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The characteristic feature of chronic peritoneal damage in peritoneal dialysis (PD) is a decline in ultrafiltration capacity associated with pathological fibrosis and angiogenesis. The pathogenesis of peritoneal fibrosis is attributed to bioincompatible factors of PD fluid and peritonitis. Uremia is associated with peritoneal membrane inflammation that affects fibrosis, neoangiogenesis, and baseline peritoneal membrane function. Net ultrafiltration volume is affected by capillary surface area, vasculopathy, peritoneal fibrosis, and lymphangiogenesis. Many inflammatory cytokines induce fibrogenic growth factors, with crosstalk between macrophages and fibroblasts. Transforming growth factor (TGF)-β and vascular endothelial growth factor (VEGF)-A are the key mediators of fibrosis and angiogenesis, respectively. Bioincompatible factors of PD fluid upregulate TGF-β expression by mesothelial cells that contributes to the development of fibrosis. Angiogenesis and lymphangiogenesis can progress during fibrosis via TGF-β–VEGF-A/C pathways. Complement activation occurs in fungal peritonitis and progresses insidiously during PD. Analyses of the human peritoneal membrane have clarified the mechanisms by which encapsulating peritoneal sclerosis develops. Different effects of dialysates on the peritoneal membrane were also recognized, particularly in terms of vascular damage. Understanding the pathophysiologies of the peritoneal membrane will lead to preservation of peritoneal membrane function and improvements in technical survival, mortality, and quality of life for PD patients.

Dietary guidelines for obesity typically focus on three food groups (carbohydrates, fat, and protein) and caloric restriction. Intake of noncaloric nutrients, such as salt, are rarely discussed. However, recently high salt intake has been reported to predict the development of obesity and insulin resistance. The mechanism for this effect is unknown. Here we show that high intake of salt activates the aldose reductase–fructokinase pathway in the liver and hypothalamus, leading to endogenous fructose production with the development of leptin resistance and hyperphagia that cause obesity, insulin resistance, and fatty liver. A high-salt diet was also found to predict the development of diabetes and nonalcoholic fatty liver disease in a healthy population. These studies provide insights into the pathogenesis of obesity and diabetes and raise the potential for reduction in salt intake as an additional interventional approach for reducing the risk for developing obesity and metabolic syndrome.

Development of a novel agent against life-threatening sepsis requires the in-depth understanding of the relevant pathophysiology and therapeutic targets. Given the function of microRNAs (miRNAs) as potent oligonucleotide therapeutics, here we investigated the pathophysiological role of exogenously applied miRNA in sepsis-induced multiple organ injury. In vitro, miR-16, miR-126, miR-146a, and miR-200b suppressed the production of pro-inflammatory cytokines in RAW264.7 macrophage cells after lipopolysaccharide (LPS) stimulation. Of these, miR-146a displayed the most highly suppressive effect, wherein the transcriptional activity of nuclear factor kappa B (NF-κB) was decreased via targeting of interleukin 1 receptor-associated kinase 1 and tumor necrosis receptor-associated factor 6. Sepsis was induced in mice via cecal ligation and puncture (CLP) and an intravenous injection of a complex of miR-146a-expressing plasmid and polyethyleneimine. Treatment with this complex significantly decreased the level of serum inflammatory cytokines, attenuated organ injury including kidney injury, and led to increased survival from polymicrobial sepsis induced by CLP. miR-146a-expressing plasmid was abundantly distributed in splenic macrophages, but not in renal parenchymal cells. CLP mice treated with miR-146a displayed significantly decreased NF-κB activation and splenocyte apoptosis. Splenectomy diminished the anti-inflammatory effects of miR-146a. The collective results support the conclusion that the induction of miR-146a expression in splenic macrophages prevents excessive inflammation and sepsis-induced multiple organ injury. This study establishes a novel and critical pathophysiological role for splenic macrophage interference in sepsis-related organ injury.

