Unilateral ureteral obstruction: beyond obstruction

Fluorimetric Tool to Discriminate Glomerular and Tubular Injuries In Vivo

The etiology and pathological complexity of acute kidney injury (AKI) pose great challenges for early diagnosis, typing, and personalized treatment. It is an important reason for poor prognosis and high mortality of AKI. In order to provide a relatively noninvasive diagnostic and typing method for AKI, we proposed the pathological changes of albumin permeability after glomerular injury and reabsorption efficiency after tubular injury as potential entry points. Thus, a renal tubule labeling fluorescent dye which features albumin concentration-related fluorescence intensity was used to fit these pathological changes. Utilizing this fluorescence assay, we realized urinary tract obstruction imaging as early as 12 h after morbidity. For glomerular and tubular injury discrimination, compared to a healthy control, membranous nephropathy as a representative glomerular injury resulted in enhanced fluorescence intensity of the kidney due to increased albumin penetration, while renal tubular injury caused insufficient dye reabsorption to exhibit weakened fluorescence intensity. The significant differences demonstrated the feasibility of this approach for fluorescence imaging-based AKI typing in vivo.

Lipidomic study of kidney in a mouse model with urine flow obstruction

Obstructed urine flow is known to cause structural and functional kidney damage leading to renal fibrosis. However, limited information is available on the change in kidney lipids during urinary tract obstruction. In this study, we investigated the change in lipidome in a mouse model with unilateral ureteral obstruction (UUO). The establishment of the UUO model was confirmed by histopathological examination using transmission electron microscopy. Untargeted liquid chromatography/mass spectrometry was carried out over a time course of 4 and 7 days. Compared to the sham control, the UUO kidney at 7 days showed dilatation of the renal tubule with loss of brush borders and thickening of the capillary endothelium. In the kidney lipidomes obtained from the UUO 7 days group compared to the control, a significant decrease of ceramide, sphingomyelin, phosphatidylcholine, lysophospholipids, and phosphatidylethanolamine was observed, whereas cholesteryl esters, free fatty acids, phosphatidylglycerol, and cardiolipins were significantly increased. The present study revealed the disturbed lipid metabolism in the UUO model, which may provide a clue to potential lipid pathways and therapeutic targets for the early stage of renal fibrosis.

Progranulin deficiency attenuates tubulointerstitial injury in a mouse unilateral ureteral obstruction model

Progranulin (PGRN) may have two opposing effects-inflammation and anti-inflammation-in different diseases. Although previous studies have reported that PGRN is involved in liver fibrosis, its involvement in tubulointerstitial fibrosis remains to be fully elucidated. Herein, we investigated these issues using PGRN-knockout (KO) mice treated with unilateral ureteral obstruction (UUO). Eight-week-old male PGRN-KO and wild-type (WT) mice were euthanized 3 and 7 days following UUO, and their kidneys were harvested for histopathological analysis. The renal expression of PGRN was evaluated by immunohistochemical and/or western blot analyses. The renal mRNA levels of markers related to inflammation (Il1b, Tnf, Il6, Ccl2, and Adgre1) and fibrosis (Tgfb1, Acta2, Fn1, and Col1a2) were evaluated using quantitative PCR. Histological changes such as renal tubular atrophy, urinary casts, and tubulointerstitial fibrosis were significantly improved in UUO-KO mice compared with UUO-WT mice. Quantitative PCR revealed that the mRNA expression levels of all inflammation- and fibrosis-related markers were lower in UUO-KO mice than in UUO-WT mice at 3 and/or 7 days after UUO. Moreover, PGRN and GRN protein levels were higher in the kidneys of UUO-WT mice than in mice that did not undergo UUO. Elevated GRN levels associated with excess PGRN levels may be involved in the occurrence of renal inflammation and fibrosis in UUO mice.

Loss of NLRP6 increases the severity of kidney fibrosis

While NLRP3 contributes to kidney fibrosis, the function of most NOD-like receptors (NLRs) in chronic kidney disease (CKD) remains unexplored. To identify further NLR members involved in the pathogenesis of CKD, we searched for NLR genes expressed by normal kidneys and differentially expressed in human CKD transcriptomics databases. For NLRP6, lower kidney expression correlated with decreasing glomerular filtration rate. The role and molecular mechanisms of Nlrp6 in kidney fibrosis were explored in wild-type and Nlrp6-deficient mice and cell cultures. Data mining of single-cell transcriptomics databases identified proximal tubular cells as the main site of Nlrp6 expression in normal human kidneys and tubular cell Nlrp6 was lost in CKD. We confirmed kidney Nlrp6 downregulation following murine unilateral ureteral obstruction. Nlrp6-deficient mice had higher kidney p38 MAPK activation and more severe kidney inflammation and fibrosis. Similar results were obtained in adenine-induced kidney fibrosis. Mechanistically, profibrotic cytokines transforming growth factor beta 1 (TGF-β1) and TWEAK decreased Nlrp6 expression in cultured tubular cells, and Nlrp6 downregulation resulted in increased TGF-β1 and CTGF expression through p38 MAPK activation, as well as in downregulation of the antifibrotic factor Klotho, suggesting that loss of Nlrp6 promotes maladaptive tubular cell responses. The pattern of gene expression following Nlrp6 targeting in cultured proximal tubular cells was consistent with maladaptive transitions for proximal tubular cells described in single-cell transcriptomics datasets. In conclusion, endogenous constitutive Nlrp6 dampens sterile kidney inflammation and fibrosis. Loss of Nlrp6 expression by tubular cells may contribute to CKD progression.

Renal inflammation combined with renal function reserve reduction accelerate kidney aging via pentose phosphate pathway

Aging is closely associated with inflammation, which affects renal function reserve (RFR) in the kidneys. This study aims to investigate the impact of reduced RFR reduction on kidney aging and the influence of renal inflammation and RFR reduction on this process. Natural aging rats and those subjected to unilateral nephrectomy (UNX), 1/6 nephrectomy (1/6NX), and unilateral ureteral obstruction (UUO) were observed at 6, 12, 18, and 21 months. Our findings suggest that RFR reduction and renal inflammation can accelerate kidney aging, and inflammation contributes more. Metabolomics analysis revealed alterations in amino acid metabolism contribute to RFR decline. Furthermore, experiments in vitro confirmed the involvement of pentose phosphate pathway (PPP) in promoting aging though inflammation. Our research provides novel insights into for the mechanism of kidney aging and provides indirect support for clinical treatment decisions, such as addressing kidney inflammation, stones, or tumors that may necessitate partial or complete nephrectomy.

Role of urinary N-acetyl-beta-D-glucosaminidase in predicting the prognosis of antenatal hydronephrosis

PURPOSE

Urinary biomarkers are known to be able to diagnose renal damage caused by obstruction at an early stage. We evaluated the usefulness of urine N-acetyl-beta-D-glucosaminidase (NAG) to determine the prognosis of antenatal hydronephrosis.

MATERIALS AND METHODS

From January 2019 to December 2021, a retrospective study was performed on patients with grade 3 or 4 hydronephrosis. We analyzed the ultrasonographic findings and the urinary NAG/Cr ratio between the laparoscopic pyeloplasty (LP) group and active surveillance (AS) group.

RESULTS

A total of 21 children underwent LP for ureteropelvic junction (UPJ) obstruction and 14 children underwent AS. The mean age at the time of examination was 3.7 months (1.7-7.5 months) in the LP and 5.2 months (0.5-21.5 months) in the AS (p=0.564). The mean anteroposterior pelvic diameter was 30.0 mm (15.0-49.0 mm) in the LP and 16.7 mm (9.0-31.3 mm) in the AS (p=0.003). The mean renal parenchymal thickness was 2.6 mm (1.2-3.7 mm) in the LP and 3.8 mm (2.9-5.5 mm) in the AS (p=0.017). The urinary NAG/Cr ratio was 26.1 IU/g (9.8-47.4 IU/g) in the LP and 11.1 IU/g (2.6-18.1 IU/g) in the AS (p=0.003). After LP, the urinary NAG/Cr ratio was significantly reduced to 10.4 IU/g (3.4-14.2 IU/g) (p=0.023).

CONCLUSIONS

The urinary NAG/Cr ratio, one of the biomarkers of acute renal injury, is closely related to the degree of hydronephrosis. Therefore, it may be useful to determine whether to perform surgery on the UPJ obstruction and to predict the prognosis.

