Age-related glomerulosclerosis and interstitial fibrosis in Milan normotensive rats: a podocyte disease

Interleukin-15 in kidney disease and therapeutics

PURPOSE OF REVIEW

Interleukin 15 (IL-15) is a member of the IL-2 family of common gamma chain receptor cytokines with well described anti-inflammatory, pro-survival and pro-proliferative signaling properties. The cytoprotective role of IL-15 in the kidney is now coming into focus with recent reports of its beneficial actions in various forms of kidney disease. This review will summarize what is currently known about IL-15 signaling in the kidney and highlight recent evidence of its beneficial effects on kidney physiology.

RECENT FINDINGS

IL-15 and its heterotrimeric receptor are expressed throughout the kidney. Like all IL-2 family cytokines, IL-15 can activate signaling through the Janus Kinase (JAK)/Signal transducer of activated T-cells (STAT), phosphoinositol-3 kinase (PI-3K)/AKT and mitogen activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathways and recent evidence suggests that STAT5B is an essential transcriptional mediator of prosurvival signaling in glomerular visceral epithelial cells (i.e. podocytes). IL-15 has also been shown to suppress pro-apoptotic signaling in models of acute kidney injury and pro-fibrotic signaling in models of chronic kidney disease.

SUMMARY

The cytoprotective properties of IL-15 suggest that it may have potential as a nonimmunosuppresive therapeutic for kidney disease. A novel class of IL-15 immunotherapies has emerged for the treatment cancer and some have demonstrated efficacy in clinical trials. These well tolerated IL-15 agonists could possibly be repurposed for the treatment of kidney disease and warrant further exploration.

Renal Expression and Localization of the Receptor for (Pro)renin and Its Ligands in Rodent Models of Diabetes, Metabolic Syndrome, and Age-Dependent Focal and Segmental Glomerulosclerosis

The (pro)renin receptor ((P)RR), a versatile protein found in various organs, including the kidney, is implicated in cardiometabolic conditions like diabetes, hypertension, and dyslipidemia, potentially contributing to organ damage. Importantly, changes in (pro)renin/(P)RR system localization during renal injury, a critical information base, remain unexplored. This study investigates the expression and topographic localization of the full length (FL)-(P)RR, its ligands (renin and prorenin), and its target cyclooxygenase-2 and found that they are upregulated in three distinct animal models of renal injury. The protein expression of these targets, initially confined to specific tubular renal cell types in control animals, increases in renal injury models, extending to glomerular cells. (P)RR gene expression correlates with protein changes in a genetic model of focal and segmental glomerulosclerosis. However, in diabetic and high-fat-fed mice, (P)RR mRNA levels contradict FL-(P)RR immunoreactivity. Research on diabetic mice kidneys and human podocytes exposed to diabetic glucose levels suggests that this inconsistency may result from disrupted intracellular (P)RR processing, likely due to increased Munc18-1 interacting protein 3. It follows that changes in FL-(P)RR cellular content mechanisms are specific to renal disease etiology, emphasizing the need for consideration in future studies exploring this receptor's involvement in renal damage of different origins.

Podocyte Senescence and Aging

As the population in many industrial countries is aging, the risk, incidence, and prevalence of CKD increases. In the kidney, advancing age results in a progressive decrease in nephron number and an increase in glomerulosclerosis. In this review, we focus on the effect of aging on glomerular podocytes, the post-mitotic epithelial cells critical for the normal integrity and function of the glomerular filtration barrier. The podocytes undergo senescence and transition to a senescence-associated secretory phenotype typified by the production and secretion of inflammatory cytokines that can influence neighboring glomerular cells by paracrine signaling. In addition to senescence, the aging podocyte phenotype is characterized by ultrastructural and functional changes; hypertrophy; cellular, oxidative, and endoplasmic reticulum stress; reduced autophagy; and increased expression of aging genes. This results in a reduced podocyte health span and a shortened life span. Importantly, these changes in the pathways/processes characteristic of healthy podocyte aging are also often similar to pathways in the disease-induced injured podocyte. Finally, the better understanding of podocyte aging and senescence opens therapeutic options to slow the rate of podocyte aging and promote kidney health.

Associations between nephron number and podometrics in human kidneys

Podocyte loss and resultant nephron loss are common processes in the development of glomerulosclerosis and chronic kidney disease. While the cortical distribution of glomerulosclerosis is known to be non-uniform, the relationship between the numbers of non-sclerotic glomeruli (NSG), podometrics and zonal differences in podometrics remain incompletely understood. To help define this, we studied autopsy kidneys from 50 adults with median age 68 years and median eGFR 73.5 mL/min/1.73m² without apparent glomerular disease in a cross-sectional analysis. The number of NSG per kidney was estimated using the physical dissector/fractionator combination, while podometrics were estimated using model-based stereology. The number of NSG per kidney was directly correlated with podocyte number per tuft and podocyte density. Each additional 100,000 NSG per kidney was associated with 26 more podocytes per glomerulus and 16 podocytes per 10⁶ μm³ increase in podocyte density. These associations were independent of clinical factors and cortical zone. While podocyte number per glomerulus was similar in the three zones, superficial glomeruli were the smallest and had the highest podocyte density but smallest podocytes. Increasing age and hypertension were associated with lower podocyte number, with age mostly affecting superficial glomeruli, and hypertension mostly affecting juxtamedullary glomeruli. Thus, in this first study to report a direct correlation between the number of NSG and podometrics, we suggest that podocyte number is decreasing in NSG of individuals losing nephrons. However, another possible interpretation may be that more nephrons might protect against further podocyte loss.

Upregulated PD-1 signaling antagonizes glomerular health in aged kidneys and disease

With an aging population, kidney health becomes an important medical and socioeconomic factor. Kidney aging mechanisms are not well understood. We previously showed that podocytes isolated from aged mice exhibit increased expression of programmed cell death protein 1 (PD-1) surface receptor and its 2 ligands (PD-L1 and PD-L2). PDCD1 transcript increased with age in microdissected human glomeruli, which correlated with lower estimated glomerular filtration rate and higher segmental glomerulosclerosis and vascular arterial intima-to-lumen ratio. In vitro studies in podocytes demonstrated a critical role for PD-1 signaling in cell survival and in the induction of a senescence-associated secretory phenotype. To prove PD-1 signaling was critical to podocyte aging, aged mice were injected with anti-PD-1 antibody. Treatment significantly improved the aging phenotype in both kidney and liver. In the glomerulus, it increased the life span of podocytes, but not that of parietal epithelial, mesangial, or endothelial cells. Transcriptomic and immunohistochemistry studies demonstrated that anti-PD-1 antibody treatment improved the health span of podocytes. Administering the same anti-PD-1 antibody to young mice with experimental focal segmental glomerulosclerosis (FSGS) lowered proteinuria and improved podocyte number. These results suggest a critical contribution of increased PD-1 signaling toward both kidney and liver aging and in FSGS.

