Protective Role of MAVS Signaling for Murine Lipopolysaccharide-Induced Acute Kidney Injury.

Despite treatment advances, acute kidney injury (AKI)-related mortality rates are still high in hospitalized adults, often due to sepsis. Sepsis and AKI could synergistically worsen the outcomes of critically ill patients. TLR4 signaling and mitochondrial antiviral signaling protein (MAVS) signaling are innate immune responses essential in kidney diseases, but their involvement in sepsis-associated AKI (SA-AKI) remains unclear. We studied the role of MAVS in kidney injury related to the TLR4 signaling pathway using a murine LPS-induced AKI model in wild-type and MAVS-knockout mice. We confirmed the importance of M1 macrophage in SA-AKI through in vivo assessment of inflammatory responses. The TLR4 signaling pathway was upregulated in activated bone marrow-derived macrophages, in which MAVS helped maintain the LPS-suppressed TLR4 mRNA level. MAVS regulated redox homeostasis via NADPH oxidase Nox2 and mitochondrial reverse electron transport in macrophages to alleviate the TLR4 signaling response to LPS. Hypoxia-inducible factor 1α (HIF-1α) and AP-1 were key regulators of TLR4 transcription and connected MAVS-dependent reactive oxygen species signaling with the TLR4 pathway. Inhibition of succinate dehydrogenase could partly reduce inflammation in LPS-treated bone marrow-derived macrophages without MAVS. These findings highlight the renoprotective role of MAVS in LPS-induced AKI by regulating reactive oxygen species generation-related genes and maintaining redox balance. Controlling redox homeostasis through MAVS signaling may be a promising therapy for SA-AKI.

Protective effect of d-alanine against acute kidney injury.

Recent studies have revealed the connection between amino acid chirality and diseases. We have previously reported that the gut microbiota produces various d-amino acids in a murine acute kidney injury (AKI) model. Here, we further explored the pathophysiological role of d-alanine (d-Ala) in AKI. Levels of d-Ala were evaluated in a murine AKI model. We analyzed transcripts of the N-methyl-d-aspartate (NMDA) receptor, a receptor for d-Ala, in tubular epithelial cells (TECs). The therapeutic effect of d-Ala was then assessed in vivo and in vitro. Finally, the plasma level of d-Ala was evaluated in patients with AKI. The Grin genes encoding NMDA receptor subtypes were expressed in TECs. Hypoxic conditions change the gene expression of Grin1, Grin2A, and Grin2B. d-Ala protected TECs from hypoxia-related cell injury and induced proliferation after hypoxia. These protective effects are associated with the chirality of d-Ala. d-Ala inhibits reactive oxygen species (ROS) production and improves mitochondrial membrane potential, through NMDA receptor signaling. The ratio of d-Ala to l-Ala was increased in feces, plasma, and urine after the induction of ischemia-reperfusion (I/R). Moreover, Enterobacteriaceae, such as Escherichia coli and Klebsiella oxytoca, produce d-Ala. Oral administration of d-Ala ameliorated kidney injury after the induction of I/R in mice. Deficiency of NMDA subunit NR1 in tubular cells worsened kidney damage in AKI. In addition, the plasma level of d-Ala was increased and reflected the level of renal function in patients with AKI. In conclusion, d-Ala has protective effects on I/R-induced kidney injury. Moreover, the plasma level of d-Ala reflects the estimated glomerular filtration rate in patients with AKI. d-Ala could be a promising therapeutic target and potential biomarker for AKI.NEW & NOTEWORTHY d-Alanine has protective effects on I/R-induced kidney injury. d-Ala inhibits ROS production and improves mitochondrial membrane potential, resulting in reduced TEC necrosis by hypoxic stimulation. The administration of d-Ala protects the tubules from I/R injury in mice. Moreover, the plasma level of d-Ala is conversely associated with eGFR in patients with AKI. Our data suggest that d-Ala is an appealing therapeutic target and a potential biomarker for AKI.

Rare toxin A-negative and toxin B-positive strain of Clostridioides difficile from Japan lacking a complete tcdA gene.

INTRODUCTION: Clostridioides difficile (C. difficile) produces three kinds of toxins: toxin A (enterotoxin), toxin B (cytotoxin), and C. difficile transferase (CDT), a binary toxin. Some strains show positivity only for toxin B. These strains reportedly possess a gene for toxin A, tcdA. However, toxin A production is inhibited due to a mutated stop codon and/or deletion within the tcdA gene. Here for the first case in Japan, we describe toxin genomes and proteins of a strain possessing only toxin B and lacking a complete tcdA gene, along with clinical manifestations. METHODS: C. difficile was isolated from the bloody stool of a 60-year-old female patient treated with meropenem. Although a rapid detection kit of toxins (C. DIFF QUIK CHEK COMPLETE®, TechLab, Blacksburg, VA, USA) showed positivity, Western blotting detected no toxins. Therefore, we explored the strain's toxin genes and their sequences to determine whether the strain possessed a toxin. RESULTS: Polymerase chain reaction did not identify toxin genes. Whole-genome sequencing analysis showed that a gene for toxin A, tcdA, was completely deleted in the strain. Moreover, 701 mutations and some deletions/insertions were identified on the tcdB gene. CONCLUSIONS: We isolated a rare strain of C. difficile producing only toxin B and lacking a complete tcdA gene herein Japan. The possibility of a false negative needs to be considered with a genetic method for a diagnose of C. difficile infection.

Relationships between kidney dysfunction and left ventricular diastolic dysfunction: a hospital-based retrospective study.

