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The role of microRNAs in regulating tubulointerstitial fibrosis, a key feature of progressive chronic kidney disease, is of significant importance. LIN28A has been reported to attenuate renal fibrosis in obstructive nephropathy. Here, our objective was to investigate the precise biological function of the miR-92a-3p/LIN28A axis in tubulointerstitial fibrosis. The human renal proximal tubular epithelial (HK-2) cell line was exposed to transforming growth factor (TGF)-β1, establishing an in vitro model mimicking tubulointerstitial fibrosis. Luciferase reporter assay was utilized to investigate the relationship between miR-92a-3p and LIN28A. Cell transfection techniques were employed to modify the expression of miR-92a-3p and LIN28A. An in vivo model of tubulointerstitial fibrosis was created by inducing unilateral ureteral obstruction (UUO) in C57BL/6N mice. Our initial observations showed that TGF-β1 treatment of HK-2 cells and the UUO mice model led to an increase in miR-92a-3p expression and a decrease in LIN28A expression. We confirmed that miR-92a-3p directly targeted LIN28A in HK-2 cells. In TGF-β1-stimulated HK-2 cells, knocking down miR-92a-3p notably reduced the levels of alpha smooth muscle actin and vimentin and concurrently enhanced the expression of E-cadherin. These changes were counteracted upon transfection with si-LIN28A. Thus, directing interventions toward miR-92a-3p holds the potential to emerge as a viable therapeutic approach for addressing tubulointerstitial fibrosis.

The role of microRNAs in regulating tubulointerstitial fibrosis, a key feature of progressive chronic kidney disease, is of significant importance. LIN28A has been reported to attenuate renal fibrosis in obstructive nephropathy. Here, our objective was to investigate the precise biological function of the miR-92a-3p/LIN28A axis in tubulointerstitial fibrosis. The human renal proximal tubular epithelial (HK-2) cell line was exposed to transforming growth factor (TGF)-β1, establishing an in vitro model mimicking tubulointerstitial fibrosis. Luciferase reporter assay was utilized to investigate the relationship between miR-92a-3p and LIN28A. Cell transfection techniques were employed to modify the expression of miR-92a-3p and LIN28A. An in vivo model of tubulointerstitial fibrosis was created by inducing unilateral ureteral obstruction (UUO) in C57BL/6N mice. Our initial observations showed that TGF-β1 treatment of HK-2 cells and the UUO mice model led to an increase in miR-92a-3p expression and a decrease in LIN28A expression. We confirmed that miR-92a-3p directly targeted LIN28A in HK-2 cells. In TGF-β1-stimulated HK-2 cells, knocking down miR-92a-3p notably reduced the levels of alpha smooth muscle actin and vimentin and concurrently enhanced the expression of E-cadherin. These changes were counteracted upon transfection with si-LIN28A. Thus, directing interventions toward miR-92a-3p holds the potential to emerge as a viable therapeutic approach for addressing tubulointerstitial fibrosis. [ABSTRACT FROM AUTHOR]

Diabetic nephropathy(DN) is the primary factor leading to the advancement of end-stage renal disease.Tubulointerstitial fibrosis(TIF) is a crucial element that impacts renal function in DN.When exposed to high levels of glucose,the activation of inflammasomes can trigger cell death pathways,including pyroptosis.This can potentially lead to TIF,which in turn causes the decline of renal function.This article focuses on the pathogenic mechanisms of TIF resulting from DN.This study reviews the potential of blocking pyroptosis to slow down the course of DN,providing a new and promising target for therapeutic intervention in the treatment of DN.

Metabolic acidosis is a frequent complication of chronic kidney disease and is associated with a number of adverse outcomes, including worsening kidney function, poor musculoskeletal health, cardiovascular events, and death. Mechanisms that prevent metabolic acidosis detrimentally promote further kidney damage, creating a cycle between acid accumulation and acid-mediated kidney injury. Disrupting this cycle through the provision of alkali, most commonly using sodium bicarbonate, is hypothesized to preserve kidney function while also mitigating adverse effects of excess acid on bone and muscle. However, results from clinical trials have been conflicting. There is also significant interest to determine whether sodium bicarbonate might improve patient outcomes for those who do not have overt metabolic acidosis. Such individuals are hypothesized to be experiencing acid-mediated organ damage despite having a normal serum bicarbonate concentration, a state often referred to as subclinical metabolic acidosis. Results from small- to medium-sized trials in individuals with subclinical metabolic acidosis have also been inconclusive. Well-powered clinical trials to determine the efficacy and safety of sodium bicarbonate are necessary to determine if this intervention improves patient outcomes. [ABSTRACT FROM AUTHOR]

Purpose: To elucidate the role of cordycepin in modulating autophagy and mitigating renal tubular interstitial fibrosis in a rat model of unilateral ureteral obstruction (UUO). Methods: Forty male Sprague-Dawley (SD) rats were assigned to four groups: control, sham, UUO and cordyceps-treated groups (10 rats per group). The UUO and cordyceps groups underwent surgery to induce unilateral ureteral obstruction. The cordyceps group received intravenous cordycepin (10 mg/kg) daily for 14 days, while the control and UUO groups received normal saline. Histopathological examination, assessment of fibrosis markers (a-SMA, collagen III) and autophagy markers (Atg5, LC3II/I) were conducted. Results: The UUO group exhibited significant tubular damage and interstitial fibrosis, with elevated serum levels of pro-inflammatory and oxidative markers (p < 0.05). Cordycepin treatment attenuated these pathological changes, evidenced by reduced fibrosis, inflammation and oxidative stress. Enhanced autophagic activity was observed in the cordycepin group, suggesting a potential mechanism of its renoprotective effect. Conclusion: Cordyceps is effective in inhibiting renal tubulointerstitial fibrosis, potentially through the activation of autophagy and reduction of inflammation and oxidative stress. Future studies should focus on unraveling the specific molecular mechanisms of cordycepin's action and assessing its applicability in CKD treatment. [ABSTRACT FROM AUTHOR]

Recent studies have shown that endogenous metabolites act via aryl hydrocarbon receptor (AhR) signalling pathway in tubulointerstitial fibrosis (TIF) pathogenesis. However, the mechanisms underlying endogenous metabolite-mediated AhR activation are poorly characterised. In this study, we conducted untargeted metabolomics analysis to identify the significantly altered intrarenal metabolites in a mouse model of unilateral ureteral obstruction (UUO). We found that the levels of the metabolite 1-methoxypyrene (MP) and the mRNA expression of AhR and its target genes CYP1A1, CYP1A2, CYP1B1 and COX-2 were progressively increased in the obstructed kidney at Weeks 1, 2 and 3. Furthermore, these changes were positively correlated with progressive TIF in UUO mice. In NRK-52E, RAW 264.7 and NRK-49F cells, MP dose-dependently upregulated the mRNA expression of AhR and its four target genes and the protein expression of nuclear AhR, accompanied by the upregulated protein expression of collagen I, α-SMA and fibronectin, as well as downregulated E-cadherin expression. Consistently, oral administration of MP in mice progressively enhanced AhR activity and upregulated profibrotic protein expression in the kidneys; these effects were partially inhibited by AhR knockdown in MP-treated mice and cell lines. In addition, we screened and identified erythro-guaiacylglycerol-β-ferulic acid ether (GFA), which was isolated from Semen plantaginis, as a new AhR antagonist. GFA significantly attenuated TIF in MP-treated NRK-52E cells and mice by partially antagonising AhR activity. Our results suggest that MP activates AhR signalling, thus mediating TIF through epithelial-mesenchymal transition and macrophage-myofibroblast transition. MP is a crucial metabolite that contributes to TIF via AhR signalling pathway.

