Where the Action Is—Leukocyte Recruitment in Atherosclerosis

Atherosclerosis is the leading cause of death worldwide and leukocyte recruitment is a key element of this phenomenon, thus allowing immune cells to enter the arterial wall. There, in concert with accumulating lipids, the invading leukocytes trigger a plethora of inflammatory responses which promote the influx of additional leukocytes and lead to the continued growth of atherosclerotic plaques. The recruitment process follows a precise scheme of tethering, rolling, firm arrest, crawling and transmigration and involves multiple cellular and subcellular players. This review aims to provide a comprehensive up-to-date insight into the process of leukocyte recruitment relevant to atherosclerosis, each from the perspective of endothelial cells, monocytes and macrophages, neutrophils, T lymphocytes and platelets. In addition, therapeutic options targeting leukocyte recruitment into atherosclerotic lesions—or potentially arising from the growing body of insights into its precise mechanisms—are highlighted.

Cytoplasmic zinc promotes IL-1β production by monocytes and macrophages through mTORC1-induced glycolysis in rheumatoid arthritis

Zinc metabolically reprograms monocytes and macrophages to promote inflammation in rheumatoid arthritis.

Thalidomide-based inhibitor for TNF-α: designing and Insilico evaluation

Background Inflammatory diseases are the vast array of disorders caused by inflammation. During most inflammatory events, many cytokines expressions were modulated, and one such cytokine is tumor necrosis factor-alpha (TNF-α). TNF-α is mainly secreted by monocytes and macrophages. Notably, it has been proposed as a therapeutic target for several diseases. The anti-TNF biology approach is mainly based on monoclonal antibodies. The fusion protein and biosimilars are prevalent in treating inflammation for decades. Only a few small molecule inhibitors are available to inhibit the expression of TNF-α, and one such promising drug was thalidomide. Therefore, the study was carried out to design thalidomide-based small molecule inhibitors for TNF-α. The main objective of our study is to design thalidomide analogs to inhibit TNF-α using the insilico approach. Results Several thalidomide analogs were designed using chemsketch. After filtration of compounds through ‘Lipinski rule of 5’ by Molinspiration tool, as a result, five compounds were selected. All these compounds were subjected to molecular docking, and the study showed that all five compounds had good binding energy. However, based on ADMET predictions, two compounds (S3 and S5) were eliminated. Conclusions Our preliminary results suggest that S1, S2, S4 compounds showed potential ligand binding capacity with TNF-α and, interestingly, with limited or no toxicity. Our preliminary investigation and obtained results have fashioned more interest for further in vitro studies.

The Role of miRNA in Regulating the Fate of Monocytes in Health and Cancer

Monocytes represent a heterogeneous population of blood cells that provide a link between innate and adaptive immunity. The unique potential of monocytes as both precursors (e.g., of macrophages) and effector cells (as phagocytes or cytotoxic cells) makes them an interesting research and therapeutic target. At the site of a tumor, monocytes/macrophages constitute a major population of infiltrating leukocytes and, depending on the type of tumor, may play a dual role as either a bad or good indicator for cancer recovery. The functional activity of monocytes and macrophages derived from them is tightly regulated at the transcriptional and post-transcriptional level. This review summarizes the current understanding of the role of small regulatory miRNA in monocyte formation, maturation and function in health and cancer development. Additionally, signatures of miRNA-based monocyte subsets and the influence of exogenous miRNA generated in the tumor environment on the function of monocytes are discussed.

Inflammasome activation in neutrophils of patients with severe COVID-19

Infection by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) engages the inflammasome in monocytes and macrophages and leads to the cytokine storm in COVID-19. Neutrophils, the most abundant leukocytes, release neutrophil extracellular traps (NETs), which have been implicated in the pathogenesis of COVID-19. Our recent study shows that activation of the NLRP3 inflammasome is important for NET release in sterile inflammation. However, the role of neutrophil inflammasome formation in human disease is unknown. We hypothesized that SARS-COV-2 infection may induce inflammasome activation in neutrophils. We also aimed to assess the localization of inflammasome formation, (i.e. ASC speck assembly), and timing relative to NETosis in stimulated neutrophils by real time video microscopy. Neutrophils isolated from severe COVID-19 patients demonstrated that approximately 2% of neutrophils in both the peripheral blood and tracheal aspirates presented ASC speck. ASC speck was observed in neutrophils with an intact poly-lobulated nucleus, suggesting early formation during neutrophil activation. Additionally, 40% of nuclei were positive for citrullinated histone H3, and there was a significant correlation between speck formation and nuclear histone citrullination. Time-lapse microscopy in LPS-stimulated neutrophils from fluorescent ASC reporter mice showed that ASC speck formed transiently and at the microtubule organizing center, long before NET release. Our study shows that ASC speck is present in neutrophils from COVID-19 patients with respiratory failure and that it forms early in NETosis. Our findings suggest that inhibition of neutrophil inflammasomes may be beneficial in COVID-19.

Inside-out Signalling From Aminopeptidase N (CD13) To Complement Receptor 3 (CR3, CD11b/CD18)

Upon ligand engagement, certain receptors can activate an integrin through a mechanism called inside-out signalling. This phenomenon prepares the cell for the next steps of the process it will perform. CR3 (Complement receptor 3), the most abundant β2 integrin in monocytes and macrophages, and CD13 (aminopeptidase N) are two immune receptors with overlapping activities: adhesion, phagocytosis of opsonized particles, and respiratory burst induction. They can be found together in functional signalling microdomains, or lipid rafts, on the surface of human leukocytes. Thus, given their common functions, shared physical location and the fact that some phagocytic and adhesion receptors activate a selection of integrins, we hypothesized that CD13 could activate CR3 through an inside-out signalling mechanism. To test this hypothesis, we first ascertained the activation of CR3 after CD13 crosslinking in human monocyte-derived macrophages. We used an integrated analysis of bioinformatics and experimental data to suggest two possible signalling cascades that could explain the phenomenon. Finally, we show that the non-receptor tyrosine kinase Syk is a key attenuator of this pathway. Our results demonstrated that, even in the absence of canonical signalling motifs, and despite having a noticeably short cytoplasmic tail (7-10 amino acids), CD13 was capable of triggering an inside-out signalling cascade, adding a new function to those already known for this moonlighting protein.

