The renal (myo-)fibroblast: a heterogeneous group of cells

Salvianolic acid B in fibrosis treatment: a comprehensive review

Fibrosis is a public health issue of great concern characterized by the excessive deposition of extracellular matrix, leading to the destruction of parenchymal tissue and organ dysfunction that places a heavy burden on the global healthcare system due to its high incidence, disability, and mortality. Salvianolic acid B (SalB) has positively affected various human diseases, including fibrosis. In this review, we concentrate on the anti-fibrotic effects of SalB from a molecular perspective while providing information on the safety, adverse effects, and drug interactions of SalB. Additionally, we discuss the innovative SalB formulations, which give some references for further investigation and therapeutic use of SalB's anti-fibrotic qualities. Even with the encouraging preclinical data, additional research is required before relevant clinical trials can be conducted. Therefore, we conclude with recommendations for future studies. It is hoped that this review will provide comprehensive new perspectives on future research and product development related to SalB treatment of fibrosis and promote the efficient development of this field.

Kidney fibrosis: Emerging diagnostic and therapeutic strategies

An increasing number of patients worldwide suffers from chronic kidney disease (CKD). CKD is accompanied by kidney fibrosis, which affects all compartments of the kidney, i.e., the glomeruli, tubulointerstitium, and vasculature. Fibrosis is the best predictor of progression of kidney diseases. Currently, there is no specific anti-fibrotic therapy for kidney patients and invasive renal biopsy remains the only option for specific detection and quantification of kidney fibrosis. Here we review emerging diagnostic approaches and potential therapeutic options for fibrosis. We discuss how translational research could help to establish fibrosis-specific endpoints for clinical trials, leading to improved patient stratification and potentially companion diagnostics, and facilitating and optimizing development of novel anti-fibrotic therapies for kidney patients.

Aligned Lovastatin-loaded Electrospun Nanofibers Regulate Collagen Organization and Reduce Scar Formation

Excessive scar formation caused by cutaneous injury leads to pruritus, pain, contracture, dyskinesia, and unpleasant appearance. Functional wound dressings are designed to accelerate wound healing and reduce scar formation. In this study, we fabricated aligned or random polycaprolactone/silk fibroin electrospun nanofiber membranes with or without lovastatin loading, and then evaluated their scar-inhibitory effects on wounds under a specific tension direction. The nanofiber membranes exhibited good controlled-release performance, mechanical properties, hydrophilicity, and biocompatibility. Furthermore, nanofibers' perpendicular placement to the tension direction of the wound most effectively reduced scar formation (the scar area decreased by 66.9%) and promoted skin regeneration in vivo. The mechanism was associated with its aligned nanofibers regulated collagen organization in the early stage of wound healing. Moreover, lovastatin-loaded nanofibers inhibited myofibroblast differentiation and migration. Both tension direction-perpendicular topographical cues and lovastatin synergistically inhibited mechanical transduction and fibrosis progression, further reducing scar formation. In summary, our study may provide an effective scar prevention strategy in which individualized dressings can be designed according to the local mechanical force direction of patients' wounds, and the addition of lovastatin can further inhibit scar formation. STATEMENT OF SIGNIFICANCE: In vivo, cells and collagen are always arranged parallel to the tension direction. However, the aligned topographic cues themselves promote myofibroblast differentiation and exacerbate scar formation. Electrospun nanofibers' perpendicular placement to the tension direction of the wound most effectively reduces scar formation and promotes skin regeneration in vivo. The mechanism is associated with its tension direction-perpendicular nanofibers reregulate collagen organization in the early stage of wound healing. In addition, tension direction-perpendicular topographical cue and lovastatin could inhibit mechanical transduction and fibrosis progression synergistically, further reducing scar formation. This study proves that combining topographical cues of wound dressing and drugs would be a promising therapy for clinical scar management.

Klotho Supplementation Reverses Renal Dysfunction and Interstitial Fibrosis in Remnant Kidney

INTRODUCTION

While recent investigations show that klotho exerts renoprotective actions, it has not been fully addressed whether klotho protein supplementation reverses renal damage.

METHODS

The impacts of subcutaneous klotho supplementation on rats with subtotal nephrectomy were examined. Animals were divided into 3 groups: group 1 (short remnant [SR]): remnant kidney for 4 weeks, group 2 (long remnant [LR]): remnant kidney for 12 weeks, and group 3 (klotho supplementation [KL]): klotho protein (20 μg/kg/day) supplementation on the remnant kidney. Blood pressure, blood and urine compositions with conventional methods such as enzyme-linked immunosorbent assay and radioimmunoassay, kidney histology, and renal expressions of various genes were analyzed. In vitro studies were also performed to support in vivo findings.

RESULTS

Klotho protein supplementation decreased albuminuria (-43%), systolic blood pressure (-16%), fibroblast growth factor (FGF) 23 (-51%) and serum phosphate levels (-19%), renal angiotensin II concentration (-43%), fibrosis index (-70%), renal expressions of collagen I (-55%), and transforming growth factor β (-59%) (p < 0.05 for all). Klotho supplementation enhanced fractional excretion of phosphate (+45%), glomerular filtration rate (+76%), renal expressions of klotho (+148%), superoxide dismutase (+124%), and bone morphogenetic protein (BMP) 7 (+174%) (p < 0.05 for all).

CONCLUSION

Our data indicated that klotho protein supplementation inactivated renal renin-angiotensin system, reducing blood pressure and albuminuria in remnant kidney. Furthermore, exogenous klotho protein supplementation elevated endogenous klotho expression to increase phosphate excretion with resultant reductions in FGF23 and serum phosphate. Finally, klotho supplementation reversed renal dysfunction and fibrosis in association with improved BMP7 in remnant kidney.

ZEB2 controls kidney stromal progenitor differentiation and inhibits abnormal myofibroblast expansion and kidney fibrosis

FOXD1+ cell-derived stromal cells give rise to pericytes and fibroblasts that support the kidney vasculature and interstitium but are also major precursors of myofibroblasts. ZEB2 is a SMAD-interacting transcription factor that is expressed in developing kidney stromal progenitors. Here we show that Zeb2 is essential for normal FOXD1+ stromal progenitor development. Specific conditional knockout of mouse Zeb2 in FOXD1+ stromal progenitors (Zeb2 cKO) leads to abnormal interstitial stromal cell development, differentiation, and kidney fibrosis. Immunofluorescent staining analyses revealed abnormal expression of interstitial stromal cell markers MEIS1/2/3, CDKN1C, and CSPG4 (NG2) in newborn and 3-week-old Zeb2-cKO mouse kidneys. Zeb2-deficient FOXD1+ stromal progenitors also took on a myofibroblast fate that led to kidney fibrosis and kidney failure. Cell marker studies further confirmed that these myofibroblasts expressed pericyte and resident fibroblast markers, including PDGFRβ, CSPG4, desmin, GLI1, and NT5E. Notably, increased interstitial collagen deposition associated with loss of Zeb2 in FOXD1+ stromal progenitors was accompanied by increased expression of activated SMAD1/5/8, SMAD2/3, SMAD4, and AXIN2. Thus, our study identifies a key role of ZEB2 in maintaining the cell fate of FOXD1+ stromal progenitors during kidney development, whereas loss of ZEB2 leads to differentiation of FOXD1+ stromal progenitors into myofibroblasts and kidney fibrosis.

Kidney and lipids: novel potential therapeutic targets for dyslipidemia in kidney disease?

INTRODUCTION

Altered lipid distribution and metabolism may lead to the development and/or progression of chronic kidney disease (CKD). Dyslipidemia is a major risk factor for CKD and increases the risk of cardiovascular events and mortality. Therefore, lipid-lowering treatments may decrease cardiovascular risk and prevent death.

AREAS COVERED

Key players involved in regulating lipid accumulation in the kidney; contribution of lipids to CKD progression, lipotoxicity, and mitochondrial dysfunction in kidney disease; recent therapeutic approaches for dyslipidemia.

