Extracellular Matrix in Kidney Fibrosis: More Than Just a Scaffold

Hepatic and proximal tubule angiotensinogen play distinct roles in kidney dysfunction, glomerular and tubular injury, and fibrosis progression

Components of the renin-angiotensin system, including angiotensinogen (AGT), are critical contributors to chronic kidney disease (CKD) development and progression. However, the specific role of tissue-derived AGTs in CKD has not been fully understood. To define the contribution of liver versus kidney AGT in the CKD development, we performed 5/6 nephrectomy (Nx), an established CKD model, in wild-type (WT), proximal tubule (PT)- or liver-specific AGT knockout (KO) mice. Nx significantly elevated intrarenal AGT expression and elevated blood pressure (BP) in WT mice. The increase of intrarenal AGT protein was completely blocked in liver-specific AGT KO mice with BP reduction, suggesting a crucial role for liver AGT in BP regulation during CKD. Nx-induced glomerular and kidney injury and dysfunction, as well as fibrosis, were all attenuated to a greater extent in liver-specific AGT KO mice compared with PT-specific AGT KO and WT mice. However, the suppression of interstitial fibrosis in PT- and liver-specific AGT KO mouse kidneys was comparable. Our findings demonstrate that liver AGT acts as a critical contributor in driving glomerular and tubular injury, renal dysfunction, and fibrosis progression, whereas the role of PT AGT was limited to interstitial fibrosis progression in chronic renal insufficiency. Our results provide new insights for the development of tissue-targeted renin-angiotensin system intervention in the treatment of CKD.NEW & NOTEWORTHY Chronic kidney disease (CKD) is a major unmet medical need with no effective treatment. Current findings demonstrate that hepatic and proximal tubule angiotensinogen have distinct roles in tubular and glomerular injury, fibrogenesis, and renal dysfunction during CKD development. As renin-angiotensin system components, including angiotensinogen, are important targets for treating CKD in the clinic, the results from our study may be applied to developing better tissue-targeted treatment strategies for CKD and other fibroproliferative diseases.

Extracellular matrix-natural killer cell interactome: an uncharted territory in health and disease

Extracellular matrix (ECM) constantly undergoes remodeling to maintain the tissue homeostasis and an impaired ECM remodeling is a hallmark of many diseases, including cancer, infections, and inflammatory disorders. ECM has recently become recognized to regulate the immune response in peripheral tissues. Most immune cells express a diverse array of ECM receptors that, upon engagement by their cognate ECM ligands, can regulate their movement and effector functions. Natural killer (NK) cells are innate lymphocytes capable of mounting a swift cytotoxic immunity against cancer and virally infected cells using germline-encoded activating and inhibitory receptors. Regulation of NK cell effector function by ECM proteins in peripheral tissues is an emerging field with major implications for maintaining tolerance in normal tissues and controlling solid cancers, viral infections, and inflammatory diseases. The development of novel therapeutics targeting ECM-NK cell interplay represents a promising strategy to promote health and combat many diseases affecting solid organs.

Kidney-on-a-Chip: Mechanical Stimulation and Sensor Integration

Bioengineered in vitro models of the kidney offer unprecedented opportunities to better mimic the in vivo microenvironment. Kidney-on-a-chip technology reproduces 2D or 3D features which can replicate features of the tissue architecture, composition, and dynamic mechanical forces experienced by cells in vivo. Kidney cells are exposed to mechanical stimuli such as substrate stiffness, shear stress, compression, and stretch, which regulate multiple cellular functions. Incorporating mechanical stimuli in kidney-on-a-chip is critically important for recapitulating the physiological or pathological microenvironment. This review will explore approaches to applying mechanical stimuli to different cell types using kidney-on-a-chip models and how these systems are used to study kidney physiology, model disease, and screen for drug toxicity. We further discuss sensor integration into kidney-on-a-chip for monitoring cellular responses to mechanical or other pathological stimuli. We discuss the advantages, limitations, and challenges associated with incorporating mechanical stimuli in kidney-on-a-chip models for a variety of applications. Overall, this review aims to highlight the importance of mechanical stimuli and sensor integration in the design and implementation of kidney-on-a-chip devices.

Lactacystin-induced kidney fibrosis: Protection by melatonin and captopril

Lactacystin is a specific proteasome inhibitor that blocks the hydrolysis of intracellular proteins by ubiquitin/proteasome system inhibition. The administration of lactacystin to rats induced hypertension and remodeling of the left ventricle and aorta. This study tested whether lactacystin induces structural and fibrotic rebuilding of the kidneys and whether melatonin and captopril can prevent these potential changes. Six weeks of lactacystin administration to rats increased their average systolic blood pressure (SBP). In the kidneys, lactacystin reduced glomerular density, increased the glomerular tuft area, and enhanced hydroxyproline concentrations. It also elevated the intraglomerular proportion including the amounts of collagen (Col) I and Col III. Lactacystin also raised the tubulointerstitial amounts of Col I and the sum of Col I and Col III with no effect on vascular/perivascular collagen. Six weeks of captopril treatment reduced SBP, while melatonin had no effect. Both melatonin and captopril increased glomerular density, reduced the glomerular tuft area, and lowered the hydroxyproline concentration in the kidneys. Both drugs reduced the proportion and total amounts of intraglomerular and tubulointerstitial Col I and Col III. We conclude that chronic lactacystin treatment stimulated structural and fibrotic remodeling of the kidneys, and melatonin and captopril partly prevented these alterations. Considering the effect of lactacystin on both the heart and kidneys, chronic treatment with this drug may be a prospective model of cardiorenal damage suitable for testing pharmacological drugs as protective agents.

A Molecular Mechanism Study to Reveal Hirudin's Downregulation to PI3K/AKT Signaling Pathway through Decreasing PDGFRβ in Renal Fibrosis Treatment

Chronic kidney disease (CKD) is identified as a widespread chronic progressive disease jeopardizing public health which characterized by gradually loss of renal function. However, there is no efficient therapy to prevail over this disease. Our study was attempting to reveal hirudin's regulation to renal fibrosis as well as the molecular mechanism. We built renal fibrosis models on both cell and animal levels, which were subsequently given with hirudin disposal; then, we performed the transwell assay to estimate the cells' migration and had our detection to relevant proteins with western blot and immunofluorescence. Finally, we commenced both the identification and the determination to the hirudin targeted proteins and its downstream signaling pathways with the methods of network pharmacology. And the results turned out that when it was compared with the model group, the group with hirudin addition came with the suppression in the migration of renal tubular epithelial cells NRK-52E and with a conspicuous decline in the expressions of fibronectin, N-cadherin, vimentin, TGF-β, and snail. After that, we predicted that there were 17 hirudin target points mainly involving in the PI3K-AKT signaling pathway. Our outcomes of the animal level demonstrated that the conditions of interstitial fibrosis, severe tubular dilatation or atrophy, inflammatory cell infiltration, and massive accumulation of interstitial collagen in the model group were withdrawn after the addition of hirudin. In addition, p-PDGFRβ, p-PI3K, and p-AKT protein expressions were significantly reduced, and the PI3K/AKT pathway was downregulated after hirudin treatment in the model group of NRK-52E cells and animals. Therefore, we had our conclusion that hirudin is capable of suppressing the PI3K-AKT signaling pathway as well as the EMT by decreasing PDGFRβ phosphorylation.