Urinary Soluble CD163 Levels Predict IgA Nephropathy Remission Status

Noninvasive biomarkers of disease activity are needed to predict disease remission status in patients with IgA nephropathy (IgAN). Soluble CD163 (sCD163), shed by monocytes and macrophages, is a potential biomarker in diseases associated with excessive macrophage activation. We investigated the association of urinary sCD163 (u-sCD163) with histopathological activity and clinical manifestations in 349 patients with biopsy-diagnosed IgAN. U-sCD163 was measured via enzyme-linked immunosorbent assay. In patients with IgAN, higher u-sCD163 levels were associated with histological lesions of greater severity, as well as more proteinuria and poorer renal function. Additionally, u-sCD163 was correlated with infiltration of tubulointerstitial CD163+ macrophages. High u-sCD163 levels (>3.57 ng/mg Cr) were associated with a 2.66-fold greater risk for IgAN remission failure in adjusted analyses. Adding u-sCD163 levels to the model containing clinical data at biopsy and MEST-C score significantly improved the risk prediction of IgAN remission status (AUC 0.788). Together, our results suggest that u-sCD163 may be a useful noninvasive biomarker to evaluate disease severity and remission status of IgAN.

Differential Internalization of Thrombin-Derived Host Defense Peptides into Monocytes and Macrophages

Proteolytic cleavage of thrombin generates C-terminal host defense peptides exerting multiple immunomodulatory effects in response to bacterial stimuli. Previously, we reported that thrombin-derived C-terminal peptides (TCPs) are internalized in monocytes and macrophages in a time- and temperature-dependent manner. In this study, we investigated which endocytosis pathways are responsible for the internalization of TCPs. Using confocal microscopy and flow cytometry, we show that both clathrin-dependent and clathrin-independent pathways are involved in the internalization of the prototypic TCP GKY25 in RAW264.7 and human monocyte-derived M1 macrophages, whereas the uptake of GKY25 in monocytic THP-1 cells is mainly dynamin-dependent. Internalized GKY25 was transported to endosomes and finally lysosomes, where it remained detectable for up to 10 h. Comparison of GKY25 uptake with that of the natural occurring TCPs HVF18 and FYT21 indicates that the pathway of TCP endocytosis is not only cell type-dependent but also depends on the length and composition of the peptide as well as the presence of LPS and bacteria. Finally, using neutron reflectometry, we show that the observed differences between HVF18 and the other 2 TCPs may be explained partially by differences in membrane insertion. Taken together, we show that TCPs are differentially internalized into monocytes and macrophages.

GPR84 signaling promotes intestinal mucosal inflammation via enhancing NLRP3 inflammasome activation in macrophages

The putative medium-chain free fatty acid receptor GPR84 is a G protein-coupled receptor primarily expressed in myeloid cells that constitute the innate immune system, including neutrophils, monocytes, and macrophages in the periphery and microglia in the brain. The fact that GPR84 expression in leukocytes is remarkably increased under acute inflammatory stimuli such as lipopolysaccharide (LPS) and TNFα suggests that it may play a role in the development of inflammatory and fibrotic diseases. Here we demonstrate that GPR84 is highly upregulated in inflamed colon tissues of active ulcerative colitis (UC) patients and dextran sulfate sodium (DSS)-induced colitis mice. Infiltrating GPR84+ macrophages are significantly increased in the colonic mucosa of both the UC patients and the mice with colitis. Consistently, GPR84−/− mice are resistant to the development of colitis induced by DSS. GPR84 activation imposes pro-inflammatory properties in colonic macrophages through enhancing NLRP3 inflammasome activation, while the loss of GPR84 prevents the M1 polarization and properties of proinflammatory macrophages. CLH536, a novel GPR84 antagonist discovered by us, suppresses colitis by reducing the polarization and function of pro-inflammatory macrophages. These results define a unique role of GPR84 in innate immune cells and intestinal inflammation, and suggest that GPR84 may serve as a potential drug target for the treatment of UC.

miR-155 overexpressing monocytes resemble HLA highISG15 + synovial tissue macrophages from patients with rheumatoid arthritis and induce polyfunctional CD4+ T cell activation

MicroRNAs (miRs) are known to regulate pro-inflammatory effector functions of myeloid cells, and miR dysregulation is implicated in rheumatoid arthritis (RA), a condition characterised by inflammation and destruction of the joints. We showed previously that miR-155 is increased in myeloid cells in RA and induces pro-inflammatory activation of monocytes and macrophages, however its role at the interface between innate and adaptive immunity was not defined. Here, RNA-sequencing revealed that overexpression of miR-155 in healthy donor monocytes conferred a specific gene profile which bears similarities to that of RA synovial fluid-derived CD14+ cells and HLA highISG15 + synovial tissue macrophages, both of which are characterised by antigen presenting pathways. In line with this, monocytes in which miR-155 was overexpressed, displayed increased expression of HLA-DR and both co-stimulatory and co-inhibitory molecules, and induced activation of polyfunctional T cells. Together, these data underpin the notion that miR-155-driven myeloid cell activation in the synovium contributes not only to inflammation but may also influence the adaptive immune response.