Collateral DNA damage and NAD+ dependence caused by reactive oxygen species signaling in inflammatory macrophages

Adoption of Warburg metabolism is critical for macrophage activation in response to lipopolysaccharide (LPS). Macrophages stimulated with LPS (without or with interferon-γ) increase expression of nicotinamide phosphoribosyltransferase (NAMPT), a key enzyme in NAD+ salvage, and loss of NAMPT activity alters their inflammatory potential. However, events leading to NAD+ salvage-dependence in these cells remain poorly defined. We show that NAD+ depletion and increased NAMPT expression occur rapidly after inflammatory activation and coincide with DNA damage caused by reactive oxygen species (ROS). ROS are produced by Complex III of the mitochondrial electron transport chain, and are required for macrophage activation. We show that DNA damage is associated with PARP activation, which results in NAD+ consumption and in this setting increased NAMPT expression allows the maintenance of NAD+ pools sufficient for GAPDH activity and Warburg metabolism. Our findings provide an integrated explanation for dependency on the NAD+ salvage pathway in inflammatory macrophages. RNA-seq was performed on bone marrow-derived macrophages (triplicate) exposed to lipopolysaccharide, interferon gamma or interleukin 4.