune and inflammatory diseases. While positive regulators of TLR signaling, such as protein serine/threonine kinases, have been studied intensively, only little is known about phosphatases, which counterbalance and limit TLR signaling. In this review, we summarize protein phosphorylation events and their roles in the TLR pathway and highlight the involvement of protein phosphatases as negative regulators at specific steps along the TLR-initiated signaling cascade. Then, we focus on individual phosphatase families, specify the function of individual enzymes in TLR signaling in more detail and give perspectives for future research. A better understanding of phosphatase-mediated regulation of TLR signaling could provide novel access points to mitigate excessive immune activation and to modulate innate immune signaling.

CqPP2A inhibits white spot syndrome virus infection by up-regulating antimicrobial substances expression in red claw crayfish Cherax quadricarinatus

Protein phosphatase 2A (PP2A) is an important serine/threonine phosphatase, a highly conserved enzyme widely expressed in eukaryotic cells, which accounts for a majority of the serine/threonine phosphatase activity in cells implicated in regulation of immune signaling pathways and antiviral response. However, most of studies about PP2A have been conducted in mammals but few in crustaceans. In this study, two subunits of PP2A (named as CqPP2Ab and CqPP2Ac) were characterized to be involved in white spot syndrome virus (WSSV) infection in the haematopoietic tissue (Hpt) cells from red claw crayfish Cherax quadricarinatus. The open reading frame (ORF) of CqPP2Ab was 1341 bp encoding 446 amino acids with seven WD40 domains, and the ORF of CqPP2Ac was 930 bp encoding 309 amino acids with a PP2Ac domain. Tissue distribution analysis showed that the mRNA transcript of CqPP2Ab and CqPP2Ac were both widely expressed in all the tested tissues with the highest expression in hemocyte, followed by high expression in Hpt. The gene expressions of CqPP2Ab and CqPP2Ac were both significantly down-regulated at 6 h post WSSV infection (6 hpi) in Hpt cells. Importantly, the expression of viral immediate early gene IE1 and late viral gene envelope protein VP28 were both significantly increased post WSSV infection after gene silencing of CqPP2Ab or CqPP2Ac in Hpt cells, suggesting that CqPP2Ab and CqPP2Ac could inhibit WSSV infection in Hpt cells, probably by increasing the antimicrobial substances expression in consideration to the significantly reduced expression of anti-lipopolysaccharide factor, crustin, and lysozyme after gene silencing of CqPP2Ab or CqPP2Ac, respectively. These findings provide a new light on the mechanism of WSSV infection and the antiviral response in crustaceans.

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.

Fingolimod Phosphate (FTY720-P) Activates Protein Phosphatase 2A in Human Monocytes and Inhibits Monosodium Urate Crystal-Induced Interleukin-1β Production

Gout is a chronic inflammatory arthritis caused by monosodium urate monohydrate (MSU) crystal deposits in joints of lower limbs. Phagocytic uptake of MSU crystals by joint-resident macrophages and recruited circulating monocytes results in IL-1β expression and production. Current acute gout treatments have serious toxicities and suffer suboptimal clinical outcomes. Protein phosphatase 2A (PP2A) plays an important role in regulating signaling pathways relevant to inflammation. We hypothesized that innate immune danger signals, e.g., lipopolysaccharide (LPS) and soluble uric acid (sUA), prime human monocytes toward MSU crystal phagocytosis and that increased IL-1β production mediated by a reduction in PP2A activity and restoring PP2A activity exerts an anti-inflammatory effect in this setting. Priming monocytes with LPS + sUA increased cytosolic pro-IL-1β and mature IL-1β and enhanced MSU crystal phagocytosis and its downstream IL-1β expression (P < 0.001). A combination of LPS + sUA priming and MSU crystals reduced PP2A activity in monocytes by 60% (P = 0.013). PP2A catalytic subunit gene knockdown reduced PP2A activity and exacerbated MSU crystal-induced IL-1β expression and secretion (P < 0.0001). Fingolimod (FTY720) and its active metabolite, fingolimod phosphate (FTY720-P), were evaluated for their ability to activate PP2A in human monocytes over 24 hours. FTY720 and FTY720-P activated PP2A to a similar extent, and maximal enzyme activity occurred at 24 hours for FTY720 and at 6 hours for FTY720-P. FTY720-P (2.5 μM) reduced pro-IL-1β production and IL-1β secretion in primed and MSU crystal-stimulated monocytes (P < 0.0001) without changing the magnitude of crystal phagocytosis. We conclude that PP2A is a promising new target in acute gout. SIGNIFICANCE STATEMENT: The activity of protein phosphatase 2A (PP2A) is implicated in the enhanced expression and production of IL-1β by human monocytes in response to priming with soluble uric acid and lipopolysaccharide and phagocytosis of monosodium urate monohydrate (MSU) crystals. Fingolimod phosphate activates PP2A in human monocytes and reduces cytosolic pro-IL-1β content and its conversion to biologically active IL-1β in human monocytes exposed to MSU crystals.

