Epithelial-mesenchymal transition (EMT) in kidney fibrosis: fact or fantasy?

Role of mitochondria in pathogenesis and therapy of renal fibrosis

Renal fibrosis, specifically tubulointerstitial fibrosis, represents the predominant pathological consequence observed in the context of progressive chronic kidney conditions. The pathogenesis of renal fibrosis encompasses a multifaceted interplay of mechanisms, including but not limited to interstitial fibroblast proliferation, activation, augmented production of extracellular matrix (ECM) components, and impaired ECM degradation. Notably, mitochondria, the intracellular organelles responsible for orchestrating biological oxidation processes in mammalian cells, assume a pivotal role within this intricate milieu. Mitochondrial dysfunction, when manifest, can incite a cascade of events, including inflammatory responses, perturbed mitochondrial autophagy, and associated processes, ultimately culminating in the genesis of renal fibrosis. This comprehensive review endeavors to furnish an exegesis of mitochondrial pathophysiology and biogenesis, elucidating the precise mechanisms through which mitochondrial aberrations contribute to the onset and progression of renal fibrosis. We explored how mitochondrial dysfunction, mitochondrial cytopathy and mitochondrial autophagy mediate ECM deposition and renal fibrosis from a multicellular perspective of mesangial cells, endothelial cells, podocytes, macrophages and fibroblasts. Furthermore, it succinctly encapsulates the most recent advancements in the realm of mitochondrial-targeted therapeutic strategies aimed at mitigating renal fibrosis.

Bile Acid Receptor Agonist Reverses Transforming Growth Factor-β1-Mediated Fibrogenesis in Human Induced Pluripotent Stem Cells-Derived Kidney Organoids

Chronic kidney disease progresses through the replacement of functional tissue compartments with fibrosis, a maladaptive repair process. Shifting kidney repair toward a physiologically intact architecture, rather than fibrosis, is key to blocking chronic kidney disease progression. Much research into the mechanisms of fibrosis is performed in rodent models with less attention to the human genetic context. Recently, human induced pluripotent stem cell (iPSC)-derived organoids have shown promise in overcoming the limitation. In this study, we developed a fibrosis model that uses human iPSC-based 3-dimensional renal organoids, in which exogenous transforming growth factor-β1 (TGF-β1) induced the production of extracellular matrix. TGF-β1-treated organoids showed tubulocentric collagen 1α1 production by regulating downstream transcriptional regulators, Farnesoid X receptor, phosphorylated mothers against decapentaplegic homolog 3 (p-SMAD3), and transcriptional coactivator with PDZ-binding motif (TAZ). Increased nuclear TAZ expression was confirmed in the tubular epithelium in human kidney biopsies with tubular injury and early fibrosis. A dual bile acid receptor agonist (INT-767) increased Farnesoid X receptor and reduced p-SMAD3 and TAZ, attenuating TGF-β1-induced fibrosis in kidney organoids. Finally, we show that TAZ interacted with TEA-domain transcription factors and p-SMAD3 with TAZ and TEA-domain transcription factor 4 coregulating collagen 1α1 gene transcription. In summary, we establish a novel, readily manipulable fibrogenesis model and posit a role for bile acid receptor agonism early in renal parenchymal fibrosis.

Continuous genetic monitoring of transient mesenchymal gene activities in distal tubule and collecting duct epithelial cells during renal fibrosis

Epithelial cells (ECs) have been proposed to contribute to myofibroblasts or fibroblasts through epithelial-mesenchymal transition (EMT) during renal fibrosis. However, since EMT may occur dynamically, transiently, and reversibly during kidney fibrosis, conventional lineage tracing based on Cre-loxP recombination in renal ECs could hardly capture the transient EMT activity, yielding inconsistent results. Moreover, previous EMT research has primarily focused on renal proximal tubule ECs, with few reports of distal tubules and collecting ducts. Here, we generated dual recombinases-mediated genetic lineage tracing systems for continuous monitoring of transient mesenchymal gene expression in E-cadherin+ and EpCAM+ ECs of distal tubules and collecting ducts during renal fibrosis. Activation of key EMT-inducing transcription factor (EMT-TF) Zeb1 and mesenchymal markers αSMA, vimentin, and N-cadherin, were investigated following unilateral ureteral obstruction (UUO). Our data revealed that E-cadherin+ and EpCAM+ ECs did not transdifferentiate into myofibroblasts, nor transiently expressed these mesenchymal genes during renal fibrosis. In contrast, in vitro a large amount of cultured renal ECs upregulated mesenchymal genes in response to TGF-β, a major inducer of EMT.

From inflammation to renal fibrosis: A one-way road in autoimmunity?

Renal fibrosis is now recognized as a main determinant of renal pathology to include chronic kidney disease. Deposition of pathological matrix in the walls of glomerular capillaries, the interstitial space, and around arterioles predicts and contributes to the functional demise of the nephron and its surrounding vasculature. The recent identification of the major cell populations of fibroblast precursors in the kidney interstitium such as pericytes and tissue-resident mesenchymal stem cells, or bone-marrow-derived macrophages, and in the glomerulus such as podocytes, parietal epithelial and mesangial cells, has enabled the study of the fibrogenic process thought the lens of involved immunological pathways. Besides, a growing body of evidence is supporting the role of the lymphatic system in modulating the immunological response potentially leading to inflammation and ultimately renal damage. These notions have moved our understanding of renal fibrosis to be recognized as a clinical entity and new main player in autoimmunity, impacting directly the management of patients.

SPHK1/S1P/S1PR pathway promotes the progression of peritoneal fibrosis by mesothelial-mesenchymal transition

Long-term exposure to non-physiologically compatible dialysate inevitably leads to peritoneal fibrosis (PF) in patients undergoing peritoneal dialysis (PD), and there is no effective prevention or treatment for PF. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid produced after catalysis by sphingosine kinase (SPHK) 1/2 and activates signals through the S1P receptor (S1PR) via autocrine or paracrine. However, the role of SPHK1/S1P/S1PR signaling has never been elucidated in PF. In our research, we investigated S1P levels in peritoneal effluents and demonstrated the role of SPHK1/S1P/S1PR pathway in peritoneal fibrosis. It was found that S1P levels in peritoneal effluents were positively correlated with D/P Cr (r = 0.724, p < .001) and negatively correlated with 4 h ultrafiltration volume (r = -0.457, p < .001). S1PR1 and S1PR3 on peritoneal cells were increased after high glucose exposure in vivo and in vitro. Fingolimod was applied to suppress S1P/S1PR pathway. Fingolimod restored mouse peritoneal function by reducing interstitial hyperplasia, maintaining ultrafiltration volume, reducing peritoneal transport solute rate, and mitigating the protein expression changes of fibronectin, vimentin, α-SMA, and E-cadherin induced by PD and S1P. Fingolimod preserved the morphology of the human peritoneal mesothelial cells, MeT-5A, and moderated the mesothelial-mesenchymal transition (MMT) process. We further delineated that SPHK1 was elevated in peritoneal cells after high glucose exposure and suppression of SPHK1 in MeT-5A cells reduced S1P release. Overexpression of SPHK1 in MeT-5A cells increased S1P levels in the supernatant and fostered the MMT process. PF-543 treatment, targeting SPHK1, alleviated deterioration of mouse peritoneal function. In conclusion, S1P levels in peritoneal effluent were correlated with the deterioration of peritoneal function. SPHK1/S1P/S1PR pathway played an important role in PF.