Abstract Background Tubulointerstitial fibrosis plays an important role in the progression of diabetic kidney disease (DKD). Sacubitril/valsartan (Sac/Val) exerts a robust beneficial effect in DKD. However, the potential functional effect of Sac/Val on tubulointerstitial fibrosis in DKD is still largely unclear. Methods Streptozotocin-induced diabetic mice were given Sac/Val or Val by intragastric administration once a day for 12 weeks. The renal function, the pathological changes of tubule injury and tubulointerstitial fibrosis, as well as mitochondrial morphology of renal tubules in mice, were evaluated. Genome-wide gene expression analysis was performed to identify the potential mechanisms. Meanwhile, human tubular epithelial cells (HK-2) were cultured in high glucose condition containing LBQ657/valsartan (LBQ/Val). Further, mitochondrial functions and Sirt1/PGC1α pathway of tubular epithelial cells were assessed by Western blot, Real-time-PCR, JC-1, MitoSOX or MitoTracker. Finally, the Sirt1 specific inhibitor, EX527, was used to explore the potential effects of Sirt1 signaling in vivo and in vitro. Results We found that Sac/Val significantly ameliorated the decline of renal function and tubulointerstitial fibrosis in DKD mice. The enrichment analysis of gene expression indicated metabolism as an important modulator in DKD mice with Sac/Val administration, in which mitochondrial homeostasis plays a pivotal role. Then, the decreased expression of Tfam and Cox IV;, as well as changes of mitochondrial function and morphology, demonstrated the disruption of mitochondrial homeostasis under DKD conditions. Interestingly, Sac/Val administration was found to restore mitochondrial homeostasis in DKD mice and in vitro model of HK-2 cells. Further, we demonstrated that Sirt1/PGC1α, a crucial pathway in mitochondrial homeostasis, was activated by Sac/Val both in vivo and in vitro. Finally, the beneficial effects of Sac/Val on mitochondrial homeostasis and tubulointerstitial fibrosis was partially abolished in the presence of Sirt1 specific inhibitor. Conclusions Taken together, we demonstrate that Sac/Val ameliorates tubulointerstitial fibrosis by restoring Sirt1/PGC1α pathway-mediated mitochondrial homeostasis in DKD, providing a theoretical basis for delaying the progression of DKD in clinical practice.

Background: Tubulointerstitial fibrosis plays an important role in the progression of diabetic kidney disease (DKD). Sacubitril/valsartan (Sac/Val) exerts a robust beneficial effect in DKD. However, the potential functional effect of Sac/Val on tubulointerstitial fibrosis in DKD is still largely unclear. Methods: Streptozotocin-induced diabetic mice were given Sac/Val or Val by intragastric administration once a day for 12 weeks. The renal function, the pathological changes of tubule injury and tubulointerstitial fibrosis, as well as mitochondrial morphology of renal tubules in mice, were evaluated. Genome-wide gene expression analysis was performed to identify the potential mechanisms. Meanwhile, human tubular epithelial cells (HK-2) were cultured in high glucose condition containing LBQ657/valsartan (LBQ/Val). Further, mitochondrial functions and Sirt1/PGC1α pathway of tubular epithelial cells were assessed by Western blot, Real-time-PCR, JC-1, MitoSOX or MitoTracker. Finally, the Sirt1 specific inhibitor, EX527, was used to explore the potential effects of Sirt1 signaling in vivo and in vitro. Results: We found that Sac/Val significantly ameliorated the decline of renal function and tubulointerstitial fibrosis in DKD mice. The enrichment analysis of gene expression indicated metabolism as an important modulator in DKD mice with Sac/Val administration, in which mitochondrial homeostasis plays a pivotal role. Then, the decreased expression of Tfam and Cox IV;, as well as changes of mitochondrial function and morphology, demonstrated the disruption of mitochondrial homeostasis under DKD conditions. Interestingly, Sac/Val administration was found to restore mitochondrial homeostasis in DKD mice and in vitro model of HK-2 cells. Further, we demonstrated that Sirt1/PGC1α, a crucial pathway in mitochondrial homeostasis, was activated by Sac/Val both in vivo and in vitro. Finally, the beneficial effects of Sac/Val on mitochondrial homeostasis and tubulointerstitial fibrosis was partially abolished in the presence of Sirt1 specific inhibitor. Conclusions: Taken together, we demonstrate that Sac/Val ameliorates tubulointerstitial fibrosis by restoring Sirt1/PGC1α pathway-mediated mitochondrial homeostasis in DKD, providing a theoretical basis for delaying the progression of DKD in clinical practice. [ABSTRACT FROM AUTHOR]

Our previous study found that miR‐26a alleviates aldosterone‐induced tubulointerstitial fibrosis (TIF). However, the effect of miR‐26a on TIF in diabetic kidney disease (DKD) remains unclear. This study clarifies the role and possible mechanism of exogenous miR‐26a in controlling the progression of TIF in DKD models. Firstly, we showed that miR‐26a was markedly decreased in type 2 diabetic db/db mice and mouse tubular epithelial cells (mTECs) treated with high glucose (HG, 30 mM) using RT‐qPCR. We then used adeno‐associated virus carrying miR‐26a and adenovirus miR‐26a to enhance the expression of miR‐26a in vivo and in vitro. Overexpressing miR‐26a alleviated the TIF in db/db mice and the extracellular matrix (ECM) deposition in HG‐stimulated mTECs. These protective effects were caused by reducing expression of protease‐activated receptor 4 (PAR4), which involved in multiple pro‐fibrotic pathways. The rescue of PAR4 expression reversed the anti‐fibrosis activity of miR‐26a. We conclude that miR‐26a alleviates TIF in DKD models by directly targeting PAR4, which may provide a novel molecular strategy for DKD therapy. [ABSTRACT FROM AUTHOR]

The energy needs of tubular epithelial components, especially proximal tubular epithelial cells (PTECs), are high and they heavily depend on aerobic metabolism. As a result, they are particularly vulnerable to various injuries caused by factors such as ischemia, proteinuria, toxins, and elevated glucose levels. Initial metabolic and phenotypic changes in PTECs after injury are likely an attempt at survival and repair. Nevertheless, in cases of recurrent or prolonged injury, PTECs have the potential to undergo a transition to a secretory state, leading to the generation and discharge of diverse bioactive substances, including transforming growth factor-b, Wnt ligands, hepatocyte growth factor, interleukin (IL)-1b, lactic acid, exosomes, and extracellular vesicles. By promoting fibroblast activation, macrophage recruitment, and endothelial cell loss, these bioactive compounds stimulate communication between epithelial cells and other interstitial cells, ultimately worsening renal damage. This review provides a summary of the latest findings on bioactive compounds that facilitate the communication between these cellular categories, ultimately leading to the advancement of tubulointerstitial fibrosis (TIF). [ABSTRACT FROM AUTHOR]

Tubulointerstitial fibrosis (TIF) plays a crucial role in the progression of diabetic kidney disease (DKD). However, the underlying molecular mechanisms remain obscure. The present study aimed to examine whether transmembrane member 16A (TMEM16A), a Ca2+-activated chloride channel, contributes to the development of TIF in DKD. Interestingly, we found that TMEM16A expression was significantly up-regulated in tubule of murine model of DKD, which was associated with development of TIF. In vivo inhibition of TMEM16A channel activity with specific inhibitors Ani9 effectively protects against TIF. Then, we found that TMEM16A activation induces tubular mitochondrial dysfunction in in vivo and in vitro models, with the evidence of the TMEM16A inhibition with specific inhibitor. Mechanically, TMEM16A mediated tubular mitochondrial dysfunction through inhibiting PGC-1α, whereas overexpression of PGC-1α could rescue the changes. In addition, TMEM16A-induced fibrogenesis was dependent on increased intracellular Cl−, and reducing intracellular Cl− significantly blunted high glucose-induced PGC-1α and profibrotic factors expression. Taken together, our studies demonstrated that tubular TMEM16A promotes TIF by suppressing PGC-1α-mediated mitochondrial homeostasis in DKD. Blockade of TMEM16A may serve as a novel therapeutic approach to ameliorate TIF. [ABSTRACT FROM AUTHOR]

Zhaohua Yang,1,&ast; Jinying Wei,1,&ast; Yashu Wang,1 Yunxia Du,1 Shan Song,1 Jiawei Li,2 Ziyuan Su,2 Yonghong Shi,1 Haijiang Wu1 1Department of Pathology, Hebei Medical University, Shijiazhuang, 050017, People’s Republic of China; 2Basic Medical College, Hebei Medical University, Shijiazhuang, 050017, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Haijiang Wu, Email haijianglaoqi@163.comBackground: The primary pathophysiology of diabetic kidney disease (DKD) is tubulointerstitial fibrosis (TIF), and an essential contributing element is excessive extracellular matrix deposition. Irisin is a polypeptide formed by splitting fibronectin type III domain containing 5 (FNDC5), which participates in a number of physiological and pathological processes.Methods: The purpose of this article is to examine irisin’s function in DKD and analyze both its in vitro and in vivo effects. The Gene Expression Omnibus (GEO) database was used to download GSE30122, GSE104954, and GSE99325. Analysis of renal tubule samples from nondiabetic and diabetic mice identified 94 differentially expressed genes (DEGs). The transforming growth factor beta receptor 2 (TGFBR2), irisin, and TGF-β 1 were utilized as DEGs to examine the impact of irisin on TIF in diabetic kidney tissue, according to the datasets retrieved from the GEO database and Nephroseq database. Additionally, the therapeutic impact of irisin was also examined using Western blot, RT-qPCR, immunofluorescence, immunohistochemistry, and kits for detecting mouse biochemical indices.Results: In vitro, the findings demonstrated that irisin not only down-regulated the expression of Smad4 and β-catenin but also reduced the expression of proteins linked to fibrosis, the epithelial-mesenchymal transition (EMT), and mitochondrial dysfunction in HK-2 cells maintained in high glucose (HG) environment. In vivo, overexpressed FNDC5 plasmid was injected into diabetic mice to enhance its expression. Our studies found that overexpressed FNDC5 plasmid not only reversed the biochemical parameters and renal morphological characteristics of diabetic mice but also alleviated EMT and TIF by inhibiting Smad4/β-catenin signaling pathway.Conclusion: The above experimental results revealed that irisin could reduce TIF in diabetic mice via regulating the Smad4/β-catenin pathway.Keywords: irisin, diabetic kidney disease, tubulointerstitial fibrosis, Smad4, β-catenin