EXPERT OPINION

The precise mechanisms for regulating lipid metabolism, particularly in kidney disease, are poorly understood. Guidelines for lipid-lowering therapy for CKD are controversial. Several hypolipemic therapies are available, but compared to others, statin therapy is the most common. No clinical trial has evaluated the efficacy of proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9i) in preventing cardiovascular events or improving kidney function among patients with CKD or kidney transplant recipients. Attractive alternatives, such as PCSK9-small interfering RNA (siRNA) molecules or evinacumab are available. Additionally, several promising agents, such as cyclodextrins and the FXR/TGR5 dual agonist, INT-767, can improve renal lipid metabolism disorders and delay CKD progression. Drugs targeting mitochondrial dysfunction could be an option for the treatment of dyslipidemia and lipotoxicity, particularly in renal diseases.

The Role of Mesothelin in Activation of Portal Fibroblasts in Cholestatic Liver Injury

Fibrosis is a common consequence of abnormal wound healing, which is characterized by infiltration of myofibroblasts and formation of fibrous scar. In liver fibrosis, activated Hepatic Stellate Cells (aHSCs) and activated Portal Fibroblasts (aPFs) are the major contributors to the origin of hepatic myofibroblasts. aPFs are significantly involved in the pathogenesis of cholestatic fibrosis, suggesting that aPFs may be a primary target for anti-fibrotic therapy in cholestatic injury. aPFs are distinguishable from aHSCs by specific markers including mesothelin (Msln), Mucin 16 (Muc16), and Thymus cell antigen 1 (Thy1, CD90) as well as fibulin 2, elastin, Gremlin 1, ecto-ATPase nucleoside triphosphate diphosphohydrolase 2. Msln plays a critical role in activation of PFs, via formation of Msln-Muc16-Thy1 complex that regulates TGFβ1/TGFβRI-mediated fibrogenic signaling. The opposing pro- and anti-fibrogenic effects of Msln and Thy1 are key components of the TGFβ1-induced activation pathway in aPFs. In addition, aPFs and activated lung and kidney fibroblasts share similarities across different organs with expression of common markers and activation cascade including Msln-Thy1 interaction. Here, we summarize the potential function of Msln in activation of PFs and development of cholestatic fibrosis, offering a novel perspective for anti-fibrotic therapy targeting Msln.

Signaling pathways of chronic kidney diseases, implications for therapeutics

Chronic kidney disease (CKD) is a chronic renal dysfunction syndrome that is characterized by nephron loss, inflammation, myofibroblasts activation, and extracellular matrix (ECM) deposition. Lipotoxicity and oxidative stress are the driving force for the loss of nephron including tubules, glomerulus, and endothelium. NLRP3 inflammasome signaling, MAPK signaling, PI3K/Akt signaling, and RAAS signaling involves in lipotoxicity. The upregulated Nox expression and the decreased Nrf2 expression result in oxidative stress directly. The injured renal resident cells release proinflammatory cytokines and chemokines to recruit immune cells such as macrophages from bone marrow. NF-κB signaling, NLRP3 inflammasome signaling, JAK-STAT signaling, Toll-like receptor signaling, and cGAS-STING signaling are major signaling pathways that mediate inflammation in inflammatory cells including immune cells and injured renal resident cells. The inflammatory cells produce and secret a great number of profibrotic cytokines such as TGF-β1, Wnt ligands, and angiotensin II. TGF-β signaling, Wnt signaling, RAAS signaling, and Notch signaling evoke the activation of myofibroblasts and promote the generation of ECM. The potential therapies targeted to these signaling pathways are also introduced here. In this review, we update the key signaling pathways of lipotoxicity, oxidative stress, inflammation, and myofibroblasts activation in kidneys with chronic injury, and the targeted drugs based on the latest studies. Unifying these pathways and the targeted therapies will be instrumental to advance further basic and clinical investigation in CKD.

Tubular Cell Dropout in Preimplantation Deceased Donor Biopsies as a Predictor of Delayed Graft Function

Supplemental Digital Content is available in the text.

Background.

Delayed graft function (DGF) affects over 25% of deceased donor kidney transplants (DDKTs) and is associated with increased cost, worsened graft outcomes, and mortality. While approaches to preventing DGF have focused on minimizing cold ischemia, donor factors such as acute tubular injury can influence risk. There are currently no pharmacologic therapies to modify DGF risk or promote repair, in part due to our incomplete understanding of the biology of preimplantation tubular injury.

Methods.

We collected intraoperative, preimplantation kidney biopsies from 11 high-risk deceased donors and 10 living donors and followed transplant recipients for graft function. We performed quantitative high-dimensional histopathologic analysis using imaging mass cytometry to determine the cellular signatures that distinguished deceased and living donor biopsies as well as deceased donor biopsies which either did or did not progress to DGF.

Results.

We noted decreased tubular cells (P < 0.0001) and increased macrophage infiltration (P = 0.0037) in high-risk DDKT compared with living donor biopsies. For those high-risk DDKTs that developed postimplant DGF (n = 6), quantitative imaging mass cytometry analysis showed a trend toward reduced tubular cells (P = 0.02) and increased stromal cells (P = 0.04) versus those that did not (n = 5). Notably, these differences were not identified by conventional histopathologic evaluation.

Conclusions.

The current study identifies donor tubular cell loss as a precursor of DGF pathogenesis and highlights an area for further investigation and potential therapeutic intervention.

Interplay between extracellular matrix components and cellular and molecular mechanisms in kidney fibrosis

Chronic kidney disease (CKD) is characterized by pathological accumulation of extracellular matrix (ECM) proteins in renal structures. Tubulointerstitial fibrosis is observed in glomerular diseases as well as in the regeneration failure of acute kidney injury (AKI). Therefore, finding antifibrotic therapies comprises an intensive research field in Nephrology. Nowadays, ECM is not only considered as a cellular scaffold, but also exerts important cellular functions. In this review, we describe the cellular and molecular mechanisms involved in kidney fibrosis, paying particular attention to ECM components, profibrotic factors and cell-matrix interactions. In response to kidney damage, activation of glomerular and/or tubular cells may induce aberrant phenotypes characterized by overproduction of proinflammatory and profibrotic factors, and thus contribute to CKD progression. Among ECM components, matricellular proteins can regulate cell-ECM interactions, as well as cellular phenotype changes. Regarding kidney fibrosis, one of the most studied matricellular proteins is cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), currently considered as a fibrotic marker and a potential therapeutic target. Integrins connect the ECM proteins to the actin cytoskeleton and several downstream signaling pathways that enable cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. In kidney fibrosis, there is an increase in ECM deposition, lower ECM degradation and ECM proteins cross-linking, leading to an alteration in the tissue mechanical properties and their responses to injurious stimuli. A better understanding of these complex cellular and molecular events could help us to improve the antifibrotic therapies for CKD.

Evaluation of the Therapeutic Effects of Protocatechuic Aldehyde in Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most severe chronic kidney diseases in diabetes and is the main cause of end-stage renal disease (ESRD). Protocatechuic aldehyde (PCA) is a natural product with a variety of effects on pulmonary fibrosis. In this study, we examined the effects of PCA in C57BL/KS db/db male mice. Kidney morphology, renal function indicators, and Western blot, immunohistochemistry, and hematoxylin and eosin (H&E) staining data were analyzed. The results revealed that treatment with PCA could reduce diabetic-induced renal dysfunction, as indicated by the urine albumin-to-creatinine ratio (db/m: 120.1 ± 46.1μg/mg, db/db: 453.8 ± 78.7 µg/mg, db/db + 30 mg/kg PCA: 196.6 ± 52.9 µg/mg, db/db + 60 mg/kg PCA: 163.3 ± 24.6 μg/mg, p < 0.001). However, PCA did not decrease body weight, fasting plasma glucose, or food and water intake in db/db mice. H&E staining data revealed that PCA reduced glomerular size in db/db mice (db/m: 3506.3 ± 789.3 μm², db/db: 6538.5 ± 1818.6 μm², db/db + 30 mg/kg PCA: 4916.9 ± 1149.6 μm², db/db + 60 mg/kg PCA: 4160.4 ± 1186.5 μm²p < 0.001). Western blot and immunohistochemistry staining indicated that PCA restored the normal levels of diabetes-induced fibrosis markers, such as transforming growth factor-beta (TGF-β) and type IV collagen. Similar results were observed for epithelial–mesenchymal transition-related markers, including fibronectin, E-cadherin, and α-smooth muscle actin (α-SMA). PCA also decreased oxidative stress and inflammation in the kidney of db/db mice. This research provides a foundation for using PCA as an alternative therapy for DN in the future.