BACKGROUND: Preclinical left ventricular diastolic dysfunction (LVDD) is a high-risk state for heart failure. Kidney dysfunction is a known risk factor for heart failure, but its association with asymptomatic LVDD is not well-known. METHODS: A hospital-based retrospective cohort study was conducted on patients who underwent echocardiogram between 2006 and 2016 to assess the association between baseline kidney function and LVDD on echocardiogram. E/e' ratio was defined as the ratio of peak velocity of early diastolic left ventricular inflow (E) to mitral annular velocity (e'). The primary outcome was time to development of LVDD, which was defined as E/e' ratio > 14. The changes in the E/e' ratio and other echocardiographic parameters were assessed using a mixed effects model. RESULTS: Among 1167 patients, the mean age was 61 years, and the mean baseline E/e' ratio and ejection fraction were 9.6 and 69%, respectively. During a median follow-up of 3.2 years, 231 (19.8%) people developed LVDD. According to eGFR (mL/min/1.73 m2), the risk for LVDD based on hazard ratio [95% confidence interval (95% CI)] was 1.20 (0.82, 1.75) for 60 to < 90, 1.42 (0.87, 2.31) for 45 to < 60, and 2.57 (1.61, 4.09) for < 45 (P trend < 0.001). The adjusted risks (95% CI) for annual change in E/e' ratio was 0.09 (0.03, 0.14) overall and 0.28 (0.11, 0.45) in the lowest eGFR group; the trend in changes in annual E/e' ratio by baseline eGFR was significant (P trend = 0.01). CONCLUSIONS: Relatively low kidney function was related with the risks for LVDD. Long-term cohort studies are warranted to confirm the association between LVDD and symptomatic heart failure in patients with kidney dysfunction.

Higher serum levels of autotaxin and phosphatidylserine-specific phospholipase A1 in patients with lupus nephritis.

BACKGROUND: Recent studies revealed that lysophospholipids (LPLs) and related molecules, such as autotaxin (ATX) and phosphatidylserine-specific phospholipase A1 (PS-PLA1 ), are candidates for novel biomarkers in melanoma, glaucoma and diabetic nephropathy. However, it is not clear whether serum levels of ATX/ PS-PLA1 would be associated with pathological and clinical findings of lupus nephritis (LN). METHODS: In this retrospective cohort study, serum samples were collected from 39 patients with LN and 37 patients with other glomerular diseases. The serum levels of ATX and PS-PLA1 were evaluated for an association with renal pathology and clinical phenotypes of LN. RESULTS: The serum levels of ATX and PS-PLA1 were higher in the patients with LN as compared to those with other glomerular diseases. Among the classes of LN, the patients with class IV showed the trend of lower serum levels of ATX. Moreover, the patients with lower levels of ATX exhibited higher scores of activity index (AI) and chronicity index (CI). The level of ATX tended to be negatively correlated with AI and CI. These results might be explained by the effect of treatment, because the serum levels of ATX and PS-PLA1 were inversely correlated with the daily amount of oral prednisolone. Moreover, they did not reflect the level of proteinuria or kidney survival in LN patients. CONCLUSION: Although the serum levels of ATX and PS-PLA1 were affected by the treatment, these levels were higher in the patients with LN. The potential clinical benefits of these markers need to be clarified in further studies.

Erythropoietin signal protected human umbilical vein endothelial cells from high glucose-induced injury.

AIM: High glucose (HG) induces endothelial injury in vasculature, leading to tissue injury in diabetic condition. Therefore, diabetes is one of the major cause of end-stage kidney disease as well as cardiovascular diseases. Chronic inflammation is involved in the progression of HG-induced cell injury. Recently, it has been reported that erythropoietin (EPO) protects the tissues from some kind of injury, such as hypoxia and mechanical stress. However, the contribution of EPO to HG-induced tissue injury remains to be explored. Therefore, we hypothesized that EPO protects endothelial cells from HG-induced injury via the regulation of inflammatory and anti-inflammatory balance. METHODS: We performed genome-wide transcriptome profiling in human umbilical vein endothelial cells (HUVEC), which were stimulated by HG with/without EPO treatment and detected the expression of inflammation associated genes. RESULTS: The expression pattern of mRNA expression in HG stimulated HUVEC with/without EPO were different in hieralchial clustering analysis. While inflammatory cytokines/chemokines mRNA expression were increased by the HG stimulation in HUVEC, Th2-related cytokine receptors and intracellular signaling molecules showed the reduced mRNA expression levels. EPO treatment reduced inflammatory cytokines/chemokines mRNA expression and increased Th2-related cytokine mRNA expression levels. Moreover, EPO stimulation increased mRNA expression of EPO receptor and ß-common receptor. CONCLUSION: EPO signaling protects HG-induced cell injury by the regulation of immune balance.

Gut microbiota-derived D-serine protects against acute kidney injury.

Gut microbiota-derived metabolites play important roles in health and disease. D-amino acids and their L-forms are metabolites of gut microbiota with distinct functions. In this study, we show the pathophysiologic role of D-amino acids in association with gut microbiota in humans and mice with acute kidney injury (AKI). In a mouse kidney ischemia/reperfusion model, the gut microbiota protected against tubular injury. AKI-induced gut dysbiosis contributed to the altered metabolism of D-amino acids. Among the D-amino acids, only D-serine was detectable in the kidney. In injured kidneys, the activity of D-amino acid oxidase was decreased. Conversely, the activity of serine racemase was increased. The oral administration of D-serine mitigated the kidney injury in B6 mice and D-serine-depleted mice. D-serine suppressed hypoxia-induced tubular damage and promoted posthypoxic tubular cell proliferation. Finally, the D-serine levels in circulation were significantly correlated with the decrease in kidney function in AKI patients. These results demonstrate the renoprotective effects of gut-derived D-serine in AKI, shed light on the interactions between the gut microbiota and the kidney in both health and AKI, and highlight D-serine as a potential new therapeutic target and biomarker for AKI.