Glomerular epithelial-myofibroblast transdifferentiation in the evolution of glomerular crescent formation

Immunosuppressant Agents as Add-On Therapy Failed to Improve the Outcome of Immunoglobulin A Nephropathy with Crescent Score C1

INTRODUCTION

The renoprotective benefits of adding immunosuppressant therapy to corticosteroid (CS) treatment for immunoglobulin A nephropathy (IgAN) patients with less than 25% crescent formation (C1) remain uncertain, warranting further research.

METHODS

A retrospective study was conducted on IgAN patients with crescent C1 lesions confirmed by renal biopsy at Xinqiao Hospital between May 1, 2017, and May 1, 2020. Patients were stratified into either the CS treatment group or the CS combined with an additional immunosuppressant therapy group. Follow-up assessments were conducted within 24 months. Propensity score analysis was used to match patients receiving CS and CS + immunosuppressant drug treatment in a 1:1 ratio. Primary outcomes included changes in estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio (UACR). Subgroup analyses were performed to evaluate the benefits of different populations. Composite endpoint outcomes comprised a 30% eGFR decrease, end-stage kidney disease (ESKD) necessitating dialysis or transplant, or kidney disease-related mortality. Adverse events were also compared between the two groups.

RESULTS

296 IgAN patients with C1 lesions were included in the analysis. Baseline characteristics indicated that IgAN patients in the CS + immunosuppressant group exhibited poorer renal function and higher UACR levels. Propensity score analysis effectively minimized the influence of baseline clinical characteristics, including age, serum creatinine, initial eGFR, UACR, and 24-h proteinuria. Both treatment groups demonstrated continuous eGFR improvement and significant UACR reduction during follow-up, especially at 6 months. However, no significant differences in eGFR and UACR reduction rates were observed between the two groups throughout the entire follow-up period, both before and after matching. Subgroup analysis revealed improved eGFR in both treatment groups, notably among patients with an initial eGFR below 90 mL/min/1.73 m2. Conversely, IgAN patients with C1 lesions and a cellular crescent ratio exceeding 50% treated with CS and immunosuppressant therapy experienced a significant improvement in renal function and a decline in urinary protein creatinine ratio. Composite endpoint outcomes did not significantly differ between the two groups, while the incidence of adverse events was comparable.

CONCLUSION

Our findings suggest that the addition of immunosuppressant therapy to corticosteroid monotherapy did not confer significant therapeutic advantages in patients with C1 lesions compared to CS monotherapy, although some specific patient populations appeared to derive modest benefits from this combined approach.

Differential expression of epithelial and smooth muscle lineage-specific markers of metanephros in one-humped camel foetuses

The development of the metanephros in one-humped camels involves a complex series of interactions between epithelial and mesenchymal cells. As a result, there is a synchronized differentiation process of stromal, vascular and epithelial cell types during glomerulogenesis, angiogenesis and tubulogenesis. In the current work, the metanephros of camel foetuses were divided into four stages where kidneys from each stage were processed and immunoassayed, followed by quantitative analysis to determine target protein intensities throughout metanephrogenesis in the camel. This study demonstrated robust expression of α-smooth muscle actin (α-SMA) in the glomerular mesangium, as well as in interlobular and glomerular arterioles during the earlier stages of development. However, in the late stages, α-SMA expression became more localized around the blood capillaries in both the cortex and medulla. Strong expression of CD34 was observed in the immature glomerular and peritubular endothelial cells within the subcapsular zone, as well as in the glomerular, proximal tubular and distal tubular epithelium of stage one foetuses, although its expression gradually diminished with foetal maturation. The expression pattern of osteopontin was prominently observed in the distal convoluted tubules throughout all stages, however, no expression was detected in the proximal tubules, glomeruli and arterioles. E-cadherin was detected in the developing renal tubular epithelial cells but not in the glomeruli. In conclusion, this study reveals the spatiotemporal distribution of key proteins, including α-SMA, CD34, Osteopontin and E-cadherin, which play a crucial role in metanephrogenesis in camel foetuses.

Three Diseases Mediated by Different Immunopathologic Mechanisms-ANCA-Associated Vasculitis, Anti-Glomerular Basement Membrane Disease, and Immune Complex-Mediated Glomerulonephritis-A Common Clinical and Histopathologic Picture: Rapidly Progressive Crescentic Glomerulonephritis

Immune mechanisms play an important role in the pathogenesis of glomerulonephritis (GN), with autoimmunity being the main underlying pathogenetic process of both primary and secondary GN. We present three autoimmune diseases mediated by different autoimmune mechanisms: glomerulonephritis in vasculitis mediated by anti-neutrophil cytoplasmic antibodies (ANCAs), glomerulonephritis mediated by anti-glomerular basement membrane antibodies (anti-GBM antibodies), and immune complex-mediated glomerulonephritis. Some of these diseases represent a common clinical and histopathologic scenario, namely rapidly progressive crescentic glomerulonephritis. This is a severe illness requiring complex therapy, with the main role being played by therapy aimed at targeting immune mechanisms. In the absence of immune therapy, the crescents, the characteristic histopathologic lesions of this common presentation, progress toward fibrosis, which is accompanied by end-stage renal disease (ESRD). The fact that three diseases mediated by different immunopathologic mechanisms have a common clinical and histopathologic picture reveals the complexity of the relationship between immunopathologic mechanisms and their clinical expression. Whereas most glomerular diseases progress by a slow process of sclerosis and fibrosis, the glomerular diseases accompanied by glomerular crescent formation can progress, if untreated, in a couple of months into whole-nephron glomerulosclerosis and fibrosis. The outcome of different immune processes in a common clinical and histopathologic phenotype reveals the complexity of the relationship of the kidney with the immune system. The aim of this review is to present different immune processes that lead to a common clinical and histopathologic phenotype, such as rapidly progressive crescentic glomerulonephritis.

Glucosidase inhibitor, Nimbidiol ameliorates renal fibrosis and dysfunction in type-1 diabetes

Diabetic nephropathy is characterized by excessive accumulation of extracellular matrix (ECM) leading to renal fibrosis, progressive deterioration of renal function, and eventually to end stage renal disease. Matrix metalloproteinases (MMPs) are known to regulate synthesis and degradation of the ECM. Earlier, we demonstrated that imbalanced MMPs promote adverse ECM remodeling leading to renal fibrosis in type-1 diabetes. Moreover, elevated macrophage infiltration, pro-inflammatory cytokines and epithelial‒mesenchymal transition (EMT) are known to contribute to the renal fibrosis. Various bioactive compounds derived from the medicinal plant, Azadirachta indica (neem) are shown to regulate inflammation and ECM proteins in different diseases. Nimbidiol is a neem-derived diterpenoid that is considered as a potential anti-diabetic compound due to its glucosidase inhibitory properties. We investigated whether Nimbidiol mitigates adverse ECM accumulation and renal fibrosis to improve kidney function in type-1 diabetes and the underlying mechanism. Wild-type (C57BL/6J) and type-1 diabetic (C57BL/6-Ins2^Akita/J) mice were treated either with saline or with Nimbidiol (0.40 mg kg^-1 d^-1) for eight weeks. Diabetic kidney showed increased accumulation of M1 macrophages, elevated pro-inflammatory cytokines and EMT. In addition, upregulated MMP-9 and MMP-13, excessive collagen deposition in the glomerular and tubulointerstitial regions, and degradation of vascular elastin resulted to renal fibrosis in the Akita mice. These pathological changes in the diabetic mice were associated with functional impairments that include elevated resistive index and reduced blood flow in the renal cortex, and decreased glomerular filtration rate. Furthermore, TGF-β1, p-Smad2/3, p-P38, p-ERK1/2 and p-JNK were upregulated in diabetic kidney compared to WT mice. Treatment with Nimbidiol reversed the changes to alleviate inflammation, ECM accumulation and fibrosis and thus, improved renal function in Akita mice. Together, our results suggest that Nimbidiol attenuates inflammation and ECM accumulation and thereby, protects kidney from fibrosis and dysfunction possibly by inhibiting TGF-β/Smad and MAPK signaling pathways in type-1 diabetes.

TGF ‐β1 peptide‐based inhibitor P144 ameliorates renal fibrosis after ischemia–reperfusion injury by modulating alternatively activated macrophages

Objectives

Ischemia–reperfusion injury (IRI) is a major cause of chronic renal fibrosis. Currently, numerous therapies have shown a minimal effect on the blockade of fibrosis progression. Here, the therapeutic potential of peptide‐based TGF‐β1 inhibitor P144 in IRI‐induced renal fibrosis and the underlying mechanism were analyzed.

