#2709 THE INVOLVEMENT OF NRF2-MEDIATED ANTIOXIDANT SYSTEM IN MYELOPEROXIDASE-POSITIVE ANTINEUTROPHIL CYTOPLASMIC ANTIBODY-ASSOCIATED VASCULITIS
Authors: Ueda Yusho , Nakazawa Daigo , Harashima-Miyoshi Atsuko , Shiratori-Aso Satoka , Saori Nishio , Tomaru Utano , Ishizu Akihiro , Atsumi Tatsuya 
Published: June 2023

Abstract

Background and Aims
Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease pathologically characterized by vascular necrosis with inflammation. The necrotic lesions consist of ANCA-mediated neutrophil extracellular traps (NETs). During AAV, activated neutrophils form NETs via reactive oxygen spices (ROS)s-mediated signaling pathway. The excessive NETs lead to endothelial vascular damage and serve as autoantigens against ANCAs in a vicious cycle. Although the role of NETs in AAV has been revealed, its treatment for targeting NETs remains unestablished. Since nuclear factor-erythroid 2-related factor 2 (Nrf2) regulates antioxidant proteins against oxidative stress and functions as a defense system, we investigated the role of Nrf2 in the development of AAV.

Method
In vitro, human neutrophils treated with the Nrf2 activator bardoxolone methyl (Bard) were stimulated with ANCA, and the effects on NETs formation and signaling pathways including intracellular ROS were evaluated by cell imaging and biochemical approaches. The effects of Nrf2 activators on NETs-induced cytotoxicity were examined using human renal glomerular endothelial cells (HRGECs). Nrf2 knockout or WT mouse-derived neutrophils were stimulated with anti-MPO antibody to induce NETs. In vivo studies, Bard was administered to ANCA-transfer AAV model or spontaneous AAV developing mice models (SCG/Kj). Renal function was assessed by biochemical analysis, and the expression of ROS and antioxidant protein NAD(P)H Quinone Dehydrogenase 1 (NQO1) in tissues was evaluated by fluorescent immunostaining and immunoblotting. The formation of NETs in the glomeruli was evaluated by immunostaining and glomerular vascular endothelial damage was assessed by the expression of CD31 and TUNEL positivity. To assess the role of Nrf2 in immunological abnormality during AAV, murine splenocytes were collected and flow cytometry were conducted using CD4, CD8, B220, MCHCII, CD11c, F4/80, Ly 6G, Ly6b, and CD11b antibodies. Moreover, to assess the genetic role of Nrf2 in AAV, we established SCG/Kj mice carrying a germ-line deletion of the Nrf2-genes. A spontaneous mouse model of vasculitis genetically deficient in Nrf2 was analyzed by the same parameters to evaluate the effect of Nrf2. N1 offspring mice were generated by crossing Nrf2-/- mice with SCG/Kj mice. These backcrossed mice were obtained by crossing Nrf2-/- mice to background SCG/Kj mice for three generations. The experimental group was mated to N4 heterozygous mice, and female mice in the experimental group were analyzed at 18 weeks.

Results
In vitro, pharmacological activation of Nrf2 suppressed ANCA-induced NETs via the upregulation of NQO1 and inhibition of ROS. While, Nrf2-deficienet neutrophils showed the massive NETs in response to ANCA, compared to WT neutrophils. Furthermore, Nrf2 activation directly protected endothelium from cellular injury caused by the exposure of ANCA-mediated NETs. In vivo, the pharmacological activation of Nrf2 ameliorated glomerulonephritis in two kinds of AAV models through the upregulation of antioxidant and inhibition of ROS-mediated NETs. In contrast, Nrf2 genetic deficiency exacerbated vasculitis in spontaneous AAV model. The activation of Nrf2 regulated the expansion of splenocytes in AAV mice. In particular, pan-T cells in spleen and the infiltration of Th17 cells in kidney were suppressed by Nrf2 activation.

Conclusion
During ANCA-stimulation in neutrophils, the activation of Nrf2 initiates antioxidant system and inhibits intracellular ROS, leading to the suppression of NETs formation. Nrf2 may be a novel therapeutic target for AAV.