Interferon gamma-induced gene expression of the novel secretory phospholipase A2 type IID in human monocyte-derived macrophages is inhibited by lipopolysaccharide

High purity of human secreted phospholipase A2 group IIE in Pichia pastoris using basal salts medium comparison with YPD medium

Secreted phospholipase A2s (sPLA2s) are a group of enzymes with 6-8 disulfide bonds that participate in numerous physiological processes by catalyzing the hydrolysis of phospholipids at the sn-2 position. Due to their high content of disulfide bonds and hydrolytic activity toward cell membranes, obtaining the protein of sPLA2s in the soluble and active form is challenging, which hampers their functional study. In this study, one member of recombinant human sPLA2s, tag-free group IIE (GIIE), was expressed in Pichia pastoris. The protein GIIE was purified from the crude culture supernatant by a two-step chromatography procedure, a combination of cation exchange and size-exclusion chromatography. In the shake flask fermentation, Protein of GIIE with higher purity was successfully obtained, using basal salts medium (BSM) instead of YPD medium. In the large-scale fermentation, each liter of BSM produced a final yield of 1.2 mg pure protein GIIE. This protocol will facilitate further research of GIIE and provide references for the production of other sPLA2 members.

Proteomic profiling of MIS-C patients indicates heterogeneity relating to interferon gamma dysregulation and vascular endothelial dysfunction

Multi-system Inflammatory Syndrome in Children (MIS-C) is a major complication of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection in pediatric patients. Weeks after an often mild or asymptomatic initial infection with SARS-CoV-2 children may present with a severe shock-like picture and marked inflammation. Children with MIS-C present with varying degrees of cardiovascular and hyperinflammatory symptoms. Here we perform a comprehensive analysis of the plasma proteome of more than 1400 proteins in children with SARS-CoV-2. We hypothesize that the proteome would reflect heterogeneity in hyperinflammation and vascular injury, and further identify pathogenic mediators of disease. We show that protein signatures demonstrate overlap between MIS-C, and the inflammatory syndromes macrophage activation syndrome (MAS) and thrombotic microangiopathy (TMA). We demonstrate that PLA2G2A is an important marker of MIS-C that associates with TMA. We find that IFNγ responses are dysregulated in MIS-C patients, and that IFNγ levels delineate clinical heterogeneity.

Proteomic Profiling of MIS-C Patients Reveals Heterogeneity Relating to Interferon Gamma Dysregulation and Vascular Endothelial Dysfunction

Multi-system Inflammatory Syndrome in Children (MIS-C) is a major complication of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic in pediatric patients. Weeks after an often mild or asymptomatic initial infection with SARS-CoV-2 children may present with a severe shock-like picture and marked inflammation. Children with MIS-C present with varying degrees of cardiovascular and hyperinflammatory symptoms. We performed a comprehensive analysis of the plasma proteome of more than 1400 proteins in children with SARS-CoV-2. We hypothesized that the proteome would reflect heterogeneity in hyperinflammation and vascular injury, and further identify pathogenic mediators of disease. Protein signatures demonstrated overlap between MIS-C, and the inflammatory syndromes macrophage activation syndrome (MAS) and thrombotic microangiopathy (TMA). We demonstrate that PLA2G2A is a key marker of MIS-C that associates with TMA. We found that IFNγ responses are dysregulated in MIS-C patients, and that IFNγ levels delineate clinical heterogeneity.

Group IID, IIE, IIF and III secreted phospholipase A2s

Among the 11 members of the secreted phospholipase A₂ (sPLA₂) family, group IID, IIE, IIF and III sPLA₂s (sPLA₂-IID, -IIE, -IIF and -III, respectively) are “new” isoforms in the history of sPLA₂ research. Relative to the better characterized sPLA₂s (sPLA₂-IB, -IIA, -V and -X), the enzymatic properties, distributions, and functions of these “new” sPLA₂s have remained obscure until recently. Our current studies using knockout and transgenic mice for a nearly full set of sPLA₂s, in combination with comprehensive lipidomics, have revealed unique and distinct roles of these “new” sPLA₂s in specific biological events. Thus, sPLA₂-IID is involved in immune suppression, sPLA₂-IIE in metabolic regulation and hair follicle homeostasis, sPLA₂-IIF in epidermal hyperplasia, and sPLA₂-III in male reproduction, anaphylaxis, colonic diseases, and possibly atherosclerosis. In this article, we overview current understanding of the properties and functions of these sPLA₂s and their underlying lipid pathways in vivo.