Materials and Methods

The unilateral ischemia–reperfusion injury with the contralateral nephrectomy model was established, and the P144 was administered intravenously 1d/14d after the onset of IRI. The histopathology and immunofluorescence staining were used to detect renal fibrosis and macrophage infiltration. The in vivo fluorescence imaging was used to measure the bio‐distribution of P144. The transwell assays were used to observe the migration of macrophages. RT‐qPCR and western blot were used to analyze TGF‐β1 signaling.

Results

P144 ameliorated the accumulation of extracellular matrix in the kidney and improved the renal function in the unilateral ischemia–reperfusion injury plus contralateral nephrectomy model. Mechanistically, P144 downregulated the TGF‐β1‐Smad3 signaling at both the transcriptional and translational levels and further reduced the TGF‐β1‐dependent infiltration of macrophages to the injured kidney. Additionally, P144 blocked the polarization of macrophages to an M2‐like phenotype induced by TGF‐β1 in vitro, but showed no effect on their proliferation.

Conclusions

Our study showed that the TGF‐β1 peptide‐based inhibitor P144 decreased renal fibrosis through the blockade of the TGF‐β1–Smad3 signaling pathway and the modulation of macrophage polarization, suggesting its potential therapeutic use in IRI‐induced renal fibrosis.

Urine Single-Cell RNA Sequencing in Focal Segmental Glomerulosclerosis Reveals Inflammatory Signatures

INTRODUCTION

Individuals with focal segmental glomerular sclerosis (FSGS) typically undergo kidney biopsy only once, which limits the ability to characterize kidney cell gene expression over time.

METHODS

We used single-cell RNA sequencing (scRNA-seq) to explore disease-related molecular signatures in urine cells from subjects with FSGS. We collected 17 urine samples from 12 FSGS subjects and captured these as 23 urine cell samples. The inflammatory signatures from renal epithelial and immune cells were evaluated in bulk gene expression data sets of FSGS and minimal change disease (MCD) (The Nephrotic Syndrome Study Network [NEPTUNE] study) and an immune single-cell data set from lupus nephritis (Accelerating Medicines Partnership).

RESULTS

We identified immune cells, predominantly monocytes, and renal epithelial cells in the urine. Further analysis revealed 2 monocyte subtypes consistent with M1 and M2 monocytes. Shed podocytes in the urine had high expression of marker genes for epithelial-to-mesenchymal transition (EMT). We selected the 16 most highly expressed genes from urine immune cells and 10 most highly expressed EMT genes from urine podocytes as immune signatures and EMT signatures, respectively. Using kidney biopsy transcriptomic data from NEPTUNE, we found that urine cell immune signature and EMT signature genes were more highly expressed in FSGS biopsies compared with MCD biopsies.

CONCLUSION

The identification of monocyte subsets and podocyte expression signatures in the urine samples of subjects with FSGS suggests that urine cell profiling might serve as a diagnostic and prognostic tool in nephrotic syndrome. Furthermore, this approach may aid in the development of novel biomarkers and identifying personalized therapies targeting particular molecular pathways in immune cells and podocytes.

DACH1, a novel target of miR-218, participates in the regulation of cell viability, apoptosis, inflammatory response, and epithelial-mesenchymal transition process in renal tubule cells treated by high-glucose

Objective: This report was designed to assess the functional role of miR-218/dachshund family transcription factor 1 (DACH1) in diabetic kidney disease (DKD) and investigate its possible molecular mechanism.Materials and Methods: From the GEO database, we downloaded different datasets for analyzing the expression of miR-218 and DACH1 in DKD. TargetScan was adopted to predict the binding sites between miR-218 and DACH1, which was further verified by dual-luciferase reporter assays. The renal proximal tubule cells (HK-2) treated with high glucose (HG) were used as an in vitro model. QRT-PCR and western blot were used to determine the expression of DACH1 and other relative factors. Cell counting kit-8 and flow cytometer were applied to detect cell viability and apoptosis. The levels of inflammatory cytokines were determined by an ELISA assay.Results: A prominent raise of miR-218 was observed in DKD through bioinformatics analysis, which was further confirmed in the HG-induced model. DACH1 is a target of miR-218. miR-218 reduced cell viability and induced apoptosis by negatively regulating DACH1. Moreover, upregulating miR-218 in HG models increased the concentrations of pro-inflammatory cytokines TNF-α and IL-1β, reduced the level of anti-inflammatory cytokine IL-10, and promoted the epithelial-mesenchymal transition (EMT) process, which is possibly achieved by targeting DACH1. While downregulating miR-218 showed the opposite results.Conclusion: These data demonstrated that, under an in vitro HG environment, miR-218 suppressed the HK-2 cells proliferation, promoted apoptosis, caused an inflammatory response, and facilitated the EMT process largely by targeting DACH1, providing an insight into the therapeutic intervention of DKD.

Intraglomerular Monocyte/Macrophage Infiltration and Macrophage-Myofibroblast Transition during Diabetic Nephropathy Is Regulated by the A2B Adenosine Receptor

Diabetic nephropathy (DN) is considered the main cause of kidney disease in which myofibroblasts lead to renal fibrosis. Macrophages were recently identified as the major source of myofibroblasts in a process known as macrophage–myofibroblast transition (MMT). Adenosine levels increase during DN and in vivo administration of MRS1754, an antagonist of the A_2B adenosine receptor (A_2BAR), attenuated glomerular fibrosis (glomerulosclerosis). We aimed to investigate the association between A_2BAR and MMT in glomerulosclerosis during DN. Kidneys/glomeruli of non-diabetic, diabetic, and MRS1754-treated diabetic (DM+MRS1754) rats were processed for histopathologic, transcriptomic, flow cytometry, and cellular in vitro analyses. Macrophages were used for in vitro cell migration/transmigration assays and MMT studies. In vivo MRS1754 treatment attenuated the clinical and histopathological signs of glomerulosclerosis in DN rats. Transcriptomic analysis demonstrated a decrease in chemokine-chemoattractants/cell-adhesion genes of monocytes/macrophages in DM+MRS1754 glomeruli. The number of intraglomerular infiltrated macrophages and MMT cells increased in diabetic rats. This was reverted by MRS1754 treatment. In vitro cell migration/transmigration decreased in macrophages treated with MRS1754. Human macrophages cultured with adenosine and/or TGF-β induced MMT, a process which was reduced by MRS1754. We concluded that pharmacologic blockade of A_2BAR attenuated some clinical signs of renal dysfunction and glomerulosclerosis, and decreased intraglomerular macrophage infiltration and MMT in DN rats.

Diverse Role of TGF-β in Kidney Disease

Inflammation and fibrosis are two pathological features of chronic kidney disease (CKD). Transforming growth factor-β (TGF-β) has been long considered as a key mediator of renal fibrosis. In addition, TGF-β also acts as a potent anti-inflammatory cytokine that negatively regulates renal inflammation. Thus, blockade of TGF-β inhibits renal fibrosis while promoting inflammation, revealing a diverse role for TGF-β in CKD. It is now well documented that TGF-β1 activates its downstream signaling molecules such as Smad3 and Smad3-dependent non-coding RNAs to transcriptionally and differentially regulate renal inflammation and fibrosis, which is negatively regulated by Smad7. Therefore, treatments by rebalancing Smad3/Smad7 signaling or by specifically targeting Smad3-dependent non-coding RNAs that regulate renal fibrosis or inflammation could be a better therapeutic approach. In this review, the paradoxical functions and underlying mechanisms by which TGF-β1 regulates in renal inflammation and fibrosis are discussed and novel therapeutic strategies for kidney disease by targeting downstream TGF-β/Smad signaling and transcriptomes are highlighted.

TGF-β/Smad and Renal Fibrosis

Renal fibrosis is characterized by excessive deposition of extracellular matrix (ECM) that disrupts and replaces functional parenchyma, which leads to organ failure. It is known as the major pathological mechanism of chronic kidney disease (CKD). Although CKD has an impact on no less than 10% of the world population, therapeutic options are still limited. Regardless of etiology, elevated TGF-β levels are highly correlated with the activated pro-fibrotic pathways and disease progression. TGF-β, the key driver of renal fibrosis, is involved in a dynamic pathophysiological process that leads to CKD and end-stage renal disease (ESRD). It is becoming clear that epigenetics regulates renal programming, and therefore, the development and progression of renal disease. Indeed, recent evidence shows TGF-β1/Smad signaling regulates renal fibrosis via epigenetic-correlated mechanisms. This review focuses on the function of TGF-β/Smads in renal fibrogenesis, and the role of epigenetics as a regulator of pro-fibrotic gene expression.