The functions of hydrogen sulfide on the urogenital system of both males and females: from inception to the present

Hydrogen sulfide (H2S) is known as a chemical gas in nature with both enzymatic and non-enzymatic biosynthesis in different human organs. A couple of studies have demonstrated the function of H2S in regulating the homeostasis of the human body. Additionally, they have shown its synthesis, measurement, chemistry, protective effects, and interaction in various aspects of scientific evidence. Furthermore, many researches have demonstrated the beneficial impacts of H2S on genital organs and systems. According to various studies, it is recognized that H2S-producing enzymes and the endogenous production of H2S are expressed in male and female reproductive systems in different mammalian species. The main goal of this comprehensive review is to assess the potential therapeutic impacts of this gasotransmitter in the male and female urogenital system and find underlying mechanisms of this agent. This narrative review investigated the articles that were published from the 1970s to 2022. The review's primary focus is the impacts of H2S on the male and female urogenital system. Medline, CINAHL, PubMed, and Google scholar databases were searched. Keywords used in this review were "Hydrogen sulfide," "H2S," "urogenital system," and "urogenital tract". Numerous studies have demonstrated the therapeutic and protective effects of sodium hydrosulfide (Na-HS) as an H2S donor on male and female infertility disorders. Furthermore, it has been observed that H2S plays a significant role in improving different diseases such as ameliorating sperm parameters. The specific localization of H2S enzymes in the urogenital system provides an excellent opportunity to comprehend its function and role in various disorders related to this system. It is noteworthy that H2S has been demonstrated to be produced in endocrine organs and exhibit diverse activities. Moreover, it is important to recognize that alterations in H2S biosynthesis are closely linked to endocrine disorders. Therefore, hormones can be pivotal in regulating H2S production, and H2S synthesis pathways may aid in establishing novel therapeutic strategies. H2S possesses pharmacological effects on essential disorders, such as anti-inflammation, anti-apoptosis, and anti-oxidant activities, which render it a valuable therapeutic agent for human urogenital disease. Furthermore, this agent shows promise in ameliorating the detrimental effects of various male and female diseases. Despite the limited clinical research, studies have demonstrated that applying H2S as an anti-oxidant source could ameliorate adverse effects of different conditions in the urogenital system. More clinical studies are required to confirm the role of this component in clinical settings.

Reno-protective effect of protocatechuic acid is independent of sex-related differences in murine model of UUO-induced kidney injury

BACKGROUND

Obstructive nephropathy is a condition often caused by urinary tract obstruction either anatomical (e.g., tumors), mechanical (e.g., urolithiasis), or compression (e.g., pregnancy) and can progress to chronic kidney disease (CKD). Studies have shown sexual dimorphism in CKD, where males were found to have a more rapid decline in kidney function following kidney injury compared to age-matched females. Protocatechuic acid (PCA), an anti-oxidant and anti-inflammatory polyphenolic compound, has demonstrated promising effects in mitigating drug-induced kidney injuries. The current study aims to explore sexual dimorphism in kidney injury after unilateral ureteral obstruction (UUO) and assess whether PCA treatment can mitigate kidney injury in both sexes.

METHODS

UUO was induced in 10-12 weeks old male and female C57BL/6J mice. Mice were categorized into four groups (n = 6-8/group); Sham, Sham plus PCA (100 mg/kg, I.P daily), UUO, and UUO plus PCA.

RESULTS

After 2 weeks of induction of UUO, markers of kidney oxidative stress (TBARs), inflammation (IL-1α and IL-6), tubular injury (neutrophil gelatinase-associated lipocalin, NGAL and urinary kidney injury molecule-1, KIM-1), fibrosis (Masson's trichrome staining, collagen IV expression, MMP-2 and MMP-9) and apoptosis (TUNEL+ cells, active caspase-1 and caspase-3) were significantly elevated in both males and females relative to their sham counterparts. Males exhibited significantly greater kidney oxidative stress, inflammation, fibrosis, and apoptosis after induction of UUO when compared to females. PCA treatment significantly attenuated UUO-induced kidney injury, inflammation, fibrosis, and apoptosis in both sexes.

CONCLUSION

Our findings suggest a differential gender response to UUO-induced kidney injury with males being more sensitive to UUO-induced kidney inflammation, fibrosis, and apoptosis than age-matched females. Importantly, PCA treatment reduced UUO-induced kidney injury in a sex-independent manner which might be attributed to its anti-oxidant, anti-inflammatory, anti-fibrotic, and anti-apoptotic properties.

Long noncoding RNA: An emerging diagnostic and therapeutic target in kidney diseases

Long noncoding RNAs (lncRNAs) have critical roles in the development of many diseases including kidney disease. An increasing number of studies have shown that lncRNAs are involved in kidney development and that their dysregulation can result in distinct disease processes, including acute kidney injury, chronic kidney disease, and renal cell carcinoma. Understanding the roles of lncRNAs in kidney disease may provide new diagnostic and therapeutic opportunities in the clinic. This review provides an overview of lncRNA characteristics, and biological function and discusses specific studies that provide insight into the function and potential application of lncRNAs in kidney disease treatment.

Nrf2/HO-1 as a therapeutic target in renal fibrosis

Chronic kidney disease (CKD) is one of the most prevalent chronic diseases and affects between 10 and 14 % of the world's population. The World Health Organization estimates that by 2040, the disease will be fifth in prevalence. End-stage CKD is characterized by renal fibrosis, which can eventually lead to kidney failure and death. Renal fibrosis develops due to multiple injuries and involves oxidative stress and inflammation. In the human body, nuclear factor erythroid 2-related factor 2 (Nrf2) plays an important role in the expression of antioxidant, anti-inflammatory, and cytoprotective genes, which prevents oxidative stress and inflammation damage. Heme oxygenase (HO-1) is an inducible homolog influenced by heme products and after exposure to cellular stress inducers such as oxidants, inflammatory chemokines/cytokines, and tissue damage as an outcome or downstream of Nrf2 activation. HO-1 is known for its antioxidative properties, which play an important role in regulating oxidative stress. In renal diseases-induced tissue fibrosis and xenobiotics-induced renal fibrosis, Nrf2/HO-1 has been targeted with promising results. This review summarizes these studies and highlights the interesting bioactive compounds that may assist in attenuating renal fibrosis mediated by HO-1 activation. In conclusion, Nrf2/HO-1 signal activation could have a renoprotective effect strategy against CKD caused by oxidative stress, inflammation, and consequent renal fibrosis.

Structure-Based Optimization and Biological Evaluation of Potent and Selective MMP-7 Inhibitors for Kidney Fibrosis

Matrix metalloproteinase-7 (MMP-7) has been shown to play important roles in pathophysiological processes involved in the development/progression of diseases such as cancer and fibrosis. We discovered selective MMP-7 inhibitors composed of arylsulfonamide, carboxylate, and short peptides by a molecular hybridization approach. These compounds interacted with MMP-7 via multiple hydrogen bonds in the cocrystal structures. To obtain compounds for in vivo evaluation, we attempted structural optimization, particularly targeting Tyr167 at the S3 subsite through structure-based drug design, and identified compound 15 as showing improved MMP-7 potency and MMP subtype selectivity. A novel π-π stacking interaction with Tyr167 was achieved when 4-pyridylalanine was introduced as the P3 residue. Compound 15 suppressed the progression of kidney fibrosis in a dose-dependent manner in a mouse model of unilateral ureteral obstruction. Thus, we demonstrated, for the first time, that potent and selective MMP-7 inhibitors could prevent the progression of kidney fibrosis.

SCARF Genes in COVID-19 and Kidney Disease: A Path to Comorbidity-Specific Therapies

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19), which has killed ~7 million persons worldwide. Chronic kidney disease (CKD) is the most common risk factor for severe COVID-19 and one that most increases the risk of COVID-19-related death. Moreover, CKD increases the risk of acute kidney injury (AKI), and COVID-19 patients with AKI are at an increased risk of death. However, the molecular basis underlying this risk has not been well characterized. CKD patients are at increased risk of death from multiple infections, to which immune deficiency in non-specific host defenses may contribute. However, COVID-19-associated AKI has specific molecular features and CKD modulates the local (kidney) and systemic (lung, aorta) expression of host genes encoding coronavirus-associated receptors and factors (SCARFs), which SARS-CoV-2 hijacks to enter cells and replicate. We review the interaction between kidney disease and COVID-19, including the over 200 host genes that may influence the severity of COVID-19, and provide evidence suggesting that kidney disease may modulate the expression of SCARF genes and other key host genes involved in an effective adaptive defense against coronaviruses. Given the poor response of certain CKD populations (e.g., kidney transplant recipients) to SARS-CoV-2 vaccines and their suboptimal outcomes when infected, we propose a research agenda focusing on CKD to develop the concept of comorbidity-specific targeted therapeutic approaches to SARS-CoV-2 infection or to future coronavirus infections.

Obstructive nephropathy and molecular pathophysiology of renal interstitial fibrosis

The kidneys play a key role in maintaining total body homeostasis. The complexity of this task is reflected in the unique architecture of the organ. Ureteral obstruction greatly affects renal physiology by altering hemodynamics, changing glomerular filtration and renal metabolism, and inducing architectural malformations of the kidney parenchyma, most importantly renal fibrosis. Persisting pathological changes lead to chronic kidney disease, which currently affects ∼10% of the global population and is one of the major causes of death worldwide. Studies on the consequences of ureteral obstruction date back to the 1800s. Even today, experimental unilateral ureteral obstruction (UUO) remains the standard model for tubulointerstitial fibrosis. However, the model has certain limitations when it comes to studying tubular injury and repair, as well as a limited potential for human translation. Nevertheless, ureteral obstruction has provided the scientific community with a wealth of knowledge on renal (patho)physiology. With the introduction of advanced omics techniques, the classical UUO model has remained relevant to this day and has been instrumental in understanding renal fibrosis at the molecular, genomic, and cellular levels. This review details key concepts and recent advances in the understanding of obstructive nephropathy, highlighting the pathophysiological hallmarks responsible for the functional and architectural changes induced by ureteral obstruction, with a special emphasis on renal fibrosis.

