Telomere shortening in kidneys with age

Pathological mechanisms of kidney disease in ageing

The kidney is a metabolically active organ that requires energy to drive processes such as tubular reabsorption and secretion, and shows a decline in function with advancing age. Various molecular mechanisms, including genomic instability, telomere attrition, inflammation, autophagy, mitochondrial function, and changes to the sirtuin and Klotho signalling pathways, are recognized regulators of individual lifespan and pivotal factors that govern kidney ageing. Thus, mechanisms that contribute to ageing not only dictate renal outcomes but also exert a substantial influence over life expectancy. Conversely, kidney dysfunction, in the context of chronic kidney disease (CKD), precipitates an expedited ageing trajectory in individuals, leading to premature ageing and a disconnect between biological and chronological age. As CKD advances, age-related manifestations such as frailty become increasingly conspicuous. Hence, the pursuit of healthy ageing necessitates not only the management of age-related complications but also a comprehensive understanding of the processes and markers that underlie systemic ageing. Here, we examine the hallmarks of ageing, focusing on the mechanisms by which they affect kidney health and contribute to premature organ ageing. We also review diagnostic methodologies and interventions for premature ageing, with special consideration given to the potential of emerging therapeutic avenues to target age-related kidney diseases.

SenNet recommendations for detecting senescent cells in different tissues

Once considered a tissue culture-specific phenomenon, cellular senescence has now been linked to various biological processes with both beneficial and detrimental roles in humans, rodents and other species. Much of our understanding of senescent cell biology still originates from tissue culture studies, where each cell in the culture is driven to an irreversible cell cycle arrest. By contrast, in tissues, these cells are relatively rare and difficult to characterize, and it is now established that fully differentiated, postmitotic cells can also acquire a senescence phenotype. The SenNet Biomarkers Working Group was formed to provide recommendations for the use of cellular senescence markers to identify and characterize senescent cells in tissues. Here, we provide recommendations for detecting senescent cells in different tissues based on a comprehensive analysis of existing literature reporting senescence markers in 14 tissues in mice and humans. We discuss some of the recent advances in detecting and characterizing cellular senescence, including molecular senescence signatures and morphological features, and the use of circulating markers. We aim for this work to be a valuable resource for both seasoned investigators in senescence-related studies and newcomers to the field.

Cellular senescence and kidney aging

Life expectancy is increasing worldwide, and by 2050 the proportion of the world's population over 65 years of age is estimated to surpass 1.5 billion. Kidney aging is associated with molecular and physiological changes that cause a loss of renal function and of regenerative potential. As the aging population grows, it is crucial to understand the mechanisms underlying these changes, as they increase the susceptibility to developing acute kidney injury (AKI) and chronic kidney disease (CKD). Various cellular processes and molecular pathways take part in the complex process of kidney aging. In this review, we will focus on the phenomenon of cellular senescence as one of the involved mechanisms at the crossroad of kidney aging, age-related disease, and CKD. We will highlight experimental and clinical findings about the role of cellular senescence in kidney aging and CKD. In addition, we will review challenges in senescence research and emerging therapeutic aspects. We will highlight the great potential of senolytic strategies for the elimination of harmful senescent cells to promote healthy kidney aging and to avoid age-related disease and CKD. This review aims to give insight into recent discoveries and future developments, providing a comprehensive overview of current knowledge on cellular senescence and anti-senescent therapies in the kidney field.

Differential Methylation of Telomere-Related Genes Is Associated with Kidney Disease in Individuals with Type 1 Diabetes

Diabetic kidney disease (DKD) represents a major global health problem. Accelerated ageing is a key feature of DKD and, therefore, characteristics of accelerated ageing may provide useful biomarkers or therapeutic targets. Harnessing multi-omics, features affecting telomere biology and any associated methylome dysregulation in DKD were explored. Genotype data for nuclear genome polymorphisms in telomere-related genes were extracted from genome-wide case-control association data (n = 823 DKD/903 controls; n = 247 end-stage kidney disease (ESKD)/1479 controls). Telomere length was established using quantitative polymerase chain reaction. Quantitative methylation values for 1091 CpG sites in telomere-related genes were extracted from epigenome-wide case-control association data (n = 150 DKD/100 controls). Telomere length was significantly shorter in older age groups (p = 7.6 × 10^-6). Telomere length was also significantly reduced (p = 6.6 × 10^-5) in DKD versus control individuals, with significance remaining after covariate adjustment (p = 0.028). DKD and ESKD were nominally associated with telomere-related genetic variation, with Mendelian randomisation highlighting no significant association between genetically predicted telomere length and kidney disease. A total of 496 CpG sites in 212 genes reached epigenome-wide significance (p ≤ 10^-8) for DKD association, and 412 CpG sites in 193 genes for ESKD. Functional prediction revealed differentially methylated genes were enriched for Wnt signalling involvement. Harnessing previously published RNA-sequencing datasets, potential targets where epigenetic dysregulation may result in altered gene expression were revealed, useful as potential diagnostic and therapeutic targets for intervention.