Transforming growth factor-β1/Smad3-independent epithelial-mesenchymal transition in type I collagen glomerulopathy

The glomerulofibrotic Col1a2-deficient mouse model demonstrates glomerular homotrimeric type I collagen deposition in mesangial and subendothelial spaces. In this report, we investigate the role of transforming growth factor β1 (TGF-β1) in myofibroblast activation and epithelial-mesenchymal transition (EMT) in this glomerulopathy. Immunohistochemical analyses of glomerular α-sma, desmin, vimentin, and proliferating cell nuclear antigen demonstrated parietal epithelial cell proliferation and EMT in late stages of the glomerulopathy in the Col1a2-deficient mice. Glomerular TGF-β1 RNA and protein were not elevated in 1- and 3-month-old mice as determined by quantitative reverse transcriptase-polymerase chain reaction and protein immunoassay analyses. To investigate further whether TGF-β1 plays a role in the glomerulopathy outside of the 1- and 3-month time periods, the Col1a2-deficient mice were bred with Smad3 knockout mice. If the glomerular fibrosis in the Col1a2-deficient mice is mediated by the TGF-β1/Smad3 transcription pathway, it was hypothesized that the resultant Col1a2-deficient/Smad3-deficient mice would exhibit attenuated glomerular homotrimer deposition. However, the Col1a2-deficient/Smad3-deficient kidneys were similarly affected as compared to age-matched Col1a2-deficient kidneys, suggesting that homotrimeric type I collagen deposition in the Col1a2-deficient mouse is independent of TGF-β1/Smad3 signaling. Deposition of homotrimeric type I collagen appears to be the initiating event in this glomerulopathy, providing evidence that EMT and myofibroblast activation occur following initiation, consistent with a secondary wound-healing response independent of TGF-β1.

Progression of renal fibrosis in congenital CKD model rats with reduced number of nephrons

A congenital reduction in the number of nephrons is a critical risk factor for both onset of chronic kidney disease (CKD) and its progression to end-stage kidney disease (ESKD). Hypoplastic kidney (HPK) rats have only about 20% of the normal number of nephrons and show progressive CKD. This study used an immunohistological method to assess glomerular and interstitial pathogenesis in male HPK rats aged 35-210days. CD68 positive-macrophages were found to infiltrate into glomeruli in HPK rats aged 35 and 70days and to infiltrate into interstitial tissue in rats aged 140 and 210days. HPK rats aged 35 and 70days showed glomerular hypertrophy, loss of normal linear immunostaining of podocine, and increased expression of PDGFr-β, TGF-β, collagens, and fibronectin, with all of these alterations gradually deteriorating with age. α-SMA-positive myofibroblasts were rarely detected in glomerular tufts, whereas α-SMA-positive glomerular parietal epithelium (GPE) cells were frequently observed along Bowman's capsular walls. The numbers of PDGFr-β-positive fibroblasts in interstitial tissue were increased in rats aged 35days and older, whereas interstitial fibrosis, characterized by the increased expression of tubular PDGF-BB, the appearance of myofibroblasts doubly positive for PDGFr-β and α-SMA, and increased expression of collagens and fibronectin, were observed in rats aged 70 and older. These results clearly indicate that congenital CKD with only 20% of nephrons cause renal fibrosis in rats.

Epithelial-mesenchymal transition in pediatric nephropathies

INTRODUCTION

Epithelial-mesenchymal transition (EMT) is a process in which epithelial cells may express mesenchymal cell markers with subsequent change in their functions, and it may be part of the etiopathogenesis of kidney disease.

OBJECTIVE

The aim of this study was to evaluate the immunexpression of some EMT inducers and markers in frequent nephropathies in pediatric patients.

METHODS

59 patients aged 2-18 years old were selected and divided into 6 groups of frequent nephropathies in children and adolescents, as well as one control group. Urea and creatinine data of the patients were recorded. TGF-β3, fibronectin, α-SMA and vimentin were evaluated by immunohistochemistry.

RESULTS

Glomerular TGF-β3 was higher in the Lupus Nephritis and Acute Diffuse Glomerulonephritis (ADGN) groups than in the control group. Glomerular fibronectin was higher in the Podocytopathy, Lupus Nephritis, ADGN and Membranous Glomerulopathy patients than in control subjects. The expression of α-SMA was higher in the tubulointerstitial compartment of ADGN and Membranous Glomerulopathy groups than in the control group. Glomerular α-SMA was higher in ADGN patients than in control and Berger's Disease groups. Glomerular vimentin was higher in individuals with ADGN than in those with Podocytopathy, Lupus Nephritis, Berger's Disease and Thin Basement Membrane Disease/Alport Syndrome. There was a positive correlation between fibronectin in the tubulointerstitial compartment and creatinine levels, between α-SMA and vimentin in both tubulointerstitial and glomerular compartments, and between urea and creatinine levels of patients, regardless of their nephropathy (p<0.05 for all results).

CONCLUSION

These markers may possibly be used as indicators of renal functional impairment in various nephropathies in pediatric patients.

Classifying murine glomerulonephritis using optical coherence tomography and optical coherence elastography

Acute glomerulonephritis caused by antiglomerular basement membrane marked by high mortality. The primary reason for this is delayed diagnosis via blood examination, urine analysis, tissue biopsy, or ultrasound and X-ray computed tomography imaging. Blood, urine, and tissue-based diagnoses can be time consuming, while ultrasound and CT imaging have relatively low spatial resolution, with reduced sensitivity. Optical coherence tomography is a noninvasive and high-resolution imaging technique that provides superior spatial resolution (micrometer scale) as compared to ultrasound and CT. Changes in tissue properties can be detected based on the optical metrics analyzed from the OCT signals, such as optical attenuation and speckle variance. Furthermore, OCT does not rely on ionizing radiation as with CT imaging. In addition to structural changes, the elasticity of the kidney can significantly change due to nephritis. In this work, OCT has been utilized to quantify the difference in tissue properties between healthy and nephritic murine kidneys. Although OCT imaging could identify the diseased tissue, its classification accuracy is clinically inadequate. By combining optical metrics with elasticity, the classification accuracy improves from 76% to 95%. These results show that OCT combined with OCE can be a powerful tool for identifying and classifying nephritis. Therefore, the OCT/OCE method could potentially be used as a minimally invasive tool for longitudinal studies during the progression and therapy of glomerulonephritis as well as complement and, perhaps, substitute highly invasive tissue biopsies. Elastic-wave propagation in mouse healthy and nephritic kidneys.

TGF-β: the master regulator of fibrosis

Transforming growth factor-β (TGF-β) is the primary factor that drives fibrosis in most, if not all, forms of chronic kidney disease (CKD). Inhibition of the TGF-β isoform, TGF-β1, or its downstream signalling pathways substantially limits renal fibrosis in a wide range of disease models whereas overexpression of TGF-β1 induces renal fibrosis. TGF-β1 can induce renal fibrosis via activation of both canonical (Smad-based) and non-canonical (non-Smad-based) signalling pathways, which result in activation of myofibroblasts, excessive production of extracellular matrix (ECM) and inhibition of ECM degradation. The role of Smad proteins in the regulation of fibrosis is complex, with competing profibrotic and antifibrotic actions (including in the regulation of mesenchymal transitioning), and with complex interplay between TGF-β/Smads and other signalling pathways. Studies over the past 5 years have identified additional mechanisms that regulate the action of TGF-β1/Smad signalling in fibrosis, including short and long noncoding RNA molecules and epigenetic modifications of DNA and histone proteins. Although direct targeting of TGF-β1 is unlikely to yield a viable antifibrotic therapy due to the involvement of TGF-β1 in other processes, greater understanding of the various pathways by which TGF-β1 controls fibrosis has identified alternative targets for the development of novel therapeutics to halt this most damaging process in CKD.

Stimulation of transforming growth factor-beta-1 and contact with type I collagen cooperatively facilitate irreversible transdifferentiation in proximal tubular cells

Background

By transdifferentiation, proximal tubular cells (PTC) have been considered as a source of interstitial myofibroblasts. We examined the combined effect of transforming growth factor-beta-1 (TGF-β1) stimulation and contact with type I collagen on PTC transdifferentiation.

Methods

Human kidney-2 cells were grown on type I substratum with the concurrent stimulation of TGF-β1.

