Inflammatory macrophage dependence on NAD+ salvage is a consequence of reactive oxygen species–mediated DNA damage

Abstract

The H2.0-like homeobox transcription factor (HLX) regulates hematopoietic differentiation and is overexpressed in Acute Myeloid Leukemia (AML), but the mechanisms underlying these functions remain unclear. We demonstrate here that HLX overexpression leads to a myeloid differentiation block both in zebrafish and human hematopoietic stem and progenitor cells (HSPCs). We show that HLX overexpression leads to downregulation of genes encoding electron transport chain (ETC) components and upregulation of PPARδ gene expression in zebrafish and human HSPCs. HLX overexpression also results in AMPK activation. Pharmacological modulation of PPARδ signaling relieves the HLX-induced myeloid differentiation block and rescues HSPC loss upon HLX knockdown but it has no effect on AML cell lines. In contrast, AMPK inhibition results in reduced viability of AML cell lines, but minimally affects myeloid progenitors. This newly described role of HLX in regulating the metabolic state of hematopoietic cells may have important therapeutic implications.

Cell‐intrinsic metabolic regulation of mononuclear phagocyte activation: Findings from the tip of the iceberg

“…12,29 A decline in OXPHOS is also apparent after stimulation with LPS alone, but is not as marked as in LPS-stimulated DCs. 29,30 This reflects a requirement for IFNγ as well as LPS to promote maximal NO production in macrophages, but not DCs.…”

“…In this way, alternative activation although dependent on glucose and respiration, does not require the de novo NAD+ synthesis pathway which is essential for inflammatory macrophage activation, as discussed above. 29 In IL-4-activated macrophages reduced Δψ m due to PGE2 co-stimulation results in a loss of spare respiratory capacity and a reduction in the expression of some alternative activation markers, such as Retnla. This effect was found to be due to the ability of Δψ to regulate the transcriptional activity of ETV1.…”

“…The importance of this pathway in inflammatory macrophages is illustrated by the fact that FK866, an inhibitor of NAMPT, results in reductions in NAD+, glycolysis, and inflammatory activation, which can be reversed by the addition of nicotinamide mononucleotide, the NAD+ salvage pathway intermediate downstream of NAMPT. 29 We would argue that the ability of FK866 to regulate inflammatory activation reflects the inhibitory effects of NAD+ depletion on GAPDH. Direct targeting of GAPDH by koningic acid (heptelidic acid), which covalently modifies the active site cysteine, results in similar effects on activation as those observed using FK866.…”

“…Direct targeting of GAPDH by koningic acid (heptelidic acid), which covalently modifies the active site cysteine, results in similar effects on activation as those observed using FK866. 29 Moreover, there is a recent realization that dimethylfumarte, a drug used extensively for the treatment of psoriasis, a disease caused by…”

The impact of PARPs and ADP-ribosylation on inflammation and host–pathogen interactions

“…A recent report indicates that cellautonomous production of NAD ± via the kynurenine pathway (KP) is required to induce normal inflammatory macrophage activation and that the de novo NAD ± synthesis can be impaired in aged macrophages (Minhas et al 2019). Another study proposed a mechanism linking the NAD ± salvage pathway to LPS-induced PARP1 consumption of NAD ± (Cameron et al 2019). In LPS-stimulated macrophages, an increase in reactive oxygen species induces DNA damage, which in turn activates PARP1, leading to a reduction of available NAD ± .…”