Background Thromboembolic events are prevalent in chronic kidney disease (CKD) patients due to increased thrombin generation leading to a hypercoagulable state. We previously demonstrated that inhibition of protease-activated receptor-1 (PAR-1) by vorapaxar reduces kidney fibrosis. Methods We used an animal model of unilateral ischemia–reperfusion injury-induced CKD to explore the tubulovascular crosstalk mechanisms of PAR-1 in acute kidney injury (AKI)-to-CKD transition. Results During the early phase of AKI, PAR-1-deficient mice exhibited reduced kidney inflammation, vascular injury, and preserved endothelial integrity and capillary permeability. During the transition phase to CKD, PAR-1 deficiency preserved kidney function and diminished tubulointerstitial fibrosis via downregulated transforming growth factor-β/Smad signaling. Maladaptive repair in the microvasculature after AKI further exacerbated focal hypoxia with capillary rarefaction, which was rescued by stabilization of hypoxia-inducible factor and increased tubular vascular endothelial growth factor A in PAR-1-deficient mice. Chronic inflammation was also prevented with reduced kidney infiltration by both M1- and M2-polarized macrophages. In thrombin-induced human dermal microvascular endothelial cells (HDMECs), PAR-1 mediated vascular injury through activation of NF-κB and ERK MAPK pathways. Gene silencing of PAR-1 exerted microvascular protection via a tubulovascular crosstalk mechanism during hypoxia in HDMECs. Finally, pharmacologic blockade of PAR-1 with vorapaxar improved kidney morphology, promoted vascular regenerative capacity, and reduced inflammation and fibrosis depending on the time of initiation. Conclusions Our findings elucidate a detrimental role of PAR-1 in vascular dysfunction and profibrotic responses upon tissue injury during AKI-to-CKD transition and provide an attractive therapeutic strategy for post-injury repair in AKI. [ABSTRACT FROM AUTHOR]

Introduction: Inflammatory cell infiltration is a novel hallmark of diabetic kidney disease (DKD), in part, by activated macrophages. Macrophage-to-tubular epithelial cell communication may play an important role in renal fibrosis. Circular RNAs (circRNAs) have been reported in the pathogenesis of various human diseases involving macrophages activation, including DKD. However, the exact mechanism of circRNAs in macrophage infiltration and renal fibrosis of DKD remains obscure. Methods: In our study, a novel circRNA circUBXN7 was identified in DKD patients using microarray. The function of circUBXN7 in vitro and in vivo was investigated by qRT-PCR, western blot, and immunofluorescence. Finally, a dual-luciferase reporter assay, ChIP, RNA pull-down, RNA immunoprecipitation and rescue experiments were performed to investigate the mechanism of circUBXN7. Results: We demonstrated that the expression of circUBXN7 was significantly upregulated in the plasma of DKD patients and correlated with renal function, which might serve as an independent biomarker for DKD patients. According to investigations, ectopic expression of circUBXN7 promoted macrophage activation, EMT and fibrosis in vitro, and increased macrophage infiltration, EMT, fibrosis and proteinuria in vivo. Mechanistically, circUBXN7 was transcriptionally upregulated by transcription factor SP1 and could reciprocally promote SP1 mRNA stability and activation via directly binding to the m6A-reader IGF2BP2 in DKD. Conclusion: CircUBXN7 is highly expressed in DKD patients may provide the potential biomarker and therapeutic target for DKD. [ABSTRACT FROM AUTHOR]

Tubulointerstitial fibrosis is an important pathological feature of diabetic nephropathy that is associated with impaired renal function. However, the mechanism by which fibrosis occurs in diabetic nephropathy is unclear. Differentially expressed genes were identified from transcriptome profiles of renal tissue from diabetic patients and unilateral ureteral obstruction mice and intersected to obtain genes that may be involved in diabetic fibrosis. Biological function analysis and protein–protein interaction network analysis were performed. ROC curve and Pearson correlation analysis between hub genes were performed and glomerular filtration rate estimated. Finally, the RNA levels of hub genes were measured using real-time PCR. A total of 283 genes were identified as potentially involved in diabetic nephropathy fibrosis. TYROBP, CTSS, LCP2, LUM and TLR7 were identified as aberrantly expressed hub genes. Immune cell infiltration analysis demonstrated higher numbers of cytotoxic lymphocytes, B lineage cells, monocyte lineage cells, myeloid dendritic cells, neutrophils, and fibroblasts in the diabetic nephropathy group. The areas under ROC curves for TYROBP, CTSS, LCP2, LUM and TLR7 were 0.9167, 0.9583, 0.9917, 0.93333, and 0.9583, respectively (P < 0.001), and their correlation coefficients with estimated glomerular filtration rate were − 0.8332, − 0.752, − 0.7875, − 0.7567, and − 0.7136, respectively (P < 0.001). The RNA levels of TYROBP, CTSS, LUM and TLR7 were upregulated in high-glucose-treated human renal tubular epithelial cells (P < 0.005). Our study identified TYROBP, CTSS, LCP2, LUM and TLR7 as potentially involved in diabetic nephropathy fibrosis. Furthermore, TYROBP, CTSS, LUM and TLR7 may be associated with epithelial–mesenchymal transition of tubular epithelial cells. [ABSTRACT FROM AUTHOR]

Renal fibrosis is the final common pathophysiological pathway in chronic kidney disease (CKD) regardless of the underlying cause of kidney injury. Tubulointerstitial fibrosis (TIF) is considered to be the key pathological predictor of CKD progression. Currently, the gold‐standard tool to identify TIF is kidney biopsy, an invasive method that carries risks. Non‐invasive diagnostics rely on an estimation of glomerular filtration rate and albuminuria to assess kidney function, but these fail to diagnose early CKD accurately or to predict progressive decline in kidney function. In this review, we summarize the current and emerging molecular biomarkers that have been studied in various clinical settings and in animal models of kidney disease and that are correlated with the degree of TIF. We examine the potential of these biomarkers to diagnose TIF non‐invasively and to predict disease progression. We also examine the potential of new technologies and non‐invasive diagnostic approaches in assessing TIF. Limitations of current and potential biomarkers are discussed and knowledge gaps identified. [ABSTRACT FROM AUTHOR]

Diabetic kidney disease continues to be the leading cause of chronic kidney disease, often advancing to end stage kidney disease. In addition to the well characterized glomerular alterations including mesangial expansion, podocyte injury, and glomerulosclerosis, tubulointerstitial fibrosis is also an important component of diabetic kidney injury. Similarly, tubulointerstitial fibrosis is a critical component of any chronic kidney injury. Therefore, sensitive and quantitative identification of tubulointerstitial fibrosis is critical for the assessment of long-term prognosis of kidney disease. Here, we employed phasor approach to fluorescence lifetime imaging, commonly known as FLIM, to understand tissue heterogeneity and calculate changes in the tissue autofluorescence lifetime signatures due to diabetic kidney disease. FLIM imaging was performed on cryostat sections of snap-frozen biopsy material of patients with diabetic nephropathy. There was an overall increase in phase lifetime (τphase) with increased disease severity. Multicomponent phasor analysis shows the distinctive differences between the different disease states. Thus, phasor autofluorescence lifetime imaging, which does not involve any staining, can be used to understand and evaluate the severity of kidney disease.