Silencing of METTL3 prevents the proliferation, migration, epithelial-mesenchymal transition, and renal fibrosis of high glucose-induced HK2 cells by mediating WISP1 in m6A-dependent manner

Diabetic nephropathy (DN) is one of the most serious complications in diabetic patients. And m6A modifications mediated by METTL3 are involved multiple biological processes. However, the specific function and mechanism of METTL3 in DN remains unclear. DN model mice were first established with streptozotocin, and WISP1 expression was confirmed by qRT-PCR. Then the influences of WISP1 or/and METTL3 on the proliferation, migration, and epithelial-mesenchymal transition (EMT) and fibrosis-related proteins of high glucose (HG)-induced HK2 cells or HK2 cells were tested through CCK-8, wound healing, and western blot. We first revealed that WISP1 was highly expressed in renal tissues of DN model mice and HG-induced HK2 cells. Functionally, WISP1 or METTL3 silencing could weaken the proliferation, migration, EMT, and fibrosis of HG-treated HK2 cells, and WISP1 or METTL3 overexpression could induce the proliferation, migration, EMT, and fibrosis of HK2 cells. Additionally, METTL3 silencing could decrease WISP1 m6A modification, and silencing of METTL3 also could notably suppress the biological functions of HG-induced HK2 cells by downregulating WISP1. Silencing of METTL3 prevents DN development process by decreasing WISP1 with m6A modification pattern. Therefore, we suggest that METTL3/WISP1 axis might be a novel therapeutic target for DN.

Sodium glucose cotransporter 2 inhibitor suppresses renal injury in rats with renal congestion

Renal congestion is an issue of cardiorenal syndrome in patients with heart failure. Recent clinical and basic studies suggest a renoprotective potential of sodium-glucose cotransporter (SGLT) 2 inhibitors. However, the effect on renal congestion and its mechanism is not fully understood. Thus, we aimed to clarify the effect of SGLT inhibition in a renal congestion model. Renal congestion was induced in the left kidney of male Sprague-Dawley rats by ligation of the inferior vena cava between the renal veins. The SGLT2 inhibitor tofogliflozin or vehicle was orally administered daily from the day before IVC ligation until two days after surgery. On the third postoperative day, both the right control kidney and the left congested kidney were harvested and analyzed. Kidney weight and water content was increased, and renal injury and fibrosis were observed in the left congested kidney. Kidney weight gain and hydration were improved with tofogliflozin treatment. Additionally, this treatment effectively reduced renal injury and fibrosis, particularly in the renal cortex. SGLT2 expression was observed in the congested kidney, but suppressed in the damaged tubular cells. Molecules associated with inflammation were increased in the congested kidney and reversed by tofogliflozin treatment. Mitochondrial dysfunction provoked by renal congestion was also improved by tofogliflozin treatment. Tofogliflozin protects against renal damage induced by renal congestion. SGLT2 inhibitors could be a candidate strategy for renal impairment associated with heart failure.

Renal Fibrosis Is Alleviated through Targeted Inhibition of IL-11-Induced Renal Tubular Epithelial-to-Mesenchymal Transition

Renal fibrosis is a pathologic process that leads to irreversible renal failure without effective treatment. Epithelial-to-mesenchymal transition (EMT) plays a key role in this process. The current study found that aberrant expression of IL-11 is critically involved in tubular EMT. IL-11 and its receptor subunit alpha-1 (IL-11Rα1) were significantly induced in renal tubular epithelial cells (RTECs) in unilateral ureteral obstruction (UUO) kidneys, co-localized with transforming growth factor-β1. IL-11 knockdown ameliorated UUO-induced renal fibrosis in vivo and transforming growth factor-β1-induced EMT in vitro. IL-11 intervention directly induced the transdifferentiation of RTECs to the mesenchymal phenotype and increased the synthesis of profibrotic mediators. The EMT response induced by IL-11 was dependent on the sequential activation of STAT3 and extracellular signal-regulated kinase 1/2 signaling pathways and the up-regulation of metadherin in RTECs. Micheliolide (MCL) competitively inhibited the binding of IL-11 with IL-11Rα1, suppressing the activation of STAT3 and extracellular signal-regulated kinase 1/2-metadherin pathways, ultimately inhibiting renal tubular EMT and interstitial fibrosis induced by IL-11. In addition, treatment with dimethylaminomicheliolide, a pro-drug of MCL for in vivo use, significantly ameliorated renal fibrosis exacerbated by IL-11 in the UUO model. These findings suggest that IL-11 is a promising target in renal fibrosis and that MCL/dimethylaminomicheliolide exerts its antifibrotic effect by suppressing IL-11/IL-11Rα1 interaction and blocking its downstream effects.

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.

Nicotine promotes renal interstitial fibrosis via upregulation of XIAP in an alpha7-nAChR-dependent manner

Renal fibrosis, characterized by excessive accumulation of the extracellular matrix in the renal tubulointerstitium, can lead to chronic kidney disease (CKD), resulting in a heavy burden on families and society. Clinical studies have shown that smoking is closely associated with CKD deterioration in patients with diabetes, hypertension, polycystic kidney disease, and kidney transplantation. However, the mechanism of action of nicotine in renal fibrosis pathogenesis remains largely unknown. X-linked inhibitor of apoptosis (XIAP), a member of the inhibitor of apoptosis protein (IAP) family, is involved in apoptosis, necroptosis, autophagy, and immune response. Here, the upregulated expression of XIAP and α7 nicotine acetylcholine receptor (α7-nAChR) was determined in the kidneys of the CKD smoking group in human and animal studies. A significant positive correlation between XIAP and cotinine was observed. In addition, the nuclear translocation and transcriptional activity of SP1 were promoted when nicotine bound to α7-nAChR, resulting in XIAP overexpression and renal interstitial fibrosis progression. This phenotype can be reversed by the nicotine receptor subtype α7-nAChR antagonists methyllycaconitine. Our results revealed the complex underlying mechanism of nicotine in promoting renal fibrosis by altering SP1 nucleocytoplasmic translocation and regulating XIAP expression. These results provide novel insights into the pathogenesis and treatment of CKD.

Hypoxia and renal fibrosis

Renal fibrosis is the final stage of most progressive kidney diseases. Chronic kidney disease (CKD) is associated with high comorbidity and mortality. Thus, preventing fibrosis and thereby preserving kidney function increases the quality of life and prolongs the survival of patients with CKD. Many processes such as inflammation or metabolic stress modulate the progression of kidney fibrosis. Hypoxia has also been implicated in the pathogenesis of renal fibrosis, and oxygen sensing in the kidney is of outstanding importance for the body. The dysregulation of oxygen sensing in the diseased kidney is best exemplified by the loss of stimulation of erythropoietin production from interstitial cells in the fibrotic kidney despite anemia. Furthermore, hypoxia is present in acute or chronic kidney diseases and may affect all cell types present in the kidney including tubular and glomerular cells as well as resident immune cells. Pro- and antifibrotic effects of the transcription factors hypoxia-inducible factors 1 and 2 have been described in a plethora of animal models of acute and chronic kidney diseases, but recent advances in sequencing technologies now allow for novel and deeper insights into the role of hypoxia and its cell type-specific effects on the progression of renal fibrosis, especially in humans. Here, we review existing literature on how hypoxia impacts the development and progression of renal fibrosis.

The complex pathology of diabetic nephropathy in humans

This review summarizes the pathomorphological sequences of nephron loss in human diabetic nephropathy (DN). The relevant changes may be derived from two major derangements. First, a failure in the turnover of the glomerular basement membrane (GBM) based on an increased production of GBM components by podocytes and endothelial cells leading to the thickening of the GBM and accumulation of worn-out GBM in the mesangium. This failure may account for the direct pathway to glomerular compaction and sclerosis based on the continuous deposition of undegraded GBM material in the mesangium. Second, an increased leakiness together with an increased propensity of glomerular capillaries to proliferate leads to widespread plasma exudations. Detrimental are those that produce giant insudative spaces within Bowman's capsule, spreading around the entire glomerular circumference and along the glomerulo-tubular junction onto the tubule resulting in tubular obstruction and retroactively to glomerulosclerosis. Tubular atrophy and interstitial fibrosis develop secondarily by transfer of the glomerular damage onto the tubule. Interstitial fibrosis is locally initiated and apparently stimulated by degenerating tubular epithelia. This leads to a focal distribution of interstitial fibrosis and tubular atrophy accompanied by a varying interstitial mononuclear cell infiltration. Spreading of fibrotic areas between intact nephrons, much less to the glomerulus, has not been encountered.