Results

Following addition of TGF-β1, cells acquired an elongated fibroblastic appearance and an increase in α-smooth muscle actin (α-SMA) expression, a myofibroblastic marker. Upon addition of TGF-β1, E-cadherin expression, an epithelial marker, was reduced, while cytokeratin expression, another epithelial marker, remained unaltered. Following removal of TGF-β1, PTC regained an epithelial appearance and E-cadherin expression reverted to the unstimulated level, suggesting incomplete and reversible transdifferentiation. Addition of TGF-β1 to cells grown on type I collagen demonstrated a cooperatively increased α-SMA expression and decreased E-cadherin and cytokeratin expressions, suggesting more complete transdifferentiation. Co-stimulation of TGF-β1 and contact with type I collagen led to a stable cell phenotype and persistently decreased E-cadherin, which was not reversed upon removal of TGF-β1, indicating irreversible transdifferentiation. Addition of TGF-β1 or type I collagen caused a 4-fold increase in migratory cell number as compared to the control, whereas addition of both TGF-β1 and type I collagen led to an 11-fold increase.

Conclusions

TGF-β1 alone results in a reversible and incomplete transdifferentiation. The combination of TGF-β1 and exposure to type I collagen leads to an irreversible and complete PTC transdifferentiation.

Effects of A2BR on the biological behavior of mouse renal fibroblasts during hypoxia

Fibroblasts are the effector cells of collagen secretion in renal interstitial fibrosis (RIF), and their proliferation and activation are essential for the development of RIF. Hypoxic ischemia in local tissues has been identified in chronic kidney diseases (CKDs), with adenosine (ADO) as a key signaling molecule. The current study investigated the association between ADO and the biological behavior of renal fibroblasts by establishing an in vitro hypoxia cell model. This aimed to provide experimental evidence for the prevention and treatment of RIF. NIH3T3 fibroblasts were exposed to hypoxia, and the subtypes of the ADO receptor (AR) on the cell surface were identified by a TaqMan probe‑based assay. Cells were divided into the following four groups: i) Control; ii) 5'‑N‑ethylcarboxamidoadenosine (NECA); iii) PT, NECA + 8‑phenyltheophylline (PT); and iv) MRS, NECA + N‑(4‑cyanophenyl)‑2‑[4‑(2,3,6,7‑tetrahydro‑2,6‑dioxo‑1,3‑dipropyl‑1H‑purin‑8‑yl)phenoxy]‑acetamide (MRS1754). The mRNA levels of transforming growth factor‑β1 (TGF‑β1), procollagen α1 (I) and α‑smooth muscle actin (α‑SMA) were measured following 24, 48, and 72 h of hypoxia. Cell proliferation was evaluated by a 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide assay at 0, 12, 24, 48 and 72 h. The results demonstrated that A2BR was the predominant AR subtype present in hypoxia‑stimulated fibroblasts. NECA significantly induced fibroblast proliferation and upregulated the expression of TGF‑β1, procollagen α1 (I) and α‑SMA mRNA, while 8‑PT and MRS1754 inhibited fibroblast proliferation and downregulated the expression of TGF‑β1, procollagen α1 (I) and α‑SMA mRNA. The blockage of A2BR in hypoxia significantly inhibited the proliferation and activation of fibroblasts, and reduced the production of profibrotic cytokines, thus preventing the generation and development of fibrosis.

Diverse origins of the myofibroblast—implications for kidney fibrosis

Fibrosis is the common end point of chronic kidney disease. The persistent production of inflammatory cytokines and growth factors leads to an ongoing process of extracellular matrix production that eventually disrupts the normal functioning of the organ. During fibrosis, the myofibroblast is commonly regarded as the predominant effector cell. Accumulating evidence has demonstrated a diverse origin of myofibroblasts in kidney fibrosis. Proposed major contributors of myofibroblasts include bone marrow-derived fibroblasts, tubular epithelial cells, endothelial cells, pericytes and interstitial fibroblasts; the published data, however, have not yet clearly defined the relative contribution of these different cellular sources. Myofibroblasts have been reported to originate from various sources, irrespective of the nature of the initial damage responsible for the induction of kidney fibrosis. Here, we review the possible relevance of the diversity of myofibroblast progenitors in kidney fibrosis and the implications for the development of novel therapeutic approaches. Specifically, we discuss the current status of preclinical and clinical antifibrotic therapy and describe targeting strategies that might help support resident and circulating cells to maintain or regain their original functional differentiation state. Such strategies might help these cells resist their transition to a myofibroblast phenotype to prevent, or even reverse, the fibrotic state.

The glomerular parietal epithelial cell's responses are influenced by SM22 alpha levels

Background

Studies have shown in several diseases initially affecting podocytes, that the neighboring glomerular parietal epithelial cells (PECs) are secondarily involved. The PEC response might be reparative under certain circumstances, yet injurious under others. The factors governing these are not well understood. We have shown that SM22α, an actin-binding protein considered a marker of smooth muscle differentiation, is upregulated in podocytes and PECs in several models of podocyte disease. However, the impact of SM22α levels on PECs is not known.

Methods

Experimental glomerular disease, characterized by primary podocyte injury, was induced in aged-matched SM22α +/+ and SM22α -/- mice by intraperitoneal injection of sheep anti-rabbit glomeruli antibody. Immunostaining methods were employed on days 7 and 14 of disease.

Results

The number of PEC transition cells, defined as cells co-expressing a PEC protein (PAX2) and podocyte protein (Synaptopodin) was higher in diseased SM22α -/- mice compared with SM22α +/+ mice. WT1 staining along Bowman’s capsule is higher in diseased SM22α -/- mice. This was accompanied by increased PEC proliferation (measured by ki-67 staining), and an increase in immunostaining for the progenitor marker NCAM, in a subpopulation of PECs in diseased SM22α -/- mice. In addition, immunostaining for vimentin and alpha smooth muscle actin, markers of epithelial-to-mesenchymal transition (EMT), was lower in diseased SM22α -/- mice compared to diseased SM22α+/+ mice.

Conclusion

SM22α levels may impact how PECs respond following a primary podocyte injury in experimental glomerular disease. Absent/lower levels favor an increase in PEC transition cells and PECs expressing a progenitor marker, and a lower EMT rate compared to SM22α +/+ mice, where SM22 levels are markedly increased in PECs.

Hepatic progenitor cells in liver regeneration: current advances and clinical perspectives

When there is a massive loss of hepatocytes and/or an inhibition in the proliferative capacity of the mature hepatocytes, activation of a dormant cell population of resident hepatic progenitor cells (HPCs) occurs. Depending on the type of liver damage HPCs generate new hepatocytes and biliary cells to repopulate the liver placing them as potential candidates for cell therapy in human liver failure. Liver injury specific mechanisms through which HPCs differentiate towards mature epithelial cell types are recently become understood. Such new insights will enable us not only to direct HPCs behaviour for therapeutic purposes, but also to develop clinically feasible methods for in vivo differentiation of other stem cell types towards functional hepatocytes. This review aimed to provide the current improved knowledge of the role of HPCs niche and its signals in directing the behaviour and fate of HPCs and to translate this basic knowledge of HPCs activation/differentiation into its clinical applications.

Upregulation of transglutaminase and ε (γ-glutamyl)-lysine in the Fisher-Lewis rat model of chronic allograft nephropathy

Background. Tissue transglutaminase (TG2), a cross-linking enzyme, modulates deposition of extracellular matrix protein in renal fibrosis. This study aimed to examine TG2 and its cross-link product ε(γ-glutamyl)-lysine in the Fisher-Lewis rat renal transplantation (RTx) model of chronic allograft nephropathy (CAN). Materials and Methods. Left renal grafts from male Fisher and Lewis were transplanted into Lewis rats, generating allografts and isografts, respectively. Blood pressure, renal function, and proteinuria were monitored for up to 52 weeks. At termination, CAN was assessed in the renal tissue by light and electron microscopy, TG2 and ε(γ-glutamyl)-lysine by immunofluorescence, and the urinary ε(γ-glutamyl)-lysine by high performance liquid chromatography. Results. Compared to the isograft, the allografts were hypertensive, proteinuric, and uraemic and developed CAN. Extracellular TG2 (glomerulus: 64.55 ± 17.61 versus 2.11 ± 0.17, P < 0.001; interstitium: 13.72 ± 1.62 versus 3.19 ± 0.44, P < 0.001), ε(γ-glutamyl)-lysine (glomerulus: 21.74 ± 2.71 versus 1.98 ± 0.37, P < 0.01; interstitium: 37.96 ± 17.06 versus 0.42 ± 0.11, P < 0.05), TG2 enzyme activity (1.09 ± 0.13 versus 0.41 ± 0.03 nmol/h/mg protein, P < 0.05), TG2 mRNA (20-fold rise), and urinary ε(γ-glutamyl)-lysine (534.2 ± 198.4 nmol/24 h versus 57.2 ± 4.1 nmol/24 h, P < 0.05) levels were significantly elevated in the allografts and showed a positive linear correlation with tubulointerstitial fibrosis. Conclusion. CAN was associated with upregulation of renal TG2 pathway, which has a potential for pharmacological intervention. The elevated urinary ε(γ-glutamyl)-lysine, measured for the first time in RTx, is a potential biomarker of CAN.