Hyperuricemia (HUA)-induced oxidative stress is a crucial contributor to hyperuricemic nephropathy (HN), but the molecular mechanisms underlying the disturbed redox homeostasis in kidneys remain elusive. Using RNA sequencing, together with biochemical analyses, we found that nuclear factor erythroid 2-related factor 2 (NRF2) expression and nuclear localization levels were increased in early HN progression and then gradually declined below the baseline level. We identified the impaired activity of the NRF2-activated antioxidant pathway as a driver of oxidative damage in HN progression. Through nrf2 deletion, we further confirmed aggravated kidney damage in nrf2 knockout HN mice compared with HN mice. In contrast, the pharmacological agonist of NRF2 improved kidney function and alleviated renal fibrosis in mice. Mechanistically, the activation of NRF2 signaling reduced oxidative stress by restoring mitochondrial homeostasis and reducing NADPH oxidase 4 (NOX4) expression in vivo or in vitro. Moreover, the activation of NRF2 promoted the expression levels of heme oxygenase 1 (HO-1) and quinone oxidoreductase 1 (NQO1) and enhanced the antioxidant capacity of cells. Furthermore, the activation of NRF2 ameliorated renal fibrosis in HN mice through the downregulation of the transforming growth factor-beta 1 (TGF-β1) signaling pathway and ultimately delayed the progression of HN. Collectively, these results suggested NRF2 as a key regulator in improving mitochondrial homeostasis and fibrosis in renal tubular cells by reducing oxidative stress, upregulating the antioxidant signaling pathway, and downregulating the TGF-β1 signaling pathway. The activation of NRF2 represents a promising strategy to restore redox homeostasis and combat HN. [ABSTRACT FROM AUTHOR]

Objectives Fibrocytes, the extracellular matrix-producing cells derived from bone marrow progenitors, contribute to organ fibrosis. We investigated the presence and characteristics of fibrocytes in the peripheral blood and kidney of patients with lupus nephritis (LN), and the association of the abundance of fibrocytes with renal tubular epithelial cells (RTECs) in LN fibrogenesis. Methods Fibrocytes were identified with type I collagen (colI), α-smooth muscle actin (α-SMA), CD34 and CD45 using flow cytometry and confocal imaging. The associations between the levels of fibrocytes and pathological features of patients with LN were analysed. The contribution of RTECs to fibrocyte generation was determined using LN sera-treated HK-2 cells. Results Spindle-shaped fibrocytes (colI+α-SMA+CD34+CD45+ cells) were present in the peripheral blood and their abundance was especially high in LN patients with interstitial fibrosis compared with healthy control. Renal fibrocytes (colI+α-SMA+CD45+ cells) were found in the tubulointerstitium in patients with LN, and their numbers were significantly associated with the degrees of chronicity indices including interstitial fibrosis and renal dysfunction. Stimulation of peripheral blood mononuclear cells with supernatants from LN serum-treated HK-2 cells led to a significant generation of fibrocytes, which was abrogated by the addition of IL-6 neutralizing antibody. Conclusion Fibrocytes were significantly increased in the blood and kidney tissue of patients with LN, especially those with interstitial fibrosis. Fibrocytes could be differentiated from blood cells, with an active contribution from RTECs. Our results show a possible link between fibrocytes and tubulointerstitial fibrosis, which may serve as a novel therapeutic target for LN fibrogenesis. [ABSTRACT FROM AUTHOR]

Tubulointerstitial fibrosis (TIF), a common end result of almost all progressive chronic kidney diseases (CKD), is also the best predictor of kidney survival. Almost all cells in the kidney are involved in the progression of TIF. Myofibroblasts, the primary producers of extracellular matrix, have previously received a great deal of attention; however, a large body of emerging evidence reveals that proximal tubule (PT) plays a central role in TIF progression. In response to injury, renal tubular epithelial cells (TECs) transform into inflammatory and fibroblastic cells, producing various bioactive molecules that drive interstitial inflammation and fibrosis. Here we reviewed the increasing evidence for the key role of the PT in promoting TIF in tubulointerstitial and glomerular injury and discussed the therapeutic targets and carrier systems involving the PT that holds particular promise for treating patients with fibrotic nephropathy.

Canonical transient receptor potential-6 (TRPC6) channels have been implicated in familial and acquired forms of focal and segmental glomerulosclerosis (FSGS), and in renal fibrosis following ureteral obstruction in mice. TRPC6 channels also appear to play a role in driving glomerular disease in aging and in autoimmune glomerulonephritis. In the present study, we examine the role of TRPC6 in the proteinuric state caused by prolonged albumin overload (AO) in Sprague Dawley rats induced by daily injections of exogenous albumin. This was assessed in rats with a global and constitutive inactivation of TRPC6 channels (Trpc6del/del rats) and in wild-type littermates (Trpc6wt/wt rats). AO for 14 and 28 days caused increased urine albumin excretion that was significantly attenuated in Trpc6del/del rats compared to Trpc6wt/wt controls. AO overload did not induce significant glomerulosclerosis or azotemia in either genotype. AO induced mild tubulointerstitial disease characterized by fibrosis, hypercellularity and increased expression of markers of fibrosis and inflammation. Those changes were equally severe in Trpc6wt/wt and Trpc6del/del rats. Immunoblot analysis of renal cortex indicated that AO increased the abundances of TRPC3 and TRPC6, and caused a nearly complete loss of TRPC5 in Trpc6wt/wt rats. The increase in TRPC3 and the loss of TRPC5 occurred to the same extent in Trpc6del/del rats. These data also suggest that TRPC6 plays a role in the normal function of the glomerular filtration barrier. However, whether TRPC6 inactivation protects the tubulointerstitial compartments in Sprague Dawley rats depends on the disease model examined. [ABSTRACT FROM AUTHOR]

Renal tubulointerstitial fibrosis (TIF), characterized by epithelial-to-mesenchymal transition (EMT) of renal tubular epithelial cells, is the typical pathological alteration in diabetic nephropathy. Gentiopicroside (GPS), a natural compound with anti-inflammatory activity, has been demonstrated to alleviate glomerulosclerosis, whereas whether GPS inhibits TIF via regulating inflammation remains unclear. In this study, diabetic db/db mice and high glucose (HG)-stimulated renal tubular epithelial cells (NRK-52E) were applied to explore the effects and mechanisms of GPS on TIF. The results in vivo showed that GPS effectively improves glycolipid metabolism disorder, renal dysfunction, and TIF. In particular, GPS treatment reversed the abnormal expressions of EMT marker proteins including elevated α-smooth muscle actin and vimentin and decreased E-cadherin in the kidney of db/db mice. Moreover, GPS treatment also inhibited protein expressions of angiotensinⅡ type 1 receptor (AT1R) and CK2α and the activation of the NF-κB pathway. Importantly, the aforementioned effects of GPS acted in vivo were further observed in vitro in HG-stimulated NRK-52E cells, which were independent of its effects on glucose and lipid-lowering activity but were reversed by AT1R over-expression. Together, our results indicate that GPS that directly inhibits the CK2/NF-κB inflammatory signaling pathway via AT1R may also contribute to the amelioration of TIF in diabetes. [ABSTRACT FROM AUTHOR]

Diabetic kidney disease is one of the most serious microvascular complications of diabetes. It progresses irreversibly to end-stage renal disease if left untreated. Bone morphogenetic protein (BMP)-7 is a negative regulator of organ fibrosis and may also play an essential role in tubulointerstitial fibrosis. This study aimed to investigate the precise role and potential molecular mechanisms of BMP-7 in the progression of diabetic nephropathy. In this study, BMP-7 was overexpressed in vivo after the replication of the diabetic rat model using streptozotocin. The results showed that BMP-7 inhibited the phosphorylation of related mitogen-activated protein kinase (MAPK) pathways while upregulating the inhibitor of differentiation (Id2) expression and effectively ameliorated pathological renal injury. Further in vitro validation showed that the inhibition of the phosphorylation of MAPKs at a high glucose concentration in renal tubular epithelial cells was followed by the upregulation of Id2 protein expression, suggesting that BMP-7 could improve diabetic nephropathy by upregulating Id2 protein levels through the BMP-7–MAPK signaling pathway. Previous laboratory studies found that oxymatrine improved renal fibrotic lesions. However, the exact mechanism is unclear. The present study showed that oxymatrine treatment in a diabetic rat model upregulated BMP-7 protein expression and inhibited MAPK pathway protein phosphorylation levels. These results suggested that oxymatrine improved the epithelial-to-mesenchymal transition process in the early stage of diabetic kidney disease by regulating the BMP-7–MAPK pathway and ameliorated renal tubulointerstitial fibrosis. [ABSTRACT FROM AUTHOR]

Diabetic kidney disease is one of the most serious microvascular complications of diabetes. It progresses irreversibly to end-stage renal disease if left untreated. Bone morphogenetic protein (BMP)-7 is a negative regulator of organ fibrosis and may also play an essential role in tubulointerstitial fibrosis. This study aimed to investigate the precise role and potential molecular mechanisms of BMP-7 in the progression of diabetic nephropathy. In this study, BMP-7 was overexpressed in vivo after the replication of the diabetic rat model using streptozotocin. The results showed that BMP-7 inhibited the phosphorylation of related mitogen-activated protein kinase (MAPK) pathways while upregulating the inhibitor of differentiation (Id2) expression and effectively ameliorated pathological renal injury. Further in vitro validation showed that the inhibition of the phosphorylation of MAPKs at a high glucose concentration in renal tubular epithelial cells was followed by the upregulation of Id2 protein expression, suggesting that BMP-7 could improve diabetic nephropathy by upregulating Id2 protein levels through the BMP-7–MAPK signaling pathway. Previous laboratory studies found that oxymatrine improved renal fibrotic lesions. However, the exact mechanism is unclear. The present study showed that oxymatrine treatment in a diabetic rat model upregulated BMP-7 protein expression and inhibited MAPK pathway protein phosphorylation levels. These results suggested that oxymatrine improved the epithelial-to-mesenchymal transition process in the early stage of diabetic kidney disease by regulating the BMP-7–MAPK pathway and ameliorated renal tubulointerstitial fibrosis.