Dissecting pulmonary fibroblasts heterogeneity in lung development, health and diseases

Lung fibroblasts are the major components in the connective tissue of the pulmonary interstitium and play essential roles in the developing of postnatal lung, synthesizing the extracellular matrix and maintaining the integrity of the lung architecture. Fibroblasts are activated in various disease conditions and exhibit functional heterogeneities according to their origin, spatial location, activated state and microenvironment. In recent years, advances in technology have enabled researchers to identify fibroblast subpopulations in both mouse and human. Here, we discuss pulmonary fibroblast heterogeneity, focusing on the developing, healthy and pathological lung conditions. We firstly review the expression profiles of fibroblasts during lung development, and then consider fibroblast diversity according to different anatomical sites of lung architecture. Subsequently, we discuss fibroblast heterogeneity in genetic lineage. Finally, we focus on how fibroblast heterogeneity may shed light on different pathological lung conditions such as fibrotic diseases, infectious diseases including COVID-19, and lung cancers. We emphasize the importance of comparative studies to illuminate the overlapping characteristics, expression profiles and signaling pathways of the fibroblast subpopulations across disease conditions, a better characterization of the functional complexity rather than the expression of a particular gene may have important therapeutic applications.

Prediction models combining zonulin, LPS, and LBP predict acute kidney injury and hepatorenal syndrome-acute kidney injury in cirrhotic patients

The development of acute kidney injury (AKI) and hepatorenal syndrome-acute kidney injury (HRS-AKI) in cirrhosis has been associated with intestinal barrier dysfunction and gut-kidney crosstalk. We use the related markers such as zonulin, lipopolysaccharides (LPS), and lipopolysaccharide-binding protein (LBP) to predict AKI and HRS-AKI in cirrhotic patients and evaluate their in vitro effects on intestinal (Caco-2) cells and renal tubular (HK-2) cells. From 2013 to 2020, we enrolled 70 cirrhotic patients and developed prediction models for AKI and HRS-AKI over a six-month period. There were 13 (18.6%) and 8 (11.4%) cirrhotic patients developed AKI and HRS-AKI. The prediction models incorporated zonulin, LPS, LBP, C-reactive protein, age, and history of hepatitis B for AKI, and zonulin, LPS, LBP, total bilirubin, and Child-Pugh score for HRS-AKI. The area under curve (AUC) for the prediction of AKI and HRS-AKI was 0.94 and 0.95, respectively. Furthermore, the conditioned medium of LPS+hrLBP pre-treated Caco-2 cells induced apoptosis, necrosis, and zonulin release in HK-2 cells, demonstrating the communication between them. This study found that zonulin, LPS, and LBP are potential practical markers for predicting AKI and HRS-AKI in cirrhotic patients, which may serve as potential targets for renal outcomes in cirrhotic patients.

JAK/STAT signaling in diabetic kidney disease

Diabetic kidney disease (DKD) is the most important microvascular complication of diabetes and the leading cause of end-stage renal disease (ESRD) worldwide. The Janus kinase/signal transducer and activator of the transcription (JAK/STAT) signaling pathway, which is out of balance in the context of DKD, acts through a range of metabolism-related cytokines and hormones. JAK/STAT is the primary signaling node in the progression of DKD. The latest research on JAK/STAT signaling helps determine the role of this pathway in the factors associated with DKD progression. These factors include the renin-angiotensin system (RAS), fibrosis, immunity, inflammation, aging, autophagy, and EMT. This review epitomizes the progress in understanding the complicated explanation of the etiologies of DKD and the role of the JAK/STAT pathway in the progression of DKD and discusses whether it can be a potential target for treating DKD. It further summarizes the JAK/STAT inhibitors, natural products, and other drugs that are promising for treating DKD and discusses how these inhibitors can alleviate DKD to explore possible potential drugs that will contribute to formulating effective treatment strategies for DKD in the near future.

Endothelial-to-mesenchymal transition: New insights into vascular calcification

With the continuous progress of atherosclerosis research, the significant pathological change of it--vascular calcification (VC), gains increasing attention. In recent years, numerous studies have demonstrated that it is an independent predictor of death risk of cardiovascular disease, and it has a strong correlation with poor clinical prognosis. As the world's population continues to age, the occurrence of VC is expected to reach its highest point in the near future. Therefore, it is essential to investigate ways to prevent or even reverse this process for clinical purposes. Endothelial-to-mesenchymal transition (EndMT) describes the progressive differentiation of endothelial cells into mesenchymal stem cells (MSCs) under various stimuli and acquisition of pluripotent cell characteristics. More and more studies show that EndMT plays a vital role in various cardiovascular diseases, including atherosclerosis, vascular calcification and heart valvular disease. EndMT is also involved in the formation and progression of VC. This review vividly describes the history, characteristics of EndMT and how it affects the endothelial cell process, then focuses on the relationship between vascular endothelium, EndMT, amino acid metabolism, and vascular calcification. Finally, it overviews the signal pathway of EndMT and drugs targeting EndMT, hoping to provide new ideas and a theoretical basis for studying potential therapeutic targets of VC.

Capybara Oil Improves Renal Pathophysiology and Inflammation in Obese Mice

Obesity is an inflammatory disease associated with secondary diseases such as kidney disease, which can cause lipotoxicity, inflammation and loss of organ function. Polyunsaturated fatty acids act in the production of lipid mediators and have anti-inflammatory characteristics. In this work, the objective was to evaluate renal histopathology in obese mice and the effects of treatment with capybara oil (CO) (5000 mg/kg/day for 4 weeks). Parameters such as body mass, lipid profile, systolic blood pressure, urinary creatinine and protein excretion, structure and ultrastructure of the renal cortex, fibrosis, tissue inflammation and oxidative stress were analyzed. CO treatment in obese mice showed improvement in the lipid profile and reduction in systolic blood pressure levels, in addition to beneficial remodeling of the renal cortex. Our data demonstrated that CO decreased inflammation, oxidative stress and renal fibrosis, as evidenced by quantifying the expression of TNF-α, IL-10, CAT, SOD, α-SMA and TGF-β. Although treatment with CO did not show improvement in renal function, ultrastructural analysis showed that the treatment was effective in restoring podocytes and pedicels, with restructuring of the glomerular filtration barrier. These results demonstrate, for the first time, that treatment with CO is effective in reducing kidney damage, being considered a promising treatment for obesity.

The Uremic Toxin Indoxyl Sulfate Accelerates Senescence in Kidney Proximal Tubule Cells

Kidney fibrosis is the common final pathway of nearly all chronic and progressive nephropathies. One cause may be the accumulation of senescent cells that secrete factors (senescence associated secretory phenotype, SASP) promoting fibrosis and inflammation. It has been suggested that uremic toxins, such as indoxyl sulfate (IS), play a role in this. Here, we investigated whether IS accelerates senescence in conditionally immortalized proximal tubule epithelial cells overexpressing the organic anion transporter 1 (ciPTEC-OAT1), thereby promoting kidney fibrosis. Cell viability results suggested that the tolerance of ciPTEC-OAT1 against IS increased in a time-dependent manner at the same dose of IS. This was accompanied by SA-β-gal staining, confirming the accumulation of senescent cells, as well as an upregulation of p21 and downregulation of laminB1 at different time points, accompanied by an upregulation in the SASP factors IL-1β, IL-6 and IL-8. RNA-sequencing and transcriptome analysis revealed that IS accelerates senescence, and that cell cycle appears to be the most relevant factor during the process. IS accelerates senescence via TNF-α and NF-ĸB signalling early on, and the epithelial-mesenchymal transition process at later time points. In conclusion, our results suggest that IS accelerates cellular senescence in proximal tubule epithelial cells.

