Aging in the glomerulus

Mesangial Expansion by Morphometry at 5 y After Kidney Transplantation: Incidence, Risk Factors, and Association With Graft Loss

Background

Mesangial expansion (ME) is an understudied histologic lesion in renal allografts. The current Banff mm score is not reproducible and may miss important ME features. The study aimed to improve the quantification of ME using morphometry, assess changes over time, and determine its association with allograft loss.

Methods

We studied ME in 1-y and 5-y surveillance biopsies in 835 kidney transplants performed between January 2000 and December 2013. ME was assessed using the Banff mm score by a central pathologist and by morphometry. We derived 3 different morphometric measures: (1) %ME mm (%glomeruli with ME in ≥2 lobules, like Banff mm); (2) %MEany (%glomeruli with any ME lesion); and (3) %ME area (sum of all ME areas/all glomerular tuft areas). Unadjusted and adjusted Cox models assessed the risk of death-censored allograft loss.

Results

From 1- to 5-y biopsies, the mean Banff mm score increased from 0.18 to 0.34, whereas %ME mm increased from 2.5% to 13.3%. Banff mm score had modest correlations with morphometric ME measures. Moderate-severe %ME mm was present in 20.1% of 5-y biopsies, whereas only 6.6% of Banff mm scores were. In general, higher ME on both 1- and 5-y biopsies was associated with a deceased donor, older recipient age, recipient diabetes/obesity (present in >50% of severely affected biopsies), higher hemoglobin A1c at 5 y posttransplant, and recurrent kidney disease. Higher ME on 5-y biopsies was associated with delayed graft function. A higher Banff mm score at 1-y biopsy and morphometry ME measures at 5-y biopsy were associated with rejection during the first year posttransplant. Morphometric ME measures were associated with allograft loss independent of Banff scores and all clinical characteristics, including kidney function and recurrent disease. The model with %MEany had the highest c-statistic (0.872).

Conclusions

Banff mm score underestimates the pervasiveness of ME in 5-y biopsies. ME is common and associated with alloimmune and nonalloimmune causes of graft loss.

High-Dose Fenofibrate Stimulates Multiple Cellular Stress Pathways in the Kidney of Old Rats

We investigated the age-related effects of the lipid-lowering drug fenofibrate on renal stress-associated effectors. Young and old rats were fed standard chow with 0.1% or 0.5% fenofibrate. The kidney cortex tissue structure showed typical aging-related changes. In old rats, 0.1% fenofibrate reduced the thickening of basement membranes, but 0.5% fenofibrate exacerbated interstitial fibrosis. The PCR array for stress and toxicity-related targets showed that 0.1% fenofibrate mildly downregulated, whereas 0.5% upregulated multiple genes. In young rats, 0.1% fenofibrate increased some antioxidant genes' expression and decreased the immunoreactivity of oxidative stress marker 4-HNE. However, the activation of cellular antioxidant defenses was impaired in old rats. Fenofibrate modulated the expression of factors involved in hypoxia and osmotic stress signaling similarly in both age groups. Inflammatory response genes were variably modulated in the young rats, whereas old animals presented elevated expression of proinflammatory genes and TNFα immunoreactivity after 0.5% fenofibrate. In old rats, 0.1% fenofibrate more prominently than in young animals induced phospho-AMPK and PGC1α levels, and upregulated fatty acid oxidation genes. Our results show divergent effects of fenofibrate in young and old rat kidneys. The activation of multiple stress-associated effectors by high-dose fenofibrate in the aged kidney warrants caution when applying fenofibrate therapy to the elderly.

Population Pharmacokinetics of Digoxin in Nonagenarian Patients: Optimization of the Dosing Regimen

OBJECTIVE

The aim of this study was to develop a population pharmacokinetic model of digoxin in patients over 90 years old and to propose an equation for adjusting digoxin dose in this population.

METHODS

We included 326 nonagenarian patients admitted to Severo Ochoa University Hospital (Spain) who received digoxin and were under therapeutic drug monitoring. All data were retrospectively collected, and population modeling was performed with non-linear mixed-effect modeling software (NONMEM®). One- and two-compartment models were tested to calculate digoxin clearance (Cl), volume of distribution (Vd), absorption rate constant (Ka), and bioavailability (bioavailable fraction, F). The covariates were evaluated by stepwise covariate model building, and the final model was internally validated by bootstrap analysis with 1000 resamples. External validation was performed with another population of 95 patients with the same characteristics as the modeling group.

RESULTS

The population was 26% males, with a mean age of 93.2 years (90-103 years), mean creatinine 1.11 mg/dL (0.42-3.81 mg/dL), and mean total body weight 61.2 kg (40-100 kg). The pharmacokinetics of digoxin were best described by a one-compartment model (ADVAN2 TRANS2), with first-order conditional estimation with interaction. The covariates with influence on our model were creatinine clearance based on the Cockcroft-Gault equation (CG), serum potassium (K), co-administration of loop diuretics, and sex: Cl/F = 4.55 · (CG/36.4)0.468 · 0.83LD · 1.21SEX; Vd/F = 355 · (K/4.3)-0.849; Ka = 1.22 h-1 [where LD indicates loop diuretics (1 for administered, 0 for otherwise) and SEX indicates patient sex (1 for male, 0 for female)]. Based on our results, we proposed an equation to adjust the digoxin dosing regimen in nonagenarian patients: dose (mg) = 0.144 · (CG/36.4)0.468 · 0.83LD · 1.21SEX.

