Role of PDGF B-chain and PDGF receptors in rat tubular regeneration after acute injury

Effect of Tyrosine Kinase Inhibitor Therapy on Estimated Glomerular Filtration Rate in Patients with Chronic Myeloid Leukemia

INTRODUCTION

The advent of tyrosine kinase inhibitors (TKIs) was revolutionary in the management of chronic myeloid leukemia (CML). Although TKIs were generally considered to be safe, they can be associated with renal injury. We evaluated the effect of TKIs on renal functions in a cohort of patients with long-term follow-up.

MATERIAL AND METHODS

We retrospectively examined patients with chronic phase CML treated with TKIs. We analyzed the estimated glomerular filtration rate (eGFR) of patients from the initiation of TKI to the last follow-up. eGFR values of CML patients were compared to those of patients with stage 1 or 2 chronic kidney disease (CKD).

RESULTS

A total of 195 patients with CML and 138 patients with CKD were examined. eGFR decline was 1.556 ml/min/1.73m2/year for patients with CML (P = .221). Patients receiving second-generation TKIs (2GTKI) were estimated to have 0.583 ml/min/1.73m2 higher eGFR value than that of the imatinib group, but it was not significant (P = .871). eGFR of patients who had used bosutinib had a downward trend. Duration of TKI therapy, age, and hypertension were found to be significant factors in eGFR decline for CML patients. Lower baseline GFR was associated with an increased risk of CKD development.

CONCLUSION

Imatinib could result in a decline in eGFR which was clinically similar to early-stage CKD patients. We did not observe significant kidney function deterioration in patients receiving 2GTKIs including dasatinib and nilotinib. We recommend close renal function monitoring in patients receiving imatinib, especially for elderly patients with lower baseline eGFR and hypertension.

Role of perivascular cells in kidney homeostasis, inflammation, repair and fibrosis

Perivascular niches in the kidney comprise heterogeneous cell populations, including pericytes and fibroblasts, with distinct functions. These perivascular cells have crucial roles in preserving kidney homeostasis as they maintain microvascular networks by stabilizing the vasculature and regulating capillary constriction. A subset of kidney perivascular cells can also produce and secrete erythropoietin; this ability can be enhanced with hypoxia-inducible factor-prolyl hydroxylase inhibitors, which are used to treat anaemia in chronic kidney disease. In the pathophysiological state, kidney perivascular cells contribute to the progression of kidney fibrosis, partly via transdifferentiation into myofibroblasts. Moreover, perivascular cells are now recognized as major innate immune sentinels in the kidney that produce pro-inflammatory cytokines and chemokines following injury. These mediators promote immune cell infiltration, leading to persistent inflammation and progression of kidney fibrosis. The crosstalk between perivascular cells and tubular epithelial, immune and endothelial cells is therefore a key process in physiological and pathophysiological states. Here, we examine the multiple roles of kidney perivascular cells in health and disease, focusing on the latest advances in this field of research.

Renal Safety Profile of BCR-ABL Tyrosine Kinase Inhibitors in a Real-Life Setting: A Study Based on Vigibase®, the WHO Pharmacovigilance Database

Background: Alongside their BCR-ABL specificity, TKIs used in chronic myeloid leukemia also target other tyrosine kinases expressed in the kidney such as PDGFR, c-KIT, SRC, and VEGFR, which may result in specific renal adverse drug reaction (ADR). To evaluate the renal safety profile in real-life conditions, a case/non-case study was performed on VigiBase®, the WHO global safety database. Methods: From 7 November 2001 to 2 June 2021, all cases in which the involvement of imatinib, dasatinib, nilotinib, bosutinib, and ponatinib was suspected in the occurrence of renal ADR were extracted from VigiBase®. Disproportionality analyses were assessed using the reporting odds ratio. Results: A total of 1409 cases were included. Imatinib accounts for half of the reported cases. A signal of disproportionate reporting (SDR) of renal failure and fluid retention was found for the five TKIs. Only dasatinib and nilotinib were related to an SDR for nephrotic syndrome. Nilotinib and ponatinib were related to an SDR for renal artery stenosis, while dasatinib was related to an SDR for thrombotic microangiopathy. No SDR for tubulointerstitial nephritis was observed. Conclusion: This study identified a new safety signal, nephrotic syndrome, for nilotinib and highlights the importance of post-marketing safety surveillance.

Comparison of Biomarkers Between Hepatic Tumors in Rat Models and a Dog

BACKGROUND/AIM

N1S1 rat models are commonly used in human medicine to study hepatocellular carcinoma (HCC). However, their use in veterinary medicine has not been reported. Thus, the aim of this study was to investigate whether the N1S1 rat models could be used to study canine HCC.

MATERIALS AND METHODS

The animals were divided into four groups: normal rat, N1S1 rat, normal dog, and HCC dog. Liver tissues of all animals were evaluated for vascular endothelial growth factor (VEGF), epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR)-α, PDGFR-β, and c-kit by immunohistochemistry. Slides of each factor were scored according to the percentage of stained tumor cells and intensity of the staining.

RESULTS

Scores of VEGF and c-kit were high both in the tumor groups (the N1S1 rat and HCC dog groups) and the normal groups of dogs and rats. PDGFR-α was lower in the N1S1 rat group than that in the normal rat group (p=0.0042). It was also lower in the HCC dog group compared to the normal dog group (p=0.0008). PDGFR-β was higher in the HCC dog group than that in the normal dog group (p=0.0023) but was not detectable in the rat groups. EGFR was not detectable in any group.

CONCLUSION

Based on immunochemistry results, PDGFR-α and PDGFR-β can be used as biomarkers of canine HCC. Because PDGFR-α showed consistency between rats and dogs, it can be used for studying canine HCC.

The Role of Tubule-Interstitial Crosstalk in Renal Injury and Recovery

Renal epithelial cells show remarkable regenerative capacity to recover from acute injury, which involves specific phenotypic changes, but also significant profibrotic tubule-interstitial crosstalk. Tubule-derived profibrotic stimuli and subsequent myofibroblast activation and extracellular matrix deposition have been linked closely with decline of renal function and nephron loss. However, recent data have questioned the view of purely detrimental effects of myofibroblast activation in the injured kidney and even suggested its beneficial role for epithelial regeneration. This article reviews the current understanding of the underlying mechanisms of tubular cell turnover, new suggested pathways of proregenerative tubular-interstitial crosstalk, and relevant insights of proliferation-enhancing effects of myofibroblasts on epithelial cells in nonrenal tissues.

Potential targeted therapy and diagnosis based on novel insight into growth factors, receptors, and downstream effectors in acute kidney injury and acute kidney injury-chronic kidney disease progression

Acute kidney injury (AKI) is defined as a rapid decline in renal function and is characterized by excessive renal inflammation and programmed death of resident cells. AKI shows high morbidity and mortality, and severe or repeated AKI can transition to chronic kidney disease (CKD) or even end-stage renal disease (ESRD); however, very few effective and specific therapies are available, except for supportive treatment. Growth factors, such as epidermal growth factor (EGF), insulin-like growth factor (IGF), and transforming growth factor-β (TGF-β), are significantly altered in AKI models and have been suggested to play critical roles in the repair process of AKI because of their roles in cell regeneration and renal repair. In recent years, a series of studies have shown evidence that growth factors, receptors, and downstream effectors may be highly involved in the mechanism of AKI and may function in the early stage of AKI in response to stimuli by regulating inflammation and programmed cell death. Moreover, certain growth factors or correlated proteins act as biomarkers for AKI due to their sensitivity and specificity. Furthermore, growth factors originating from mesenchymal stem cells (MSCs) via paracrine signaling or extracellular vesicles recruit leukocytes or repair intrinsic cells and may participate in AKI repair or the AKI-CKD transition. In addition, growth factor-modified MSCs show superior therapeutic potential compared to that of unmodified controls. In this review, we summarized the current therapeutic and diagnostic strategies targeting growth factors to treat AKI in clinical trials. We also evaluated the possibilities of other growth factor-correlated molecules as therapeutic targets in the treatment of AKI and the AKI-CKD transition.