Inflammatory processes in renal fibrosis

Many types of kidney injury induce inflammation as a protective response. However, unresolved inflammation promotes progressive renal fibrosis, which can culminate in end-stage renal disease. Kidney inflammation involves cells of the immune system as well as activation of intrinsic renal cells, with the consequent production and release of profibrotic cytokines and growth factors that drive the fibrotic process. In glomerular diseases, the development of glomerular inflammation precedes interstitial fibrosis; although the mechanisms linking these events are poorly understood, an important role for tubular epithelial cells in mediating this link is gaining support. Data have implicated macrophages in promoting both glomerular and interstitial fibrosis, whereas limited evidence suggests that CD4(+) T cells and mast cells are involved in interstitial fibrosis. However, macrophages can also promote renal repair when the cause of renal injury can be resolved, highlighting their plasticity. Understanding the mechanisms by which inflammation drives renal fibrosis is necessary to facilitate the development of therapeutics to halt the progression of chronic kidney disease.

Expression of Ser729 phosphorylated PKCepsilon in experimental crescentic glomerulonephritis: an immunohistochemical study

PKCε, a DAG-dependent, Ca2+- independent kinase attenuates extent of fibrosis following tissue injury, suppresses apoptosis and promotes cell quiescence. In crescentic glomerulonephritis (CGN), glomerular epithelial cells (GEC) contribute to fibro-cellular crescent formation while they also transdifferentiate to a mesenchymal phenotype. The aim of this study was to assess PKCε expression in CGN. Using an antibody against PKC-ε phosphorylated at Ser729, we assessed its localization in rat model of immune-mediated rapidly progressive CGN. In glomeruli of control animals, pPKCε was undetectable. In animals with CGN, pPKCε was expressed exclusively in glomerular epithelial cells (GEC) and in GEC comprising fibrocellular crescents that had acquired a myofibroblast-type phenotype. In non-immune GEC injury induced by puromycin aminonucleoside and resulting in proteinuria of similar magnitude as in CGN, pPKCε expression was absent. There was constitutive pPKCε expression in distal convoluted tubules, collecting ducts and thick segments of Henley's loops in both control and experimental animals. We propose that pPKCε expression occurring in GEC and in fibrocellular crescentic lesions in CGN may facilitate PKCε dependent pathologic processes.

CD44 immunoreactivity in the developing human kidney: a marker of renal progenitor stem cells?

CD44 is a transmembrane adhesion glycoprotein, functioning as a hyaluronan receptor and participating in the uptake and degradation of hyaluronan. Recently, CD44 has been proposed in the adult kidney as a marker of activated glomerular parietal epithelial cells, the putative niche stem cells that, in case of damage to podocytes, might migrate inside the glomerular tuft and undergo transition to podocytes. Here, immunoreactivity for CD44 was tested in 18 human fetuses and newborns with a gestational age ranging from 11 to 39 weeks. CD44 immunoreactivity was observed in all but one developing kidneys, being localized in several renal cell types including intraglomerular, capsular, cortical and medullary interstitial cells and nerve cells. In some cases, CD44 marked scattered cells in nephrogenic subcapsular zone. Our data indicate that CD44 is involved in human nephrogenesis, probably marking a subset of progenitor/stem cells involved in early phases of kidney development and, putatively, in podocyte and/or interstitial cell differentiation.

Plasma leakage through glomerular basement membrane ruptures triggers the proliferation of parietal epithelial cells and crescent formation in non-inflammatory glomerular injury

Glomerular crescents are most common in rapidly progressive glomerulonephritis but also occur in non-inflammatory chronic glomerulopathies; thus, factors other than inflammation should trigger crescent formation, eg vascular damage and plasma leakage. Here we report that Alport nephropathy in Col4A3-deficient Sv129 mice is complicated by diffuse and global crescent formation in which proliferating parietal epithelial cells are the predominant cell type. Laminin staining and transmission and acellular scanning electron microscopy of acellular glomeruli documented disruptions and progressive disintegration of the glomerular basement membrane in Col4A3-deficient mice. FITC-dextran perfusion further revealed vascular leakage from glomerular capillaries into Bowman's space, further documented by fibrin deposits in the segmental crescents. Its pathogenic role was validated by showing that the fibrinolytic activity of recombinant urokinase partially prevented crescent formation. In addition, in vitro studies confirmed an additional mitogenic potential of serum on murine and human parietal epithelial cells. Furthermore, loss of parietal cell polarity and unpolarized secretion of extracellular matrix components were evident within fibrocellular crescents. Among 665 human Alport nephropathy biopsies, crescent formation was noted in 0.4%. We conclude that glomerular vascular injury and GBM breaks cause plasma leakage which triggers a wound healing programme involving the proliferation of parietal cells and their loss of polarity. This process can trigger cellular and fibrocellular crescent formation even in the absence of cellular inflammation and rupture of the Bowman's capsule.

Sirolimus modulates HIVAN phenotype through inhibition of epithelial mesenchymal transition

HIV-associated nephropathy (HIVAN) is characterized by proliferative phenotype in the form of collapsing glomerulopathy and microcystic dilatation of tubules. Recently, epithelial mesenchymal transition (EMT) of renal cells has been demonstrated to contribute to the pathogenesis of proliferative HIVAN phenotype. We hypothesized that sirolimus would modulate HIVAN phenotype by attenuating renal cell EMT. In the present study, we evaluated the effect of sirolimus on the development of renal cell EMT as well as on display of HIVAN phenotype in a mouse model of HIVAN (Tg26). Tg26 mice receiving normal saline (TgNS) showed enhanced proliferation of both glomerular and tubular cells when compared to control mice-receiving normal saline (CNS); on the other hand, Tg26 mice receiving sirolimus (TgS) showed attenuated renal cell proliferation when compared with TgNS. TgNS also showed increased number of α-SMA-, vimentin-, and FSP1-positive cells (glomerular as well as tubular) when compared with CNS; however, TgS showed reduced number of SMA, vimentin, and FSP1+ve renal cells when compared to TgNS. Interestingly, sirolimus preserved renal epithelial cell expression of E-cadherin in TgS. Since sirolimus attenuated renal cell ZEB expression (a repressor of E-cadherin transcription), it appears that sirolimus may be attenuating renal cell EMT by preserving epithelial cell E-cadherin expression.

Glomerular parietal epithelial cells of adult murine kidney undergo EMT to generate cells with traits of renal progenitors

Glomerular parietal epithelial cells (GPECs) are known to revert to embryonic phenotype in response to renal injury. However, the mechanism of de-differentiation in GPECs and the underlying cellular processes are not fully understood. In the present study, we show that cultured GPECs of adult murine kidney undergo epithelial-mesenchymal transition (EMT) to generate cells, which express CD24, CD44 and CD29 surface antigens. Characterization by qRT-PCR and immunostaining of these clonogenic cells demonstrate that they exhibit metastable phenotype with co-expression of both epithelial (cytokeratin-18) and mesenchymal (vimentin) markers. Transcript analysis by qRT-PCR revealed high expression of metanephric mesenchymal (Pax-2, WT-1, Six-1, Eya-1, GDNF) and uteric bud (Hoxb-7, C-Ret) genes in these cells, indicating their bipotent progenitor status. Incubation of GPECs with EMT blocker Prostaglandin E2, resulted in low expression of renal progenitor markers reflecting the correlation between EMT and acquired stemness in these cells. Additional in vitro renal commitment assays confirmed their functional staminality. When injected into E13.5 kidney rudiments, the cells incorporated into the developing kidney primordia and co-culture with E13.5 spinal cord resulted in branching and tubulogenesis in these cells. When implanted under renal capsule of unilaterally nephrectomized mice, these cells differentiated into immature glomeruli and vascular ducts. Our study demonstrates that EMT plays a major role in imparting plasticity to terminally differentiated GPECs by producing metastable cells with traits of kidney progenitors. The present study would improve our understanding on epithelial cell plasticity, furthering our knowledge of its role in renal repair and regeneration.