Renal tubulointerstitial fibrosis (TIF), characterized by epithelial-to-mesenchymal transition (EMT) of renal tubular epithelial cells, is the typical pathological alteration in diabetic nephropathy. Gentiopicroside (GPS), a natural compound with anti-inflammatory activity, has been demonstrated to alleviate glomerulosclerosis, whereas whether GPS inhibits TIF via regulating inflammation remains unclear. In this study, diabetic db/db mice and high glucose (HG)-stimulated renal tubular epithelial cells (NRK-52E) were applied to explore the effects and mechanisms of GPS on TIF. The results in vivo showed that GPS effectively improves glycolipid metabolism disorder, renal dysfunction, and TIF. In particular, GPS treatment reversed the abnormal expressions of EMT marker proteins including elevated α-smooth muscle actin and vimentin and decreased E-cadherin in the kidney of db/db mice. Moreover, GPS treatment also inhibited protein expressions of angiotensinⅡ type 1 receptor (AT1R) and CK2α and the activation of the NF-κB pathway. Importantly, the aforementioned effects of GPS acted in vivo were further observed in vitro in HG-stimulated NRK-52E cells, which were independent of its effects on glucose and lipid-lowering activity but were reversed by AT1R over-expression. Together, our results indicate that GPS that directly inhibits the CK2/NF-κB inflammatory signaling pathway via AT1R may also contribute to the amelioration of TIF in diabetes.

Kidney aging is a normal physiological process associates with various molecular, morphologic and functional changes in the kidney tissues. This work was designed to study microscopically the structural changes in the kidney tissue of aged rats compared to young rats. Male Sprague–Dawley rats were used 10 young rats (4 months) and 10 aged rats (24 months). Rats were transcardially perfused with 4% paraformaldehyde. The kidneys were post fixed for 24 hours in 4 % PFA then proceeded for normal histopathology and light microscopic examination. Kidney tissue of aged rats showed serious morphological changes such as segmental glomerulosclerosis, pericapsular fibrosis, tubulointerstitial fibrosis, perivascular fibrosis, inflammatory cell infiltration, tubular dilatation, intra-tubular cast formation and tubular atrophy. These changes were compared to the normal histological appearance of glomeruli, tubules, interstitium and blood vessels of young rat kidneys. In addition, the kidney tissue of the aged rats showed compensatory glomerular hypertrophy, tubular hyperplasia and endothelial proliferation. Renal aging involves several degenerative changes in kidney structure and these alterations interfere with the physiologic functions and end with chronic renal failure.

Hyperuricemia (HUA)-induced oxidative stress is a crucial contributor to hyperuricemic nephropathy (HN), but the molecular mechanisms underlying the disturbed redox homeostasis in kidneys remain elusive. Using RNA sequencing, together with biochemical analyses, we found that nuclear factor erythroid 2-related factor 2 (NRF2) expression and nuclear localization levels were increased in early HN progression and then gradually declined below the baseline level. We identified the impaired activity of the NRF2-activated antioxidant pathway as a driver of oxidative damage in HN progression. Through nrf2 deletion, we further confirmed aggravated kidney damage in nrf2 knockout HN mice compared with HN mice. In contrast, the pharmacological agonist of NRF2 improved kidney function and alleviated renal fibrosis in mice. Mechanistically, the activation of NRF2 signaling reduced oxidative stress by restoring mitochondrial homeostasis and reducing NADPH oxidase 4 (NOX4) expression in vivo or in vitro. Moreover, the activation of NRF2 promoted the expression levels of heme oxygenase 1 (HO-1) and quinone oxidoreductase 1 (NQO1) and enhanced the antioxidant capacity of cells. Furthermore, the activation of NRF2 ameliorated renal fibrosis in HN mice through the downregulation of the transforming growth factor-beta 1 (TGF-β1) signaling pathway and ultimately delayed the progression of HN. Collectively, these results suggested NRF2 as a key regulator in improving mitochondrial homeostasis and fibrosis in renal tubular cells by reducing oxidative stress, upregulating the antioxidant signaling pathway, and downregulating the TGF-β1 signaling pathway. The activation of NRF2 represents a promising strategy to restore redox homeostasis and combat HN.

Chronic kidney disease (CKD) was a major public health problem worldwide. Renal fibrosis, especially tubulointerstitial fibrosis, is final manifestation of CKD. Many studies have demonstrated that TGF-β/Smad signaling pathway plays a crucial role in renal fibrosis. Therefore, targeted inhibition of TGF-β/Smad signaling pathway can be used as a potential therapeutic measure for tubulointerstitial fibrosis. At present, a variety of targeting TGF-β1 and its downstream Smad proteins have attracted attention. Natural products used as potential therapeutic strategies for tubulointerstitial fibrosis have the characteristics of acting on multiple targets by multiple components and few side effects. With the continuous research and technique development, more and more molecular mechanisms of natural products have been revealed, and there are many natural products that inhibited tubulointerstitial fibrosis via TGF-β/Smad signaling pathway. This review summarized the role of TGF-β/Smad signaling pathway in tubulointerstitial fibrosis and natural products against tubulointerstitial fibrosis by targeting TGF-β/Smad signaling pathway. Additionally, many challenges and opportunities are presented for inhibiting renal fibrosis in the future. [ABSTRACT FROM AUTHOR]

Objective: To explore the pharmacological mechanisms of Chongcaoyishen decoction (CCYSD) against chronic kidney disease (CKD) via network pharmacology analysis combined with experimental validation.Methods: The bioactive components and potential regulatory targets of CCYSD were extracted from the TCMSP database, and the putative CKD-related target proteins were collected from the GeneCards and OMIM database. We matched the active ingredients with gene targets and conducted regulatory networks through Perl5 and R 3.6.1. The network visualization analysis was performed by Cytoscape 3.7.1, which contains ClueGO plug-in for GO and KEGG analysis. In vivo experiments were performed on 40 male SD rats, which were randomly divided into the control group (n = 10), sham group (n = 10), UUO group (n = 10), and CCYSD group (n = 10). A tubulointerstitial fibrosis model was constructed by unilateral ureteral obstruction through surgery and treated for seven consecutive days with CCYSD (0.00657 g/g/d). At the end of treatment, the rats were euthanized and the serum and kidney were collected for further detection.Results: In total, 53 chemical compounds from CCYSD were identified and 12,348 CKD-related targets were collected from the OMIM and GeneCards. A total of 130 shared targets of CCYSD and CKD were acquired by Venn diagram analysis. Functional enrichment analysis suggested that CCYSD might exert its pharmacological effects in multiple biological processes, including oxidative stress, apoptosis, inflammatory response, autophagy, and fiber synthesis, and the potential targets might be associated with JAK-STAT and PI3K-AKT, as well as other signaling pathways. The results of the experiments revealed that the oxidative stress in the UUO group was significantly higher than that in normal state and was accompanied by severe tubulointerstitial fibrosis (TIF), which could be effectively reversed by CCYSD (p < 0.05). Meanwhile, aggravated mitochondrial injury and autophagy was observed in the epithelial cells of the renal tubule in the UUO group, compared to the normal ones (p < 0.05), while the intervention of CCYSD could further activate the autophagy and reduce the mitochondrial injury (p < 0.05).Conclusion: We provide an integrative network pharmacology approach combined with in vivo experiments to explore the underlying mechanisms governing the CCYSD treatment of CKD, which indicates that the relationship between CCYSD and CKD is related to its activation of autophagy, promotion of mitochondrial degradation, and reduction of tissue oxidative stress injury, promoting the explanation and understanding of the biological mechanism of CCYSD in the treatment of CKD.

