Adipocyte GPX4 protects against inflammation, hepatic insulin resistance and metabolic dysregulation.

OBJECTIVES: Metabolic inflammation is a hallmark of obesity and related disorders, afflicting substantial morbidity and mortality to individuals worldwide. White visceral and subcutaneous adipose tissue not only serves as energy storage but also controls metabolism. Adipose tissue inflammation, commonly observed in human obesity, is considered a critical driver of metabolic perturbation while molecular hubs are poorly explored. Metabolic stress evoked by e.g. long-chain fatty acids leads to oxidative perturbation of adipocytes and production of inflammatory cytokines, fuelling macrophage infiltration and systemic low-grade inflammation. Glutathione peroxidase 4 (GPX4) protects against lipid peroxidation, accumulation of oxygen-specific epitopes and cell death, collectively referred to as ferroptosis. Here, we explore the function of adipocyte GPX4 in mammalian metabolism. METHODS: We studied the regulation and function of GPX4 in differentiated mouse adipocytes derived from 3T3-L1 fibroblasts. We generated two conditional adipocyte-specific Gpx4 knockout mice by crossing Gpx4fl/fl mice with Adipoq-Cre+ (Gpx4-/-AT) or Fabp4-Cre+ (Gpx4+/-Fabp4) mice. Both models were metabolically characterized by a glucose tolerance test and insulin resistance test, and adipose tissue lipid peroxidation, inflammation and cell death were assessed by quantifying oxygen-specific epitopes, transcriptional analysis of chemokines, quantification of F4/80+ macrophages and TUNEL labelling. RESULTS: GPX4 expression was induced during and required for adipocyte differentiation. In mature adipocytes, impaired GPX4 activity spontaneously evoked lipid peroxidation and expression of inflammatory cytokines such as TNF-α, interleukin 1ß (IL-1ß), IL-6 and the IL-8 homologue CXCL1. Gpx4-/-AT mice spontaneously displayed adipocyte hypertrophy on a chow diet, which was paralleled by the accumulation of oxygen-specific epitopes and macrophage infiltration in adipose tissue. Furthermore, Gpx4-/-AT mice spontaneously developed glucose intolerance, hepatic insulin resistance and systemic low-grade inflammation, when compared to wildtype littermates, which was similarly recapitulated in Gpx4+/-Fabp4 mice. Gpx4-/-AT mice exhibited no signs of adipocyte death. CONCLUSION: Adipocyte GPX4 protects against spontaneous metabolic dysregulation and systemic low-grade inflammation independent from ferroptosis, which could be therapeutically exploited in the future.

Complement and Fungal Dysbiosis as Prognostic Markers and Potential Targets in PDAC Treatment.

Pancreatic ductal adenocarcinoma (PDAC) is still hampered by a dismal prognosis. A better understanding of the tumor microenvironment within the pancreas and of the factors affecting its composition is of utmost importance for developing new diagnostic and treatment tools. In this context, the complement system plays a prominent role. Not only has it been shown to shape a T cell-mediated immune response, but it also directly affects proliferation and apoptosis of the tumor cells, influencing angiogenesis, metastatic spread and therapeutic resistance. This makes complement proteins appealing not only as early biomarkers of PDAC development, but also as therapeutic targets. Fungal dysbiosis is currently the new kid on the block in tumorigenesis with cancer-associated mycobiomes extracted from several cancer types. For PDAC, colonization with the yeast Malassezia seems to promote cancer progression, already in precursor lesions. One responsible mechanism appears to be complement activation via the lectin pathway. In the present article, we review the role of the complement system in tumorigenesis, presenting observations that propose it as the missing link between fungal dysbiosis and PDAC development. We also present the results of a small pilot study supporting the crucial interplay between the complement system and Malassezia colonization in PDAC pathogenesis.

Tofacitinib-Induced Modulation of Intestinal Adaptive and Innate Immunity and Factors Driving Cellular and Systemic Pharmacokinetics.