CONCLUSIONS

The greatest influence on digoxin clearance came from renal function calculated by the Cockcroft-Gault equation. Vd was decreased by K. The model developed showed a precise predictive performance to be applied for therapeutic drug monitoring.

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.

Molecular Mechanisms Associated with Aging Kidneys and Future Perspectives

The rapid growth of the elderly population is making the need for extensive and advanced information about age-related organ dysfunction a crucial research area. The kidney is one of the organs most affected by aging. Aged kidneys undergo functional decline, characterized by a reduction in kidney size, decreased glomerular filtration rate, alterations in renal blood flow, and increased inflammation and fibrosis. This review offers a foundation for understanding the functional and molecular mechanisms of aging kidneys and for selecting identifying appropriate targets for future treatments of age-related kidney issues.

Assessing the effects of aging on the renal endothelial cell landscape using single-cell RNA sequencing

Endothelial cells (ECs) with senescence-associated secretory phenotypes (SASP) have been identified as a key mechanism of aging that contributes to various age-related kidney diseases. In this study, we used single-cell RNA sequencing (scRNA-seq) to create a transcriptome atlas of murine renal ECs and identify transcriptomic changes that occur during aging. We identified seven different subtypes of renal ECs, with glomerular ECs and angiogenic ECs being the most affected by senescence. We confirmed our scRNA-seq findings by using double immunostaining for an EC marker (CD31) and markers of specialized EC phenotypes. Our analysis of the dynamics of capillary lineage development revealed a chronic state of inflammation and compromised glomerular function as prominent aging features. Additionally, we observed an elevated pro-inflammatory and pro-coagulant microenvironment in aged glomerular ECs, which may contribute to age-related glomerulosclerosis and renal fibrosis. Through intercellular communication analysis, we also identified changes in signaling involved in immune regulation that may contribute to a hostile microenvironment for renal homeostasis and function. Overall, our findings provide new insights into the mechanisms of aging in the renal endothelium and may pave the way for the discovery of diagnostic biomarkers and therapeutic interventions against age-related kidney diseases.

Early renal impairment affects hormonal regulators of calcium and bone metabolism and Wnt signalling and the response to vitamin D supplementation in healthy older adults

Bone and renal metabolism are regulated by common factors and there is extensive cross-talk between these organs (the 'renal-bone-axis'). Ageing is associated with physiological changes including reduced bone mass, renal function and tissue sensitivity to regulatory hormones, impacting the renal-bone axis. We aimed to investigate the influence of estimated Glomerular Filtration Rate (eGFR) on plasma concentrations of vitamin D metabolites, Wnt signalling and bone metabolism in a dose ranging vitamin D₃ RCT (12,000 IU, 24,000 IU, 48,000 IU/month for 1 year; n = 379, >70 y) with a baseline eGFR > 30 mL/min/1.73 m². Participants were categorised on basis of eGFR (≥60 or mL/min/1.73 m²) based on 5 commonly used algorithms for eGFR. Differences between eGFR categories were tested with ANCOVA. Before supplementation commenced, a lower eGFR was associated with significantly higher concentrations of c-terminal and intact Fibroblast Growth Factor-23 (cFGF23; iFGF23), intact Parathyroid Hormone (iPTH) and Sclerostin (SOST) and lower Klotho, 1,25-dihydroxy Vitamin D (1,25(OH)₂D) and Dickkopf-related Protein 1 (DKK1) concentrations. Differences between eGFR groups in 25-hydroxy Vitamin D (25(OH)D), 24,25-dihydroxy Vitamin D (24,25(OH)₂D) and iPTH were only detected with eGFR based on Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Modification in Diet for Renal Disease (MDRD-4) algorithms. Differences in Bone Mineral Density and Content (BMD; BMC) and bone turnover markers were detected only with Cockcroft-Gault (CG). Pre- and post- supplementation comparisons showed differences in the response to supplementation by eGFR group. Plasma 25(OH)D, 24,25(OH)₂D, 1,25(OH)₂D and DKK1 increased and iPTH and C-terminal telopeptide (CTX) decreased in both groups. Plasma iFGF23, bone specific alkaline phosphatase (BAP) and Procollagen 1 intact N-terminal Propeptide (PINP) increased and phosphate decreased only in the group with eGFR ≥ 60 mL/min/1.73 m². Findings were largely consistent across all eGFR algorithms. Post-supplementation, cFGF23, iFGF23, iPTH and SOST remained significantly higher in the lower eGFR group. Plasma 1,25(OH)₂D and Klotho did no longer differ between eGFR groups. This was found for all eGFR algorithms, with the exception of iPTH and iFGF23, which were not significantly different with eGFR based on CG. Differences in BMD and BMC were detected with CKD-EPI-creatinine and MDRD-4 but not GC. This study showed that even a moderate decline in eGFR is associated with alterations in vitamin D metabolism, Wnt signalling and bone turnover markers. Renal function influenced the response to vitamin D supplementation. Supplementation increased Vitamin D metabolites in the group with moderate renal impairment to concentrations comparable to those found in the group with normal renal function. However, although CTX decreased, an increase in bone formation markers was not found in the group with eGFR 60 mL/min/1.73 m². In conclusion, vitamin D supplementation had beneficial effects on markers of the renal-bone axis in older people with both normal and impaired renal function.

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.

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.

