Cell cycle regulatory proteins in glomerular disease

Targeting WIP1 phosphatase promotes partial remission in experimental collapsing glomerulopathy

Collapsing focal segmental glomerulosclerosis (FSGS), also known as collapsing glomerulopathy (CG), is the most aggressive variant of FSGS and is characterized by a rapid progression to kidney failure. Understanding CG pathogenesis represents a key step for the development of targeted therapies. Previous work implicated the telomerase protein component TERT in CG pathogenesis, as transgenic TERT expression in adult mice resulted in a CG resembling that seen in human primary CG and HIV-associated nephropathy (HIVAN). Here, we used the telomerase-induced mouse model of CG (i-TERTci mice) to identify mechanisms to inhibit CG pathogenesis. Inactivation of WIP1 phosphatase, a p53 target acting in a negative feedback loop, blocked disease initiation in i-TERTci mice. Repression of disease initiation upon WIP1 deficiency was associated with senescence enhancement and required transforming growth factor-β functions. The efficacy of a pharmacologic treatment to reduce disease severity in both i-TERTci mice and in a mouse model of HIVAN (Tg26 mice) was then assessed. Pharmacologic inhibition of WIP1 enzymatic activity in either the telomerase mice with CG or in the Tg26 mice promoted partial remission of proteinuria and ameliorated kidney histopathologic features. Histological as well as high-throughput sequencing methods further showed that selective inhibition of WIP1 does not promote kidney fibrosis or inflammation. Thus, our findings suggest that targeting WIP1 may be an effective therapeutic strategy for patients with CG.

New biomarkers in acute kidney injury

Acute kidney injury (AKI) is a commonly encountered clinical syndrome. Although it often complicates community acquired illness, it is more common in hospitalized patients, particularly those who are critically ill or who have undergone major surgery. Approximately 20% of hospitalized adult patients develop an AKI during their hospital care, and this rises to nearly 60% in the critically ill, depending on the population being considered. In general, AKI is more common in older adults, in those with preexisting chronic kidney disease and in those with known risk factors for AKI (including diabetes and hypertension). The development of AKI is associated with an increase in both mortality and morbidity, including the development of post-AKI chronic kidney disease. Currently, AKI is defined by a rise in serum creatinine from either a known or derived baseline value and/or oliguria or anuria. However, clinicians may fail to recognize the initial development of AKI because of a delay in the rise of serum creatinine or because of inaccurate urine output monitoring. This, in turn, delays any putative measures to treat AKI or to limit its degree. Consequently, efforts have focused on new biomarkers associated with AKI that may allow early recognition of this syndrome with the intent that this will translate into improved patient outcomes. Here we outline current biomarkers associated with AKI and explore their potential in aiding diagnosis, understanding the pathophysiology and directing therapy.

Long non‑coding RNA L13Rik promotes high glucose-induced mesangial cell hypertrophy and matrix protein expression by regulating miR-2861/CDKN1B axis

Background

Diabetic nephropathy (DN) is a frequent microvascular complication of diabetes. Glomerular mesangial cell (MC) hypertrophy occurs at the initial phase of DN and plays a critical role in the pathogenesis of DN. Given the role of long non coding RNA (lncRNA) in regulating MC hypertrophy and extracellular matrix (ECM) accumulation, our aim was to identify functional lncRNAs during MC hypertrophy.

Methods

Here, an lncRNA, C920021L13Rik (L13Rik for short), was identified to be up-regulated in DN progression. The expression of L13Rik in DN patients and diabetic mice was assessed using quantitative real-time PCR (qRT-PCR), and the function of L13Rik in regulating HG-induced MC hypertrophy and ECM accumulation was assessed through flow cytometry and western blotting analysis.

Results

The L13Rik levels were significantly increased while the miR-2861 levels were decreased in the peripheral blood of DN patients, the renal tissues of diabetic mice, and HG-treated MCs. Functionally, both L13Rik depletion and miR-2861 overexpression effectively reduced HG-induced cell hypertrophy and ECM accumulation. Mechanistically, L13Rik functioned as a competing endogenous RNA (ceRNA) to sponge miR-2861, resulting in the de-repression of cyclin-dependent kinase inhibitor 1B (CDKN1B), a gene known to regulate cell cycle and MC hypertrophy.

Conclusions

Collectively, the current results demonstrate that up-regulated L13Rik is correlated with DN and may be a hopeful therapeutic target for DN.