Transcriptional profiling provides insights into metronomic cyclophosphamide-activated, innate immune-dependent regression of brain tumor xenografts

Background

Cyclophosphamide treatment on a six-day repeating metronomic schedule induces a dramatic, innate immune cell-dependent regression of implanted gliomas. However, little is known about the underlying mechanisms whereby metronomic cyclophosphamide induces innate immune cell mobilization and recruitment, or about the role of DNA damage and cell stress response pathways in eliciting the immune responses linked to tumor regression.

Methods

Untreated and metronomic cyclophosphamide-treated human U251 glioblastoma xenografts were analyzed on human microarrays at two treatment time points to identify responsive tumor cell-specific factors and their upstream regulators. Mouse microarray analysis across two glioma models (human U251, rat 9L) was used to identify host factors and gene networks that contribute to the observed immune and tumor regression responses.

Results

Metronomic cyclophosphamide increased expression of tumor cell-derived DNA damage, cell stress, and cell death genes, which may facilitate innate immune activation. Increased expression of many host (mouse) immune networks was also seen in both tumor models, including complement components, toll-like receptors, interferons, and cytolysis pathways. Key upstream regulators activated by metronomic cyclophosphamide include members of the interferon, toll-like receptor, inflammatory response, and PPAR signaling pathways, whose activation may contribute to anti-tumor immunity. Many upstream regulators inhibited by metronomic cyclophosphamide, including hypoxia-inducible factors and MAP kinases, have glioma-promoting activity; their inhibition may contribute to the therapeutic effectiveness of the six-day repeating metronomic cyclophosphamide schedule.

Conclusions

Large numbers of responsive cytokines, chemokines and immune regulatory genes linked to innate immune cell recruitment and tumor regression were identified, as were several immunosuppressive factors that may contribute to the observed escape of some tumors from metronomic CPA-induced, immune-based regression. These factors may include useful biomarkers that facilitate discovery of clinically effective immunogenic metronomic drugs and treatment schedules, and the selection of patients most likely to be responsive to immunogenic drug scheduling.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1358-y) contains supplementary material, which is available to authorized users.

Nonbactericidal secreted phospholipase A2s are potential anti-inflammatory factors in the mammary gland

The recent burst of duplication and divergence of the bovine PLA2G2D genes is considered typical of immune response genes, and it was recently shown that PLA2G2D is abundantly expressed in mouse leukocytes and acts as an immunosuppressive phospholipase. Analysis of 1,143 Holstein bulls indicated that the four common haplotypes spanning PLA2G2D display copy number variation ranging from 1 to 4 per haploid genome. Association of the fourth haplotype with negative total merit remained significant (P < 0.002) when corrected for population relatedness. We compared the lipase and bactericidal activities of bovine pancreatic PLA2G1B with human PLA2G2A and G2D and bovine PLA2G2D1 and G2D4 proteins, which had been subcloned, expressed, and refolded by us, and the impact of point mutations in the calcium binding site was investigated. All tested phospholipases were ineffective bactericides of Escherichia coli isolated from bovine mastitis. However, in lactating mice treated with E. coli or lipopolysaccharide (LPS), intramammary injection of bovine PLA2G1B relieved visual and histological inflammation and reduced blood levels of infiltrating lactose. Further studies are warranted to determine whether the observed anti-inflammatory effect involves competitive binding of the receptor Pla2r1 which may mimic the LPS resistance effect in Pla2r1-deficient mice.

Lymphoid tissue phospholipase A2 group IID resolves contact hypersensitivity by driving antiinflammatory lipid mediators

PLA2G2D ameliorates skin inflammation through mobilizing pro-resolving lipid mediators.