Lupus nephritis (LN) is a life-threatening complication of systemic lupus erythematosus. The 2003 pathological classification of LN was revised in 2016; it quantitatively evaluates the interstitium in addition to the glomeruli. We performed a retrospective multi-centre cohort study and investigated the utility of the 2016 classification—including the activity index (AI), chronicity index (CI), and each pathological component to predict complete remission or renal function decline, defined as 1.5-fold increase in serum creatinine levels—and compare with that of the 2003 classification. Ninety-one consecutive adult patients with first-onset class III/IV LN who were newly prescribed any immunosuppressants were enrolled and followed up for a median of 51 months from January 2004. Cox regression analysis demonstrated the subclasses based on the 2003 classification, which mainly evaluate glomerular lesions, were not associated with clinical outcomes. After adjustments for estimated glomerular filtration rate and urinary protein levels, higher CI and higher interstitial fibrosis and lower hyaline deposit scores were associated with renal functional decline. Similarly, higher CI and interstitial inflammation scores were associated with failure to achieve complete remission. Therefore, the 2016 classification can predict the clinical outcomes more precisely than the 2003 classification.

In Japan, rituximab (RTX) for adult-onset frequently relapsing (FR)/steroid-dependent (SD) minimal change disease (MCD) is not explicitly reimbursed by insurance, and its standard regimen has not been established. We conducted a cross-sectional web-based survey between November and December 2021. The participants were nephrologists certified by the Japanese Society of Nephrology and answered 7 items about RTX for adult MCD. Factors related to the experience of RTX administration at their facilities were estimated by generalized estimating equations. Of 380 respondents, 181 (47.6%) reported the experience of RTX use for adult MCD at their current facilities. Those who worked at university hospitals (vs. non-university hospitals, proportion difference 13.7%) and at facilities with frequent kidney biopsies (vs. 0 cases/year, 19.2% for 1-40 cases/year; 37.9% for 41-80 cases/year; 51.9% for ≥ 81 cases/year) used RTX more frequently. Of 181 respondents, 28 (15.5%) answered that there was no insurance coverage for RTX treatment. Of 327 respondents who had the opportunity to treat MCD, which was a possible indication for RTX, 178 (54.4%) indicated withholding of RTX administration. The most common reason was the cost due to lack of insurance coverage (141, 79.2%). Regarding RTX regimens for FR/SD MCD, introduction treatment with a single body surface area-based dose of 375 mg/m2 and maintenance treatment with a 6-month interval were the most common. This survey revealed the nephrologists' characteristics associated with RTX use, the barriers to RTX use, and the variation in the regimens for adult MCD in Japan.

The epidemic of chronic kidney disease in Nicaragua (Mesoamerican nephropathy) has been linked with recurrent dehydration. Here we tested whether recurrent dehydration may cause renal injury by activation of the polyol pathway, resulting in the generation of endogenous fructose in the kidney that might subsequently induce renal injury via metabolism by fructokinase. Wild-type and fructokinase-deficient mice were subjected to recurrent heat-induced dehydration. One group of each genotype was provided water throughout the day and the other group was hydrated at night, after the dehydration. Both groups received the same total hydration in 24h. Wild-type mice that received delayed hydration developed renal injury, with elevated serum creatinine, increased urinary NGAL, proximal tubular injury, and renal inflammation and fibrosis. This was associated with activation of the polyol pathway, with increased renal cortical sorbitol and fructose levels. Fructokinase-knockout mice with delayed hydration were protected from renal injury. Thus, recurrent dehydration can induce renal injury via a fructokinase-dependent mechanism, likely from the generation of endogenous fructose via the polyol pathway. Access to sufficient water during the dehydration period can protect mice from developing renal injury. These studies provide a potential mechanism for Mesoamerican nephropathy.

High salt intake is a primary cause of over-hydration in chronic kidney disease (CKD) patients. Inflammatory markers are predictors of CKD mortality; however, the pathogenesis of inflammation remains unclear. Sodium storage in tissues has recently emerged as an issue of concern. The binding of sodium to tissue glycosaminoglycans and its subsequent release regulates local tonicity. Many cell types express tonicity-responsive enhancer-binding protein (TonEBP), which is activated in a tonicity-dependent or tonicity-independent manner. Macrophage infiltration was observed in the heart, peritoneal wall, and para-aortic tissues in salt-loading subtotal nephrectomized mice, whereas macrophages were not prominent in tap water-loaded subtotal nephrectomized mice. TonEBP was increased in the heart and peritoneal wall, leading to the upregulation of inflammatory mediators associated with cardiac fibrosis and peritoneal membrane dysfunction, respectively. Reducing salt loading by a diuretic treatment or changing to tap water attenuated macrophage infiltration, TonEBP expression, and inflammatory marker expression. The role of TonEBP may be crucial during the cardiac fibrosis and peritoneal deterioration processes induced by sodium overload. Anti-interleukin-6 therapy improved cardiac inflammation and fibrosis and peritoneal membrane dysfunction. Further studies are necessary to establish a strategy to regulate organ dysfunction induced by TonEBP activation in CKD patients.