Mouse 4T1 Breast Cancer Cell-Derived Exosomes Induce Proinflammatory Cytokine Production in Macrophages via miR-183

Tumor-associated macrophages (TAMs) play a critical role in the tumor inflammatory microenvironment and facilitate tumor growth and metastasis. Most types of tumors aberrantly express microRNAs (miRNAs), which can be transferred between cells by exosomes and can regulate gene expression in recipient cells, but it remains unclear whether tumor-derived miRNAs are transferred by exosomes and regulate the TAM phenotype. We report that mouse 4T1 breast cancer cell-derived exosomes enhanced TAM expression of IL-1β, IL-6, and TNF-α and that inhibition of 4T1-cell exosome secretion through short hairpin RNA-mediated Rab27a/b depletion repressed tumor growth and metastasis and markedly downregulated IL-1β, IL-6, and TNF-α in a 4T1 breast tumor model. Furthermore, miRNA expression profiling revealed that three miRNAs (miR-100-5p, miR-183-5p, and miR-125b-1-3p) were considerably more abundant in 4T1 cell exosomes than in mouse bone marrow-derived macrophages, indicating potential exosome-mediated transfer of the miRNAs, and, notably, miR-183-5p was found to be transferred from 4T1 cells to macrophages through exosomes. Moreover, PPP2CA was verified as an miR-183-5p target gene, and PPP2CA downregulation enhanced NF-κB signaling and promoted macrophage expression of IL-1β, IL-6, and TNF-α. Lastly, when miR-183-5p was downregulated in exosomes through miR-183-5p sponge expression in 4T1 cells, these 4T1-derived exosomes triggered diminished p65 phosphorylation and IL-1β, IL-6, and TNF-α secretion, and the miRNA downregulation also led to repression of tumor growth and metastasis in the 4T1 breast tumor model in vivo. Thus, miR-183-5p expressed in tumor cells was transferred to macrophages by exosomes and promoted the secretion of proinflammatory cytokines by inhibiting PPP2CA expression, which contributed to tumor progression in a breast cancer model.

Lactobacillus salivarius alleviates inflammation via NF-κB signaling in ETEC K88-induced IPEC-J2 cells

Background

Enterotoxigenic Escherichia coli (ETEC) K88 commonly colonize in the small intestine and keep releasing enterotoxins to impair the intestinal barrier function and trigger inflammatory reaction. Although Lactobacillus salivarius (L. salivarius) has been reported to enhance intestinal health, it remains to be seen whether there is a functional role of L. salivarius in intestinal inflammatory response in intestinal porcine epithelial cell line (IPEC-J2) when stimulated with ETEC K88. In the present study, IPEC-J2 cells were first treated with L. salivarius followed by the stimulation of ETEC K88 for distinct time period. ETEC K88 adherent status, pattern recognition receptors (PRRs) mRNA, mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) activation, the release of pro-inflammation cytokines and cell integrity were examined.

