Yoshimasa Ito

Structural variations of N-glycans critically regulate glycoprotein functions and are involved in various human diseases. N-Acetylglucosaminyltransferase-III (GnT-III or MGAT3) is highly expressed in the brain and kidney and is an N-glycan branching enzyme that biosynthesizes the unique N-glycan branch designated as bisecting GlcNAc. Its roles in Alzheimer's disease and cancer have been revealed, but the functions of bisecting GlcNAc in the kidney are poorly understood. Here, we show that kidneys in the GnT-III-knockout (KO) mouse exhibit impaired body fluid balance and present interstitial edema. To understand the molecular mechanisms further, we biochemically purified the glycoproteins modified by GnT-III in the mouse kidney and identified these proteins using proteomics. We found that the proteins involved in the pathway for angiotensin II (Ang II) metabolism are modified by GnT-III, and that the subcellular localization of angiotensin-converting enzyme was altered in GnT-III-KO cells. Furthermore, the pathology in models of Ang II-related disease was slightly more severe in GnT-III-KO than in wild-type mice. Our data indicate a protective role for bisecting GlcNAc in the mouse kidney, highlighting a newly described link between specific N-glycan structures and renal functions.

Tryptophan (TRP) metabolism through the kynurenine pathway generates multiple biologically active metabolites with diverse immunomodulatory effects, but their roles in glomerulonephritis (GN), particularly in innate immunity, remain poorly understood. Using a nephrotoxic serum-induced GN (NTS-GN) model, we first analyzed mice deficient in key TRP-metabolizing enzymes of the kynurenine pathway: Indoleamine 2,3-dioxygenase 1 and 2 (IDO1 and IDO2), and kynurenine 3-monooxygenase (KMO), and found that Ido1-deficient mice exhibited exacerbated kidney injury and glomerular neutrophil infiltration, whereas Ido2 deficiency had no significant impact. In contrast, Kmo-deficient mice showed reduced crescent formation. Unexpectedly, the concentration of kynurenic acid (KYNA), a downstream metabolite of IDO1, was elevated in the kidney cortex of Ido1-deficient mice. Exogenous KYNA administration improved survival, ameliorated renal injury, and reduced neutrophil infiltration in Ido1-deficient mice, indicating its protective effect against antibody-mediated injury. Moreover, KYNA suppressed immune complex-mediated neutrophil spreading, attenuated FcγR-dependent Syk phosphorylation, and reduced VEGF secretion in vitro. Our results position KYNA as a key modulator of neutrophil-driven inflammation in antibody-mediated GN. This study uncovers distinct roles for kynurenine pathway enzymes and highlights the TRP-KYNA pathway as a promising immunometabolic target for controlling innate immune responses in GN.

Extracellular histones induce endothelial damage, resulting in lung haemorrhage; however, the underlying mechanism remains unclear. Factor XIII, as a Ca2+-dependent cross-linking enzyme in blood, mediates fibrin deposition. As another isozyme, transglutaminase 2 (TG2) has a catalytic activity distributing in most tissues. Herein, we investigated whether TG2 promotes fibrin deposition and mediates the adhesion of platelets to ECs in histone-induced acute lung injury (ALI). We evaluated the lung histology and the adhesion of platelets to endothelial cells (ECs) after injecting histones to wild-type (WT) C57BL/6J and TG2 knockout (TG2-/-) mice, and administered a TG2 inhibitor (NC9) to WT mice. Pulmonary haemorrhage was more severe in TG2-/- mice than that in WT mice. The area of fibrin deposition and the proportion of CD41+CD31+ cells were lower in TG2-/- mice than in WT mice. Pre-treatment of NC9 decreased the area of fibrin deposition and the proportion of CD41+CD31+ cells in WT mice. These results suggest that TG2 prevents from pulmonary haemorrhage in ALI by promoting the adhesion of platelets to ECs and the fibrin deposition.