Pyruvate kinase M2 mediates fibroblast proliferation to promote tubular epithelial cell survival in acute kidney injury

Acute kidney injury (AKI) is a devastating condition with high morbidity and mortality rates. The pathological features of AKI are tubular injury, infiltration of inflammatory cells, and impaired vascular integrity. Pyruvate kinase is the final rate-limiting enzyme in the glycolysis pathway. We previously showed that pyruvate kinase M2 (PKM2) plays an important role in regulating the glycolytic reprogramming of fibroblasts in renal interstitial fibrosis. The present study aimed to determine the role of PKM2 in fibroblast activation during the pathogenesis of AKI. We found increased numbers of S100A4 positive cells expressing PKM2 in renal tissues from mice with AKI induced via folic acid or ischemia/reperfusion (I/R). The loss of PKM2 in fibroblasts impaired fibroblast proliferation and promoted tubular epithelial cell death including apoptosis, necroptosis, and ferroptosis. Mechanistically, fibroblasts produced less hepatocyte growth factor (HGF) in response to a loss of PKM2. Moreover, in two AKI mouse models, fibroblast-specific deletion of PKM2 blocked HGF signal activation and aggravated AKI after it was induced in mice via ischemia or folic acid. Fibroblast proliferation mediated by PKM2 elicits pro-survival signals that repress tubular cell death and may help to prevent AKI progression. Fibroblast activation mediated by PKM2 in AKI suggests that targeting PKM2 expression could be a novel strategy for treating AKI.

SeqStain is an efficient method for multiplexed, spatialomic profiling of human and murine tissues

Spatial organization of molecules and cells in complex tissue microenvironments provides essential organizational cues in health and disease. A significant need exists for improved visualization of these spatial relationships. Here, we describe a multiplex immunofluorescence imaging method, termed SeqStain, that uses fluorescent-DNA-labeled antibodies for immunofluorescent staining and nuclease treatment for de-staining that allows selective enzymatic removal of the fluorescent signal. SeqStain can be used with primary antibodies, secondary antibodies, and antibody fragments to efficiently analyze complex cells and tissues. Additionally, incorporation of specific endonuclease restriction sites in antibody labels allows for selective removal of fluorescent signals while retaining other signals that can serve as marks for subsequent analyses. The application of SeqStain on human kidney tissue provided a spatialomic profile of the organization of >25 markers in the kidney, highlighting it as a versatile, easy-to-use, and gentle new technique for spatialomic analyses of complex microenvironments.

Using Zebrafish as a Disease Model to Study Fibrotic Disease

In drug discovery, often animal models are used that mimic human diseases as closely as possible. These animal models can be used to address various scientific questions, such as testing and evaluation of new drugs, as well as understanding the pathogenesis of diseases. Currently, the most commonly used animal models in the field of fibrosis are rodents. Unfortunately, rodent models of fibrotic disease are costly and time-consuming to generate. In addition, present models are not very suitable for screening large compounds libraries. To overcome these limitations, there is a need for new in vivo models. Zebrafish has become an attractive animal model for preclinical studies. An expanding number of zebrafish models of human disease have been documented, for both acute and chronic diseases. A deeper understanding of the occurrence of fibrosis in zebrafish will contribute to the development of new and potentially improved animal models for drug discovery. These zebrafish models of fibrotic disease include, among others, cardiovascular disease models, liver disease models (categorized into Alcoholic Liver Diseases (ALD) and Non-Alcoholic Liver Disease (NALD)), and chronic pancreatitis models. In this review, we give a comprehensive overview of the usage of zebrafish models in fibrotic disease studies, highlighting their potential for high-throughput drug discovery and current technical challenges.

Tbx18-positive cells-derived myofibroblasts contribute to renal interstitial fibrosis via transforming growth factor-β signaling

It has been demonstrated that the T-box family transcription factor 18 (Tbx18) -positive cells give rise to renal mesenchymal cells and contribute to the development of the urinary system. However, it is unclear whether Tbx18-positive cells are the origin of the myofibroblasts during renal fibrosis. The present study aimed to determine the contribution of Tbx18-positive cells in kidney fibrosis and their underlying mechanism. We show that Tbx18-positive cells contribute to the development of the urinary system, especially renal fibroblasts. Following unilateral ureteral obstruction (UUO), genetic fate tracing results demonstrated that Tbx18-positive cells not only proliferate but also expand and differentiate into fibroblasts and myofibroblasts, indicating that they may act as profibrotic progenitors. Cell culture results suggest that transforming growth factor (TGF)-β promotes Tbx18-positive cells differentiation into myofibroblasts and assist their contribution to kidney fibrosis. Overall, the present study demonstrated that Tbx18-positive cells may act as profibrotic progenitor cells in a pathological condition of UUO-induced injury. Moreover, TGF-β may play a role in differentiation of Tbx18-positive cells into myofibroblasts in kidney fibrosis. These findings may provide a potential target on Tbx18-positive myofibroblast progenitors in the treatment of renal fibrosis.

Three-dimensional coculture provides an improved in vitro model for papillary renal cell carcinoma

Papillary renal cell carcinoma (pRCC) represents the second most common kidney cancer and can be distinguished from other types based on its unique histological architecture and specific pattern of genomic alterations. Sporadic type 1 pRCC is almost universally driven by focal or chromosomal amplification of the receptor tyrosine kinase MET, although the specific mode of its activation is unclear. Although the MET receptors found in human tumor specimens appear highly active, those found on the surface of in vitro-cultured tumor cells are only weakly activated in the absence of exogenous hepatocyte growth factor ligand. Furthermore, pRCC cells cultured in standard two-dimensional conditions with serum fail to respond functionally to MET knockdown or the selective MET inhibitor capmatinib despite clear evidence of kinase inhibition at the molecular level. To better model pRCC in vitro, we developed a three-dimensional coculture system in which renal tumor cells are layered on top of primary fibroblasts in a fashion that mimics the papillary architecture of human tumors. In this three-dimensional spheroid model, the tumor cells survive and proliferate in the absence of serum due to trophic support of hepatocyte growth factor-producing fibroblasts. Unlike tumor cells grown in monoculture, the proliferation of cocultured tumor cells is sensitive to capmatinib and parallels inhibition of MET kinase activity. These findings demonstrate the importance of stromal fibroblasts in pRCC and indicate that accurate in vitro representation of this disease requires the presence of both tumor and fibroblast cells in a structured coculture model.NEW & NOTEWORTHY Two-dimensional monoculture of papillary renal cancer cells fails to replicate several features of the disease found in humans. We hypothesized that this discordance results from lack of trophic support from renal fibroblasts, which are involved in the architecture of human papillary renal tumors. We found that three-dimensional layering of renal cancer cells on top of a fibroblast core using magnetic bioprinting produces a structured spheroid that more faithfully mimics the behavior of human tumors.