The adducin saga: pleiotropic genomic targets for precision medicine in human hypertension-vascular, renal, and cognitive diseases

Hypertension is a leading risk factor for stroke, heart disease, chronic kidney disease, vascular cognitive impairment, and Alzheimer's disease. Previous genetic studies have nominated hundreds of genes linked to hypertension, and renal and cognitive diseases. Some have been advanced as candidate genes by showing that they can alter blood pressure or renal and cerebral vascular function in knockout animals; however, final validation of the causal variants and underlying mechanisms has remained elusive. This review chronicles 40 years of work, from the initial identification of adducin (ADD) as an ACTIN-binding protein suggested to increase blood pressure in Milan hypertensive rats, to the discovery of a mutation in ADD1 as a candidate gene for hypertension in rats that were subsequently linked to hypertension in man. More recently, a recessive K572Q mutation in ADD3 was identified in Fawn-Hooded Hypertensive (FHH) and Milan Normotensive (MNS) rats that develop renal disease, which is absent in resistant strains. ADD3 dimerizes with ADD1 to form functional ADD protein. The mutation in ADD3 disrupts a critical ACTIN-binding site necessary for its interactions with actin and spectrin to regulate the cytoskeleton. Studies using Add3 KO and transgenic strains, as well as a genetic complementation study in FHH and MNS rats, confirmed that the K572Q mutation in ADD3 plays a causal role in altering the myogenic response and autoregulation of renal and cerebral blood flow, resulting in increased susceptibility to hypertension-induced renal disease and cerebral vascular and cognitive dysfunction.

Podocyte Aging: Why and How Getting Old Matters

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

Acute kidney injury and aging

Our aging population is growing and developing treatments for age-related diseases such as Alzheimer's and Parkinson's disease has taken on an increasing urgency and is accompanied by high public awareness. The already high and rising incidence of acute kidney injury (AKI) in the elderly, however, has received relatively little attention despite the potentially fatal outcomes associated with an episode of AKI in this age group. When discussing AKI and aging, one should consider two aspects: first, elderly patients have an increased susceptibility to an AKI episode, and second, they have decreased kidney repair after AKI given the high incidence of progression to chronic kidney disease (CKD). It is unclear if the same factors that drive the increased susceptibility to AKI could be playing a role in the decreased repair capacity or if they are totally different and unrelated. This review will examine current knowledge on the risk factors for the increased susceptibility to AKI in the elderly and will also explore potential aspects that might contribute to a decreased kidney repair response in this age group.

Global transcriptomic changes occur in aged mouse podocytes

Glomerular podocytes undergo structural and functional changes with advanced age, that increase susceptibility of aging kidneys to worse outcomes following superimposed glomerular diseases. To delineate transcriptional changes in podocytes in aged mice, RNA-seq was performed on isolated populations of reporter-labeled (tdTomato) podocytes from multiple young (two to three months) and advanced aged mice (22 to 24 months, equivalent to 70 plus year old humans). Of the 2,494 differentially expressed genes, 1,219 were higher and 1,275 were lower in aged podocytes. Pathway enrichment showed that major biological processes increased in aged podocytes included immune responses, non-coding RNA metabolism, gene silencing and MAP kinase signaling. Conversely, aged podocytes showed downregulation of developmental, morphogenesis and metabolic processes. Canonical podocyte marker gene expression decreased in aged podocytes, with increases in apoptotic and senescence genes providing a mechanism for the progressive loss of podocytes seen with aging. In addition, we revealed aberrations in the podocyte autocrine signaling network, identified the top transcription factors perturbed in aged podocytes, and uncovered candidate gene modulations that might promote healthy aging in podocytes. The transcriptional signature of aging is distinct from other kidney diseases. Thus, our study provides insights into biomarker discovery and molecular targeting of the aging process itself within podocytes.

Podocyte-targeted Heme Oxygenase (HO)-1 overexpression exacerbates age-related pathology in the rat kidney

Although Heme Oxygenase-1 (HO-1) induction in various forms of kidney injury is protective, its role in age-related renal pathology is unknown. In the ageing kidney there is nephron loss and lesions of focal glomerulosclerosis, interstitial fibrosis, tubular atrophy and arteriolosclerosis. Underlying mechanisms include podocyte (visceral glomerular epithelial cell/GEC) injury. To assess whether HO-1 can attenuate ageing - related lesions, rats with GEC-targeted HO-1 overexpression (GEC^HO-1 rats) were generated using a Sleeping Beauty (SB) transposon system and extent of lesions over a 12-month period were assessed and compared to those in age-matched wild-type (WT) controls. GEC^HO-1 rats older than 6 months developed albuminuria that was detectable at 6 months and became significantly higher compared to age-matched WT controls at 12 months. In GEC^HO-1 rats, lesions of focal segmental and global glomerulosclerosis as well as tubulointerstitial lesions were prominent while podocytes were edematous with areas of foot process effacement and glomerular basement membrane thickening and wrinkling. GEC^HO-1 rats also developed hemoglobinuria and hemosiderinuria associated with marked tubular hemosiderin deposition and HO-1 induction, while there was depletion of splenic iron stores. Kidney injury was of sufficient magnitude to increase serum lactate dehydrogenase (LDH) and was oxidative in nature as shown by increased expression of 8-hydroxydeoxyguanosine (8-OHdg, a byproduct of oxidative DNA damage) in podocytes and tubular epithelial cells. These observations highlight a detrimental effect of podocyte-targeted HO-1 overexpression on ageing-related renal pathology and point to increased renal iron deposition as a putative underlying mechanism.

A Mutation in γ-Adducin Impairs Autoregulation of Renal Blood Flow and Promotes the Development of Kidney Disease

BACKGROUND

The genes and mechanisms involved in the association between diabetes or hypertension and CKD risk are unclear. Previous studies have implicated a role for γ-adducin (ADD3), a cytoskeletal protein encoded by Add3.

METHODS

We investigated renal vascular function in vitro and in vivo and the susceptibility to CKD in rats with wild-type or mutated Add3 and in genetically modified rats with overexpression or knockout of ADD3. We also studied glomeruli and primary renal vascular smooth muscle cells isolated from these rats.

