Role of C/EBP-α in Adriamycin-induced podocyte injury

Adriamycin-induced nephropathy models: elucidating CKD pathophysiology and advancing therapeutic strategies

The Adriamycin-induced nephropathy (AN) model plays a crucial role in advancing our understanding of and research on chronic kidney disease (CKD). This review outlines methodologies for generating AN models in mice and rats, discusses their pathophysiologic and molecular characteristics, highlights their advantages and limitations, describes therapeutic interventions that have been evaluated in these models, and presents future research perspectives. The AN model replicates key features observed in human CKD, such as proteinuria, podocyte injury, glomerulosclerosis, and tubulointerstitial fibrosis. Notably, genetic factors significantly influence the onset and severity of AN, with mutations in the Prkdc gene linked to nephrotoxicity and systemic toxicity. To evaluate therapeutic interventions for CKD, agents such as ACE inhibitors, corticosteroids, and SGLT2 inhibitors have been tested in the AN model, demonstrating promising renoprotective effects. However, the systemic toxicity of Adriamycin and variability across models pose limitations, highlighting the need for caution when translating findings to human CKD. Future advancements in genetic engineering and the application of CRISPR-Cas9 technology are expected to improve the fidelity of AN models to human disease. Additionally, discovery of biomarkers by using the AN model enables us to improve early diagnosis. These efforts are anticipated to deepen our understanding of CKD pathophysiology and contribute to developing more effective diagnostic tools and targeted therapies.

Cells of all trades - on the importance of spatial positioning of senescent cells in development, healing and aging

Biological processes are often spatially regulated, ensuring molecular and cellular events occur in their most strategically advantageous locations. Cellular senescence, marked by cell cycle arrest and hypersecretion, is recognized as an important part of physiological processes like development and healing, but it also contributes to aging and disease. However, the spatial distribution of senescent cells and its physiological and pathological impact remain unclear. Here we compile evidence on senescent cell localization in development, healing, and aging. We emphasize the significance of their spatial patterns and speculate on the effects of disrupted spatial positioning of senescence in relation to pathologies. To summarize the specific spatial functions of senescent cells, we propose to refer to them as 'barrier' and 'conductor' functions. The 'barrier' function of senescent cells, due to their altered morphology and apoptosis resistance, separates tissues and builds a border between two environments. The conductor function, with the secretion of signaling factors, influences the surrounding area and stimulates migration, differentiation, or proliferation, among other processes. Overall, this Review explores the spatial patterning of cellular senescence in biological processes, highlighting its dual roles as 'barrier' and 'conductor' functions, and examines the implications of senescent cell distribution in development, healing, aging, and disease.

SA4503 Mitigates Adriamycin-Induced Nephropathy via Sigma-1 Receptor in Animal and Cell-Based Models

Background/Objectives: The Sigma-1 receptor (Sigmar1), an intracellular chaperone protein, is ubiquitously expressed throughout the body, but its role in peripheral organs, such as the kidneys, remains unclear. Here, we investigated the protective effects and molecular mechanisms of SA4503, a selective Sigmar1 agonist, on Adriamycin (ADR)-induced renal glomerular injury. Methods: Using in vitro and in vivo models, we evaluated the effects of SA4503 on ADR-induced podocyte injury, including podocyte survival, albumin permeability, urinary albumin levels, and Sigmar1-nephrin interactions. NE-100, a Sigmar1 antagonist, was co-administered to validate the specificity of the effects of SA4503. Results: Sigmar1 was highly expressed in podocytes and mouse kidney tissues. SA4503 significantly reduced ADR-induced podocyte injury and urinary albumin leakage in mice. Mechanistically, SA4503 preserved Sigmar1-nephrin interactions, which were disrupted in ADR-treated kidneys. This protective effect was abolished by NE-100 co-treatment, confirming the Sigmar1-dependency of SA4503's action. Conclusions: These findings demonstrate that the activation of Sigmar1 by SA4503 protects against ADR-induced podocyte injury and glomerular damage, likely by stabilizing Sigmar1-nephrin interactions. Therefore, Sigmar1 represents a promising therapeutic target for glomerular diseases such as nephrotic syndrome.