Perivascular mesenchymal cells (PMCs), which include pericytes, give rise to myofibroblasts that contribute to chronic kidney disease progression. Several PMC markers have been identified; however, PMC heterogeneity and functions are not fully understood. Here, we describe a novel subset of renal PMCs that express Meflin, a glycosylphosphatidylinositol-anchored protein that was recently identified as a marker of fibroblasts essential for cardiac tissue repair. Tracing the lineage of Meflin + PMCs, which are found in perivascular and periglomerular areas and exhibit renin-producing potential, showed that they detach from the vasculature and proliferate under disease conditions. Although the contribution of Meflin + PMCs to conventional α-SMA + myofibroblasts is low, they give rise to fibroblasts with heterogeneous α-SMA expression patterns. Genetic ablation of Meflin + PMCs in a renal fibrosis mouse model revealed their essential role in collagen production. Consistent with this, human biopsy samples showed that progressive renal diseases exhibit high Meflin expression. Furthermore, Meflin overexpression in kidney fibroblasts promoted bone morphogenetic protein 7 signals and suppressed myofibroblastic differentiation, implicating the roles of Meflin in suppressing tissue fibrosis. These findings demonstrate that Meflin marks a PMC subset that is functionally distinct from classic pericytes and myofibroblasts, highlighting the importance of elucidating PMC heterogeneity.

Acute kidney injury is associated with high mortality, especially in intensive care unit patients. The polyol pathway is a metabolic route able to convert glucose into fructose. Here we show the detrimental role of endogenous fructose production by the polyol pathway and its metabolism through fructokinase in the pathogenesis of ischaemic acute kidney injury (iAKI). Consistent with elevated urinary fructose in AKI patients, mice undergoing iAKI show significant polyol pathway activation in the kidney cortex characterized by high levels of aldose reductase, sorbitol and endogenous fructose. Wild type but not fructokinase knockout animals demonstrate severe kidney injury associated with ATP depletion, elevated uric acid, oxidative stress and inflammation. Interestingly, both the renal injury and dysfunction in wild-type mice undergoing iAKI is significantly ameliorated when exposed to luteolin, a recently discovered fructokinase inhibitor. This study demonstrates a role for fructokinase and endogenous fructose as mediators of acute renal disease. The polyol pathway, which converts glucose into sorbitol and fructose, is active in chronic conditions like hepatic steatosis and chronic kidney disease. Here, Andres-Hernando et al . show that fructose production promotes renal injury and fructokinase inhibition protects against kidney damage during ischaemic acute kidney disease.

The influence of body mass or metabolic capacity on the association between alcohol consumption and lower risks of developing chronic kidney disease (CKD) is not fully elucidated. We examined whether the body mass index (BMI) affects the association between drinking alcohol and CKD. We defined CKD as an estimated glomerular filtration rate decline < 60 mL/min/1.73 m 2 and/or positive proteinuria (≥ 1+). Participants were 11,175 Japanese individuals aged 40–74 years without baseline CKD who underwent annual health checkups. Daily alcohol consumption at baseline was estimated using a questionnaire, and the participants were categorized as “infrequent (occasionally, rarely or never),” “light (< 20 g/day),” “moderate (20–39 g/day),” and “heavy (≥ 40 g/day).” Over a median 5-year observation period, 936 participants developed CKD. Compared with infrequent drinkers, light drinkers were associated with low CKD risks; adjusted hazard ratios (95% confidence intervals) were 0.81 (0.69–0.95). Stratified by BMI (kg/m 2 ), moderate drinkers in the low (< 18.5), normal (18.5–24.9), and high (≥ 25.0) BMI groups had adjusted hazard ratios (95% confidence intervals) of 3.44 (1.60–7.42), 0.75 (0.58–0.98), and 0.63 (0.39–1.04), respectively. Taken together, the association between alcohol consumption and CKD incidence was not the same in all the individuals, and individual tolerance must be considered.