OBJECTIVE: By interfering with multiple cytokines, human Janus kinase inhibitors (JAKis) are of growing importance in the treatment of malignant and inflammatory conditions. Although tofacitinib has demonstrated efficacy as the first-in-class JAKi in ulcerative colitis many aspects concerning its mode of action and pharmacokinetics remain unresolved. DESIGN: We studied tofacitinib's impact on various primary human innate and adaptive immune cells. In-depth in vivo studies were performed in dextran sodium sulfate-induced colitis in mice. Immune populations were characterized by flow cytometry and critical transcription factors and effector cytokines were analyzed. Pharmacokinetics of tofacitinib was studied by liquid chromatography-tandem mass spectrometry. RESULTS: Tofacitinib inhibited proliferation in CD4+ and CD8+ T cells along with Th1 and Th17 differentiation, while Th2 and regulatory T cell lineages were largely unaffected. Monocytes and macrophages were directed toward an anti-inflammatory phenotype and cytokine production was suppressed in intestinal epithelial cells. These findings were largely reproducible in murine cells of the inflamed mucosa in dextran sulfate sodium colitis. Short-term treatment with tofacitinib had little impact on the mouse microbiota. Strikingly, the degree of inflammation and circulating tofacitinib levels showed a strong positive correlation. Finally, we identified inflammation-induced equilibrative nucleoside transporters as regulators of tofacitinib uptake into leukocytes. CONCLUSIONS: We provide a detailed analysis of the cell-specific immune-suppressive effects of the JAKis tofacitinib on innate and adaptive immunity and reveal that intestinal inflammation critically impacts tofacitinib's pharmacokinetics in mice. Furthermore, we describe an unappreciated mechanism-namely induction of equilibrative nucleoside transporters-enhancing baseline cellular uptake that can be inhibited pharmaceutically.

Faecal Biomarkers in Inflammatory Bowel Diseases: Calprotectin Versus Lipocalin-2-a Comparative Study.

BACKGROUND AND AIMS: Faecal biomarkers, particularly calprotectin [FCAL], have become important diagnostic and monitoring tools in inflammatory bowel diseases [IBD]. As FCAL is mainly produced by neutrophils, we hypothesised that faecal lipocalin-2 [FLCN2], also expressed by intestinal epithelial cells [IEC], could be beneficial in specific clinical situations. METHODS: We compared clinical and endoscopic activity-related correlations between FCAL and FLCN2, assayed from the same sample, in a cohort of 132 patients (72 Crohn's disease [CD]) and 40 controls. A detailed analysis of cellular origins was done by confocal microscopy and flow cytometry. To evaluate the potential to detect low-grade inflammation, we studied faecal and tissue concentrations in a cohort with clinical, endoscopic, and histological remission. RESULTS: There was an excellent correlation between FCAL and FLCN2 [rS = 0.87, p <0.001] and comparable sensitivity and specificity to predict clinical and endoscopic disease activity, with optimal thresholds for endoscopic activity of 73.4 and 1.98 µg/g in ulcerative colitis [UC] and 78.4 and 0.56 µg/g in Crohn's disease for FCAL and FLCN2, respectively. Strong co-expression of both proteins was observed in granulocytes and macrophages. IECs expressed LCN2 but not CAL. In our IBD cohort in deep remission neither FCAL nor FLCN2 was different from controls; yet mucosal LCN2 but not CAL expressions remained elevated in the rectum of UC and the ileum of CD patients. CONCLUSIONS: This study corroborates the diagnostic equivalence of FLCN2 and FCAL in IBD. In remission, persistent mucosal overexpression renders LCN2 an attractive candidate for molecular inflammation warranting further investigation.

Targeting NAD immunometabolism limits severe graft-versus-host disease and has potent antileukemic activity.

Acute graft-versus-host disease (aGVHD) and tumor relapse remain major complications after allogeneic hematopoietic stem cell transplantation. Alloreactive T cells and cancer cells share a similar metabolic phenotype to meet the bioenergetic demands necessary for cellular proliferation and effector functions. Nicotinamide adenine dinucleotide (NAD) is an essential co-factor in energy metabolism and is constantly replenished by nicotinamide phosphoribosyl-transferase (Nampt), the rate-limiting enzyme in the NAD salvage pathway. Here we show, that Nampt blockage strongly ameliorates aGVHD and limits leukemic expansion. Nampt was highly elevated in serum of patients with gastrointestinal GVHD and was particularly abundant in human and mouse intestinal T cells. Therapeutic application of the Nampt small-molecule inhibitor, Fk866, strongly attenuated experimental GVHD and caused NAD depletion in T-cell subsets, which displayed differential susceptibility to NAD shortage. Fk866 robustly inhibited expansion of alloreactive but not memory T cells and promoted FoxP3-mediated lineage stability in regulatory T cells. Furthermore, Fk866 strongly reduced the tumor burden in mouse leukemia and graft-versus-leukemia models. Ex vivo studies using lymphocytes from GVHD patients demonstrated potent antiproliferative properties of Fk866, suggesting potential clinical utility. Thus, targeting NAD immunometabolism represents a novel approach to selectively inhibit alloreactive T cells during aGVHD with additional antileukemic efficacy.