Aging modulates the effects of ischemic injury upon mesenchymal cells within the renal interstitium and microvasculature

The renal mesenchyme contains heterogeneous cells, including interstitial fibroblasts and pericytes, with key roles in wound healing. Although healing is impaired in aged kidneys, the effect of age and injury on the mesenchyme remains poorly understood. We characterized renal mesenchymal cell heterogeneity in young vs old animals and after ischemia‐reperfusion‐injury (IRI) using multiplex immunolabeling and single cell transcriptomics. Expression patterns of perivascular cell markers (α‐SMA, CD146, NG2, PDGFR‐α, and PDGFR‐β) correlated with their interstitial location. PDGFR‐α and PDGFR‐β co‐expression labeled renal myofibroblasts more efficiently than the current standard marker α‐SMA, and CD146 was a superior murine renal pericyte marker. Three renal mesenchymal subtypes; pericytes, fibroblasts, and myofibroblasts, were recapitulated with data from two independently performed single cell transcriptomic analyzes of murine kidneys, the first dataset an aging cohort and the second dataset injured kidneys following IRI. Mesenchymal cells segregated into subtypes with distinct patterns of expression with aging and following injury. Baseline uninjured old kidneys resembled post‐ischemic young kidneys, with this phenotype further exaggerated following IRI. These studies demonstrate that age modulates renal perivascular/interstitial cell marker expression and transcriptome at baseline and in response to injury and provide tools for the histological and transcriptomic analysis of renal mesenchymal cells, paving the way for more accurate classification of renal mesenchymal cell heterogeneity and identification of age‐specific pathways and targets.

Pattern of Tumor-Infiltrating Lymphocytes in Mixed Epithelial and Stromal Tumor of the Kidney: A Review of Five Cases

Mixed epithelial and stromal tumor of the kidney (MESTK), a benign rare tumor with malignant transformation potential, is thought to be derived from fetal or immature cells originating from the mesonephric and Müllerian ducts. However, due to its rarity, little is known about the anti-tumor immune responses in MESTK. Herein, we present five cases of MESTK and evaluate the population of tumor-infiltrating lymphocytes (TILs) using a freshly obtained MESTK sample. Microscopically, TILs were scattered or clustered in large aggregates in the stroma in all five cases; furthermore, three cases exhibited heavy, large lymphocytic aggregates with no well-organized tertiary lymphoid structures with germinal centers. Flow cytometric analysis of TILs in one freshly obtained MESTK sample revealed that >40% of CD3⁺ T cells were effector memory Fas⁺CD28⁻ γδ T cells expressing high levels of programmed cell death protein 1 and inducible T-cell co-stimulator, but low levels of CD44 and CD27. Most αß T cells exhibited a naïve phenotype. Additionally, we detected many activated class-switched CD21⁺CD27⁺ B cells as well as CD11c^highIgM^high marginal zone B-like and CD27⁻CD21⁻CD23⁻ immunoglobulin (Ig)D^highIgM^low age-associated B-like cells. Collectively, for the first time, we report the immune microenvironment pattern of MESTK to oncogenic stress.

BMPER Ameliorates Renal Fibrosis by Inhibiting Tubular Dedifferentiation and Fibroblast Activation

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

Kidney Allograft Fibrosis: Diagnostic and Therapeutic Strategies

Interstitial fibrosis with tubule atrophy (IF/TA) is the response to virtually any sustained kidney injury and correlates inversely with kidney function and allograft survival. IF/TA is driven by various pathways that include hypoxia, renin-angiotensin-aldosterone system, transforming growth factor (TGF)-β signaling, cellular rejection, inflammation and others. In this review we will focus on key pathways in the progress of renal fibrosis, diagnosis and therapy of allograft fibrosis. This review discusses the role and origin of myofibroblasts as matrix producing cells and therapeutic targets in renal fibrosis with a particular focus on renal allografts. We summarize current trends to use multi-omic approaches to identify new biomarkers for IF/TA detection and to predict allograft survival. Furthermore, we review current imaging strategies that might help to identify and follow-up IF/TA complementary or as alternative to invasive biopsies. We further discuss current clinical trials and therapeutic strategies to treat kidney fibrosis.Supplemental Visual Abstract; http://links.lww.com/TP/C141.

Janus-Faced: Molecular Mechanisms and Versatile Nature of Renal Fibrosis

Renal fibrosis is a major hallmark of CKD, regardless of the underlying etiology. In fibrosis development and progression, myofibroblasts play a pivotal role, producing extracellular matrix and interacting with various resident cells in the kidney. Over the past decade, the origin of myofibroblasts has been thoroughly investigated. Emerging evidence suggests that renal myofibroblasts originate from several cellular sources, including resident fibroblasts, pericytes, and bone marrow-derived cells. The contribution of resident fibroblasts is most crucial, and currently available data strongly suggest the importance of functional heterogeneity and plasticity of fibroblasts in kidney disease progression. Resident fibroblasts acquire distinct phenotypes based on their local microenvironment and exert multifactorial functions. For example, age-dependent alterations of renal fibroblasts make a significant contribution to the formation of tertiary lymphoid tissues, which promote local inflammation after injury in the aged kidney. In conjunction with fibrosis development, dysfunction of resident fibroblasts provokes unique pathologic conditions including renal anemia and peritubular capillary loss, both of which are major complications of CKD. Although renal fibrosis is considered detrimental in general, recent studies suggest it has beneficial roles, such as maintaining functional crosstalk with injured proximal tubular cells and supporting their regeneration. These findings provide novel insight into the mechanisms of renal fibrosis, which could be regarded as an adaptive process of kidney injury and repair. Precise understanding of the functional heterogeneity of resident fibroblasts and myofibroblasts has the potential to facilitate the development of novel therapeutics against kidney diseases. In this review, we describe the current perspective on the origin of myofibroblasts and fibroblast heterogeneity, with special emphasis on the dual aspects of renal fibrosis, both beneficial and detrimental, in CKD progression.

PLK1 Inhibition alleviates transplant-associated obliterative bronchiolitis by suppressing myofibroblast differentiation

Chronic allograft dysfunction (CAD) resulting from fibrosis is the major limiting factor for long-term survival of lung transplant patients. Myofibroblasts promote fibrosis in multiple organs, including the lungs. In this study, we identified PLK1 as a promoter of myofibroblast differentiation and investigated the mechanism by which its inhibition alleviates transplant-associated obliterative bronchiolitis (OB) during CAD. High-throughput bioinformatic analyses and experiments using the murine heterotopic tracheal transplantation model revealed that PLK1 is upregulated in grafts undergoing CAD as compared with controls, and that inhibiting PLK1 alleviates OB in vivo. Inhibition of PLK1 in vitro reduced expression of the specific myofibroblast differentiation marker α-smooth muscle actin (α-SMA) and decreased phosphorylation of both MEK and ERK. Importantly, we observed a similar phenomenon in human primary fibroblasts. Our results thus highlight PLK1 as a promising therapeutic target for alleviating transplant-associated OB through suppression of TGF-β1-mediated myofibroblast differentiation.

Spatio-temporal patterning of different connexins in developing and postnatal human kidneys and in nephrotic syndrome of the Finnish type (CNF)

Connexins (Cxs) are membrane-spanning proteins which enable flow of information important for kidney homeostasis. Changes in their spatiotemporal patterning characterize blood vessel abnormalities and chronic kidney diseases (CKD). We analysed spatiotemporal expression of Cx37, Cx40, Cx43 and Cx45 in nephron and glomerular cells of developing, postnatal kidneys, and nephrotic syndrome of the Finnish type (CNF) by using immunohistochemistry, statistical methods and electron microscopy. During kidney development, strong Cx45 expression in proximal tubules and decreasing expression in glomeruli was observed. In developing distal nephron, Cx37 and Cx40 showed moderate-to-strong expression, while weak Cx43 expression gradually increased. Cx45/Cx40 co-localized in mesangial and granular cells. Cx43 /Cx45 co-localized in podocytes, mesangial and parietal epithelial cells, and with podocyte markers (synaptopodin, nephrin). Different Cxs co-expressed with endothelial (CD31) and VSMC (α -SMA) markers in vascular walls. Peak signalling of Cx37, Cx43 and Cx40 accompanied kidney nephrogenesis, while strongest Cx45 signalling paralleled nephron maturation. Spatiotemporal Cxs patterning indicate participation of Cx45 in differentiation of proximal tubules, and Cx43, Cx37 and Cx40 in distal tubules differentiation. CNF characterized disorganized Cx45 expression in proximal tubules, increased Cx43 expression in distal tubules and overall elevation of Cx40 and Cx37, while Cx40 co-localized with increased number of interstitial myofibroblasts.