Integrated bioinformatical analysis, machine learning and in vitro experiment-identified m6A subtype, and predictive drug target signatures for diagnosing renal fibrosis

Renal biopsy is the gold standard for defining renal fibrosis which causes calcium deposits in the kidneys. Persistent calcium deposition leads to kidney inflammation, cell necrosis, and is related to serious kidney diseases. However, it is invasive and involves the risk of complications such as bleeding, especially in patients with end-stage renal diseases. Therefore, it is necessary to identify specific diagnostic biomarkers for renal fibrosis. This study aimed to develop a predictive drug target signature to diagnose renal fibrosis based on m6A subtypes. We then performed an unsupervised consensus clustering analysis to identify three different m6A subtypes of renal fibrosis based on the expressions of 21 m6A regulators. We evaluated the immune infiltration characteristics and expression of canonical immune checkpoints and immune-related genes with distinct m6A modification patterns. Subsequently, we performed the WGCNA analysis using the expression data of 1,611 drug targets to identify 474 genes associated with the m6A modification. 92 overlapping drug targets between WGCNA and DEGs (renal fibrosis vs. normal samples) were defined as key drug targets. A five target gene predictive model was developed through the combination of LASSO regression and stepwise logistic regression (LASSO-SLR) to diagnose renal fibrosis. We further performed drug sensitivity analysis and extracellular matrix analysis on model genes. The ROC curve showed that the risk score (AUC = 0.863) performed well in diagnosing renal fibrosis in the training dataset. In addition, the external validation dataset further confirmed the outstanding predictive performance of the risk score (AUC = 0.755). These results indicate that the risk model has an excellent predictive performance for diagnosing the disease. Furthermore, our results show that this 5-target gene model is significantly associated with many drugs and extracellular matrix activities. Finally, the expression levels of both predictive signature genes EGR1 and PLA2G4A were validated in renal fibrosis and adjacent normal tissues by using qRT-PCR and Western blot method.

The progress and prospect of natural components in rhubarb (Rheum ribes L.) in the treatment of renal fibrosis

Background: Renal fibrosis is a key pathological change that occurs in the progression of almost all chronic kidney diseases . CKD has the characteristics of high morbidity and mortality. Its prevalence is increasing each year on a global scale, which seriously affects people’s health and quality of life. Natural products have been used for new drug development and disease treatment for many years. The abundant natural products in R. ribes L. can intervene in the process of renal fibrosis in different ways and have considerable therapeutic prospects.

Purpose: The etiology and pathology of renal fibrosis were analyzed, and the different ways in which the natural components of R. ribes L. can intervene and provide curative effects on the process of renal fibrosis were summarized. Methods: Electronic databases, such as PubMed, Life Science, MEDLINE, and Web of Science, were searched using the keywords ‘R. ribes L.’, ‘kidney fibrosis’, ‘emodin’ and ‘rhein’, and the various ways in which the natural ingredients protect against renal fibrosis were collected and sorted out.

Results: We analyzed several factors that play a leading role in the pathogenesis of renal fibrosis, such as the mechanism of the TGF-β/Smad and Wnt/β-catenin signaling pathways. Additionally, we reviewed the progress of the treatment of renal fibrosis with natural components in R. ribes L. and the intervention mechanism of the crucial therapeutic targets.

Conclusion: The natural components of R. ribes L. have a wide range of intervention effects on renal fibrosis targets, which provides new ideas for the development of new anti-kidney fibrosis drugs.

The interstitium at the developing nephron in the fetal kidney during advanced pregnancy - a microanatomical inventory

Background

A series of noxae can evoke the termination of nephron formation in preterm and low birth weight babies. This results in oligonephropathy with severe consequences for health in the later life. Although the clinical parameters have been extensively investigated, little is known about the initial damage. Previous pathological findings indicate the reduction in width of the nephrogenic zone and the lack of S-shaped bodies. Current morphological investigations suggest that due to the mutual patterning beside the forming nephron, also its structural neighbors, particularly the interjacent interstitium, must be affected. However, beside the findings on integrative and mastering functions, systematic microanatomical data explaining the configuration of the interstitium at the developing nephron in the fetal kidney during advanced pregnancy is not available. Therefore, this work explains the typical features.

Results

The generated data depicts that the progenitor cells, nephrogenic niche, pretubular aggregate, and mesenchymal-to-epithelial transition are restricted to the subcapsular interstitium. During the proceeding development, only the distal pole of the renal vesicles and comma- and S-shaped bodies stays in further contact with it. The respective proximal pole is positioned opposite the peritubular interstitium at the connecting tubule of an underlying but previously formed nephron. The related medial aspect faces the narrow peritubular interstitium of a collecting duct (CD) ampulla first only at its tip, then at its head, conus, and neck, and finally at the differentiating CD tubule. The lateral aspect starts at the subcapsular interstitium, but then it is positioned along the wide perivascular interstitium of the neighboring ascending perforating radiate artery. When the nephron matures, the interstitial configuration changes again.

Conclusions

The present investigation illustrates that the interstitium at the forming nephron in the fetal kidney consists of existing, transient, stage-specific, and differently far matured compartments. According to the developmental needs, it changes its shape by formation, degradation, fusion, and rebuilding.

Natural products: potential drugs for the treatment of renal fibrosis

With the increasing prevalence and mortality, chronic kidney disease (CKD) has become a world public health problem. As the primary pathological manifestation in CKD, renal fibrosis is often used as a critical target for the treatment of CKD and inhibits the progression of CKD to end-stage renal disease (ESRD). As a potential drug, natural products have been confirmed to have the potential as a routine or supplementary therapy for chronic kidney disease, which may target renal fibrosis and act through various pharmacological activities such as anti-inflammatory and anti-oxidation of natural products. This article briefly introduces the pathological mechanism of renal fibrosis and systematically summarizes the latest research on the treatment of renal fibrosis with natural products of Chinese herbal medicines.

The fibrogenic niche in kidney fibrosis: components and mechanisms

Kidney fibrosis, characterized by excessive deposition of extracellular matrix (ECM) that leads to tissue scarring, is the final common outcome of a wide variety of chronic kidney diseases. Rather than being distributed uniformly across the kidney parenchyma, renal fibrotic lesions initiate at certain focal sites in which the fibrogenic niche is formed in a spatially confined fashion. This niche provides a unique tissue microenvironment that is orchestrated by a specialized ECM network consisting of de novo-induced matricellular proteins. Other structural elements of the fibrogenic niche include kidney resident and infiltrated inflammatory cells, extracellular vesicles, soluble factors and metabolites. ECM proteins in the fibrogenic niche recruit soluble factors including WNTs and transforming growth factor-β from the extracellular milieu, creating a distinctive profibrotic microenvironment. Studies using decellularized ECM scaffolds from fibrotic kidneys show that the fibrogenic niche autonomously promotes fibroblast proliferation, tubular injury, macrophage activation and endothelial cell depletion, pathological features that recapitulate key events in the pathogenesis of chronic kidney disease. The concept of the fibrogenic niche represents a paradigm shift in understanding of the mechanism of kidney fibrosis that could lead to the development of non-invasive biomarkers and novel therapies not only for chronic kidney disease, but also for fibrotic diseases of other organs.

Renoprotection of Microcystin-RR in Unilateral Ureteral Obstruction-Induced Renal Fibrosis: Targeting the PKM2-HIF-1α Pathway

Renal fibrosis is a pathological characteristic of the endpoint of chronic kidney disease (CKD), which remains a major public health problem. None of the current therapies is effective in stopping kidney fibrosis progression. In light of our novel detection of a potential antifibrosis of microcystins (MCs), we investigate the renoprotection effect of MCs with UUO-induced renal fibrosis. The treatment of MCs was initiated in model animals in advance of UUO operation. After determining that the antifibrotic effect of MCs was independent of its toxicity, our study focused on the renoprotection of microcystin-RR (MC-RR), a lower toxic congener of MCs, in UUO mice and the cell models in vitro. The co-immunoprecipitation assay and recombination plasmid transfection were used in the investigation of the mechanism of antifibrosis of MC-RR. The data show that MC-RR substantially exerts an effect on renoprotection with suppression of the expression of TGF-β1/Smad signaling molecules and a blockage in epithelial dedifferentiation and myofibroblast activation in UUO model animals. MC-RR shows a binding directly to pyruvate kinase M2 (PKM2), downregulates PKM2-HIF-1α signaling, restores the inhibited expression of MMP-7 and MMP-13, and reduces the upregulated expression of MMP-9 in UUO renal tissues. The current study demonstrates a novel effect of MC-RR on renoprotection in kidney damage, which could be conducted in therapeutics for chronic kidney disease.