Results

Aside from an inhibited adhesion of ETEC K88 to IPEC-J2 cells, L. salivarius was capable of remarkably attenuating the expression levels of interleukin (IL)-1β, tumor necrosis factor-α (TNF-α), IL-8, Toll-like receptor (TLR) 4, nucleotide-binding oligomerization domain (NOD)-like receptor pyrin domain-containing protein (NLRP) 3 and NLRP6. This alternation was accompanied by a significantly decreased phosphorylation of p38 MAPK and p65 NF-κB during ETEC K88 infection with L. salivarius pretreatment. Western blot analysis revealed that L. salivarius increased the expression levels of zona occludens 1 (ZO-1) and occludin (P < 0.05) in ETEC K88-infected IPEC-J2 cells. Compared with ETEC K88-infected groups, the addition of L. salivarius as well as extra inhibitors for MAPKs and NF-κB to ETEC K88-infected IPEC-J2 cells had the capability to reduce pro-inflammatory cytokines.

Conclusions

Collectively, our results suggest that L. salivarius might reduce inflammation-related cytokines through attenuating phosphorylation of p38 MAPK and blocking the NF-κB signaling pathways. Besides, L. salivarius displayed a potency in the enhancement of IPEC-J2 cell integrity.

Experimental Control of Macrophage Pro-Inflammatory Dynamics Using Predictive Models

Macrophage activity is a major component of the healthy response to infection and injury that consists of tightly regulated early pro-inflammatory activation followed by anti-inflammatory and regenerative activity. In numerous diseases, however, macrophage polarization becomes dysregulated and can not only impair recovery, but can promote further injury and pathogenesis, e.g., after trauma or in diabetic ulcers. Dysregulated macrophages may either fail to polarize or become chronically polarized, resulting in increased production of cytotoxic factors, diminished capacity to clear pathogens, or failure to promote tissue regeneration. In these cases, a method of predicting and dynamically controlling macrophage polarization will enable a new strategy for treating diverse inflammatory diseases. In this work, we developed a model-predictive control framework to temporally regulate macrophage polarization. Using RAW 264.7 macrophages as a model system, we enabled temporal control by identifying transfer function models relating the polarization marker iNOS to exogenous pro- and anti-inflammatory stimuli. These stimuli-to-iNOS response models were identified using linear autoregressive with exogenous input terms (ARX) equations and were coupled with non-linear elements to account for experimentally identified supra-additive and hysteretic effects. Using this model architecture, we were able to reproduce experimentally observed temporal iNOS dynamics induced by lipopolysaccharides (LPS) and interferon gamma (IFN-γ). Moreover, the identified model enabled the design of time-varying input trajectories to experimentally sustain the duration and magnitude of iNOS expression. By designing transfer function models with the intent to predict cell behavior, we were able to predict and experimentally obtain temporal regulation of iNOS expression using LPS and IFN-γ from both naïve and non-naïve initial states. Moreover, our data driven models revealed decaying magnitude of iNOS response to LPS stimulation over time that could be recovered using combined treatment with both LPS and IFN-γ. Given the importance of dynamic tissue macrophage polarization and overall inflammatory regulation to a broad number of diseases, the temporal control methodology presented here will have numerous applications for regulating immune activity dynamics in chronic inflammatory diseases.

Inhibition of protein phosphatase-2A with LB-100 enhances antitumor immunity against glioblastoma

PURPOSE

Glioblastoma (GBM) carries a dismal prognosis despite standard multimodal treatment with surgery, chemotherapy and radiation. Immune checkpoint inhibitors, such as PD1 blockade, for treatment of GBM failed to show clinical benefit. Rational combination strategies to overcome resistance of GBM to checkpoint monotherapy are needed to extend the promise of immunotherapy to GBM management. Emerging evidence suggests that protein phosphatase 2A (PP2A) plays a critical role in the signal transduction pathways of both adaptive and innate immune cells and that inhibition of PP2A could enhance cancer immunity. We investigated the use of a PP2A inhibitor, LB-100, to enhance antitumor efficacy of PD1 blockade in a syngeneic glioma model.

METHODS

C57BL/6 mice were implanted with murine glioma cell line GL261-luc or GL261-WT and randomized into 4 treatment arms: (i) control, (ii) LB-100, (iii) PD1 blockade and (iv) combination. Survival was assessed and detailed profiling of tumor infiltrating leukocytes was performed.