Dysregulated mesenchymal PDGFR-β drives kidney fibrosis

Kidney fibrosis is characterized by expansion and activation of platelet-derived growth factor receptor-β (PDGFR-β)-positive mesenchymal cells. To study the consequences of PDGFR-β activation, we developed a model of primary renal fibrosis using transgenic mice with PDGFR-β activation specifically in renal mesenchymal cells, driving their pathological proliferation and phenotypic switch toward myofibroblasts. This resulted in progressive mesangioproliferative glomerulonephritis, mesangial sclerosis, and interstitial fibrosis with progressive anemia due to loss of erythropoietin production by fibroblasts. Fibrosis induced secondary tubular epithelial injury at later stages, coinciding with microinflammation, and aggravated the progression of hypertensive and obstructive nephropathy. Inhibition of PDGFR activation reversed fibrosis more effectively in the tubulointerstitium compared to glomeruli. Gene expression signatures in mice with PDGFR-β activation resembled those found in patients. In conclusion, PDGFR-β activation alone is sufficient to induce progressive renal fibrosis and failure, mimicking key aspects of chronic kidney disease in humans. Our data provide direct proof that fibrosis per se can drive chronic organ damage and establish a model of primary fibrosis allowing specific studies targeting fibrosis progression and regression.

Evaluating Renal Fibrosis with R2* Histogram Analysis of the Whole Cortex in a Unilateral Ureteral Obstruction Model

RATIONALE AND OBJECTIVES

The aim of this study was to use histogram analysis to assess the correlation between blood oxygen-level dependent magnetic resonance imaging (BOLD-MRI) and renal fibrosis induced by unilateral ureteral obstruction (UUO) in an animal model for a long experimental period.

MATERIALS AND METHODS

The rabbits were randomly divided into a control group (n = 6) and a UUO group (n = 30). The rabbits in the UUO group underwent left ureteral obstruction surgery. BOLD-MRI examinations were performed at 2, 4, 6, and 8 weeks after ligation. After the examinations, nephrectomy was performed for histologic evaluation. Histogram analysis of the left renal cortex (C) R2* values was performed to measure the mean, median, 10th percentile, 90th percentile, skewness, and kurtosis for all kidneys. Masson trichrome staining was used to assess the percentage of fibrotic area.

RESULTS

The histogram R2* values of the mean, median, 10th percentile, and 90th percentile at week 2 were all lower than those at baseline. Over the course of UUO progression, there were statistical differences between the histogram R2* values at any other two time points, except between weeks 4 and 6, and weeks 6 and 8. A close correlation was found between the percentage of fibrotic area and R2* values (mean: F = 21.49, p = 0.0001, R² = 0.49, median: F = 30.07, p < 0.0001, R² = 0.58, 10th percentile: F = 31.02, p < 0.0001, R² = 0.59, 90th percentile: F = 24.13, p < 0.0001, R² = 0.52).

CONCLUSION

BOLD-MRI could reflect the formation and progression of renal fibrosis in a rabbit UUO model; however, the value of BOLD-MRI in the long-term evaluation of fibrosis is limited.

Identification of a pro-angiogenic functional role for FSP1-positive fibroblast subtype in wound healing

Fibrosis accompanying wound healing can drive the failure of many different organs. Activated fibroblasts are the principal determinants of post-injury pathological fibrosis along with physiological repair, making them a difficult therapeutic target. Although activated fibroblasts are phenotypically heterogeneous, they are not recognized as distinct functional entities. Using mice that express GFP under the FSP1 or αSMA promoter, we characterized two non-overlapping fibroblast subtypes from mouse hearts after myocardial infarction. Here, we report the identification of FSP1-GFP⁺ cells as a non-pericyte, non-hematopoietic fibroblast subpopulation with a predominant pro-angiogenic role, characterized by in vitro phenotypic/cellular/ultrastructural studies and in vivo granulation tissue formation assays combined with transcriptomics and proteomics. This work identifies a fibroblast subtype that is functionally distinct from the pro-fibrotic αSMA-expressing myofibroblast subtype. Our study has the potential to shift our focus towards viewing fibroblasts as molecularly and functionally heterogeneous and provides a paradigm to approach treatment for organ fibrosis.

Activated fibroblasts are key contributors to tissue repair after cardiac injury. Here, Saraswati et al. identify and characterize a subpopulation of FSP1-positive cardiac fibroblasts with proangiogenic properties in infarcted hearts.

Immune cells and inflammation in AKI to CKD progression

Acute kidney injury (AKI) is a common clinical state resulting from pathogenic conditions such as ischemic and toxic insults. The pathophysiology of AKI shares common pathogenic denominators including cell death/injury, inflammation, and fibrosis, regardless of the initiating insults. Recent clinical studies have shown that a single episode of AKI can lead to subsequent chronic kidney disease (CKD). Although the involvement of multiple types of cells in the pathophysiology of AKI is becoming increasingly clear, the precise mechanisms for this "AKI to CKD progression" are still unknown, and no drug has been shown to halt this progression. An increasing number of epidemiological studies have also revealed that the presence of aging greatly increases the risk of AKI to CKD progression, and chronic inflammation is increasingly recognized as an important determinant factor for this progression. In this review article, we first describe the current understanding of the pathophysiology of AKI to CKD progression based on multiple types of cells. In particular, we will highlight the recent findings in regard to the mechanisms for chronic inflammation after AKI. Subsequently, we will focus on the mechanisms responsible for the increased risk of AKI to CKD progression in the elderly. Finally, we highlight our recent finding of age-dependent tertiary lymphoid tissue formation and its roles in AKI to CKD progression and speculate on the potential therapeutic opportunities that come from targeting aberrant inflammation after AKI.

Human dendritic cell-specific ICAM-3-grabbing non-integrin downstream signaling alleviates renal fibrosis via Raf-1 activation in systemic candidiasis

We generated a human dendritic cell-specific ICAM-3-grabbing non-integrin (DC-SIGN) transgenic mouse in which renal tubular epithelial cells expressed DC-SIGN. The transgenic mice were infected with Candida albicans intravenously to study how DC-SIGN expression affected the pathogenesis of systemic candidiasis. We discovered that, while C. albicans infection induced renal fibrosis in both transgenic and littermate control mice, the transgenic mice had significantly lower levels of Acta2, Col1a2, Col3a1, and Col4a1 mRNA transcripts compared to the controls. KIM-1, an emerging biomarker for kidney injury, along with Tnf, Il6, and Tgfb1 transcripts, were lower in infected transgenic mice, and yet, the levels of Il10 remained comparable to the controls. While renal CD45⁺ infiltrating cells were the source of Tnf, Il6, and Il10, LTL⁺ renal proximal tubular epithelial cells were TGF-β1 producers in both infected transgenic and littermate controls. DC-SIGN-expressing tubular epithelial cells produced less TGF-β1 in response to C. albicans infection. In vivo experiments demonstrated that renal proximal tubular epithelial cell production of TGF-β1 was key to C. albicans-induced renal fibrosis and injury. Infection of transgenic mice induced a marked increase of phosphorylated Raf-1 and p38 in the kidney. However, ERK1/2 and JNK phosphorylation was more pronounced in the infected-littermate controls. Interestingly, treating the infected transgenic mice with a Raf-1 inhibitor increased the levels of the Tgfb1, Kim1, and Acta2 transcripts. These results indicate that DC-SIGN signaling, through activation of Raf-1 and p38 and suppression of JNK and ERK1/2 phosphorylation, reduces TGF-β1 production and C. albicans-induced renal fibrosis. Our study reveals for the first time the effect of DC-SIGN expression on C. albicans-induced renal fibrosis.

