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Nucleotides released from palmitate-activated murine macrophages attract neutrophils.

ABSTRACT: Obesity and elevation of circulating free fatty acids are associated with an accumulation and proinflammatory polarization of macrophages within metabolically active tissues, such as adipose tissue, muscle, liver, and pancreas. Beyond macrophages, neutrophils also accumulate in adipose and muscle tissues during high-fat diets and contribute to a state of local inflammation and insulin resistance. However, the mechanisms by which neutrophils are recruited to these tissues are largely unknown. Here we used a cell culture system as proof of concept to show that, upon exposure to a saturated fatty acid, palmitate, macrophages release nucleotides that attract neutrophils. Moreover, we found that palmitate up-regulates pannexin-1 channels in macrophages that mediate the attraction of neutrophils, shown previously to allow transfer of nucleotides across membranes. These findings suggest that proinflammatory macrophages release nucleotides through pannexin-1, a process that may facilitate neutrophil recruitment into metabolic tissues during obesity.

SUBMITTER: Tam TH

PROVIDER: S-EPMC7152762 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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Nucleotides released from palmitate-activated murine macrophages attract neutrophils.

Tam Theresa H TH Chan Kenny L KL Boroumand Parastoo P Liu Zhi Z Brozinick Joseph T JT Bui Hai Hoang HH Roth Kenneth K Wakefield C Brent CB Penuela Silvia S Bilan Philip J PJ Klip Amira A

The Journal of biological chemistry 20200304 15

Obesity and elevation of circulating free fatty acids are associated with an accumulation and proinflammatory polarization of macrophages within metabolically active tissues, such as adipose tissue, muscle, liver, and pancreas. Beyond macrophages, neutrophils also accumulate in adipose and muscle tissues during high-fat diets and contribute to a state of local inflammation and insulin resistance. However, the mechanisms by which neutrophils are recruited to these tissues are largely unknown. Her ...[more]

PMID: 32132172

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Project description:Background: Although adverse food reactions are commonly divided into immunoglobulin E (IgE) mediated food allergy (FA), and non-IgE FA, the current literature is providing support for the role of innate immune responses as an important component of non-IgE FA. Using a commercially available leukocyte activation (LA) assay, a recent quantitative study of total extracellular DNA released in cellular supernatants of human peripheral blood mononuclear cells exposed either to positive or negative tested foods demonstrated that leukocytes exposed to foods with positive LA test results showed higher DNA content than those exposed to foods with negative LA test results. In humans, the origin of DNA might be either the nucleus or the mitochondria. Analysis of emerging data from several laboratories, including our own, suggests that mitochondrial DNA induces inflammatory responses through induction of proinflammatory cytokines. Objective: This pilot study was designed primarily to convey the finding, and relevance of, mitochondrial DNA in the form of neutrophil extracellular traps (NET) as a new pathogenetic mechanism for innate immune-mediated non-IgE FA. Methods: The study population consisted of a total of six subjects, four in a major FA study group and two in a subgroup. Neutrophils were isolated and treated with food antigens that elicited positive and negative LA responses, and the released free DNA was analyzed for the cellular site of origin by using real-time polymerase chain reaction and for leukocyte calprotectin and S100 calcium-binding protein A12 (S100A12) proteins as markers of NETs. Results: We showed that cellular supernatants from neutrophils treated with foods that elicit positive LA responses can contain increased DNA levels of nuclear as well as mitochondrial origin. Supernatants from neutrophils treated with negative tested food (LA) responses did not induce the release of nuclear or mitochondrial DNA. Conclusion: Analysis of our data suggested that the induction of NETs that contain proinflammatory mitochondrial DNA may provide the critical link necessary for a better understanding of the pathogenesis of non-IgE-mediated FA. These discoveries may not only facilitate better diagnostic tests of FA but should also improve clinical management of allergic and other inflammatory diseases.

Project description:BackgroundMacrophage-derived factors contribute to whole-body insulin resistance, partly by impinging on metabolically active tissues. As proof of principle for this interaction, conditioned medium from macrophages treated with palmitate (CM-PA) reduces insulin action and glucose uptake in muscle cells. However, the mechanism whereby CM-PA confers this negative response onto muscle cells remains unknown.Methodology/principal findingsL6-GLUT4myc myoblasts were exposed for 24 h to palmitate-free conditioned medium from RAW 264.7 macrophages pre-treated with 0.5 mM palmitate for 6 h. This palmitate-free CM-PA, containing selective cytokines and chemokines, inhibited myoblast insulin-stimulated insulin receptor substrate 1 (IRS1) tyrosine phosphorylation, AS160 phosphorylation, GLUT4 translocation and glucose uptake. These effects were accompanied by a rise in c-Jun N-terminal kinase (JNK) activation, degradation of Inhibitor of ?B? (I?B?), and elevated expression of proinflammatory cytokines in myoblasts. Notably, CM-PA caused IRS1 phosphorylation on Ser1101, and phosphorylation of novel PKC? and ?. Co-incubation of myoblasts with CM-PA and the novel and conventional PKC inhibitor Gö6983 (but not with the conventional PKC inhibitor Gö6976) prevented PKC? and ? activation, JNK phosphorylation, restored I?B? mass and reduced proinflammatory cytokine production. Gö6983 also restored insulin signalling and glucose uptake in myoblasts. Moreover, co-silencing both novel PKC ? and ? isoforms in myoblasts by RNA interference, but not their individual silencing, prevented the inflammatory response and restored insulin sensitivity to CM-PA-treated myoblasts.Conclusions/clinical significanceThe results suggest that the block in muscle insulin action caused by CM-PA is mediated by novel PKC? and PKC?. This study re-establishes the participation of macrophages as a relay in the action of fatty acids on muscle cells, and further identifies PKC? and PKC? as key elements in the inflammatory and insulin resistance responses of muscle cells to macrophage products. Furthermore, it portrays these PKC isoforms as potential targets for the treatment of fatty acid-induced, inflammation-linked insulin resistance.

Dataset Information

Nucleotides released from palmitate-activated murine macrophages attract neutrophils.

Publications

Nucleotides released from palmitate-activated murine macrophages attract neutrophils.

Similar Datasets

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