Research Progress of Chinese Herbal Medicine Intervention in Renal Interstitial Fibrosis

Chronic kidney diseases usually cause renal interstitial fibrosis, the prevention, delay, and treatment of which is a global research hotspot. However, no definite treatment options are available in modern medicine. Chinese herbal medicine has a long history, rich varieties, and accurate treatment effects. Hitherto, many Chinese herbal medicine studies have emerged to improve renal interstitial fibrosis. This paper reviews the mechanisms of renal interstitial fibrosis and recent studies on the disease intervention with Chinese herbal medicine through literature search, intend to reveal the importance of Chinese herbal medicine in renal interstitial fibrosis. The results show that Chinese herbal medicine can improve renal interstitial fibrosis, and the effects of Chinese herbal medicine on specific pathological mechanisms underlying renal interstitial fibrosis have been explored. Additionally, the limitations and advantages of Chinese herbal medicine in the treatment of renal interstitial fibrosis, possible research directions, and new targets of Chinese herbal medicine are discussed to provide a basis for studies of renal interstitial fibrosis.

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.

A diabetic milieu increases ACE2 expression and cellular susceptibility to SARS-CoV-2 infections in human kidney organoids and patient cells

It is not well understood why diabetic individuals are more prone to develop severe COVID-19. To this, we here established a human kidney organoid model promoting early hallmarks of diabetic kidney disease development. Upon SARS-CoV-2 infection, diabetic-like kidney organoids exhibited higher viral loads compared with their control counterparts. Genetic deletion of the angiotensin-converting enzyme 2 (ACE2) in kidney organoids under control or diabetic-like conditions prevented viral detection. Moreover, cells isolated from kidney biopsies from diabetic patients exhibited altered mitochondrial respiration and enhanced glycolysis, resulting in higher SARS-CoV-2 infections compared with non-diabetic cells. Conversely, the exposure of patient cells to dichloroacetate (DCA), an inhibitor of aerobic glycolysis, resulted in reduced SARS-CoV-2 infections. Our results provide insights into the identification of diabetic-induced metabolic programming in the kidney as a critical event increasing SARS-CoV-2 infection susceptibility, opening the door to the identification of new interventions in COVID-19 pathogenesis targeting energy metabolism.

Blocking connexin 43 and its promotion of ATP release from renal tubular epithelial cells ameliorates renal fibrosis

Whether metabolites derived from injured renal tubular epithelial cells (TECs) participate in renal fibrosis is poorly explored. After TEC injury, various metabolites are released and among the most potent is adenosine triphosphate (ATP), which is released via ATP-permeable channels. In these hemichannels, connexin 43 (Cx43) is the most common member. However, its role in renal interstitial fibrosis (RIF) has not been fully examined. We analyzed renal samples from patients with obstructive nephropathy and mice with unilateral ureteral obstruction (UUO). Cx43-KSP mice were generated to deplete Cx43 in TECs. Through transcriptomics, metabolomics, and single-cell sequencing multi-omics analysis, the relationship among tubular Cx43, ATP, and macrophages in renal fibrosis was explored. The expression of Cx43 in TECs was upregulated in both patients and mice with obstructive nephropathy. Knockdown of Cx43 in TECs or using Cx43-specific inhibitors reduced UUO-induced inflammation and fibrosis in mice. Single-cell RNA sequencing showed that ATP specific receptors, including P2rx4 and P2rx7, were distributed mainly on macrophages. We found that P2rx4- or P2rx7-positive macrophages underwent pyroptosis after UUO, and in vitro ATP directly induced pyroptosis by macrophages. The administration of P2 receptor or P2X7 receptor blockers to UUO mice inhibited macrophage pyroptosis and demonstrated a similar degree of renoprotection as Cx43 genetic depletion. Further, we found that GAP 26 (a Cx43 hemichannel inhibitor) and A-839977 (an inhibitor of the pyroptosis receptor) alleviated UUO-induced fibrosis, while BzATP (the agonist of pyroptosis receptor) exacerbated fibrosis. Single-cell sequencing demonstrated that the pyroptotic macrophages upregulated the release of CXCL10, which activated intrarenal fibroblasts. Cx43 mediates the release of ATP from TECs during renal injury, inducing peritubular macrophage pyroptosis, which subsequently leads to the release of CXCL10 and activation of intrarenal fibroblasts and acceleration of renal fibrosis.

Extracellular Vesicles Mediate Immune Responses to Tissue-Associated Self-Antigens: Role in Solid Organ Transplantations

Transplantation is a treatment option for patients diagnosed with end-stage organ diseases; however, long-term graft survival is affected by rejection of the transplanted organ by immune and nonimmune responses. Several studies have demonstrated that both acute and chronic rejection can occur after transplantation of kidney, heart, and lungs. A strong correlation has been reported between de novo synthesis of donor-specific antibodies (HLA-DSAs) and development of both acute and chronic rejection; however, some transplant recipients with chronic rejection do not have detectable HLA-DSAs. Studies of sera from such patients demonstrate that immune responses to tissue-associated antigens (TaAgs) may also play an important role in the development of chronic rejection, either alone or in combination with HLA-DSAs. The synergistic effect between HLA-DSAs and antibodies to TaAgs is being established, but the underlying mechanism is yet to be defined. We hypothesize that HLA-DSAs damage the transplanted donor organ resulting in stress and leading to the release of extracellular vesicles, which contribute to chronic rejection. These vesicles express both donor human leukocyte antigen (HLA) and non-HLA TaAgs, which can activate antigen-presenting cells and lead to immune responses and development of antibodies to both donor HLA and non-HLA tissue-associated Ags. Extracellular vesicles (EVs) are released by cells under many circumstances due to both physiological and pathological conditions. Primarily employing clinical specimens obtained from human lung transplant recipients undergoing acute or chronic rejection, our group has demonstrated that circulating extracellular vesicles display both mismatched donor HLA molecules and lung-associated Ags (collagen-V and K-alpha 1 tubulin). This review focuses on recent studies demonstrating an important role of antibodies to tissue-associated Ags in the rejection of transplanted organs, particularly chronic rejection. We will also discuss the important role of extracellular vesicles released from transplanted organs in cross-talk between alloimmunity and autoimmunity to tissue-associated Ags after solid organ transplantation.

Genetic Disorders of the Extracellular Matrix: From Cell and Gene Therapy to Future Applications in Regenerative Medicine

Metazoans have evolved to produce various types of extracellular matrix (ECM) that provide structural support, cell adhesion, cell-cell communication, and regulated exposure to external cues. Epithelial cells produce and adhere to a specialized sheet-like ECM, the basement membrane, that is critical for cellular homeostasis and tissue integrity. Mesenchymal cells, such as chondrocytes in cartilaginous tissues and keratocytes in the corneal stroma, produce a pericellular matrix that presents optimal levels of growth factors, cytokines, chemokines, and nutrients to the cell and regulates mechanosensory signals through specific cytoskeletal and cell surface receptor interactions. Here, we discuss laminins, collagen types IV and VII, and perlecan, which are major components of these two types of ECM. We examine genetic defects in these components that cause basement membrane pathologies such as epidermolysis bullosa, Alport syndrome, rare pericellular matrix-related chondrodysplasias, and corneal keratoconus and discuss recent advances in cell and gene therapies being developed for some of these disorders. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Effect of crude Ganoderma applanatum polysaccharides as a renoprotective agent against carbon tetrachloride-induced early kidney fibrosis in mice

Background and Aim:

Interstitial fibrosis is the final stage of chronic kidney injury, which begins with an inflammatory process. Crude Ganoderma applanatum polysaccharides are known to have anti-inflammatory properties. The potential role of crude G. applanatum polysaccharides in renal fibrosis through pro-inflammatory cytokines needs further investigation. This study aimed to determine the renoprotective effect of crude G. applanatum polysaccharide extract in mice with carbon tetrachloride (CCL₄)-induced early kidney fibrosis.

Materials and Methods:

This study was conducted for 4 weeks using 24 male BALB/c mice selected for their metabolic stability. The mice were randomly divided into six groups, including control (CG), model (MG), silymarin group and crude G. applanatum polysaccharide extract groups comprising doses of 25, 50, and 100 mg/kg body weight. After sacrificing the mice, whole blood was analyzed for urea and creatine levels, and kidney tissue was prepared to assess tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), hyaluronic acid (HA), and laminin levels, both using enzyme-linked immunosorbent assay. Kidney histology was determined using hematoxylin and eosin staining, while the extracellular matrix (ECM) components were stained using Masson’s trichome staining. The α-smooth muscle actin (α-SMA) concentration was determined using immunohistochemistry. These parameters were measured to determine the effectiveness of the crude G. applanatum polysaccharide extract in preventing interstitial fibrosis.