The DR1‑CSE/H2S system inhibits renal fibrosis by downregulating the ERK1/2 signaling pathway in diabetic mice

Glomerular mesangial cell (MC) proliferation and extracellular matrix deposition are the main pathological changes in diabetic nephropathy. Hydrogen sulfide (H2S) inhibits the proliferation of MCs. Dopamine 1 receptors (DR1) are expressed in MCs and serve important physiological roles. However, it is unclear whether DR1 activation inhibits MC proliferation by increasing endogenous H2S. The present study found that the production of H2S and the expression of DR1 and cystathionine‑γ‑lyase (CSE) were decreased in the renal tissues of diabetic mice and high glucose (HG)‑induced MCs. SKF38393 (a DR1 agonist) increased the production of H2S and the expression of DR1 and CSE and NaHS (an exogenous H2S donor) only increased H2S production and CSE expression but not DR1 expression. HG increased the thickness of the glomerular basement membrane, cell viability and proliferation, the expression of cyclin D1, PCNA, collagen 1 and α‑smooth muscle actin and the activity of phosphorylated ERK1/2 and decreased the expression of P21 and MMP9. SKF38393 and NaHS reversed the effects of HG. PPG (a CSE inhibitor) abolished the beneficial effects of SKF38393. The beneficial effects of SKF38393 were similar to those of PD98059 (an ERK1/2 inhibitor). Taken together, the findings suggested that the DR1‑CSE/H2S pathway activation attenuated diabetic MC proliferation and extracellular matrix deposition by downregulating the ERK1/2 signaling pathway.

Clinical adoption of Nephrocheck® in the early detection of acute kidney injury

Acute kidney injury is a common complication of acute illnesses and is associated with increased morbidity and mortality. Over the past years several acute kidney injury biomarkers for diagnostication, decision-making processes, and prognosis of acute kidney injury and its outcomes have been developed and validated. Among these biomarkers, tissue inhibitor of metalloproteinase-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7), the so-called cell cycle arrest biomarkers, showed a superior profile of accuracy and stability even in patients with substantial comorbidities. Therefore, in 2014, the US Food and Drug Administration approved the use of the product of TIMP-2 and IGFBP7 ([TIMP-2] × [IGFBP7]), known as cell cycle arrest biomarkers, to aid critical care physicians and nephrologists in the early prediction of acute kidney injury in the critical care setting. To date, Nephrocheck® is the only commercially available test for [TIMP-2] × [IGFBP7]. In this narrative review, we describe the growing clinical and investigational momentum of biomarkers, focusing on [TIMP-2] × [IGFBP7], as one of the most promising candidate biomarkers. Additionally, we review the current state of clinical implementation of Nephrocheck®.

Current understanding and future directions in the application of TIMP-2 and IGFBP7 in AKI clinical practice

NephroCheck® is the commercial name of a combined product of two urinary biomarkers, tissue inhibitor of metalloproteinases-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7), expressed as [TIMP-2]·[IGFBP7], used to identify patients at high risk of acute kidney injury (AKI). AKI is a common and harmful complication especially in critically-ill patients, which can induce devastating short- and long-term outcomes. Over the past decade, numerous clinical studies have evaluated the utility of several biomarkers (e.g. neutrophil gelatinase-associated lipocalin, interleukin-18, liver-type fatty acid binding protein and kidney injury molecule-1, cystatin C) in the early diagnosis and risk stratification of AKI. Among all these biomarkers, [TIMP-2]·[IGFBP7] was confirmed to be superior in early detection of AKI, before the decrease of renal function is evident. In 2014, the US Food and Drug Administration permitted marketing of NephroCheck® (Astute Medical) (measuring urinary [TIMP-2]·[IGFBP7]) to determine if certain critically-ill patients are at risk of developing moderate to severe AKI. It has since been applied to clinical work in many hospitals of the United States and Europe to improve the diagnostic accuracy and outcomes of AKI patients. Now, more and more research is devoted to the evaluation of its application value, meaning and method in different clinical settings. In this review, we summarize the current research status of [TIMP-2]·[IGFBP7] and point out its future directions.

The Potential for Renal Injury Elicited by Physical Work in the Heat

An epidemic of chronic kidney disease (CKD) is occurring in laborers who undertake physical work in hot conditions. Rodent data indicate that heat exposure causes kidney injury, and when this injury is regularly repeated it can elicit CKD. Studies in humans demonstrate that a single bout of exercise in the heat increases biomarkers of acute kidney injury (AKI). Elevations in AKI biomarkers in this context likely reflect an increased susceptibility of the kidneys to AKI. Data largely derived from animal models indicate that the mechanism(s) by which exercise in the heat may increase the risk of AKI is multifactorial. For instance, heat-related reductions in renal blood flow may provoke heterogenous intrarenal blood flow. This can promote localized ischemia, hypoxemia and ATP depletion in renal tubular cells, which could be exacerbated by increased sodium reabsorption. Heightened fructokinase pathway activity likely exacerbates ATP depletion occurring secondary to intrarenal fructose production and hyperuricemia. Collectively, these responses can promote inflammation and oxidative stress, thereby increasing the risk of AKI. Equivalent mechanistic evidence in humans is lacking. Such an understanding could inform the development of countermeasures to safeguard the renal health of laborers who regularly engage in physical work in hot environments.