De novo expression of podocyte proteins in parietal epithelial cells in experimental aging nephropathy

A progressive decrease in podocyte number underlies the development of glomerulosclerosis and reduced kidney function in aging nephropathy. Recent data suggest that under certain disease states, parietal epithelial cells (PECs) begin to express proteins considered specific to podocytes. To determine whether this phenomenon increases in aging kidneys, 4-, 12-, and 20-mo ad libitum-fed and 20-mo calorie-restricted (CR) rats were studied. Single and double immunostaining were performed with antibodies to the PEC protein paired box gene 2 (PAX2) and tight junction protein claudin-1, the podocyte-specific protein Wilms' tumor 1 (WT-1), and the proliferating cell protein (Ki-67). ImageJ software measured Bowman's basement membrane (BBM) length and glomerular tuft area in individual glomeruli from each animal to assess glomerular size. The results showed that in aged ad libitum rats, the decrease in number of podocytes/glomerular tuft area was accompanied by an increase in the number of PECs/BBM length at 12 and 20 mo (P < 0.01 vs. 4 mo). The increase in PEC number was due to proliferation (increase in PAX2/Ki-67 double-positive cells). Aging was accompanied by a progressive increase in the number of glomerular cells double staining for PAX2 and WT-1. In contrast, the control 20-mo-old CR rats had no increase in glomerular size, and podocyte and PEC number were not altered. These results suggest that although the number of PECs and PECs expressing podocyte proteins increase in aging nephropathy, they are likely not sufficient to compensate for the decrease in podocyte number.

Epidermal growth factor receptor promotes glomerular injury and renal failure in rapidly progressive crescentic glomerulonephritis

Rapidly progressive glomerulonephritis (RPGN) is a clinical a morphological expression of severe glomerular injury. Glomerular injury manifests as a proliferative histological pattern (“crescents”) with accumulation of T cells and macrophages, and proliferation of intrinsic glomerular cells. We show de novo induction of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in intrinsic glomerular epithelial cells (podocytes) from both mice and humans with RPGN. HB-EGF induction increases phosphorylation of the EGFR/ErbB1 receptor in mice with RPGN. In HB-EGF-deficient mice, EGFR activation in glomeruli is absent and the course of RPGN is improved. Autocrine HB-EGF induces a phenotypic switch in podocytes in vitro. Conditional deletion of the Egfr gene from podocytes of mice alleviates the severity of RPGN. Pharmacological blockade of EGFR also improves the course of RPGN, even when started 4 days after the induction of experimental RPGN. This suggests that targeting the HB-EGF/EGFR pathway could also be beneficial for treatment of human RPGN.

Epithelial-mesenchymal transition in chronic liver disease: fibrogenesis or escape from death?

The possibility that epithelial-mesenchymal transition (EMT) could contribute to hepatic fibrogenesis in chronic liver diseases as reported in other organs, particularly the kidney, reinforced the concept that activated hepatic stellate cells were not the only key players in the hepatic fibrogenic process and that other cell types, either hepatic (i.e. portal fibroblast) or extrahepatic (bone marrow-derived cells and circulating fibrocytes) could contribute to this process. The possibility of the rapid mobilization of a large amount of fibrogenic cells by EMT after liver tissue injury made this phenomenon a relevant and suitable target for anti-fibrogenic strategies. Following an initial enthusiasm for the discovery of this novel pathway in fibrogenesis and the publication of a several highly quoted papers, more recent research has started to cast serious doubts upon the real relevance of this phenomenon in human fibrogenetic disorders. The debate on the authenticity of EMT or at least on its real contribution to the fibrogenic process has become very animated, sometimes reaching levels of "religious" integralism. The overall result is a general confusion on the meaning and on the definition of several key aspects. The aim of this article is to analyze and discuss the evidence supporting or confuting this possibility in order to reach reasonable and useful conclusions.

Reversal of hepatic fibrosis: pathophysiological basis of antifibrotic therapies

Chronic liver injuries of different etiologies eventually lead to fibrosis, a scarring process associated with increased and altered deposition of extracellular matrix in the liver. Progression of fibrosis has a major worldwide clinical impact due to the high number of patients affected by chronic liver disease which can lead to severe complications, expensive treatment, a possible need for liver transplantation, and death. Liver fibrogenesis is characterized by activation of hepatic stellate cells and other extracellular matrix producing cells. Liver fibrosis may regress following specific therapeutic interventions. Other than removing agents causing chronic liver damage, no antifibrotic drug is currently available in clinical practice. The extent of liver fibrosis is variable between individuals, even after controlling for exogenous factors. Thus, host genetic factors are considered to play an important role in the process of liver scarring. Until recently it was believed that this process was irreversible. However, emerging experimental and clinical evidence is starting to show that even cirrhosis in its early stages is potentially reversible.

Reversal of hepatic fibrosis: pathophysiological basis of antifibrotic therapies

Chronic liver injuries of different etiologies eventually lead to fibrosis, a scarring process associated with increased and altered deposition of extracellular matrix in the liver. Progression of fibrosis has a major worldwide clinical impact due to the high number of patients affected by chronic liver disease which can lead to severe complications, expensive treatment, a possible need for liver transplantation, and death. Liver fibrogenesis is characterized by activation of hepatic stellate cells and other extracellular matrix producing cells. Liver fibrosis may regress following specific therapeutic interventions. Other than removing agents causing chronic liver damage, no antifibrotic drug is currently available in clinical practice. The extent of liver fibrosis is variable between individuals, even after controlling for exogenous factors. Thus, host genetic factors are considered to play an important role in the process of liver scarring. Until recently it was believed that this process was irreversible. However, emerging experimental and clinical evidence is starting to show that even cirrhosis in its early stages is potentially reversible.

Early differential expression of oncostatin M in obstructive nephropathy

Interstitial fibrosis plays a major role in progression of renal diseases. Oncostatin M (OSM) is a cytokine that regulates cell survival, differentiation, and proliferation. Renal tissue from patients with chronic obstructive nephropathy was examined for OSM expression. The elevated levels in diseased human kidneys suggested possible correlation between OSM level and kidney tissue fibrosis. Indeed, unilateral ureteral obstruction (UUO), a model of renal fibrosis, increased OSM and OSM receptor (OSM-R) expression in a time-dependent manner within hours following UUO. In vitro, OSM overexpression in tubular epithelial cells (TECs) resulted in epithelial-myofibroblast transdifferentiation. cDNA microarray technology identified up-regulated expression of immune modulators in obstructed compared with sham-operated kidneys. In vitro, OSM treatment up-regulated CC chemokine ligand CCL7, and CXC chemokine ligand (CXCL)-14 mRNA in kidney fibroblasts. In vivo, treatment of UUO mice with neutralizing anti-OSM antibody decreased renal chemokines expression. In conclusion, OSM is up-regulated in kidney tissue early after urinary obstruction. Therefore, OSM might play an important role in initiation of renal fibrogenesis, possibly by inducing myofibroblast transdifferentiation of TECs as well as leukocyte infiltration. This process may, in turn, contribute in part to progression of obstructive nephropathy and makes OSM a promising therapeutic target in renal fibrosis.

Role of smooth muscle protein SM22α in glomerular epithelial cell injury

Podocytes are considered terminally differentiated cells in the mature kidney under normal conditions. In the face of injury, podocytes may proceed along several possible pathways, including dedifferentiation and proliferation, persistent cell cycle arrest, hypertrophy, apoptosis, or necrosis. There is mounting evidence that transdifferentiation into a dysregulated phenotype may also be a potential cell fate. We have previously reported that the transcript of SM22α, an actin-binding protein considered one of the earliest markers of smooth muscle differentiation, is upregulated nearly 70-fold in glomeruli of rats with passive Heymann nephritis (PHN). In contrast, the SM22α transcript is absent in normal adult rat glomeruli. The purpose of this study was to define SM22α's expression during kidney development and its role in glomerular diseases characterized by podocyte injury and proteinuria. During glomerulogenesis and podocyte differentiation, SM22α was expressed in glomeruli. This expression disappeared with glomerular maturation. Along with SM22α induction in PHN, confirmed at both mRNA and protein levels, SM22α was also induced across a broad range of proteinuric diseases, including experimental animal models (puromycin aminonucleoside nephropathy, adriamycin nephropathy, passive nephrotoxic nephritis, and diet-induced obesity) and human diseases (collapsing glomerulopathy, diabetic nephropathy, classic focal segmental glomerulosclerosis, IgA nephropathy, minimal-change disease, membranous nephropathy, and membranoproliferative glomerulonephritis). Crescentic glomerulonephritis was induced in SM22α +/+ and SM22α -/- mice by intraperitoneal injection of sheep anti-rabbit glomeruli antibody 12.5 mg/20 g body wt × 2 doses (n = 12-15/group), with mice euthanized at 7 and 14 days. Compared with SM22α -/- mice, SM22α +/+ mice demonstrated worse disease by histopathological parameters. In addition, there was greater apoptosis (cleaved caspase-3 immunostaining), fewer podocytes (Wilms' tumor-1 immunostaining), and less proliferation (Ki-67 immunostaining) in diseased SM22α +/+ mice. Furthermore, there was decreased activation of Erk1/2 in diseased SM22α +/+ mice. We conclude that the de novo expression of SM22α in glomerular epithelial cells affects the course of crescentic glomerulonephritis.