RESULTS

This study identified a K572Q mutation in ADD3 in fawn-hooded hypertensive (FHH) rats-a mutation previously reported in Milan normotensive (MNS) rats that also develop kidney disease. Using molecular dynamic simulations, we found that this mutation destabilizes a critical ADD3-ACTIN binding site. A reduction of ADD3 expression in membrane fractions prepared from the kidney and renal vascular smooth muscle cells of FHH rats was associated with the disruption of the F-actin cytoskeleton. Compared with renal vascular smooth muscle cells from Add3 transgenic rats, those from FHH rats had elevated membrane expression of BKα and BK channel current. FHH and Add3 knockout rats exhibited impairments in the myogenic response of afferent arterioles and in renal blood flow autoregulation, which were rescued in Add3 transgenic rats. We confirmed these findings in a genetic complementation study that involved crossing FHH and MNS rats that share the ADD3 mutation. Add3 transgenic rats showed attenuation of proteinuria, glomerular injury, and kidney fibrosis with aging and mineralocorticoid-induced hypertension.

CONCLUSIONS

This is the first report that a mutation in ADD3 that alters ACTIN binding causes renal vascular dysfunction and promotes the susceptibility to kidney disease.

Protosappanin-A and oleanolic acid protect injured podocytes from apoptosis through inhibition of AKT-mTOR signaling

Protosappanin-A (PrA) and oleanolic acid (OA), which are important effective ingredients isolated from Caesalpinia sappan L., exhibit therapeutic potential in multiple diseases. This study focused on exploring the mechanisms of PrA and OA function in podocyte injury. An in vitro model of podocyte injury was induced by the sC5b-9 complex and assays such as cell viability, apoptosis, immunofluorescence, quantitative real-time polymerase chain reaction, and western blot were performed to further investigate the effects and mechanisms of PrA and OA in podocyte injury. The models of podocyte injury were verified to be successful as seen through significantly decreased levels of nephrin, podocin, and CD2AP and increased level of desmin. The sC5b-9-induced podocyte apoptosis was inhibited in injured podocytes treated with PrA and OA, accompanied by increased protein levels of nephrin, podocin, CD2AP, and Bcl2 and decreased levels of desmin and Bax. The p-AKT/p-mTOR levels were also reduced by treatment of PrA and OA while AKT/mTOR was unaltered. Further, the effects of PrA and OA on injured podocytes were similar to that of LY294002 (a PI3K-AKT inhibitor). PrA and OA were also seen to inhibit podocyte apoptosis and p-AKT/p-mTOR levels induced by IGF-1 (a PI3K-AKT activator). Our data demonstrate that PrA and OA can protect podocytes from injury or apoptosis, which may occur through inhibition of the abnormal activation of AKT-mTOR signaling.

Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

High-fat diet-induced obesity causes an inflammatory microenvironment in the kidneys of aging Long-Evans rats

Background

Obesity is a risk factor for chronic kidney disease (CKD). While the exact mechanisms remain unclear, inflammation may be a consequence of obesity that directly impacts the kidneys. The aim of this study was to examine the inflammatory status of the kidneys and potential ongoing renal damage, i.e., tubular damage and fibrosis after long-term obesity maintained through persistent consumption of a high-fat diet (HFD).

Results

Twenty-four-week-old male Long-Evans (LEV) rats were continuously fed a control diet (CD) or HFD for 51 weeks. The mean body weight was higher in HFD-fed rats than in control diet-fed rats and markedly elevated during the last 24 weeks. Blood analyses revealed no substantial alterations in renal functional parameters by HFD consumption but a substantial increase in creatine kinase, a muscle loss marker. Magnetic resonance imaging (MRI) was utilized to quantify rat quadriceps muscle mass. The data showed that HFD-induced obesity in LEV rats was accompanied by minor decreases in muscle mass and strength at 75 weeks of age. Rat kidney inflammatory status was evaluated using histological and immunohistological techniques. The number of foci with immune cell infiltrates and infiltrating monocytes/macrophages was significantly increased in HFD-fed rat kidneys at week 75. Renal fibrosis parameters, including glomerulosclerosis and tubular damage, were also markedly increased in renal tissues from HFD-fed rats compared to the controls. The significant increase in tubular protein casts in HFD-fed rat tissues indicated that renal function was already disturbed. Rat kidney inflammatory status was further evaluated using the simultaneous profiling of twenty-two inflammatory markers in kidney tissue extracts. Consistently, MCP-1 and eotaxin (CCL11) levels were elevated in obese LEV rat kidneys.

Conclusions

Compared to CD-fed rats, HFD-fed obese LEV rats show significant damage of renal structures with aging. These subtle changes may sensitize the kidneys to the development of progressive CKD.

Electronic supplementary material

The online version of this article (10.1186/s12950-019-0219-x) contains supplementary material, which is available to authorized users.

Impaired myogenic response of the afferent arteriole contributes to the increased susceptibility to renal disease in Milan normotensive rats

Milan normotensive (MNS) rats are more susceptible to the development of renal disease than Milan hypertensive (MHS) rats, but the genes and pathways involved are unknown. This study compared the myogenic response of isolated perfused afferent arterioles (Af‐Art) and autoregulation of renal blood flow (RBF) and glomerular capillary pressure (Pgc) in 6–9‐week‐old MNS and MHS rats. The diameter of the Af‐Art of MHS rats decreased significantly from 14.3 ± 0.5 to 11.5 ± 0.6 μm when perfusion pressure was elevated from 60 to 120 mmHg. In contrast, the diameter of Af‐Art of MNS rats did not decrease. RBF was well autoregulated in MHS rats, but it increased by 26% in MNS rats. Pgc rose by 11 mmHg when renal perfusion pressure (RPP) was increased from 100 to 140 mmHg in MNS but not in MHS rats. Protein excretion increased from 10 ± 1 to 245 ± 36 mg/day in MNS rats as they aged from 3 to 11 months but it did not increase in MHS rats. We also compared the development of proteinuria in MNS and MHS rats following the induction of diabetes with streptozotocin. Protein excretion rose from 16 ± 3 to 234 ± 43 mg/day in MNS rats, but it remained unaltered in MHS rats. These data indicate that the myogenic response of the Af‐art is impaired in MNS rats and increased transmission of pressure to the glomerulus may contribute to renal injury in MNS rats similar to what is seen in fawn‐hooded hypertensive and Dahl salt‐sensitive rats.