Harnessing Genomic Analysis to Explore the Role of Telomeres in the Pathogenesis and Progression of Diabetic Kidney Disease

The prevalence of diabetes is increasing globally, and this trend is predicted to continue for future decades. Research is needed to uncover new ways to manage diabetes and its co-morbidities. A significant secondary complication of diabetes is kidney disease, which can ultimately result in the need for renal replacement therapy, via dialysis or transplantation. Diabetic kidney disease presents a substantial burden to patients, their families and global healthcare services. This review highlights studies that have harnessed genomic, epigenomic and functional prediction tools to uncover novel genes and pathways associated with DKD that are useful for the identification of therapeutic targets or novel biomarkers for risk stratification. Telomere length regulation is a specific pathway gaining attention recently because of its association with DKD. Researchers are employing both observational and genetics-based studies to identify telomere-related genes associated with kidney function decline in diabetes. Studies have also uncovered novel functions for telomere-related genes beyond the immediate regulation of telomere length, such as transcriptional regulation and inflammation. This review summarises studies that have revealed the potential to harness therapeutics that modulate telomere length, or the associated epigenetic modifications, for the treatment of DKD, to potentially slow renal function decline and reduce the global burden of this disease.

Telomere Attrition in Chronic Kidney Diseases

Telomeres are dynamic DNA nucleoprotein structures located at the end of chromosomes where they maintain genomic stability. Due to the end replication problem, telomeres shorten with each cell division. Critically short telomeres trigger cellular senescence, which contributes to various degenerative and age-related diseases, including chronic kidney diseases (CKDs). Additionally, other factors such as oxidative stress may also contribute to accelerated telomere shortening. Indeed, telomeres are highly susceptible to oxidative damage due to their high guanine content. Here, we provide a comprehensive review of studies examining telomere length (TL) in CKDs to highlight the association between TL and the development and progression of CKDs in humans. We then focus on studies investigating TL in patients receiving kidney replacement therapy. The mechanisms of the relationship between TL and CKD are not fully understood, but a shorter TL has been associated with decreased kidney function and the progression of nephropathy. Interestingly, telomere lengthening has been observed in some patients in longitudinal studies. Hemodialysis has been shown to accelerate telomere erosion, whereas the uremic milieu is not reversed even in kidney transplantation patients. Overall, this review aims to provide insights into the biological significance of telomere attrition in the pathophysiology of kidney disease, which may contribute to the development of new strategies for the management of patients with CKDs.

Influence of telomerase activity and initial distribution on human follicular aging: Moving from a discrete to a continuum model

A discrete model is proposed for the temporal evolution of a population of cells sorted according to their telomeric length. This model assumes that, during cell division, the distribution of the genetic material to daughter cells is asymmetric, i.e. chromosomes of one daughter cell have the same telomere length as the mother, while in the other daughter cell telomeres are shorter. Telomerase activity and cell death are also taken into account. The continuous model is derived from the discrete model by introducing the generational age as a continuous variable in [0,h], being h the Hayflick limit, i.e. the number of times that a cell can divide before reaching the senescent state. A partial differential equation with boundary conditions is obtained. The solution to this equation depends on the initial telomere length distribution. The initial and boundary value problem is solved exactly when the initial distribution is of exponential type. For other types of initial distributions, a numerical solution is proposed. The model is applied to the human follicular growth from preantral to preovulatory follicle as a case study and the aging rate is studied as a function of telomerase activity, the initial distribution and the Hayflick limit. Young, middle and old cell-aged initial normal distributions are considered. In all cases, when telomerase activity decreases, the population ages and the smaller the h value, the higher the aging rate becomes. However, the influence of these two parameters is different depending on the initial distribution. In conclusion, the worst-case scenario corresponds to an aged initial telomere distribution.

