Pro-inflammatory cytokines secreted by adipose tissue macrophages (ATMs) contribute to chronic low-grade inflammation and obesity-induced insulin resistance. Recent studies have shown that adipose tissue hypoxia promotes an inflammatory phenotype in ATMs. However, our understanding of how hypoxia modulates the response of ATMs to free fatty acids within obese adipose tissue is limited. We examined the effects of hypoxia (1% O 2 ) on the pro-inflammatory responses of human monocyte-derived macrophages to the saturated fatty acid palmitate. Compared with normoxia, hypoxia significantly increased palmitate-induced mRNA expression and protein secretion of IL-6 and IL-1␤. Although palmitate-induced endoplasmic reticulum stress and nuclear factor B pathway activation were not enhanced by hypoxia, hypoxia increased the activation of JNK and p38 mitogen-activated protein kinase signaling in palmitate-treated cells. Inhibition of JNK blocked the hypoxic induction of pro-inflammatory cytokine expression, whereas knockdown of hypoxia-induced transcription factors HIF-1␣ and HIF-2␣ alone or in combination failed to reduce IL-6 and only modestly reduced IL-1␤ gene expression in palmitate-treated hypoxic macrophages. Enhanced pro-inflammatory cytokine production and JNK activity under hypoxia were prevented by inhibiting reactive oxygen species generation. In addition, silencing of dual-specificity phosphatase 16 increased normoxic levels of IL-6 and IL-1␤ and reduced the hypoxic potentiation in palmitate-treated macrophages. The secretome of hypoxic palmitate-treated macrophages promoted IL-6 and macrophage chemoattractant protein 1 expression in primary human adipocytes, which was sensitive to macrophage JNK inhibition. Our results reveal that the coexistence of hypoxia along with free fatty acids exacerbates macrophage-mediated inflammation.

Arachidonate 15-lipoxygenase (ALOX15) and arachidonate 15-lipoxygenase, type B (ALOX15B) catalyze the dioxygenation of polyunsaturated fatty acids and are upregulated in human alternatively activated macrophages (AAMs) induced by Th2 cytokine interleukin-4 (IL-4) and/or interleukin-13. Known primarily for roles in bioactive lipid mediator synthesis, 15-lipoxygenases (15-LOXs) have been implicated in various macrophage functions including efferocytosis and ferroptosis. Using a combination of inhibitors and siRNAs to suppress 15-LOX isoforms, we studied the role of 15-LOXs in cellular cholesterol homeostasis and immune function in naïve and AAMs. Silencing or inhibiting the 15-LOX isoforms impaired sterol regulatory element binding protein (SREBP)-2 signaling by inhibiting SREBP-2 processing into mature transcription factor and reduced SREBP-2 binding to sterol regulatory elements and subsequent target gene expression. Silencing ALOX15B reduced cellular cholesterol and the cholesterol intermediates desmosterol, lanosterol, 24,25-dihydrolanosterol, and lathosterol as well as oxysterols in IL-4-stimulated macrophages. In addition, attenuating both 15-LOX isoforms did not generally affect IL-4 gene expression but rather uniquely impacted IL-4-induced CCL17 production in an SREBP-2-dependent manner resulting in reduced T cell migration to macrophage conditioned media. In conclusion, we identified a novel role for ALOX15B, and to a lesser extent ALOX15, in cholesterol homeostasis and CCL17 production in human macrophages.

No abstract

TNF is a central cytokine in the pathogenesis of rheumatoid arthritis (RA). Elevated level of TNF causes local inflammation that affects immune cells and fibroblast-like synoviocytes (FLS). Nowadays, only 20–30% of patients experience remission after the standard of care therapy—antibodies against TNF. Interestingly, responders show reduced levels of GLUT1 and GAPDH, highlighting a potential link to cellular metabolism. The aim of the study was to investigate whether TNF directly affects the metabolic phenotype of FLS. Real-time respirometry displayed TNF-induced upregulation of glycolysis along with a modest increase of oxidative phosphorylation in FLS from healthy donors. In addition, TNF stimulation enhanced HIF1A and GLUT1 expression. The upregulation of HIF1A and GLUT1 reflects their enriched level in FLS from RA patients (RA-FLS). The inhibition of TAK1, HIF1a and hexokinase deciphered the importance of TNF/TAK1/HIF1A/glycolysis signaling axis. To prove that inhibition of glycolysis reduced the pathogenic phenotype, we showed that 2-deoxyglucose, a hexokinase inhibitor, partially decreased secretion of RA biomarkers. In summary, we identified a direct role of TNF on glycolytic reprogramming of FLS and confirmed the potency of immunometabolism for RA. Further studies are needed to evaluate the therapeutic impact especially regarding non-responder data.

Allogeneic bone marrow transplantation (allo-BMT) is currently the only way to cure many hematoproliferative disorders. However, allo-BMT use is limited by severe complications, the foremost being graft-versus-host disease (GVHD). Due to the lack of efficiency of the existing methods of GVHD prophylaxis, new methods are being actively explored, including the use of donors' multipotent mesenchymal stromal cells (MMSC). In this work, we analyzed the results of acute GVHD (aGVHD) prophylaxis by means of MMSC injections after allo-BMT in patients with hematological malignancies. The study included 77 patients. They were randomized into two groups - those receiving standard prophylaxis of aGVHD and those who were additionally infused with MMSC derived from the bone marrow of hematopoietic stem cell donors. We found that the infusion of MMSC halves the incidence of aGVHD and increases the overall survival of patients. Four of 39 MMSC samples were ineffective for preventing aGVHD. Analysis of individual donor characteristics (gender, age, body mass index) and the MMSC properties of these donors (growth parameters, level of expression of 30 genes involved in proliferation, differentiation, and immunomodulation) revealed no significant difference between the MMSC that were effective or ineffective for preventing aGVHD. We used multiple logistic regression to establish a combination of features that characterize the most suitable MMSC samples for the prevention of aGVHD. A model predicting MMSC sample success for aGVHD prophylaxis was constructed. Significant model parameters were increased relative expression of the FGFR1 gene in combination with reduced expression levels of the PPARG and IGF1 genes. Depending on the chosen margin for probability of successful application of MMSC, this model correctly predicts the outcome of the use of MMSC in 82-94% of cases. The proposed model of prospective evaluation of the effectiveness of MMSC samples will enable prevention of the development of aGVHD in the maximal number of patients.