Chronic kidney disease (CKD) was a major public health problem worldwide. Renal fibrosis, especially tubulointerstitial fibrosis, is final manifestation of CKD. Many studies have demonstrated that TGF-β/Smad signaling pathway plays a crucial role in renal fibrosis. Therefore, targeted inhibition of TGF-β/Smad signaling pathway can be used as a potential therapeutic measure for tubulointerstitial fibrosis. At present, a variety of targeting TGF-β1 and its downstream Smad proteins have attracted attention. Natural products used as potential therapeutic strategies for tubulointerstitial fibrosis have the characteristics of acting on multiple targets by multiple components and few side effects. With the continuous research and technique development, more and more molecular mechanisms of natural products have been revealed, and there are many natural products that inhibited tubulointerstitial fibrosis via TGF-β/Smad signaling pathway. This review summarized the role of TGF-β/Smad signaling pathway in tubulointerstitial fibrosis and natural products against tubulointerstitial fibrosis by targeting TGF-β/Smad signaling pathway. Additionally, many challenges and opportunities are presented for inhibiting renal fibrosis in the future.

Abstract Background Increased gene transcription of hypoxia‐induced mediators of fibrosis in renal tissue has been identified in experimentally induced, ischemic chronic kidney disease (CKD). Objective To characterize hypoxia‐induced profibrotic pathways in naturally occurring CKD in cats. Animals Twelve client‐owned cats with CKD and 8 healthy control cats. Methods In this prospective, cross‐sectional study, bilateral renal tissue samples were assessed histologically for inflammation, tubular atrophy, and fibrosis, and by reverse transcription‐quantitative PCR for characterization of transcript levels of hypoxia‐inducible factor‐1α (HIF1A), matrix metalloproteinases‐2 (MMP2), ‐7 (MMP7), and ‐9 (MMP9), tissue inhibitor of metalloproteinase‐1 (TIMP1), transforming growth factor‐β1 (TGFB1), and vascular endothelial growth factor‐A (VEGFA). Linear mixed models were used to compare gene transcription between diseased and healthy kidneys, and to examine the association between transcript levels and serum creatinine concentration for all cats, and between transcript levels and histologic scores of diseased kidneys. Results Kidneys from cats with CKD had significantly higher transcript levels of HIF1A, MMP2, MMP7, MMP9, TIMP1, and TGFB1 (all P < .001), and lower levels of VEGFA (P = .006) than those from control cats. Transcript levels of MMP7 (P = .05) and TIMP1 (P = .005) were positively associated with serum creatinine in cats with CKD, but not in control cats. In diseased kidneys, transcript levels of MMP2 (P = .002), MMP7 (P = .02), and TIMP1 (P = .02) were positively, whereas those of VEGFA (P = .003) were negatively, associated with histologic score severity. Conclusion and Clinical Significance Evaluation of the expression of the corresponding proteins in larger populations could identify therapeutic targets and/or biomarkers of tubulointerstitial fibrosis in cats.

Abstract Background Lupus nephritis is one of the most common and severe complications of systemic lupus erythematosus, of which poor prognosis is indicated by aggravated renal hypoxia and tubulointerstitial fibrosis. Cell adhesion molecules play a key role in the progression of lupus nephritis tubulointerstitial lesion, including P-selectin, which mediates the rolling of leukocytes and subsequent adhesion and infiltration and then initiates the inflammatory immune response and ischemia and hypoxia injury. However, the effects and mechanisms of P-selectin in lupus nephritis remain to be investigated, and a noninvasive measurement of lupus nephritis tubulointerstitial hypoxia and fibrosis remains to be explored. Methods Thirty-four MRL/lpr mice were randomly divided into the following three groups: MRL/lpr, saline, and anti-P-selectin, which consisted of no treatment, treatment with normal saline, and treatment with anti-P-selectin monoclonal antibody (mAb) from 12 to 16 weeks of age, respectively. Ten male C57BL/6 mice of the same age served as normal controls. 24-h urinary protein, urinary albumin–creatinine ratio, and periodic acid–Schiff were used to assess kidney damage; Western blot or immunohistochemical staining of the hypoxia probe Hypoxyprobe™-1, hypoxia-inducible factor 1α (HIF-1α), and CD31 were used to evaluate hypoxia in renal tissue; and NADPH oxidase subunit gp91phox and p22phox were used to examine renal oxidative stress. The correlation between kidney injury and blood oxygen level–dependent magnetic resonance imaging (BOLD-MRI) was calculated to assess the clinical value of BOLD-MRI. Results P-selectin is upregulated in lupus nephritis. Blocking P-selectin with mAb alleviated renal tubulointerstitial fibrosis, renal hypoxia, and peritubular capillary loss, without alteration of the levels of lupus activity indicators, anti-dsDNA antibody, or complement C3. BOLD-MRI showed that the reduced R2* values in the renal cortex and medulla of lupus mice were increased when treated with anti-P-selectin mAb as compared with those treated with normal saline, which were negatively correlated with Hypoxyprobe™-1 hypoxia probe and the expression of HIF-1α. Conclusions Early intervention of lupus nephritis with anti-P-selectin mAb can significantly improve the hypoxic state of the kidney and reduce the severity of tubulointerstitial lesions. BOLD-MRI techniques are noninvasive and can dynamically evaluate the changes in renal lesions and intrarenal oxygenation levels before and after treatment in lupus nephritis.

Nephrotic syndrome is the most common clinical presentation of glomerular disease in elderly patients, and renal biopsy is an important diagnostic resource. The aim of this study was to describe nephrotic syndrome among elderly patients in Brazil, focusing on tubulointerstitial and vascular involvement. This was a retrospective study of patients over 65 years of age with nephrotic syndrome who underwent renal biopsy between January 2012 and December 2019. Of the 123 renal biopsies that occurred during the study period, 44 (35.8%) were performed for the investigation of nephrotic syndrome. Among those 44 cases, the main etiologies were membranous nephropathy in 13 cases (29.5%), amyloidosis in ten (22.7%), non-collapsing focal segmental glomerulosclerosis (FSGS) in four (9.1%), and collapsing FSGS in four (9.1%). Patients with minimal change disease (MCD) had the lowest degree of interstitial fibrosis compared with the other glomerulopathies, and histological signs of acute tubular necrosis (ATN) were less common among those with amyloidosis than among those with membranous nephropathy, FSGS, or MCD (P=0.0077). Of the patients with ATN, the frequency of acute kidney injury (AKI) was highest in those with MCD (P

Hyperuricemic nephropathy (HN) is a global metabolic disorder characterized by uric acid (UA) metabolism dysfunction, resulting in hyperuricemia (HUA) and tubulointerstitial fibrosis (TIF). Sodium-dependent glucose transporter 2 inhibitor, dapagliflozin, has shown potential in reducing serum UA levels in patients with chronic kidney disease (CKD), though its protective effects against HN remain uncertain. This study investigates the functional, pathological, and molecular changes in HN through histological, biochemical, and transcriptomic analyses in patients, HN mice, and UA-stimulated HK-2 cells. Findings indicate UA-induced tubular dysfunction and fibrotic activation, which dapagliflozin significantly mitigates. Transcriptomic analysis identifies estrogen-related receptor α (ERRα), a downregulated transcription factor in HN. ERRα knockin mice and ERRα-overexpressed HK-2 cells demonstrate UA resistance, while ERRα inhibition exacerbates UA effects. Dapagliflozin targets ERRα, activating the ERRα-organic anion transporter 1 (OAT1) axis to enhance UA excretion and reduce TIF. Furthermore, dapagliflozin ameliorates renal fibrosis in non-HN CKD models, underscoring the therapeutic significance of the ERRα-OAT1 axis in HN and CKD., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Elderly patients are prone to develop hyper- or hypokalemia, since they are susceptible to drugs or diets that affect the urinary or fecal potassium (K+) excretion. In aging mouse kidneys, in addition to glomerulosclerosis, proximal tubular atrophy, and atherosclerosis in renal arterioles, there was diffuse tubulointerstitial fibrosis with a number of inflammatory leukocytes infiltrating into the cortical interstitium. Since these pathological features greatly influence renal K+ handling, slowing the progression of kidney aging would fundamentally reduce the risk of developing hyper- or hypokalemia. Immunohistochemistry demonstrated the overexpression of K+ channels (Kv1.3) in leukocytes within the cortical interstitium, which was strongly associated with "chronic inflammation" in aging kidneys and the subsequent progression of renal fibrosis. In our basic studies, antihypertensive drugs (benidipine, nifedipine, verapamil, diltiazem) and anticholesterol drugs (lovastatin, simvastatin, pravastatin) strongly suppressed the leukocyte Kv1.3 channels and thus exerted anti-inflammatory effects. Given such pharmacological properties of these drugs, they may also be useful in slowing the progression of tubulointerstitial fibrosis in aging kidneys and reducing the risk of hyper- or hypokalemia in elderly patients.