Genetic Variation in the H19-IGF2 Cluster Might Confer Risk of Developing Impaired Renal Function

The H19-IGF2 imprinted gene region could be implicated in the risk of developing impaired renal function (IRF). Our aim was to determine the association of several common H19-IGF2 variants and IRF in a cohort of elderly healthy individuals. The study involved 675 individuals >65 years of age, 184 with type 2 diabetes mellitus (T2DM), and 105 with IRF (estimated glomerular filtration rate [eGFR] <60). They were genotyped for two common H19 single nucleotide polymorphisms (SNPs) (rs2839698 and rs10732516), one H19-IGF2 intergenic indel (rs201858505), and one indel in the 3'UTR of the IGF2. For the H19 SNPs, we also determined the allele present in the methylated chromosome through genotyping the DNA digested with a methylation-sensitive endonuclease. None of the four H19-IGF2 variants was associated with IRF in our cohort. We found a significantly higher frequency of the 3'UTR IGF2 deletion (D) in the eGFR <60 group (p = 0.01; odds ratio = 1.16, 95% confidence interval = 1.10-2.51). This association was independent of age and T2DM, two strong predictors of IRF. In conclusion, a common indel variant in the 3'UTR of the IGF2 gene was associated with the risk of IRF. This association could be explained by the role of IGF2 in podocyte survival, through regulation of IGF2 expression by differential binding of miRNAs to the indel sequences. Functional studies should be necessary to clarify this issue.

Involvement of NF-κBIZ and related cytokines in age-associated renal fibrosis

Chronic inflammation is a major contributor to age-related nephropathic changes, including renal fibrosis. In this study, various experimental paradigms were designed to delineate the role played by NF-κBIZ (also known as IκBζ) in age-associated renal fibrosis. Analyses based on RNA-sequencing findings obtained by next generation sequencing (NGS) revealed the upregulations of NF-κBIZ and of IL-6 and MCP-1 (both known to be regulated by NF-κBIZ) during aging. The up-regulation of NF-κBIZ in aged rat kidneys coincided with increased macrophage infiltration. In LPS-treated macrophages, oxidative stress was found to play a pivotal role in NF-κBIZ expression, suggesting age-related oxidative stress is associated with NF-κBIZ activation. Furthermore, these in vitro findings were confirmed in LPS-treated old rats, which showed higher levels of oxidative stress and NF-κBIZ in kidneys than LPS-treated young rats. Additional in vitro experiments using macrophages and kidney fibroblasts demonstrated NF-κBIZ and related cytokines participate in fibrosis. In particular, increased levels of NF-κBIZ-associated cytokines in macrophages significantly up-regulated TGF-β induced kidney fibroblast activation. Moreover, experiments with NF-κBIZ knocked down macrophages showed reduced TGF-β-induced kidney fibroblast activation. The findings of the present study provide evidence regarding an involvement of NF-κBIZ in age-associated progressive renal fibrosis and provides potential targets for its prevention.

High resolution molecular and histological analysis of renal disease progression in ZSF1 fa/faCP rats, a model of type 2 diabetic nephropathy

ZSF1 rats exhibit spontaneous nephropathy secondary to obesity, hypertension, and diabetes, and have gained interest as a model system with potentially high translational value to progressive human disease. To thoroughly characterize this model, and to better understand how closely it recapitulates human disease, we performed a high resolution longitudinal analysis of renal disease progression in ZSF1 rats spanning from early disease to end stage renal disease. Analyses included metabolic endpoints, renal histology and ultrastructure, evaluation of a urinary biomarker of fibrosis, and transcriptome analysis of glomerular-enriched tissue over the course of disease. Our findings support the translational value of the ZSF1 rat model, and are provided here to assist researchers in the determination of the model’s suitability for testing a particular mechanism of interest, the design of therapeutic intervention studies, and the identification of new targets and biomarkers for type 2 diabetic nephropathy.

Estimated glomerular filtration rate (eGFR), 25(OH) D3, chronic kidney disease (CKD), the MYH9 (myosin heavy chain 9) gene in old and very elderly people

It is known that the common physiological denominator of the ageing process is an attenuation of functional performance with respect to the situation of young people and adults. However, since the first cohort-based longitudinal studies, it has not been possible to establish a "linear" relationship between age and glomerular filtration in all cases. This does not mean that there is no physiological ageing process at all; in addition to those already elucidated, its mechanisms include cell senescence, podocyte dysfunction, a vitamin D deficiency, and homozygotic forms of the MYH9 gene. The aim of the present work was to analyse the prevalence of chronic kidney disease (CKD) and, where possible, the correlation between CKD, defined by an eGFR < 60 ml/min/1.73 m(2), plasma 25(OH)D3 levels and the MYH9 gene in a population of elderly and very elderly persons. These parameters have not been evaluated previously in populations of elderly and very elderly patients. It is concluded that a moderate decrease in the eGFR occurs with age. This does not imply the presence of CKD in elderly people, since in most individuals the reduced eGFR is not accompanied by anaemia, and no individuals show hypocalcaemia, hyperphosphataemia or a high Alb/Cr ratio. Here we observed a lower Hb level and an elevated Alb/Cr ratio in subjects heterozygotic for the MYH9 gene. This could be interpreted in the sense that the gene could exert some protective effect on renal function, whereas the heterozygotic form (allele A) of the MYH9 gene could be considered a very early marker, a new risk factor for the appearance of CKD, or a sign of renal frailty in elderly people.

Changes in glomerular parietal epithelial cells in mouse kidneys with advanced age

Kidney aging is accompanied by characteristic changes in the glomerulus, but little is known about the effect of aging on glomerular parietal epithelial cells (PECs), nor if the characteristic glomerular changes in humans and rats also occur in very old mice. Accordingly, a descriptive analysis was undertaken in 27-mo-old C57B6 mice, considered advanced age. PEC density was significantly lower in older mice compared with young mice (aged 3 mo), and the decrease was more pronounced in juxtamedullary glomeruli compared with outer cortical glomeruli. In addition to segmental and global glomerulosclerosis in older mice, staining for matrix proteins collagen type IV and heparan sulfate proteoglycan were markedly increased in Bowman's capsules of older mouse glomeruli, consistent with increased extracellular matrix production by PECs. De novo staining for CD44, a marker of activated and profibrotic PECs, was significantly increased in aged glomeruli. CD44 staining was more pronounced in the juxtamedullary region and colocalized with phosphorylated ERK. Additionally, a subset of aged PECs de novo expressed the epithelial-to-mesenchymal transition markers α-smooth muscle and vimentin, with no changes in epithelial-to-mesenchymal transition markers E-cadherin and β-catenin. The mural cell markers neural/glial antigen 2, PDGF receptor-β, and CD146 as well as Notch 3 were also substantially increased in aged PECs. These data show that mice can be used to better understand the aging kidney and that PECs undergo substantial changes, especially in juxtamedullary glomeruli, that may participate in the overall decline in glomerular structure and function with advancing age.