Kidney fibrosis: from mechanisms to therapeutic medicines

Chronic kidney disease (CKD) is estimated to affect 10-14% of global population. Kidney fibrosis, characterized by excessive extracellular matrix deposition leading to scarring, is a hallmark manifestation in different progressive CKD; However, at present no antifibrotic therapies against CKD exist. Kidney fibrosis is identified by tubule atrophy, interstitial chronic inflammation and fibrogenesis, glomerulosclerosis, and vascular rarefaction. Fibrotic niche, where organ fibrosis initiates, is a complex interplay between injured parenchyma (like tubular cells) and multiple non-parenchymal cell lineages (immune and mesenchymal cells) located spatially within scarring areas. Although the mechanisms of kidney fibrosis are complicated due to the kinds of cells involved, with the help of single-cell technology, many key questions have been explored, such as what kind of renal tubules are profibrotic, where myofibroblasts originate, which immune cells are involved, and how cells communicate with each other. In addition, genetics and epigenetics are deeper mechanisms that regulate kidney fibrosis. And the reversible nature of epigenetic changes including DNA methylation, RNA interference, and chromatin remodeling, gives an opportunity to stop or reverse kidney fibrosis by therapeutic strategies. More marketed (e.g., RAS blockage, SGLT2 inhibitors) have been developed to delay CKD progression in recent years. Furthermore, a better understanding of renal fibrosis is also favored to discover biomarkers of fibrotic injury. In the review, we update recent advances in the mechanism of renal fibrosis and summarize novel biomarkers and antifibrotic treatment for CKD.

F-box and leucine-rich repeat 6 promotes gastric cancer progression via the promotion of epithelial-mesenchymal transition

BACKGROUND

F-box and leucine-rich repeat 6 (FBXL6) have reportedly been associated with several cancer types. However, the role and mechanisms of FBXL6 in gastric cancer (GC) require further elucidation.

AIM

To investigate the effect of FBXL6 in GC tissues and cells and the underlying mechanisms.

METHODS

TCGA and GEO database analysis was performed to evaluate the expression of FBXL6 in GC tissues and adjacent normal tissues. Reverse transcription-quantitative polymerase chain reaction, immunofluorescence, and western blotting were used to detect the expression of FBXL6 in GC tissue and cell lines. Cell clone formation, 5-ethynyl-2’-deoxyuridine (EdU) assays, CCK-8, transwell migration assay, and wound healing assays were performed to evaluate the malignant biological behavior in GC cell lines after transfection with FBXL6-shRNA and the overexpression of FBXL6 plasmids. Furthermore, in vivo tumor assays were performed to prove whether FBXL6 promoted cell proliferation in vivo.

RESULTS

FBXL6 expression was upregulated more in tumor tissues than in adjacent normal tissues and positively associated with clinicopathological characteristics. The outcomes of CCK-8, clone formation, and Edu assays demonstrated that FBXL6 knockdown inhibited cell proliferation, whereas upregulation of FBXL6 promoted proliferation in GC cells. Additionally, the transwell migration assay revealed that FBXL6 knockdown suppressed migration and invasion, whereas the overexpression of FBXL6 showed the opposite results. Through the subcutaneous tumor implantation assay, it was evident that the knockdown of FBXL6 inhibited GC graft tumor growth in vivo. Western blotting showed that the effects of FBXL6 on the expression of the proteins associated with the epithelial-mesenchymal transition-associated proteins in GC cells.

CONCLUSION

Silencing of FBXL6 inactivated the EMT pathway to suppress GC malignancy in vitro. FBXL6 can potentially be used for the diagnosis and targeted therapy of patients with GC.

[Towards understanding chronic kidney disease]

Chronic kidney disease (CKD) is a global health problem affecting almost 15% of the population worldwide. After renal injury, there is a nephron loss and remaining nephrons ensure the glomerular filtration rate (GFR) with compensatory hyperplasia and hypertrophy: This is called the nephron reduction. After nephron reduction, renal function will gradually decline and lead to chronic end-stage renal failure. Whatever the initial cause of the renal injury, recent data suggest there are common molecular mechanisms at the origin of CKD progression. Moreover, the renal lesions are very reproducible with glomerulosclerosis, tubular atrophy and partial epithelio-mesenchymal transition, interstitial fibrosis and vascular abnormalities. The physiopathology of CKD progression is unclear but some hypotheses have been described: i) the nephron "overwork", supported by recent works showing that the nephron reduction leads to hyperfiltration by the remaining nephrons and the stability of the GFR; ii) the "podocyte adaptation" theory, reflected by the importance of the podocytopathy in CKD progression and the crucial role of residual proteinuria in renal lesion development; iii) the activation of EGFR signaling pathways in surgical nephron reduction model and its involvement in CKD progression. Finally, CKD progression remains poorly understood and further studies will be necessary to discover new CKD molecular pathways and to develop new therapeutic insight in CKD management.

Anlotinib Alleviates Renal Fibrosis via Inhibition of the ERK and AKT Signaling Pathways

Purpose

We examined whether anlotinib can attenuate folic acid-induced and unilateral ureteral obstruction-induced renal fibrosis and explored the underlying antifibrotic mechanism.

Materials and Methods

We have evaluated the effects of anlotinib on folic acid-induced and unilateral ureteral obstruction-induced renal fibrosis in mice through in vivo experiments of unilateral ureteral obstruction or folic acid-induced interstitial fibrosis and in vitro models of transforming growth factor-β1 induced HK-2 human renal proximal tubule cells. Serum renal function parameters and inflammatory cytokine levels were measured, and histological changes of renal injury and fibrosis were analyzed by HE staining and immunohistochemistry. Immunohistochemistry and Western blotting were used to determine the mechanism of action of anlotinib in ameliorating renal fibrosis.

Results

Anlotinib improved proteinuria and reduced renal impairment in folic acid-induced mouse models of renal fibrosis. Anlotinib reduced tubular injury, deposition of tubular extracellular matrix, and expression of alpha-smooth muscle actin, transforming growth factor-β1, and cytosolic inflammatory factors compared with controls.

Conclusions

Anlotinib ameliorated renal function, improved extracellular matrix deposition, reduced protein levels of epithelial-mesenchymal transition markers, and decreased cellular inflammatory factors. Anlotinib reduced renal injury and fibrosis by inhibiting the transforming growth factor-β1 signaling pathway through AKT and ERK channels.

Is the proximal tubule the focus of tubulointerstitial fibrosis?

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.

Emodin ameliorates renal injury and fibrosis via regulating the miR-490-3p/HMGA2 axis

Renal fibrosis is a major pathological feature of chronic kidney disease (CKD). While emodin is reported to elicit anti-fibrotic effects on renal injury, little is known about its effects on microRNA (miRNA)-modulated mechanisms in renal fibrosis. In this study, we established a unilateral ureteral obstruction (UUO) model and a transforming growth factor (TGF)-β1-induced normal rat renal tubular epithelial cell line (NRK-52E) model to investigate the protective effects of emodin on renal fibrosis and its miRNA/target gene mechanisms. Dual-luciferase assay was performed to confirm the direct binding of miRNA and target genes in HEK293 cells. Results showed that oral administration of emodin significantly ameliorated the loss of body weight and the increase in physicochemical parameters, including serum uric acid, creatinine, and urea nitrogen in UUO mice. Inflammatory cytokines, including tumor necrosis factor-α, monocyte chemoattractant protein-1, and interleukin (IL)-1β, but not IL-6, were down-regulated by emodin administration. Emodin decreased the expression levels of TGF-β1 and fibrotic-related proteins, including alpha-smooth muscle actin, Collagen IV, and Fibronectin, and increased the expression of E-cadherin. Furthermore, miR-490-3p was decreased in UUO mice and negatively correlated with increased expression of high migration protein A2 (HMGA2). We further confirmed HMGA2 was the target of miR-490-3p. Transfection of miR-490-3p mimics decreased, while transfection of miR-490-3p inhibitors increased fibrotic-related proteins and HMGA2 expression levels in TGF-β1-induced NRK-52E cells. Furthermore, transfection of miR-490-3p mimics enhanced the anti-fibrotic effects of emodin, while transfection of miR-490-3p inhibitors abolished the protective effects of emodin. Thus, as a novel target of emodin that prevents renal fibrosis in the HMGA2-dependent signaling pathway, miR-490-3p has potential implications in CKD pathology.