NMDA Receptor Hypofunction in the Aging-Associated Malfunction of Peripheral Tissue

Glutamatergic transmission through NMDA receptors (NMDARs) is important for the function of peripheral tissues. In the bone, NMDARs and its co-agonist, D-serine participate in all the phases of the remodeling. In the vasculature, NMDARs exerts a tonic vasodilation decreasing blood perfusion in the corpus cavernosum and the filtration rate in the renal glomerulus. NMDARs are relevant for the skin turnover regulating the proliferation and differentiation of keratinocytes and the formation of the cornified envelope (CE). The interference with NMDAR function in the skin leads to a slow turnover and repair. As occurs with the brain and cognitive functions, the manifestations of a hypofunction of NMDARs resembles those observed during aging. This raises the question if the deterioration of the glomerular vasculature, the bone remodeling and the skin turnover associated with age could be related with a hypofunction of NMDARs. Furthermore, the interference of D-serine and the effects of its supplementation on these tissues, suggest that a decrease of D-serine could account for this hypofunction pointing out D-serine as a potential therapeutic target to reduce or even prevent the detriment of the peripheral tissue associated with aging.

Aging-Related Functional and Structural Changes in Renal Tissues: Lesson from a Camel Model

Renal aging is a progressive, physiological, and anatomical change that naturally occurs in all animal species. To date, no information is available concerning the aging-related structural and functional changes in camel kidneys. A total of 25 healthy male camels (14 aged 4–6 years and 11 aged 18–22 years) were included in this study. After the camels were slaughtered, samples were collected from all the camels’ kidneys and prepared for histopathological, immunohistochemical, and gene expression evaluations. The most striking observation was the significant decline in the immunohistochemical abundance of podocin and the significant upregulation of smoothening in the aging camels’ kidneys. However, the nonsignificant changes have reported for nephrin, calbindin, autophagy 5 (ATG5), aquaporin 1, and toll-like receptor 9. Furthermore, the mRNA expressions of sirtuin 1, superoxide dismutase 1, superoxide dismutase 2, peroxisome proliferator-activated receptor alpha, B-cell lymphoma 2 (Bcl-2), and erythropoietin were significantly decreased in the aging camels’ kidneys. While the significant upregulation of Bcl-2-associated X protein and the nonsignificant increase in ATG5 expression levels were reported in the aging camels’ kidneys. The present findings provide better understanding of the complex events and initiating factors of aging, allowing for the development of a future therapeutic strategy to preserve adequate renal function throughout life.

Differential effects of sodium chloride and monosodium glutamate on kidney of adult and aging mice

Monosodium Glutamate (MSG) is used as flavour enhancer, with potential beneficial effects due to its nutritional value. Given the decline in kidney functions during aging, we investigated the impact of MSG voluntary intake on the kidney of male mice, aged 6 or 18 months. For 2 months, they freely consumed water (control group), sodium chloride (0.3% NaCl) or MSG (1% MSG) in addition to standard diet. Young animals consuming sodium chloride presented signs of proteinuria, hyperfiltration, enhanced expression and excretion of Aquaporin 2 and initial degenerative reactions suggestive of fibrosis, while MSG-consuming mice were similar to controls. In old mice, aging-related effects including proteinuria and increased renal corpuscle volume were observed in all groups. At an advanced age, MSG caused no adverse effects on the kidney compared to controls, despite the presence of a sodium moiety, similar to sodium chloride. These data show that prolonged MSG intake in mice has less impact on kidney compared to sodium chloride, that already in young animals induced some effects on kidney, possibly related to hypertension.

The ageing kidney: Molecular mechanisms and clinical implications

As human life expectancy keeps increasing, ageing populations present a growing challenge for clinical practices. Human ageing is associated with molecular, structural, and functional changes in a variety of organ systems, including the kidney. During the ageing process, the kidney experiences progressive functional decline as well as macroscopic and microscopic histological alterations, which are accentuated by systemic comorbidities like hypertension and diabetes mellitus, or by preexisting or underlying kidney diseases. Although ageing per se does not cause kidney injury, physiologic changes associated with normal ageing processes are likely to impair the reparative capacity of the kidney and thus predispose older people to acute kidney disease, chronic kidney disease and other renal diseases. Mechanistically, cell senescence plays a key role in renal ageing, involving a number of cellular signaling mechanisms, many of which may be harnessed as international targets for slowing or even reversing kidney ageing. This review summarizes the clinical characteristics of renal ageing, highlights the latest progresses in deciphering the role of cell senescence in renal ageing, and envisages potential interventional strategies and novel therapeutic targets for preventing or improving renal ageing in the hope of maintaining long-term kidney health and function across the life course.

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.