Results:

Administration of crude G. applanatum polysaccharides effectively prevented increases in kidney weight and physiological enzymes, pro-inflammatory cytokines, and ECM production compared with those in the MG, as evidenced by the low levels of urea, creatinine, TNF-α, IL-6, HA, and laminin. Histopathological results also showed that crude G. applanatum polysaccharides prevented the occurrence of inflammatory infiltration, desquamated nuclei, cytoplasm debris, rupture at the brush border, dilatation of the glomeruli space and lumen of the proximal tubule, and necrotic cells compared with the MG. Masson’s trichrome staining revealed lower collagen levels in the interstitial tubules of kidney tissue than those in the MG. Immunohistochemical analysis revealed low α-SMA expression in the crude G. applanatum polysaccharides treatment groups than that in the MG.

Conclusion:

The crude polysaccharide extract of G. applanatum has a protective effect that prevents the progression of kidney fibrosis in mice.

Toxicity of benzyl benzoate as a food additive and pharmaceutical agent

Benzyl benzoate (BB), one of the benzyl derivates, is a component of brown aromatic resin in cinnamon oil and cough syrups and it is widely used in various fields in the perfume, pharmaceutical, and food industries. It is absorbed and hydrolyzed to benzoic acid and benzyl alcohol. Two different doses of BB (25 mg kg-1 body weight and 100 mg kg-1 body weight) were orally administered to 5-week old male rats for 90 days. Histopathological, morphological, hematological, and biochemical assays were performed in toxicological evaluations. Initial/final body weights, relative organ weights, and food and water consumptions of rats did not change significantly. There were statistically significant differences in terms of monocyte, neutrophil, lymphocyte %, and serum AST levels in control and BB treatment groups. Several histopathological findings were observed in liver, kidney, thymus, prostate, and epididymis tissues of the rats in the treatment groups. Immunohistochemical examinations were also performed in the tissues for fibronectin (FN), type IV collagen, transforming growth factor β (TGF-β), matrix metalloproteinase-2 (MMP-2), and tissue inhibitor of metalloproteinase-2 (TIMP-2). Alterations in immunolocalization of these markers were observed between the control and the treatment groups. No changes were detected in the sperm count, daily sperm production, and sperm morphology.

Epithelial–Fibroblast Crosstalk Protects against Acidosis-Induced Inflammatory and Fibrotic Alterations

Pathogenesis of chronic kidney disease (CKD) is accompanied by extracellular acidosis inflammation, fibrosis and epithelial-to-mesenchymal transition (EMT). The aim of this study was to assess the influence of acidosis on tubule epithelial cells (NRK-52E) and fibroblasts (NRK-49F) in dependence of cellular crosstalk. NRK-52E and NRK-49F were used in mono- and co-cultures, and were treated with acidic media (pH 6.0) for 48 h. The intracellular proteins were measured by Western blot. Secreted proteins were measured by ELISA. Distribution of E-cadherin was assessed by immunofluorescence and epithelial barrier function by FITC-dextran diffusion. Inflammation: Acidosis led to an increase in COX-2 in NRK-52E and TNF in NRK-49F in monoculture. In co-culture, this effect was reversed. EMT: Acidosis led to an increase in vimentin protein in both cell lines, whereas in co-culture, the effect was abolished. In NRK-52E, the E-cadherin expression was unchanged, but subcellular E-cadherin showed a disturbed distribution, and cellular barrier function was decreased. Fibrosis: Monoculture acidosis led to an increased secretion of collagen I and fibronectin in NRK-52E and collagen I in NRK-49F. In co-culture, the total collagen I secretion was unchanged, and fibronectin secretion was decreased. Intercellular crosstalk between epithelial cells and fibroblasts has a protective function regarding the development of acidosis-induced damage.

First Characterization of ADAMTS-4 in Kidney Tissue and Plasma of Patients with Chronic Kidney Disease-A Potential Novel Diagnostic Indicator

Background: We have previously shown that metzincin protease ADAMTS-4 accompanies renal fibrogenesis, as it appears in the blood of hemodialysis patients. Methods: Native kidney (NKB) and kidney transplant (TXCI) biopsy samples as well as plasma from patients with various stages of CKD were compared to controls. In paired analysis, 15 TXCI samples were compared with their zero-time biopsies (TX0). Tissues were evaluated and scored (interstitial fibrosis and tubular atrophy (IFTA) for NKB and Banff ci for TXCI). Immunohistochemical (IHC) staining for ADAMTS-4 and BMP-1 was performed. Plasma ADAMTS-4 was detected using ELISA. Results: ADAMTS-4 IHC expression was significantly higher in interstitial compartment (INT) of NKB and TXCI group in peritubular capillaries (PTC) and interstitial stroma (INT). Patients with higher stages of interstitial fibrosis (ci > 1 and IFTA > 1) expressed ADAMTS-4 in INT more frequently in both groups (p = 0.005; p = 0.013; respectively). In paired comparison, TXCI samples expressed ADAMTS-4 in INT and PTC more often than TX0. ADAMTS-4 plasma concentration varied significantly across CKD stages, being highest in CKD 2 and 3 compared to other groups (p = 0.0064). Hemodialysis patients had higher concentrations of ADAMTS-4 compared to peritoneal dialysis (p < 0.00001). Conclusion: ADAMTS-4 might have a significant role in CKD as a potential novel diagnostic indicator.

RNA-binding proteins and their role in kidney disease

RNA-binding proteins (RBPs) are of fundamental importance for post-transcriptional gene regulation and protein synthesis. They are required for pre-mRNA processing and for RNA transport, degradation and translation into protein, and can regulate every step in the life cycle of their RNA targets. In addition, RBP function can be modulated by RNA binding. RBPs also participate in the formation of ribonucleoprotein complexes that build up macromolecular machineries such as the ribosome and spliceosome. Although most research has focused on mRNA-binding proteins, non-coding RNAs are also regulated and sequestered by RBPs. Functional defects and changes in the expression levels of RBPs have been implicated in numerous diseases, including neurological disorders, muscular atrophy and cancers. RBPs also contribute to a wide spectrum of kidney disorders. For example, human antigen R has been reported to have a renoprotective function in acute kidney injury (AKI) but might also contribute to the development of glomerulosclerosis, tubulointerstitial fibrosis and diabetic kidney disease (DKD), loss of bicaudal C is associated with cystic kidney diseases and Y-box binding protein 1 has been implicated in the pathogenesis of AKI, DKD and glomerular disorders. Increasing data suggest that the modulation of RBPs and their interactions with RNA targets could be promising therapeutic strategies for kidney diseases.

Selenium Deficiency Leads to Changes in Renal Fibrosis Marker Proteins and Wnt/β-Catenin Signaling Pathway Components

Renal fibrosis is the final result of the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD). Earlier studies confirmed that selenium (Se) displays a close association with kidney diseases. However, the correlation between Se and fibrosis has rarely been explored. Thus, this article mainly aimed to investigate the effect of Se deficiency on renal fibrosis and the Wnt/β-catenin signaling pathway. Twenty BALB/c mice were fed a diet containing 0.02-mg/kg Se (Se-deficient diet) or 0.18-mg/kg Se (standard diet) for 20 weeks. A human glomerular mesangial cell (HMC) cell line was transfected with lentiviral TRNAU1AP-shRNA vector to establish a stable Se deficiency model in vitro. As indicated in this study, the glutathione (GSH) content in the Se-deficient group displayed an obvious decline compared with that in the control group, whereas the content of malondialdehyde (MDA) was obviously elevated. The results of Masson staining showed fibrosis around the renal tubules, and the results of immunohistochemistry showed that the area of positive fibronectin expression increased. In the Se-deficient group, the levels of collagen I, collagen III, matrix metalloproteinase 9 (MMP9), and other fibrosis-related proteins changed significantly in vivo and in vitro. Compared with the control group, the TRNAU1AP-shRNA group showed markedly reduced cell proliferation and migration abilities. Our data indicate that Se deficiency can cause kidney damage and renal fibrosis. Furthermore, the Wnt pathway is critical for the development of tissue and organ fibrosis. The data of this study demonstrated that the expression of Wnt5a, β-catenin, and dishevelled 1 (Dvl-1) was significantly upregulated in the Se-deficient group. Therefore, the Wnt/β-catenin pathway may play an important role in renal fibrosis caused by Se deficiency.