Cryptotanshinone modulates proliferation, apoptosis, and fibrosis through inhibiting AR and EGFR/STAT3 axis to ameliorate benign prostatic hyperplasia progression

Benign prostatic hyperplasia (BPH) is a chronic proliferative non-tumorous disease that mainly bothers males older than 50 and significantly disturbs the quality of life. Cryptotanshinone (CTS), a herbal extract, has been proven with therapeutic effects on various diseases. However, the effects and possible mechanisms of CTS in BPH have not yet been elucidated. This study aims to investigate the efficacy of CTS on the BPH-associated pathological processes and the possible mechanisms underlying it. Herein, CTS was intragastrically administrated to estradiol/testosterone (E2/T) (1:100)-induced BPH rats, and finasteride (Fi) was used as the positive control. Human benign prostatic hyperplasia epithelial cells (BPH-1) and normal human prostate stromal cells (WPMY-1) were used for the in vitro experiments. Results indicated that E2/T injection was able to induce BPH manifestation, featured with increased prostate index. Furthermore, it accelerated proliferation, epithelial-mesenchymal transition (EMT), stromal collagen deposition, and inhibited apoptosis of rat prostate. However, the administration of CTS partially reversed the changes mentioned above. The therapeutic effects of CTS on BPH were also confirmed by in vitro experiments. The efficacy of CTS on these processes might be attributed to the suppression of AR and EGFR/STAT3 axis activity. In conclusion, CTS might suppress BPH progression by modulating proliferation, apoptosis, EMT, and stromal collagen deposition via suppressing AR and EGFR/STAT3 axis.

Human kidney organoids model of Esculentoside A nephrotoxicity to investigate the role of epithelial-mesenchymal transition via STING signaling

Radix Phytolaccae (RP) has a long medicinal history and is commonly used to treat systemic edema and ascites in Asia. Although RP is known to cause nephrotoxicity, the role of its main constituent, Esculentoside A (EsA), in nephrotoxicity remains undetermined. We used kidney organoids derived from human inducible pluripotent stem cells (iPSCs) to model EsA nephrotoxicity accurately. Kidney organoids were differentiated and treated with EsA at doses of 0, 15, 30, or 60 μM for 48 h. The in vitro model was compared to a mouse model of EsA nephrotoxicity (intraperitoneally injected, 25 mg·kg^-1). The mechanisms were investigated. Cell viability decreased dose-dependently after treatment with EsA. As polarity was lost, tubular cells decreased, similar to mouse EsA nephrotoxicity with upregulated vimentin expression and a stimulator of the interferon gene (STING). Furthermore, 60 μM EsA could induce endothelial inflammation, lead to mitochondrial damage and activate STING by translocating mtDNA into the cytoplasm to develop an inflammatory cascade and destroy renal endothelial cells with interstitial changes. The data suggest that kidney organoids derived from iPSCs are promising for investigating nephrotoxicity. EsA nephrotoxicity involves the epithelial-mesenchymal transition via STING signaling.

circCAPRIN1 interacts with STAT2 to promote tumor progression and lipid synthesis via upregulating ACC1 expression in colorectal cancer

BACKGROUND

Circular RNAs (circRNAs) generated by back-splicing of precursor mRNAs (pre-mRNAs) are often aberrantly expressed in cancer cells. Accumulating evidence has revealed that circRNAs play a critical role in the progression of several cancers, including colorectal cancer (CRC). However, the current understandings of the emerging functions of circRNAs in CRC lipid metabolism and the underlying molecular mechanisms are still limited. Here, we aimed to explore the role of circCAPRIN1 in regulating CRC lipid metabolism and tumorigenesis.

METHODS

circRNA microarray was performed with three pairs of tumor and non-tumor tissues from CRC patients. The expression of circRNAs were determined by quantitative PCR (qPCR) and in situ hybridization (ISH). The endogenous levels of circRNAs in CRC cells were manipulated by transfection with lentiviruses overexpressing or silencing circRNAs. The regulatory roles of circRNAs in the occurrence of CRC were investigated both in vitro and in vivo using gene expression array, RNA pull-down/mass spectrometry, RNA immunoprecipitation assay, luciferase reporter assay, chromatin immunoprecipitation analysis, and fluorescence in situ hybridization (FISH).

RESULTS

Among circRNAs, circCAPRIN1 was most significantly upregulated in CRC tissue specimens. circCAPRIN1 expression was positively correlated with the clinical stage and unfavorable prognosis of CRC patients. Downregulation of circCAPRIN1 suppressed proliferation, migration, and epithelial-mesenchymal transition of CRC cells, while circCAPRIN1 overexpression had opposite effects. RNA sequencing and gene ontology analysis indicated that circCAPRIN1 upregulated the expressions of genes involved in CRC lipid metabolism. Moreover, circCAPRIN1 promoted lipid synthesis by enhancing Acetyl-CoA carboxylase 1 (ACC1) expression. Further mechanistic assays demonstrated that circCAPRIN1 directly bound signal transducer and activator of transcription 2 (STAT2) to activate ACC1 transcription, thus regulating lipid metabolism and facilitating CRC tumorigenesis.

CONCLUSIONS

These findings revealed the oncogenic role and mechanism of circCAPRIN1 in CRC. circCAPRIN1 interacted with STAT2 to promote CRC tumor progression and lipid synthesis by enhancing the expression of ACC1. circCAPRIN1 may be considered as a novel potential diagnostic and therapeutic target for CRC patients.

Cellular phenotypic transitions in diabetic nephropathy: An update

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in diabetes and is the most common cause of end stage renal disease (ESRD). Renal fibrosis is the final pathological change in DN. It is widely believed that cellular phenotypic switching is the cause of renal fibrosis in diabetic nephropathy. Several types of kidney cells undergo activation and differentiation and become reprogrammed to express markers of mesenchymal cells or podocyte-like cells. However, the development of targeted therapy for DN has not yet been identified. Here, we discussed the pathophysiologic changes of DN and delineated the possible origins that contribute to myofibroblasts and podocytes through phenotypic transitions. We also highlight the molecular signaling pathways involved in the phenotypic transition, which would provide valuable information for the activation of phenotypic switching and designing effective therapies for DN.

N6-methyladenine RNA Methylation Epigenetic Modification and Kidney Diseases

RNA methylation modification is a rapidly developing field in epigenetics. N6-methyladensine (m⁶A) is the most common internal modification in eukaryotic mRNA. m⁶A group regulates RNA splicing, stability, translocation, and translation. Enzymes catalyzing this process were termed as writers, erasers, and readers. Recent studies have focused on exploring the role of RNA methylation in human diseases. RNA methylation modifications, particularly m⁶A, play important roles in the pathogenesis of kidney diseases. In this review, we provide a brief description of m⁶A and summarize the impact of m⁶A on acute and chronic kidney disease (CKD) and possible future study directions for this research.

Exosomes derived from mesenchymal stem cells attenuate diabetic kidney disease by inhibiting cell apoptosis and epithelial-to-mesenchymal transition via miR-424-5p

Diabetic kidney disease (DKD) is well-acknowledged as one of the most common complications in diabetes mellitus. Recent studies have demonstrated the promising role of mesenchymal stem cell-derived exosomes (MSC-exos) as a cell-free treatment strategy for DKD. The present study sought to investigate the therapeutic potential and the underlying mechanisms of MSC-exos in DKD. The authentication of MSC-exos was validated by western blot, transmission electron microscope (TEM), and nanosight tracking analysis (NTA). Apoptosis was detected by western blot, TUNEL staining, and flow cytometry. Epithelial-to-mesenchymal transition (EMT) was evaluated by western blot and immunofluorescence. The relationship between miR-424-5p and Yes-associated protein 1 (YAP1) was revealed by dual luciferase reporter assay. We observed that MSC-exos could attenuate DKD by decreasing cell apoptosis and inhibiting epithelial-to-mesenchymal transition (EMT) in diabetic kidneys in db/db mice. Besides, we documented that MSC-exos could reverse high glucose-induced apoptosis and EMT in HK2 cells. Interestingly, miR-424-5p derived from MSC-exos could inhibit YAP1 activation in HK2 cells, resulting in alleviation of high glucose-induced cell apoptosis and EMT. Our study provides novel insights into MSC-exos-mediated protective effect in DKD. MSC-exos could inhibit high glucose-induced apoptosis and EMT through miR-424-5p targeting of YAP1.