Novel Model of Oxalate Diet-Induced Chronic Kidney Disease in Dahl-Salt-Sensitive Rats

Diet-induced models of chronic kidney disease (CKD) offer several advantages, including clinical relevance and animal welfare, compared with surgical models. Oxalate is a plant-based, terminal toxic metabolite that is eliminated by the kidneys through glomerular filtration and tubular secretion. An increased load of dietary oxalate leads to supersaturation, calcium oxalate crystal formation, renal tubular obstruction, and eventually CKD. Dahl-Salt-Sensitive (SS) rats are a common strain used to study hypertensive renal disease; however, the characterization of other diet-induced models on this background would allow for comparative studies of CKD within the same strain. In the present study, we hypothesized that SS rats on a low-salt, oxalate rich diet would have increased renal injury and serve as novel, clinically relevant and reproducible CKD rat models. Ten-week-old male SS rats were fed either 0.2% salt normal chow (SS-NC) or a 0.2% salt diet containing 0.67% sodium oxalate (SS-OX) for five weeks.Real-time PCR demonstrated an increased expression of inflammatory marker interleukin-6 (IL-6) (p < 0.0001) and fibrotic marker Timp-1 metalloproteinase (p < 0.0001) in the renal cortex of SS-OX rat kidneys compared with SS-NC. The immunohistochemistry of kidney tissue demonstrated an increase in CD-68 levels, a marker of macrophage infiltration in SS-OX rats (p < 0.001). In addition, SS-OX rats displayed increased 24 h urinary protein excretion (UPE) (p < 0.01) as well as significant elevations in plasma Cystatin C (p < 0.01). Furthermore, the oxalate diet induced hypertension (p < 0.05). A renin-angiotensin-aldosterone system (RAAS) profiling (via liquid chromatography-mass spectrometry; LC-MS) in the SS-OX plasma showed significant (p < 0.05) increases in multiple RAAS metabolites including angiotensin (1-5), angiotensin (1-7), and aldosterone. The oxalate diet induces significant renal inflammation, fibrosis, and renal dysfunction as well as RAAS activation and hypertension in SS rats compared with a normal chow diet. This study introduces a novel diet-induced model to study hypertension and CKD that is more clinically translatable and reproducible than the currently available models.

Cold Shock Domain Protein DbpA Orchestrates Tubular Cell Damage and Interstitial Fibrosis in Inflammatory Kidney Disease

DNA-binding protein A (DbpA) belongs to the Y-box family of cold shock domain proteins that exert transcriptional and translational activities in the cell via their ability to bind and regulate mRNA. To investigate the role of DbpA in kidney disease, we utilized the murine unilateral ureter obstruction (UUO) model, which recapitulates many features of obstructive nephropathy seen in humans. We observed that DbpA protein expression is induced within the renal interstitium following disease induction. Compared with wild-type animals, obstructed kidneys from Ybx3-deficient mice are protected from tissue injury, with a significant reduction in the number of infiltrating immune cells as well as in extracellular matrix deposition. RNAseq data from UUO kidneys show that Ybx3 is expressed by activated fibroblasts, which reside within the renal interstitium. Our data support a role for DbpA in orchestrating renal fibrosis and suggest that strategies targeting DbpA may be a therapeutic option to slow disease progression.

Salt-sensitive hypertension after reversal of unilateral ureteral obstruction

The incidence of ureter obstruction is increasing and patients recovering from this kidney injury often progress to chronic kidney injury. There is evidence that a long-term consequence of recovery from ureter obstruction is an increased risk for salt-sensitive hypertension. A reversal unilateral ureteral obstruction (RUUO) model was used to study long-term kidney injury and salt-sensitive hypertension. In this model, we removed the ureteral obstruction at day 10 in mice. Mice were divided into four groups: (1) normal salt diet, (2) high salt diet, (3) RUUO normal salt diet, and (4) RUUO high salt diet. At day 10, the mice were fed a normal or high salt diet for 4 weeks. Blood pressure was measured, and urine and kidney tissue collected. There was a progressive increase in blood pressure in the RUUO high salt diet group. RUUO high salt group had decreased sodium excretion and glomerular injury. Renal epithelial cell injury was evident in RUUO normal and high salt mice as assessed by neutrophil gelatinase-associated lipocalin (NGAL). Kidney inflammation in the RUUO high salt group involved an increase in F4/80 positive macrophages; however, CD3+ positive T cells were not changed. Importantly, RUUO normal and high salt mice had decreased vascular density. RUUO was also associated with renal fibrosis that was further elevated in RUUO mice fed a high salt diet. Overall, these findings demonstrate long-term renal tubular injury, inflammation, decreased vascular density, and renal fibrosis following reversal of unilateral ureter obstruction that could contribute to impaired sodium excretion and salt-sensitive hypertension.

Obstructive uropathy – acute and chronic medical management

Obstructive uropathy is an important cause of acute and chronic kidney disease. Decompression of the urinary tract is an essential aspect of treatment. The cause and aetiology of obstruction typically determine the surgical approach. Acute relief of obstruction is frequently complicated by fluid and electrolyte imbalance. Standard therapeutic interventions for acute or chronic renal failure also apply for cases of obstructive uropathy. This narrative review summarises the early and long-term medical management of obstructive uropathy.

Acteoside alleviates UUO-induced inflammation and fibrosis by regulating the HMGN1/TLR4/TREM1 signaling pathway

PURPOSE

Acteoside (Act), a phenylethanoid compound that was first isolated from mullein, has been widely used for the investigation of anti-inflammatory and anti-fibrotic effect. However, the mechanism of Act against unilateral ureteral obstruction (UUO)-mediated renal injury is largely unknown. Therefore, this study aimed to explore the effects of Act on UUO rats and possible mechanisms.

METHODS

A total of 20 Sprague-Dawley (SD) rats were divided randomly into three groups (n ≥ 6): (i) sham-operated group (Sham); (ii) UUO group (UUO+Saline); and (iii) UUO + Act 40 mg/kg/day, (UUO+Act); Continuous gavage administration for 2 weeks postoperatively, while the rats in Sham and UUO+saline groups were given equal amounts of saline. All rats were sacrificed after 14 days, the urine and blood samples were collected for biochemical analysis, the renal tissues were collected for pathological staining and immunohistochemistry. Correlations between individual proteins were analyzed by Pearson correlation analysis.

RESULTS

The results of renal function indexes and histopathological staining showed that Act could improve renal function by reducing serum creatinine, blood urea nitrogen and urine protein at the same time, Act could alleviate renal inflammation and fibrosis. In addition, the results of immunohistochemistry showed that Act could reduce the expression of inflammation and kidney injury-related proteins F4/80, Mcp-1, KIM-1 proteins, as well as the expression of fibrosis-related protein α-SMA and β-catenin. More importantly, Act can also reduce the expression of HMGN1, TLR4 and TREM-1 proteins.

CONCLUSION

These data demonstrate that Act can ameliorate UUO-induced renal inflammation and fibrosis in rats probably through triggering HMGN1/TLR4/TREM-1 pathway.

Type IV Collagen and SOX9 Are Molecular Targets of BET Inhibition in Experimental Glomerulosclerosis

Progressive glomerulonephritis (GN) is characterized by an excessive accumulation of extracellular (ECM) proteins, mainly type IV collagen (COLIV), in the glomerulus leading to glomerulosclerosis. The current therapeutic approach to GN is suboptimal. Epigenetic drugs could be novel therapeutic options for human disease. Among these drugs, bromodomain and extra-terminal domain (BET) inhibitors (iBETs) have shown beneficial effects in experimental kidney disease and fibrotic disorders. Sex-determining region Y-box 9 (SOX9) is a transcription factor involved in regulating proliferation, migration, and regeneration, but its role in kidney fibrosis is still unclear. We investigated whether iBETs could regulate ECM accumulation in experimental GN and evaluated the role of SOX9 in this process. For this purpose, we tested the iBET JQ1 in mice with anti-glomerular basement membrane nephritis induced by nephrotoxic serum (NTS). In NTS-injected mice, JQ1 treatment reduced glomerular ECM deposition, mainly by inhibiting glomerular COLIV accumulation and Col4a3 gene overexpression. Moreover, chromatin immunoprecipitation assays demonstrated that JQ1 inhibited the recruitment and binding of BRD4 to the Col4a3 promoter and reduced its transcription. Active SOX9 was found in the nuclei of glomerular cells of NTS-injured kidneys, mainly in COLIV-stained regions. JQ1 treatment blocked SOX9 nuclear translocation in injured kidneys. Moreover, in vitro JQ1 blocked TGF-β1-induced SOX9 activation and ECM production in cultured mesangial cells. Additionally, SOX9 gene silencing inhibited ECM production, including COLIV production. Our results demonstrated that JQ1 inhibited SOX9/COLIV, to reduce experimental glomerulosclerosis, supporting further research of iBET as a potential therapeutic option in progressive glomerulosclerosis.