The Proteome of Antibody-Mediated Rejection: From Glomerulitis to Transplant Glomerulopathy

Antibody-mediated rejection (ABMR) is the leading cause of allograft failure in kidney transplantation. Its histological hallmark is represented by lesions of glomerulitis i.e., inflammatory cells within glomeruli. Current therapies for ABMR fail to prevent chronic allograft damage i.e., transplant glomerulopathy, leading to allograft loss. We used laser microdissection of glomeruli from formalin-fixed allograft biopsies combined with mass spectrometry-based proteomics to describe the proteome modification of 11 active and 10 chronic active ABMR cases compared to 8 stable graft controls. Of 1335 detected proteins, 77 were deregulated in glomerulitis compared to stable grafts, particularly involved in cellular stress mediated by interferons type I and II, leukocyte activation and microcirculation remodeling. Three proteins extracted from this protein profile, TYMP, WARS1 and GBP1, showed a consistent overexpression by immunohistochemistry in glomerular endothelial cells that may represent relevant markers of endothelial stress during active ABMR. In transplant glomerulopathy, 137 proteins were deregulated, which favor a complement-mediated mechanism, wound healing processes through coagulation activation and ultimately a remodeling of the glomerular extracellular matrix, as observed by light microscopy. This study brings novel information on glomerular proteomics of ABMR in kidney transplantation, and highlights potential targets of diagnostic and therapeutic interest.

The Glomerulus According to the Mesangium

The glomerulus is the functional unit for filtration of blood and formation of primary urine. This intricate structure is composed of the endothelium with its glycocalyx facing the blood, the glomerular basement membrane and the podocytes facing the urinary space of Bowman's capsule. The mesangial cells are the central hub connecting and supporting all these structures. The components as a unit ensure a high permselectivity hindering large plasma proteins from passing into the urine while readily filtering water and small solutes. There has been a long-standing interest and discussion regarding the functional contribution of the different cellular components but the mesangial cells have been somewhat overlooked in this context. The mesangium is situated in close proximity to all other cellular components of the glomerulus and should be considered important in pathophysiological events leading to glomerular disease. This review will highlight the role of the mesangium in both glomerular function and intra-glomerular crosstalk. It also aims to explain the role of the mesangium as a central component involved in disease onset and progression as well as signaling to maintain the functions of other glomerular cells to uphold permselectivity and glomerular health.

Aryl Hydrocarbon Receptor Mechanisms Affecting Chronic Kidney Disease

The aryl hydrocarbon receptor (AHR) is a basic helix-loop-helix transcription factor that binds diverse endogenous and xenobiotic ligands, which regulate AHR stability, transcriptional activity, and cell signaling. AHR activity is strongly implicated throughout the course of chronic kidney disease (CKD). Many diverse organic molecules bind and activate AHR and these ligands are reported to either promote glomerular and tubular damage or protect against kidney injury. AHR crosstalk with estrogen, peroxisome proliferator-activated receptor-γ, and NF-κB pathways may contribute to the diversity of AHR responses during the various forms and stages of CKD. The roles of AHR in kidney fibrosis, metabolism and the renin angiotensin system are described to offer insight into CKD pathogenesis and therapies.

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.

Kidney organoids: current knowledge and future directions

The kidney is a highly complex organ in the human body. Although creating an in vitro model of the human kidney is challenging, tremendous advances have been made in recent years. Kidney organoids are in vitro kidney models that are generated from stem cells in three-dimensional (3D) cultures. They exhibit remarkable degree of similarities with the native tissue in terms of cell type, morphology, and function. The establishment of 3D kidney organoids facilitates a mechanistic study of cell communications, and these organoids can be used for drug screening, disease modeling, and regenerative medicine applications. This review discusses the cellular complexity during in vitro kidney generation. We intend to highlight recent progress in kidney organoids and the applications of these relatively new technologies.

Midazolam Ameliorates Hyperglycemia-Induced Glomerular Endothelial Dysfunction by Inhibiting Transglutaminase 2 in Diabetes

Midazolam is an anesthetic widely used for anxiolysis and sedation; however, to date, a possible role for midazolam in diabetic kidney disease remains unknown. Here, we investigated the effect of midazolam on hyperglycemia-induced glomerular endothelial dysfunction and elucidated its mechanism of action in kidneys of diabetic mice and human glomerular microvascular endothelial cells (HGECs). We found that, in diabetic mice, subcutaneous midazolam treatment for 6 weeks attenuated hyperglycemia-induced elevation in urine albumin/creatinine ratios. It also ameliorated hyperglycemia-induced adherens junction disruption and subsequent microvascular leakage in glomeruli of diabetic mice. In HGECs, midazolam suppressed high glucose-induced vascular endothelial-cadherin disruption and endothelial cell permeability via inhibition of intracellular Ca²⁺ elevation and subsequent generation of reactive oxygen species (ROS) and transglutaminase 2 (TGase2) activation. Notably, midazolam also suppressed hyperglycemia-induced ROS generation and TGase2 activation in glomeruli of diabetic mice and markedly improved pathological alterations in glomerular ultrastructure in these animals. Analysis of kidneys from diabetic Tgm2^−/− mice further revealed that TGase2 played a critical role in microvascular leakage. Overall, our findings indicate that midazolam ameliorates hyperglycemia-induced glomerular endothelial dysfunction by inhibiting ROS-mediated activation of TGase2.

Effects of estimated glomerular filtration rate on clinical outcomes in patients with intracerebral hemorrhage

BACKGROUND

The influence of chronic kidney disease (CKD) on the severity and prognosis of spontaneous intracerebral hemorrhage (ICH) has been scarcely investigated. We aimed to explore the association of admission estimated glomerular filtration rate (eGFR) levels with hemorrhagic stroke severity and outcomes in ICH patients.

MATERIALS AND METHODS

The patients enrolled in this study were from the China Stroke Center Alliance study (CSCA). Patients were divided into four groups according to differences in eGFR at admission (≥90; 60-89; 45-59; < 45). Multivariable logistic regression analysis was used to determine the association of the eGFR at admission with hemorrhagic stroke severity, in-hospital complications, discharge disposition, and in-hospital mortality after ICH.

RESULTS

A total of 85,167 patients with acute ICH were included in the analysis. Among them, 9493 (11.1%) had a baseline eGFR<60 ml/min/1.73 m2. A low eGFR was associated with an increased risk of in-hospital mortality [eGFR 60-89 ml/min/1.73 m2, odds ratio (OR) 1.36 (95% confidence interval (CI) 1.21-1.53); eGFR 45-59, 2.35 (1.97-2.82); eGFR<45, 4.18 (3.7-4.72); P for trend < 0.0001], non-routine discharge [eGFR 60-89, 1.11 (1.03-1.2); eGFR 45-59, 1.16 (1-1.35); eGFR<45, 1.37 (1.23-1.53); P for trend < 0.0001], hemorrhagic stroke severity [eGFR 60-89, 1 (0.95-1.05); eGFR 45-59, 1.39 (1.26-1.53); eGFR<45, 1.81 (1.67-1.96); P for trend < 0.0001], in-hospital complications of pneumonia [eGFR 60-89, 1.1 (1.05-1.14); eGFR 45-59, 1.3 (1.2-1.4); eGFR<45, 1.66 (1.57-1.76); P for trend < 0.0001] and hydrocephalus [eGFR 60-89, 0.99 (0.87-1.12); eGFR 45-59, 1.37 (1.1-1.7); eGFR<45, 1.54 (1.32-1.8); P for trend = 0.0139] after adjusting for confounding factors. With the decline in eGFR, the risk of hematoma evacuation increased in patients with an eGFR 45 to 59 ml/min/1.73 m2 (OR 1.48; 95% CI 1.37-1.61). No significant association between differences in eGFR at baseline and in-hospital complication of recurrent intracerebral hemorrhage was observed.

