Aquaporin-3 regulates endosome-to-cytosol transfer via lipid peroxidation for cross presentation

Abstract

Antigen cross presentation, whereby exogenous antigens are presented by MHC class I molecules to CD8+ T cells, is essential for generating adaptive immunity to pathogens and tumor cells. Following endocytosis, it is widely understood that protein antigens must be transferred from endosomes to the cytosol where they are subject to ubiquitination and proteasome degradation prior to being translocated into the endoplasmic reticulum (ER), or possibly endosomes, via the TAP1/TAP2 complex. Revealing how antigens egress from endocytic organelles (endosome-to-cytosol transfer, ECT), however, has proved vexing. Here, we used two independent screens to identify the hydrogen peroxide-transporting channel aquaporin-3 (AQP3) as a regulator of ECT. AQP3 overexpression increased ECT, whereas AQP3 knockout or knockdown decreased ECT. Mechanistically, AQP3 appears to be important for hydrogen peroxide entry into the endosomal lumen where it affects lipid peroxidation and subsequent antigen release. AQP3-mediated regulation of ECT was functionally significant, as AQP3 modulation had a direct impact on the efficiency of antigen cross presentation in vitro. Finally, AQP3-/- mice exhibited a reduced ability to mount an anti-viral response and cross present exogenous extended peptide. Together, these results indicate that the AQP3-mediated transport of hydrogen peroxide can regulate endosomal lipid peroxidation and suggest that compromised membrane integrity and coordinated release of endosomal cargo is a likely mechanism for ECT.

Widespread discrepancy in Nnt genotypes and genetic backgrounds complicates granzyme A and other knockout mouse studies

“…Whether all the phenotypes reported for Gzma -/- mice ( Supplementary file 1 ) are compromised by Nnt and/or the mixed background remains unclear and would require new experiments to resolve, similar to those described herein for CHIKV arthritis. However, Nnt has been reported to affect redox regulation and activation in macrophages ( Ripoll et al, 2012 ; Salerno et al, 2019 ), with an intact Nnt gene conceivably reducing cross-presentation ( Dingjan et al, 2016 ; Nalle et al, 2020 ) and CD8 T cell responses ( Oberkampf et al, 2018 ). In addition, 6N vs. 6J background differences (as herein) have shown clear phenotypes in a wide range of settings ( Leskov et al, 2017 ; Morales-Hernandez et al, 2018 ; Rao et al, 2020 ; Salerno et al, 2019 ; Vozenilek et al, 2018 ; Williams et al, 2021 ; Wolf et al, 2016 ).…”

Signaling Mechanisms and Pharmacological Modulators Governing Diverse Aquaporin Functions in Human Health and Disease

“…AQP3 in endosomes is needed for immune response development in mice. Adaptive immunity to pathogens starts with the presentation to CD8 + T-cells of a foreign antigen, which after ubiquitination and proteasome degradation must be released into the cytosol; this process requires AQP3 thought to act by enabling H 2 O 2 entry into the endosome to cause lipid peroxidation and release [539]. AQP8 in the inner mitochondrial membrane was shown to confer Hg 2+ -sensitive water permeability in liver cell mitochondria [540].…”

The Delivery of Extracellular “Danger” Signals to Cytosolic Sensors in Phagocytes

“…Similarly, a-Tocopherol, an antioxidant which scavenges the ROS produced by the NADPH oxidase, reduces ROS-induced lipid peroxidation as well as the release of endocytosed proteins into the cytosol (47). Further evidence in support of ROS-induced membrane destabilization was provided by Nalle et al who demonstrated that aquaporin-3 (AQP3) transports hydrogen peroxide into endocytic organelles where it contributes to lipid peroxidation, membrane destabilization and protein release to the cytosol (49). It is worth mentioning, that apart from ROSdependent lipid modification, other lipid modifications on endocytic organelles, such as the accumulation of sphingosinebased lipids, have been proposed although there is no direct evidence for these modifications in the escape of endocytosed proteins into the cytosol as yet [reviewed in (50)].…”