Development of Cell Therapies for Renal Disease and Regenerative Medicine

The incidence of renal disease is gradually increasing worldwide, and this condition has become a major public health problem because it is a trigger for many other chronic diseases. Cell therapies using multipotent mesenchymal stromal cells, hematopoietic stem cells, macrophages, and other cell types have been used to induce regeneration and provide a cure for acute and chronic kidney disease in experimental models. This review describes the advances in cell therapy protocols applied to acute and chronic kidney injuries and the attempts to apply these treatments in a clinical setting.

The Protective Effect of Zebularine, an Inhibitor of DNA Methyltransferase, on Renal Tubulointerstitial Inflammation and Fibrosis

Renal fibrosis, the final pathway of chronic kidney disease, is caused by genetic and epigenetic mechanisms. Although DNA methylation has drawn attention as a developing mechanism of renal fibrosis, its contribution to renal fibrosis has not been clarified. To address this issue, the effect of zebularine, a DNA methyltransferase inhibitor, on renal inflammation and fibrosis in the murine unilateral ureteral obstruction (UUO) model was analyzed. Zebularine significantly attenuated renal tubulointerstitial fibrosis and inflammation. Zebularine decreased trichrome, α-smooth muscle actin, collagen IV, and transforming growth factor-β1 staining by 56.2%. 21.3%, 30.3%, and 29.9%, respectively, at 3 days, and by 54.6%, 41.9%, 45.9%, and 61.7%, respectively, at 7 days after UUO. Zebularine downregulated mRNA expression levels of matrix metalloproteinase (MMP)-2, MMP-9, fibronectin, and Snail1 by 48.6%. 71.4%, 31.8%, and 42.4%, respectively, at 7 days after UUO. Zebularine also suppressed the activation of nuclear factor-κB (NF-κB) and the expression of pro-inflammatory cytokines, including tumor necrosis factor-α, interleukin (IL)-1β, and IL-6, by 69.8%, 74.9%, and 69.6%, respectively, in obstructed kidneys. Furthermore, inhibiting DNA methyltransferase buttressed the nuclear expression of nuclear factor (erythroid-derived 2)-like factor 2, which upregulated downstream effectors such as catalase (1.838-fold increase at 7 days, p < 0.01), superoxide dismutase 1 (1.494-fold increase at 7 days, p < 0.05), and NAD(P)H: quinone oxidoreduate-1 (1.376-fold increase at 7 days, p < 0.05) in obstructed kidneys. Collectively, these findings suggest that inhibiting DNA methylation restores the disrupted balance between pro-inflammatory and anti-inflammatory pathways to alleviate renal inflammation and fibrosis. Therefore, these results highlight the possibility of DNA methyltransferases as therapeutic targets for treating renal inflammation and fibrosis.

MK-2206 Alleviates Renal Fibrosis by Suppressing the Akt/mTOR Signaling Pathway In Vivo and In Vitro

Renal fibrosis is a common pathological feature of various kidney diseases, leading to irreversible renal failure and end-stage renal disease. However, there are still no effective treatments to reverse renal fibrosis. This study aimed to explore the potential mechanism of a targeted drug for fibrosis. Here, unilateral ureteral obstruction (UUO)-treated mice and a TGF-β1-treated human renal tubular epithelial cell line (HK-2 cells) were used as models of renal fibrosis. Based on the changes of mRNA in UUO kidneys detected by transcriptome sequencing, MK-2206, an Akt inhibitor, was predicted as a potential drug to alleviate renal fibrosis through bioinformatics. We dissolved UUO mice with MK-2206 by gastric gavage and cultured TGF-β-induced HK-2 cells with MK-2206. Histopathological examinations were performed after MK-2206 intervention, and the degree of renal fibrosis, as well as the expression of Akt/mTOR pathway-related proteins, were evaluated by immunohistochemical staining, immunofluorescence staining, and Western blot. The results showed that MK-2206 significantly improved the pathological structure of the kidney. Furthermore, MK-2206 intervention effectively inhibited UUO- and TGF-β1-induced epithelial-mesenchymal transition, fibroblast activation, and extracellular matrix deposition. Mechanistically, MK-2206 treatment attenuated the activation of the Akt/mTOR signaling pathway. Taken together, our study revealed for the first time that MK-2206 is a promising drug for the improvement of renal fibrosis.

Renoprotective Effects of Luteolin: Therapeutic Potential for COVID-19-Associated Acute Kidney Injuries

Acute kidney injury (AKI) has been increasingly reported in critically-ill COVID-19 patients. Moreover, there was significant positive correlation between COVID-19 deaths and renal disorders in hospitalized COVID-19 patients with underlying comorbidities who required renal replacement therapy. It has suggested that death in COVID-19 patients with AKI is 3-fold higher than in COVID-19 patients without AKI. The pathophysiology of COVID-19-associated AKI could be attributed to unspecific mechanisms, as well as COVID-19-specific mechanisms such as direct cellular injury, an imbalanced renin-angiotensin-aldosterone system, pro-inflammatory cytokines elicited by the viral infection and thrombotic events. To date, there is no specific treatment for COVID-19 and its associated AKI. Luteolin is a natural compound with multiple pharmacological activities, including anticoronavirus, as well as renoprotective activities against kidney injury induced by sepsis, renal ischemia and diverse nephrotoxic agents. Therefore, in this review, we mechanistically discuss the anti-SARS-CoV-2 and renoprotective activities of luteolin, which highlight its therapeutic potential in COVID-19-AKI patients.

Sulforaphane Protects against Unilateral Ureteral Obstruction-Induced Renal Damage in Rats by Alleviating Mitochondrial and Lipid Metabolism Impairment

Unilateral ureteral obstruction (UUO) is an animal rodent model that allows the study of obstructive nephropathy in an accelerated manner. During UUO, tubular damage is induced, and alterations such as oxidative stress, inflammation, lipid metabolism, and mitochondrial impairment favor fibrosis development, leading to chronic kidney disease progression. Sulforaphane (SFN), an isothiocyanate derived from green cruciferous vegetables, might improve mitochondrial functions and lipid metabolism; however, its role in UUO has been poorly explored. Therefore, we aimed to determine the protective effect of SFN related to mitochondria and lipid metabolism in UUO. Our results showed that in UUO SFN decreased renal damage, attributed to increased mitochondrial biogenesis. We showed that SFN augmented peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) and nuclear respiratory factor 1 (NRF1). The increase in biogenesis augmented the mitochondrial mass marker voltage-dependent anion channel (VDAC) and improved mitochondrial structure, as well as complex III (CIII), aconitase 2 (ACO2) and citrate synthase activities in UUO. In addition, lipid metabolism was improved, observed by the downregulation of cluster of differentiation 36 (CD36), sterol regulatory-element binding protein 1 (SREBP1), fatty acid synthase (FASN), and diacylglycerol O-acyltransferase 1 (DGAT1), which reduces triglyceride (TG) accumulation. Finally, restoring the mitochondrial structure reduced excessive fission by decreasing the fission protein dynamin-related protein-1 (DRP1). Autophagy flux was further restored by reducing beclin and sequestosome (p62) and increasing B-cell lymphoma 2 (Bcl2) and the ratio of microtubule-associated proteins 1A/1B light chain 3 II and I (LC3II/LC3I). These results reveal that SFN confers protection against UUO-induced kidney injury by targeting mitochondrial biogenesis, which also improves lipid metabolism.

Gut–Kidney Axis Investigations in Animal Models of Chronic Kidney Disease

Chronic kidney disease (CKD) is an incurable disease in which renal function gradually declines, resulting in no noticeable symptoms during the early stages and a life-threatening disorder in the latest stage. The changes that accompany renal failure are likely to influence the gut microbiota, or the ecosystem of micro-organisms resident in the intestine. Altered gut microbiota can display metabolic changes and become harmful to the host. To study the gut–kidney axis in vivo, animal models should ideally reproduce the disorders affecting both the host and the gut microbiota. Murine models of CKD, but not dog, manifest slowed gut transit, similarly to patient. Animal models of CKD also reproduce altered intestinal barrier function, as well as the resulting leaky gut syndrome and bacterial translocation. CKD animal models replicate metabolic but not compositional changes in the gut microbiota. Researchers investigating the gut–kidney axis should pay attention to the selection of the animal model (disease induction method, species) and the setting of the experimental design (control group, sterilization method, individually ventilated cages) that have been shown to influence gut microbiota.