Following our previous reports on mesangial sclerosis and vascular proliferation in diabetic nephropathy (DN) (Kriz W, Löowen J, Federico G, van den Born J, Gröone E, Gröone HJ. Am J Physiol Renal Physiol 312: F1101-F1111, 2017; Löowen J, Gröone E, Gröone HJ, Kriz W. Am J Physiol Renal Physiol 317: F399-F410, 2019), we now describe the advanced stages of DN terminating in glomerular obsolescence and tubulointerstitial fibrosis based on a total of 918 biopsies. The structural aberrations emerged from two defects: 1) increased synthesis of glomerular basement membrane (GBM) components by podocytes and endothelial cells leading to an accumulation of GBM material in the mesangium and 2) a defect of glomerular vessels consisting of increased leakiness and an increased propensity to proliferate. Both defects may lead to glomerular degeneration. The progressing compaction of accumulated worn-out GBM material together with the retraction of podocytes out of the tuft and the collapse and hyalinosis of capillaries results in a shrunken tuft that fuses with Bowman's capsule (BC) to glomerular sclerosis. The most frequent pathway to glomerular decay starts with local tuft expansions that result in contacts of structurally intact podocytes to the parietal epithelium initiating the formation of tuft adhesions, which include the penetration of glomerular capillaries into BC. Exudation of plasma from such capillaries into the space between the parietal epithelium and its basement membrane causes the formation of insudative fluid accumulations within BC spreading around the glomerular circumference and, via the glomerulotubular junction, onto the tubule. Degeneration of the corresponding tubule develops secondarily to the glomerular damage, either due to cessation of filtration in cases of global sclerosis or due to encroachment of the insudative spaces. The degenerating tubules induce the proliferation of myofibroblasts resulting in interstitial fibrosis. [ABSTRACT FROM AUTHOR]

Background/Aims: Stress-induced cell senescence, which contributes to cell cycle arrest and is independent of age, plays an important role in chronic kidney disease (CKD) progression. DcR2, as a senescent marker, exclusively expressed in senescent tubular epithelia. The objective of this study was to examine whether urinary DcR2 (uDcR2) could be a potential biomarker for tubulointerstitial fibrosis (TIF) in patients with immunoglobulin A nephropathy (IgAN). Methods: This study included 210 IgAN patients and 80 healthy volunteers, with uDcR2 levels measured using enzyme-linked immunosorbent assay. We examined the relationship among uDcR2/Cr levels, renal function, and pathological parameters, using regression analysis to identify risk factors for TIF and the area under the curve (AUC) approach to predict TIF. Renal DcR2 expression was quantified by immunohistochemistry. Co-expression of DcR2 with fibrotic markers (α-smooth muscle actin [α-SMA], collagen III) was analyzed by confocal microscopy. Results: Levels of uDcR2/Cr were significantly higher in IgAN patients and in those with more severe TIF, compared with healthy controls. Serum DcR2 levels were similar across groups. The proportion of IgAN patients with stages 1–2 CKD and T0 was highest among those with uDcR2/Cr 201 ng/g had stages 4–5 CKD and T2. Levels of uDcR2/Cr were positively associated with urinary albumin to creatinine ratio (ACR), urinary N-acetyl-β-D-glucosaminidase (uNAG)/Cr, and TIF scores and negatively associated with estimated glomerular filtration rate (eGFR). uDcR2/Cr, uNAG, ACR, and eGFR were independent predictors for TIF, with AUC of 0.907 for uDcR2/Cr. This AUC value was higher than that observed for eGFR, uNAG/Cr, or ACR. The sensitivity and specificity of uDcR2/Cr in predicting TIF were 87.0 and 80.5%, respectively. Moreover, uDcR2/Cr levels were positively associated with the percentage of renal DcR2 expression. Renal DcR2 co-localized with α-SMA and collagen III in the kidneys of IgAN patients. Conclusions: Levels of uDcR2/Cr were closely associated with the severity of TIF and renal function parameters. uDcR2/Cr represents a potential biomarker for predicting TIF in IgAN patients.

Aim. To assess the role of remodeling of small diameter kidney arteries in the prognosis of progression of tubulointerstitial fibrosis in patients with chronic glomerulonephritis.Material and methods. The study involved 97 patients with primary glomerulonephritis. The average age of patients was 37,27±1,2 years. The inclusion criterion was the presence of indications for renal biopsy. Renal biopsy was used to analyze renal tissue, in particular, for determining of tubulointerstitial fibrosis (TIF). Based on TIF sign, the patients were divided in 2 groups. The first group includes patients with TIF, the second — without TIF. Vasometry, a measurement of the renal arteries structures, was performed as part of renal biopsy. Parameters of internal and external diameters, wall thickness, intima, media, intima-media complex, vascular mass were analyzed.Results. The influence of the size of the inner and outer diameters of the interlobular artery (MA) on the studied risk was established. Probability of TIF developing increases with decreasing of MA inner diameter (χ2-criterion =5,34, p=0,02) and increasing of MA outer diameter (χ2-criterion =7,77, p=0,005). Intimal thickness does not have a statistically significant effect on the risk of TIF developing (p=0,29), whereas media thickness has a high statistical significance in renal tissue remodeling (χ2-criterion =13,71, p=0,0002). A statistically significant effect of an increase in the vascular mass on the risk of TIF was determined (χ2-criterion =6,55, p=0,01).Conclusion. We established that changes in the structure of small diameter kidney arteries in chronic glomerulonephritis occurs according to a hypertrophic type. Remodeling of small diameter kidney arteries plays significant role on the risk of TIF.

Canonical transient receptor potential-6 (TRPC6) channels have been implicated in familial and acquired forms of focal and segmental glomerulosclerosis (FSGS), and in renal fibrosis following ureteral obstruction in mice. TRPC6 channels also appear to play a role in driving glomerular disease in aging and in autoimmune glomerulonephritis. In the present study, we examine the role of TRPC6 in the proteinuric state caused by prolonged albumin overload (AO) in Sprague Dawley rats induced by daily injections of exogenous albumin. This was assessed in rats with a global and constitutive inactivation of TRPC6 channels (Trpc6del/del rats) and in wild-type littermates (Trpc6wt/wt rats). AO for 14 and 28 days caused increased urine albumin excretion that was significantly attenuated in Trpc6del/del rats compared to Trpc6wt/wt controls. AO overload did not induce significant glomerulosclerosis or azotemia in either genotype. AO induced mild tubulointerstitial disease characterized by fibrosis, hypercellularity and increased expression of markers of fibrosis and inflammation. Those changes were equally severe in Trpc6wt/wt and Trpc6del/del rats. Immunoblot analysis of renal cortex indicated that AO increased the abundances of TRPC3 and TRPC6, and caused a nearly complete loss of TRPC5 in Trpc6wt/wt rats. The increase in TRPC3 and the loss of TRPC5 occurred to the same extent in Trpc6del/del rats. These data also suggest that TRPC6 plays a role in the normal function of the glomerular filtration barrier. However, whether TRPC6 inactivation protects the tubulointerstitial compartments in Sprague Dawley rats depends on the disease model examined.

Increasing evidence supports a role of proximal tubular (PT) injury in the progression of diabetic kidney disease (DKD), in patients with or without proteinuria. Research on the mechanisms of the PT injury in DKD could help us to identify potential new biomarkers and drug targets for DKD. A high glucose transport state and mismatched local hypoxia in the PT of diabetes patients may be the initiating factors causing PT injury. Other mechanism such as mitochondrial dysfunction, reactive oxygen species (ROS) overproduction, ER stress, and deficiency of autophagy interact with each other leading to more PT injury by forming a vicious circle. PT injury eventually leads to the development of tubulointerstitial inflammation and fibrosis in DKD. Many downstream signaling pathways have been demonstrated to mediate these diseased processes. This review focuses mostly on the novel mechanisms of proximal renal tubular injury in DKD and we believe such review could help us to better understand the pathogenesis of DKD and identify potential new therapies for this disease.