Successful Treatment of End-stage Renal Disease in a Patient With Chronic Myeloid Leukemia by Kidney Transplantation and Tyrosine Kinase Inhibitors: A Case Report

Consensus regarding kidney transplantation feasibility in patients with chronic myeloid leukemia (CML) well controlled by tyrosine kinase inhibitors has not yet been achieved. Here, we report a patient with CML well controlled by tyrosine kinase inhibitors who developed end-stage renal disease during treatment and underwent kidney transplantation. CML activity has been carefully and successfully controlled for 4 years post-transplant. Very cautious dose adjustment and temporary cessation of nilotinib were required because kidney function fluctuated in reference to the doses of nilotinib.

Bioactive Compounds for the Treatment of Renal Disease

Kidney diseases including acute kidney injury and chronic kidney disease are among the largest health issues worldwide. Dialysis and kidney transplantation can replace a significant portion of renal function, however these treatments still have limitations. To overcome these shortcomings, a variety of innovative efforts have been introduced, including cell-based therapies. During the past decades, advances have been made in the stem cell and developmental biology, and tissue engineering. As part of such efforts, studies on renal cell therapy and artificial kidney developments have been conducted, and multiple therapeutic interventions have shown promise in the pre-clinical and clinical settings. More recently, therapeutic cell-secreting secretomes have emerged as a potential alternative to cell-based approaches. This approach involves the use of renotropic factors, such as growth factors and cytokines, that are produced by cells and these factors have shown effectiveness in facilitating kidney function recovery. This review focuses on the renotropic functions of bioactive compounds that provide protective and regenerative effects for kidney tissue repair, based on the available data in the literature.

Renal Interstitial Platelet-Derived Growth Factor Receptor-β Cells Support Proximal Tubular Regeneration

BACKGROUND

The kidney is considered to be a structurally stable organ with limited baseline cellular turnover. Nevertheless, single cells must be constantly replaced to conserve the functional integrity of the organ. PDGF chain B (PDGF-BB) signaling through fibroblast PDGF receptor-β (PDGFRβ) contributes to interstitial-epithelial cell communication and facilitates regenerative functions in several organs. However, the potential role of interstitial cells in renal tubular regeneration has not been examined.

METHODS

In mice with fluorescent protein expression in renal tubular cells and PDGFRβ-positive interstitial cells, we ablated single tubular cells by high laser exposure. We then used serial intravital multiphoton microscopy with subsequent three-dimensional reconstruction and ex vivo histology to evaluate the cellular and molecular processes involved in tubular regeneration.

RESULTS

Single-tubular cell ablation caused the migration and division of dedifferentiated tubular epithelial cells that preceded tubular regeneration. Moreover, tubular cell ablation caused immediate calcium responses in adjacent PDGFRβ-positive interstitial cells and the rapid migration thereof toward the injury. These PDGFRβ-positive cells enclosed the injured epithelium before the onset of tubular cell dedifferentiation, and the later withdrawal of these PDGFRβ-positive cells correlated with signs of tubular cell redifferentiation. Intraperitoneal administration of trapidil to block PDGFRβ impeded PDGFRβ-positive cell migration to the tubular injury site and compromised the recovery of tubular function.

CONCLUSIONS

Ablated tubular cells are exclusively replaced by resident tubular cell proliferation in a process dependent on PDGFRβ-mediated communication between the renal interstitium and the tubular system.

Unilateral nephrectomy diminishes ischemic acute kidney injury through enhanced perfusion and reduced pro-inflammatory and pro-fibrotic responses

While unilateral nephrectomy (UNx) is suggested to protect against ischemia-reperfusion injury (IRI) in the remaining kidney, the mechanisms underlying this protection remain to be elucidated. In this study, functional MRI was employed in a renal IRI rat model to reveal global and regional changes in renal filtration, perfusion, oxygenation and sodium handling, and microarray and pathway analyses were conducted to identify protective molecular mechanisms. Wistar rats were randomized to either UNx or sham UNx immediately prior to 37 minutes of unilateral renal artery clamping or sham operation under sevoflurane anesthesia. MRI was performed 24 hours after reperfusion. Blood and renal tissue were harvested. RNA was isolated for microarray analysis and QPCR validation of gene expression results. The perfusion (T1 value) was significantly enhanced in the medulla of the post-ischemic kidney following UNx. UNx decreased the expression of fibrogenic genes, i.a. Col1a1, Fn1 and Tgfb1 in the post-ischemic kidney. This was associated with a marked decrease in markers of activated myofibroblasts (Acta2/α-Sma and Cdh11) and macrophages (Ccr2). This was most likely facilitated by down-regulation of Pdgfra, thus inhibiting pericyte-myofibroblast differentiation, chemokine production (Ccl2/Mcp1) and macrophage infiltration. UNx reduced ischemic histopathologic injury. UNx may exert renoprotective effects against IRI through increased perfusion in the renal medulla and alleviation of the acute pro-inflammatory and pro-fibrotic responses possibly through decreased myofibroblast activation. The identified pathways involved may serve as potential therapeutic targets and should be taken into account in experimental models of IRI.

Bosutinib versus Placebo for Autosomal Dominant Polycystic Kidney Disease

Overactivation of Src has been linked to the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). This phase 2, multisite study assessed the efficacy and safety of bosutinib, an oral dual Src/Bcr-Abl tyrosine kinase inhibitor, in patients with ADPKD. Patients with ADPKD, eGFR≥60 ml/min per 1.73 m2, and total kidney volume ≥750 ml were randomized 1:1:1 to bosutinib 200 mg/d, bosutinib 400 mg/d, or placebo for ≤24 months. The primary endpoint was annualized rate of kidney enlargement in patients treated for ≥2 weeks who had at least one postbaseline magnetic resonance imaging scan that was preceded by a 30-day washout (modified intent-to-treat population). Of 172 enrolled patients, 169 received at least one study dose. Per protocol amendment, doses for 24 patients who initially received bosutinib at 400 mg/d were later reduced to 200 mg/d. The annual rate of kidney enlargement was reduced by 66% for bosutinib 200 mg/d versus placebo (1.63% versus 4.74%, respectively; P=0.01) and by 82% for pooled bosutinib versus placebo (0.84% versus 4.74%, respectively; P<0.001). Over the treatment period, patients receiving placebo or bosutinib had similar annualized eGFR decline. Gastrointestinal and liver-related adverse events were the most frequent toxicities. In conclusion, compared with placebo, bosutinib at 200 mg/d reduced kidney growth in patients with ADPKD. The overall gastrointestinal and liver toxicity profile was consistent with the profile in prior studies of bosutinib; no new toxicities were identified. (ClinicalTrials.gov: NCT01233869).

Inhibition of Glomerular Mesangial Cell Proliferation by siPDGF-B- and siPDGFR-β-Containing Chitosan Nanoplexes

Mesangioproliferative glomerulonephritis is a disease that has a high incidence in humans. In this disease, the proliferation of glomerular mesangial cells and the production of extracellular matrix are important. In recent years, the RNAi technology has been widely used in the treatment of various diseases due to its capability to inhibit the gene expression with high specificity and targeting. The objective of this study was to decrease mesangial cell proliferation by knocking down PDGF-B and its receptor, PDGFR-β. To be able to use small interfering RNAs (siRNAs) in the treatment of this disease successfully, it is necessary to develop appropriate delivery systems. Chitosan, which is a biopolymer, is used as a siRNA delivery system in kidney drug targeting. In order to deliver siRNA molecules targeted at PDGF-B and PDGFR-β, chitosan/siRNA nanoplexes were prepared. The in vitro characterization, transfection studies, and knockdown efficiencies were studied in immortalized and primary rat mesangial cells. In addition, the effects of chitosan nanoplexes on mesangial cell proliferation and migration were investigated. After in vitro transfection, the PDGF-B and PDGFR-β gene silencing efficiencies of PDGF-B and PDGFR-β targeting siRNA-containing chitosan nanoplexes were 74 and 71% in immortalized rat mesangial cells and 66 and 62% in primary rat mesangial cells, respectively. siPDGF-B- and siPDGFR-β-containing nanoplexes indicated a significant decrease in mesangial cell migration and proliferation. These results suggested that mesangial cell proliferation may be inhibited by silencing of the PDGF-B signaling pathway. Gene silencing approaches with chitosan-based gene delivery systems have promise for the efficient treatment of renal disease.

