NAD+ Released during Inflammation Participates in T Cell Homeostasis by Inducing ART2-Mediated Death of Naive T Cells In Vivo

Abstract

Mono ADP-ribosyltransferase 2 (ART2) is an ectoenzyme expressed on mouse T lymphocytes, which catalyze the transfer of ADP-ribose groups from NAD+ onto several target proteins. In vitro, ADP-ribosylation by ART2 activates the P2X7 ATP receptor and is responsible for NAD+-induced T cell death (NICD). Yet, the origin of extracellular NAD+ and the role of NICD in vivo remain elusive. In a model of acute inflammation induced by polyacrylamide beads, we demonstrate release of NAD+ into exudates during the early phase of the inflammatory response. This leads to T cell depletion in the draining lymph nodes from wild-type and, more severely, from mice lacking the CD38 NAD+ glycohydrolase, whereas no effect is observed in ART2-deficient animals. Intravenous injection of NAD+ used to exacerbate NICD in vivo results in fast and dramatic ART2- and P2X7-dependent depletion of CD4+ and CD8+ T lymphocytes, which can affect up to 80% of peripheral T cells in CD38−/− mice. This affects mainly naive T cells as most cells surviving in vivo NAD+ treatment exhibit the phenotype of recently activated/memory cells. Consistently, treatment with NAD+ abolishes primary Ab response to a T-dependent Ag in NICD-susceptible CD38−/− mice but has no effect on the secondary response when given several days after priming. Unexpectedly NAD+ treatment improves the response in their wild-type BALB/c counterparts. We propose that NAD+ released during early inflammation facilitates the expansion of primed T cells, through ART2-driven death of resting cells, thus contributing to the dynamic regulation of T cell homeostasis.

NAD+ and ATP Released from Injured Cells Induce P2X7-Dependent Shedding of CD62L and Externalization of Phosphatidylserine by Murine T Cells

“…That activation of P2X 7 by ADP-ribosylation can play a role in physiological settings has been demonstrated previously by our finding that NAD ϩ released at inflammatory sites induces ART2-dependent shedding of CD62L and T cell death in draining lymph nodes (6). The results of the present study provide an additional plausible scenario for the activation of P2X 7 in vivo, i.e., by NAD ϩ and ATP released during hemolysis.…”

“…It is likely that the mechanisms described in this study with mechanically disrupted erythrocytes act also in these and other settings in vivo. Indeed, recent results from three different mouse models of inflammation support the notion that nucleotides released during tissue injury induce P2X 7 activation on T cells in vivo (6,18,25). Firstly, injection of Con A induces T cell-dependent hepatitis that is accompanied by fulminant liver cell damage as evidenced by the release of cytosolic enzymes into the circulation.…”

“…Indeed, these changes were corrected when CD38 deficiency was combined with ART2 deficiency. Thirdly, local inflammatory responses induced by s.c. injection of Biogel lead to release of NAD into the inflammatory pouch, causing shedding of CD62L by T cells in the draining but not in the nondraining lymph nodes (6).…”

“…Mounting evidence indicates that these nucleotides play important roles also as signaling molecules in the extracellular environment (1,2). In the context of the immune system of higher organisms, it has been proposed that the release of NAD ϩ and ATP from lysed cells may alert cells of the immune system to tissue damage (2)(3)(4)(5)(6). Indeed, lymphocytes and macrophages are equipped with numerous sensors for extracellular NAD ϩ and ATP, including nucleotide-metabolizing ecto-enzymes and nucleotide receptors (7,8).…”

Sirtuins and inflammation: Friends or foes?

“…Although administration of NAD could represent the most straightforward approach to increase intracellular NAD concentrations, the widespread expression of NAD-degrading ectoenzymes represent a likely mechanism affecting exogenously administered NAD bioavailability before it could reach the initially targeted cells. Moreover, systemic administration of NAD could also affect lymphocyte numbers through the process of NAD-Induced Cell Death (NICD) [60]. As previously discussed, exogenous nicotinamide, a vitamin B3 component representing the major NAD precursor in mammalian cells and displaying low toxicity in vivo [45], may represent an ideal alternative to affect intracellular NAD levels.…”