Targeted Disruption of CD38 Accelerates Autoimmune Diabetes in NOD/Lt Mice by Enhancing Autoimmunity in an ADP-Ribosyltransferase 2-Dependent Fashion

Abstract

Ubiquitously expressed CD38 and T cell-expressed ADP-ribosyltransferase 2 (ART2) are ectoenzymes competing for NAD substrate. CD38 exerts pleiotropic actions in hemopoietic and nonhemopoietic compartments via effects on calcium mobilization. ART2 is an ADP-ribosyltransferase on naive CD4+ and CD8+ T cells. ART2-catalyzed ADP-ribosylation of the P2X7 purinoreceptor elicits apoptosis. Transfer of a genetically disrupted CD38 allele into the autoimmune diabetes-prone NOD/Lt background accelerated diabetes onset in both sexes, whereas transfer of a disrupted ART2 complex had no effect. However, the fact that the accelerated pathogenesis mediated by CD38 deficiency required ART2 activity was demonstrated by combining both ART2 and CD38 deficiencies. Reciprocal bone marrow reconstitution studies demonstrated accelerated diabetes only when CD38-deficient bone marrow was transferred into CD38-deficient recipients. Neither decreases in β cell function nor viability were indicated. Rather, the balance between T-effectors and T-regulatory cells was disturbed in CD38-deficient but ART2-intact NOD mice. In these mice, significant reductions in total viable CD8+ T cells were observed. This was accompanied by an age-dependent increase in a diabetogenic CD8 clonotype. This in turn correlated with impaired T-regulatory development (10-fold reduction in Foxp3 mRNA expression). These changes were corrected when CD38 deficiency was combined with ART2 deficiency. Both ART2-deficient and CD38/ART2 combined deficient T cells were resistant to NAD-induced killing in vitro, whereas CD38-deficient but ART2-intact T cells showed increased sensitivity, particularly the CD4+CD25+ subset. Unexpectedly, diabetes development in the combined CD38/ART2 stock was strongly suppressed, possibly through epistatic interactions between genes linked to the targeted CD38 on Chromosome 5 and the ART2 complex on Chromosome 7.

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

“…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.…”

“…Secondly, genetic ablation of the major ecto-NADglycohydrolase CD38 results in elevated tissue NAD levels and enhanced levels of T cell surface ADP-ribosylation (24). Transfer of the deficient CD38 allele into the autoimmune diabetesprone NOD/Lt background resulted in accelerated disease progression, correlating with an enhanced sensitivity of regulatory T cells to ART2-dependent NAD-induced cell death in these mice (25). Indeed, these changes were corrected when CD38 deficiency was combined with ART2 deficiency.…”

“…Cells from CD38-deficient mice do not metabolize ecto-NAD ϩ efficiently, and the resulting higher levels of ecto-NAD ϩ lead to a higher level of ART-mediated cell surface protein ADP-ribosylation (24). CD38-deficient mice show enhanced sensitivity to insulin-dependent diabetes mellitus, which is dependent on the presence of ART2.2 (25). Likely, this reflects the enhanced activity of ART2.2 in these mice as a consequence of increased levels of extracellular NAD ϩ (24).…”

Suppressed Insulin Signaling and Increased Apoptosis inCd38-Null Islets

“…We and others did not observe a significant defect in glucose tolerance in Cd38 Ϫ/Ϫ mice on the C57BL/6 genetic background (58). It is possible that genetics could account for the differences in whole-body glucose metabolism.…”

“…Interestingly, cytokines responsible for ␤-cell apoptosis in type 1 diabetes, namely tumor necrosis factor ␣, interleukin-1␤, and interferon ␥, have all been shown to alter CD38 expression in other cells types (65,66). While this report was in revision, Leiter et al (58) reported that CD38 deficiency significantly accelerated diabetes in NOD mice. While the CD38 Ϫ/Ϫ : NOD study focused largely on the roles of CD38 in the immune system, their results also pointed to effects in nonhematopoietic cells (58).…”