Remote Ischemic Preconditioning and Protection of the Kidney--A Novel Therapeutic Option

OBJECTIVE

Acute kidney injury is a common complication in critically ill patients and is associated with increased morbidity and mortality. Sepsis, major surgery, and nephrotoxic drugs are the most common causes of acute kidney injury. There is currently no effective strategy available to prevent or treat acute kidney injury. Therefore, novel treatment regimens are required to decrease acute kidney injury prevalence and to improve clinical outcomes. Remote ischemic preconditioning, triggered by brief episodes of ischemia and reperfusion applied in distant tissues or organs before the injury of the target organ, attempts to invoke adaptive responses that protect against acute kidney injury. We sought to evaluate the clinical evidence for remote ischemic preconditioning as a potential strategy to protect the kidney and to review the underlying mechanisms in light of recent studies.

DATA SOURCES

We searched PubMed for studies reporting the effect of remote ischemic preconditioning on kidney function in surgical patients (search terms: "remote ischemic preconditioning," "kidney function," and "surgery"). We also reviewed bibliographies of relevant articles to identify additional citations.

STUDY SELECTION

Published studies, consisting of randomized controlled trials, are reviewed.

DATA EXTRACTION

The authors used consensus to summarize the evidence behind the use of remote ischemic preconditioning.

DATA SYNTHESIS

In addition, the authors suggest patient populations and clinical scenarios in which remote ischemic preconditioning might be best applied.

CONCLUSIONS

Several experimental and clinical studies have shown tissue-protective effects of remote ischemic preconditioning in various target organs, including the kidneys. Remote ischemic preconditioning may offer a novel, noninvasive, and inexpensive treatment strategy for decreasing acute kidney injury prevalence in high-risk patients. Although many new studies have further advanced our knowledge in this area, the appropriate intensity of remote ischemic preconditioning, its mechanisms of action, and the role of biomarkers for patient selection and monitoring are still unknown.

Histone Lysine Methylation in TGF-β1 Mediated p21 Gene Expression in Rat Mesangial Cells

Transforming growth factor beta1- (TGF-β1-) induced p21-dependent mesangial cell (MC) hypertrophy plays a key role in the pathogenesis of chronic renal diseases including diabetic nephropathy (DN). Increasing evidence demonstrated the role of posttranscriptional modifications (PTMs) in the event; however, the precise regulatory mechanism of histone lysine methylation remains largely unknown. Here, we examined the roles of both histone H3 lysine 4 and lysine 9 methylations (H3K4me/H3K9me) in TGF-β1 induced p21 gene expression in rat mesangial cells (RMCs). Our results indicated that TGF-β1 upregulated the expression of p21 gene in RMCs, which was positively correlated with the increased chromatin marks associated with active genes (H3K4me1/H3K4me2/H3K4me3) and negatively correlated with the decreased levels of repressive marks (H3K9me2/H3K9me3) at p21 gene promoter. TGF-β1 also elevated the recruitment of the H3K4 methyltransferase (HMT) SET7/9 to the p21 gene promoter. SET7/9 gene silencing with small interfering RNAs (siRNAs) significantly abolished the TGF-β1 induced p21 gene expression. Taken together, these results reveal the key role of histone H3Kme in TGF-β1 mediated p21 gene expression in RMC, partly through HMT SET7/9 occupancy, suggesting H3Kme and SET7/9 may be potential renoprotective agents in managing chronic renal diseases.

Diagnostic Criteria for Acute Kidney Injury: Present and Future

Acute kidney injury (AKI) is a clinical diagnosis guided by standard criteria based on changes in serum creatinine, urine output, or both. Severity of AKI is determined by the magnitude of increase in serum creatinine or decrease in urine output. Patients manifesting both oliguria and azotemia and those in which these impairments are persistent are more likely to have worse disease and worse outcomes. Short- and long-term outcomes are worse when patients have some stage of AKI by both criteria. New biomarkers for AKI may substantially aid in the risk assessment and evaluation of patients at risk for AKI.

Cell-cycle arrest and acute kidney injury: the light and the dark sides

Acute kidney injury (AKI) is a common consequence of systemic illness or injury and it complicates several forms of major surgery. Two major difficulties have hampered progress in AKI research and clinical management. AKI is difficult to detect early and its pathogenesis is still poorly understood. We recently reported results from multi-center studies where two urinary markers of cell-cycle arrest, tissue inhibitor of metalloproteinases-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7) were validated for development of AKI well ahead of clinical manifestations—azotemia and oliguria. Cell-cycle arrest is known to be involved in the pathogenesis of AKI and this ‘dark side’ may also involve progression to chronic kidney disease. However, cell-cycle arrest has a ‘light side’ as well, since this mechanism can protect cells from the disastrous consequences of entering cell division with damaged DNA or insufficient bioenergetic resources during injury or stress. Whether we can use the light side to help prevent AKI remains to be seen, but there is already evidence that cell-cycle arrest biomarkers are indicators of both sides of this complex physiology.

