NAMPT-Mediated Salvage Synthesis of NAD+ Controls Morphofunctional Changes of Macrophages

Abstract

Functional morphodynamic behavior of differentiated macrophages is strongly controlled by actin cytoskeleton rearrangements, a process in which also metabolic cofactors ATP and NAD(H) (i.e. NAD+ and NADH) and NADP(H) (i.e. NADP+ and NADPH) play an essential role. Whereas the link to intracellular ATP availability has been studied extensively, much less is known about the relationship between actin cytoskeleton dynamics and intracellular redox state and NAD+-supply. Here, we focus on the role of nicotinamide phosphoribosyltransferase (NAMPT), found in extracellular form as a cytokine and growth factor, and in intracellular form as one of the key enzymes for the production of NAD+ in macrophages. Inhibition of NAD+ salvage synthesis by the NAMPT-specific drug FK866 caused a decrease in cytosolic NAD+ levels in RAW 264.7 and Maf-DKO macrophages and led to significant downregulation of the glycolytic flux without directly affecting cell viability, proliferation, ATP production capacity or mitochondrial respiratory activity. Concomitant with these differential metabolic changes, the capacity for phagocytic ingestion of particles and also substrate adhesion of macrophages were altered. Depletion of cytoplasmic NAD+ induced cell-morphological changes and impaired early adhesion in phagocytosis of zymosan particles as well as spreading performance. Restoration of NAD+ levels by NAD+, NMN, or NADP+ supplementation reversed the inhibitory effects of FK866. We conclude that direct coupling to local, actin-based, cytoskeletal dynamics is an important aspect of NAD+’s cytosolic role in the regulation of morphofunctional characteristics of macrophages.

SIRT1 regulates macrophage self‐renewal

“…In contrast to NAM, NMN did not show any inhibitory effect on cell cycle progression (Fig J). This result was consistent with previous observations showing that NAD + depletion using the drug FK866 also had no effect on Maf‐DKO macrophage proliferation (Venter et al , ). NAD + is also a co‐factor of poly(ADP—ribose)polymerases (PARPs), enzymes that regulate DNA damage sensing, apoptosis, cellular stress and ageing, (Saldeen et al , ) and similarly release NAM as a by‐product of the enzymatic reaction.…”

Efferocytosis Fuels Requirements of Fatty Acid Oxidation and the Electron Transport Chain to Polarize Macrophages for Tissue Repair

“…Thus, mitochondrial NAD + is coupled to NAD + /NADH balance in the cytosol. In macrophages, the synthesis of NAD + by nicotinamide phosphoribosyl-transferase (NAMPT) promotes cytoskeletal activation during cellular adhesion (Venter et al, 2014). NAD + accumulation in efferocytes required Risp, and additional reductions in nicotinate and nicotinamide are consistent with efferocytic regulation of the NAD + pool.…”

Increased expression of NAMPT in PBMC from patients with acute coronary syndrome and in inflammatory M1 macrophages

“…Our findings suggest that NAMPT enzymatic activity could contribute to this process. Venter et al have recently showed that FK866 promotes downregulation of metabolic activity in macrophages accompanied by impaired phagocytic and adhesion capacity in these cells [31]. Moreover, intracellular NAD levels have been shown to regulate TNF in a sirtuin-dependent manner in THP-1 macrophages [32].…”