Unsaturated fatty acids as modulators of macrophage respiratory burst in the immune response against Rhodococcus equi and Pseudomonas aeruginosa

Transcriptom and miRNA data of PUFA-enriched stimulated murine macrophage and human endothelial cell lines

Inflammation is associated with the adaptation of macrophages and endothelial cells, and the dysregulation of these differentiation processes has been directly linked to both acute and chronic disease states. As cells in constant contact with blood, macrophages and endothelial cells are also under the direct influence of immunomodulatory dietary components such as polyunsaturated fatty acids (PUFA). RNA sequencing analyses allow us to understand the global changes in gene expression occurring during cell differentiation, including both transcriptional (transcriptome) and post-transcriptional (miRNAs) levels. We generated a comprehensive RNA sequencing dataset of parallel transcriptome and miRNA profiles of PUFA-enriched and pro-inflammatory stimulated macrophages and endothelial cells aiming to uncover the underlying molecular mechanisms. PUFA concentrations and duration of supplementation were based on dietary ranges, allowing for metabolism and plasma membrane uptake of fatty acids. The dataset may serve as a resource to study transcriptional and post-transcriptional changes associated with macrophage polarisation and endothelial dysfunction in inflammatory settings and their modulation by omega-3 and omega-6 fatty acids.

miRNA-Mediated Priming of Macrophage M1 Differentiation Differs in Gram-Positive and Gram-Negative Settings

A proper regulation of macrophage polarization is essential for the organism's health and pathogen control. Differentiation control is known to occur at the transcriptional as well as the posttranscriptional levels. The mechanisms involved, however, have not yet been fully elucidated. In this study, we co-cultured macrophages with viable Gram-positive and Gram-negative bacteria to mimic macrophage differentiation to the M1-like type in an inflammatory milieu. We found that Gram-positive stimulation resulted in increased expressions of miR-7a-5p, miR-148a-3p, miR-155-5p, and miR-351-5p. Of note, these miRNAs were found to target inhibitory mediators of the Rac1-PI3K-Akt pathway and the MyD88-dependent pathway. In contrast, Gram-negative stimulation-induced downregulation of miR-9-5p, miR-27b-3p, miR-93-5p, and miR-106b-5p is known to target key members of the Rac1-PI3K-Akt pathway and the MyD88-dependent pathway. These results, taken together, point to a fine-tuning of macrophage polarization by TLR-induced changes in macrophage miRNA profiles. Here, the miRNA-mediated priming of M1 differentiation seems to differ in the Gram-positive and Gram-negative settings in terms of the mechanism and miRNAs involved.

Reactive oxygen species inhibits Listeria monocytogenes invasion into HepG2 epithelial cells

Listeria monocytogenes (Lm) can colonize human gastrointestinal tract and subsequently cross the intestinal barrier. Reactive oxygen species (ROS) are produced by NADPH oxidase. However, the role of ROS in bacterial invasion remains to be less understood. Herein, we investigated the impact of ROS on Lm invasion to HepG2 using NADPH oxidase inhibitor, diphenyleneiodonium chloride (DPI), as well as the ROS scavenger, N-acetyl cysteine (NAC). Our results showed that inhibiting ROS increased the invasive capability of Lm. Moreover, after Lm infection, inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin 1beta (IL-1β) in HepG2 were significantly upregulated. However, after inhibiting ROS, the expression levels of TNF-α and IL-1β were downregulated, indicating a failure of host cells to activate the immune mechanism. Taken together, ROS in Lm might be as a signal for host cells to sense Lm invasion and then stimulate cells to activate the immune mechanism.

Lipid raft localization of TLR2 and its co-receptors is independent of membrane lipid composition

BACKGROUND

Toll like receptors (TLRs) are an important and evolutionary conserved class of pattern recognition receptors associated with innate immunity. The recognition of Gram-positive cell wall constituents strongly depends on TLR2. In order to be functional, TLR2 predominantly forms a heterodimer with TLR1 or TLR6 within specialized membrane microdomains, the lipid rafts. The membrane lipid composition and the physicochemical properties of lipid rafts are subject to modification by exogenous fatty acids. Previous investigations of our group provide evidence that macrophage enrichment with polyunsaturated fatty acids (PUFA) induces a reordering of lipid rafts and non-rafts based on the incorporation of supplemented PUFA as well as their elongation and desaturation products.