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.

Role of Receptor Tyrosine Kinase Signaling in Renal Fibrosis

Renal fibrosis can be induced in different renal diseases, but ultimately progresses to end stage renal disease. Although the pathophysiologic process of renal fibrosis have not been fully elucidated, it is characterized by glomerulosclerosis and/or tubular interstitial fibrosis, and is believed to be caused by the proliferation of renal inherent cells, including glomerular epithelial cells, mesangial cells, and endothelial cells, along with defective kidney repair, renal interstitial fibroblasts activation, and extracellular matrix deposition. Receptor tyrosine kinases (RTKs) regulate a variety of cell physiological processes, including metabolism, growth, differentiation, and survival. Many studies from in vitro and animal models have provided evidence that RTKs play important roles in the pathogenic process of renal fibrosis. It is also showed that tyrosine kinases inhibitors (TKIs) have anti-fibrotic effects in basic research and clinical trials. In this review, we summarize the evidence for involvement of specific RTKs in renal fibrosis process and the employment of TKIs as a therapeutic approach for renal fibrosis.

Inhibition of Notch Signaling Ameliorates Acute Kidney Failure and Downregulates Platelet-Derived Growth Factor Receptor β in the Mouse Model

Ischemic acute kidney injury (AKI) is associated with high morbidity and frequent complications. Repeated episodes of AKI may lead to end-stage renal failure. The pathobiology of regeneration in AKI is not well understood and there is no effective clinical therapy that improves regeneration. The Notch signaling pathway plays an essential role in kidney development and has been implicated in tissue repair in the adult kidney. Here, we found that kidneys after experimental AKI in mice showed increased expression of Notch receptors, specifically Notch1-3, of the Notch ligands Jagged-1 (Jag1), Jag2 and Delta-like-4 (Dll4) and of the Notch target genes Hes1, Hey2, HeyL, Sox9 and platelet-derived growth factor receptor β (Pdgfrb). Treatment of ischemic mice with the x03B3;-secretase inhibitor DBZ blocked Notch signaling and specifically downregulated the expression of Notch3 and the Notch target genes Hes1, Hey2, HeyL and Pdgfrb. After DBZ treatment, the mice developed less interstitial edema and displayed altered interstitial inflammation patterns. Furthermore, serum urea and creatinine levels were significantly decreased from 6 h onwards when compared to control mice treated with DMSO only. Our data are consistent with an amelioration of the severity of kidney injury by blocking Notch activation following AKI, and suggest an involvement of Notch-regulated Pdgfrb in AKI pathogenesis.

Estimated glomerular filtration rate changes in patients with chronic myeloid leukemia treated with tyrosine kinase inhibitors

BACKGROUND

Chronic use of tyrosine kinase inhibitors (TKIs) may lead to previously unrecognized adverse events. This study evaluated the incidence of acute kidney injury (AKI) and chronic kidney disease (CKD) in chronic-phase (CP) chronic myeloid leukemia (CML) patients treated with imatinib, dasatinib, and nilotinib.

METHODS

Four hundred sixty-eight newly diagnosed CP CML patients treated with TKIs were analyzed. The molecular and cytogenetic response data, creatinine, and glomerular filtration rate (GFR) were followed from the start of therapy to the last follow-up (median, 52 months). GFR was estimated with the Modification of Diet in Renal Disease equation.

RESULTS

Nineteen patients (4%) had TKI-associated AKI. Imatinib was associated with a higher incidence of AKI in comparison with dasatinib and nilotinib (P = .014). Fifty-eight patients (14%) developed CKD while they were receiving a TKI; 49 of these patients (84%) did so while they were being treated with imatinib (P < .001). Besides imatinib, age, a history of hypertension, and diabetes mellitus were also associated with the development of CKD. In patients with no CKD at the baseline, imatinib was shown to reduce GFR over time. Interestingly, imatinib did not cause a significant decline in the GFRs of patients with a history of CKD. Imatinib, dasatinib, and nilotinib increased the mean GFR after 3 months of treatment, and nilotinib led with the most significant increase (P < .001). AKI or CKD had no significant impact on overall cytogenetic and molecular response rates or survival.

CONCLUSIONS

The administration of TKIs may be safe in the setting of CKD in CP CML patients, but close monitoring is still warranted.

PDGF and the progression of renal disease

Progressive renal diseases represent a global medical problem, in part because we currently lack effective treatment strategies. Inhibition of platelet-derived growth factors (PDGFs) might represent one such novel strategy. PDGFs are required for normal kidney development by the recruitment of mesenchymal cells to both glomeruli and the interstitium. PDGFs are expressed in renal mesenchymal cells and, upon injury, in epithelial and infiltrating cells. They exert autocrine and paracrine effects on PDGF receptor-bearing mesenchymal cells, i.e. mesangial cells, fibroblasts and vascular smooth-muscle cells, which are crucially involved in progressive renal diseases. Proliferation but also migration and activation of these mesenchymal cells are the major effects mediated by PDGFs. These actions predefine the major roles of PDGFs in renal pathology, particularly in mesangioproliferative glomerulonephritis and interstitial fibrosis. Whereas for the former, the role of PDGFs is very well described and established, the latter is increasingly better documented as well. An involvement of PDGFs in other renal diseases, e.g. acute kidney injury, vascular injury and hypertensive as well as diabetic nephropathy, is less well established or presently unknown. Nevertheless, PDGFs represent a promising therapeutic option for progressive renal diseases, especially those characterized by mesangial cell proliferation and interstitial fibrosis. Clinical studies are eagerly awaited, in particular, since several drugs inhibiting PDGF signalling are available for clinical testing.

Targeting CTGF, EGF and PDGF pathways to prevent progression of kidney disease

Chronic kidney disease (CKD) is a major health and economic burden with a rising incidence. During progression of CKD, the sustained release of proinflammatory and profibrotic cytokines and growth factors leads to an excessive accumulation of extracellular matrix. Transforming growth factor β (TGF-β) and angiotensin II are considered to be the two main driving forces in fibrotic development. Blockade of the renin-angiotensin-aldosterone system has become the mainstay therapy for preservation of kidney function, but this treatment is not sufficient to prevent progression of fibrosis and CKD. Several factors that induce fibrosis have been identified, not only by TGF-β-dependent mechanisms, but also by TGF-β-independent mechanisms. Among these factors are the (partially) TGF-β-independent profibrotic pathways involving connective tissue growth factor, epidermal growth factor and platelet-derived growth factor and their receptors. In this Review, we discuss the specific roles of these pathways, their interactions and preclinical evidence supporting their qualification as additional targets for novel antifibrotic therapies.