CONCLUSIONS

Low eGFR at baseline was associated with an increased risk of in-hospital mortality, non-routine discharge, hemorrhagic stroke severity and in-hospital complications such as pneumonia, hydrocephalus and hematoma evacuation in acute ICH patients.

Shifting Paradigms for Suppressing Fibrosis in Kidney Transplants: Supplementing Perfusion Solutions With Anti-fibrotic Drugs

Great efforts have been made toward addressing the demand for donor kidneys. One of the most promising approaches is to use kidneys from donation after circulatory death donors. These kidneys, however, suffer from more severe ischemia and reperfusion injury than those obtained via donation after brain death and are thus more prone to develop interstitial fibrosis and tubular atrophy. Even though machine perfusion is increasingly used to reduce ischemia and reperfusion injury, there are no effective treatments available to ameliorate interstitial fibrosis and tubular atrophy, forcing patients to resume dialysis, undergo re-transplantation, or suffer from premature death. Safe and effective anti-fibrotic therapies are therefore greatly desired. We propose a new therapeutic approach in which machine perfusion solutions are supplemented with anti-fibrotic compounds. This allows the use of higher concentrations than those used in humans whilst eliminating side effects in other organs. To the authors' knowledge, no one has reviewed whether such an approach could reduce interstitial fibrosis and tubular atrophy; we therefore set out to explore its merit. In this review, we first provide background information on ischemia and reperfusion injury as well as interstitial fibrosis and tubular atrophy, after which we describe currently available approaches for preserving donor kidneys. We then present an evaluation of selected compounds. To identify promising compounds, we analyzed publications describing the effects of anti-fibrotic molecules in precision-cut kidneys slices, which are viable explants that can be cultured ex vivo for up to a few days whilst retaining functional and structural features. LY2109761, galunisertib, imatinib, nintedanib, and butaprost were shown to exert anti-fibrotic effects in slices within a relatively short timeframe (<48 h) and are therefore considered to be excellent candidates for follow-up ex vivo machine perfusion studies.

The cell membrane repair protein MG53 modulates transcription factor NF-κB signaling to control kidney fibrosis

Kidney fibrosis is associated with the progression of acute kidney injury to chronic kidney disease. MG53, a cell membrane repair protein, has been shown to protect against injury to kidney epithelial cells and acute kidney injury. Here, we evaluated the role of MG53 in modulation of kidney fibrosis in aging mice and in mice with unilateral ureteral obstruction (UUO) a known model of progressive kidney fibrosis. Mice with ablation of MG53 developed more interstitial fibrosis with age than MG53-intact mice of the same age. Similarly, in the absence of MG53, kidney fibrosis was exaggerated compared to mice with intact MG53 in the obstructed kidney compared to the contralateral unobstructed kidney or the kidneys of sham operated mice. The ureteral obstructed kidneys from MG53 deficient mice also showed significantly more inflammation than ureteral obstructed kidneys from MG53 intact mice. In vitro experiments demonstrated that MG53 could enter the nuclei of proximal tubular epithelial cells and directly interact with the p65 component of transcription factor NF-κB, providing a possible explanation of enhanced inflammation in the absence of MG53. To test this, enhanced MG53 expression through engineered cells or direct recombinant protein delivery was given to mice subject to UUO. This reduced NF-κB activation and inflammation and attenuated kidney fibrosis. Thus, MG53 may have a therapeutic role in treating chronic kidney inflammation and thereby provide protection against fibrosis that leads to the chronic kidney disease phenotype.

Endogenously-Produced Hyaluronan and Its Potential to Regulate the Development of Peritoneal Adhesions

Formation of peritoneal adhesions (PA) is one of the major complications following intra-abdominal surgery. It is primarily caused by activation of the mesothelial layer and underlying tissues in the peritoneal membrane resulting in the transition of mesothelial cells (MCs) and fibroblasts to a pro-fibrotic phenotype. Pro-fibrotic transition of MCs—mesothelial-to-mesenchymal transition (MMT), and fibroblasts activation to myofibroblasts are interconnected to changes in cellular metabolism and culminate in the deposition of extracellular matrix (ECM) in the form of fibrotic tissue between injured sides in the abdominal cavity. However, ECM is not only a mechanical scaffold of the newly synthetized tissue but reciprocally affects fibrosis development. Hyaluronan (HA), an important component of ECM, is a non-sulfated glycosaminoglycan consisting of N-acetyl-D-glucosamine (GlcNAc) and D-glucuronic acid (GlcUA) that can affect the majority of processes involved in PA formation. This review considers the role of endogenously produced HA in the context of different fibrosis-related pathologies and its overlap in the development of PA.

Drug-Induced Nephrotoxicity Assessment in 3D Cellular Models

The kidneys are often involved in adverse effects and toxicity caused by exposure to foreign compounds, chemicals, and drugs. Early predictions of these influences are essential to facilitate new, safe drugs to enter the market. However, in current drug treatments, drug-induced nephrotoxicity accounts for 1/4 of reported serious adverse reactions, and 1/3 of them are attributable to antibiotics. Drug-induced nephrotoxicity is driven by multiple mechanisms, including altered glomerular hemodynamics, renal tubular cytotoxicity, inflammation, crystal nephropathy, and thrombotic microangiopathy. Although the functional proteins expressed by renal tubules that mediate drug sensitivity are well known, current in vitro 2D cell models do not faithfully replicate the morphology and intact renal tubule function, and therefore, they do not replicate in vivo nephrotoxicity. The kidney is delicate and complex, consisting of a filter unit and a tubular part, which together contain more than 20 different cell types. The tubular epithelium is highly polarized, and maintaining cellular polarity is essential for the optimal function and response to environmental signals. Cell polarity depends on the communication between cells, including paracrine and autocrine signals, as well as biomechanical and chemotaxis processes. These processes affect kidney cell proliferation, migration, and differentiation. For drug disposal research, the microenvironment is essential for predicting toxic reactions. This article reviews the mechanism of drug-induced kidney injury, the types of nephrotoxicity models (in vivo and in vitro models), and the research progress related to drug-induced nephrotoxicity in three-dimensional (3D) cellular culture models.

Assessing and counteracting fibrosis is a cornerstone of the treatment of CKD secondary to systemic and renal limited autoimmune disorders

Chronic kidney disease (CKD) is an increasing cause of morbidity and mortality worldwide. Besides the higher prevalence of diabetes, hypertension and aging worldwide, immune mediated disorders remain an important cause of kidney disease and are especially prevalent in young adults. Regardless of the initial insult, final pathway to CKD and kidney failure is always the loss of normal tissue and fibrosis development, in which the dynamic equilibrium between extracellular matrix synthesis and degradation is disturbed, leading to excessive production and accumulation. During fibrosis, a multitude of cell types intervene at different levels, but myofibroblasts and inflammatory cells are considered critical in the process. They exert their effects through different molecular pathways, of which transforming growth factor β (TGF-β) has demonstrated to be of particular importance. Additionally, CKD itself promotes fibrosis due to the accumulation of toxins and hormonal changes, and proteinuria is simultaneously a manifestation of CKD and a specific driver of renal fibrosis. Pathways involved in renal fibrosis and CKD are closely interrelated, and although important advances have been made in our knowledge of them, it is still necessary to translate them into clinical practice. Given the complexity of this process, it is highly likely that its treatment will require a multi-target strategy to control the origin of the damage but also the mechanisms that perpetuate it. Fortunately, rapid technology development over the last years and new available drugs in the nephrologist's armamentarium give reasons for optimism that more personalized assistance for CKD and renal fibrosis will appear in the future.

