Reducing Cholesterol in Resting Macrophage Activates NF-kB through Mitochondria, Resulting in Epigenomic Reprogramming to Dampen Inflammation in Activated Macrophages

Abstract

Cholesterol plays an important role in macrophage functions including their immune response1. Recently, NF-kB was shown to reprogram the epigenome in macrophages2. Here, we show that NF-kB pathway is activated in resting macrophages when cholesterol is reduced by statin or methyl-{beta}-cyclodextrin (MCD). Activated NF-kB increases the expression of histone-modifying enzymes, such as demethylase JMJD3. We provide evidence that the epigenome in these macrophages is reprogrammed, likely driven by NF-kB and histone modifications2. We also show that cholesterol reduction in macrophages results in suppression of mitochondria respiration. Specifically, cholesterol levels in the inner membrane of the mitochondria is reduced, which impairs the efficiency of ATP synthase (complex V). Consequently, protons accumulate in the intermembrane space to active NF-kB and JMJD3, thereby modifying the epigenome. When subsequently challenged by the inflammatory stimulus lipopolysaccharide (LPS), cholesterol-reduced macrophages generate responses that are less pro-inflammatory and more homeostatic, which should favour inflammation resolution. Taken together, we describe a mechanism by which the level of mitochondrial cholesterol in resting macrophages regulates the epigenome through NF-kB, thereby preparing macrophage for future immune activation.