Resolution of inflammation is an active process that is mediated in part by antiinflammatory lipid mediators. Although phospholipase A₂ (PLA₂) enzymes have been implicated in the promotion of inflammation through mobilizing lipid mediators, the molecular entity of PLA₂ subtypes acting upstream of antiinflammatory lipid mediators remains unknown. Herein, we show that secreted PLA₂ group IID (PLA2G2D) is preferentially expressed in CD11c⁺ dendritic cells (DCs) and macrophages and displays a pro-resolving function. In hapten-induced contact dermatitis, resolution, not propagation, of inflammation was compromised in skin and LNs of PLA2G2D-deficient mice (Pla2g2d^−/−), in which the immune balance was shifted toward a proinflammatory state over an antiinflammatory state. Bone marrow-derived DCs from Pla2g2d^−/− mice were hyperactivated and elicited skin inflammation after intravenous transfer into mice. Lipidomics analysis revealed that PLA2G2D in the LNs contributed to mobilization of a pool of polyunsaturated fatty acids that could serve as precursors for antiinflammatory/pro-resolving lipid mediators such as resolvin D1 and 15-deoxy-Δ^12,14-prostaglandin J₂, which reduced Th1 cytokine production and surface MHC class II expression in LN cells or DCs. Altogether, our results highlight PLA2G2D as a “resolving sPLA₂” that ameliorates inflammation through mobilizing pro-resolving lipid mediators and points to a potential use of this enzyme for treatment of inflammatory disorders.

Role of macrophage activation in the lipid metabolism of postprandial triacylglycerol-rich lipoproteins

The potential link between the inflammatory effects of postprandial lipemia and the induction of macrophage foam cell formation by triacylglycerol-rich lipoproteins (TGRL) was studied using postprandial triacylglycerol-rich lipoproteins (ppTGRL) derived from human volunteers and primary human monocyte-derived macrophages (HMDM). Subjects were fed a test meal high in dairy fat, followed three hours later by isolation of serum ppTGRL. Pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes were induced in HMDM by treatment with lipopolysaccharide (LPS) or dexamethasone (DEX), respectively. ppTGRL caused a dose-dependent increase in both triacylglycerol (TG) and cholesterol (CH) accumulation in the cells. TG accumulation was unaffected by LPS or DEX treatment, but LPS as compared with DEX-treated HMDM were found to accumulate more CH, and this effect was greater than that induced by ppTGRL in untreated cells. LPS-treatment had no effect on lipid uptake from ppTGRL (via the LDLr, scavenger receptors or SR-B1) or on CH efflux, but the CH synthesis inhibitor mevinolin abolished the difference between CH accumulation in LPS-and DEX-treated cells, suggesting that CH synthesis is enhanced in the inflammatory state. Phospholipid (PL) synthesis was increased in inflammatory M1 as compared with anti-inflammatory M2 HMDM. Moreover, TG synthesis was decreased by ppTGRL in DEX-treated as compared with untreated cells. We conclude, therefore, inflammation causes a greater increase in the accumulation of neutral lipids than ppTGRL in macrophages, and that this effect is related to modulation of PL metabolism and possibly also CH synthesis. Thus, the inflammatory phenotype of macrophages influences their lipid metabolism, and is, therefore, likely to modulate the induction of macrophage lipid accumulation by lipoproteins associated with foam cell formation.

Effect of allergy and inflammation on eicosanoid gene expression in CFTR deficiency

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) is a complicating factor in cystic fibrosis (CF), affecting 2-15% of patients. We hypothesized that sensitization/challenge of CFTR(-/-) mice with an Aspergillus fumigatus (Af) extract will affect eicosanoid pathway gene expression, impacting ABPA and CF.

METHODS

FABP-hCFTR(+/-)-CFTR(-/-) mice were sensitized/challenged with an Af extract and gene expression of lung mRNA was evaluated for >40 genes, with correlative data in human CF (IB3.1) and CFTR-corrected (S9) bronchoepithelial cell lines.

RESULTS

Pla2g4c, Pla2g2c, Pla2g2d and Pla2g5 were induced in response to Af in CFTR(-/-) mice. Interestingly, PLA2G2D was induced by LPS, IL-2, IL-6, IL-13, and Af only in CFTR-deficient human IB3.1 cells. Prostanoid gene expression was relatively constant, however, several 12/15-lipoxygenase genes were induced in response to Af. Numerous cytokines also caused differential expression of ALOX15 only in IB3.1 cells.