RESULTS

Dual PP2A and PD1 blockade significantly improved survival compared with monotherapy alone. Combination therapy resulted in complete regression of tumors in about 25% of mice. This effect was dependent on CD4 and CD8 T cells and cured mice established antigen-specific secondary protective immunity. Analysis of tumor lymphocytes demonstrated enhanced CD8 infiltration and effector function.

CONCLUSION

This is the first preclinical investigation of the effect of combining PP2A inhibition with PD1 blockade for GBM. This novel combination provided effective tumor immunotherapy and long-term survival in our animal GBM model.

CD44 Receptor Mediates Urate Crystal Phagocytosis by Macrophages and Regulates Inflammation in A Murine Peritoneal Model of Acute Gout

Gout is a chronic arthritis caused by the deposition of poorly soluble monosodium urate monohydrate (MSU) crystals in peripheral joints. Resident macrophages initiate inflammation in response to MSU mediated by NF-κB nuclear translocation and NLRP3 inflammasome activation. We investigated the role of CD44, a transmembrane receptor, in mediating MSU phagocytosis by macrophages. We used an antibody that sheds the extracellular domain (ECD) of CD44 to study the role of the receptor and its associated protein phosphatase 2A (PP2A) in macrophage activation. We also studied the significance of CD44 in mediating MSU inflammation in-vivo. Cd44^−/− BMDMs showed reduced MSU phagocytosis, LDH release, IL-1β expression and production compared to Cd44^+/+ BMDMs. Elevated CD44 staining was detected intracellularly and CD44 colocalized with α-tubulin as a result of MSU exposure and ECD-shedding reduced MSU phagocytosis in murine and human macrophages. Anti-CD44 antibody treatment reduced NF-κB p65 subunit nuclear levels, IL-1β expression, pro-IL-1β and IL-8 production in MSU stimulated THP-1 macrophages (p < 0.01). The effect of the antibody was mediated by an enhancement in PP2A activity. CD44 ECD-shedding reduced the conversion of procaspase-1 to active caspase-1, caspase-1 activity and resultant generation of mature IL-1β in macrophages. Neutrophil and monocyte influx and upregulated production of IL-1β was evident in wildtype mice. MSU failed to trigger neutrophil and monocyte recruitment in Cd44^−/− mice and lower IL-1β levels were detected in peritoneal lavages from Cd44^−/− mice (p < 0.01). Anti-CD44 antibody treatment reduced neutrophil and monocyte recruitment and resulted in reduced lavage IL-1β levels in the same model. CD44 plays a biologically significant role in mediating phagocytosis of MSU and downstream inflammation and is a novel target in gout treatment.

PP2ACα of Alveolar Macrophages Is a Novel Protective Factor for LPS-Induced Acute Respiratory Distress Syndrome

Protein phosphatase 2A (PP2A) is one main serine/threonine phosphatase in eukaryotes, and its activation changes have been linked to modulation of numerous pathological processes, such as cancer, inflammation, fibrosis, and neurodegenerative diseases. Acute respiratory distress syndrome (ARDS), the major cause of respiratory failure, remains with limited therapies available up to now. Alveolar macrophages (AMs) are essential to innate immunity and host defense, participating in the pathogenesis of ARDS. As a result, AMs are considered as a potential therapeutic target for ARDS. In our study, we firstly found that PP2A activity was significantly decreased in the lipopolysaccharide (LPS)-stimulated AMs. Furthermore, adoptive transfer of AMs with enhanced PP2A enzyme activity that was improved by C2-ceramide prior to LPS exposure alleviated acute lung inflammation. Conversely, AM-specific ablation of PP2ACα exacerbated inflammatory responses to LPS. Mechanistically, PP2ACα negatively regulates LPS-induced cytokine secretion of AMs by NF-κB and MAPK pathways. Together, these findings provide the evidence to guide the development of novel therapeutic options targeting PP2ACα for ARDS/acute lung injury.