Endothelin and endothelin antagonists in chronic kidney disease

The incidence and prevalence of chronic kidney disease (CKD), with diabetes and hypertension accounting for the majority of cases, is on the rise, with up to 160 million individuals worldwide predicted to be affected by 2020. Given that current treatment options, primarily targeted at the renin-angiotensin system, only modestly slow down progression to end-stage renal disease, the urgent need for additional effective therapeutics is evident. Endothelin-1 (ET-1), largely through activation of endothelin A receptors, has been strongly implicated in renal cell injury, proteinuria, inflammation, and fibrosis leading to CKD. Endothelin receptor antagonists (ERAs) have been demonstrated to ameliorate or even reverse renal injury and/or fibrosis in experimental models of CKD, whereas clinical trials indicate a substantial antiproteinuric effect of ERAs in diabetic and nondiabetic CKD patients even on top of maximal renin-angiotensin system blockade. This review summarizes the role of ET in CKD pathogenesis and discusses the potential therapeutic benefit of targeting the ET system in CKD, with attention to the risks and benefits of such an approach.

Pharmacological and genetic depletion of fibrinogen protects from kidney fibrosis

Fibrinogen (Fg) has been implicated in the pathogenesis of several fibrotic disorders by acting as a profibrotic ligand for a variety of cellular surface receptors and by modulating the provisional fibrin matrix formed after injury. We demonstrated increased renal Fg expression after unilateral ureteral obstruction and folic acid (FA) nephropathy in mice, respectively. Urinary Fg excretion was also increased in FA nephropathy. Using in vitro and in vivo approaches, our results suggested that IL-6 mediates STAT3 activation in kidney fibrosis and that phosphorylated (p)STAT3 binds to Fgα, Fgβ, and Fgγ promoters in the kidney to regulate their transcription. Genetically modified Fg heterozygous mice (∼75% of normal plasma Fg levels) exhibited only 3% kidney interstitial fibrosis and tubular atrophy after FA nephropathy compared with 24% for wild-type mice. Fibrinogenolysis through Ancrod administration after FA reduced interstitial fibrosis more than threefold compared with vehicle-treated control mice. Mechanistically, we show that Fg acts synergistically with transforming growth factor (TGF)-β1 to induce fibroblast proliferation and activates TGF-β1/pSMAD2 signaling. This study offers increased understanding of Fg expression and molecular interactions with TGF-β1 in the progression to kidney fibrosis and, importantly, indicates that fibrinogenolytics like Ancrod present a treatment opportunity for a yet intractable disease.

Mitochondrial autophagy involving renal injury and aging is modulated by caloric intake in aged rat kidneys

BACKGROUND

A high-calorie (HC) diet induces renal injury and promotes aging, and calorie restriction (CR) may ameliorate these responses. However, the effects of long-term HC and CR on renal damage and aging have been not fully determined. Autophagy plays a crucial role in removing protein aggregates and damaged organelles to maintain intracellular homeostasis and function. The role of autophagy in HC-induced renal damage is unknown.

METHODS

We evaluated the expression of LC3/Atg8 as a marker of the autophagosome; p62/SQSTM1; polyubiquitin aggregates as markers of autophagy flux; Ambra1, PINK1, Parkin and Bnip3 as markers of mitophagy; 8-hydroxydeoxyguanosine (8-OHdG) as a marker of DNA oxidative damage; and p16 as a marker of organ aging by western blot and immunohistochemical staining in the kidneys of 24-month-old Fischer 344 rats. We also observed mitochondrial structure and autolysosomes by transmission electron microscopy.

RESULTS

Expression of the autophagosome formation marker LC3/Atg8 and markers of mitochondrial autophagy (mitophagy) were markedly decreased in the kidneys of the HC group, and markedly increased in CR kidneys. p62/SQSTM1 and polyubiquitin aggregates increased in HC kidneys, and decreased in CR kidneys. Transmission electron microscopy demonstrated that HC kidneys showed severe abnormal mitochondrial morphology with fewer autolysosomes, while CR kidneys exhibited normal mitochondrial morphology with numerous autolysosomes. The level of 8-hydroxydeoxyguanosine was increased in HC kidneys and decreased in CR kidneys. Markers of aging, such as p16 and senescence-associated-galactosidase, were increased significantly in the HC group and decreased significantly in the CR group.

CONCLUSION

The study firstly suggests that HC diet inhibits renal autophagy and aggravates renal oxidative damage and aging, while CR enhances renal autophagy and ameliorates oxidative damage and aging in the kidneys.

Proximal tubular cells contain a phenotypically distinct, scattered cell population involved in tubular regeneration

Regeneration of injured tubular cells occurs after acute tubular necrosis primarily from intrinsic renal cells. This may occur from a pre-existing intratubular stem/progenitor cell population or from any surviving proximal tubular cell. In this study, we characterize a CD24-, CD133-, and vimentin-positive subpopulation of cells scattered throughout the proximal tubule in normal human kidney. Compared to adjacent 'normal' proximal tubular cells, these CD24-positive cells contained less cytoplasm, fewer mitochondria, and no brush border. In addition, 49 marker proteins are described that are expressed within the proximal tubules in a similar scattered pattern. For eight of these markers, we confirmed co-localization with CD24. In human biopsies of patients with acute tubular necrosis (ATN), the number of CD24-positive tubular cells was increased. In both normal human kidneys and the ATN biopsies, around 85% of proliferating cells were CD24-positive - indicating that this cell population participates in tubular regeneration. In healthy rat kidneys, the novel cell subpopulation was absent. However, upon unilateral ureteral obstruction (UUO), the novel cell population was detected in significant amounts in the injured kidney. In summary, in human renal biopsies, the CD24-positive cells represent tubular cells with a deviant phenotype, characterized by a distinct morphology and marker expression. After acute tubular injury, these cells become more numerous. In healthy rat kidneys, these cells are not detectable, whereas after UUO, they appeared de novo - arguing against the notion that these cells represent a pre-existing progenitor cell population. Our data indicate rather that these cells represent transiently dedifferentiated tubular cells involved in regeneration.

Insulin-like growth factor-II is produced by, signals to and is an important survival factor for the mature podocyte in man and mouse

Podocytes are crucial for preventing the passage of albumin into the urine and, when lost, are associated with the development of albuminuria, renal failure and cardiovascular disease. Podocytes have limited capacity to regenerate, therefore pro-survival mechanisms are critically important. Insulin-like growth factor-II (IGF-II) is a potent survival and growth factor; however, its major function is thought to be in prenatal development, when circulating levels are high. IGF-II has only previously been reported to continue to be expressed in discrete regions of the brain into adulthood in rodents, with systemic levels being undetectable. Using conditionally immortalized human and ex vivo adult mouse cells of the glomerulus, we demonstrated the podocyte to be the major glomerular source and target of IGF-II; it signals to this cell via the IGF-I receptor via the PI3 kinase and MAPK pathways. Functionally, a reduction in IGF signalling causes podocyte cell death in vitro and glomerular disease in vivo in an aged IGF-II transgenic mouse that produces approximately 60% of IGF-II due to a lack of the P2 promoter of this gene. Collectively, this work reveals the fundamental importance of IGF-II in the mature podocyte for glomerular health across mammalian species.