Tubulointerstitial fibrosis is both a pathological manifestation of chronic kidney disease and a driving force for the progression of kidney disease. A previous study has shown that bone morphogenetic protein-binding endothelial cell precursor-derived regulator (BMPER) is involved in lung fibrogenesis. However, the role of BMPER in renal fibrosis remains unknown. In the present study, the expression of BMPER was examined by real-time PCR, Western blot and immunohistochemical staining. The in vitro effects of BMPER on tubular dedifferentiation and fibroblast activation were analyzed in cultured HK-2 and NRK-49F cells. The in vivo effects of BMPER were dissected in unilateral ureteral obstruction (UUO) mice by delivery of BMPER gene via systemic administration of plasmid vector. We reported that the expression of BMPER decreased in the kidneys of UUO mice and HK-2 cells. TGF-β1 increased inhibitor of differentiation-1 (Id-1) and induced epithelial mesenchymal transition in HK-2 cells, and knockdown of BMPER aggravated Id-1 up-regulation, E-cadherin loss, and tubular dedifferentiation. On the contrary, exogenous BMPER inhibited Id-1 up-regulation, prevented E-cadherin loss and tubular dedifferentiation after TGF-β1 exposure. In addition, exogenous BMPER suppressed fibroblast activation by hindering Erk1/2 phosphorylation. Knockdown of low-density lipoprotein receptor-related protein 1 abolished the inhibitory effect of BMPER on Erk1/2 phosphorylation and fibroblast activation. Moreover, delivery of BMPER gene improved renal tubular damage and interstitial fibrosis in UUO mice. Therefore, BMPER inhibits TGF-β1-induced tubular dedifferentiation and fibroblast activation and may hold therapeutic potential for tubulointerstitial fibrosis.

Background/Aims: Renal tubular epithelial cells and fibroblasts are the main sources of myofibroblasts, and these cells produce the extracellular matrix during tubulointerstitial fibrosis (TIF). Histone deacetylases (HDAC) inhibitors exert an antifibrogenic effect in the skin, liver and lung. Sirtuin 2 (SIRT2), which is a class III HDAC, is an important member of NAD+-dependent protein deacetylases. The current study evaluated the role of SIRT2 in renal TIF. Methods: Immunohistochemical staining and Western blot were performed to evaluate SIRT2 expression in TIF patients and unilateral urethral obstruction (UUO) mice. Western blot was used to assess the protein levels of SIRT2, α-SMA, collagen III, fibronectin, and MDM2 in tubular epithelial cells and fibroblasts. The specific inhibitor AGK2 was used to inhibit SIRT2 activity, and targeted siRNA was used to suppress SIRT2 expression. Results: SIRT2 expression increased in the tubulointerstitium of TIF patients and UUO mice. SIRT2 inhibition ameliorated TIF in UUO mice. SIRT2 expression in tubular cells was unchanged after exposure to TGF-β1. The SIRT2-specifc inhibitor AGK2 did not attenuate TGF-β1-induced tubular epithelial-mesenchymal transition. However, SIRT2 was upregulated in fibroblasts, and fibroblasts were activated after TGF-β1 treatment. Genetic knockdown and chemical inhibition of SIRT2 attenuated TGF-β1-induced fibroblast activation. We also explored the downstream signaling of SIRT2 during fibroblast activation. Genetic knockdown and chemical inhibition of SIRT2 suppressed TGF-β1-induced increase in MDM2 expression, and inhibition of the MDM2-p53 interaction using Nutlin-3 did not suppress SIRT2 upregulation. Conclusion: Our results suggest that SIRT2 participates in the activation of fibroblasts and TIF, which is mediated via regulation of the MDM2 pathway, and the downregulation of SIRT2 may be a therapeutic strategy for renal fibrosis.

Background Tubulointerstitial fibrosis is a powerful predictor of future progression inimmunoglobulin A (IgA) nephropathy (IgAN). Proximal tubular epithelial cells (PTECs), in concert with infiltrating macrophages, are regarded as the agents provocateurs for driving this fibrotic process. However, evidence is now emerging for a contributory role of the distal nephron. The aim of this study was to examine the potential influence of macrophages on collecting duct epithelial cells (CDECs) and their combined role in the progression of IgAN. Methods CDECs were cultured with macrophage-conditioned media (MCM) generated from human monocyte cell lines U937 and THP-1 stimulated with or without 100 μg/mL galactose-deficient IgA1. CDECs were analysed for evidence of inflammation and fibrosis. Results Staining of IgAN biopsies for CD68+ macrophages revealed the presence of macrophages juxtaposed to collecting ducts and within their lumina. CDEC exposed to MCM from IgA1-stimulated THP-1 cells (THP-1-IgA-MCM) exhibited markedly increased expression of neutrophil-associated gelatinase (NGAL) and proinflammatory cytokinesinterleukin (IL)-1β, tumour necrosis factor-α, IL-6 and IL-8 compared with MCM from non-IgA-stimulated THP-1 cells (THP-1-MCM). U937-IgA-MCM increased fibronectin levels and reduced E-cadherinmRNA expression. THP-1-IgA-MCM-derived exosomes induced similar increases in NGAL and cytokine expression while in cross-over experiments exosomes extracted from IL-1β-exposed CDEC induced IL-1β and IL-6 mRNA expression in both sets of macrophages. MiRnome analysis revealed that microRNA (miR)-146a, -155 and -200b exhibited a >2-fold increase in expression in CDEC treated with THP-1-IgA-MCM compared with THP-1-MCM. Enforced miR-146a suppression further enhanced NGAL expression, while ectopic miR-146a over-expression downregulated it. NGAL mRNA and miR-146a were upregulated in the biopsies of patients with progressive IgAN compared with non-progressive IgAN. Conclusions Taken together, these data suggest that CDEC–macrophage interactions potentially contribute to the tubulointerstitial fibrosis characteristic of progressive IgAN. [ABSTRACT FROM AUTHOR]

Objectives: The severity of interstitial fibrosis/tubular atrophy (IFTA) is the most important determinant of the irreversible progression of chronic kidney disease (CKD). Prolidase is the key enzyme in collagen turnover and is associated with an extracellular matrix increase. We aimed to evaluate the relationship between the presence and degree of IFTA and serum prolidase enzyme activity (SPEA) in patients undergoing a renal biopsy. Methods: This cross-sectional study included 56 patients who underwent a renal biopsy (30 males; mean age 45.3 ± 16.8 years) and also 54 healthy volunteers (21 males; mean age 42.7 ± 8.2 years). IFTA scoring was performed on the basis of percentage of IFTA presence in renal biopsy tissues (1=<10%; 2=10–24%; 3=25–50%; 4=>50%). SPEA was measured by spectrophotometric method. Results: The proteinuria and SPEA levels of the patients were significantly higher than the controls (p<0.001 and p<0.001, respectively). SPEA decreased significantly when the IFTA score increased (p<0.002). In the correlation analysis, the IFTA score was negatively correlated with SPEA (rs=−0.461, p<0.001), and positively correlated with proteinuria (rs=0.274, p=0.041). Conclusion: These findings suggest that increased collagen turnover decreases over time concerning the progression of renal fibrosis. Monitoring of SPEA level may useful as a biomarker for early determination of CKD progression and severity. [ABSTRACT FROM AUTHOR]

Background: Increased gene transcription of hypoxia‐induced mediators of fibrosis in renal tissue has been identified in experimentally induced, ischemic chronic kidney disease (CKD). Objective: To characterize hypoxia‐induced profibrotic pathways in naturally occurring CKD in cats. Animals Twelve client‐owned cats with CKD and 8 healthy control cats. Methods: In this prospective, cross‐sectional study, bilateral renal tissue samples were assessed histologically for inflammation, tubular atrophy, and fibrosis, and by reverse transcription‐quantitative PCR for characterization of transcript levels of hypoxia‐inducible factor‐1α (HIF1A), matrix metalloproteinases‐2 (MMP2), ‐7 (MMP7), and ‐9 (MMP9), tissue inhibitor of metalloproteinase‐1 (TIMP1), transforming growth factor‐β1 (TGFB1), and vascular endothelial growth factor‐A (VEGFA). Linear mixed models were used to compare gene transcription between diseased and healthy kidneys, and to examine the association between transcript levels and serum creatinine concentration for all cats, and between transcript levels and histologic scores of diseased kidneys. Results: Kidneys from cats with CKD had significantly higher transcript levels of HIF1A, MMP2, MMP7, MMP9, TIMP1, and TGFB1 (all P <.001), and lower levels of VEGFA (P =.006) than those from control cats. Transcript levels of MMP7 (P =.05) and TIMP1 (P =.005) were positively associated with serum creatinine in cats with CKD, but not in control cats. In diseased kidneys, transcript levels of MMP2 (P =.002), MMP7 (P =.02), and TIMP1 (P =.02) were positively, whereas those of VEGFA (P =.003) were negatively, associated with histologic score severity. Conclusion and Clinical Significance: Evaluation of the expression of the corresponding proteins in larger populations could identify therapeutic targets and/or biomarkers of tubulointerstitial fibrosis in cats. [ABSTRACT FROM AUTHOR]