Renal fibrosis: Primacy of the proximal tubule

Tubulointerstitial fibrosis (TIF) is the hallmark of chronic kidney disease and best predictor of renal survival. Many different cell types contribute to TIF progression including tubular epithelial cells, myofibroblasts, endothelia, and inflammatory cells. Previously, most of the attention has centered on myofibroblasts given their central importance in extracellular matrix production. However, emerging data focuses on how the response of the proximal tubule, a specialized epithelial segment vulnerable to injury, plays a central role in TIF progression. Several proximal tubular responses such as de-differentiation, cell cycle changes, autophagy, and metabolic changes may be adaptive initially, but can lead to maladaptive responses that promote TIF both through autocrine and paracrine effects. This review discusses the current paradigm of TIF progression and the increasingly important role of the proximal tubule in promoting TIF both in tubulointerstitial and glomerular injuries. A better understanding and appreciation of the role of the proximal tubule in TIF has important implications for therapeutic strategies to halt chronic kidney disease progression.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

Complement Activation During Ischemia/Reperfusion Injury Induces Pericyte-to-Myofibroblast Transdifferentiation Regulating Peritubular Capillary Lumen Reduction Through pERK Signaling

Pericytes are one of the principal sources of scar-forming myofibroblasts in chronic kidneys disease. However, the modulation of pericyte-to-myofibroblast transdifferentiation (PMT) in the early phases of acute kidney injury is poorly understood. Here, we investigated the role of complement in inducing PMT after transplantation. Using a swine model of renal ischemia/reperfusion (I/R) injury, we found the occurrence of PMT after 24 h of I/R injury as demonstrated by reduction of PDGFRβ⁺/NG2⁺ cells with increase in myofibroblasts marker αSMA. In addition, PMT was associated with significant reduction in peritubular capillary luminal diameter. Treatment by C1-inhibitor (C1-INH) significantly preserved the phenotype of pericytes maintaining microvascular density and capillary lumen area at tubulointerstitial level. In vitro, C5a transdifferentiated human pericytes in myofibroblasts, with increased αSMA expression in stress fibers, collagen I production, and decreased antifibrotic protein Id2. The C5a-induced PMT was driven by extracellular signal-regulated kinases phosphorylation leading to increase in collagen I release that required both non-canonical and canonical TGFβ pathways. These results showed that pericytes are a pivotal target of complement activation leading to a profibrotic maladaptive cellular response. Our studies suggest that C1-INH may be a potential therapeutic strategy to counteract the development of PMT and capillary lumen reduction in I/R injury.

Characterisation of feline renal cortical fibroblast cultures and their transcriptional response to transforming growth factor β1

Background

Chronic kidney disease (CKD) is common in geriatric cats, and the most prevalent pathology is chronic tubulointerstitial inflammation and fibrosis. The cell type predominantly responsible for the production of extra-cellular matrix in renal fibrosis is the myofibroblast, and fibroblast to myofibroblast differentiation is probably a crucial event. The cytokine TGF-β1 is reportedly the most important regulator of myofibroblastic differentiation in other species. The aim of this study was to isolate and characterise renal fibroblasts from cadaverous kidney tissue of cats with and without CKD, and to investigate the transcriptional response to TGF-β1.

Results

Cortical fibroblast cultures were successfully established from the kidney tissue of cats with normal kidney function (FCF) and cats with chronic kidney disease (CKD-FCF). Both cell types expressed the mesenchymal markers vimentin, CD44 and CD29, and were negative for the epithelial marker cytokeratin, mesangial cell marker desmin and endothelial cell marker vWF. Only CKD-FCF expressed VCAM-1, a cell marker associated with inflammation. Incubation with TGF-β1 (0–10 ng/ml) induced a concentration dependent change in cell morphology, and upregulation of myofibroblast marker gene α-SMA expression alongside collagen 1α1, fibronectin, TGF-β1 and CTGF mRNA. These changes were blocked by the TGF-β1 receptor 1 antagonist SB431542 (5 μM).

Conclusions

FCF and CKD-FCF can be cultured via a simple method and represent a model for the investigation of the progression of fibrosis in feline CKD. The findings of this study suggest TGF-β1 may be involved in fibroblast-myofibroblast transition in feline CKD, as in other species.

C/EBP homologous protein (CHOP) deficiency ameliorates renal fibrosis in unilateral ureteral obstructive kidney disease

Renal tubulointerstitial fibrosis is an important pathogenic feature in chronic kidney disease and end-stage renal disease, regardless of the initiating insults. A recent study has shown that CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP) is involved in acute ischemia/reperfusion-related acute kidney injury through oxidative stress induction. However, the influence of CHOP on chronic kidney disease-correlated renal fibrosis remains unclear. Here, we investigated the role of CHOP in unilateral ureteral obstruction (UUO)-induced experimental chronic tubulointerstital fibrosis. The CHOP knockout and wild type mice with or without UUO were used. The results showed that the increased expressions of renal fibrosis markers collagen I, fibronectin, α-smooth muscle actin, and plasminogen activator inhibitor-1 in the kidneys of UUO-treated wild type mice were dramatically attenuated in the kidneys of UUO-treated CHOP knockout mice. CHOP deficiency could also ameliorate lipid peroxidation and endogenous antioxidant enzymes depletion, tubular apoptosis, and inflammatory cells infiltration in the UUO kidneys. These results suggest that CHOP deficiency not only attenuates apoptotic death and oxidative stress in experimental renal fibrosis, but also reduces local inflammation, leading to diminish UUO-induced renal fibrosis. Our findings support that CHOP may be an important signaling molecule in the progression of chronic kidney disease.

Ablation of FGFR2 in Fibroblasts Ameliorates Kidney Fibrosis after Ischemia/Reperfusion Injury in Mice

Background

Fibroblast growth factors (FGFs) are heparin-binding proteins involved in a variety of biological processes. However, the role and mechanisms of FGF/FGFR2 signaling in fibroblast activation and kidney fibrosis need further investigation.

Methods

In this study, a mouse model with fibroblast-specific FGFR2 gene disruption was generated. The knockouts were born normal and no kidney dysfunction or histological abnormality was found within 2 months after birth. A kidney ischemia/reperfusion injury (IRI) model was created.

Results

Kidney fibrosis was developed in the control littermates within 2 and 4 weeks after IRI, while in the knockouts, total collagen deposition, fibronectin, and alpha smooth muscle actin expression were decreased compared to those in the control littermates. In addition, the numbers of Ki-67-positive interstitial cells as well as TUNEL-positive interstitial cells were lower in the knockout kidneys at 4 weeks after IRI. Phosphorylated extracellular regulated protein kinase 1/2 was decreased in the knockout kidneys at 2 and 4 weeks after IRI compared to those in the control littermates.

Conclusion

These results suggest that FGF/FGFR2 signaling may promote the proliferation and activation of kidney fibroblasts, which contribute to the development of kidney fibrosis.

Therapeutic pro-fibrogenic signaling pathways in fibroblasts

Myofibroblasts (MFs) play a critical role in the progression of chronic inflammatory and fibroproliferative diseases in different tissues/organs, whatever the etiology. Fibrosis is preceded and sustained by persistent injury and inflammatory response in a profibrogenic scenario involving mutual interactions, operated by several mediators and pathways, of MFs and related precursor cells with innate immunity cells and virtually any cell type in a defined tissue. These interactions, mediators and related signaling pathways are critical in initiating and perpetuating the differentiation of precursor cells into MFs that in different tissues share peculiar traits and phenotypic responses, including the ability to proliferate, produce ECM components, migrate and contribute to the modulation of inflammatory response and tissue angiogenesis. Literature studies related to liver, lung and kidney fibrosis have outlined a number of MF-related core regulatory fibrogenic signaling pathways conserved across these different organs and potentially targetable in order to develop effective antifibrotic therapeutic strategies.