Rapamycin ameliorates IgA nephropathy via cell cycle-dependent mechanisms

IgA nephropathy is the most frequent type of glomerulonephritis worldwide. The role of cell cycle regulation in the pathogenesis of IgA nephropathy has been studied. The present study was designed to explore whether rapamycin ameliorates IgA nephropathy via cell cycle-dependent mechanisms. After establishing an IgA nephropathy model, rats were randomly divided into four groups. Coomassie Brilliant Blue was used to measure the 24-h urinary protein levels. Renal function was determined using an autoanalyzer. Proliferation was assayed via Proliferating Cell Nuclear Antigen (PCNA) immunohistochemistry. Rat mesangial cells were cultured and divided into the six groups. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) and flow cytometry were used to detect cell proliferation and the cell cycle phase. Western blotting was performed to determine cyclin E, cyclin-dependent kinase 2, p27(Kip1), p70S6K/p-p70S6K, and extracellular signal-regulated kinase 1/2/p- extracellular signal-regulated kinase 1/2 protein expression. A low dose of the mammalian target of rapamycin (mTOR) inhibitor rapamycin prevented an additional increase in proteinuria, protected kidney function, and reduced IgA deposition in a model of IgA nephropathy. Rapamycin inhibited mesangial cell proliferation and arrested the cell cycle in the G1 phase. Rapamycin did not affect the expression of cyclin E and cyclin-dependent kinase 2. However, rapamycin upregulated p27(Kip1) at least in part via AKT (also known as protein kinase B)/mTOR. In conclusion, rapamycin can affect cell cycle regulation to inhibit mesangial cell proliferation, thereby reduce IgA deposition, and slow the progression of IgAN.

Simvastatin increases ADAMTS13 expression in podocytes

INTRODUCTION

ADAMTS13 is a specific von Willebrand factor-cleaving protease. Severe deficiency of ADAMTS13 is the main cause of thrombotic thrombocytopenic purpura. ADAMTS13 is mainly synthesized and released from hepatic stellate cells and endothelial cells, but is also expressed in other cells, including kidney podocytes. Simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, has a beneficial effect on atherosclerosis and also has anti-inflammatory and antithrombotic properties. A recent study indicates that ADAMTS13 reduces inflammatory plaque formation during early atherosclerosis in mice. In our study, we investigated the effects of simvastatin on inflammatory cytokines-induced ADAMTS13 expression in podocytes.

MATERIALS AND METHODS

A conditionally immortalized mouse podocyte cell line was utilized to study the expression of ADAMTS13 in podocytes. The influence of TNF-α, IL-4, IL-6 and simvastatin on ADAMTS13 was investigated. ADAMTS13 mRNA levels in podocytes were measured by using real-time PCR and protein levels were detected by Western blotting.

RESULTS

Simvastatin significantly up-regulated the expression levels of ADAMTS13 mRNA and protein in podocytes. IL-6 decreased ADAMTS13 expression, and TNF-α had no significant effects on ADAMTS13 expression in podocytes. IL-4 reduced ADAMTS13 mRNA expression but not its protein level. Simvastatin was able also reversed the inhibitory effect of IL-6.

CONCLUSIONS

We demonstrate that simvastatin increases the expression of ADAMTS13 in a dose-dependent manner in podocytes, which likely contributes to the antithrombotic property of statin. Different inflammatory cytokines have different effects on the levels of ADAMTS13 mRNA expression and protein within podocytes.

Mechanistic connection between inflammation and fibrosis

Fibrosis of the kidney is caused by the prolonged injury and deregulation of normal wound healing and repair processes, and by an excess deposition of extracellular matrices. Despite intensive research, our current understanding of the precise mechanism of fibrosis is limited. There is a connection between fibrotic events involving inflammatory and non-inflammatory glomerulonephritis, inflammatory cell infiltration, and podocyte loss. The current review will discuss the inflammatory response after renal injury that leads to fibrosis in relation to non-inflammatory mechanisms.

De novo expression of podocyte proteins in parietal epithelial cells during experimental glomerular disease

Studies have shown that certain cells of the glomerular tuft begin to express proteins considered unique to other cell types upon injury. Little is known about the response of parietal epithelial cells (PEC) to injury. To determine whether PECs change their phenotype upon injury to also express proteins traditionally considered podocyte specific, the following four models of glomerular disease were studied: the transforming growth factor (TGF)-beta1 transgenic mouse model of global glomerulosclerosis, the adriamycin model of focal segmental glomerulosclerosis (FSGS), the anti-glomerular basement membrane (GBM) model of crescentic glomerulonephritis, and the passive Heymann nephritis model of membranous nephropathy. Double immunostaining was performed with antibodies to podocyte-specific proteins (synaptopodin and Wilms' tumor 1) and antibodies to PEC specific proteins (paired box gene 8 and claudin-1). No double staining was detected in normal mice. In contrast, the results showed a statistical increase in the number of cells attached to Bowman basement membrane that were double-positive for both podocyte/PEC proteins in TGF-beta1 transgenic, anti-GBM, and membranous animals. Double-positive cells for both podocyte and PEC proteins were also statistically increased in the glomerular tuft in TGF-beta1 transgenic, anti-GBM, and FSGS mice. These results are consistent with glomerular cells coexpressing podocyte and PEC proteins in experimental glomerular disease, but not under normal circumstances.