METHODS

In the present study we investigated potential constraining effects of membrane microdomain reorganization on the clustering of TLR2 with its co-receptors TLR1 and TLR6 within lipid rafts. To this end, RAW264.7 macrophages were supplemented with either docosahexaenoic acid (DHA) or arachidonic acid (AA) and analyzed for receptor expression and microdomain localization in context of TLR stimulation.

RESULTS AND CONCLUSIONS

Our analyses showed that receptor levels and microdomain localization were unchanged by PUFA supplementation. The TLR2 pathway, in contrast to the TLR4 signaling cascade, is not affected by exogenous PUFA at the membrane level.

Impact of Polyunsaturated Fatty Acids on miRNA Profiles of Monocytes/Macrophages and Endothelial Cells-A Pilot Study

Alteration of miRNAs and dietary polyunsaturated fatty acids (PUFAs) underlies vascular inflammation. PUFAs are known to be incorporated into the cell membrane of monocytes/macrophages or endothelial cells, the major cellular players of vascular diseases, thereby affecting cellular signal transduction. Nevertheless, there are no investigations concerning the PUFA impact on miRNA expression by these cells. With regard to the key role miRNAs play for overall cellular functionality, this study aims to elucidate whether PUFAs affect miRNA expression profiles. To this end, the monocyte/macrophage cell line RAW264.7 and the endothelial cell line TIME were enriched with either docosahexaenoic acid (DHA; n3-PUFA) or arachidonic acid (AA; n6-PUFA) until reaching a stable incorporation into the plasma membrane and, at least in part, exposed to an inflammatory milieu. Expressed miRNAs were determined by deep sequencing, and compared to unsupplemented/unstimulated controls. Data gained clearly show that PUFAs in fact modulate miRNA expression of both cell types analyzed regardless the presence/absence of an inflammatory stimulator. Moreover, certain miRNAs already linked to vascular inflammation were found to be affected by cellular PUFA enrichment. Hence, vascular inflammation appears to be influenced by dietary fatty acids, inter alia, via PUFA-mediated modulation of the type and amount of miRNAs synthesized by cells involved in the inflammatory process.

IBD: In Food We Trust

BACKGROUND AND AIMS

Both science and patients associate diet with inflammatory bowel disease [IBD]. There is no doubt that links between IBD and diet are numerous, based on both epidemiological studies and experimental studies. However, scientific evidence to support dietary advice is currently lacking, and dietary counselling for IBD patients is often limited in clinical practice to the improvement of nutrient intake. This review aimed to focus on both patient's beliefs about and molecular mechanisms for crosstalk between nutrients and inflammation.

METHODS

A literature search using PubMed was performed to identify relevant studies on diet and/or nutrients and their role in IBD. Pubmed [from inception to January 20, 2016] was searched using the terms: 'Crohn', 'colitis',' intestinal epithelial cells', and a list of terms relating to diet or numerous specific nutrients. Terms associated with nutrients were individually tested in the context of IBD. Reference lists from studies selected were manually searched to identify further relevant reports. Manuscripts about diet in the context of IBD from basic science, epidemiological studies, or clinical trials were selected and reviewed. Only articles published in English were included.

RESULTS

Epidemiological studies highlight the key role of diet in IBD development, and many IBD patients report diet as a triggering factor in relapse of disease. In addition, we present research on the impact of nutrients on innate immunity.

CONCLUSION

Diet may offer an alternative approach to restoring deficient innate immunity in IBD, and this may be the scientific rationale for providing dietary counselling for IBD patients.