Resveratrol Pretreatment Ameliorates Concanavalin A-Induced Advanced Renal Glomerulosclerosis in Aged Mice through Upregulation of Sirtuin 1-Mediated Klotho Expression

Aging kidneys are characterized by an increased vulnerability to glomerulosclerosis and a measurable decline in renal function. Evidence suggests that renal and systemic klotho and sirtuin 1 (SIRT1) deficiencies worsen kidney damage induced by exogenous stresses. The aim of this study was to explore whether resveratrol would attenuate concanavalin A (Con A)-induced renal oxidative stress and advanced glomerulosclerosis in aged mice. Aged male C57BL/6 mice were treated orally with resveratrol (30 mg/kg) seven times (12 h intervals) prior to the administration of a single tail-vein injection of Con A (20 mg/kg). The plasma and urinary levels of kidney damage markers were evaluated. The kidney histopathology, renal parameters, and oxidative stress levels were measured. Furthermore, klotho was downregulated in mouse kidney mesangial cells that were pretreated with 25 µM resveratrol followed by 20 µg/mL Con A. The urinary albumin/creatinine ratio, blood urea nitrogen, kidney mesangial matrix expansion, tubulointerstitial fibrosis, and renal levels of α-smooth muscle actin, transforming growth factor beta, fibronectin, procollagen III propeptide, and collagen type I significantly increased in Con A-treated aged mice. Aged mice kidneys also showed markedly increased levels of 8-hydroxydeoxyguanosine (8-OH-dG) and reactive oxygen species (ROS), with reduced superoxide dismutase activity and levels of glutathione, klotho, and SIRT1 after Con A challenge. Furthermore, in kidney mesangial cells, klotho silencing abolished the effects of resveratrol on the Con A-mediated elevation of the indices of oxidative stress and the expression of glomerulosclerosis-related factors. These findings suggest that resveratrol protects against Con A-induced advanced glomerulosclerosis in aged mice, ameliorating renal oxidative stress via the SIRT1-mediated klotho expression.

Connectivity mapping of glomerular proteins identifies dimethylaminoparthenolide as a new inhibitor of diabetic kidney disease

While blocking the renin angiotensin aldosterone system (RAAS) has been the main therapeutic strategy to control diabetic kidney disease (DKD) for many years, 25-30% of diabetic patients still develop the disease. In the present work we adopted a systems biology strategy to analyze glomerular protein signatures to identify drugs with potential therapeutic properties in DKD acting through a RAAS-independent mechanism. Glomeruli were isolated from wild type and type 1 diabetic (Ins2Akita) mice treated or not with the angiotensin-converting enzyme inhibitor (ACEi) ramipril. Ramipril efficiently reduced the urinary albumin/creatine ratio (ACR) of Ins2Akita mice without modifying DKD-associated renal-injuries. Large scale quantitative proteomics was used to identify the DKD-associated glomerular proteins (DKD-GPs) that were ramipril-insensitive (RI-DKD-GPs). The raw data are publicly available via ProteomeXchange with identifier PXD018728. We then applied an in silico drug repurposing approach using a pattern-matching algorithm (Connectivity Mapping) to compare the RI-DKD-GPs's signature with a collection of thousands of transcriptional signatures of bioactive compounds. The sesquiterpene lactone parthenolide was identified as one of the top compounds predicted to reverse the RI-DKD-GPs's signature. Oral treatment of 2 months old Ins2Akita mice with dimethylaminoparthenolide (DMAPT, a water-soluble analogue of parthenolide) for two months at 10 mg/kg/d by gavage significantly reduced urinary ACR. However, in contrast to ramipril, DMAPT also significantly reduced glomerulosclerosis and tubulointerstitial fibrosis. Using a system biology approach, we identified DMAPT, as a compound with a potential add-on value to standard-of-care ACEi-treatment in DKD.

CD44 impacts glomerular parietal epithelial cell changes in the aged mouse kidney

CD44 contributes to the activation of glomerular parietal epithelial cells (PECs). Although CD44 expression is higher in PECs of healthy aged mice, the biological role of CD44 in PECs in this context remains unclear. Accordingly, young (4 months) and aged (24 months) CD44-/- mice were compared to age-matched CD44+/+ mice, both aged in a nonstressed environment. Parietal epithelial cell densities were similar in both young and aged CD44+/+ and CD44-/- mice. Phosphorylated ERK 1/2 (pERK) was higher in aged CD44+/+ mice. Vimentin and α-SMA, markers of changes to the epithelial cell phenotype, were present in PECs in aged CD44+/+ mice, but absent in aged CD44-/- mice in both outer cortical (OC) and juxtamedullary (JM) glomeruli. Because age-related glomerular hypertrophy was lower in CD44-/- mice, mTOR activation was assessed by phospho-S6 ribosomal protein (pS6RP) staining. Parietal epithelial cells and glomerular tuft staining for pS6RP was lower in aged CD44-/- mice compared to aged CD44+/+ mice. Podocyte density was higher in aged CD44-/- mice in both OC and JM glomeruli. These changes were accompanied by segmental and global glomerulosclerosis in aged CD44+/+ mice, but absent in aged CD44-/- mice. These results show that the increase in CD44 in PECs in aged kidneys contributes to several changes to the glomerulus during healthy aging in mice, and may involve ERK and mTOR activation.

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.