Podocyte senescence: from molecular mechanisms to therapeutics

As an important component of the glomerular filtration membrane, the state of the podocytes is closely related to kidney function, they are also key cells involved in aging and play a central role in the damage caused by renal aging. Therefore, understanding the aging process of podocytes will allow us to understand their susceptibility to injury and identify targeted protective mechanisms. In fact, the process of physiological aging itself can induce podocyte senescence. Pathological stresses, such as oxidative stress, mitochondrial damage, secretion of senescence-associated secretory phenotype, reduced autophagy, oncogene activation, altered transcription factors, DNA damage response, and other factors, play a crucial role in inducing premature senescence and accelerating aging. Senescence-associated-β-galactosidase (SA-β-gal) is a marker of aging, and β-hydroxybutyric acid treatment can reduce SA-β-gal activity to alleviate cellular senescence and damage. In addition, CCAAT/enhancer-binding protein-α, transforming growth factor-β signaling, glycogen synthase kinase-3β, cycle-dependent kinase, programmed cell death protein 1, and plasminogen activator inhibitor-1 are closely related to aging. The absence or elevation of these factors can affect aging through different mechanisms. Podocyte injury is not an independent process, and injured podocytes interact with the surrounding epithelial cells or other kidney cells to mediate the injury or loss of podocytes. In this review, we discuss the manifestations, molecular mechanisms, biomarkers, and therapeutic drugs for podocyte senescence. We included elamipretide, lithium, calorie restriction, rapamycin; and emerging treatment strategies, such as gene and immune therapies. More importantly, we summarize how podocyte interact with other kidney cells.

ATP dynamics as a predictor of future podocyte structure and function after acute ischemic kidney injury in female mice

Acute kidney injury (AKI), typically caused by ischemia, is a common clinical complication with a poor prognosis. Although proteinuria is an important prognostic indicator of AKI, the underlying causal mechanism remains unclear. In vitro studies suggest that podocytes have high ATP demands to maintain their structure and function, however, analyzing their ATP dynamics in living kidneys has been technically challenging. Here, using intravital imaging to visualize a FRET-based ATP biosensor expressed systemically in female mice due to their suitability for glomerular imaging, we monitor the in vivo ATP dynamics in podocytes during ischemia reperfusion injury. ATP levels decrease during ischemia, but recover after reperfusion in podocytes, exhibiting better recovery than in glomerular endothelial cells. However, prolonged ischemia results in insufficient ATP recovery in podocytes, which is inversely correlated with mitochondrial fragmentation and foot process effacement during the chronic phase. Furthermore, preventing mitochondrial fission via pharmacological inhibition ameliorates podocyte injury in vitro, ex vivo, and in vivo. Thus, these findings provide several insights into how ATP depletion and mitochondrial fragmentation contribute to podocyte injury after ischemic AKI and could potentially be therapeutic targets.

C/EBPα-mediated ACSL4-dependent ferroptosis exacerbates tubular injury in diabetic kidney disease

Diabetic kidney disease (DKD) is a prevalent and debilitating complication of diabetes characterized by progressive renal function decline and a lack of effective treatment options. Here, we investigated the role of the transcription factor CCAAT/enhancer binding protein alpha (C/EBPα) in DKD pathogenesis. Analysis of renal biopsy samples revealed increased C/EBPα expression in patients with DKD. Using RNA sequencing and proteomics, we explored the mechanisms through which the C/EBPα contributes to DKD. Our findings demonstrated that C/EBPα exacerbated tubular injury by promoting acyl-CoA synthetase long-chain family member 4 (ACSL4)-dependent ferroptosis. We identified that C/EBPα upregulated ACSL4 expression by binding to its transcription regulatory sequence (TRS), leading to elevated lipid peroxidation and ferroptosis. Furthermore, inhibition or genetic ablation of C/EBPα attenuated ferroptosis and mitigated tubular injury in DKD. These results highlighted the C/EBPα-ACSL4-ferroptosis pathway as a promising therapeutic target for DKD treatment.

C/EBPα aggravates renal fibrosis in CKD through the NOX4-ROS-apoptosis pathway in tubular epithelial cells

BACKGROUND

Chronic kidney disease (CKD) is a prevalent renal disorder with various risk factors. Emerging evidence indicates that the transcriptional factor CCAAT/enhancer binding protein alpha (C/EBPα) may be associated with renal fibrosis. However, the precise role of C/EBPα in CKD progression remains unexplored.

METHODS

We investigated the involvement of C/EBPα in CKD using two distinct mouse models induced by folic acid (FA) and unilateral ureteral obstruction (UUO). Additionally, we used RNA sequencing and KEGG analysis to identify potential downstream pathways governed by C/EBPα.