Macrophage Migration Inhibitory Factor Limits Renal Inflammation and Fibrosis by Counteracting Tubular Cell Cycle Arrest

Renal fibrosis is a common underlying process of progressive kidney diseases. We investigated the role of macrophage migration inhibitory factor (MIF), a pleiotropic proinflammatory cytokine, in this process. In mice subjected to unilateral ureteral obstruction, genetic deletion or pharmacologic inhibition of MIF aggravated fibrosis and inflammation, whereas treatment with recombinant MIF was beneficial, even in established fibrosis. In two other models of progressive kidney disease, global Mif deletion or MIF inhibition also worsened fibrosis and inflammation and associated with worse kidney function. Renal MIF expression was reduced in tubular cells in fibrotic compared with healthy murine and human kidneys. Bone marrow chimeras showed that Mif expression in bone marrow-derived cells did not affect fibrosis and inflammation after UUO. However, Mif gene deletion restricted to renal tubular epithelial cells aggravated these effects. In LPS-stimulated tubular cell cultures, Mif deletion led to enhanced G2/M cell-cycle arrest and increased expression of the CDK inhibitor 1B (p27Kip1) and of proinflammatory and profibrotic mediators. Furthermore, MIF inhibition reduced tubular cell proliferation in vitro In all three in vivo models, global Mif deletion or MIF inhibition caused similar effects and attenuated the expression of cyclin B1 in tubular cells. Mif deletion also resulted in reduced tubular cell apoptosis after UUO. Recombinant MIF exerted opposing effects on tubular cells in vitro and in vivo Our data identify renal tubular MIF as an endogenous renoprotective factor in progressive kidney diseases, raising the possibility of pharmacologic intervention with MIF pathway agonists, which are in advanced preclinical development.

Resident fibroblasts in the kidney: a major driver of fibrosis and inflammation

Background

Chronic kidney disease (CKD) is a leading cause of end stage renal disease (ESRD) and cardiovascular morbidity and mortality worldwide, resulting in a growing social and economic burden. The prevalence and burden of CKD is anticipated to further increase over the next decades as a result of aging.

Main body of abstract

In the pathogenesis of CKD, irrespective of the etiology, resident fibroblasts are key players and have been demonstrated to play crucial roles for disease initiation and progression. In response to injury, resident fibroblasts transdifferentiate into myofibroblasts that express alpha smooth muscle actin (αSMA) and have an increased capacity to produce large amounts of extracellular matrix (ECM) proteins, leading to renal fibrosis. In addition to this fundamental role of fibroblasts as drivers for renal fibrosis, growing amounts of evidence have shown that resident fibroblasts are also actively involved in initiating and promoting inflammation during kidney injury. During the myofibroblastic transition described above, resident fibroblasts activate NF-κB signaling and produce pro-inflammatory cytokines and chemokines, promoting inflammation. Furthermore, under aging milieu, resident fibroblasts transdifferentiate into several distinct phenotypic fibroblasts, including CXCL13/CCL19-producing fibroblasts, retinoic acid-producing fibroblasts, and follicular dendritic cells, in response to injury and orchestrate tertiary lymphoid tissue (TLT) formation, which results in uncontrolled aberrant inflammation and retards tissue repair. Anti-inflammatory agents can improve myofibroblastic transdifferentiation and abolish TLT formation, suggesting that targeting these inflammatory fibroblasts can potentially ameliorate kidney disease.

Short conclusion

Beyond its conventional role as an executor of fibrosis, resident fibroblasts display more pro-inflammatory phenotypes and contribute actively to driving inflammation during kidney injury.

Ablation of endothelial prolyl hydroxylase domain protein-2 promotes renal vascular remodelling and fibrosis in mice

Accumulating evidence demonstrates that hypoxia-inducible factor (HIF-α) hydroxylase system has a critical role in vascular remodelling. Using an endothelial-specific prolyl hydroxylase domain protein-2 (PHD2) knockout (PHD2^EC KO) mouse model, this study investigates the regulatory role of endothelial HIF-α hydroxylase system in the development of renal fibrosis. Knockout of PHD2 in EC up-regulated the expression of HIF-1α and HIF-2α, resulting in a significant decline of renal function as evidenced by elevated levels of serum creatinine. Deletion of PHD2 increased the expression of Notch3 and transforming growth factor (TGF-β1) in EC, thus further causing glomerular arteriolar remodelling with an increased pericyte and pericyte coverage. This was accompanied by a significant elevation of renal resistive index (RI). Moreover, knockout of PHD2 in EC up-regulated the expression of fibroblast-specific protein-1 (FSP-1) and increased interstitial fibrosis in the kidney. These alterations were strongly associated with up-regulation of Notch3 and TGF-β1. We concluded that the expression of PHD2 in endothelial cells plays a critical role in renal fibrosis and vascular remodelling in adult mice. Furthermore, these changes were strongly associated with up-regulation of Notch3/TGF-β1 signalling and excessive pericyte coverage.

Highly Expressed Antisense Noncoding RNA in the INK4 Locus Promotes Growth and Invasion of Renal Clear Carcinoma Cells via the β-Catenin Pathway

Long noncoding RNA (lncRNA) antisense noncoding RNA in the INK4 locus (ANRIL) is involved in several human cancers. However, the role of ANRIL in renal cell carcinoma (RCC) remains unclear. This study aimed to explore whether, and how, ANRIL affects the progression of RCC. First, the expression of ANRIL in clinical tumor tissues and four kinds of RCC cell lines was evaluated. After transfection, cell viability, colony number, apoptosis, migration, and invasion were assessed. The expression of proteins related to apoptosis, epithelial-to-mesenchymal transition (EMT), and the β-catenin signaling pathway was then assessed. In addition, the effect of IWR-endo (β-catenin inhibitor) on cell viability, migration, and invasion, as well as β-catenin expression, was also evaluated. The results showed that ANRIL was highly expressed in RCC tissues and RCC cell lines. ANRIL significantly promoted cell proliferation, migration, invasion, and EMT but inhibited cell apoptosis. Additionally, the expression levels of β-catenin, Ki-67, glycogen synthase kinase 3β (GSK-3β), phosphorylated GSK-3β, T-cell transcription factor 4 (TCF-4), and leukemia enhancer factor 1 (LEF-1) were all markedly upregulated by ANRIL. The effect of ARNIL silencing was opposite to that of ANRIL overexpression. The effect of ARNIL on proliferation, migration, and invasion of RCC cells was found to be reversed by IWR-endo. In conclusion, ANRIL, which is highly expressed in RCC, acted as a carcinogen in RCC cells through the activation of the β-catenin pathway.

Crucial Role of Mesangial Cell-derived Connective Tissue Growth Factor in a Mouse Model of Anti-Glomerular Basement Membrane Glomerulonephritis

Connective tissue growth factor (CTGF) coordinates the signaling of growth factors and promotes fibrosis. Neonatal death of systemic CTGF knockout (KO) mice has hampered analysis of CTGF in adult renal diseases. We established 3 types of CTGF conditional KO (cKO) mice to investigate a role and source of CTGF in anti-glomerular basement membrane (GBM) glomerulonephritis. Tamoxifen-inducible systemic CTGF (Rosa-CTGF) cKO mice exhibited reduced proteinuria with ameliorated crescent formation and mesangial expansion in anti-GBM nephritis after induction. Although CTGF is expressed by podocytes at basal levels, podocyte-specific CTGF (pod-CTGF) cKO mice showed no improvement in renal injury. In contrast, PDGFRα promoter-driven CTGF (Pdgfra-CTGF) cKO mice, which predominantly lack CTGF expression by mesangial cells, exhibited reduced proteinuria with ameliorated histological changes. Glomerular macrophage accumulation, expression of Adgre1 and Ccl2, and ratio of M1/M2 macrophages were all reduced both in Rosa-CTGF cKO and Pdgfra-CTGF cKO mice, but not in pod-CTGF cKO mice. TGF-β1-stimulated Ccl2 upregulation in mesangial cells and macrophage adhesion to activated mesangial cells were decreased by reduction of CTGF. These results reveal a novel mechanism of macrophage migration into glomeruli with nephritis mediated by CTGF derived from mesangial cells, implicating the therapeutic potential of CTGF inhibition in glomerulonephritis.