Epithelial-mesenchymal transition: from molecular mechanisms, redox regulation to implications in human health and disease

Epithelial to mesenchymal transition (EMT) is a fundamental process, paradigmatic of the concept of cell plasticity, that leads epithelial cells to lose their polarization and specialized junctional structures, to undergo cytoskeleton reorganization, and to acquire morphological and functional features of mesenchymal-like cells. Although EMT has been originally described in embryonic development, where cell migration and tissue remodeling have a primary role in regulating morphogenesis in multicellular organisms, recent literature has provided evidence suggesting that the EMT process is a more general biological process that is also involved in several pathophysiological conditions, including cancer progression and organ fibrosis. This review offers first a comprehensive introduction to describe major relevant features of EMT, followed by sections dedicated on those signaling mechanisms that are known to regulate or affect the process, including the recently proposed role for oxidative stress and reactive oxygen species (ROS). Current literature data involving EMT in both physiological conditions (i.e., embryogenesis) and major human diseases are then critically analyzed, with a special final focus on the emerging role of hypoxia as a relevant independent condition able to trigger EMT.

HIVAN phenotype: consequence of epithelial mesenchymal transdifferentiation

Human immunodeficiency virus (HIV)-1-associated nephropathy (HIVAN) is characterized by proliferation of glomerular and tubular epithelial cells. We studied the role of epithelial mesenchymal transdifferentiation (EMT) in the development of HIVAN phenotype. Renal cortical sections from six FVB/N (control) and six Tg26 (HIVAN) mice were immunolabeled for PCNA, alpha-smooth muscle actin (alpha-SMA), fibroblast-specific protein-1 (FSP1), CD3, and F4/80. Since periglomerular cells (PGCs) and peritubular cells (PTCs) did not show any labeling for CD3 and F4/80 but showed labeling for alpha-SMA or FSP1, it appears that these were myofibroblasts that migrated from either glomerular or tubular sites, respectively. Occurrence of EMT was also supported by diminished expression of E-cadherin by renal epithelial cells in Tg26 mice. Interestingly, Tg26 mice also showed enhanced renal tissue expression of ZEB2; henceforth, it appears that transcription of molecules required for maintenance of de novo renal epithelial cell phenotype was suppressed. To evaluate the role of ANG II, Tg26 mice in groups of three were administered either normal saline or telmisartan (an AT1 receptor blocker) for 2 wk, followed by evaluation for renal cell EMT. Renal cortical section of Tg26 mice showed a sevenfold increase (P < 0.001) in parietal epithelial cell (PEC)-PGC and a threefold increase (P < 0.01) in tubular cell (TC)-PTC proliferation (PCNA-positive cells). Similarly, both PECs-PGCs and TCs-PTCs in Tg26 mice showed enhanced expression of alpha-SMA and FSP1. Both PECs and podocytes contributed to the glomerular proliferative phenotype, but the contribution of PECs was much greater. Telmisartan-receiving Tg26 mice (TRM) showed attenuated number of proliferating PECs-PGCs and TCs-PTCs compared with saline-receiving Tg26 mice (SRM). Similarly, TRM showed diminished expression of alpha-SMA and FSP1 by both PECs-PGCs and TCs-PTCs compared with SRM. We conclude that EMT contributes to the manifestation of the proliferative phenotype in HIVAN mice.

The enigmatic parietal epithelial cell is finally getting noticed: a review

Although the normal glomerulus comprises four resident cell types, least is known about the parietal epithelial cells (PECs). This comprehensive review addresses the cellular origin of PECs, discusses the normal structure and protein makeup of PECs, describes PEC function, and defines the responses to injury in disease and how these events lead to clinical events. The data show that PECs have unique properties and that new functions are being recognized such as their role in differentiating into podocytes during disease.

Inactivation of TIF1gamma cooperates with Kras to induce cystic tumors of the pancreas

Inactivation of the Transforming Growth Factor Beta (TGFbeta) tumor suppressor pathway contributes to the progression of Pancreatic Ductal AdenoCarcinoma (PDAC) since it is inactivated in virtually all cases of this malignancy. Genetic lesions inactivating this pathway contribute to pancreatic tumor progression in mouse models. Transcriptional Intermediary Factor 1 gamma (TIF1gamma) has recently been proposed to be involved in TGFbeta signaling, functioning as either a positive or negative regulator of the pathway. Here, we addressed the role of TIF1gamma in pancreatic carcinogenesis. Using conditional Tif1gamma knockout mice (Tif1gamma(lox/lox)), we selectively abrogated Tif1gamma expression in the pancreas of Pdx1-Cre;Tif1gamma(lox/lox) mice. We also generated Pdx1-Cre;LSL-Kras(G12D);Tif1gamma(lox/lox) mice to address the effect of Tif1gamma loss-of-function in precancerous lesions induced by oncogenic Kras(G12D). Finally, we analyzed TIF1gamma expression in human pancreatic tumors. In our mouse model, we showed that Tif1gamma was dispensable for normal pancreatic development but cooperated with Kras activation to induce pancreatic tumors reminiscent of human Intraductal Papillary Mucinous Neoplasms (IPMNs). Interestingly, these cystic lesions resemble those observed in Pdx1-Cre;LSL-Kras(G12D);Smad4(lox/lox) mice described by others. However, distinctive characteristics, such as the systematic presence of endocrine pseudo-islets within the papillary projections, suggest that SMAD4 and TIF1gamma don't have strictly redundant functions. Finally, we report that TIF1gamma expression is markedly down-regulated in human pancreatic tumors by quantitative RT-PCR and immunohistochemistry supporting the relevance of these findings to human malignancy. This study suggests that TIF1gamma is critical for tumor suppression in the pancreas, brings new insight into the genetics of pancreatic cancer, and constitutes a promising model to decipher the respective roles of SMAD4 and TIF1gamma in the multifaceted functions of TGFbeta in carcinogenesis and development.

Inactivation of TIF1gamma cooperates with Kras to induce cystic tumors of the pancreas

Inactivation of the Transforming Growth Factor Beta (TGFβ) tumor suppressor pathway contributes to the progression of Pancreatic Ductal AdenoCarcinoma (PDAC) since it is inactivated in virtually all cases of this malignancy. Genetic lesions inactivating this pathway contribute to pancreatic tumor progression in mouse models. Transcriptional Intermediary Factor 1 gamma (TIF1γ) has recently been proposed to be involved in TGFβ signaling, functioning as either a positive or negative regulator of the pathway. Here, we addressed the role of TIF1γ in pancreatic carcinogenesis. Using conditional Tif1γ knockout mice (Tif1γ^lox/lox), we selectively abrogated Tif1γ expression in the pancreas of Pdx1-Cre;Tif1γ^lox/lox mice. We also generated Pdx1-Cre;LSL-Kras^G12D;Tif1γ^lox/lox mice to address the effect of Tif1γ loss-of-function in precancerous lesions induced by oncogenic Kras^G12D. Finally, we analyzed TIF1γ expression in human pancreatic tumors. In our mouse model, we showed that Tif1γ was dispensable for normal pancreatic development but cooperated with Kras activation to induce pancreatic tumors reminiscent of human Intraductal Papillary Mucinous Neoplasms (IPMNs). Interestingly, these cystic lesions resemble those observed in Pdx1-Cre;LSL-Kras^G12D;Smad4^lox/lox mice described by others. However, distinctive characteristics, such as the systematic presence of endocrine pseudo-islets within the papillary projections, suggest that SMAD4 and TIF1γ don't have strictly redundant functions. Finally, we report that TIF1γ expression is markedly down-regulated in human pancreatic tumors by quantitative RT–PCR and immunohistochemistry supporting the relevance of these findings to human malignancy. This study suggests that TIF1γ is critical for tumor suppression in the pancreas, brings new insight into the genetics of pancreatic cancer, and constitutes a promising model to decipher the respective roles of SMAD4 and TIF1γ in the multifaceted functions of TGFβ in carcinogenesis and development.

