Abstract 17012: Biochemical Parallelism to Decipher How the Endothelium Governs Monocyte Differentiation
The physiologic cues that skew circulating monocytes towards distinct macrophage (MF) subsets are not clearly defined. Since the endothelium is a gatekeeper for circulating monocytes entering tissues, it is poised to deliver differentiation signals to infiltrating monocytes. We hypothesized that the endothelial cell (EC), depending on its activation state, would give rise to distinct phenotypic and functional MF subsets. EC pre-treated with interferon gamma (IFNγ), but not other inflammatory cytokines, diverted MF differentiation away from a homeostatic MF subset and towards an inflammatory MF subset. Yet, deciphering the gene expression program in EC responsible for skewing monocyte differentiation presented a formidable task. This problem was solved by a novel approach we term biochemical parallelism. First, a high-throughput flow cytometry approach was developed to identify small molecules that “mimicked” IFNγ in regards to polarizing EC to trigger inflammatory MF. Subsequently, IFNγ and active small molecules - as well as structural analogues that were inactive- were compared by whole genome expression profiling. Of over 800 nuclear factors induced by IFNγ, this approach narrowed the candidate genes to 4 transcription factors (TF). Forced expression of the candidate TF revealed that only activating transcription factor 3 (ATF3) reprogrammed the EC to trigger inflammatory MF. Transcriptome analysis of EC with forced expression of ATF3 revealed that the transcriptome was highly enriched for IFNγ-related genes. Finally, we screened a small molecule library of FDA-approved compounds and found that tolfenamic acid - a non-steroidal anti-inflammatory drug - polarized the endothelium to trigger inflammatory MF. While such effects may contribute to host-protective effects in cancer prevention, it may also provide an explanation for the increased cardiovascular events associated with this class of drugs. In conclusion, we demonstrate that the activation state of the endothelium can govern MF subset differentiation, and outline how biochemical parallelism can help decipher complex biological processes, while providing a novel methodology to identify small compounds with potential therapeutic value or unanticipated risk.
- © 2011 by American Heart Association, Inc.