FINDINGS

Cebpa knockout significantly shielded mice from renal fibrosis and reduced reactive oxygen species (ROS) levels in both the FA and UUO models. Primary tubular epithelial cells (PTECs) lacking Cebpa exhibited reduced apoptosis and ROS accumulation following treatment with TGF-β. RNA sequencing analysis suggested that apoptosis is among the primary pathways regulated by C/EBPα, and identified NADPH oxidoreductase 4 (NOX4) as a key protein upregulated upon C/EBPα induction (ICCB280). Treatment with l-Theanine, a potential NOX4 inhibitor, mitigated renal fibrosis and inflammation in both the FA and UUO mouse models.

INTERPRETATION

Our study unveils a role for C/EBPα in suppressing renal fibrosis, mitigating ROS accumulation, and reducing cell apoptosis. Furthermore, we investigate whether these protective effects are mediated by C/EBPα's regulation of NOX4 expression. These findings present a promising therapeutic target for modulating ROS and apoptosis in renal tubular cells, potentially offering an approach to treating CKD and other fibrotic diseases.

Adriamycin-Induced Podocyte Injury Disrupts the YAP-TEAD1 Axis and Downregulates Cyr61 and CTGF Expression

The most severe forms of kidney diseases are often associated with irreversible damage to the glomerular podocytes, the highly specialized epithelial cells that encase glomerular capillaries and regulate the removal of toxins and waste from the blood. Several studies revealed significant changes to podocyte cytoskeletal structure during disease onset, suggesting possible roles of cellular mechanosensing in podocyte responses to injury. Still, this topic remains underexplored partly due to the lack of appropriate in vitro models that closely recapitulate human podocyte biology. Here, we leveraged our previously established method for the derivation of mature podocytes from human induced pluripotent stem cells (hiPSCs) to help uncover the roles of yes-associated protein (YAP), a transcriptional coactivator and mechanosensor, in podocyte injury response. We found that while the total expression levels of YAP remain relatively unchanged during Adriamycin (ADR)-induced podocyte injury, the YAP target genes connective tissue growth factor (CTGF) and cysteine-rich angiogenic inducer 61 (Cyr61) are significantly downregulated. Intriguingly, TEAD1 is significantly downregulated in podocytes injured with ADR. By examining multiple independent modes of cellular injury, we found that CTGF and Cyr61 expression are downregulated only when podocytes were exposed to molecules known to disrupt the cell's mechanical integrity or cytoskeletal structure. To our knowledge, this is the first report that the YAP-TEAD1 signaling axis is disrupted when stem cell-derived human podocytes experience biomechanical injury. Together, these results could help improve the understanding of kidney disease mechanisms and highlight CTGF and Cyr61 as potential therapeutic targets or biomarkers for patient stratification.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

Pifithrin-α ameliorates glycerol induced rhabdomyolysis and acute kidney injury by reducing p53 activation

Objectives

Rhabdomyolysis is a series of symptoms caused by the dissolution of striped muscle, and acute kidney injury (AKI) is a potential complication of severe rhabdomyolysis. The underlying causes of AKI are remarkably complex and diverse. Here, we aim to investigate whether pifithrin-α protected against rhabdomyolysis-induced AKI and to determine the involved mechanisms.

Methods

Intramuscular injection in the right thigh caudal muscle of C57BL/6J mice with 7.5 ml/kg saline (Group A) or of the same volume 50% glycerol was used to induce rhabdomyolysis and subsequent AKI (Group B). Pifithrin-α was injected intraperitoneally 4 h before (Group C) or 4 h after (Group D) the glycerol injection. Serum creatine kinase, blood urea nitrogen, and creatinine were determined, and the renal cortex was histologically analyzed. Renal expression levels of interested mRNAs and proteins were determined and compared, too.

Results

Intramuscular injection of glycerol induced rhabdomyolysis and subsequent AKI in mice (Groups B–D). Renal function reduction and histologic injury of renal tubular epithelial cells were associated with increased p53 activation, oxidative stress, and inflammation. Notably, compared with pifithrin-α rescue therapy (Group D), pretreatment of pifithrin-α (Group C) protected the mice from severe injury more effectively.

Conclusions

Our present study suggests that p53 may be a therapeutic target of AKI caused by glycerol, and the inhibition of p53 can block glycerol-mediated AKI by using pharmacological agents instead of genetic inhibitory approaches, which further supports that p53 played a pivotal role in renal tubular injury when challenged with glycerol.