Isoandrographolide from Andrographis paniculata ameliorates tubulointerstitial fibrosis in ureteral obstruction-induced mice, associated with negatively regulating AKT/GSK-3β/β-cat signaling pathway

Tubulointerstitial fibrosis (TIF) is a prominent pathological manifestation for the progression of almost all chronic kidney diseases (CKDs) to end-stage renal failure. However, there exist few efficient therapies to cure TIF. Our recent results showed that (8R, 12S)-isoandrographolide (ISA), a diterpenoid lactone ingredient of traditional Chinese herbal Andrographis paniculata (Burm.f.) Nees, exhibited anti-pulmonary fibrosis in silica-induced mice. Herein, we investigated the therapeutic effect of ISA on TIF, using mice subjected to unilateral ureteral obstruction (UUO) and human kidney proximal tubular epithelial (HK-2) cells treated with transforming growth factor-β1 (TGF-β1) or tumor necrosis factor-α (TNF-α). The pathological changes and collagen deposition results displayed that ISA administration significantly attenuated inflammatory response, ameliorated TIF, and protected the kidney injury. Interestingly, ISA revealed much lower cytotoxicity on HK-2 cells, but exhibited stronger inhibitory effect on tubular epithelial mesenchymal transformation (EMT) and inflammation, as compared to andrographolide (AD), the major ingredient of A. paniculata extract that has been reported to ameliorate TIF in diabetic nephropathy mice. It was further clarified that the amelioration of TIF by ISA was associated with suppressing the aberrant activation of AKT/GSK-3β/β-catenin pathway through network pharmacology analysis and experimental validation. Taken together, these findings indicate that ISA is a promising lead compound for development of anti-TIF, and even broad-spectrum anti-fibrotic drugs.

Inhibitory Effects of Rhein on Renal Interstitial Fibrosis via the SHH-Gli1 Signal Pathway

Background. Rhein is the main extract of Rheum palmatum L., which has been proved to improve the renal function of chronic kidney disease, but its mechanism is not clear. Therefore, this experiment explored the potential pharmacological effect of rhein on renal interstitial fibrosis rats. Methods. This study explores the potential pharmacological action of rhein. In this work, we investigate the potential pharmacological action of rhein in unilateral urethral obstruction (UUO) rats. Thirty Sprague Dawley rats were randomly divided into three groups: sham, UUO, and rhein (rhein-treated UUO rats) groups. The left ureters of the UUO group rats were exposed and bluntly dissected. The rhein group rats were administered an intragastric gavage of rhein (2 mg·kg−1·d−1) for 14 d. Kidney function-related indicators were monitored in these rats, while indexes of pathologic aspects were determined histologically. The expression of α-SMA, TGF-β1, SHH, Gli1, and Snail was quantified using real-time polymerase chain reaction and western blotting. The NRK-49F cells were incubated with and without SHH (100 ng·ml−1) for 48 hours. The SHH-activated NRK-49F cells were incubated with cyclopamine (CNP, 20 umol L−1) or rhein (1 ng·ml−1). The Gli1 and Snail mRNA and protein level were detected. Results. In the in vivo experiment, the results exhibited that UUO caused renal pathological damages. However, these changes could be significantly reversed by the administration of rhein. Compared with the untreated UUO group, the rhein group showed reduced kidney tubular atrophy and necrosis, interstitial fibrosis, hyperplasia, and abnormal deposition of extracellular matrix. Rhein reduced the RNA and protein expression of SHH, Gli1, and Snail of the UUO rats. In the in vitro experiment, CNP or rhein treatment decreased the expression of Gli1 and Snail on mRNA and protein levels in SHH-induced NRK-49F cells, suggesting that CNP or rhein suppresses SHH-induced NRK-49F activation. Taken together, these results demonstrated that rhein suppresses SHH-Gli1-Snail signal pathway activation, with potential implications for the treatment of renal fibrosis. Conclusions. Treatment with rhein remarkably ameliorated renal interstitial fibrosis in UUO rats by regulating the SHH-Gli1-Snail signal pathway.

Endothelial Activin Receptor-Like Kinase 1 (ALK1) Regulates Myofibroblast Emergence and Peritubular Capillary Stability in the Early Stages of Kidney Fibrosis

Renal tubulo-interstitial fibrosis is characterized by the excessive accumulation of extracellular matrix (ECM) in the tubular interstitium during chronic kidney disease. The main source of ECM proteins are emerging and proliferating myofibroblasts. The sources of myofibroblasts in the renal tubular interstitium have been studied during decades, in which the epithelial contribution of the myofibroblast population through the epithelial-to-mesenchymal (EMT) process was assumed to be the major mechanism. However, it is now accepted that the EMT contribution is very limited and other mechanisms such as the proliferation of local resident fibroblasts or the transdifferentiation of endothelial cells seem to be more relevant. Activin receptor-like kinase 1 (ALK1) is a type I receptor which belongs to the transforming growth factor beta (TGF-β) superfamily, with a key role in tissue fibrosis and production of ECM by myofibroblast. Predominantly expressed in endothelial cells, ALK1 also plays an important role in angiogenesis and vessel maturation, but the relation of these processes with kidney fibrosis is not fully understood. We show that after 3 days of unilateral ureteral obstruction (UUO), ALK1 heterozygous mice (Alk1^+/−) display lower levels of kidney fibrosis associated to a lower number of myofibroblasts. Moreover, Alk1^+/− mice have a lower degree of vascular rarefaction, showing improved peritubular microvasculature after UUO. All these data suggest an important role of ALK1 in regulating vascular rarefaction and emergence of myofibroblasts.

β-Elemene Attenuates Renal Fibrosis in the Unilateral Ureteral Obstruction Model by Inhibition of STAT3 and Smad3 Signaling via Suppressing MyD88 Expression

Renal fibrosis is a chronic pathological process that seriously endangers human health. However, the current therapeutic options for this disease are extremely limited. Previous studies have shown that signaling factors such as JAK2/STAT3, Smad3, and Myd88 play a regulatory role in renal fibrosis, and β-elemene is a plant-derived sesquiterpenoid organic compound that has been shown to have anti-inflammatory, anti-cancer, and immunomodulatory effects. In the present study, the anti-fibrotic effect of β-elemene was demonstrated by in vivo and in vitro experiments. It was shown that β-elemene inhibited the synthesis of extracellular matrix-related proteins in unilateral ureteral obstruction mice, and TGF-β stimulated rat interstitial fibroblast cells, including α-smooth muscle actin, vimentin, and connective tissue growth factor, etc. Further experiments showed that β-elemene reduced the expression levels of the above-mentioned fibrosis-related proteins by blocking the phosphorylation of JAK2/STAT3, Smad3, and the expression or up-regulation of MyD88. Notably, knockdown of MyD88 attenuated the phosphorylation levels of STAT3 and Smad3 in TGF-β stimulated NRK49F cell, which may be a novel molecular mechanism by which β-elemene affects renal interstitial fibrosis. In conclusion, this study elucidated the anti-interstitial fibrosis effect of β-elemene, which provides a new direction for future research and development of drugs related to chronic kidney disease.

Current kidney function parameters overestimate kidney tissue repair in reversible experimental kidney disease

Although underlying mechanisms and the clinical course of kidney disease progression are well described, less is known about potential disease reversibility. Therefore, to analyze kidney recovery, we adapted a commonly used murine chronic kidney disease (CKD) model of 2,8- dihydroxyadenine (2,8-DHA) crystal-induced nephropathy to study disease recovery and efficacy of disease-modifying interventions. The recovery phase after CKD was characterized by improved kidney function after two weeks which remained stable thereafter. By contrast, even after eight weeks recovery, tubular injury and inflammation were only partially reduced and fibrosis persisted. Deep-learning-based histologic analysis of 8,604 glomeruli and 596,614 tubular cross sections revealed numerous tubules had undergone either prominent dilation or complete atrophy, leading to atubular glomeruli and irreversible nephron loss. We confirmed these findings in a second CKD model, reversible unilateral ureteral obstruction, in which a rapid improvement of glomerular filtration rate during recovery also did not reflect the permanent histologic kidney injury. In 2,8-DHA nephropathy, increased drinking volume was highly effective in disease prevention. However, in therapeutic approaches, high fluid intake was only effective in moderate but not severe CKD and established tissue injury was again poorly reflective of kidney function parameters. The injury was particularly localized in the medulla, which is often not analyzed. Thus, recovery after crystal- or obstruction-induced CKD is characterized by ongoing tissue injury, fibrosis, and nephron loss, but not reflected by standard measures of kidney function. Hence, our data might aid in designing kidney recovery studies and suggest the need for biomarkers specifically monitoring intra-kidney tissue injury.