Inactivation of the TGFβ tumor suppressor pathway contributes to the progression of Pancreatic Ductal AdenoCarcinoma (PDAC), a devastating malignancy. Transcriptional Intermediary Factor 1γ (TIF1γ) has recently been proposed to be involved in TGFβ signaling, a pathway inactivated in virtually all cases of this malignancy. To address the role of TIF1γ in pancreatic carcinogenesis, we used conditional Tif1γ knockout mice. In a genetic background expressing a constitutively active mutation of KRAS oncogene (Kras^G12D) recurrently found in patients with PDAC, Tif1γ inactivation induces pancreatic precancerous lesions resembling those observed in the absence of Smad4, a key player involved TGFβ signal transduction. This observation strengthens the notion that TIF1γ plays an active role in TGFβ signaling. Interestingly, we also found that TIF1γ expression was markedly down-regulated in human pancreatic tumors supporting the relevance of our findings to human malignancy. Characterization of new players involved in the outbreak of early pancreatic lesions that will eventually evolve into invasive pancreatic cancer is crucial to detect the disease earlier and eventually develop new therapeutic drugs.

Origin of renal cell carcinomas

Cancer is a heritable disorder of somatic cells: environment and heredity are both important in the carcinogenic process. The primal force is the "two hits" of Knudson's hypothesis, which has proved true for many tumours, including renal cell carcinoma. Knudson et al. [1, 2] recognised that familial forms of cancer might hold the key to the identification of important regulatory elements known as tumour-suppressor genes. Their observations (i.e., that retinoblastoma tend to be multifocal in familial cases and unifocal in sporadic presentation) led them to propose a two-hit theory of carcinogenesis. Furthermore, Knudson postulated that patients with the familial form of the cancer would be born with one mutant allele and that all cells in that organ or tissue would be at risk, accounting for early onset and the multifocal nature of the disease. In contrast, sporadic tumours would develop only if a mutation occurred in both alleles within the same cell, and, as each event would be expected to occur with low frequency, most tumours would develop late in life and in a unifocal manner [3, 4]. The kidney is affected in a variety of inherited cancer syndromes. For most of them, both the oncogene/tumour-suppressor gene involved and the respective germline mutations have been identified. Each of the inherited syndromes predisposes to distinct types of renal carcinoma. Families with hereditary predisposition to cancer continue to provide a unique opportunity for the identification and characterisation of genes involved in carcinogenesis. A surprising number of genetic syndromes predispose to the development of renal cell carcinoma, and genes associated with five of these syndromes have been already identified: VHL, MET, FH, BHD and HRPT2. Few cancers have as many different types of genetic predisposition as renal cancer, although to date only a small proportion of renal cell cancers can be explained by genetic predisposition.

C3G overexpression in glomerular epithelial cells during anti-GBM-induced glomerulonephritis

The guanine nucleotide exchange factor C3G, along with the CrkII adaptor protein, mediates GTP activation of the small GTPase proteins Rap1 and R-Ras, facilitating their activation of downstream signaling pathways, which had been found to be important in the pathogenesis of glomerulonephritis. We found that expression of C3G protein was upregulated in glomerular epithelial cells in an experimental model of accelerated anti-GBM antibody-induced glomerulonephritis expression. To determine the consequence of its increased expression, we transfected C3G (using adenoviral constructs) into cultured glomerular epithelial cells and measured the activated forms (i.e., GTP-bound) forms of Rap1 and R-Ras. Activation of Rap1 was not affected by C3G; however, the basal level of GTP-bound R-Ras was decreased. Further, C3G over-expression enhanced the activation of R-Ras in response to endothelin. Overexpression of C3G also led to a significant reduction in glomerular epithelial cell spreading and decreased the cells' E-cadherin expression and augmented their migration. We found that C3G was overexpressed in accelerated anti-GBM antibody-induced glomerulonephritis and suggest that this modulates glomerular epithelial cell morphology and behavior.

Establishment of conditionally immortalized mouse glomerular parietal epithelial cells in culture

Parietal epithelial cells (PEC) are major constituents of crescents in crescentic glomerulonephritis. The purpose of these studies was to establish an immortalized PEC cell line with similar characteristics to PEC in vivo for use in future mechanistic studies. Glomeruli were isolated from H-2Kb tsA58 transgenic mice (ImmortoMouse) by standard differential sieving, and several candidate PEC cell lines were obtained by subcloning outgrowths of cells from capsulated glomeruli. One clone, designated mouse PEC (mPEC), was extensively characterized. mPEC exhibited a compact cell body with typical epithelial morphology when grown in permissive conditions, but the cell shape changed to polygonal after 14 d in growth-restrictive conditions. mPEC but not podocytes used as a negative control expressed claudin-1, claudin-2, and protein gene product 9.5, which are proteins specific to PEC in vivo, and did not express the podocyte-specific proteins synaptopodin and nephrin. The junctional proteins zonula occludens-1 and beta-catenin stained positively in both mPEC and podocytes, but the staining pattern at cell-cell contacts was intermittent in mPEC and linear in podocytes. Finally, mPEC had thin bundled cortical F-actin filaments and no F-actin projections compared with podocytes, which exhibited thick bundled cortical F-actin filaments and interdigitating F-actin projections at cell-cell contacts. We conclude that immortalized mPEC in culture exhibit specific features of PEC in vivo and that these cells are distinct from podocytes, despite having the same mesenchymal origin. This mPEC line will assist in future mechanistic studies of PEC and enhance our understanding of glomerular injury.

Cytokines in epithelial-mesenchymal transition: a new insight into obstructive nephropathy

PURPOSE

Tubulointerstitial fibrosis is the final common pathway to end stage renal disease. The pathophysiology of renal fibrosis involves fibroblast proliferation, macrophage infiltration, the elaboration of cytokines and other proinflammatory mediators, and an imbalance in extracellular matrix deposition and degradation. Although the exact origin of activated fibroblasts remains uncertain, emerging evidence indicates that mature tubular epithelial cells are capable of transforming into myofibroblasts under pathological conditions, a process that is called epithelial-mesenchymal transition.

MATERIALS AND METHODS

We reviewed the pertinent literature from January 1980 through June 2007 with regard to the contribution of epithelial-mesenchymal transition to renal fibrogenesis.

RESULTS

Epithelial-mesenchymal transition is an orchestrated, highly regulated process that proceeds in stepwise fashion and appears to contribute significantly to renal fibrosis and the progression of chronic renal disease. Several cytokines and growth factors regulate epithelial-mesenchymal transition, of which transforming growth factor-beta1 is the most studied.

CONCLUSIONS

Epithelial-mesenchymal transition is a cellular mechanism that has long been recognized as a central feature of normal development. However, increasing evidence implicates epithelial-mesenchymal transition in the pathophysiology of tubulointerstitial fibrosis and chronic renal disease. Recent insights into the molecular events and intrinsic signaling pathways that are active during epithelial-mesenchymal transition have evoked novel therapeutic strategies aimed at halting the onset and progression of chronic renal fibrosis.

Lymphocytes are dispensable for glomerulonephritis but required for renal interstitial fibrosis in matrix defect-induced Alport renal disease

One current theory for the emergence of glomerular nephritis implicates Th1-type cellular responses associated with delayed-type hypersensitivity, involving T cells and macrophages. Using a mouse model for progressive glomerulonephritis, we investigate the role of B and T cells in the pathogenesis of glomerular inflammation. Deletion of alpha3 chain of type IV collagen in mice (alpha3(IV) collagen null mice) results in GBM defects, glomerulonephritis and tubulointerstitial inflammation, fibrosis and significant immune infiltration including activated B- and T-lymphocytes. To evaluate the contribution of lymphocytes to the pathogenesis of glomerulonephritis and renal fibrosis, we generated mice that are deficient in both the alpha3(IV) collagen and Rag-1 (alpha3/Rag-1 DKO). Lymphocyte deficiency significantly reduces fibrosis in the renal interstitium, but ultrastructural GBM defects persist. Interestingly, glomerulonephritis in the double null mice persists at a similar level with comparable proteinuria. Here we demonstrate that despite the presence of B-cell and T-cells in the inflamed glomeruli, their deletion does not impede the emergence of glomerulonephritis but has a negative impact on the progression of renal interstitial fibrosis.