Podocyte Aging: Why and How Getting Old Matters

The effects of healthy aging on the kidney, and how these effects intersect with superimposed diseases, are highly relevant in the context of the population's increasing longevity. Age-associated changes to podocytes, which are terminally differentiated glomerular epithelial cells, adversely affect kidney health. This review discusses the molecular and cellular mechanisms underlying podocyte aging, how these mechanisms might be augmented by disease in the aged kidney, and approaches to mitigate progressive damage to podocytes. Furthermore, we address how biologic pathways such as those associated with cellular growth confound aging in humans and rodents.

AT2R deficiency in mice accelerates podocyte dysfunction in diabetic progeny in a sex-dependent manner

AIMS/HYPOTHESIS

The angiotensin II receptor type 2 (AT₂R) may be a potential therapeutic target for the treatment of hypertension and chronic kidney disease (CKD). The expression and function of AT₂R in the vasculature and kidney appear sexually dimorphic. We hypothesised that Agtr2 knockout dams (AT₂RKO) with gestational diabetes would program their offspring for subsequent hypertension and CKD in a sex-dependent manner.

METHODS

Age- and sex-matched offspring of non-diabetic and diabetic dams of wild-type (WT) and AT₂RKO mice were followed from 4 to 20 weeks of age and were monitored for development of hypertension and nephropathy; a mouse podocyte cell line (mPOD) was also studied.

RESULTS

Body weight was progressively lower in female compared with male offspring throughout the lifespan. Female but not male offspring from diabetic AT₂RKO dams developed insulin resistance. Compared with the offspring of non-diabetic dams, the progeny of diabetic dams had developed more hypertension and nephropathy (apparent glomerulosclerosis with podocyte loss) at 20 weeks of age; this programming was more pronounced in the offspring of AT₂RKO diabetic dams, particularly female AT₂RKO progeny. Female AT₂RKO offspring had lower basal ACE2 glomerular expression, resulting in podocyte loss. The aberrant ACE2/ACE ratio was far more diminished in glomeruli of female progeny of diabetic AT₂RKO dams than in male progeny. Knock-down of Agtr2 in mPODs confirmed the in vivo data.

CONCLUSIONS/INTERPRETATION

AT₂R deficiency accelerated kidney programming in female progeny of diabetic dams, possibly due to loss of protective effects of ACE2 expression in the kidney.

A Personalized Glomerulus Chip Engineered from Stem Cell-Derived Epithelium and Vascular Endothelium

Progress in understanding kidney disease mechanisms and the development of targeted therapeutics have been limited by the lack of functional in vitro models that can closely recapitulate human physiological responses. Organ Chip (or organ-on-a-chip) microfluidic devices provide unique opportunities to overcome some of these challenges given their ability to model the structure and function of tissues and organs in vitro. Previously established organ chip models typically consist of heterogenous cell populations sourced from multiple donors, limiting their applications in patient-specific disease modeling and personalized medicine. In this study, we engineered a personalized glomerulus chip system reconstituted from human induced pluripotent stem (iPS) cell-derived vascular endothelial cells (ECs) and podocytes from a single patient. Our stem cell-derived kidney glomerulus chip successfully mimics the structure and some essential functions of the glomerular filtration barrier. We further modeled glomerular injury in our tissue chips by administering a clinically relevant dose of the chemotherapy drug Adriamycin. The drug disrupts the structural integrity of the endothelium and the podocyte tissue layers, leading to significant albuminuria as observed in patients with glomerulopathies. We anticipate that the personalized glomerulus chip model established in this report could help advance future studies of kidney disease mechanisms and the discovery of personalized therapies. Given the remarkable ability of human iPS cells to differentiate into almost any cell type, this work also provides a blueprint for the establishment of more personalized organ chip and 'body-on-a-chip' models in the future.

Roles of Krüppel-like factor 5 in kidney disease

Transcription factor Krüppel-like factor 5 (KLF5) is a member of the Krüppel-like factors' (KLFs) family. KLF5 regulates a number of cellular functions, such as apoptosis, proliferation and differentiation. Therefore, KLF5 can play a role in many diseases, including, cancer, cardiovascular disease and gastrointestinal disorders. An important role for KLF5 in the kidney was recently reported, such that KLF5 regulated podocyte apoptosis, renal cell proliferation, tubulointerstitial inflammation and renal fibrosis. In this review, we have summarized the available information in the literature with a brief description on how transcriptional, post-transcriptional and post-translational modifications of KLF5 modulate its function in a variety of organs including the kidney with a focus of its importance on the pathogenesis of various kidney diseases. Furthermore, we also have outlined the current and possible mechanisms of KLF5 activation in kidney diseases. These studies suggest a need for more systemic investigations, particularly for generation of animal models with renal cell-specific deletion or overexpression of KLF5 gene to examine direct contributions of KLF5 to various kidney diseases. This will promote further experimentation in the development of therapies to prevent or treat various kidney diseases.