Resolvin D1 Prevents Epithelial-to-Mesenchymal Transition and Reduces Collagen Deposition by Stimulating Autophagy in Intestinal Fibrosis

BACKGROUND

Intestinal fibrosis is the most common complication of inflammatory bowel disease; nevertheless, specific therapies are still unavailable. Resolvin D1 (RvD1), a typical endogenous ω-3 fatty acid-derived lipid mediator, has attracted wide attention due to its remarkable anti-fibrosis effects. However, the efficacy and mechanisms of RvD1 in intestinal fibrosis remain unclear.

AIM

To investigate the protective effect of RvD1 in a dextran sulfate sodium (DSS)-induced intestinal fibrosis model and explore the molecular mechanisms underlying its anti-fibrotic effect.

METHODS

A DSS-induced intestinal fibrosis model and intestinal epithelial-to-mesenchymal transition (EMT) model were used to observe the efficacy of RvD1, and fibroblasts were stimulated with conditioned medium with or without TGF-β1 to investigate the probable mechanisms of RvD1 in intestinal fibrosis disease.

RESULTS

Intestinal fibrosis was effectively alleviated by RvD1 in a DSS-induced model, both preventively and therapeutically, and autophagy inhibition-induced EMT in intestinal epithelial cells was significantly suppressed in vivo and in vitro. Furthermore, RvD1 reduced epithelial cell EMT paracrine signaling, which promoted the differentiation of local fibroblasts into myofibroblasts.

CONCLUSIONS

Our results suggested that RvD1 reduces autophagy-induced EMT in intestinal epithelial cells and ameliorates intestinal fibrosis by disrupting epithelial-fibroblast crosstalk.

Molecular mechanisms and physiological functions of autophagy in kidney diseases

Autophagy is a highly conserved cellular progress for the degradation of cytoplasmic contents including micromolecules, misfolded proteins, and damaged organelles that has recently captured attention in kidney diseases. Basal autophagy plays a pivotal role in maintaining cell survival and kidney homeostasis. Accordingly, dysregulation of autophagy has implicated in the pathologies of kidney diseases. In this review, we summarize the multifaceted role of autophagy in kidney aging, maladaptive repair, tubulointerstitial fibrosis and discuss autophagy-related drugs in kidney diseases. However, uncertainty still remains as to the precise mechanisms of autophagy in kidney diseases. Further research is needed to clarify the accurate molecular mechanism of autophagy in kidney diseases, which will facilitate the discovery of a promising strategy for the prevention and treatment of kidney diseases.

The role of the macrophage-to-myofibroblast transition in renal fibrosis

Renal fibrosis causes structural and functional impairment of the kidney, which is a dominant component of chronic kidney disease. Recently, a novel mechanism, macrophage-to-myofibroblast transition (MMT), has been identified as a crucial component in renal fibrosis as a response to chronic inflammation. It is a process by which bone marrow-derived macrophages differentiate into myofibroblasts during renal injury and promote renal fibrosis. Here, we summarized recent evidence and mechanisms of MMT in renal fibrosis. Understanding this phenomenon and its underlying signal pathway would be beneficial to find therapeutic targets for renal fibrosis in chronic kidney disease.

Influence of sphingomyelin metabolism during epithelial-mesenchymal transition associated with aging in the renal papilla

The renal collecting ducts (CD) are formed by a fully differentiated epithelium, and their tissue organization and function require the presence of mature cell adhesion structures. In certain circumstances, the cells can undergo de-differentiation by a process called epithelial-mesenchymal transition (EMT), in which the cells lose their epithelial phenotype and acquire the characteristics of the mesenchymal cells, which includes loss of cell-cell adhesion. We have previously shown that in renal papillary CD cells, cell adhesion structures are located in sphingomyelin (SM)-enriched plasma membrane microdomains and the inhibition of SM synthase 1 activity induced CD cells to undergo an EMT process. In the present study, we evaluated the influence of SM metabolism during the EMT of the cells that form the CD of the renal papilla during aging. To this end, primary cultures of renal papillary CD cells from young, middle-, and aged-rats were performed. By combining biochemical and immunofluorescence studies, we found experimental evidence that CD cells undergo an increase in spontaneous and reversible EMT during aging and that at least one of the reasons for this phenomenon is the decrease in SM content due to the combination of decreased SM synthase activity and an increase in SM degradation mediated by neutral sphingomyelinase. Age is a risk factor for many diseases, among which renal fibrosis is included. Our findings highlight the importance of sphingolipids and particularly SM as a modulator of the fate of CD cells and probably contribute to the development of treatments to avoid or reverse renal fibrosis during aging.

IL-33 attenuates renal fibrosis via group2 innate lymphoid cells

Renal fibrosis is a common pathway in the progression of various kidney diseases and injuries. Unilateral ureteral obstruction (UUO) induces renal fibrosis, and immune responses profoundly affect its pathogenesis. Group2 innate lymphoid cells (ILC2s) are strongly activated by interleukin (IL) -33, which is a member of IL-1 family and recognize as alarmin. ILC2s quickly produce large amounts of type 2 cytokines including IL-5 and IL-13, which are involved in inflammation, tissue homeostasis, and wound healing. However, the relationship between renal fibrosis and ILC2s has been unclear. In the present study, we investigated the roles of the ILC2/L-33 axis in renal fibrosis using a UUO model. We found that kidney ILC2s decreased in UUO-affected kidneys compared with their counterpart kidneys despite IL-33 upregulation. There was no effect of reactive oxygen species or TGF-β from reduced ILC2 caused by UUO. Pretreatment with IL-33 before UUO induced ILC2s and Tregs in kidneys and alleviated renal fibrosis. Furthermore, this protective effect was maintained even when CD4⁺T cells was depleted. These findings demonstrated that ILC2s play a predominant role in the suppressive function of renal fibrosis mediated by pretreatment with IL-33. In contrast, post-treatment with IL-33 after UUO increased ILC2s in kidneys but had no therapeutic effect on renal fibrosis. Our findings suggest that ILC2s have potential roles in the prevention of renal fibrosis and can serve as a therapeutic and diagnostic target.

Targeting inflammation for the treatment of Diabetic Kidney Disease: a five-compartment mechanistic model

Diabetic kidney disease (DKD) is the leading cause of kidney failure worldwide. Mortality and morbidity associated with DKD are increasing with the global prevalence of type 2 diabetes. Chronic, sub-clinical, non-resolving inflammation contributes to the pathophysiology of renal and cardiovascular disease associated with diabetes. Inflammatory biomarkers correlate with poor renal outcomes and mortality in patients with DKD. Targeting chronic inflammation may therefore offer a route to novel therapeutics for DKD. However, the DKD patient population is highly heterogeneous, with varying etiology, presentation and disease progression. This heterogeneity is a challenge for clinical trials of novel anti-inflammatory therapies. Here, we present a conceptual model of how chronic inflammation affects kidney function in five compartments: immune cell recruitment and activation; filtration; resorption and secretion; extracellular matrix regulation; and perfusion. We believe that the rigorous alignment of pathophysiological insights, appropriate animal models and pathology-specific biomarkers may facilitate a mechanism-based shift from recruiting ‘all comers’ with DKD to stratification of patients based on the principal compartments of inflammatory disease activity.

Experimental Aristolochic Acid Nephropathy: A Relevant Model to Study AKI-to-CKD Transition

Aristolochic acid nephropathy (AAN) is a progressive tubulointerstitial nephritis caused by the intake of aristolochic acids (AA) contained in Chinese herbal remedies or contaminated food. AAN is characterized by tubular atrophy and interstitial fibrosis, characterizing advanced kidney disease. It is established that sustained or recurrent acute kidney injury (AKI) episodes contribute to the progression of CKD. Therefore, the study of underlying mechanisms of AA-induced nephrotoxicity could be useful in understanding the complex AKI-to-CKD transition. We developed a translational approach of AKI-to-CKD transition by reproducing human AAN in rodent models. Indeed, in such models, an early phase of acute tubular necrosis was rapidly followed by a massive interstitial recruitment of activated monocytes/macrophages followed by cytotoxic T lymphocytes, resulting in a transient AKI episode. A later chronic phase was then observed with progressive tubular atrophy related to dedifferentiation and necrosis of tubular epithelial cells. The accumulation of vimentin and αSMA-positive cells expressing TGFβ in interstitial areas suggested an increase in resident fibroblasts and their activation into myofibroblasts resulting in collagen deposition and CKD. In addition, we identified 4 major actors in the AKI-to-CKD transition: (1) the tubular epithelial cells, (2) the endothelial cells of the interstitial capillary network, (3) the inflammatory infiltrate, and (4) the myofibroblasts. This review provides the most comprehensive and informative data we were able to collect and examines the pending questions.

