Intracellular NAD levels regulate tumor necrosis factor protein synthesis in a sirtuin-dependent manner

Abstract

Uncontrolled TNF-α synthesis is known to play an important role in numerous inflammatory disorders, and multiple transcriptional and post-transcriptional regulatory mechanisms have therefore evolved to dampen the production of this important pro-inflammatory cytokine. By examining the anti-inflammatory properties of the vitamin B3 constituent nicotinamide, we have uncovered a novel regulatory pathway controlling TNF-α production. Exogenous nicotinamide inhibits TNF-α secretion through modulation of mRNA translation efficiency. Moreover, the capacity to produce TNF-α appears to be directly correlated with intracellular NAD levels, suggesting that a NAD-dependent biological event that can be inhibited by nicotinamide controls TNF-α synthesis in cells of the immune system. Sirtuins represent NAD-dependent deacetylases involved in regulation of gene expression in both mammals and yeasts, and are known to be inhibited by nicotinamide. We demonstrate herein that similarly to nicotinamide, structurally unrelated sirtuin inhibitors downregulate TNF-α secretion with minimal effect on TNF-α gene transcription. By over-expressing individual sirtuin members in cell lines transiently expressing TNF-α, we have identified SIRT6 as a sirtuin member able to upregulate TNF-α synthesis in vitro. In agreement with this finding, bone-marrow derived dendritic cells from SIRT6 KO mice display reduced TNF-α synthesis in response to CpG. Collectively, these data delineate a novel relationship between metabolism and the inflammatory response, by uncovering the role of SIRT6 in the control of TNF-α secretion.

Sirtuins and inflammation: Friends or foes?

“…Using different approaches, both studies led to the identification of SIRT6 as the sirtuin member able to positively regulate TNF and IFN synthesis. Notably, , over-expression of an enzymatically active (but not a catalytically inactive) form of SIRT6 led to supraoptimal production of TNF by upregulating the translational efficiency of TNF mRNA [49]. In agreement with this observation, dowregulation of intracellular NAD levels and sirtuin inhibitors reduced TNF protein synthesis with no significant effect on TNF mRNA accumulation in response to microbial stimulation.…”

“…In contrast to the anti-inflammatory role generally attributed to sirtuins, we and others have recently reported a possible positive regulatory role for SIRT6 in the induction of proinflammatory cytokine expression, in both innate and adaptive immune cells [49], [50]. In…”

“…It is noteworthy however that nicotinamide, the prototypic sirtuin inhibitor, 18 displays anti-inflammatory properties both in vitro and in vivo [49], [73]. Although nicotinamide may represent a general inhibitor for all NAD-consuming reactions, we and others have been able to confirm the potential beneficial role of sirtuin inhibitors as antiinflammatory compounds both in vitro and in vivo [49], [50], although these observations need to be further extended to more clinically relevant settings.…”

“…A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 13 these studies, reduction of intracellular NAD levels, obtained by inhibiting the enzymatic activity of Nampt, led to reduced secretion of selected cytokines (such as TNFIL-6 and/or IFN) by immune cells, while leaving other pro-inflammatory mediators (such as CCL5/Rantes) unaffected [49], [50]. Surprisingly, several sirtuin inhibitors could reproduce these effects, suggesting therefore that the NAD-sirtuin axis could also represent a positive regulatory loop required for adequate cytokine secretion.…”

Suppression of leukocyte infiltration and cartilage degradation by selective inhibition of pre-B cell colony-enhancing factor/visfatin/nicotinamide phosphoribosyltransferase: Apo866-mediated therapy in human fibroblasts and murine collagen-induced arthrit

“…The recently developed small molecule inhibitor APO866 has been shown to act as a competitive inhibitor of PBEF/NAMPT activity by inhibiting binding of its natural substrate, nicotinamide (14,15). Moreover, in vivo, APO866 displays antiinflammatory effects, and favorable results have been obtained with APO866 treatment in murine tumor models and models of inflammation (16)(17)(18)(19)(20)(21).…”