Growth differentiation factor-15 preserves Klotho expression in acute kidney injury and kidney fibrosis

Growth differentiation factor-15 (GDF15) is a member of the GDF subfamily with potential kidney protective functions. Here, we explored the impact of GDF15 on the expression of the kidney protective factor Klotho in models of acute kidney injury and kidney fibrosis in mice. GDF15 was the most upregulated GDF family gene in experimental toxic acute kidney injury and in kidney fibrosis transcriptomics. GDF15 function was explored in toxic acute kidney injury in genetically modified mice and following treatment with GDF15. Gdf15-deficient mice developed more severe toxic acute kidney injury (folic acid or cisplatin) while GDF15 overexpression or GDF15 administration were protective. Kidney expression of Klotho was more severely depressed in Gdf15-deficient mice and was preserved by GDF15 overexpression or GDF15 treatment. Moreover, increased plasma calcitriol levels inversely correlated with kidney Klotho across models with diverse levels of GDF15 availability. Kidney fibrosis induced by unilateral ureteral obstruction was more severe in Gdf15-deficient mice while GDF15 overexpression decreased kidney injury and preserved Klotho expression. GDF15 increased Klotho expression in vivo in healthy mice, in cultured tubular cells, and prevented Klotho downregulation by inflammatory factors in tubular cells by preventing transcription factor NF-ĸB activation. Thus, spontaneous increased kidney expression of endogenous GDF15 is not enough to prevent kidney injury, but further increments in GDF15 are kidney protecting and preserve expression of the kidney protective factor Klotho within the kidney in acute and chronic settings.

Nobiletin Alleviates Ferroptosis-Associated Renal Injury, Inflammation, and Fibrosis in a Unilateral Ureteral Obstruction Mouse Model

Nobiletin (Nob), a critical active flavonoid of citrus fruits, has received attention for its superior physical functions, which have shown to improve the progression of diseases. Chronic kidney disease (CKD) is recognized as a global health problem, and its mortality and morbidity rates are worsened with an increased risk of accompanying disorders. In this study, we aimed to elucidate whether Nob treatment ameliorates kidney fibrosis and also to identify the potential signaling networks in a unilateral ureteral obstructive (UUO) mouse model, which was used to mimic the progression of CKD. Six-week-old C57BL/6J mice were orally treated with 50 mg/kg of Nob for 14 constitutive days after UUO surgery. We found that the administration of Nob diminished kidney fibrosis and the expression of EMT markers, ameliorated oxidative stress and ferroptosis-associated injury, and mitigated the inflammatory response in the kidneys of UUO mice. Our results suggested that Nob treatment has antiferroptosis, anti-inflammatory, and antifibrotic effects, improving the progression of CKD in UUO mice. Nob may serve as a potential therapeutic candidate for the improvement of progressive CKD in further studies.

Extracellular Vesicles in Redox Signaling and Metabolic Regulation in Chronic Kidney Disease

Chronic kidney disease (CKD) is a world health problem increasing dramatically. The onset of CKD is driven by several mechanisms; among them, metabolic reprogramming and changes in redox signaling play critical roles in the advancement of inflammation and the subsequent fibrosis, common pathologies observed in all forms of CKD. Extracellular vesicles (EVs) are cell-derived membrane packages strongly associated with cell-cell communication since they transfer several biomolecules that serve as mediators in redox signaling and metabolic reprogramming in the recipient cells. Recent studies suggest that EVs, especially exosomes, the smallest subtype of EVs, play a fundamental role in spreading renal injury in CKD. Therefore, this review summarizes the current information about EVs and their cargos’ participation in metabolic reprogramming and mitochondrial impairment in CKD and their role in redox signaling changes. Finally, we analyze the effects of these EV-induced changes in the amplification of inflammatory and fibrotic processes in the progression of CKD. Furthermore, the data suggest that the identification of the signaling pathways involved in the release of EVs and their cargo under pathological renal conditions can allow the identification of new possible targets of injury spread, with the goal of preventing CKD progression.

Molecular Mechanisms of Kidney Injury and Repair

Chronic kidney disease (CKD) will become the fifth global cause of death by 2040, thus emphasizing the need to better understand the molecular mechanisms of damage and regeneration in the kidney. CKD predisposes to acute kidney injury (AKI) which, in turn, promotes CKD progression. This implies that CKD or the AKI-to-CKD transition are associated with dysfunctional kidney repair mechanisms. Current therapeutic options slow CKD progression but fail to treat or accelerate recovery from AKI and are unable to promote kidney regeneration. Unraveling the cellular and molecular mechanisms involved in kidney injury and repair, including the failure of this process, may provide novel biomarkers and therapeutic tools. We now review the contribution of different molecular and cellular events to the AKI-to-CKD transition, focusing on the role of macrophages in kidney injury, the different forms of regulated cell death and necroinflammation, cellular senescence and the senescence-associated secretory phenotype (SAPS), polyploidization, and podocyte injury and activation of parietal epithelial cells. Next, we discuss key contributors to repair of kidney injury and opportunities for their therapeutic manipulation, with a focus on resident renal progenitor cells, stem cells and their reparative secretome, certain macrophage subphenotypes within the M2 phenotype and senescent cell clearance.

Tubule-derived INHBB promotes interstitial fibroblast activation and renal fibrosis

Upstream stimuli for myofibroblast activation are of considerable interest for understanding the mechanisms underlying renal fibrosis. Activin B, a member of the TGF-β family, exists as a homodimer of inhibin subunit beta B (INHBB), but its role in renal fibrosis remains unknown. We found that INHBB expression was significantly increased in various renal fibrosis models and human chronic kidney disease specimens with renal fibrosis. Notably, the increase of INHBB occurred mainly in the tubular epithelial cells (TECs). In vivo, inhibiting INHBB blocked the activation of interstitial fibroblasts and ameliorated the renal fibrosis induced by unilateral ureteral obstruction or ischemia-reperfusion injury, while ectopic expression of INHBB in the TECs was able to activate interstitial fibroblasts and initiate interstitial fibrosis. In vitro, overexpression of INHBB in TECs led to the secretion of activin B, thereby promoting the proliferation and activation of interstitial fibroblasts through activin B/Smad signaling. Furthermore, inhibition of activin B/Smad signaling attenuated the fibrotic response caused by tubular INHBB. Mechanistically, the upregulation of INHBB depended on the transcription factor Sox9 in the injured TECs. Clinical analyses also identified a positive correlation between Sox9 and INHBB expression in human specimens, suggesting the Sox9/INHBB axis as a positive regulator of renal fibrosis. In conclusion, tubule-derived INHBB is implicated in the pathogenesis of renal fibrosis by activating the surrounding fibroblasts in a paracrine manner, thereby exhibiting as a potential therapeutic target. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Pediatric urology research in 2020: A bibliometric analysis of the top 100 most cited articles

BACKGROUND

Pediatric Urology deals with genitourinary diseases. Present study aimed to collect the top-cited article in Pediatric Urology in order to define the most debated and studied topics.

METHODS

The journals reported in "Urology & Nephrology" category of the 2019 edition of Journal Citation Reports, together with the most relevant journals of "Transplantation," "Pediatrics," and "Surgery" categories, were browsed. The articles of interest in Pediatric Urology with more than 50 citations were collected. A bibliometric analysis was performed to collect the top 100 cited articles.

RESULTS

The top-cited articles were published in 27 journals (23%), with a median impact factor of 2.676 (IQR 1.981-5.642). Seventeen of them (63%) belonged to "Urology and Nephrology" category. The median number of citations was 82 (IQR 64-113). The most productive journal, with 23 articles, was "The Journal of Urology." Forty-eight top-cited articles were Guidelines or Reviews of the literature and only four papers were randomized controlled trials. The most relevant topic was "congenital anomalies" with 18 articles. As to minimally invasive surgery, eight studies were identified. All of them dealt with robotic-assisted laparoscopic surgery. Two articles reported the current evidence about transitional care.

CONCLUSIONS

The top-cited articles were dispersed among journals of different areas. Current scientific literature deal with congenital anomalies, more specifically with obstructive uropathies and hypospadias. In the last decade, one of the most relevant innovation in pediatric urology was the introduction of robotic surgery. Transitional care has become a timely topic.

Kidney-Draining Lymph Node Fibrosis Following Unilateral Ureteral Obstruction

Although the primary organ has been the subject of intense investigation in the field of organ fibrosis over the past several decades, the presence of lymph node fibrosis due to persistent activation of the immune response in its partner organ remains largely unknown. Previously, we demonstrated that activation of the immune response following ischemia-reperfusion injury (IRI) and crescentic glomerulonephritis (CGN) in the kidney was associated with extracellular matrix (ECM) production by fibroblastic reticular cells (FRCs) of the kidney-draining lymph node (KLN). Here, we sought to determine whether FRCs in the KLN become similarly fibrogenic following unilateral ureteral obstruction (UUO) of the kidney. We subjected 6-8-week-old C57BL/6J mice to UUO for 2, 7, and 14 days. We examined the microarchitecture of the kidney and KLN by immunofluorescence staining at each timepoint, and we quantified immune cell populations in the KLN by flow cytometry. The contralateral kidney unaffected by UUO and its partner KLN were used as controls. We found through immunofluorescence staining that FRCs increased production of ECM fibers and remodeled the microarchitecture of the UUO KLN, contributing to fibrosis that mirrored the changes in the kidney. We also observed by flow cytometry that the populations of CD11b+ antigen-presenting cells, CD11c+ dendritic cells, and activated CD4+ and CD8+ T cells were significantly higher in the UUO KLN than the KLN draining the unaffected contralateral kidney. Expression of the TGFβ/TGFβR signaling pathway was upregulated and colocalized with FRCs in the UUO KLNs, suggesting a possible mechanism behind the fibrosis. Both release of ureteral ligation at 2 days following UUO and depletion of FRCs at the time of injury onset halted the progression of fibrosis in both the kidney and the KLN. These findings for the first time highlight the association between fibrosis both in the kidney and the KLN during UUO, and they lay the groundwork for future studies that will investigate more deeply the mechanisms behind the connection between FRCs and KLN fibrosis.