Nitrative Stress-Related Autophagic Insufficiency Participates in Hyperhomocysteinemia-Induced Renal Aging

The kidneys are important organs that are susceptible to aging. Hyperhomocysteinemia (HHcy) is a risk factor for nephropathy and is associated with chronic nephritis, purpuric nephritis, and nephrotic syndrome. Numerous studies have shown that elevated serum homocysteine levels can damage the kidneys; however, the underlying mechanism of HHcy on kidney damage remains unclear. In this study, we make use of a diet-induced HHcy rat model and in vitro cell culture to explore the role of autophagy in HHcy-induced renal aging and further explored the underlying mechanism. We demonstrated that HHcy led to the development of renal aging. Promoted kidney aging and autophagic insufficiency were involved in HHcy-induced renal aging. HHcy decreased the expression of transcription factor EB (TFEB), the key transcription factor of autophagy-related genes in renal tissue. Further experiments showed that nitrative stress levels were increased in the kidney of HHcy rats. Interestingly, pretreatment with the peroxynitrite (ONOO⁻) scavenger FeTMPyP not only reduced the Hcy-induced nitrative stress in vitro but also partially attenuated the decrease in TFEB in both protein and mRNA levels. Moreover, our results indicated that HHcy reduced TFEB expression and inhibited TFEB-mediated autophagy activation by elevating nitrative stress. In conclusion, this study showed an important role of autophagic insufficiency in HHcy-induced renal aging, in which downregulation of TFEB plays a major role. Furthermore, downexpression of TFEB was associated with increased nitrative stress in HHcy. This study provides a novel insight into the mechanism and therapeutic strategy for renal aging.

Global glomerulosclerosis with nephrotic syndrome; the clinical importance of age adjustment

Globally sclerotic glomeruli (GSG) occur with both normal aging and kidney disease. However, it is unknown whether any GSG or only GSG exceeding that expected for age is clinically important. To evaluate this, we identified patients with a glomerulopathy that often presents with nephrotic syndrome (focal segmental glomerulosclerosis, membranous nephropathy, or minimal change disease) in the setting of the Nephrotic Syndrome Study Network (NEPTUNE), China-Digital Kidney Pathology (DiKiP), and the Southeast Minnesota cohorts. Age-based thresholds (95th percentile) for GSG based on normotensive living kidney donors were used to classify each patient into one of three groups; no GSG, GSG normal for age, or GSG abnormal for age. The risk of end-stage renal disease or a 40% decline in glomerular filtration rate during follow-up was then compared between groups. Among the 425 patients studied, 170 had no GSG, 107 had GSG normal for age, and 148 had GSG abnormal for age. Compared to those with no GSG, the risk of kidney disease progression with GSG normal for age was similar but was significantly higher with GSG abnormal for age. This increased risk with GSG abnormal for age remained significant after adjustment for interstitial fibrosis, arteriosclerosis, age, hypertension, diabetes, body mass index, glomerulopathy type, glomerular filtration rate, and proteinuria. Thus, in patients with glomerulopathy that often presents with nephrotic syndrome, global glomerulosclerosis is clinically important only if it exceeds that expected for age.

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.

The mitochondrial-targeted peptide, SS-31, improves glomerular architecture in mice of advanced age

Although age-associated changes in kidney glomerular architecture have been described in mice and man, the mechanisms are unknown. It is unclear if these changes can be prevented or even reversed by systemic therapies administered at advanced age. Using light microscopy and transmission electron microscopy, our results showed glomerulosclerosis with injury to mitochondria in glomerular epithelial cells in mice aged 26 months (equivalent to a 79-year-old human). To test the hypothesis that reducing mitochondrial damage in late age would result in lowered glomerulosclerosis, we administered the mitochondrial targeted peptide, SS-31, to aged mice. Baseline (24-month-old) mice were randomized to receive 8 weeks of SS-31, or saline, and killed at 26 months of age. SS-31 treatment improved age-related mitochondrial morphology and glomerulosclerosis. Assessment of glomeruli revealed that SS-31 reduced senescence (p16, senescence-associated-ß-Gal) and increased the density of parietal epithelial cells. However, SS-31 treatment reduced markers of parietal epithelial cell activation (Collagen IV, pERK1/2, and α-smooth muscle actin). SS-31 did not impact podocyte density, but it reduced markers of podocyte injury (desmin) and improved cytoskeletal integrity (synaptopodin). This was accompanied by higher glomerular endothelial cell density (CD31). Thus, despite initiating therapy in late-age mice, a short course of SS-31 has protective benefits on glomerular mitochondria, accompanied by temporal changes to the glomerular architecture. This systemic pharmacological intervention in old-aged animals limits glomerulosclerosis and senescence, reduces parietal epithelial cell activation, and improves podocyte and endothelial cell integrity.

Structural and Functional Changes With the Aging Kidney

Senescence or normal physiologic aging portrays the expected age-related changes in the kidney as compared to a disease that occurs in some but not all individuals. The microanatomical structural changes of the kidney with older age include a decreased number of functional glomeruli from an increased prevalence of nephrosclerosis (arteriosclerosis, glomerulosclerosis, and tubular atrophy with interstitial fibrosis), and to some extent, compensatory hypertrophy of remaining nephrons. Among the macroanatomical structural changes, older age associates with smaller cortical volume, larger medullary volume until middle age, and larger and more numerous kidney cysts. Among carefully screened healthy kidney donors, glomerular filtration rate (GFR) declines at a rate of 6.3 mL/min/1.73 m(2) per decade. There is reason to be concerned that the elderly are being misdiagnosed with CKD. Besides this expected kidney function decline, the lowest risk of mortality is at a GFR of ≥75 mL/min/1.73 m(2) for age <55 years but at a lower GFR of 45 to 104 mL/min/1.73 m(2) for age ≥65 years. Changes with normal aging are still of clinical significance. The elderly have less kidney functional reserve when they do actually develop CKD, and they are at higher risk for acute kidney injury.