The cyclin kinase inhibitor p57kip2 regulates TGF-beta-induced compensatory tubular hypertrophy: effect of the immunomodulator AS101

BACKGROUND

Compensatory tubular cell hypertrophy following unilateral nephrectomy is a cell cycle-dependent process. Our previous study showed that treatment of unilaterally nephrectomized rats with the immunomodulator AS101 partially inhibits compensatory hypertrophy of the remaining kidneys through the inhibition of IL-10-induced TGF-beta secretion by mesangial cells. The present study is focused on understanding the intracellular mechanism(s) of this phenomenon.

METHODS

A total of 120 male Sprague-Dawley rats were unilaterally nephrectomized or sham-operated and treated with AS101 or PBS. Kidney weight and protein/DNA ratio were assessed for each experimental animal. The expression of TGF-beta, PCNA, CDK 2, pRb, ppRb, p21(Waf1), p27(kip1) and p57(kip2) proteins in renal tissues was determined by western blot analysis and immunohistochemistry, and the immunoprecipitation of cyclin E complexes was performed.

RESULTS

Compensatory renal growth is initiated by proliferation of resident renal cells that precedes hypertrophy. Changes in TGF-beta expression were positively correlated with the amounts of p57(kip2), but not with p21(Waf1) and p27(kip1) expression in the remaining kidneys. Moreover, there was a marked abundance of p57(kip2) but not p21(Waf1) and p27(kip1) binding to the cyclin E complex in PBS-treated unilaterally nephrectomized rats compared to sham-operated animals. Treatment of uninephrectomized rats with AS101 reduced kidney weight and protein/DNA ratio, inhibited TGF-beta and p57(kip2) expression in the remaining kidneys, and decreased the level of p57(kip2) binding to cyclin E complexes.

CONCLUSION

These results demonstrate that TGF-beta-induced compensatory tubular cell hypertrophy is regulated in vivo by p57(kip2) but not by the p21(Waf1) and p27(kip1) cyclin kinase inhibitor proteins.

Drug-induced Kidney Disease – Pathology and Current Concepts

The kidneys can be damaged by a large number of therapeutic agents. The aim of this article is to discuss the pathological features of drug-induced renal disease as diagnosed by kidney biopsy. The literature is reviewed and cases seen by the authors that have a known drug association are analysed. Mechanisms of injury are varied and all renal structures may be affected. The tubulointerstitial compartment is most frequently involved, but glomerular and vascular lesions are seen in a significant proportion of cases. Key words: Drug, Kidney, Nephrotoxicity, Pathology

Mechanisms of progression of chronic kidney disease

Chronic kidney disease (CKD) occurs in all age groups, including children. Regardless of the underlying cause, CKD is characterized by progressive scarring that ultimately affects all structures of the kidney. The relentless progression of CKD is postulated to result from a self-perpetuating vicious cycle of fibrosis activated after initial injury. We will review possible mechanisms of progressive renal damage, including systemic and glomerular hypertension, various cytokines and growth factors, with special emphasis on the renin-angiotensin-aldosterone system (RAAS), podocyte loss, dyslipidemia and proteinuria. We will also discuss possible specific mechanisms of tubulointerstitial fibrosis that are not dependent on glomerulosclerosis, and possible underlying predispositions for CKD, such as genetic factors and low nephron number.

Accelerated expression of senescence associated cell cycle inhibitor p16INK4A in kidneys with glomerular disease

The cell cycle inhibitor p16(INK4A) (also known as cyclin-dependent kinase inhibitor 2A) is expressed in vivo in many tissues with age. The exposure of certain chronic stresses can trigger p16(INK4A) expression and a senescence-like phenotype. We studied whether p16(INK4A) expression is induced in glomerular disease (GD). We performed p16(INK4A) immunostaining on 35 biopsies with GD, 12 tubulointerstitial nephritis (TIN), and 19 normal live donor kidneys at transplantation. Based on values for 42 normal kidneys, we calculated expected nuclear p16(INK4A) expression for age and compared the observed values in diseased kidneys to those expected for age. In GD, p16(INK4A) expression was strikingly increased in glomerular and interstitial cell nuclei compared to normals and TIN, and could not be attributed to age (P<0.05). By multivariate analyses, GD was independently associated with increased nuclear p16(INK4a) expression in glomeruli (P<0.001) and interstitium (P=0.01). The p16(INK4A) expression in glomerular and interstitial cell nuclei, and tubular cytoplasm was higher in kidneys with proteinuria and with atrophy/fibrosis (P<0.05). Older age was associated with increased nuclear p16(INK4a) expression in tubules (P=0.01), and interstitial inflammation was associated with increased nuclear p16(INK4a) expression in interstitial cells (P=0.001). The p16(INK4a) staining in tubular cytoplasm was increased in both GD and TIN compared to normals (P<0.001), and was not related to age (P>0.05). Thus, kidneys with GD display increased expression of senescence marker p16(INK4A) in glomerular and interstitial cell nuclei compared to kidneys with normal aging or TIN. The findings suggest a role for somatic cell senescence mechanisms in progression of GD.