Endothelial ETS1 inhibition exacerbate blood-brain barrier dysfunction in multiple sclerosis through inducing endothelial-to-mesenchymal transition

Blood-brain barrier (BBB) dysfunction has been recognized as an early pathological feature and contributing factor in multiple sclerosis. Endothelial-to-mesenchymal transition is a process associated with endothelial dysfunction leading to the disruption of vessel stability and barrier function, yet its functional consequence in multiple sclerosis remains unclear. Here, we demonstrated that endothelial-to-mesenchymal transition accompanied the blood-brain barrier dysfunction in several neurological disorders, especially in multiple sclerosis. The activity of transcription factor ETS1, which is highly expressed in endothelial cells (ECs) and responded to an inflammatory condition, is suppressed in the central nervous system (CNS) ECs in MS and its animal model experimental autoimmune encephalomyelitis. We identify ETS1 as a central regulator of endothelial-to-mesenchymal transition (EndMT) associated with the compromise of barrier integrity. These phenotypical and functional alterations can further induce high permeability, immune infiltration, and organ fibrosis in multiple sclerosis, thus promoting disease progression. Together, these results demonstrate a functional role of EndMT in blood-brain barrier dysfunction and propose ETS1 as a potential transcriptional switch of EndMT to target the development of multiple sclerosis.

TIGAR deficiency sensitizes angiotensin-II-induced renal fibrosis and glomerular injury

Angiotensin II (Ang-II) is one of the major contributors to the progression of renal fibrosis, inflammation, glomerular injury, and chronic kidney disease. Emerging evidence suggests that renal glycolysis plays an important role in renal fibrosis and injury. TP53-induced glycolysis and apoptosis regulator (TIGAR) has been shown to regulate glycolysis. In the present study, we investigated the role of TIGAR in renal glycolysis, fibrosis, and glomerular injury during Ang-II-induced hypertension. Wild-type (WT) and TIGAR knockout (KO) mice were infused with Ang-II (1 µg/kg/min) via mini-pumps for 4 weeks. The mean arterial pressure was similar between the WT and TIGAR KO mice, associated with a comparable increase in plasma creatinine level. Ang-II infusion resulted in a significant increase in renal interstitial fibrosis and more mesangial expansion and collapsed glomerular structure in the TIGAR KO mice. These were associated with elevated expression of hypoxia-inducible factor-1 alpha, glycolytic enzymes, and transforming growth factor beta 1 in the TIGAR KO mice after Ang-II infusion when compared to that of the WT mice. The coupled-enzyme method revealed that PFK-1 activity was similarly increased in WT and TIGAR KO mice after Ang-II infusion. Our present study suggests that TIGAR is involved in Ang-II-induced renal fibrosis and glomerular injury, although it has little effect on blood pressure and renal function. Knockout of TIGAR sensitizes Ang-II-induced renal fibrosis and injury. This study provides new insights into the role of TIGAR in renal metabolism and pathological remodeling during Ang-II-induced hypertension.

Modeling injury and repair in kidney organoids reveals that homologous recombination governs tubular intrinsic repair

Kidneys have the capacity for intrinsic repair, preserving kidney architecture with return to a basal state after tubular injury. When injury is overwhelming or repetitive, however, that capacity is exceeded and incomplete repair results in fibrotic tissue replacing normal kidney parenchyma. Loss of nephrons correlates with reduced kidney function, which defines chronic kidney disease (CKD) and confers substantial morbidity and mortality to the worldwide population. Despite the identification of pathways involved in intrinsic repair, limited treatments for CKD exist, partly because of the limited throughput and predictivity of animal studies. Here, we showed that kidney organoids can model the transition from intrinsic to incomplete repair. Single-nuclear RNA sequencing of kidney organoids after cisplatin exposure identified 159 differentially expressed genes and 29 signal pathways in tubular cells undergoing intrinsic repair. Homology-directed repair (HDR) genes including Fanconi anemia complementation group D2 (FANCD2) and RAD51 recombinase (RAD51) were transiently up-regulated during intrinsic repair but were down-regulated in incomplete repair. Single cellular transcriptomics in mouse models of obstructive and hemodynamic kidney injury and human kidney samples of immune-mediated injury validated HDR gene up-regulation during tubular repair. Kidney biopsy samples with tubular injury and varying degrees of fibrosis confirmed loss of FANCD2 during incomplete repair. Last, we performed targeted drug screening that identified the DNA ligase IV inhibitor, SCR7, as a therapeutic candidate that rescued FANCD2/RAD51-mediated repair to prevent the progression of CKD in the cisplatin-induced organoid injury model. Our findings demonstrate the translational utility of kidney organoids to identify pathologic pathways and potential therapies.

An organ-derived extracellular matrix triggers in situ kidney regeneration in a preclinical model

It has not been considered that nephrons regenerate in adult mammals. We present that an organ-derived extracellular matrix in situ induces nephron regeneration in a preclinical model. A porcine kidney-derived extracellular matrix was sutured onto the surface of partial nephrectomy (PN)-treated kidney. Twenty-eight days after implantation, glomeruli, vessels, and renal tubules, characteristic of nephrons, were histologically observed within the matrix. No fibrillogenesis was observed in the matrix nor the matrix-sutured kidney, although this occurred in a PN kidney without the matrix, indicating the structures were newly induced by the matrix. The expression of renal progenitor markers, including Sall1, Six2, and WT-1, within the matrix supported the induction of nephron regeneration by the matrix. Furthermore, active blood flow was observed inside the matrix using computed tomography. The matrix provides structural and functional foundations for the development of cell-free scaffolds with a remarkably low risk of immune rejection and cancerization.

MORG1—A Negative Modulator of Renal Lipid Metabolism in Murine Diabetes

Renal fatty acid (FA) metabolism is severely altered in type 1 and 2 diabetes mellitus (T1DM and T2DM). Increasing evidence suggests that altered lipid metabolism is linked to tubulointerstitial fibrosis (TIF). Our previous work has demonstrated that mice with reduced MORG1 expression, a scaffold protein in HIF and ERK signaling, are protected against TIF in the db/db mouse model. Renal TGF-ß1 expression and EMT-like changes were reduced in mice with single-allele deficiency of MORG1. Given the well-known role of HIF and ERK signaling in metabolic regulation, here we examined whether protection was also associated with a restoration of lipid metabolism. Despite similar features of TIF in T1DM and T2DM, diabetes-associated changes in renal lipid metabolism differ between both diseases. We found that de novo synthesis of FA/cholesterol and β-oxidation were more strongly disrupted in T1DM, whereas pathological fat uptake into tubular cells mediates lipotoxicity in T2DM. Thus, diminished MORG1 expression exerts renoprotection in the diabetic nephropathy by modulating important factors of TIF and lipid dysregulation to a variable extent in T1DM and T2DM. Prospectively, targeting MORG1 appears to be a promising strategy to reduce lipid metabolic alterations in diabetic nephropathy.

