Tristetraprolin (TTP) is an RNA-binding protein and an essential factor of posttranscriptional repression of cytokine biosynthesis in macrophages. Its activity is temporally inhibited by LPS-induced p38 MAPK /MAPKAPK2/3-mediated phosphorylation, leading to a rapid increase in cytokine expression. We compared TTP expression and cytokine production in mouse bone marrow-derived macrophages of different genotypes: wild type, MAPKAP kinase 2 (MK2) deletion (MK2 knockout [KO]), MK2/3 double deletion (MK2/3 double KO [DKO]), TTP-S52A-S178A (TTPaa) knock-in, as well as combined MK2 KO/TTPaa and MK2/3 DKO/TTPaa. The comparisons reveal that MK2/3 are the only LPS-induced kinases for S52 and S178 of TTP and the role of MK2 and MK3 in the regulation of TNF biosynthesis is not restricted to phosphorylation of TTP at S52/S178 but includes independent processes, which could involve other TTP phosphorylations (such as S316) or other substrates of MK2/3 or p38 MAPK. Furthermore, we found differences in the dependence of various cytokines on the cooperation between MK2/3 deletion and TTP mutation ex vivo. In the cecal ligation and puncture model of systemic inflammation, a dramatic decrease of cytokine production in MK2/3 DKO, TTPaa, and DKO/TTPaa mice compared with wild-type animals is observed, thus confirming the role of the MK2/3/TTP signaling axis in cytokine production also in vivo. These findings improve our understanding of this signaling axis and could be of future relevance in the treatment of inflammation.

Endothelial cells can acquire a mesenchymal phenotype upon irritation [endothelial‐to‐mesenchymal transition (EndMT)]. Macrophages accumulate in the atherosclerotic plaque. This study addressed whether macrophages modulate EndMT and delineated a reciprocal effect of EndMT on macrophage functions in atherosclerosis. In atherosclerotic murine and human aortas, endothelial cells with mesenchymal markers were elevated by confocal microscopy and flow cytometric analysis. Increased EndMT master transcription factor Snail expression and extracellular matrix are consistent with enhanced EndMT in this condition. Hypoxia was detected in individual aortic EndMT cells in vivo and rapidly induced a similar EndMT phenotype in vitro. As a novel inducer of EndMT, macrophages, which are abundant in the atherosclerotic lesions, enhance mesothelial marker expression during coculture in vitro. In the reverse relationship, EndMT altered endothelial colony‐stimulating factor expression. Functionally, EndMT cell–conditioned media attenuated macrophage proliferation, antigen‐presenting cell marker expression, and TNF‐α production in response to oxidized LDL but increased oxidized LDL uptake and scavenger receptor expression. These experiments demonstrate that macrophages promote partial EndMT. In turn, EndMT cells modulate macrophage phenotype and lipid uptake. Our data suggest that EndMT shapes macrophage and endothelial cell phenotypes, thus affecting internal atherosclerotic plaque in addition to surface structure.—Helmke, A., Casper, J., Nordlohne, J., David, S., Haller, H., Zeisberg, E. M., von Vietinghoff, S. Endothelial‐to‐mesenchymal transition shapes the atherosclerotic plaque and modulates macrophage function. FASEB J. 33, 2278–2289 (2019). http://www.fasebj.org

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MiR-511-3p is embedded in intron 5 of the CD206/MRC1 gene Mrc1, expressed by macrophage and dendritic cell populations. CD206 and miR-511-3p expression are co-regulated, and their contribution to intestinal inflammation is unclear. We investigated their roles in intestinal inflammation in both mouse and human systems. Colons of CD206-deficient mice displayed normal numbers of monocytes, macrophage, and dendritic cells. In experimental colitis, CD206-deficient mice had attenuated inflammation compared with wild-type (WT) mice. However, neither a CD206 antagonist nor a blocking antibody reproduced this phenotype, suggesting that CD206 was not involved in this response. Macrophages isolated from CD206-deficient mice had reduced levels of miR-511-3p and Tlr4 compared with WT, which was associated with reduced pro-inflammatory cytokine production upon lipopolysaccharides (LPS) and fecal supernatant stimulation. Macrophages overexpressing miR-511-3p showed 50% increase of Tlr4 mRNA, whereas knockdown of miR-511-3p reduced Tlr4 mRNA levels by 60%, compared with scrambled microRNA (miRNA)-transduced cells. Response to anti-tumor necrosis factor (TNF) treatment has been associated with elevated macrophage CD206 expression in the mucosa. However, in colon biopsies no statistically significant change in miR-511-3p was detected. Taken together, our data show that miR-511-3p controls macrophage-mediated microbial responses and is involved in the regulation of intestinal inflammation.