Cell-cycle regulatory proteins in the podocyte in collapsing glomerulopathy in children

Podocyte is a terminally committed cell in G1 arrest of cell cycle, and is unable to overcome G1/S transition phase in children with minimal change disease (MCD) and classic focal segmental glomerulosclerosis (FSGS), in contrast to dysregulated proliferative phenotype of idiopathic collapsing glomerulopathy (CGN) in adults. Forty-two kidney biopsies, MCD (14), FSGS (12), CGN (4), and normal (CON) (12), were evaluated by immunohistochemistry using dual staining for expression of p27, p21, and p57, and cyclins D and A, in podocytes of children with CGN. On light microscopy, all podocytes expressed p27, whereas p21 and p57 expression was seen in a portion of podocytes in normal kidney biopsies. Cyclin D was expressed in a small percentage of podocytes. Cyclin A expression was absent in normal biopsies. The staining for p27 decreased significantly, in order, from normal (100%) to MCD (45.8%) to CGN (24.2%) to FSGS (16.6%). p21 staining was significantly decreased from normal (69.8%) to CGN (15.5%) to MCD (2.2%) to FSGS (0.6%), and the difference between CGN and MCD and FSGS was also significant. There was no significant difference in staining of p57. Cyclin D staining was significantly increased in CGN (26.8%) compared to normal (7.2%), MCD (1.6%), and FSGS (0.0%), and the difference between CGN and MCD and FSGS was also significant. De novo cyclin A staining was only observed in children with CGN. Thus, p27 and p21 but not p57 was decreased in CGN, as in FSGS when compared to normal. Both cyclins D and A staining were increased in CGN. The staining pattern in CGN would suggest that podocyte is able to overcome G1/S transition phase, and has a proliferative phenotype. We propose, based on the significant contrast observed in podocytes injury response between CGN (proliferative) and classic FSGS (non-proliferative), that CGN not be considered as a morphological variant of FSGS.

ATRA induces podocyte differentiation and alters nephrin and podocin expression in vitro and in vivo

BACKGROUND

Podocytes are terminally differentiated and highly specialized epithelial cells. The factors governing podocyte differentiation are poorly understood. We tested the hypothesis that all-trans retinoic acid (ATRA), a vitamin A derivative, induces podocyte differentiation in vitro and in vivo.

METHODS

We tested the effects of ATRA on podocytes. Primary rat, primary mouse, and immortalized mouse podocytes were exposed to ATRA (1, 5, 10, 20, 40, 50, 80, 160, and 200 micromol/L) or control (ethanol) for 72 hours. Cell morphology was examined by electron microscopy, the expression of podocyte specific proteins was measured by immunoflourescence and Western blot analysis, cell number and apoptosis were measured by 3-[4,5] dimethylthiazol-2,5-diphenyltetrazolium bromide (MTT) assay and Hoechst staining, respectively. To determine if ATRA alters podocyte differentiation in vivo, experimental injury was induced in C57BL6 mice using the antiglomerular antibody. Animals were given either daily intraperitoneal ATRA (16 mg/kg) or vehicle (corn oil). For end points, we measured proteinuria, podocyte-specific protein immunostaining, and proliferation [proliferating cell nuclear antigen (PCNA)] at days 5 and 14 (N= 5/group/time point).

RESULTS

ATRA induced podocyte process formation in vitro, and significantly increased the expression of nephrin and podocin. This coincided with a reduction in proliferation. ATRA also significantly prevented the decrease in staining for synaptopodin, nephrin, and podocin in experimental animals (P < 0.05 vs. control). This was accompanied by reduced proteinuria and decreased podocyte proliferation (P < 0.05 vs. control).

CONCLUSION

ATRA induces podocyte differentiation in vitro and in vivo and alters the expression of certain podocyte-specific proteins. Further studies are ongoing to delineate the mechanism of this effect.

Chronic kidney disease: the global challenge

The worldwide rise in the number of patients with chronic kidney disease (CKD) and consequent end-stage renal failure necessitating renal replacement therapy is threatening to reach epidemic proportions over the next decade, and only a small number of countries have robust economies able to meet the challenges posed. A change in global approach to CKD from treatment of end-stage renal disease (ESRD) to much more aggressive primary and secondary prevention is therefore imperative. In this Seminar, we examine the epidemiology of CKD worldwide, with emphasis on early detection and prevention, and the feasibility of methods for detection and primary prevention of CKD. We also review the risk factors and markers of progressive CKD. We explore current understanding of the mechanisms underlying renal scarring leading to ESRD to inform on current and future interventions as well as evidence relating to interventions to slow the progression of CKD. Finally, we make strategic recommendations based on future research to stem the worldwide growth of CKD. Consideration is given to health economics. A global and concerted approach to CKD must be adopted in both more and less developed countries to avoid a major catastrophe.