Mesenchymal Stem Cells Ameliorate Renal Inflammation in Adriamycin-induced Nephropathy

Mesenchymal stem cells (MSCs) ameliorate the renal injury in Adriamycin (ADR)-induced nephropathy, but the mechanisms underlying their efficacy remain incompletely understood. In this study, we demonstrated that MSCs increased the survival, recovered body weight loss, and decreased proteinuria and serum creatinine levels in ADR-treated mice. MSCs also prevented podocyte damage and renal fibrosis by decreasing the expression of fibronectin, collagen 1α1, and α-smooth muscle actin. From a mechanistic perspective, MSCs inhibited renal inflammation by lowering the expression of CCL4, CCL7, CCL19, IFN-α/β, TGF-β, TNF-α, and chitinase 3-like 1. In summary, our data demonstrate that MSCs improve renal functions by inhibiting renal inflammation in ADR-induced nephropathy.

C/EBPα deficiency in podocytes aggravates podocyte senescence and kidney injury in aging mice

Kidney aging leads to an increased incidence of end-stage renal disease (ESRD) in the elderly, and aging is a complex biological process controlled by signaling pathways and transcription factors. Podocyte senescence plays a central role in injury resulting from kidney aging. Here, we demonstrated the critical role of C/EBPα in podocyte senescence and kidney aging by generating a genetically modified mouse model of chronological aging in which C/EBPα was selectively deleted in podocytes and by overexpressing C/EBPα in cultured podocytes, in which premature senescence was induced by treatment with adriamycin. Moreover, we illuminated the mechanisms by which podocyte senescence causes tubular impairment by stimulating HK-2 cells with bovine serum albumin (BSA) and chloroquine. Our findings suggest that C/EBPα knockout in podocytes aggravates podocyte senescence through the AMPK/mTOR pathway, leading to glomerulosclerosis, and that subsequent albuminuria exacerbates the epithelial-mesenchymal transdifferentiation of senescent tubular cells by suppressing autophagy. These observations highlight the importance of C/EBPα as a new potential target in kidney aging.

Glomeruli from patients with nephrin mutations show increased number of ciliated and poorly differentiated podocytes

BACKGROUND

Podocytes are postmitotic, highly specialized cells which maintain the glomerular filtration barrier (GFB). Their injury is characterized by foot processes effacement and change in protein expression leading to proteinuria and end-stage kidney disease.

METHODS

Our study focuses on the morphological and immunohistochemical changes of human podocytes during normal development and postnatal period, compared to congenital nephrotic syndrome of the Finnish type (CNF). Kidney tissues taken from 17 human conceptuses 8th-38th weeks old, two healthy and three CNF kidneys were embedded in paraffin for immunohistochemical or double immunofluorescence methods, or were embedded in resin for electron microscopy. Paraffin sections were stained with markers for proliferation (Ki-67), proteins nephrin and nestin, and alpha-tubulin. Quantification of positive cells were performed using Mann Whitney and Kruskal-Wallis test.

RESULTS

Tissue analysis showed that proliferation of podocytes gradually decreased during development and disappeared in postnatal period. Decrease in number of ciliated glomerular cells and visceral podocytes (from 47% to 3%), and parietal epithelial cells (from 32% to 7%) characterized normal development. Nestin and nephrin co-expressed in developing podocytes in different cellular compartments. During development, nephrin expression increased (from 17% to 75%) and postnatally changed its pattern, while nestin positive glomerular cells decreased from 98% to 40%. CNF glomeruli displayed increased number of immature ciliated podocytes (6%) and parietal epithelial cells (9%).

CONCLUSION

Changes in cytoplasmic alpha-tubulin expression and reduced nephrin expression (20%) indicating association of incomplete podocyte maturation with failure of GFB function and appearance of prenatal proteinuria in CNF patients.