Identification of Galectin-3 as Potential Biomarkers for Renal Fibrosis by RNA-Sequencing and Clinicopathologic Findings of Kidney Biopsy

Background: Galectin-3 (Gal-3) is a multifunctional glycan-binding protein shown to be linked to chronic inflammation and fibrogenesis. Plasma Gal-3 is associated with proteinuria and renal dysfunction, but its role has never been confirmed with kidney biopsy results. In our study, we aimed to explore the expression of Gal-3 in biopsy-proven patients, and we tested the hypothesis that chronic kidney disease (CKD) leads to upregulation of plasma Gal-3 expression in corresponding biopsy findings and RNA sequencing analysis. Method: In 249 patients (male/female: 155/94, age: 57.2 ± 16.3 years) who underwent kidney biopsy, plasma levels of Gal-3 were measured to estimate the association of renal fibrosis. Relationships between plasma Gal-3 levels, estimated glomerular filtration rate (eGFR) and renal histology findings were also assessed. We further examined the gene expression of Gal-3 in RNA-sequencing analysis in biopsy-proven patients. Results: Compared to patients without CKD, CKD patients had higher levels of plasma Gal-3 (1,016.3 ± 628.1 pg/mL vs. 811.6 ± 369.6 pg/ml; P = 0.010). Plasma Gal-3 was inversely correlated with eGFR (P = 0.005) but not with proteinuria. Higher Gal-3 levels were associated with interstitial fibrosis, tubular atrophy and vascular intimal fibrosis. RNA-sequencing analysis showed the upregulation of Gal-3 in fibrotic kidney biopsy samples, and the differentially expressed genes were mainly enhanced in immune cell activation and the regulation of cell-cell adhesion. Conclusions: Plasma Gal-3 levels are inverse correlated with eGFR but positively correlated with renal fibrosis, which may be involved in the immune response and associated pathways. These findings support the role of Gal-3 as a predictive marker of renal fibrosis.

Sub-chronic oral exposure of tungsten induces markers of kidney injury

Tungsten is a naturally occurring transition element used in a broad range of applications. As a result of its extensive use, we are increasingly exposed to tungsten from our environment, including potable water, since tungsten can become bioaccessible in ground sources. The kidneys are particularly susceptible to tungsten exposure as this is the main site for tungsten excretion. In this study, we investigated the prolonged effects of tungsten on the kidneys and how this may impact injury and function. When mice were exposed to tungsten in their drinking water for 1-month, kidney function had not significantly changed. Following 3-month exposure, mice were presented with deterioration in kidney function as determined by serum and urine creatinine levels. During 3-months of tungsten exposure, murine kidneys demonstrated significant increases in the myofibroblast marker ⍺SMA, and extracellular matrix products: fibronectin, collagen, and matricellular proteins. In addition, Masson's trichrome and H&E staining revealed an increase in fibrotic tissue and vacuolization of tubular epithelial cells, respectively, from kidneys of tungsten-treated mice, indicative of renal injury. In vitro treatment of kidney fibroblasts with tungsten led to increased proliferation and upregulation of Transforming Growth Factor Beta 1 (TGFβ1), which was consistent with the appearance of fibroblast-to-myofibroblast transition (FMT) markers. Our data suggest that continuous exposure to tungsten impairs kidney function that may lead to the development of chronic kidney disease (CKD).

Endosulfan promotes cell proliferation and extracellular matrix accumulation through TGF-β/Smad signaling pathway in HRMCs

Endosulfan is an organochlorine pesticide, which poses a potential danger to human health and safety. It is known that dysfunction of glomerular mesangial cells causes glomerular sclerosis, associated with chronic kidney diseases. In the present study, we investigated the effects of endosulfan on cell proliferation and extracellular matrix accumulation (ECM) in human renal mesangial cells (HRMCs). Cells were treated with endosulfan, endosulfan (10 μM) plus specific inhibitor of TGF-β signaling (LY2109761) or antioxidant (NAC). The results showed that endosulfan significantly promoted cell proliferation, accompanied with the decrease of p27 mRNA expression and the increase in the mRNA expression levels of p21 and inflammatory factors IL-6/IL-8. qRT-PCR results showed that matrix metalloproteinase-2 (MMP2) and tissue metalloproteinase-3 (TIMP3) were down-regulated whereas laminin was up-regulated when exposure to endosulfan. Western blot results showed that p-Smad2/3 was up-regulated, while Smad7 was down-regulated when exposure to endosulfan, which were reversed in the presence of LY2109761. Endosulfan significantly decreased the activity of SOD and increased the MDA level and CAT activity, which were reversed in the presence of NAC. These findings suggest that endosulfan can cause excessive proliferation and massive accumulation of ECM through TGF-β/Smad signaling pathway, and also induced oxidative stress and inflammation in HRMCs.

Cell-Type-Specific Profibrotic Scores across Multi-Organ Systems Predict Cancer Prognosis

Simple Summary

Fibrosis is a major player and contributor in the tumor microenvironment. Profibrotic changes precede the early development and establishment of a variety of human diseases, such as fibrosis and cancer. Being able to measure such early signals at the single cell level is critically useful for identifying new mechanisms and potential drug targets for a wide range of diseases. This study was designed to computationally identify profibrotic cell populations using single-cell transcriptomic data and to identify gene signatures that could predict cancer prognosis.

Abstract

Fibrosis is a major cause of mortality. Key profibrotic mechanisms are common pathways involved in tumorigenesis. Characterizing the profibrotic phenotype will help reveal the underlying mechanisms of early development and progression of a variety of human diseases, such as fibrosis and cancer. Fibroblasts have been center stage in response to various stimuli, such as viral infections. However, a comprehensive catalog of cell types involved in this process is currently lacking. Here, we deployed single-cell transcriptomic data across multi-organ systems (i.e., heart, kidney, liver, and lung) to identify novel profibrotic cell populations based on ECM pathway activity at single-cell resolution. In addition to fibroblasts, we also reported that epithelial, endothelial, myeloid, natural killer T, and secretory cells, as well as proximal convoluted tubule cells of the nephron, were significantly actively involved. Cell-type-specific gene signatures were enriched in viral infection pathways, enhanced glycolysis, and carcinogenesis, among others; they were validated using independent datasets in this study. By projecting the signatures into bulk TCGA tumor samples, we could predict prognosis in the patients using profibrotic scores. Our profibrotic cellular phenotype is useful for identifying new mechanisms and potential drug targets at the cell-type level for a wide range of diseases involved in ECM pathway activation.

How to inhibit transforming growth factor beta safely in diabetic kidney disease

PURPOSE OF REVIEW

Diabetic kidney disease (DKD) is a leading cause of mortality and morbidity in diabetes. This review aims to discuss the major features of DKD, to identify the difficult barrier encountered in developing a therapeutic strategy and to provide a potentially superior novel approach to retard DKD.

RECENT FINDINGS

Renal inflammation and fibrosis are prominent features of DKD. Transforming growth factor beta (TGFβ) with its activity enhanced in DKD plays a key pathological profibrotic role in promoting renal fibrosis. However, TGFβ is a difficult drug target because it has multiple important physiological functions, such as immunomodulation. These physiological functions of TGFβ can be interrupted as a result of complete blockade of the TGFβ pathway if TGFβ is directly targeted, leading to catastrophic side-effects, such as fulminant inflammation. Cell division autoantigen 1 (CDA1) is recently identified as an enhancer of profibrotic TGFβ signaling and inhibitor of anti-inflammatory SIRT1. Renal CDA1 expression is elevated in human DKD as well as in rodent models of DKD. Targeting CDA1, by either genetic approach or pharmacological approach in mice, leads to concurrent attenuation of renal fibrosis and inflammation without any deleterious effects observed.

SUMMARY

Targeting CDA1, instead of directly targeting TGFβ, represents a superior approach to retard DKD.