Role of differential and cell type-specific expression of cell cycle regulatory proteins in mediating progressive glomerular injury in human IgA nephropathy

The activities of cell cycle regulatory proteins have been reported to be associated with the development of pathological lesions in glomerulonephritis. To assess the cellular mechanisms underlying the mesangial cell proliferation and glomerulosclerosis in progressive human IgA nephropathy (IgAN), we examined the expression of E2F1, Rb, c-Myc, proliferating cell nuclear antigen (PCNA), cyclins (D1, E and A), cyclin-dependent kinase 2 (CDK2) and CDK inhibitors (p21(waf1), p27(kip1), 57(kip2) and p16(ink4a)) by immunohistochemistry in renal biopsy specimens. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) was also performed to detect the presence of apoptosis. In total, 51 cases of IgAN were categorized into four subgroups according to histological severity. A dramatic upregulation of E2F1 expression in mesangial cells was identified in proliferating glomeruli, which correlated well with the proliferation index. High endogenous expression of p27(kip1) and p57(kip2) by podocytes in normal glomeruli and glomeruli with minor lesions was observed to decrease in proliferating and sclerosing glomeruli; this pattern displayed a strong inverse correlation with the mean glomerulosclerosis score and the index of glomerular lesion. Increased apoptotic activity was identified in progressive glomerular lesions of advanced IgAN, which correlated with the proliferative activity in these lesions as assessed by total expression levels of PCNA and CDK2 in glomeruli, E2F1 expression levels in the mesangium, cyclin D1 expression levels in endothelium and the c-Myc glomerular staining score. Our results suggest that the onset and magnitude of mesangial cell proliferation and glomerulosclerosis is associated with the upregulation of E2F1 by mesangial cells and the downregulation of p27(kip1) and p57(kip2) by glomerular epithelial cells. The cell type-specific and coordinated regulation of proliferative and proapoptotic activities of cell cycle regulatory proteins may play an important role in mediating progressive glomerular injury in human IgAN.

Cell-cycle regulatory proteins in podocyte cell in idiopathic nephrotic syndrome of childhood

BACKGROUND

The podocyte cell is believed to play an important role in idiopathic nephrotic syndrome (INS) of childhood. In adults with cellular and collapsing focal segmental glomerulosclerosis (FSGS), the expression of cell-cycle regulatory proteins such as p27, p57, and cyclin D is decreased and expression of cyclin A, Ki-67, and p21 is observed in podocyte cells suggestive of a dysregulated podocyte phenotype. We investigated for alterations in the expression of cyclin kinase inhibitors, p27, p57, p21, and cyclins D and A in the podocyte cell of children with INS.

METHODS

Forty-two kidney biopsies were investigated; 14 with minimal-change disease (MCD), seven with diffuse mesangial hypercellularity (DMH), 12 with FSGS, four with Alport syndrome (AS), and five normal biopsies. The sections were examined by immunohistochemistry using dual staining method. Podocyte cells were first identified by Wilm's tumor-1 staining after which expressions of cell-cycle regulatory proteins were analyzed. A quantitative analysis was performed for the proportion of podocyte cells that expressed each cell cycle regulatory protein.

RESULTS

On light microscopy, all podocyte cells expressed p27, while p57 and p21 expression was seen in a portion of podocyte cells in normal kidney biopsies. Cyclin D was expressed in a small percent of podocyte cells though the expression was more marked in mesangial and endothelial cells. Cyclin A expression was not seen in normal biopsies. The mean expression of p27 decreased significantly in order from normal (100%), MCD (45.9%), DMH (22.4%), and FSGS (16.7%), and the difference between MCD and FSGS was significant. p21 was significantly and equally reduced in MCD (2.3%), DMH (0%), and FSGS (0.7%) compared to normal (66.6%). There was no significant difference in expression of p57, cyclin D and cyclin A in the podocyte cells between normal and children with INS. Children with AS showed a significant decrease in p27 and p21 expression, while the expression of p57, cyclin D and cyclin A were unchanged from normal, thus demonstrating a pattern similar to INS.

CONCLUSION

The podocyte cell in children with INS down-regulates expression of cyclin kinase inhibitors such as p21 and p27, but not p57, but does not up-regulate cyclin D and cyclin A that are needed to overcome the G1/S transition and move the cell forward in the cell cycle process. Thus, the podocyte cell remains trapped in the G1 arrest phase. In children with INS or AS, the dysregulated podocyte phenotype is different than the one described in adults with cellular or collapsing FSGS.