Aging increases the susceptibility of hepatic inflammation, liver fibrosis and aging in response to high-fat diet in mice

We aimed to investigate whether aging increases the susceptibility of hepatic and renal inflammation or fibrosis in response to high-fat diet (HFD) and explore the underlying genetic alterations. Middle (10 months old) and old (20 months old) aged, male C57BL/6N mice were fed either a low-fat diet (4 % fat) or HFD (60 % fat) for 4 months. Young (3 months old) aged mice were included as control group. HFD-induced liver and kidney injuries were analyzed by serum and urine assay, histologic staining, immunohistochemistry, and reverse-transcription real-time quantitative polymerase chain reaction. Total RNA sequencing with next-generation technology was done with RNA extracted from liver tissues. With HFD feeding, aged was associated with higher serum alanine aminotransferase levels, marked infiltration of hepatic macrophages, and increased expression of inflammatory cytokines (MCP1, TNF-α, IL-1β, IL-6, IL-12, IL-17A). Importantly, aged mice showed more advanced hepatic fibrosis and increased expression of fibrogenic markers (Col-I-α1, αSMA, TGF-β1, TGF-β2, TGFβRII, PDGF, PDGFRβII, TIMP1) in response to HFD. Aged mice fed on HFD also showed increased oxidative stress and TLR4 expression. In the total RNA seq and gene ontology analysis of liver, old-aged HFD group showed significant up-regulation of genes linked to innate immune response, immune response, defense response, inflammatory response compared to middle-aged HFD group. Meanwhile, aging and HFD feeding showed significant increase in glomerular size and mesangial area, higher urine albumin/creatinine ratio, and advanced renal inflammation or fibrosis. However, the difference of HFD-induced renal injury between old-aged group and middle-aged group was not significant. The susceptibility of hepatic fibrosis as well as hepatic inflammation in response to HFD was significantly increased with aging. In addition, aging was associated with glomerular alterations and increased renal inflammation or fibrosis, while the differential effect of aging on HFD-induced renal injury was not remarkable as shown in the liver.

Dietary fat composition influences glomerular and proximal convoluted tubule cell structure and autophagic processes in kidneys from calorie-restricted mice

Calorie restriction (CR) has been repeatedly shown to prevent cancer, diabetes, hypertension, and other age-related diseases in a wide range of animals, including non-human primates and humans. In rodents, CR also increases lifespan and is a powerful tool for studying the aging process. Recently, it has been reported in mice that dietary fat plays an important role in determining lifespan extension with 40% CR. In these conditions, animals fed lard as dietary fat showed an increased longevity compared with mice fed soybean or fish oils. In this paper, we study the effect of these dietary fats on structural and physiological parameters of kidney from mice maintained on 40% CR for 6 and 18 months. Analyses were performed using quantitative electron microcopy techniques and protein expression in Western blots. CR mitigated most of the analyzed age-related parameters in kidney, such as glomerular basement membrane thickness, mitochondrial mass in convoluted proximal tubules and autophagic markers in renal homogenates. The lard group showed improved preservation of several renal structures with aging when compared to the other CR diet groups. These results indicate that dietary fat modulates renal structure and function in CR mice and plays an essential role in the determination of health span in rodents.

Specific renal parenchymal-derived urinary extracellular vesicles identify age-associated structural changes in living donor kidneys

Non-invasive tests to identify age and early disease-associated pathology within the kidney are needed. Specific populations of urinary extracellular vesicles (EVs) could potentially be used for such a diagnostic test. Random urine samples were obtained from age- and sex-stratified living kidney donors before kidney donation. A biopsy of the donor kidney was obtained at the time of transplantation to identify nephron hypertrophy (larger glomerular volume, cortex per glomerulus and mean profile tubular area) and nephrosclerosis (% fibrosis, % glomerulosclerosis and arteriosclerosis). Renal parenchymal-derived EVs in cell-free urine were quantified by digital flow cytometry. The relationship between these EV populations and structural pathology on the kidney biopsy was assessed. Clinical characteristics of the kidney donors (n=138, age range: 20–70 years, 50% women) were within the normative range. Overall, urine from women contained more EVs than that from men. The number of exosomes, juxtaglomerular cells and podocyte marker–positive EVs decreased (p<0.05) with increasing age. There were fewer total EVs as well as EVs positive for mesangial cell, parietal cell, descending limb of Henle's loop (simple squamous epithelium), collecting tubule-intercalated cell and monocyte chemoattractant protein-1 markers (p<0.05) in persons with nephron hypertrophy. The number of EVs positive for intercellular adhesion molecule-1, juxtaglomerular cell, podocyte, parietal cell, proximal tubular epithelial cell, distal tubular epithelial cell and collecting duct cells were fewer (p<0.05) in persons with nephrosclerosis. EVs carrying markers of cells from the renal pelvis epithelium did not associate with any indices of nephron hypertrophy or nephrosclerosis. Therefore, specific populations of EVs derived from cells of the glomerulus and nephron associate with underlying kidney structural changes. Further validation of these findings in other cohorts is needed to determine their clinical utility.