Development of a unilateral ureteral obstruction model in cynomolgus monkeys

Background

Chronic kidney disease (CKD) has a high global prevalence and large unmet need. Central to developing new CKD therapies are in vivo models in CKD. However, next-generation antibody, protein, and gene therapies are highly specific, meaning some do not cross-react with rodent targets. This complicates preclinical development, as established in vivo rodent models cannot be utilized unless tool therapeutics are also developed. Tool compounds can be difficult to develop and, if available, typically have different epitopes, sequences, and/or altered affinity, making it unclear how efficacious the lead therapeutic may be, or what dosing regimen to investigate. To address this, we aimed to develop a nonhuman primate model of CKD.

Methods

In vivo rodent unilateral ureteral obstruction (UUO) models kidney fibrosis and is commonly used due to its rapidity, consistency, and ease. We describe translation of this model to the cynomolgus monkey, specifically optimizing the model duration to allow adequate time for assessment of novel therapeutics prior to the fibrotic plateau.

Results

We demonstrated that disease developed more slowly in cynomolgus monkeys than in rodents post-UUO, with advanced fibrosis developing by 6 weeks. The tubulointerstitial fibrosis in cynomolgus monkeys was more consistent with human obstructive disease than in rodents, having a more aggressive tubular basement expansion and a higher fibroblast infiltration. The fibrosis was also associated with increased transglutaminase activity, consistent with that seen in patients with CKD.

Conclusion

This cynomolgus monkey UUO model can be used to test potential human-specific therapeutics in kidney fibrosis.

Protective Effects of Nootkatone on Renal Inflammation, Apoptosis, and Fibrosis in a Unilateral Ureteral Obstructive Mouse Model

Nootkatone is one of the major active ingredients of Alpiniae oxyphyllae, which has been used as both food and medicinal plants for the treatment of diarrhea, ulceration, and enuresis. In this study, we aimed to investigate whether nootkatone treatment ameliorated the progression of chronic kidney diseases (CKD) and clarified its underlying mechanisms in an obstructive nephropathy (unilateral ureteral obstructive; UUO) mouse model. Our results revealed that nootkatone treatment preventively decreased the pathological changes and significantly mitigated the collagen deposition as well as the protein expression of fibrotic markers. Nootkatone could also alleviate oxidative stress-induced injury, inflammatory cell infiltration, and renal cell apoptotic death in the kidneys of UUO mice. These results demonstrated for the first time that nootkatone protected against the progression of CKD in a UUO mouse model. It may serve as a potential therapeutic candidate for CKD intervention.

RCAN1.4 attenuates renal fibrosis through inhibiting calcineurin-mediated nuclear translocation of NFAT2

Chronic kidney disease (CKD) is thus deemed to a global health problem. Renal fibrosis, characterized by accumulation of extracellular matrix (ECM) components in the kidney, is considered a common pathway leading to CKD. Regulator of calcineurin1 (RCAN1), identified as a competitive endogenous inhibitor of the phosphatase calcineurin, participates in ECM deposition in various organs. However, the role of RCAN1 in renal fibrosis remains unclear. Here, unilateral ureteral obstruction (UUO), a well-known model to induce renal fibrosis in vivo, was performed on mice for a week. To overexpress RCAN1.4 in vivo, recombinant adeno-associated virus 9-packed RCAN1.4 over-expression plasm was employed in mice kidney. Lentivirus-packed RCAN1.4 over-expression plasm was employed to transfer into HK-2 and NRK-49F cells in vitro. The results indicated that RCAN1.4 expression was impaired both in UUO-induced renal fibrosis in vivo and TGF-β1-induced renal fibrosis in vitro. However, knocking in of RCAN1.4 suppressed the production of extracellular matrix (ECM) both in vivo and in vitro. Furthermore, in vitro, the apoptosis-related proteins, including the ratio of Bax/Bcl-2 and cleaved-caspase3, were elevated in cells transfected with RCAN1.4 overexpression plasmid. In addition, we found that RCAN1.4 could rugulated NFAT2 nuclear distribution by inhibiting calcineurin pathway. So overexpression of RCAN1.4 could reverse renal fibrosis, attenuate ECM related protein accumulation, promote apoptosis of myofibroblast via inhibiting Calcineurin/NFAT2 signaling pathway. Taken together, our study demonstrated that targeting RCAN1.4 may be therapeutic efficacy in renal fibrosis.

Apamin inhibits renal fibrosis via suppressing TGF-β1 and STAT3 signaling in vivo and in vitro

Renal fibrosis is a progressive and chronic process that influences kidneys with chronic kidney disease (CKD), irrespective of cause, leading to irreversible failure of renal function and end-stage kidney disease. Among the signaling related to renal fibrosis, transforming growth factor-β1 (TGF-β1) signaling is a major pathway that induces the activation of myofibroblasts and the production of extracellular matrix (ECM) molecules. Apamin, a component of bee venom (BV), has been studied in relation to various diseases. However, the effect of apamin on renal interstitial fibrosis has not been investigated. The aim of this study was to estimate the beneficial effect of apamin in unilateral ureteral obstruction (UUO)-induced renal fibrosis and TGF-β1-induced renal fibroblast activation. This study revealed that obstructive kidney injury induced an inflammatory response, tubular atrophy, and ECM accumulation. However, apamin treatment suppressed the increased expression of fibrotic-related genes, including α-SMA, vimentin, and fibronectin. Administration of apamin also attenuated the renal tubular cells injury and tubular atrophy. In addition, apamin attenuated fibroblast activation, ECM synthesis, and inflammatory cytokines such as TNF-α, IL-1β, and IL-6 by suppressing the TGF-β1-canonical and non-canonical signaling pathways. This study showed that apamin inhibits UUO-induced renal fibrosis in vivo and TGF-β1-induced renal fibroblasts activation in vitro. Apamin inhibited the inflammatory response, tubular atrophy, ECM accumulation, fibroblast activation, and renal interstitial fibrosis through suppression of TGF-β1/Smad2/3 and STAT3 signaling pathways. These results suggest that apamin might be a potential therapeutic agent for renal fibrosis. KEY MESSAGES: UUO injury can induce renal dysfunction; however, apamin administration prevents renal failure in UUO mice. Apamin inhibited renal inflammatory response and ECM deposition in UUO-injured mice. Apamin suppressed the activation of myofibroblasts in vivo and in vitro. Apamin has the anti-fibrotic effect on renal fibrosis via regulation of TGF-β1 canonical and non-canonical signaling.

Temporal characterization of mitochondrial impairment in the unilateral ureteral obstruction model in rats

Renal fibrosis is a well-known mechanism that favors chronic kidney disease (CKD) development in obstructive nephropathy, a significant pathology worldwide. Fibrosis induction involves several pathways, and although mitochondrial alterations have recently emerged as a critical factor that triggers renal damage in the obstructed kidney, the temporal mitochondrial alterations during the fibrotic induction remain unexplored. Therefore, in this work, we evaluated the time course of mitochondrial mass and bioenergetics alterations induced by a unilateral ureteral obstruction (UUO), a widely used model to study the mechanism involved in kidney fibrosis induction and progression. Our results show a marked reduction in mitochondrial oxidative phosphorylation (OXPHOS) in the obstructed kidney on days 7 to 28 of obstruction without significant mitochondrial coupling changes. Besides, we observed that mitochondrial mass was reduced, probably due to decreased biogenesis and mitophagy induction. OXPHOS impairment was associated with decreased mitochondrial biogenesis markers, the peroxisome proliferator-activated receptor γ co-activator-1alpha (PGC-1α), and nuclear respiratory factor 1 (NRF1); and also, with the induction of mitophagy in a PTEN-induced kinase 1 (PINK1) and Parkin independent way. It is concluded that the impairment of OXPHOS capacity may be explained by the reduction in mitochondrial biogenesis and the induction of mitophagy during fibrotic progression.

