BHLHE40 promotes macrophage pro-inflammatory gene expression and functions

Abstract

Macrophages are the principal innate immune cells that populate all major organs and provide the first line of cellular defense against infections and/or injuries. The immediate and early-responding macrophages must mount a robust pro-inflammatory response to protect the host by eliminating deleterious agents. The effective pro-inflammatory macrophage response requires the activation of complex transcriptional programs that modulate the dynamic regulation of inflammatory and metabolic gene expression. Therefore, transcription factors that govern pro-inflammatory and metabolic gene expression play an essential role in shaping the macrophage inflammatory response. Herein, we identify the basic helix-loop-helix family member e40 (BHLHE40), as a critical transcription factor that promotes broad pro-inflammatory and glycolytic gene expression by elevating HIF1α levels in macrophages. Our in vivo studies revealed that myeloid-BHLHE40 deficiency significantly attenuates macrophage and neutrophil recruitment to the site of inflammation. Our integrated transcriptomics and gene set enrichment analysis (GSEA) studies show that BHLHE40 deficiency broadly curtails inflammatory signaling pathways, hypoxia response, and glycolytic gene expression in macrophages. Utilizing complementary gain- and loss-of-function studies, our analyses uncovered that BHLHE40 promotes LPS-induced HIF1α mRNA and protein expression in macrophages. More importantly, forced overexpression of oxygen stable form of HIF1α completely reversed attenuated pro-inflammatory and glycolytic gene expression in BHLHE40-deficient macrophages. Collectively, these results demonstrate that BHLHE40 promotes macrophage pro-inflammatory gene expression and functions by elevating HIF1α expression in macrophages.

Keywords: BHLHE40; HIF1α; glycolysis; hypoxia; inflammation; macrophages.