Regenerative medicine for the kidney: renotropic factors, renal stem/progenitor cells, and stem cell therapy

The kidney has the capacity for regeneration and repair after a variety of insults. Over the past few decades, factors that promote repair of the injured kidney have been extensively investigated. By using kidney injury animal models, the role of intrinsic and extrinsic growth factors, transcription factors, and extracellular matrix in this process has been examined. The identification of renal stem cells in the adult kidney as well as in the embryonic kidney is an active area of research. Cell populations expressing putative stem cell markers or possessing stem cell properties have been found in the tubules, interstitium, and glomeruli of the normal kidney. Cell therapies with bone marrow-derived hematopoietic stem cells, mesenchymal stem cells, endothelial progenitor cells, and amniotic fluid-derived stem cells have been highly effective for the treatment of acute or chronic renal failure in animals. Embryonic stem cells and induced pluripotent stem cells are also utilized for the construction of artificial kidneys or renal components. In this review, we highlight the advances in regenerative medicine for the kidney from the perspective of renotropic factors, renal stem/progenitor cells, and stem cell therapies and discuss the issues to be solved to realize regenerative therapy for kidney diseases in humans.

Angiogenic and inflammatory markers in acute respiratory distress syndrome and renal injury associated to A/H1N1 virus infection

Acute kidney injury (AKI) is often associated to acute respiratory distress syndrome (ARDS) due to influenza A/H1N1 virus infection. The profile of angiogenic and inflammatory factors in ARDS patients may be relevant for AKI. We analyzed the serum levels of several angiogenic factors, cytokines, and chemokines in 32 patients with A/H1N1 virus infection (17 with ARDS/AKI and 15 ARDS patients who did not developed AKI) and in 18 healthy controls. Significantly higher levels of VEGF, MCP-1, IL-6, IL-8 and IP-10 in ARDS/AKI patients were detected. Adjusting by confusing variables, levels of MCP-1 ≥150 pg/mL (OR=12.0, p=0.04) and VEGF ≥225 pg/mL (OR=6.4, p=0.03) were associated with the development of AKI in ARDS patients. Higher levels of MCP-1 and IP-10 were significantly associated with a higher risk of death in patients with ARDS (hazard ratio (HR)=10.0, p=0.02; HR=25.5, p=0.03, respectively) even taking into account AKI. Patients with influenza A/H1N1 infection and ARDS/AKI have an over-production of MCP-1, VEGF and IP-10 possibly contributing to kidney injury and are associated to a higher risk of death.

A purpose-synthesised anti-fibrotic agent attenuates experimental kidney diseases in the rat

Background and Purpose

Locally-active growth factors have been implicated in the pathogenesis of many diseases in which organ fibrosis is a characteristic feature. In the setting of chronic kidney disease (CKD), two such pro-fibrotic factors, transforming growth factor-ß (TGF-ß) and platelet-derived growth factor (PDGF) have emerged as lead potential targets for intervention. Given the incomplete organ protection afforded by blocking the actions of TGF-ß or PDGF individually, we sought to determine whether an agent that inhibited the actions of both may have broader effects in ameliorating the key structural and functional abnormalities of CKD.

Experimental Approach

Accordingly, we studied the effects of a recently described, small molecule anti-fibrotic drug, 3-methoxy-4-propargyloxycinnamoyl anthranilate (FT011, Fibrotech Therapeutics, Australia), which should have these effects.

Key Results

In the in vitro setting, FT011 inhibited both TGF-ß1 and PDGF-BB induced collagen production as well as PDGF-BB-mediated mesangial proliferation. Consistent with these in vitro actions, when studied in a robust model of non-diabetic kidney disease, the 5/6 nephrectomised rat, FT011 attenuated the decline in GFR, proteinuria and glomerulosclerosis (p<0.05 for all). Similarly, in the streptozotocin-diabetic Ren-2 rat, a model of advanced diabetic nephropathy, FT011 reduced albuminuria, glomerulosclerosis and tubulointerstitial fibrosis.

Conclusions and Implications

Together these studies suggest that broadly antagonising growth factor actions, including those of TGF-ß1 and PDGF-BB, has the potential to protect the kidney from progressive injury in both the diabetic and non-diabetic settings.

Lysophosphatidic acid increases proximal tubule cell secretion of profibrotic cytokines PDGF-B and CTGF through LPA2- and Gαq-mediated Rho and αvβ6 integrin-dependent activation of TGF-β

After ischemia-reperfusion injury (IRI), kidney tubules show activated transforming growth factor β (TGF-β) signaling and increased expression of profibrotic peptides, platelet-derived growth factor-B (PDGF-B) and connective tissue growth factor (CTGF). If tubule repair after IRI is incomplete, sustained paracrine activity of these peptides can activate interstitial fibroblast progenitors and cause fibrosis. We show that lysophosphatidic acid (LPA), a ubiquitous phospholipid that is increased at sites of injury and inflammation, signals through LPA2 receptors and Gαq proteins of cultured proximal tubule cells to transactivate latent TGF-β in a Rho/Rho-kinase and αvβ6 integrin-dependent manner. Active TGF-β peptide then initiates signaling to increase the production and secretion of PDGF-B and CTGF. In a rat model of IRI, increased TGF-β signaling that was initiated early during reperfusion did not subside during recovery, but progressively increased, causing tubulointerstitial fibrosis. This was accompanied by correspondingly increased LPA2 and β6 integrin proteins and elevated tubule expression of TGF-β1, together with PDGF-B and CTGF. Treatment with a pharmacological TGF-β type I receptor antagonist suppressed TGF-β signaling, decreased the expression of β6 integrin, PDGF-B, and CTGF, and ameliorated fibrosis. We suggest that LPA-initiated autocrine signaling is a potentially important mechanism that gives rise to paracrine profibrotic signaling in injured kidney tubule cells.

The PDGF family in renal fibrosis

The platelet-derived growth factor (PDGF) family plays an important role in embryonic development, malignancy, wound healing, atherosclerosis, and fibrosis in multiple organs. It belongs to the best-characterized growth factor systems in normal and diseased kidneys, and there is accumulating evidence that members of the PDGF family are key players in the development of renal fibrosis independent of the underlying kidney disease. All components of the PDGF system, consisting of four isoforms (PDGF-A, -B, -C, -D) and two receptor chains (PDGFR-α and -β), are constitutively or inducibly expressed in most renal cells. They regulate multiple pathophysiologic events, ranging from cell proliferation and migration, extracellular matrix accumulation and production of pro- and anti-inflammatory mediators, to tissue permeability and hemodynamics. This review focuses on advances in defining the roles of different PDGF isoforms in the development of glomerulosclerosis and tubulointerstitial fibrosis. The recent identification of endogenous PDGF inhibitors offers additional novel therapeutic strategies.

Platelet-derived growth factor and renal disease

PURPOSE OF REVIEW

This review focuses on the recent advances in our understanding of the role of platelet-derived growth factor (PDGF) in glomerular disease.

RECENT FINDINGS

Accumulating evidence indicates a critical involvement of PDGF receptor-β (PDGFR-β) signaling in glomerular disease. Augmented signaling via PDGFR-β is involved in the pathogenesis of IgA nephropathy. Therefore, targeting PDGFR-β signaling is a viable therapeutic strategy for glomerular diseases. However, current PDGFR-β antagonists are nonspecific, and their long-term effects remain to be elucidated. To develop effective intervention therapies targeting PDGF signaling, it is necessary to clarify the specific involvement of PDGF in the pathogenesis of glomerular disease. A novel PDGFR-β targeting mouse model has provided new insight into the postnatal role of PDGFR-β in aging-related mesangial sclerosis and the glomerular remodeling after nephrectomy. Furthermore, the same study indicated the redundancy of growth factor signals underlying glomerular remodeling. In this context, other studies have suggested a role for PDGFR-α signaling and collaborating growth factors to compensate for PDGFR-β in the kidney glomerulus.

SUMMARY

Intervention in growth factor signaling could be a valuable therapeutic strategy for kidney glomerular diseases. Further studies are required to characterize the pathogenesis of these diseases for the successful development of such a therapy.