DNA Methylation - and Telomere - Based Biological Age Estimation as Markers of Biological Aging in Donors Kidneys

The biological age of an organ may represent a valuable tool for assessing its quality, especially in the elder. We examined the biological age of the kidneys [right (RK) and left kidney (LK)] and blood leukocytes in the same subject and compared these to assess whether blood mirrors kidney biological aging. Biological age was studied in n = 36 donors (median age: 72 years, range: 19-92; male: 42%) by exploring mitotic and non-mitotic pathways, using telomere length (TL) and age-methylation changes (DNAmAge) and its acceleration (AgeAcc). RK and LK DNAmAge are older than blood DNAmAge (RK vs. Blood, p = 0.0271 and LK vs. Blood, p = 0.0245) and RK and LK AgeAcc present higher score (this mean the AgeAcc is faster) than that of blood leukocytes (p = 0.0271 and p = 0.0245) in the same donor. TL of RK and LK are instead longer than that of blood (p = 0.0011 and p = 0.0098) and the increase in Remuzzi-Karpinski score is strongly correlated with kidney TL attrition (p = 0.0046). Finally, blood and kidney TL (p < 0.01) and DNAmAge (p < 0.001) were correlated. These markers can be evaluated in further studies as indicators of biological age of donor organ quality and increase the usage of organs from donors of advanced age therefore offering a potential translational research inkidney transplantation.

Renal Senescence, Telomere Shortening and Nitrosative Stress in Feline Chronic Kidney Disease

Kidney tissues from cats with naturally occurring chronic kidney disease (CKD) and adult and senior cats without CKD were assessed to determine whether telomere shortening and nitrosative stress are associated with senescence in feline CKD. The histopathologic assessment of percent global glomerulosclerosis, inflammatory infiltrate, and fibrosis was performed. Senescence and nitrosative stress were evaluated utilizing p16 and iNOS immunohistochemistry, respectively. Renal telomere length was evaluated using telomere fluorescent in situ hybridization combined with immunohistochemistry. CKD cats were found to have significantly increased p16 staining in both the renal cortex and corticomedullary junction compared to adult and senior cats. Senior cats had significantly increased p16 staining in the corticomedullary junction compared to adult cats. p16 staining in both the renal cortex and corticomedullary junction were found to be significantly correlated with percent global glomerulosclerosis, cortical inflammatory infiltrate, and fibrosis scores. p16 staining also correlated with age in non-CKD cats. Average telomere length was significantly decreased in CKD cats compared to adult and senior cats. CKD cats had significantly increased iNOS staining compared to adult cats. Our results demonstrate increased renal senescence, telomere shortening, and nitrosative stress in feline CKD, identifying these patients as potential candidates for senolytic therapy with translational potential.

Association of leukocyte telomere length with chronic kidney disease in East Asians with type 2 diabetes: a Mendelian randomization study

Background

Chronic kidney disease (CKD) is common among people with type 2 diabetes (T2D), and increases the risk of kidney failure and cardiovascular diseases. Shorter leukocyte telomere length (LTL) is associated with CKD in patients with T2D. We previously reported single-nucleotide polymorphisms (SNPs) associated with LTL in an Asian population. In this study, we elucidated the association of these SNPs with CKD in patients with T2D using the Mendelian randomization (MR) approach.

Methods

The cross-sectional association of 16 LTL SNPs with CKD, defined as an estimated glomerular filtration rate of <60 mL/min/1.73 m², was assessed among 4768 (1628 cases and 3140 controls) participants in the Singapore Study of Macro-angiopathy and Micro-vascular Reactivity in T2D and Diabetic Nephropathy cohorts. MR analysis was performed using the random-effect inverse-variance weighted (IVW) method, the weighted median, MR-Egger and Radial MR adjusted for age and sex-stratified by cohorts and ethnicity (Chinese and Malays), then meta-analyzed.

Results

Genetically determined shorter LTL was associated with increased risk of CKD in patients with T2D (meta-IVW adjusted odds ratio = 1.51, 95% confidence interval 1.12–2.12, P = 0.007, P_het = 0.547). Similar results were obtained following sensitivity analysis. MR-Egger analysis (intercept) suggested no evidence of horizontal pleiotropy (β = 0.010, P = 0.751).

Conclusions

Our findings suggest that genetically determined LTL is associated with CKD in patients with T2D. Further studies are warranted to elucidate the causal role of telomere length in CKD progression.