Animal models of FSGS: lessons for pathogenesis and treatment

Glomerulosclerosis in a heterogeneous pattern, ie, focal and segmental glomerulosclerosis (FSGS), is a common endpoint in a variety of settings, including idiopathic FSGS, and scarring secondary to other renal or systemic diseases. These different causes contribute to the diverse clinical outcomes of histological focal sclerosis, and the varying histologic manifestations of sclerosis. Numerous models have been established in the rat that aim to mirror the various elements of human glomerulosclerosis. With the availability of knockout gene technology, many, but not all of these models have been translated to mouse species. This review will focus on the remnant kidney model, the podocyte injury models of puromycin aminonucleoside or adriamycin injection, and examples of newly developed genetic models, such as knockout of CD2 associated protein (CD2AP).

Peroxisome proliferator-activated receptor-gamma agonist troglitazone protects against nondiabetic glomerulosclerosis in rats

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPAR gamma) is a member of the nuclear receptor superfamily of ligand-dependent transcriptional factors with beneficial effects in diabetes mediated by improved insulin sensitivity and lipid metabolism, but potential adverse effects in atherosclerosis by promoting in vitro foam cell formation. We explored whether a PPAR gamma agonist, troglitazone (TGL), affects sclerosis by mechanisms unrelated to insulin and lipid effects in a model of nondiabetic glomerulosclerosis.

METHODS

Adult male Sprague Dawley rats underwent 5/6 nephrectomy and were treated for 12 weeks as follows: control (CONT), no further treatment; triple antihypertensive therapy (TRX); and TGL or TGL + TRX. Functional, morphological, and molecular analyses were performed.

RESULTS

Systolic blood pressure (SBP) was increased in CONT and TGL groups (161 +/- 1 and 160 +/- 3 mm Hg), but not in TGL + TRX and TRX (120 +/- 3 vs. 126 +/- 1 mm Hg, P < 0.0001 vs. non-TRX). Serum triglyceride and cholesterol levels in all groups remained normal except for slightly higher serum cholesterol levels in TRX group. TGL groups had reduced proteinuria, serum creatinine, and glomerulosclerosis versus CONT, in contrast to no significant effect with TRX alone (sclerosis index, 0 to 4+ scale: CONT 1.99 +/- 0.42, TGL 0.85 +/- 0.12, TGL + TRX 0.56 +/- 0.14, TRX 1.30 +/- 0.21; TGL, P < 0.05; TGL + TRX, P = 0.01 vs. CONT). Glomerular cell proliferation, assessed by proliferating cell nuclear antigen (PCNA), was decreased after treatment with TGL or TGL + TRX, in parallel with decreases in glomerular p21 mRNA and p27 protein compared with CONT and TRX (PCNA + cells/glomerulus: CONT 2.04 +/- 0.64, TGL 0.84 +/- 0.21, TGL + TRX 0.30 +/- 0.07, TRX 1.38 +/- 0.37; TGL, P < 0.05, TGL + TRX, P < 0.01 vs. CONT). Glomerular plasminogen activator inhibitor-1 (PAI-1) immunostaining was decreased in TGL or TGL + TRX groups (0 to 4+ scale, CONT 2.42 +/- 0.32, TGL 1.40 +/- 0.24, TGL + TRX 1.24 +/- 0.17, TRX 2.53 +/- 0.24; TGL or TGL + TRX vs. CONT, P < 0.05), with a parallel decrease in PAI-1 mRNA by in situ hybridization. Glomerular and tubular transforming growth factor-beta (TGF-beta) mRNA expression was decreased with TGL treatment. Glomerular macrophages, present in CONT and TRX rats, did not express PPAR gamma, in contrast to PPAR gamma + macrophages in control carotid artery plaque. PPAR gamma was expressed in resident cells.

CONCLUSIONS

Our results demonstrate in vivo that the PPAR gamma ligand TGL ameliorates the progression of glomerulosclerosis in a nondiabetic model. Macrophages show phenotypic diversity in glomerular versus vascular sclerosis, with macrophage PPAR gamma expression in only the latter. PPAR gamma beneficial effects are independent of insulin/glucose effects and are associated with regulation of glomerular cell proliferation, hypertrophy, and decreased PAI-1 and TGF-beta expression.

Growth factor pathways in proliferative glomerulonephritis

Growth factor production, glomerular cell proliferation and glomerular extracellular matrix expansion are prominent features of mesangioproliferative and crescentic glomerulonephritides. Recent studies have provided additional insights into the mechanisms of mesangial cell proliferation and interaction with extracellular matrix, and have focused on selective interruption of relevant mediators of injury. Studies into mitogenic signalling and cell cycle regulation in glomerular epithelial cells support a pathogenetic role for growth factors and glomerular epithelial cell proliferation in focal segmental glomerulosclerosis, and possibly membranous nephropathy. A better appreciation of growth factor pathways may lead to new treatment strategies for human glomerulopathies.

Pathology of progressive nephropathies

The role of cell cycle regulatory proteins in progression is elucidated. Human renal biopsy data show amelioration and even regression of structural injury with interventions. Data implicate new mechanisms of the renin-aldosterone-angiotensin system in progressive injuries, including immune modulation and a direct effect of aldosterone on progression. New approaches and interventions that target these fibrotic responses show promising results.