Structural and Functional Changes With the Aging Kidney

Senescence or normal physiologic aging portrays the expected age-related changes in the kidney as compared to a disease that occurs in some but not all individuals. The microanatomical structural changes of the kidney with older age include a decreased number of functional glomeruli from an increased prevalence of nephrosclerosis (arteriosclerosis, glomerulosclerosis, and tubular atrophy with interstitial fibrosis), and to some extent, compensatory hypertrophy of remaining nephrons. Among the macroanatomical structural changes, older age associates with smaller cortical volume, larger medullary volume until middle age, and larger and more numerous kidney cysts. Among carefully screened healthy kidney donors, glomerular filtration rate (GFR) declines at a rate of 6.3 mL/min/1.73 m(2) per decade. There is reason to be concerned that the elderly are being misdiagnosed with CKD. Besides this expected kidney function decline, the lowest risk of mortality is at a GFR of ≥75 mL/min/1.73 m(2) for age <55 years but at a lower GFR of 45 to 104 mL/min/1.73 m(2) for age ≥65 years. Changes with normal aging are still of clinical significance. The elderly have less kidney functional reserve when they do actually develop CKD, and they are at higher risk for acute kidney injury.

The Inflammatory Transcription Factors NFκB, STAT1 and STAT3 Drive Age-Associated Transcriptional Changes in the Human Kidney

Human kidney function declines with age, accompanied by stereotyped changes in gene expression and histopathology, but the mechanisms underlying these changes are largely unknown. To identify potential regulators of kidney aging, we compared age-associated transcriptional changes in the human kidney with genome-wide maps of transcription factor occupancy from ChIP-seq datasets in human cells. The strongest candidates were the inflammation-associated transcription factors NFκB, STAT1 and STAT3, the activities of which increase with age in epithelial compartments of the renal cortex. Stimulation of renal tubular epithelial cells with the inflammatory cytokines IL-6 (a STAT3 activator), IFNγ (a STAT1 activator), or TNFα (an NFκB activator) recapitulated age-associated gene expression changes. We show that common DNA variants in RELA and NFKB1, the two genes encoding subunits of the NFκB transcription factor, associate with kidney function and chronic kidney disease in gene association studies, providing the first evidence that genetic variation in NFκB contributes to renal aging phenotypes. Our results suggest that NFκB, STAT1 and STAT3 underlie transcriptional changes and chronic inflammation in the aging human kidney.

The structure and function of human kidneys deteriorate steadily with age, yet little is known about the underlying causes of kidney aging. In this work, we first used a genomics approach to identify candidate regulators of gene expression changes in the aging human kidney and identified inflammation-related transcription factors NFκB, STAT1 and STAT3 as the top candidate regulators. We found that kidney aging is associated with activation of NFκB, STAT1 and STAT3 in the renal parenchyma, and that the gene expression signatures evoked by activation of these transcription factors in human renal epithelial cells mimics age-associated gene expression changes in the kidney. Furthermore, we identified specific genetic variants in the NFκB transcription factor genes RELA and NFKB1 that associate with renal function and chronic kidney disease in humans, implicating NFκB as a potential contributor to the pathogenesis of chronic kidney disease and renal dysfunction in old age. Our findings suggest that activation of the inflammatory transcription factors STAT1, STAT3 and NFκB underlie transcriptional changes and reduced renal function in the elderly.

NRF2 and NF-κB mRNA expression in chronic kidney disease: a focus on nondialysis patients

PURPOSE

To evaluate nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-kappaB (NF-κB) mRNA expression in nondialysis chronic kidney disease (CKD) patients, comparing with data from hemodialysis (HD) patients and healthy individuals.

METHODS

Twenty nondialysis CKD patients (62.0 ± 8.1 years old, 11 men, estimated glomerular filtration rate of 36.8 ± 13.6 mL/min/1.73 m(2)), twenty HD patients (55.0 ± 15.2 years old, 13 men, and dialysis vintage of 76.5 ± 46.3 months) and eleven healthy individuals (50.9 ± 8.0 years old, 6 men) were enrolled in the study. The peripheral blood mononuclear cells were isolated and processed for the evaluation of expression of NF-κB and Nrf2 by quantitative real-time polymerase chain reaction.

RESULTS

Nrf2 mRNA expression was significantly higher in nondialysis (1.12 ± 0.57) when compared to HD patients (0.58 ± 0.35, p = 0,006) but similar to healthy individuals (1.13 ± 0.64). Inversely, NF-κB mRNA expression was lower in nondialysis (1.21 ± 0.71) when compared to HD patients (2.08 ± 0.7, p < 0.0001) and similar to healthy individuals (1.04 ± 0.22). Nrf2 mRNA was positively correlated with NF-κB mRNA expression in nondialysis CKD patients (r = 0.52, p = 0.02) and healthy individuals (r = 0.77, p < 0.006). By contrast, Nrf2 mRNA was inversely correlated with NF-κB mRNA expression (r = -0.65, p = 0.003) in HD patients.

CONCLUSION

Nondialysis CKD patients may conserve regular homeostatic balance between Nrf2 and NF-κB expressions, being comparable to healthy individuals. However, HD patients seem to have Nrf2 downregulation and NF-κB upregulation. Thus, the association among Nrf2 and NF-κB expressions and nutritional status, kidney disease progression or immune deregulation deserve further investigation.

