Transcriptional and Translational Regulation of Inflammatory Mediator Production by Endogenous TGF-β in Macrophages That Have Ingested Apoptotic Cells

Abstract

We recently reported that phagocytosis of apoptotic cells inhibits the release of inflammatory cytokines by human macrophages. In this paper we show that apoptotic cell uptake by mouse J774 macrophages also inhibits the synthesis and secretion of the chemokines, macrophage inflammatory protein-2 (Mip-2), KC, and Mip-1α (but not that of monocyte chemoattractant protein-1 (MCP-1)/JE), and increases TGF-β formation. Anti-TGF-β neutralizing Abs largely reversed the inhibitory effect of apoptotic cell uptake, and accordingly, exogenous TGF-β down-regulated the synthesis of the same mediators. Apoptotic cell ingestion or TGF-β also inhibited Mip-2 and Mip-1α gene expression in LPS-treated J774 cells, whereas TNF-α mRNA levels were unaffected. Importantly, TGF-β pretreatment of J774 cells did not significantly alter chemokine and TNF mRNA stability. Finally, we found that apoptotic cell uptake and TGF-β did not modulate NF-κB or AP-1 DNA binding in J774 cells. We conclude that the decreased production of chemokines and TNF resulting from apoptotic cell ingestion is largely mediated by a common event, i.e., feedback inhibition by endogenous TGF-β, but involves different mechanisms. Whereas TNF-α production appears to be translationally down-regulated, the suppression of most chemokines investigated appears to reflect transcriptional inhibition. In a broader context, the impairment of chemokine and TNF generation by apoptotic cell uptake might represent an important mechanism contributing to the resolution of inflammation. An additional consequence could be the selective recruitment of monocytes into inflammatory sites, as MCP-1/JE production by mouse macrophages was unaffected by apoptotic cell uptake, in contrast to other chemokines.