伊藤 辰将

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.

Information on immune checkpoint inhibitor-induced vasculitides is limited, and predictors for this condition have not been identified. Therefore, we have examined the frequency of immune checkpoint inhibitor-induced vasculitides by analyzing the data recorded in the Japanese Adverse Drug Event Report database. Data from April 2004 to March 2020 were extracted, and vasculitides as an immune-related adverse event was defined according to the 2012 revised International Chapel Hill Consensus Conference Nomenclature of Vasculitides. Adverse event signals were recognized as significant when the reporting odds ratio estimates and lower limits of the corresponding 95% confidence intervals exceeded 1. The use of nivolumab showed a significant signal for vasculitides. Furthermore, significant signals of polymyalgia rheumatica were found when the patients were treated with nivolumab, pembrolizumab, and ipilimumab. In addition, the frequencies of nivolumab- and pembrolizumab-induced polymyalgia rheumatica were higher in patients aged ≥70 years and female patients, respectively. Polymyalgia rheumatica was reported in 38 patients treated with nivolumab; 31 (82%) of these were either in recovery or in remission. Further, polymyalgia rheumatica was reported in 17 patients treated with pembrolizumab; 13 (76%) of these were in recovery or remission, while three (18%) were not. Polymyalgia rheumatica was reported in 12 patients treated with ipilimumab; seven (58%) of these were in recovery or remission. Our study highlights that careful monitoring for the symptom of PMR (e.g., bilateral pain in shoulder and pelvic girdles) is required when the patients are aged >70 years and have been treated with nivolumab and when the patients are women and have been treated with pembrolizumab.

The glomerulus primarily comprises mesangial cells, glomerular microvascular endothelial cells, and podocytes. IgA nephropathy is the most common primary glomerulonephritis worldwide and has a risk of progression to end-stage renal disease. IgA nephropathy is characterized by predominant IgA deposition in the glomerular mesangial area, where TG2 is significantly enhanced. Therefore, identification of glomerular TG2 substrates is the first step in elucidating the role of TG2 as a crosslinking enzyme during disease progression. To clarify potential glomerular TG2 substrates, and to establish a procedure for substrate identification, we attempted to identify those molecules using normal mouse glomeruli. Extracts from mouse glomerular and non-glomerular fractions were treated with our established biotin-labeled substrate peptide, which specifically crosslinks to the lysine-donor substrates depending on TG2 activity. Peptide-incorporated proteins were then purified using avidin resin and identified via mass spectrometry. In parallel, we performed the identification using corresponding samples from TG2 knockout mice. Consequently, potential TG2 substrates were separately identified in glomerular and non-glomerular fractions. They were mainly identified as novel TG2 substrates and partly include the well-known substrates. These results potentially provide novel insights into the mechanism underlying IgA nephropathy and may help elucidate the physiological functions of TG2.

高齢かつ低心機能患者に腹膜透析(PD)を導入し、生活の質(QOL)のみならず心機能が改善した87歳男性の症例を報告した。10年前より腎硬化症による慢性腎不全にて加療中、心エコーでの所見で高度の低心機能を認めていたが、腎機能が不良のため心カテーテル検査による心精査を施行できなかった。うっ血性心不全を発症し入退院を繰り返していた。腎機能は緩徐に増悪したため、PDカテーテルを挿入し、体液量コントロールを目的にPD導入とした。導入後1年の時点で、心機能、SF-36v2によるQOL評価ともに改善を認めた。下腿の浮腫が消失し、経口摂取が改善し体重は増加した。本症例のように重度の低心機能例では、残腎機能が十分に保たれているうちからPD導入が望ましいと考えられた。本症例ではPDによって心機能が改善したが、心機能改善には血液透析(HD)にはない緩徐な除水に加え、さまざまな物質の除去が関与している可能性があり、今後HDと比較した検討が必要であることを指摘した。

Aneuploidy, a chromosomal numerical abnormality in the conceptus or fetus, occurs in at least 5% of all pregnancies and is the leading cause of early pregnancy loss in humans. Accumulating evidence now suggests that the correct segregation of chromosomes is affected by events occurring in prophase during meiosis I. These events include homologous chromosome pairing, sister-chromatid cohesion, and meiotic recombination. In our current study, we show that mutations in SYCP3, a gene encoding an essential component of the synaptonemal complex that is central to the interaction of homologous chromosomes, are associated with recurrent pregnancy loss. Two out of 26 women with recurrent pregnancy loss of unknown cause were found to carry independent heterozygous nucleotide alterations in this gene, neither of which was present among a group of 150 fertile women. Analysis of transcripts from minigenes harboring each of these two mutations revealed that both affected normal splicing, possibly resulting in the production of C-terminally mutated proteins. The mutant proteins were found to interact with their wild-type counterpart in vitro and inhibit the normal fiber formation of the SYCP3 protein when coexpressed in a heterologous system. These data suggest that these mutations are likely to generate an aberrant synaptonemal complex in a dominant-negative manner and contribute to abnormal chromosomal behavior that might lead to recurrent miscarriage. Combined with the fact that similar mutations have been previously identified in two males with azoospermia, our current data suggest that sexual dimorphism in response to meiotic disruption occurs even in humans.