A roadmap for the genetic analysis of renal aging

Several studies show evidence for the genetic basis of renal disease, which renders some individuals more prone than others to accelerated renal aging. Studying the genetics of renal aging can help us to identify genes involved in this process and to unravel the underlying pathways. First, this opinion article will give an overview of the phenotypes that can be observed in age-related kidney disease. Accurate phenotyping is essential in performing genetic analysis. For kidney aging, this could include both functional and structural changes. Subsequently, this article reviews the studies that report on candidate genes associated with renal aging in humans and mice. Several loci or candidate genes have been found associated with kidney disease, but identification of the specific genetic variants involved has proven to be difficult. CUBN, UMOD, and SHROOM3 were identified by human GWAS as being associated with albuminuria, kidney function, and chronic kidney disease (CKD). These are promising examples of genes that could be involved in renal aging, and were further mechanistically evaluated in animal models. Eventually, we will provide approaches for performing genetic analysis. We should leverage the power of mouse models, as testing in humans is limited. Mouse and other animal models can be used to explain the underlying biological mechanisms of genes and loci identified by human GWAS. Furthermore, mouse models can be used to identify genetic variants associated with age-associated histological changes, of which Far2, Wisp2, and Esrrg are examples. A new outbred mouse population with high genetic diversity will facilitate the identification of genes associated with renal aging by enabling high-resolution genetic mapping while also allowing the control of environmental factors, and by enabling access to renal tissues at specific time points for histology, proteomics, and gene expression.

The Expression Changes of Inflammasomes in the Aging Rat Kidneys

The mechanisms of kidney aging are not yet clear. Studies have shown that immunological inflammation is related to kidney aging. Inflammasomes are important components of innate immune system in the body. However, the function of inflammasomes and their underlying mechanisms in renal aging remain unclear. In this study, for the first time, we systematically investigated the role of the inflammasomes and the inflammatory responses activated by inflammasomes during kidney aging. We found that during kidney aging, the expression levels of the molecules associated with the activation of inflammasomes, including toll-like receptor-4 and interleukin-1 receptor (IL-1R), were significantly increased; their downstream signaling pathway molecule interleukin-1 receptor-associated kinase-4 (IRAK4) was markedly activated (Phospho-IRAK4 was obviously increased); the nuclear factor-κB (NF-κB) signaling pathway was activated (the activated NF-κB pathway molecules Phospho-IKKβ, Phospho-IκBα, and Phospho-NF-κBp65 were significantly elevated); the levels of the inflammasome components NOD-like receptor P3 (NLRP3), NLRC4, and pro-caspase-1 were prominently upregulated; and the proinflammatory cytokines IL-1β and IL-18 were notably increased in the kidneys of 24-month-old (elderly group) rats. These results showed that inflammasomes are markedly activated during the renal aging process and might induce inflamm-aging by promoting the maturation and secretion of the proinflammatory cytokines IL-1β and IL-18.

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.

Calculating the Rate of Senescence From Mortality Data: An Analysis of Data From the ERA-EDTA Registry

The rate of senescence can be inferred from the acceleration by which mortality rates increase over age. Such a senescence rate is generally estimated from parameters of a mathematical model fitted to these mortality rates. However, such models have limitations and underlying assumptions. Notably, they do not fit mortality rates at young and old ages. Therefore, we developed a method to calculate senescence rates from the acceleration of mortality directly without modeling the mortality rates. We applied the different methods to age group-specific mortality data from the European Renal Association-European Dialysis and Transplant Association Registry, including patients with end-stage renal disease on dialysis, who are known to suffer from increased senescence rates (n = 302,455), and patients with a functioning kidney transplant (n = 74,490). From age 20 to 70, senescence rates were comparable when calculated with or without a model. However, when using non-modeled mortality rates, senescence rates were yielded at young and old ages that remained concealed when using modeled mortality rates. At young ages senescence rates were negative, while senescence rates declined at old ages. In conclusion, the rate of senescence can be calculated directly from non-modeled mortality rates, overcoming the disadvantages of an indirect estimation based on modeled mortality rates.

Oral anticoagulants in older adults with atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in adults and contributes directly to adverse clinical events, ranging from ischemic stroke to heart failure and cardiovascular death. Because the incidence of AF and its attendant complications increase with age, there is a strong and growing need to develop safe, effective and widely available therapies. The following review summarizes the use of oral anticoagulants in older adults with AF, focusing on practical topics such as drug metabolism, drug-drug interactions, co-morbidities and cost considerations in a complex payer environment.

Cells of renin lineage take on a podocyte phenotype in aging nephropathy

Aging nephropathy is characterized by podocyte depletion accompanied by progressive glomerulosclerosis. Replacement of terminally differentiated podocytes by local stem/progenitor cells is likely a critical mechanism for their regeneration. Recent studies have shown that cells of renin lineage (CoRL), normally restricted to the kidney's extraglomerular compartment, might serve this role after an abrupt depletion in podocyte number. To determine the effects of aging on the CoRL reserve and if CoRL moved from an extra- to the intraglomerular compartment during aging, genetic cell fate mapping was performed in aging Ren1cCre × Rs-ZsGreen reporter mice. Podocyte number decreased and glomerular scarring increased with advanced age. CoRL number decreased in the juxtaglomerular compartment with age. There was a paradoxical increase in CoRL in the intraglomerular compartment at 52 and 64 wk of age, where a subset coexpressed the podocyte proteins nephrin, podocin, and synaptopodin. Transmission electron microscopy studies showed that a subset of labeled CoRL in the glomerulus displayed foot processes, which attached to the glomerular basement membrane. No CoRL in the glomerular compartment stained for renin. These results suggest that, despite a decrease in the reserve, a subpopulation of CoRL moves to the glomerulus after chronic podocyte depletion in aging nephropathy, where they acquire a podocyte-like phenotype. This suggests that they might serve as adult podocyte stem/progenitor cells under these conditions, albeit in insufficient numbers to fully replace podocytes depleted with age.