Analysis of Pathological Activities of CCN Proteins in Fibrotic Diseases: Kidney Fibrosis

Renal fibrosis is characterized by glomerulosclerosis and tubulointerstitial fibrosis. Transforming growth factor-β (TGF-β) is postulated to play a central role in the development of both fibrotic processes. Extracellular matrix proteins, particularly type I collagen and fibronectin, accumulate in the tissue during renal fibrogenesis. CCN2, also known as connective tissue growth factor (CTGF), is increased in the setting of fibrosis and modulates a number of downstream signaling pathways involved in the fibrogenic properties of TGF-β. Unilateral ureteral obstruction is one of the most widely used models of renal tubulointerstitial fibrosis. Herein, we describe unilateral ureteral obstruction in mice as an animal model of renal fibrosis and methods for immunohistochemical analyses of extracellular matrix proteins and CCN2. In addition, we describe the construction of podocyte-specific CCN2-transgenic mice for analyzing mesangial matrix expansion and glomerulosclerosis.

Origin and Function of the Renal Stroma in Health and Disease

The renal stroma is defined as a heterogeneous population of cells that serve both as a supportive framework and as a source of specialized cells in the renal capsule, glomerulus, vasculature, and interstitium. In this chapter, we review published evidence defining what, where, and why stromal cells are important. We describe the functions of the renal stroma andhow stromal derivatives are crucial for normal kidney function. Next, we review the specification of stromal cells from the Osr1+ intermediate mesoderm and T+ presomitic mesoderm during embryogenesis and stromal cell differentiation. We focus on stromal signaling mechanisms that act in both a cell and non-cell autonomous manner in communication with the nephron progenitor and ureteric lineages. To conclude, stromal cells and the contribution of stromal cells to renal fibrosis and chronic kidney disease are described.

Spirolactone provides protection from renal fibrosis by inhibiting the endothelial-mesenchymal transition in isoprenaline-induced heart failure in rats

Background

Fibrosis results in excessive accumulation of extracellular matrix proteins, collagen component alteration, and abnormalities in structure and is partly derived from a process called the endothelial–mesenchymal transition involving transforming growth factor β (TGF-β). We investigated whether spironolactone, an aldosterone receptor blocker, attenuated isoprenaline (Iso)-induced heart failure in rats and also studied the mechanism for the same.

Methods

Sprague–Dawley rats were subcutaneously injected with Iso to induce heart failure, which promoted renal fibrosis; rats with spironolactone treatment were given a gavage of spironolactone (30 or 60 mg/kg/d, for 21 days). Cardiac function and fibrosis indices were measured. Pathological alterations and expression of Type I and III collagen, α-smooth muscle actin, cluster of differentiation-31, and TGF-β were examined.

Results

In Iso-induced heart failure in rats, spironolactone significantly improved cardiac function and decreased myocardial fibrosis, reduced collagen fibrous proliferation in kidney, reduced expression of Type I and III collagen, increased the expression of cluster of differentiation-31, and decreased the expression of α-smooth muscle actin and TGF-β.

Conclusion

Spironolactone may prevent renal fibrosis by inhibiting the endothelial–mesenchymal transition.

Metformin Prevents Renal Fibrosis in Mice with Unilateral Ureteral Obstruction and Inhibits Ang II-Induced ECM Production in Renal Fibroblasts

Renal fibrosis is the final common pathway of chronic kidney disease (CKD), and no effective medication is available clinically for managing its progression. Metformin was initially developed as an anti-diabetic drug and recently gained attention for its potential in the treatment of other diseases. In this study, we investigated its effects on renal fibrosis in a mouse model of unilateral ureteral obstruction (UUO) in vivo and in angiotensin II (Ang II)–treated renal fibroblast NRK-49F cells in vitro. Our data showed that UUO induced renal fibrosis and combined with the activation of ERK signaling, the upregulation of fibronectin, collagen I, and transforming growth factor-β (TGF-β). The administration of metformin inhibited the activation of ERK signaling and attenuated the production of extracellular matrix (ECM) proteins and collagen deposition in the obstructed kidneys. In cultured renal fibroblasts, Ang II increased the expression of fibronectin and collagen I and also activated ERK signaling and TGF-β in a time-dependent manner. Pretreatment of the cells with metformin blocked Ang II–induced ERK signaling activation and ECM overproduction. Our results show that metformin prevents renal fibrosis, possibly through the inhibition of ERK signaling, and may be a novel strategy for the treatment of renal fibrosis.

Erythropoietin Synthesis in Renal Myofibroblasts Is Restored by Activation of Hypoxia Signaling

Erythropoietin (Epo) is produced by renal Epo-producing cells (REPs) in a hypoxia-inducible manner. The conversion of REPs into myofibroblasts and coincident loss of Epo-producing ability are the major cause of renal fibrosis and anemia. However, the hypoxic response of these transformed myofibroblasts remains unclear. Here, we used complementary in vivo transgenic and live imaging approaches to better understand the importance of hypoxia signaling in Epo production. Live imaging of REPs in transgenic mice expressing green fluorescent protein from a modified Epo-gene locus revealed that healthy REPs tightly associated with endothelium by wrapping processes around capillaries. However, this association was hampered in states of renal injury-induced inflammation previously shown to correlate with the transition to myofibroblast-transformed renal Epo-producing cells (MF-REPs). Furthermore, activation of hypoxia-inducible factors (HIFs) by genetic inactivation of HIF-prolyl hydroxylases (PHD1, PHD2, and PHD3) selectively in Epo-producing cells reactivated Epo production in MF-REPs. Loss of PHD2 in REPs restored Epo-gene expression in injured kidneys but caused polycythemia. Notably, combined deletions of PHD1 and PHD3 prevented loss of Epo expression without provoking polycythemia. Mice with PHD-deficient REPs also showed resistance to LPS-induced Epo repression in kidneys, suggesting that augmented HIF signaling counterbalances inflammatory stimuli in regulation of Epo production. Thus, augmentation of HIF signaling may be an attractive therapeutic strategy for treating renal anemia by reactivating Epo synthesis in MF-REPs.

Renal erythropoietin-producing cells in health and disease

Erythropoietin (Epo) is an indispensable erythropoietic hormone primarily produced from renal Epo-producing cells (REPs). Epo production in REPs is tightly regulated in a hypoxia-inducible manner to maintain tissue oxygen homeostasis. Insufficient Epo production by REPs causes renal anemia and anemia associated with chronic disorders. Recent studies have broadened our understanding of REPs from prototypic hypoxia-responsive cells to dynamic fibrogenic cells. In chronic kidney disease, REPs are the major source of scar-forming myofibroblasts and actively produce fibrogenic molecules, including inflammatory cytokines. Notably, myofibroblast-transformed REPs (MF-REPs) recover their original physiological properties after resolution of the disease insults, suggesting that renal anemia and fibrosis could be reversible to some extent. Therefore, understanding the plasticity of REPs will lead to the development of novel targeted therapeutics for both renal fibrosis and anemia. This review summarizes the regulatory mechanisms how hypoxia-inducible Epo gene expression is attained in health and disease conditions.