Microarray analyses of glucocorticoid and vitamin D3 target genes in differentiating cultured human podocytes

Glomerular podocytes are highly differentiated epithelial cells that are key components of the kidney filtration units. Podocyte damage or loss is the hallmark of nephritic diseases characterized by severe proteinuria. Recent studies implicate that hormones including glucocorticoids (ligand for glucocorticoid receptor) and vitamin D3 (ligand for vitamin D receptor) protect or promote repair of podocytes from injury. In order to elucidate the mechanisms underlying hormone-mediated podocyte-protecting activity from injury, we carried out microarray gene expression studies to identify the target genes and corresponding pathways in response to these hormones during podocyte differentiation. We used immortalized human cultured podocytes (HPCs) as a model system and carried out in vitro differentiation assays followed by dexamethasone (Dex) or vitamin D3 (VD3) treatment. Upon the induction of differentiation, multiple functional categories including cell cycle, organelle dynamics, mitochondrion, apoptosis and cytoskeleton organization were among the most significantly affected. Interestingly, while Dex and VD3 are capable of protecting podocytes from injury, they only share limited target genes and affected pathways. Compared to VD3 treatment, Dex had a broader and greater impact on gene expression profiles. In-depth analyses of Dex altered genes indicate that Dex crosstalks with a broad spectrum of signaling pathways, of which inflammatory responses, cell migration, angiogenesis, NF-κB and TGFβ pathways are predominantly altered. Together, our study provides new information and identifies several new avenues for future investigation of hormone signaling in podocytes.

Emerging role of autophagy in kidney function, diseases and aging

Autophagy is a highly conserved process that degrades cellular long-lived proteins and organelles. Accumulating evidence indicates that autophagy plays a critical role in kidney maintenance, diseases and aging. Ischemic, toxic, immunological, and oxidative insults can cause an induction of autophagy in renal epithelial cells modifying the course of various kidney diseases. This review summarizes recent insights on the role of autophagy in kidney physiology and diseases alluding to possible novel intervention strategies for treating specific kidney disorders by modifying autophagy.

Endothelin and the podocyte

In the past decade, research has advanced our understanding how endothelin contributes to proteinuria and glomerulosclerosis. Data from pre-clinical and clinical studies now provide evidence that proteinuric diseases such as focal segmental glomerulosclerosis and diabetic nephropathy as well as hypertension nephropathy are sensitive to treatment with endothelin receptor antagonists (ERAs). Like blockade of the renin-angiotensin system, ERA treatment-under certain conditions-may even cause disease regression, effects that could be achieved on top of renin-angiotensin-aldosterone system blockade, suggesting independent therapeutic mechanisms by which ERAs convey nephroprotection. Beneficial effects of ERAs on podocyte function, which is essential to maintain the glomerular filtration barrier, have been identified as one of the key mechanisms by which inhibition of the endothelin ETA receptor ameliorates renal structure and function. In this article, we will review pre-clinical studies demonstrating a causal role for endothelin in proteinuric chronic kidney disease (with a particular focus on functional and structural integrity of podocytes in vitro and in vivo). We will also review the evidence suggesting a therapeutic benefit of ERA treatment on the functional integrity of podocytes in humans.

Effect of 5/6 nephrectomized rat serum on epithelial-to-mesenchymal transition in vitro

Objective: To investigate whether the 5/6 nephrectomized (5/6Nx) rats’ 12-week serum could lead to tubular epithelial-to-mesenchymal transition (EMT) and its molecular mechanism, so as to probe the potential stimulation from circulation in chronic progressive kidney disease. Methods: A total of 24 Sprague Dawley (SD) rats were randomly divided into two groups: sham operation group (sham group) and 5/6Nx group. Rats were killed 12 weeks after surgery to obtain 5/6Nx rats’ 12-week serum. Then we detected the expression of E-cadherin in renal tubular epithelial cells of the remaining kidney and we investigated whether the 12th week serum of 5/6Nx rats could cause HK-2 (human kidney proximal tubular cell line) cells to transdifferentiate into fibroblasts. Results: Our data confirmed that E-cadherin expression decreased significantly in the remaining kidney at 12 weeks, and the 5/6Nx rats’ 12-week serum could suppress E-cadherin protein and mRNA expression (p < 0.05). We also found that the 5/6Nx rats’ 12-week serum could upreg-ulate ZEB1, β-catenin, and wnt3 protein expression (p < 0.05). Conclusions: Our results demonstrated that the 5/6Nx rats’ 12-week serum could suppress the expression of E-cadherin in HK-2 cells. It was partially through modulating the increase of ZEB1. The loss of E-cadherin could lead β-catenin to localize to the cytoplasm and nucleus, and feed into the Wnt signaling pathway. It means that the pathogenic serum in chronic kidney disease (CKD) plays an important role in the loss of renal function and turns to be a new avenue of research with potential clinical implications.

Glyoxalase I retards renal senescence

Although kidney functions deteriorate with age, little is known about the general morphological alterations and mechanisms of renal senescence. We hypothesized that carbonyl stress causes senescence and investigated the possible role of glyoxalase I (GLO1), which detoxifies precursors of advanced glycation end products in the aging process of the kidney. We observed amelioration of senescence in GLO1-transgenic aged rats (assessed by expression levels of senescence markers such as p53, p21(WAF1/CIP1), and p16(INK4A)) and a positive rate of senescence-associated β-galactosidase (SABG) staining, associated with reduction of renal advanced glycation end product accumulation (estimated by the amount of carboxyethyl lysine). GLO1-transgenic rats showed amelioration of interstitial thickening (observed as an age-related presentation in human renal biopsy specimens) and were protected against age-dependent decline of renal functions. We used GLO1 overexpression or knockdown in primary renal proximal tubular epithelial cells to investigate the effect of GLO1 on cellular senescence. Senescence markers were significantly up-regulated in renal proximal tubular epithelial cells at late passage and in those treated with etoposide, a chemical inducer of senescence. GLO1 cellular overexpression ameliorated and knockdown enhanced the cellular senescence phenotypes. Furthermore, we confirmed the association of decreased GLO1 enzymatic activity and age-dependent deterioration of renal function in aged humans with GLO1 mutation. These findings indicate that GLO1 ameliorates carbonyl stress to retard renal senescence.