Protein phosphatase 2A as a therapeutic target in inflammation and neurodegeneration

Protein phosphatase 2A (PP2A) is a highly complex heterotrimeric enzyme that catalyzes the selective removal of phosphate groups from protein serine and threonine residues. Emerging evidence suggests that it functions as a tumor suppressor by constraining phosphorylation-dependent signalling pathways that regulate cellular transformation and metastasis. Therefore, PP2A-activating drugs (PADs) are being actively sought and investigated as potential novel anti-cancer treatments. Here we explore the concept that PP2A also constrains inflammatory responses through its inhibitory effects on various signalling pathways, suggesting that PADs may be effective in the treatment of inflammation-mediated pathologies.

Loss of myeloid-specific protein phosphatase 2A enhances lung injury and fibrosis and results in IL-10-dependent sensitization of epithelial cell apoptosis

Protein phosphatase 2A (PP2A), a ubiquitously expressed Ser/Thr phosphatase is an important regulator of cytokine signaling and cell function. We previously showed that myeloid-specific deletion of PP2A (LysM^crePP2A^-/-) increased mortality in a murine peritoneal sepsis model. In the current study, we assessed the role of myeloid PP2A in regulation of lung injury induced by lipopolysaccharide (LPS) or bleomycin delivered intratracheally. LysM^crePP2A^-/- mice experienced increased lung injury in response to both LPS and bleomycin. LysM^crePP2A^-/- mice developed more exuberant fibrosis in response to bleomycin, elevated cytokine responses, and chronic myeloid inflammation. Bone marrow-derived macrophages (BMDMs) from LysM^crePP2A^-/- mice showed exaggerated inflammatory cytokine release under conditions of both M1 and M2 activation. Notably, secretion of IL-10 was elevated under all stimulation conditions, including activation of BMDMs by multiple Toll-like receptor ligands. Supernatants collected from LPS-stimulated LysM^crePP2A^-/- BMDMs induced epithelial cell apoptosis in vitro but this effect was mitigated when IL-10 was also depleted from the BMDMs by crossing LysM^crePP2A^-/- mice with systemic IL-10^-/- mice (LysM^crePP2A^-/- × IL-10^-/-) or when IL-10 was neutralized. Despite these findings, IL-10 did not directly induce epithelial cell apoptosis but sensitized epithelial cells to other mediators from the BMDMs. Taken together our results demonstrate that myeloid PP2A regulates production of multiple cytokines but that its effect is most pronounced on IL-10 production. Furthermore, IL-10 sensitizes epithelial cells to apoptosis in response to myeloid-derived mediators, which likely contributes to the pathogenesis of lung injury and fibrosis in this model.

TRIF Regulates BIC/miR-155 via the ERK Signaling Pathway to Control the ox-LDL-Induced Macrophage Inflammatory Response

Toll/IL-1R-domain-containing adaptor-inducing IFN-β (TRIF) is an important adaptor for TLR3- and TLR4-mediated inflammatory signaling pathways. Recent studies have shown that TRIF plays a key role in vessel inflammation and atherosclerosis; however, the precise mechanisms are unclear. We investigated the mechanisms of the TRIF-regulated inflammatory response in RAW264.7 macrophages under oxidized low-density lipoprotein (ox-LDL) stimulation. Our data show that ox-LDL induces TRIF, miR-155, and BIC expression, activates the ERK_1/2 and SOCS1-STAT3-NF-κB signaling pathways, and elevates the levels of IL-6 and TNF-α in RAW264.7 cells. Knockdown of TRIF using TRIF siRNA suppressed BIC, miR-155, IL-6, and TNF-α expression and inhibited the ERK_1/2 and SOCS1-STAT3-NF-κB signaling pathways. Inhibition of ERK_1/2 signaling also suppressed BIC and miR-155 expression. These findings suggest that TRIF plays an important role in regulating the ox-LDL-induced macrophage inflammatory response and that TRIF modulates the expression of BIC/miR-155 and the downstream SOCS1-STAT3-NF-κB signaling pathway via ERK_1/2. Therefore, TRIF might be a novel therapeutic target for atherosclerosis.