Epigenetic regulation of RCAN1 expression in kidney disease and its role in podocyte injury

Mounting evidence suggests that epigenetic modification is important in kidney disease pathogenesis. To determine whether epigenetic regulation is involved in HIV-induced kidney injury, we performed genome-wide methylation profiling and transcriptomic profiling of human primary podocytes infected with HIV-1. Comparison of DNA methylation and RNA sequencing profiles identified several genes that were hypomethylated with corresponding upregulated RNA expression in HIV-infected podocytes. Notably, we found only one hypermethylated gene with corresponding downregulated RNA expression, namely regulator of calcineurin 1 (RCAN1). Further, we found that RCAN1 RNA expression was suppressed in glomeruli in human diabetic nephropathy, IgA nephropathy, and lupus nephritis, and in mouse models of HIV-associated nephropathy and diabetic nephropathy. We confirmed that HIV infection or high glucose conditions suppressed RCAN1 expression in cultured podocytes. This suppression was alleviated upon pretreatment with DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine, suggesting that RCAN1 expression is epigenetically suppressed in the context of HIV infection and diabetic conditions. Mechanistically, increased expression of RCAN1 decreased HIV- or high glucose-induced nuclear factor of activated T cells (NFAT) transcriptional activity. Increased RCAN1 expression also stabilized actin cytoskeleton organization, consistent with the inhibition of the calcineurin pathway. In vivo, knockout of RCAN1 aggravated albuminuria and podocyte injury in mice with Adriamycin-induced nephropathy. Our findings suggest that epigenetic suppression of RCAN1 aggravates podocyte injury in the setting of HIV infection and diabetic nephropathy.

AT2 R deficiency mediated podocyte loss via activation of ectopic hedgehog interacting protein (Hhip) gene expression

Angiotensin II type 2 receptor (AT₂ R) deficiency in AT₂ R knockout (KO) mice has been linked to congenital abnormalities of the kidney and urinary tract; however, the mechanisms by which this occurs are poorly understood. In this study, we examined whether AT₂ R deficiency impaired glomerulogenesis and mediated podocyte loss/dysfunction in vivo and in vitro. Nephrin-cyan fluorescent protein (CFP)-transgenic (Tg) and Nephrin/AT₂ RKO mice were used to assess glomerulogenesis, while wild-type and AT₂ RKO mice were used to evaluate maturation of podocyte morphology/function. Immortalized mouse podocytes (mPODs) were employed for in vitro studies. AT₂ R deficiency resulted in diminished glomerulogenesis in E15 embryos, but had no impact on actual nephron number in neonates. Pups lacking AT₂ R displayed features of renal dysplasia with lower glomerular tuft volume and podocyte numbers. In vivo and in vitro studies demonstrated that loss of AT₂ R was associated with elevated NADPH oxidase 4 levels, which in turn stimulated ectopic hedgehog interacting protein (Hhip) gene expression in podocytes. Consequently, ectopic Hhip expression activation either triggers caspase-3 and p53-related apoptotic processes resulting in podocyte loss, or activates TGFβ1-Smad2/3 cascades and α-SMA expression to transform differentiated podocytes to undifferentiated podocyte-derived fibrotic cells. We analyzed HHIP expression in the kidney disease database (Nephroseq) and then validated this using HHIP immunohistochemistry staining of human kidney biopsies (controls versus focal segmental glomerulosclerosis). In conclusion, loss of AT₂ R is associated with podocyte loss/dysfunction and is mediated, at least in part, via augmented ectopic Hhip expression in podocytes. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Mature induced-pluripotent-stem-cell-derived human podocytes reconstitute kidney glomerular-capillary-wall function on a chip

An in vitro model of the human kidney glomerulus — the major site of blood filtration — could facilitate drug discovery and illuminate kidney-disease mechanisms. Microfluidic organ-on-a-chip technology has been used to model the human proximal tubule, yet a kidney-glomerulus-on-a-chip has not been possible because of the lack of functional human podocytes — the cells that regulate selective permeability in the glomerulus. Here, we demonstrate an efficient (> 90%) and chemically defined method for directing the differentiation of human induced pluripotent stem (hiPS) cells into podocytes that express markers of the mature phenotype (nephrin+, WT1+, podocin+, Pax2−) and that exhibit primary and secondary foot processes. We also show that the hiPS-cell-derived podocytes produce glomerular basement-membrane collagen and recapitulate the natural tissue/tissue interface of the glomerulus, as well as the differential clearance of albumin and inulin, when co-cultured with human glomerular endothelial cells in an organ-on-a-chip microfluidic device. The glomerulus-on-a-chip also mimics adriamycin-induced albuminuria and podocyte injury. This in vitro model of human glomerular function with mature human podocytes may facilitate drug development and personalized-medicine applications.