The aorta and the large conductive arteries are immunoprivileged tissues and are protected against inflammatory attack. A breakdown of the immunoprivilege leads to autoimmune vasculitis, such as giant cell arteritis (GCA), in which CD8+ T regulatory (Treg) cells fail to contain CD4+ T cells and macrophages, resulting in the formation of tissue-destructive granulomatous lesions. Here, we report that the molecular defect of malfunctioning CD8+ Treg cells lies in aberrant NOTCH4 signaling that deviates endosomal trafficking and minimizes exosome production. By transcriptionally controlling the profile of RAB GTPases, NOTCH4 signaling restricted membrane translocation and vesicular secretion of the enzyme NADPH oxidase 2 (NOX2). Specifically, NOTCH4hiCD8+ Treg cells increased RAB5A and RAB11A expression and suppressed RAB7A, culminating in the accumulation of early and recycling endosomes and trapping of NOX2 in an intracellular, non-secretory compartment. RAB7AloCD8+ Treg cells failed in the surface translocation and the exosomal release of NOX2. NOTCH4hi RAB5Ahi RAB7Alo RAB11Ahi CD8+ Treg cells left adaptive immunity unopposed, enabling a breakdown in tissue tolerance and aggressive vessel wall inflammation. Inhibiting NOTCH4 signaling corrected the defect and protected arteries from inflammatory insult. The study implicates NOTCH4-dependent transcriptional control of RAB proteins and intracellular vesicle trafficking in autoimmune disease and in vascular inflammation.
Ke Jin, Zhenke Wen, Bowen Wu, Hui Zhang, Jingtao Qiu, Yanan Wang, Kenneth J. Warrington, Gerald Berry, Jörg J. Goronzy, Cornelia M. Weyand