AKI in the ICU: definition, epidemiology, risk stratification, and outcomes

Acute kidney injury (AKI) has emerged as a major public health problem that affects millions of patients worldwide and leads to decreased survival and increased progression of underlying chronic kidney disease (CKD). Recent consensus criteria for definition and classification of AKI have provided more consistent estimates of AKI epidemiology. Patients, in particular those in the ICU, are dying of AKI and not just simply with AKI. Even small changes in serum creatinine concentrations are associated with a substantial increase in the risk of death. AKI is not a single disease but rather a syndrome comprising multiple clinical conditions. Outcomes from AKI depend on the underlying disease, the severity and duration of renal impairment, and the patient's renal baseline condition. The development of AKI is the consequence of complex interactions between the actual insult and subsequent activation of inflammation and coagulation. Contrary to the conventional view, recent experimental and clinical data argue against renal ischemia-reperfusion as a sine qua non condition for the development of AKI. Loss of renal function can occur without histological signs of tubular damage or even necrosis. The detrimental effects of AKI are not limited to classical well-known symptoms such as fluid overload and electrolyte abnormalities. AKI can also lead to problems that are not readily appreciated at the bedside and can extend well beyond the ICU stay, including progression of CKD and impaired innate immunity. Experimental and small observational studies provide evidence that AKI impairs (innate) immunity and is associated with higher infection rates.

The platelet-derived growth factor system in renal disease: an emerging role of endogenous inhibitors

The platelet-derived growth factor (PDGF) family consists of four isoforms which are secreted as homodimers (PDGF-AA, PDGF-BB, PDGF-CC and PDGF-DD) or heterodimers (PDGF-AB), and two receptor chains (PDGFR-α and -β). All members of the PDGF system are constitutively or inducibly expressed in renal cells and are involved in the regulation of cell proliferation and migration, the accumulation of extracellular matrix proteins and the secretion of pro- and anti-inflammatory mediators. Particular roles have been identified in mediating mesangioproliferative changes, renal interstitial fibrosis and glomerular angiogenesis. Different endogenous inhibitors of PDGF-induced biological responses exist which affect the activation/deactivation of PDGF isoforms, the activity of the PDGFRs, or which block downstream signaling pathways of the autophosphorylated PDGFRs. The novel endogenous inhibitor nephroblastoma overexpressed gene (NOV, CCN3) reduces PDGF-induced cell proliferation and is downregulated by PDGF isoforms itself. Among all identified inhibitors only few "true" PDGF antagonists have been identified. A better understanding of these inhibitors may aid in the design of novel therapeutic approaches to PDGF-mediated diseases.

Enhancement of in vitro human tubulogenesis by endothelial cell-derived factors: implications for in vivo tubular regeneration after injury

Renal proximal tubular epithelium can regenerate after various insults. To examine whether the tubular repair process is regulated by surrounding peritubular capillaries, we established an in vitro human tubulogenesis model that mimics in vivo tubular regeneration after injury. In this model, HGF, a potent renotropic factor, dose dependently induced tubular structures in human renal proximal tubular epithelial cells cultured in gels. Consistent with regenerating tubular cells after injury, HGF-induced tubular structures expressed a developmental gene, Pax-2, and a mesenchymal marker, vimentin, and formed a lumen with aquaporin-1 expression. Electron microscopic analysis showed the presence of microvilli on the apical site of the lumen, suggesting that these structures are morphologically equivalent to renal tubules in vivo. When cocultured with human umbilical vein endothelial cells (HUVEC), HGF-induced tubular formation was significantly enhanced. This could not be reproduced by the addition of VEGF, basic FGF, or PDGF. Protein array revealed that HUVEC produced various matrix metalloproteinases (MMPs). The stimulatory effects of coculture with HUVEC or HUVEC-derived conditional medium were almost completely abolished by addition of the tissue inhibitor of metalloproteinase (TIMP)-1 or TIMP-2. These data suggest that endothelial cell-derived factors including MMPs play a critical role in tubulogenesis and imply a potential role of peritubular capillary endothelium as a source of factor(s) required for tubular recovery after injury.

Expression of transforming growth factor-beta1 limits renal ischemia-reperfusion injury

BACKGROUND

Renal ischemia-reperfusion injury (IRI) largely contributes to kidney transplant dysfunction and acute kidney injury, but its pathogenesis is not fully understood. In this study, the role of transforming growth factor (TGF)-beta1 in renal IRI is investigated using TGF-beta1 deficient mice.

METHOD

Human renal tubular epithelial cells (TEC) line (HK-2) was used as an in vitro model, and cell apoptosis was determined by flow cytometric analysis. Renal IRI was induced in mice by clamping renal vein and artery for 45 min at 32 degrees C.

RESULTS

Here, we showed that in cultures of HK-2 cells, TGF-beta1 expression was up-regulated by tumor necrosis factor (TNF)-alpha. Neutralization of TGF-beta1 activity increased both spontaneous and TNF-alpha-mediated apoptosis, and knockdown of TGF-beta1 expression increased the sensitivity of cell apoptosis to TNF-alpha. In a mouse model of renal IRI, a deficiency in TGF-beta1 expression increased the severity of renal injury, as indicated by more severe renal tubular damage, higher levels of serum creatinine or blood urea nitrogen in TGF-beta1 deficient mice as compared with those in wild-type controls. Further experiments showed that the antiapoptosis of TGF-beta1 correlated with up-regulation of Bcl-2 in kidney cells.

CONCLUSION

Expression of TGF-beta1 in TECs, potentially induced by proinflammatory TNF-alpha, renders TECs resistance to cell death. In mice, TGF-beta1 deficiency results in more prone to IRI. These data imply that TGF-beta1 may act as a feedback survival factor in the resistance to kidney injury and maintenance of epithelium homeostasis.

Acute kidney injury: a springboard for progression in chronic kidney disease

Recently published epidemiological and outcome analysis studies have brought to our attention the important role played by acute kidney injury (AKI) in the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD). AKI accelerates progression in patients with CKD; conversely, CKD predisposes patients to AKI. This research gives credence to older, well-thought-out wisdom that recovery from AKI is often not complete and is marked by residual structural damage. It also mirrors older experimental observations showing that unilateral nephrectomy, a surrogate for loss of nephrons by disease, compromises structural recovery and worsens tubulointerstitial fibrosis after ischemic AKI. Moreover, review of a substantial body of work on the relationships among reduced renal mass, hypertension, and pathology associated with these conditions suggests that impaired myogenic autoregulation of blood flow in the setting of hypertension, the arteriolosclerosis that results, and associated recurrent ischemic AKI in microscopic foci play important roles in the development of progressively increasing tubulointerstitial fibrosis. How nutrition, an additional factor that profoundly affects renal disease progression, influences these events needs reevaluation in light of information on the effects of calories vs. protein and animal vs. vegetable protein on injury and progression. Considerations based on published and emerging data suggest that a pathology that develops in regenerating tubules after AKI characterized by failure of differentiation and persistently high signaling activity is the proximate cause that drives downstream events in the interstitium: inflammation, capillary rarefaction, and fibroblast proliferation. In light of this information, we advance a comprehensive hypothesis regarding the pathophysiology of AKI as it relates to the progression of kidney disease. We discuss the implications of this pathophysiology for developing efficient therapeutic strategies to delay progression and avert ESRD.

Dietary fructose causes tubulointerstitial injury in the normal rat kidney

Recent studies suggest that the metabolic syndrome is associated with renal disease. We previously reported that a high-fructose diet, but not a high-glucose diet, can induce metabolic syndrome and accelerate chronic renal disease in rats. We now examined the effects of a high-fructose diet on normal rat kidneys. Three groups of Sprague-Dawley rats were pair fed a special diet containing 60% fructose, 60% glucose, or control standard rat chow for 6 wk, and then histological studies were performed. The effect of fructose to induce cell proliferation in cultured proximal tubular cells was also performed. Fructose diet, but not glucose diet, significantly increased kidney weight by 6 wk. The primary finding was tubular hyperplasia and proliferation involving all segments of the proximal tubules while glomerular changes were not observed. This is the same site where the fructose transporters (GLUT2 and -5) as well as the key enzyme in fructose metabolism (ketohexokinase) were expressed. Consistently, fructose also induced proliferation of rat proximal tubular cells in culture. In vivo, tubular proliferation was also associated with focal tubular injury, with type III collagen deposition in the interstitium, an increase in alpha-smooth muscle actin positive myofibroblasts, and an increase in macrophage infiltration. In conclusion, a high-fructose diet induces cell proliferation and hyperplasia in proximal tubules, perhaps via a direct metabolic effect. The effect is independent of total energy intake and is associated with focal tubulointerstitial injury. These studies may provide a mechanism by which metabolic syndrome causes renal disease.

