TRAM-Related TLR4 Pathway Antagonized by IRAK-M Mediates the Expression of Adhesion/Coactivating Molecules on Low-Grade Inflammatory Monocytes

Abstract

Low-grade inflammatory monocytes critically contribute to the pathogenesis of chronic inflammatory diseases such as atherosclerosis. The elevated expression of coactivating molecule CD40 as well as key adhesion molecule CD11a is a critical signature of inflammatory monocytes from both human patients with coronary artery diseases as well as in animal models of atherosclerosis. In this study, we report that subclinical superlow-dose LPS, a key risk factor for low-grade inflammation and atherosclerosis, can potently trigger the induction of CD40 and CD11a on low-grade inflammatory monocytes. Subclinical endotoxin-derived monocytes demonstrate immune-enhancing effects and suppress the generation of regulatory CD8+CD122+ T cells, which further exacerbate the inflammatory environment conducive for chronic diseases. Mechanistically, subclinical endotoxemia activates TRAM-mediated signaling processes, leading to the activation of MAPK and STAT5, which is responsible for the expression of CD40 and CD11a. We also demonstrate that TRAM-mediated monocyte polarization can be suppressed by IRAK-M. IRAK-M–deficient monocytes have increased expression of TRAM, elevated induction of CD40 and CD11a by subclinical-dose endotoxin, and are more potent in suppressing the CD8 regulatory T cells. Mice with IRAK-M deficiency generate an increased population of inflammatory monocytes and a reduced population of CD8 T regulatory cells. In contrast, mice with TRAM deficiency exhibit a significantly reduced inflammatory monocyte population and an elevated CD8 T regulatory cell population. Together, our data reveal a competing intracellular circuitry involving TRAM and IRAK-M that modulate the polarization of low-grade inflammatory monocytes with an immune-enhancing function.

Development of Exhausted Memory Monocytes and Underlying Mechanisms

“…All animal procedures were in accordance with the U.S. National Institutes of Health Guide for the Care and Use of Laboratory Animals and approved by Institutional Animal Care and Use Committee (IACUC) of Virginia Tech. Bone marrow cells were harvested from WT and TRAM KO mice as described previously (19,25,26). Primary cells were cultured in complete RPMI 1640 media with supplemented with 10% FBS, 1% penicillin-streptomycin, and 1% L-Glutamine and 10ng/mL M-CSF (PeproTech, Rocky Hill, NJ; no.…”

“…Cells were treated with either PBS (control) or high-dose LPS (100 ng/mL) for 5 days at 37°C in a humidified 5% CO2 atmosphere. Fresh complete media supplemented with M-CSF and treatments were added every 2 days as reported previously (19,25,26). As we previously characterized, bone marrow cells cultured under such condition were monocyte-like, loosely adherent, and did not express mature macrophage marker CD71 (27).…”

“…To monitor the exhaustion of primary monocytes to persistent challenges of bacterial endotoxin LPS, we cultured murine monocytes derived from bone marrow for 5 days in the presence of M-CSF to maintain cell survival as we described (25,26), with the repetitive challenges with either PBS or high dose LPS (100ng/mL) on Day 0, 2 and 4. We then harvested the cultured cells at day 1, 3, and 5 for flow cytometry analyses of CD86, MHCII and PD-L1.…”

A Bibliometric and Knowledge-Map Analysis of Macrophage Polarization in Atherosclerosis From 2001 to 2021

“…We conclude that the hotspots of macrophage polarization in AS initially focused on its impact on obesity. Studies explored more critical targets in this area, including Nrf2 ( 59 ), Kruppel-like factor 4 ( 60 – 63 ), GLP-1/GLP-1R ( 64 ), TLR4 ( 27 , 65 ), and micro RNA ( 66 , 67 ), related to inflammation process and plaque progression. Cardiovascular disease studies, including the role of macrophage polarization in lipid metabolism, inflammatory immune response in plaques, and cerebrovascular disease, are two diseases involved in this field.…”

Imaging of Atherosclerosis with [64Cu]Cu-DOTA-TATE: a Translational Head-to-Head Comparison Study with 2-[18F]FDG, and Na[18F]F in Rabbits

“…A predictor of atherosclerosis progression, ITGAL, was also found to correlate with both [ 64 Cu]-Cu-DOTA-TATE and Na[ 18 F]F. Of all the genes investigated, ITGAL was most differentially expressed between the atherosclerotic group and the control group. ITGAL expression is a signature for in ammatory monocytes, which together with other immune cells accumulates and become atherosclerotic plaque [30,31].…”