Urinary C-type natriuretic peptide excretion: a potential novel biomarker for renal fibrosis during aging

Renal aging is characterized by structural changes in the kidney including fibrosis, which contributes to the increased risk of kidney and cardiac failure in the elderly. Studies involving healthy kidney donors demonstrated subclinical age-related nephropathy on renal biopsy that was not detected by standard diagnostic tests. Thus there is a high-priority need for novel noninvasive biomarkers to detect the presence of preclinical age-associated renal structural and functional changes. C-type natriuretic peptide (CNP) possesses renoprotective properties and is present in the kidney; however, its modulation during aging remains undefined. We assessed circulating and urinary CNP in a Fischer rat model of experimental aging and also determined renal structural and functional adaptations to the aging process. Histological and electron microscopic analysis demonstrated significant renal fibrosis, glomerular basement membrane thickening, and mesangial matrix expansion with aging. While plasma CNP levels progressively declined with aging, urinary CNP excretion increased, along with the ratio of urinary to plasma CNP, which preceded significant elevations in proteinuria and blood pressure. Also, CNP immunoreactivity was increased in the distal and proximal tubules in both the aging rat and aging human kidneys. Our findings provide evidence that urinary CNP and its ratio to plasma CNP may represent a novel biomarker for early age-mediated renal structural alterations, particularly fibrosis. Thus urinary CNP could potentially aid in identifying subjects with preclinical structural changes before the onset of symptoms and disease, allowing for the initiation of strategies designed to prevent the progression of chronic kidney disease particularly in the aging population.

Podocyte dysfunction in aging--related glomerulosclerosis

We review podocyte molecular structure and function, consider the underlying mechanisms related to podocyte dysfunction and propose that podocyte dysfunction be considered in the evaluation and management of age-associated glomerulosclerosis. With aging, progressive sympathetic activation, increased intrarenal renin-angiotensin system (RAS) activity, endothelin system and oxidative stress and reduced nitric oxide (NO)-availability can damage podocytes. Apoptosis and proliferation are the principal podocyte changes following injury with the latter leading to sclerosis and loss of nephrons. Podocyte loss can be evaluated by either determining their average number in biopsed glomeruli or by estimating podocyte number or their associated molecules in urine sediment. Podocyturia may be considered a marker of active glomerular disease. Preliminary data suggest that antiadrenergic drugs, angiotensin converting enzyme (ACE) inhibitors, RAS blocking drugs, endothelin system inhibitors and reduced oxidative stress can protect podocytes. Thus podocytes appear to play an important role in the pathogenesis, evaluation and therapy of age related glomerulosclerosis.

The inducible deletion of Drosha and microRNAs in mature podocytes results in a collapsing glomerulopathy

Micro-RNAs (miRNAs) are short (average 22 nucleotides) noncoding regulatory RNAs that inhibit gene expression by targeting complementary 3'-untranslated regions of protein-encoding mRNAs for translational repression or degradation. miRNAs play key roles in both the function and differentiation of many cell types. Drosha and Dicer, two RNAase III enzymes, function in a stepwise manner to generate a mature miRNA. Previous studies have shown that podocyte-specific deletion of Dicer during development results in proteinuric renal disease and collapsing glomerulopathy (CG); however, Dicer has functions other than the generation of miRNAs. Here we found that the podocyte-specific deletion of Drosha results in a similar phenotype to Dicer mutants, confirming that the Dicer mutant phenotype is due to the loss of miRNAs. Moreover, the inducible deletion of Drosha in 2- to 3-month-old mice (Tet-On system) resulted in CG. Thus, continuous generation of miRNAs are required for the normal function of mature podocytes and their loss leads to CG. Identifying these miRNAs may provide new insight into disease pathogenesis and novel therapeutic targets in various podocytopathies.

Implications of autophagy for glomerular aging and disease

Glomerular diseases lead to a progressive decline in renal function and account for the vast majority of end-stage kidney diseases. Injury and loss of glomerular podocytes are common determining factors of glomerular disease progression and renal failure. Podocytes are a primary glomerular target of toxic, immune, metabolic, and oxidant stress, but little is known of the factors that counteract cellular stress signaling pathways. This review focuses on recent findings that identify autophagy as a critical homeostatic and quality control mechanism maintaining glomerular homeostasis.

Autophagy influences glomerular disease susceptibility and maintains podocyte homeostasis in aging mice

Injury and loss of podocytes are leading factors of glomerular disease and renal failure. The postmitotic podocyte is the primary glomerular target for toxic, immune, metabolic, and oxidant stress, but little is known about how this cell type copes with stress. Recently, autophagy has been identified as a major pathway that delivers damaged proteins and organelles to lysosomes in order to maintain cellular homeostasis. Here we report that podocytes exhibit an unusually high level of constitutive autophagy. Podocyte-specific deletion of autophagy-related 5 (Atg5) led to a glomerulopathy in aging mice that was accompanied by an accumulation of oxidized and ubiquitinated proteins, ER stress, and proteinuria. These changes resulted ultimately in podocyte loss and late-onset glomerulosclerosis. Analysis of pathophysiological conditions indicated that autophagy was substantially increased in glomeruli from mice with induced proteinuria and in glomeruli from patients with acquired proteinuric diseases. Further, mice lacking Atg5 in podocytes exhibited strongly increased susceptibility to models of glomerular disease. These findings highlight the importance of induced autophagy as a key homeostatic mechanism to maintain podocyte integrity. We postulate that constitutive and induced autophagy is a major protective mechanism against podocyte aging and glomerular injury, representing a putative target to ameliorate human glomerular disease and aging-related loss of renal function.

Therapeutic potential of endothelin receptor antagonists for chronic proteinuric renal disease in humans

Diabetes and arterial hypertension continue to be the main causes of chronic renal failure in 2010, with a rising prevalence in part due to the worldwide obesity epidemic. Proteinuria is a main feature of chronic renal disease and mediated by defects in the glomerular filtration barrier and is as a good predictor of cardiovascular events. Indeed, chronic renal disease due to glomerulosclerosis is one of the important risk factors for the development of coronary artery disease and stroke. Glomerulosclerosis develops in response to inflammatory activation and increased growth factor production. Preclinical and first preliminary clinical studies provide strong evidence that endogenous endothelin-1 (ET-1), a 21-amino-acid peptide with strong growth-promoting and vasoconstricting properties, plays a central role in the pathogenesis of proteinuria and glomerulosclerosis via activation of its ET(A) subtype receptor involving podocyte injury. These studies have not only shown that endothelin participates in the disease processes of hypertension and glomerulosclerosis but also that features of chronic renal disease such as proteinuria and glomerulosclerosis are reversible processes. Remarkably, the protective effects of endothelin receptors antagonists (ERAs) are present even on top of concomitant treatments with inhibitors of the renin-angiotensin system. This review discusses current evidence for a role of endothelin for proteinuric renal disease and podocyte injury in diabetes and arterial hypertension and reviews the current status of endothelin receptor antagonists as a potential new treatment option in renal medicine.