Macrophage Infiltration and Cellular Proliferation in the Non-Ischemic Kidney and Heart following Prolonged Unilateral Renal Ischemia

BACKGROUND/AIMS

Although ischemic renal failure remains a major cause of morbidity and mortality, whether ischemic changes within a kidney might also have adverse effects on other organs has not been examined. Furthermore, given the protective effects of angiotensin II receptor (AT1) antagonism in renal ischemia, we considered whether a similar strategy might also modulate the response to acute renal insult.

METHODS

Unilateral renal artery ligation was performed in Sprague-Dawley rats, treated with or without the AT1 antagonist losartan (30 mg/kg/day). After 24 h of renal ischemia, changes in the contralateral kidney and heart were examined.

RESULTS

Contralateral non-ischemic kidneys displayed increased expression of platelet-derived growth factor-B (PDGF-B) in association with increased tubular cell proliferation. Gene expression for the macrophage chemokine osteopontin (OPN) was similarly increased along with substantial macrophage infiltration. In the heart, expression of OPN and macrophage numbers were increased. All of these changes, in both the heart and kidney were attenuated by losartan.

CONCLUSION

Rather than affecting a single organ, the present study demonstrates that after prolonged renal ischemia, the contralateral kidney and heart undergo changes in growth factor and chemokine expression, resulting in pathological proliferation and inflammation that can be modulated by blockade of the AT1 receptor.

Immunohistochemical study on caveolin-1alpha in regenerating process of tubular cells in gentamicin-induced acute tubular injury in rats

Caveolin-1, a principal component of caveolae, modulates growth signaling, endocytosis, and intracellular transport. We examined the expression of caveolin-1alpha and its relation to cell cycle and caveolin-interacting growth factor receptors in regenerating proximal tubules (PTs) after gentamicin-induced acute renal failure in rats. Caveolin-1alpha appeared in regenerating PTs as early as day 4 after last gentamicin, peaked at days 6 to 8, and showed cytoplasmic pattern after day 8. Immunoelectron microscopy revealed caveolin-1alpha-positive caveolae on the cell membrane and in cytoplasms in regenerating PTs at days 4 to 8 and caveolin-positivity confined to cytoplasms after day 10. The number of PT cells with proliferation markers peaked at day 6 and decreased afterwards as expression of cyclin-dependent kinase inhibitors increased. Platelet-derived growth factor receptor-beta (PDGFR-beta) and epidermal growth factor receptor (EGFR) were colocalized with caveolin-1alpha in proliferating PTs as early as day 4. Phosphorylated EGFR increased at day 8 and afterwards when caveolins dissociated from EGFR or decreased. In case of PDGFR-beta, phosphorylation seemed to be associated with the increase and association of caveolins to the receptors. Our results suggest that transient expression of caveolin-1alpha in early regenerating PTs might contribute to the regenerating process of PTs through modulating growth factor receptors.

Alterations in protein tyrosine kinase pathways in rat liver following normothermic ischemia-reperfusion

The phosphoregulation of signal transduction pathways is a complex series of reactions that modulate the cellular response to ischemia-reperfusion (I-R). The aim of this study was to evaluate the effect of normothermic liver I-R on protein tyrosine phosphorylation, production of angiogenic growth factors, and activation of signal proteins in tyrosine kinase pathways. A segmental normothermic ischemia of the liver was induced in rats by occluding the blood vessels (including the bile duct) to the median and left lateral lobes for 120 minutes. Liver extracts from either ischemic or nonischemic lobes were prepared at 0, 1, 3, and 6 hours after reperfusion. Liver tyrosine phosphorylation of proteins was examined by Western blot analysis, whereas vascular endothelial growth factor (VEGF) mRNA was analyzed by Northern blot. In ischemic liver lobes, VEGF mRNA and total protein levels increased at 1 and 3 hours after reperfusion. Tyrosine phosphorylation of the VEGF receptor Flk-1 and the platelet-derived growth factor receptor (PDGF-R) was increased only at 1 hour after reperfusion, while c-Src tyrosine phosphorylation remained increased at 3 hours and remained up to 6 hours after reperfusion. In conclusion, 1-R led to alterations in protein tyrosine phosphorylation and increased expression of VEGF in rat liver.

Expression and localization of PDGF-B, PDGF-D, and PDGF receptor in the kidney of angiotensin II-infused rat

Lipid accumulation in the kidney is a marker of tissue damage and may play a role in the development of renal injury. We have previously shown that long-term administration of angiotensin II in rats causes increased expression of transforming growth factor-beta1, coupled with an accumulation of lipids in the tubular and vascular wall cells in the kidney. In this study, we examine the regulation of expression of platelet-derived growth factor (PDGF) and its receptor system and their co-localization with lipid deposits in the kidneys of angiotensin II-infused rats. Real-time RT-PCR showed that expression of PDGF-B, PDGF-D, and PDGF receptor-beta (PDGFR-beta) mRNA was increased by angiotensin II infusion, and in situ hybridization showed the co-localization of these mRNAs. Tubular cells that had increased PDGF-B mRNA expression were positive for lipid deposition and also for cellular proliferation, which was indicated by the presence of proliferating cell nuclear antigen. By contrast, in the kidneys of angiotensin II-infused rats, apoptosis occurred in tubular cells that contained deposits of iron but not lipids. The deposition of lipids and upregulation of PDGF-B, PDGF-D, and PDGFR-beta induced by administration of angiotensin II were all suppressed by the selective angiotensin II type 1 (AT(1)) receptor antagonist losartan, but not by the nonspecific vasodilator hydralazine. The findings that lipid accumulation, upregulation of PDGF-B, PDGF-D, and PDGFR-beta, and cellular proliferation were topologically associated and regulated in an AT(1) receptor-dependent manner in the kidney of angiotensin II-infused rats suggests that these phenomena are related.

Adult kidney tubular cell population showing phenotypic plasticity, tubulogenic capacity, and integration capability into developing kidney

Using in vivo bromodeoxyuridine (BrdU) labeling, a tubular cell population (label-retaining tubular cells [LRTC]) was identified recently in normal adult kidneys, which contributes actively to the regeneration process of the kidney after injury. Here, these LRTC are characterized in vitro. The LRTC population was isolated from BrdU-treated rat kidney by FACS. Both LRTC and non-LRTC underwent proliferation and maintained an epithelial phenotype in the presence of tubulogenic growth factors such as EGF, TGF-alpha, IGF-I, and hepatocyte growth factor. It is interesting that LRTC also proliferated without epithelial markers expression in the presence of soluble factors derived from an embryonic kidney metanephric mesenchyme cell line. The type of extracellular matrix strongly influenced the phenotype of LRTC. Furthermore, in three-dimensional collagen gel culture, LRTC formed tubule-like or tubulocystic structures in response to growth factors (hepatocyte growth factor and fibroblast growth factor) that are known to induce kidney cell tubulogenesis in vitro and/or participate in renal regeneration in vivo. In contrast, non-LRTC did not form these structures. When transplanted into the metanephric kidney, LRTC but not non-LRTC were integrated into epithelial components of nephron, including the proximal tubular cells and the ureteric bud. They also differentiated into fibroblast-like cells. Collectively, these findings suggest that LRTC are an adult kidney tubular cell population that shows phenotypic plasticity, tubulogenic capacity, and integration capability into the developing kidney.