Anti-fibrotic effect of 6-bromo-indirubin-3'-oxime (6-BIO) via regulation of activator protein-1 (AP-1) and specificity protein-1 (SP-1) transcription factors in kidney cells

PAI-1 and CTGF are overexpressed in kidney diseases and cause fibrosis of the lungs, liver, and kidneys. We used a rat model of unilateral ureteral obstruction (UUO) to investigate whether 6-BIO, a glycogen synthase kinase-3β inhibitor, attenuated fibrosis by inhibiting PAI-1 and CTGF in vivo. Additionally, TGFβ-induced cellular fibrosis was observed in vitro using the human kidney proximal tubular epithelial cells (HK-2), and rat interstitial fibroblasts (NRK49F). Expression of fibrosis-related proteins and signaling molecules such as PAI-1, CTGF, TGFβ, αSMA, SMAD, and MAPK were determined in HK-2 and NRK49F cells using immunoblotting. To identify the transcription factors that regulate the expression of PAI-1 and CTGF the promoter activities of AP-1 and SP-1 were analyzed using luciferase assays. Confocal microscopy was used to observe the co-localization of AP-1 and SP-1 to PAI-1 and CTGF. Expression of PAI-1, CTGF, TGFβ, and α-SMA increased in UUO model as well as in TGFβ-treated HK-2 and NRK49F cells. Furthermore, UUO and TGFβ treatment induced the activation of P-SMAD2/3, SMAD4, P-ERK 1/2, P-P38, and P-JNK MAPK signaling pathways. PAI-1, CTGF, AP-1 and SP-1 promoter activity increased in response to TGFβ treatment. However, treatment with 6-BIO decreased the expression of proteins and signaling pathways associated with fibrosis in UUO model as well as in TGFβ-treated HK-2 and NRK49F cells. Moreover, 6-BIO treatment attenuated the expression of PAI-1 and CTGF as well as the promoter activities of AP-1 and SP-1, thereby regulating the SMAD and MAPK signaling pathways, and subsequently exerting anti-fibrotic effects on kidney cells.

IL-15 Prevents Renal Fibrosis by Inhibiting Collagen Synthesis: A New Pathway in Chronic Kidney Disease?

Chronic kidney disease (CKD), secondary to renal fibrogenesis, is a public health burden. The activation of interstitial myofibroblasts and excessive production of extracellular matrix (ECM) proteins are major events leading to end-stage kidney disease. Recently, interleukin-15 (IL-15) has been implicated in fibrosis protection in several organs, with little evidence in the kidney. Since endogenous IL-15 expression decreased in nephrectomized human allografts evolving toward fibrosis and kidneys in the unilateral ureteral obstruction (UUO) model, we explored IL-15's renoprotective role by pharmologically delivering IL-15 coupled or not with its soluble receptor IL-15Rα. Despite the lack of effects on myofibroblast accumulation, both IL-15 treatments prevented tubulointerstitial fibrosis (TIF) in UUO as characterized by reduced collagen and fibronectin deposition. Moreover, IL-15 treatments inhibited collagen and fibronectin secretion by transforming growth factor-β (TGF-β)-treated primary myofibroblast cultures, demonstrating that the antifibrotic effect of IL-15 in UUO acts, in part, through a direct inhibition of ECM synthesis by myofibroblasts. In addition, IL-15 treatments resulted in decreased expression of monocyte chemoattractant protein 1 (MCP-1) and subsequent macrophage infiltration in UUO. Taken together, our study highlights a major role of IL-15 on myofibroblasts and macrophages, two main effector cells in renal fibrosis, demonstrating that IL-15 may represent a new therapeutic option for CKD.

Perspective on Stem Cell Therapy in Organ Fibrosis: Animal Models and Human Studies

Tissue fibrosis is characterized by excessive deposition of extracellular matrix (ECM) components that result from the disruption of regulatory processes responsible for ECM synthesis, deposition, and remodeling. Fibrosis develops in response to a trigger or injury and can occur in nearly all organs of the body. Thus, fibrosis leads to severe pathological conditions that disrupt organ architecture and cause loss of function. It has been estimated that severe fibrotic disorders are responsible for up to one-third of deaths worldwide. Although intensive research on the development of new strategies for fibrosis treatment has been carried out, therapeutic approaches remain limited. Since stem cells, especially mesenchymal stem cells (MSCs), show remarkable self-renewal, differentiation, and immunomodulatory capacity, they have been intensively tested in preclinical studies and clinical trials as a potential tool to slow down the progression of fibrosis and improve the quality of life of patients with fibrotic disorders. In this review, we summarize in vitro studies, preclinical studies performed on animal models of human fibrotic diseases, and recent clinical trials on the efficacy of allogeneic and autologous stem cell applications in severe types of fibrosis that develop in lungs, liver, heart, kidney, uterus, and skin. Although the results of the studies seem to be encouraging, there are many aspects of cell-based therapy, including the cell source, dose, administration route and frequency, timing of delivery, and long-term safety, that remain open areas for future investigation. We also discuss the contemporary status, challenges, and future perspectives of stem cell transplantation for therapeutic options in fibrotic diseases as well as we present recent patents for stem cell-based therapies in organ fibrosis.

Understanding the Renal Fibrotic Process in Leptospirosis

Leptospirosis is a neglected infectious disease caused by pathogenic species of the genus Leptospira. The acute disease is well-described, and, although it resembles other tropical diseases, it can be diagnosed through the use of serological and molecular methods. While the chronic renal disease, carrier state, and kidney fibrosis due to Leptospira infection in humans have been the subject of discussion by researchers, the mechanisms involved in these processes are still overlooked, and relatively little is known about the establishment and maintenance of the chronic status underlying this infectious disease. In this review, we highlight recent findings regarding the cellular communication pathways involved in the renal fibrotic process, as well as the relationship between renal fibrosis due to leptospirosis and CKD/CKDu.

Renoprotective Effects of Maslinic Acid on Experimental Renal Fibrosis in Unilateral Ureteral Obstruction Model via Targeting MyD88

Maslinic acid (MA), also named crategolic acid, is a pentacyclic triterpene extracted from fruits and vegetables. Although various beneficial pharmacological effects of MA have been revealed, its effect on renal fibrosis remains unclear. This study was designed to clarify whether MA could attenuate renal fibrosis and determine the putative underlying molecular mechanisms. We demonstrated that MA-treated mice with unilateral ureteral obstruction (UUO) developed a histological injury of low severity and exhibited downregulated expression of fibrotic markers, including α-smooth muscle actin (α-SMA), vimentin, and fibronectin by 38, 44 and 40%, and upregulated expression of E-cadherin by 70% as compared with untreated UUO mice. Moreover, MA treatment restored the expression levels of α-SMA, connective tissue growth factor, and vimentin to 10, 7.8 and 38% of those induced by transforming growth factor (TGF)-β in NRK49F cells. MA decreased expression of Smad2/3 phosphorylation and Smad4 in UUO kidneys and TGF-β treated NRK49F cells (p < 0.05, respectively). Notably, MA specifically interferes with MyD88, an adaptor protein, thereby mitigating Smad4 nuclear expression (p < 0.01 compared to TGF-β treated group) and ameliorating renal fibrotic changes (p < 0.01 for each fibrotic markers compared to TGF-β induced cells). In addition, in the UUO model and lipopolysaccharide-induced NRK49F cells, MA treatment decreased the expression of IL-1β, TGF-α and MCP-1, ICAM-1, associated with the suppression of NF-κB signaling. These findings suggest that MA is a potential agent that can reduce renal interstitial fibrosis, to some extent, via targeting TGF-β/Smad and MyD88 signaling.

Suppression of collagen IV alpha-2 subunit by prolyl hydroxylase domain inhibition via hypoxia-inducible factor-1 in chronic kidney disease

Elevation of hypoxia-inducible factor 1 protein has been shown to be protective in acute kidney injury and HIF1α enhancing drug therapies are currently in clinical trials for the treatment of anemia of chronic kidney disease. Despite its benefits, long-term HIF1 elevation seems to be associated with additional effects in the kidneys such as tubulointerstitial fibrosis. To better understand the effects of prolonged HIF1 exposure, assessment of baseline and post-therapy levels of HIF1α and other related biomarkers is essential. In this study, we assessed the effect of HIF1α enhancement using prolyl hydroxylase inhibitor (PHD-I) DMOG, on a key profibrotic marker of kidney disease. In specific, we examined the change in expression of Collagen 4 subunit A2 in cultured urinary cells of CKD patients pre and post 24-hour exposure to 1mM DMOG. Our results show that besides HIF1α enhancement, COL4A2 protein is suppressed in presence of DMOG. To determine if this effect is mediated by HIF1, we used HIF1α gene silencing in HEK293 cells and examined the effect of DMOG on protein and gene expression of COL4A2 post 24-hour exposure. We showed that silencing HIF1α reverses and amplifies the expression of COL4A2 in HEK293 cells. Our data suggest that HIF1 directly regulates the expression of COL4A2 in kidney cells and that HIF1α enhancing therapy has suppressive effects on COL4A2 that may be clinically relevant and must be considered in determining the safety and efficacy of these drugs in the treatment of anemia.