CONCLUSIONS

The distinct regulation of PLA2G4C, PLA2G2D and ALOX15 genes in Aspergillus sensitization and/or cystic fibrosis could provide new insights into diagnosis and treatment of ABPA and CF.

Immune markers in breast milk and fetal and maternal body fluids: a systematic review of perinatal concentrations

Breastfeeding represents the continued exposure of the infant to the maternal immune environment.Uterine, perinatal, and postnatal exposure to immune factors may contribute to an infant’s risk of developing immune-mediated disorders, including allergies. A PubMed search was conducted to review studies in humans and analyze concentrations of immune markers (TGF-beta, IFN-gamma, eotaxin, CCL5, CXCL10, TNF-alpha, MCP-1, IL-1beta, IL-4, IL-5, IL-6,IL-8, IL-10, IL-12, IL-13, sCD14, sIgA, IgG4, IgM) found in maternal serum, amniotic fluid, cord serum, colostrum, transition and mature milk. Concentrations of immune markers showed large variations across samples and studies. Reports documented conflicting results. Small sample sizes, differences in population characteristics, inconsistent sample collection times, and various sample collection and measurement methods may have led to wide variations in the concentrations of immune markers. Studies analyzing the associations between immune markers in maternal fluids and infant allergies remain inconclusive because of gaps in knowledge and a lack of standardized methods.

Recent progress in phospholipase A₂ research: from cells to animals to humans

Mammalian genomes encode genes for more than 30 phospholipase A₂s (PLA₂s) or related enzymes, which are subdivided into several classes including low-molecular-weight secreted PLA₂s (sPLA₂s), Ca²+-dependent cytosolic PLA₂s (cPLA₂s), Ca²+-independent PLA₂s (iPLA₂s), platelet-activating factor acetylhydrolases (PAF-AHs), lysosomal PLA₂s, and a recently identified adipose-specific PLA. Of these, the intracellular cPLA₂ and iPLA₂ families and the extracellular sPLA₂ family are recognized as the "big three". From a general viewpoint, cPLA₂α (the prototypic cPLA₂ plays a major role in the initiation of arachidonic acid metabolism, the iPLA₂ family contributes to membrane homeostasis and energy metabolism, and the sPLA₂ family affects various biological events by modulating the extracellular phospholipid milieus. The cPLA₂ family evolved along with eicosanoid receptors when vertebrates first appeared, whereas the diverse branching of the iPLA₂ and sPLA₂ families during earlier eukaryote development suggests that they play fundamental roles in life-related processes. During the past decade, data concerning the unexplored roles of various PLA₂ enzymes in pathophysiology have emerged on the basis of studies using knockout and transgenic mice, the use of specific inhibitors, and information obtained from analysis of human diseases caused by mutations in PLA₂ genes. This review focuses on current understanding of the emerging biological functions of PLA₂s and related enzymes.

Emerging roles of secreted phospholipase A2 enzymes: Lessons from transgenic and knockout mice

Among the emerging phospholipase A(2) (PLA(2)) superfamily, the secreted PLA(2) (sPLA(2)) family consists of low-molecular-mass, Ca(2+)-requiring extracellular enzymes with a His-Asp catalytic dyad. To date, more than 10 sPLA(2) enzymes have been identified in mammals. Individual sPLA(2)s exhibit unique tissue and cellular localizations and enzymatic properties, suggesting their distinct pathophysiological roles. Despite numerous enzymatic and cell biological studies on this enzyme family in the past two decades, their precise in vivo functions still remain largely obscure. Recent studies using transgenic and knockout mice for several sPLA(2) enzymes, in combination with lipidomics approaches, have opened new insights into their distinct contributions to various biological events such as food digestion, host defense, inflammation, asthma and atherosclerosis. In this article, we overview the latest understanding of the pathophysiological functions of individual sPLA(2) isoforms fueled by studies employing transgenic and knockout mice for several sPLA(2)s.