Redox signaling pathways in unilateral ureteral obstruction (UUO)-induced renal fibrosis

Unilateral ureteral obstruction (UUO) is an experimental rodent model that mimics renal fibrosis associated with obstructive nephropathy in an accelerated manner. After UUO, the activation of the renin-angiotensin system (RAS), nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) and mitochondrial dysfunction lead to reactive oxygen species (ROS) overproduction in the kidney. ROS are secondary messengers able to induce post-translational modifications (PTMs) in redox-sensitive proteins, which activate or deactivate signaling pathways. Therefore, in UUO, it has been proposed that ROS overproduction causes changes in said pathways promoting inflammation, oxidative stress, and apoptosis that contribute to fibrosis development. Furthermore, mitochondrial metabolism impairment has been associated with UUO, contributing to renal damage in this model. Although ROS production and oxidative stress have been studied in UUO, the development of renal fibrosis associated with redox signaling pathways has not been addressed. This review focuses on the current information about the activation and deactivation of signaling pathways sensitive to a redox state and their effect on mitochondrial metabolism in the fibrosis development in the UUO model.

The Genomic Response to TGF-β1 Dictates Failed Repair and Progression of Fibrotic Disease in the Obstructed Kidney

Tubulointerstitial fibrosis is a common and diagnostic hallmark of a spectrum of chronic renal disorders. While the etiology varies as to the causative nature of the underlying pathology, persistent TGF-β1 signaling drives the relentless progression of renal fibrotic disease. TGF-β1 orchestrates the multifaceted program of kidney fibrogenesis involving proximal tubular dysfunction, failed epithelial recovery or re-differentiation, capillary collapse and subsequent interstitial fibrosis eventually leading to chronic and ultimately end-stage disease. An increasing complement of non-canonical elements function as co-factors in TGF-β1 signaling. p53 is a particularly prominent transcriptional co-regulator of several TGF-β1 fibrotic-response genes by complexing with TGF-β1 receptor-activated SMADs. This cooperative p53/TGF-β1 genomic cluster includes genes involved in cellular proliferative control, survival, apoptosis, senescence, and ECM remodeling. While the molecular basis for this co-dependency remains to be determined, a subset of TGF-β1-regulated genes possess both p53- and SMAD-binding motifs. Increases in p53 expression and phosphorylation, moreover, are evident in various forms of renal injury as well as kidney allograft rejection. Targeted reduction of p53 levels by pharmacologic and genetic approaches attenuates expression of the involved genes and mitigates the fibrotic response confirming a key role for p53 in renal disorders. This review focuses on mechanisms underlying TGF-β1-induced renal fibrosis largely in the context of ureteral obstruction, which mimics the pathophysiology of pediatric unilateral ureteropelvic junction obstruction, and the role of p53 as a transcriptional regulator within the TGF-β1 repertoire of fibrosis-promoting genes.

Deletion of delta-like 1 homologue accelerates renal inflammation by modulating the Th17 immune response

Preclinical studies have demonstrated that activation of the NOTCH pathway plays a key role in the pathogenesis of kidney damage. There is currently no information on the role of the Delta-like homologue 1 (DLK1), a NOTCH inhibitor, in the regulation of renal damage. Here, we investigated the contribution of DLK1 to experimental renal damage and the underlying molecular mechanisms. Using a Dlk1-null mouse model in the experimental renal damage of unilateral ureteral obstruction, we found activation of NOTCH, as shown by increased nuclear translocation of the NOTCH1 intracellular domain, and upregulation of Dlk2/hey-1 expression compared to wild-type (WT) littermates. NOTCH1 over-activation in Dlk1-null injured kidneys was associated with a higher inflammatory response, characterized by infiltration of inflammatory cells, mainly CD4/IL17A + lymphocytes, and activation of the Th17 immune response. Furthermore, pharmacological NOTCH blockade inhibited the transcription factors controlling Th17 differentiation and gene expression of the Th17 effector cytokine IL-17A and other related-inflammatory factors, linked to a diminution of inflammation in the injured kidneys. We propose that the non-canonical NOTCH ligand DLK1 acts as a NOTCH antagonist in renal injury regulating the Th17-mediated inflammatory response.

Non-Coding RNAs in Kidney Diseases: The Long and Short of Them

Recent progress in genomic research has highlighted the genome to be much more transcribed than expected. The formerly so-called junk DNA encodes a miscellaneous group of largely unknown RNA transcripts, which contain the long non-coding RNAs (lncRNAs) family. lncRNAs are instrumental in gene regulation. Moreover, understanding their biological roles in the physiopathology of many diseases, including renal, is a new challenge. lncRNAs regulate the effects of microRNAs (miRNA) on mRNA expression. Understanding the complex crosstalk between lncRNA–miRNA–mRNA is one of the main challenges of modern molecular biology. This review aims to summarize the role of lncRNA on kidney diseases, the molecular mechanisms involved, and their function as emerging prognostic biomarkers for both acute and chronic kidney diseases. Finally, we will also outline new therapeutic opportunities to diminish renal injury by targeting lncRNA with antisense oligonucleotides.

Induction of PDCD4 by albumin in proximal tubule epithelial cells potentiates proteinuria-induced dysfunctional autophagy by negatively targeting Atg5

The precise molecular mechanism of autophagy dysfunction in type 1 diabetes is not known. Herein, the role of programmed cell death 4 (PDCD4) in autophagy regulation in the pathogenesis of diabetic kidney disease (DKD) in vivo and in vitro was described. It was found that Pdcd4 mRNA and protein was upregulated in the streptozotocin (STZ)-induced DKD rats. In addition, a unilateral ureteral obstruction mouse model displayed an upregulation of PDCD4 in the disease group. kidney biopsy samples of human DKD patients showed an upregulation of PDCD4. Furthermore, western blotting of the STZ-induced DKD rat tissues displayed a low microtubule-associated protein 1A/1B-light chain 3 (LC3)-II, as compared to the control. It was found that albumin overload in cultured PTEC could upregulate the expression of PDCD4 and p62, and decrease the expression of LC3-II and autophagy-related 5 (Atg5) proteins. The knockout of Pdcd4 in cultured PTECs could lessen albumin-induced dysfunctional autophagy as evidenced by the recovery of Atg5 and LC3-II protein. The forced expression of PDCD4 could further suppress the expression of crucial autophagy-related gene Atg5. Herein, endogenous PDCD4 was shown to promote proteinuria-induced dysfunctional autophagy by negatively regulating Atg5. PDCD4 might therefore be a potential therapeutic target in DKD.

IDH2 gene deficiency accelerates unilateral ureteral obstruction-induced kidney inflammation through oxidative stress and activation of macrophages

Mitochondrial NADP⁺-dependent isocitrate dehydrogenase 2 (IDH2) produces NADPH, which is known to inhibit mitochondrial oxidative stress. Ureteral obstruction induces kidney inflammation and fibrosis via oxidative stress. Here, we investigated the role and underlying mechanism of IDH2 in unilateral ureteral obstruction (UUO)-induced kidney inflammation using IDH2 gene deleted mice (IDH2^-/-). Eight- to 10-week-old female IDH2^-/- mice and wild type (IDH2^+/+) littermates were subjected to UUO and kidneys were harvested 5 days after UUO. IDH2 was not detected in the kidneys of IDH2^-/- mice, while UUO decreased IDH2 in IDH2^+/+ mice. UUO increased the expressions of markers of oxidative stress in both IDH2^+/+ and IDH2^-/- mice, and these changes were greater in IDH2^-/- mice compared to IDH2^+/+ mice. Bone marrow-derived macrophages of IDH2^-/- mice showed a more migrating phenotype with greater ruffle formation and Rac1 distribution than that of IDH2^+/+ mice. Correspondently, UUO-induced infiltration of monocytes/macrophages was greater in IDH2^-/- mice compared to IDH2^+/+ mice. Taken together, these data demonstrate that IDH2 plays a protective role against UUO-induced inflammation through inhibition of oxidative stress and macrophage infiltration.

The complex interplay between kidney injury and inflammation

Acute kidney injury (AKI) has gained significant attention following patient safety alerts about the increased risk of harm to patients, including increased mortality and hospitalization. Common causes of AKI include hypovolaemia, nephrotoxic medications, ischaemia and acute glomerulonephritis, although in reality it may be undetermined or multifactorial. A period of inflammation either as a contributor to the kidney injury or resulting from the injury is almost universally seen. This article was compiled following a workshop exploring the interplay between injury and inflammation. AKI is characterized by some degree of renal cell death through either apoptosis or necrosis, together with a strong inflammatory response. Studies interrogating the resolution of renal inflammation identify a whole range of molecules that are upregulated and confirm that the kidneys are able to intrinsically regenerate after an episode of AKI, provided the threshold of damage is not too high. Kidneys are unable to generate new nephrons, and dysfunctional or repeated episodes will lead to further nephron loss that is ultimately associated with the development of renal fibrosis and chronic kidney disease (CKD). The AKI to CKD transition is a complex process mainly facilitated by maladaptive repair mechanisms. Early biomarkers mapping out this process would allow a personalized approach to identifying patients with AKI who are at high risk of developing fibrosis and subsequent CKD. This review article highlights this process and explains how laboratory models of renal inflammation and injury assist with understanding the underlying disease process and allow interrogation of medications aimed at targeting the mechanistic interplay.