Clonorchis sinensis Granulin Promotes Malignant Transformation of Hepatocyte Through EGFR-Mediated RAS/MAPK/ERK and PI3K/Akt Signaling Pathways

The biological functions of growth factor, such as granulins, have been explored in parasites, and we elucidated that Clonorchis sinensis granulin (CsGRN) promoted the metastasis of hepatocellular carcinoma in our previous study. However, it is still unclear for the malignant transformation role of CsGRN in normal human hepatocytes. In this study, by transfecting pEGFP-C1-CsGRN eukaryotic expression plasmid, a cell line with stable overexpression of CsGRN in normal hepatocyte (LO2-GRN cells) was constructed. The effects on cell proliferation were detected by carrying out cell counting kit-8 (CCK8) assay and colony formation assay. Additionally, we conducted flow cytometry analysis to determine whether the proliferation of CsGRN was due to cell cycle arrest. Subsequently, the migration ability and the invasion ability of LO2-GRN cells were evaluated through wound-healing assay and transwell assay. Meanwhile, the levels of the markers of RAS/MAPK/ERK and PI3K/Akt signaling pathways activation in LO2-GRN cells were assessed by quantitative RT-PCR and Western blot. Our results indicated that CsGRN promoted the proliferation of LO2 cells by regulating the expression of cell-cycle-related genes. Moreover, the overexpression of CsGRN regulates malignant metastasis of liver cells by inducing the upregulation of epithelial-mesenchymal transition (EMT) marker proteins. Furthermore, both mRNA and protein expression levels of p-EGFR, RAS, p-ERK, p-AKT, p-PI3K, and p-braf have been enhanced by CsGRN. These results showed that CsGRN promoted the malignant transformation of hepatocytes by regulating epidermal growth factor receptor (EGFR)-mediated RAS/MAPK/ERK and PI3K/Akt signaling pathways, which suggested that CsGRN could serve as a novel oncoprotein during Clonorchis sinensis-associated malignant transformation of hepatocytes.

[Acute kidney injury in intensive care unit: A review]

Acute kidney injury is a common complication in intensive care unit. Its incidence is variable according to the studies. It is considered to occur in more than 50 % of patients. Acute kidney injury is responsible for an increase in morbidity (length of hospitalization, renal replacement therapy) but also for excess mortality. The commonly accepted definition of acute kidney injury comes from the collaborative workgroup named Kidney Disease: Improving Global Outcomes (KDIGO). It made it possible to standardize practices and raise awareness among practitioners about monitoring plasma creatinine and also diuresis. Acute kidney injury in intensive care unit is a systemic disease including circulatory, endothelial, epithelial and cellular function involvement and an acute kidney injury is not accompanied by ad integrum repair. After prolonged injury, inadequate repair begins with a fibrotic process. Several mechanisms are involved (cell cycle arrest, epithelial-mesenchymal transition, mitochondrial dysfunction) and result in improper repair. A continuum exists between acute kidney disease and chronic kidney disease, characterized by different renal recovery phenotypes. Thus, preventive measures to prevent the occurrence of kidney damage play a major role in management. The nephrologist must be involved at every stage, from the prevention of the first acute kidney injury (upon arrival in intensive care unit) to long-term follow-up and the care of a chronic kidney disease.

Semaporin3A-inhibitor ameliorates renal fibrosis through the regulation of JNK signaling

Renal fibrosis is the common pathological pathway in progressive renal diseases. In the study, we analyzed the roles of Semaphorin 3A (SEMA3A) on renal fibrosis and the effect of SEMA3A-inhibitor (SEMA3A-I) using unilateral ureteral obstruction (UUO) mouse model. The expression of SEMA3A in the proximal tubulus and neuropilin-1 (NRP1), a recepor of SEMA3A, in fibloblast and tubular cells were increased in the UUO kidneys. The increased expression of myofibroblast marker tenascin-C and fibronection as well as renal fibrosis were increased in UUO kidneys, all of which were ameliorated by SEMA3A-I. In addition, c-Jun N-terminal kinase (JNK) signaling pathway known as the target of SEMA3A signaling, was activated in proximal tubular cells and fibroblast cells after UUO surgery while SEMA3A-I significantly attenuated the activation. In vitro, treatments with SEMA3A as well as transforming growth factor-β1 (TGF-β1) in human proximal tubular cells lost epithelial cell characters while SEMA3A-I significantly ameliorated this transformation. JNK inhibitor, SP600125, partially reversed SEMA3A and TGF-β1-induced cell transformation, indicating that JNK signaling is involved in SEMA3A-induced renal fibrosis. In addition, the treatment with SEMA3A in fibroblast cells activated the expression of tenascin-C, collagen type I and fibronection, indicating that SEMA3A may accelerate renal fibrosis through the activation of fibroblast cells. The analysis of human data revealed the positive correlation between urinary SEMA3A and urinary N-acetyl-β-D-glucosaminidase, indicating the association between SEMA3A and tubular injury. In conclusion, SEMA3A signaling is involved in renal fibrosis through JNK signaling pathway and SEMA3A-I might be the therapeutic option for protecting from renal fibrosis.

Metabolic Reprogramming in Kidney Diseases: Evidence and Therapeutic Opportunities

Metabolic reprogramming originally referred to the ability of cancer cells to metabolically adapt to changes in environmental conditions to meet both energy consumption and proliferation requirements. According to recent studies, renal cells are also capable of reprogramming their metabolism after kidney injury, and these cells undergo different kinds of metabolic reprogramming in different kidney diseases. Metabolic reprogramming also plays a role in the progression and prognosis of kidney diseases. Therefore, metabolic reprogramming is not only a prominent feature but also an important contributor to the pathophysiology of kidney diseases. Here, we briefly review kidney diseases and metabolic reprogramming and discuss new ways to treat kidney diseases.

Pathomorphological sequence of nephron loss in diabetic nephropathy

Following our previous reports on mesangial sclerosis and vascular proliferation in diabetic nephropathy (DN) (Kriz W, Löwen J, Federico G, van den Born J, Gröne E, Gröne HJ. Am J Physiol Renal Physiol 312: F1101-F1111, 2017; Löwen J, Gröne E, Gröne 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.NEW & NOTEWORTHY Based on analysis of 918 human biopsies, essential derangement in diabetic nephropathy consists of accumulation of worn-out glomerular basement membrane in the mesangium that may advance to global sclerosis. The most frequent pathway to nephron dropout starts with the penetration of glomerular capillaries into Bowman's capsule (BC), delivering an exudate into BC that spreads around the entire glomerular circumference and via the glomerulotubular junction onto the tubule, resulting in glomerular sclerosis and chronic tubulointerstitial damage.

The hepatocyte growth factor/c-met pathway is a key determinant of the fibrotic kidney local microenvironment

The kidney local microenvironment (KLM) plays a critical role in the pathogenesis of kidney fibrosis. However, the composition and regulation of a fibrotic KLM remain unclear. Through a multidisciplinary approach, we investigated the roles of the hepatocyte growth factor/c-met signaling pathway in regulating KLM formation in various chronic kidney disease (CKD) models. We performed a retrospective analysis of single-cell RNA sequencing data and determined that tubular epithelial cells and macrophages are two major cell populations in a fibrotic kidney. We then created a mathematical model that predicted loss of c-met in tubular cells would cause greater responses to injury than loss of c-met in macrophages. By generating c-met conditional knockout mice, we validated that loss of c-met influences epithelial plasticity, myofibroblast activation, and extracellular matrix synthesis/degradation, which ultimately determined the characteristics of the fibrotic KLM. Our findings open the possibility of designing effective therapeutic strategies to retard CKD.

Role of protein phosphatase 2A in kidney disease (Review)

Kidney disease affects millions of people worldwide and is a financial burden on the healthcare system. Protein phosphatase 2A (PP2A), which is involved in renal development and the function of ion-transport proteins, aquaporin-2 and podocytes, is likely to serve an important role in renal processes. PP2A is associated with the pathogenesis of a variety of different kidney diseases including podocyte injury, inflammation, tumors and chronic kidney disease. The current review aimed to discuss the structure and function of PP2A subunits in the context of kidney diseases. How dysregulation of PP2A in the kidneys causes podocyte death and the inactivation of PP2A in renal carcinoma tissues is discussed. Inhibition of PP2A activity prevents epithelial-mesenchymal transition and attenuates renal fibrosis, creating a favorable inflammatory microenvironment and promoting the initiation and progression of tumor pathogenesis. The current review also indicates that PP2A serves an important role in protection against renal inflammation. Understanding the detailed mechanisms of PP2A provides information that can be utilized in the design and application of novel therapeutics for the treatment and prevention of renal diseases.