NFkappaB promotes inflammation, coagulation, and fibrosis in the aging glomerulus

The peak prevalence of ESRD from glomerulosclerosis occurs at 70 to 79 years. To understand why old glomeruli are prone to failure, we analyzed the Fischer 344 rat model of aging under ad libitum-fed (rapid aging) and calorie-restricted (slowed aging) conditions. All glomerular cells contained genes whose expression changed "linearly" during adult life from 2 to 24 months: mesangial cells (e.g., MMP9), endothelial cells (e.g., ICAM and VCAM), parietal epithelial cells (e.g., ceruloplasmin), and podocytes (e.g., nephrin and prepronociceptin). Patterns of aging glomerular gene expression closely resembled atherosclerosis, including activation of endothelial cells, epithelial cells, and macrophages, as well as proinflammatory pathways related to cell adhesion, chemotaxis, blood coagulation, oxidoreductases, matrix metalloproteinases, and TGF-beta activation. We used a nonbiased data-mining approach to identify NFkappaB as the likely transcriptional regulator of these events. We confirmed NFkappaB activation by two independent methods: translocation of NFkappaB p50 to glomerular nuclei and ChIP assays demonstrating NFkappaB p50 binding to the kappaB motif of target genes in old versus young glomeruli. These data suggest that old glomeruli exhibit NFkappaB-associated up-regulation of a proinflammatory, procoagulable, and profibrotic phenotype compared with young glomeruli; these distinctions could explain their enhanced susceptibility to failure. Furthermore, these results provide a potential mechanistic explanation for the close relationship between ESRD and atherosclerotic organ failure as two parallel arms of age-associated NFkappaB-driven processes.

The Rowett rat strain is resistant to renal fibrosis

BACKGROUND

Genetic susceptibility to renal fibrosis may determine the individual rate of progression to renal failure. We aimed to study the progression in Rowett (RO) rats, a strain we found resistant to subtotal nephrectomy (SNX), comparing to Sprague-Dawley (SD) rats, a strain with established sensitivity in a radical ablation/infarction and diet-induced SNX model.

METHODS

Eight-week-old male RO (RO-SNX) and SD (SD-SNX, n = 5/group) rats underwent SNX and were kept on high protein and salt diet. Kidney function was monitored and the kidneys were evaluated by histology and immunohistochemistry 5 weeks after SNX.

RESULTS

RO-SNX rats had only mild proteinuria and less glomerulosclerosis, accompanied by less fibronectin and TGF-beta staining as compared to SD-SNX rats. Glomerular nitrotyrosine staining was less intense in RO-SNX vs SD-SNX, accompanied by less podocyte damage as demonstrated by desmin staining.

CONCLUSION

Our results demonstrate the importance of podocyte damage in glomerulosclerosis and that Rowett rats are protected from renal fibrosis. To our knowledge, this is the first strain of rats with unknown genetic resistance, which makes the strain attractive for studying the genetic background of renal fibrosis.

Podocytes and glomerular function with aging

Kidney function declines with age in association with the development of age-associated glomerulosclerosis. The well-established structural and functional changes with age are reviewed briefly. The modification of aging pathology by calorie restriction is discussed. The role of the podocyte as a critical cell in the aging process is considered, using animal models and human biopsy material. Newer data on changes in gene expression and possible changes in biology in the glomerulus are discussed. There is speculation on the implications of this change in biology for human disease and progression.

Reversal of proteinuric renal disease and the emerging role of endothelin

Proteinuria is a major long-term clinical consequence of diabetes and hypertension, conditions that lead to progressive loss of functional renal tissue and, ultimately, end-stage renal disease. Proteinuria is also a strong predictor of cardiovascular events. Convincing preclinical and clinical evidence exists that proteinuria and the underlying glomerulosclerosis are reversible processes. This Review outlines the mechanisms involved in the development of glomerulosclerosis--particularly those responsible for podocyte injury--with an emphasis on the potential capacity of endothelin receptor blockade to reverse this process. There is strong evidence that endothelin-1, a peptide with growth-promoting and vasoconstricting properties, has a central role in the pathogenesis of proteinuria and glomerulosclerosis, which is mediated via activation of the ET(A) receptor. Several antiproteinuric drugs, including angiotensin-converting-enzyme inhibitors, angiotensin receptor antagonists, statins and certain calcium channel blockers, inhibit the formation of endothelin-1. Preclinical studies have demonstrated that endothelin receptor antagonists can reverse proteinuric renal disease and glomerulosclerosis, and preliminary studies in humans with renal disease have shown that these drugs have remarkable antiproteinuric effects that are additive to those of standard antiproteinuric therapy. Additional clinical studies are needed.

Calcimimetic R-568 or calcitriol: equally beneficial on progression of renal damage in subtotally nephrectomized rats

Patients with renal insufficiency develop secondary hyperparathyroidism. Monotherapy with active vitamin D or calcimimetics ameliorates secondary hyperparathyroidism. We compared kidney damage in subtotally nephrectomized (SNX) rats treated with active vitamin D (calcitriol) or the calcimimetic R-568. Male Sprague-Dawley SNX and sham-operated (sham-op) rats were randomized into the following treatment groups: SNX + R-568, SNX + calcitriol, SNX + vehicle, sham-op + R-568, sham-op + calcitriol, and sham-op + vehicle. Albuminuria and blood pressure were monitored and kidneys were examined using morphometry, immunohistochemistry, quantitative RT-PCR, and in situ hybridization. Parathyroid hormone concentrations were lowered to the same extent by the two interventions, although phosphorus and the calcium-phosphorus product were reduced only by R-568 treatment. SNX rats developed marked albuminuria, which was significantly reduced in ad libitum- and pair-fed animals treated with R-568 and animals treated with calcitriol. Mean glomerular volume (6.05 +/- 1.46 vs. 2.70 +/- 0.91 mm(3)), podocyte volume (831 +/- 127 vs. 397 +/- 67 microm(3)), the degree of foot process fusion (mean width of foot processes = 958 +/- 364 vs. 272 +/- 35 nm), and glomerular basement membrane thickness (244 +/- 6 vs. 267 +/- 23 nm), as well as desmin staining, were significantly higher in vehicle-treated SNX than sham-operated animals. These changes were ameliorated with R-568 and calcitriol. In SNX, as well as sham-operated, animals, expression of the calcium-sensing receptor (protein and mRNA) was upregulated by treatment with the calcimimetic, but not calcitriol. Calcitriol and R-568 were similarly effective in ameliorating kidney damage.