Imatinib Attenuates Diabetic Nephropathy in Apolipoprotein E-Knockout Mice

In the diabetic kidney, clinical as well as experimental observations have shown an upregulation of growth factors such as PDGF. These studies, however, were not designed to address whether upregulation of PDGF is merely a manifestation of diabetic renal injury or whether PDGF plays an active role in the pathophysiology of diabetic nephropathy. The objectives of this study were first to assess whether PDGF-dependent pathways are involved in the development of diabetic nephropathy and second to determine the effects of PDGF receptor antagonism on this disorder and associated molecular and cellular processes. This study used the diabetic apolipoprotein E-knockout (apoE-KO) mouse, a recently described model of accelerated diabetic nephropathy. Diabetes was induced by injection of streptozotocin in 6-wk-old apoE-KO mice. Diabetic animals received treatment with a tyrosine kinase inhibitor that inhibits PDGF action, imatinib (STI-571, 10 mg/kg per d orally) or no treatment for 20 wk. Nondiabetic apoE-KO mice served as controls. This model of accelerated renal disease with albuminuria as well as glomerular and tubulointerstitial injury was associated with increased renal expression of PDGF-B, proliferating cells, and alpha-smooth muscle actin-positive cells. Furthermore, there was increased accumulation of type I and type IV collagen as well as macrophage infiltration. Imatinib treatment ameliorated both renal functional and structural parameters of diabetes as well as overexpression of a number of growth factors, collagens, proliferating cells, alpha-smooth muscle actin-positive cells, and macrophage infiltration within the kidney. Tyrosine kinase inhibition with imatinib seems to retard the development of experimental diabetic nephropathy.

Leukemia inhibitory factor is involved in tubular regeneration after experimental acute renal failure

Leukemia inhibitory factor (LIF) is known to play a crucial role in the conversion of mesenchyme into epithelium during nephrogenesis. This study was carried out to test the hypothesis that LIF and LIF receptor (LIFR) are involved in the renal epithelial regeneration after acute renal failure. First, the authors investigated the spatiotemporal expression of LIF and LIFR in fetal and adult rat kidney. In developing kidney, LIF was expressed in the ureteric buds and LIFR was located in nephrogenic mesenchyme and the ureteric buds; in adult kidney, LIF and LIFR expression was confined to the collecting ducts. Next, the authors examined the expression of LIF and LIFR during the recovery phase after ischemia-reperfusion injury. Real-time PCR analysis revealed that LIF mRNA expression was significantly increased from day 1 to day 7 after reperfusion and that LIFR mRNA was upregulated from day 4 to day 14. Histologic analysis demonstrated that the increased expression of LIF mRNA and protein was most marked in the outer medulla, especially in the S3 segment of the proximal tubules. To elucidate the mitogenic role of LIF in the regeneration process, cultured rat renal epithelial (NRK 52E) cells were subjected to ATP depletion (an in vitro model of acute renal failure), and LIF expression was found to be enhanced during recovery after ATP depletion. Blockade of endogenous LIF with a neutralizing antibody significantly reduced the cell number and DNA synthesis during the recovery period. These results suggest that LIF participates in the regeneration process after tubular injury.

Ischemia induces early expression of a new transcription factor (6A3-5) in kidney vascular smooth muscle cells: studies in rat and human renal pathology

Acute renal failure, characterized by rapid decline in glomerular filtration rate, is a major cause of morbidity and mortality. During the evolution of renal diseases chronic ischemia develops. Indeed, acute or chronic renal failure may occur as a result of renal ischemia, which induces cells to dedifferentiate, proliferate, or become apoptotic. In this study, we have investigated the expression of a newly identified transcription factor, 6A3-5, under in vitro and in vivo conditions. Proliferating vascular smooth muscle were investigated in response to different mitogenic agents. The 6A3-5 expression was then studied in ischemic rat kidney, induced by renal pedicle clamping, followed, or not, by reperfusion. Subsequently human renal biopsies from early kidney grafts and chronic renal diseases were also investigated for 6A3-5 protein expression by immunohistochemistry. In vitro study shows an over-expression of 6A3-5 following 2 to 4 hours stimulation by serum or Angiotensin II, of rat proliferating aortic smooth muscle cell. Moreover, in vivo study shows that this new protein is over expressed in rat kidney submitted to 45 minutes ischemia. An anti-6A3-5 antibody shows the protein to be expressed in smooth muscle cells of the arterioles and intermediate size arteries, in mesangial cells and interstitial myofibroblasts. In human biopsies of early kidney grafts and renal disease, the same up-regulation of 6A3-5, as in acute ischemic situation, is observed. This 6A3-5 expression is intimately associated with alpha-smooth muscle cell actin expression in mesangial cells, arteriolar smooth muscle cells as well as interstitial myofibroblasts. Transcription factor 6A3-5 could potentially be a novel early vascular marker of acute and chronic renal ischemic stress implicated in tissue remodeling.

Membrane repolarization is delayed in proximal tubules after ischemia-reperfusion: possible role of microtubule-organizing centers

We have previously shown that microtubule-organizing centers (MTOCs) attach to the apical network of intermediate filaments (IFs) in epithelial cells in culture and in epithelia in vivo. Because that attachment is important for the architecture of microtubules (MTs) in epithelia, we analyzed whether chemical anoxia in LLC-PK1 and CACO-2 cells or unilateral ischemia-reperfusion in rat kidney (performed under fluorane anesthesia) had an effect on the binding and distribution of MTOCs. In culture, we found that chemical anoxia induces MTOC detachment from IFs by morphological and biochemical criteria. In reperfused rat proximal tubules, noncentrosomal MTOCs were fully detached from the cytoskeleton and scattered throughout the cytoplasm at 3 days after reperfusion, when brush borders were mostly reassembled. At that time, MTs were also fully reassembled but, as expected, lacked their normal apicobasal orientation. Two apical membrane markers expressed in S2 and S3 segments were depolarized at the same stage. At 8 days after reperfusion, membrane polarity, MTOCs, and MTs were back to normal. Na+-K+-ATPase was also found redistributed, not to the apical domain but rather to an intracellular compartment, as described by others (Alejandro VS, Nelson W, Huie P, Sibley RK, Dafoe D, Kuo P, Scandling JD Jr., and Myers BD. Kidney Int 48: 1308-1315, 1995). The prolonged depolarization of the apical membrane may have implications in the pathophysiology of acute renal failure.

Activation of Src kinase in platelet-derived growth factor-B-dependent tubular regeneration after acute ischemic renal injury

We previously reported that the platelet-derived growth factor B-chain (PDGF-B)/PDGF receptor (PDGFR) axis is involved in tubular regeneration after ischemia/reperfusion injury of the kidney. In the present study, we examined the activation of Src tyrosine kinase, a crucially important signaling molecule for PDGFR, and assessed the role of Src in PDGF-B-dependent renal tubular regeneration afterischemia/reperfusion injury. Immunoblot using clone 28, a monoclonal antibody specific for the active form of Src kinases, demonstrated increased active Src expression in the injured rat kidney 6 hours after reperfusion with peak activation at 12 hours. In vitro kinase assay confirmed increased Src activity that concurred with PDGFR-beta activation as detected by the increment of receptor-phosphorylated tyrosine. Immunohistochemistry using clone 28 demonstrated that active Src was preferentially expressed in the S3 segment of the proximal tubule in reperfused kidney, where it is not normally expressed. This enhanced expression of active Src was co-localized with the increased PDGFR expression in the tubular cells that were undergoing cell proliferation cycle. Trapidil administration suppressed Src and PDGFR-beta activation in the reperfused kidney and resulted in deteriorated renal function. These findings suggest that active Src participates in PDGF-B-dependent regeneration of tubular cells from acute ischemic injury.