LPS- or Pseudomonas aeruginosa-mediated activation of the macrophage TLR4 signaling cascade depends on membrane lipid composition

It is well known that PUFA impede the LPS-mediated activation of the transcription factor NFkappaB. However, the underlying mode of action has not been clarified yet. To address this issue in a comprehensive approach, we used the monocyte/macrophage cell line RAW264.7 to investigate the consequences of a PUFA supplementation on the TLR4 pathway with a focus on (i) the gene expression of TLR4 itself as well as of its downstream mediators, (ii) the membrane microdomain localization of TLR4 and CD14, (iii) the stimulation-induced interaction of TLR4 and CD14. Our data indicate that the impairment of the TLR4-mediated cell activation by PUFA supplementation is not due to changes in gene expression of mediator proteins of the signaling cascade. Rather, our data provide evidence that the PUFA enrichment of macrophages affects the TLR4 pathway at the membrane level. PUFA incorporation into membrane lipids induces a reordering of membrane microdomains thereby affecting cellular signal transduction. It is important to note that this remodeling of macrophage rafts has no adverse effect on cell viability. Hence, microdomain disruption via macrophage PUFA supplementation has a potential as non-toxic strategy to attenuate inflammatory signaling.

Does plasma membrane lipid composition impact the miRNA-mediated regulation of vascular inflammation?

BACKGROUND

Both PUFA and miRNAs are believed to be of importance in vascular diseases. On the one hand diverse nutrition societies recommend PUFA consumption to dampen inflammatory processes. On the other hand scientists intensify efforts to use miRNAs for diagnostics or therapy in context of vascular disorders.

PRESENTATION OF THE HYPOTHESIS

There might be is a causal link between the plasma membrane lipid composition and the miRNA expression of monocytes and endothelial cells. PUFA enrichment of cells may affect the type and the amount of particular miRNAs produced. In this way dietary fatty acids are supposed to impact the miRNA-mediated regulation of vascular inflammatory processes.

PROPOSED EXPERIMENTAL SETTING TO TEST THE HYPOTHESIS

PUFA-supplemented monocytes and endothelial cells are analyzed with respect to membrane fatty acid patterns, typical markers of vascular inflammation and miRNA expression. Experiments are performed both for undifferentiated/unstimulated as well as for differentiated/stimulated cells. Verification of identified miRNA targets is performed by means of mimics/antagomirs.

IMPLICATIONS OF THE HYPOTHESIS

Innovative mechanism of action, which could point the way to a new understanding of the PUFA-mediated modulation of cellular signal transduction. If confirmed experimentally, it might stimulate vascular inflammation research and immunologic lipid science, hence, acting as source of inspiration for future therapeutic interventions in vascular diseases.

It is all about fluidity: Fatty acids and macrophage phagocytosis

Phagocytosis is an early and fundamental step for the effective clearance of disease causing agents. The ability to engulf and kill pathogens is considered as a major effector function of macrophages. In their phagocytic role macrophages are part of the first line of innate immune defense. A number of studies investigating fatty acid effects on macrophage phagocytosis have been conducted over many years. In vitro-data consistently report that alterations in macrophage membrane fatty acid composition are linked to an altered phagocytic capacity, i.e. an increase in membrane unsaturated fatty acid content is associated with an increase in engulfment and killing rate. The mode of action of fatty acids seems to be the modulation of the physical nature of the macrophage plasma membrane. It appears that the saturated-to-unsaturated fatty acid ratio of macrophage membrane phospholipids is of importance in determining macrophage phagocytic capacity. Available in vivo-data are less clear. At present, there is a lack of systematic studies elucidating key factors such as fatty acid efficacy, effective dose or dosing intervals. Without this knowledge the targeted modulation of macrophage phagocytosis in vivo by fatty acids is still a distant possibility.

Fatty acids regulation of inflammatory and metabolic genes

PURPOSE OF REVIEW

Fatty acids influence human health and diseases in various ways. In recent years, much work has been carried out to elucidate the mechanisms by which dietary fatty acids control short-term and long-term cellular functions. We have reviewed herein the most recent studies on modulation of gene expression by fatty acids. A number of genes respond to transcription factors and present a transcription factor response element in their promoter regions. Fatty acids may exert their effects on metabolism by regulating gene transcription via transcription factors. Understanding how fatty acids control expression of metabolic genes is a promising strategy to be investigated by aiming to treat metabolic diseases such as insulin resistance, obesity, and type 2 diabetes mellitus.

RECENT FINDINGS

Fatty acids exert many of their biological effects through the modulation of the activity of transcription factors, such as sterol regulatory element-binding proteins, peroxisome proliferator-activated receptors, and liver X receptors.

SUMMARY

Fatty acid action through transcription factors controls the expression of several inflammatory and metabolic genes.