PDGF receptor-alpha deficiency in glomerular mesangial cells of tenascin-C knockout mice

Tenascin-C (TNC) knockout (TNKO) mice showed reduced proliferation of mesangial cells and abnormal restoration after habu-snake venom (HSV)-induced glomerulonephritis. In this study, we examined the relationship of TNC and platelet-derived growth factor receptor (PDGFR) in glomerular mesangial cells. TNC and PDGFR-alpha and -beta transcriptions were up-regulated in wild type (WT) mice after HSV injection, but in TNKO mice PDGFR-alpha transcription was not up-regulated. Immunohistochemistry showed that PDGFR-alpha was found in mesangial areas of colocalized alpha-smooth muscle actin, but in TNKO mice it was not detectable. In vitro studies showed that the expressions of PDGFR-alpha and -beta mRNA and protein in cultured glomerular mesangial cells (GMC) of TNKO mice were lower than those in WT GMC. These results suggest that failures of both TNC and PDGFR-alpha are a candidate for abnormal restoration of TNKO mice.

Effect of trapidil, an antiplatelet and vasodilator agent on gentamicin-induced nephrotoxicity in rats

This study was carried out to evaluate the effect of trapidil, an antiplatelet and vasodilator drug, on the nephrotoxicity by an aminoglycoside, gentamicin, in rats. Forty female Wistar rats were divided into six different groups. One group served as a control group and the other groups were treated as follows: gentamicin (50 mg kg(-1) twice daily)-treated, gentamicin plus trapidil (4 or 20 mg kg(-1) daily)-treated and only trapidil-treated (4 or 20 mg kg(-1) daily) groups. Serum urea, creatinine and nitrite/nitrate levels were measured. Moreover, histopathological as well as electron microscopic examinations were performed. At a lower dose (4 mg kg(-1)) trapidil did not prevent the development of renal tubular damage by gentamicin. However, a higher dose of trapidil (20 mg kg(-1)) inhibited the ability of gentamicin to increase the levels of creatinine and urea. Furthermore, both light and electron microscopic evaluation confirmed the nephroprotective effect of the higher dose of trapidil. The level of the stable nitric oxide (NO) metabolite, nitrite, was also increased by trapidil. In conclusion, trapidil at a higher dose may protect against gentamicin nephrotoxicity. The mechanism underlying trapidil nephroprotection is not known, but may result from the antagonism of platelet-derived growth factor (PDGF), vasodilatation, inhibition of trombosit aggregation, and/or NO release.

Involvement of the activin-follistatin system in tubular regeneration after renal ischemia in rats

This study was conducted to investigate the involvement of the activin-follistatin system in renal regeneration after ischemic injury. Expression of mRNA for the activin beta(A) subunit was not detected in normal kidneys but increased markedly after renal ischemia. Immunoreactive beta(A) subunit was detected in tubular cells of the outer medulla in ischemic but not normal kidneys. Expression of mRNA for follistatin, an antagonist of activin A, was abundant in tubular cells of the outer medulla in normal kidneys and decreased significantly after renal ischemia. For assessment of the role of the activin-follistatin system in renal regeneration after ischemic injury, recombinant follistatin was intravenously infused into rats with renal ischemia, at the time of reperfusion. Exogenous follistatin prevented the histologic changes induced by ischemic injury, reduced apoptosis in tubular cells, and accelerated tubular cell proliferation. Serum levels of creatinine and blood urea nitrogen were significantly lower in follistatin-treated rats. Conversely, intravenous administration of recombinant activin A inhibited tubular cell proliferation after ischemic injury. These results indicate that the activin-follistatin system participates in renal regeneration after ischemic injury. Follistatin administered intravenously accelerates renal regeneration after renal ischemia, presumably by blocking the actions of endogenous activin.

Enhancement of glomerular heme oxygenase-1 expression in diabetic rats

An increase in oxidative stress in diabetic subjects is implicated to play a pivotal role in diabetic vascular complications. In response to oxidative stress, antioxidant enzymes are considered to be induced and protect cellular functions to keep in vivo homeostasis. However, it remains to be clarified whether antioxidant enzymes are induced against oxidative stress especially in renal glomeruli at an early stage of diabetes. To answer this question, we examined the gene expression of a variety of antioxidant enzymes in glomeruli isolated from streptozotocin-induced diabetic rats. The mRNA expression of antioxidant enzymes such as catalase, glutathione peroxidase, and CuZn-superoxide dismutase, was unaltered in glomeruli of diabetic rats and was comparable to control rats. In contrast, the mRNA expression of heme oxygenase-1 (HO-1) was enhanced in glomeruli of diabetic rats as compared with control rats. A treatment with insulin as well as with vitamin E (40 mg/kg body weight every other day, intra-peritoneal injection) normalized the mRNA expression of HO-1 in the glomeruli of diabetic rats. Immunohistochemical analysis revealed that the up-regulated expression of HO-1 protein was localized in glomerular cells of diabetic rats. In conclusion, these results provide the first evidence that among antioxidant enzymes HO-1 expression is preferentially increased in diabetic glomeruli.

Renal ischemia--reperfusion injury: an inescapable event affecting kidney transplantation outcome

Ischemia--reperfusion (I-R) injury has been shown to be a common cause of late and irreversible complications during a variety of standard medical and surgical procedures. The pathogenesis of events which follow the I-R involves both injured endothelium and activated leukocytes and their interaction. In kidney transplantation, an I-R injury occurs in situations such as graft harvesting, cold storage and surgery. Clinical consequences of I-R injury have been considered to be delayed graft function and acute rejection in the short term and chronic rejection late after transplantation. Here we focused on current knowledge of pathophysiology of renal I-R injury in kidney transplantation and on possibilities of experimental therapy.

Possible involvement of myofibroblasts in cellular recovery of uranyl acetate-induced acute renal failure in rats

Cellular recovery in acute renal failure is a form of wound healing. Fibroblast-like cells or myofibroblasts are involved in wound healing. We examined the serial changes in tubular damage and origin and kinetics of regenerating cells in uranyl acetate-induced acute renal failure, with a special emphasis on interstitial myofibroblasts. Acute renal failure was induced in rats by intravenous injection of uranyl acetate (5 mg/kg). All rats received bromodeoxyuridine intraperitoneally 1 hour before sacrifice. Serial changes in the distribution of tubular necrosis and bromodeoxyuridine-incorporated or vimentin-positive regenerating cells, and their spatial and temporal relation to alpha-smooth muscle actin-positive myofibroblasts as well as ED 1-positive monocytes/macrophages were examined. Necrotic tubules initially appeared around the corticomedullary junction after uranyl acetate injection, then spread both downstream and upstream of proximal tubules. Peritubular alpha-smooth muscle actin-positive myofibroblasts appeared and extended along the denuded tubular basement membrane, establishing network formation throughout the cortex and the outer stripe of outer medulla at days 4 to 5. Tubular regeneration originated in nonlethally injured cells in the distal end of S3 segments, which was confirmed by lectin and immunohistochemical staining using markers for tubular segment. Subsequently, upstream proliferation was noted along the tubular basement membrane firmly attached by myofibroblasts. During cellular recovery, no entry of myofibroblasts into the tubular lumen across the tubular basement membrane was noted and only a few myofibroblasts showed bromodeoxyuridine positivity. The fractional area of alpha-smooth muscle actin-positive interstitium reached a peak level at day 7 in the cortex and outer stripe of outer medulla, then gradually disappeared by day 15 and remained only around dilated tubules and in the expanded interstitium at day 21. ED 1-positive monocytes/macrophages were transiently infiltrated mainly into the region of injury. They did not show specific association with initially necrotic tubules, but some of them located in close proximity to regenerating tubules. Nonlethally injured cells at the distal end of proximal tubules are likely to be the main source of tubular regeneration, and the transient appearance of interstitial myofibroblasts attached to the tubular basement membrane immediately after tubular necrosis might play a role in promoting cellular recovery in possible association with monocytes/macrophages in uranyl acetate-induced acute renal failure.