Cellular senescence inhibits renal regeneration after injury in mice, with senolytic treatment promoting repair

The ability of the kidney to regenerate successfully after injury is lost with advancing age, chronic kidney disease, and after irradiation. The factors responsible for this reduced regenerative capacity remain incompletely understood, with increasing interest in a potential role for cellular senescence in determining outcomes after injury. Here, we demonstrated correlations between senescent cell load and functional loss in human aging and chronic kidney diseases including radiation nephropathy. We dissected the causative role of senescence in the augmented fibrosis occurring after injury in aged and irradiated murine kidneys. In vitro studies on human proximal tubular epithelial cells and in vivo mouse studies demonstrated that senescent renal epithelial cells produced multiple components of the senescence-associated secretory phenotype including transforming growth factor β1, induced fibrosis, and inhibited tubular proliferative capacity after injury. Treatment of aged and irradiated mice with the B cell lymphoma 2/w/xL inhibitor ABT-263 reduced senescent cell numbers and restored a regenerative phenotype in the kidneys with increased tubular proliferation, improved function, and reduced fibrosis after subsequent ischemia-reperfusion injury. Senescent cells are key determinants of renal regenerative capacity in mice and represent emerging treatment targets to protect aging and vulnerable kidneys in man.

Angiotensin inhibition and cellular senescence in the developing rat kidney

Cellular senescence is important for the maintenance of tissue homeostasis during normal development. In this study, we aimed to investigate the effect of renin angiotensin system (RAS) blockade on renal cell senescence in the developing rat kidney. Newborn rat pups were treated with enalapril (30 mg/kg/day) or vehicle for seven days after birth. We investigated the intrarenal expressions of cell cycle regulators p21 and p16 with immunoblots and immunohistochemistry at postnatal day 8. For the determination of renal cellular senescence, immunostaining for senescence-associated β-galactosidase (SA-β-gal) and telomerase reverse transcriptase (TERT) was also performed. Enalapril treatment showed significant alterations in cellular senescence in neonatal rat kidneys. In the enalapril-treated group, intrarenal p16 and p21 protein expressions decreased compared to controls. The expressions of both p21 and p16 were reduced throughout the renal cortex and medulla of enalapril-treated rats. The immunoreactivity of TERT in enalapril-treated kidneys was also weaker than that in control kidneys. Control kidneys revealed a clear positive SA-β-gal signal in the cortical tubules; however, SA-β-gal activity was noticeably lower in the enalapril-treated kidneys than in control kidneys. Interruption of the RAS during postnatal nephrogenesis may disrupt physiologic renal cellular senescence in the developing rat kidney.

Accelerated Kidney Aging in Diabetes Mellitus

With aging, the kidney undergoes inexorable and progressive changes in structural and functional performance. These aging-related alterations are more obvious and serious in diabetes mellitus (DM). Renal accelerated aging under DM conditions is associated with multiple stresses such as accumulation of advanced glycation end products (AGEs), hypertension, oxidative stress, and inflammation. The main hallmarks of cellular senescence in diabetic kidneys include cyclin-dependent kinase inhibitors, telomere shortening, and diabetic nephropathy-associated secretory phenotype. Lysosome-dependent autophagy and antiaging proteins Klotho and Sirt1 play a fundamental role in the accelerated aging of kidneys in DM, among which the autophagy-lysosome system is the convergent mechanism of the multiple antiaging pathways involved in renal aging under DM conditions. Metformin and the inhibitor of sodium-glucose cotransporter 2 are recommended due to their antiaging effects independent of antihyperglycemia, besides angiotensin-converting enzyme inhibitors/angiotensin receptor blockers. Additionally, diet intervention including low protein and low AGEs with antioxidants are suggested for patients with diabetic nephropathy (DN). However, their long-term benefits still need further study. Exploring the interactive relationships among antiaging protein Klotho, Sirt1, and autophagy-lysosome system may provide insight into better satisfying the urgent medical needs of elderly patients with aging-related DN.

Chronic Kidney Disease: A Vicarious Relation to Premature Cell Senescence

Chronic kidney disease (CKD), commonly fostering nonrenal complications, themselves more life threatening than renal pathology, remains enigmatic. Despite more than a century of intense research, therapeutic options to halt or reverse renal disease are rather limited. Recently, similarity between manifestations of progressive CKD and aging kidney has attracted investigative attention that revealed senescent cells and secreting proinflammatory and profibrotic mediators in all renal compartments, even at young age, in patients with kidney maladies. The overlapping features of these categories have been noticed previously and are briefly summarized herein. I propose two hypothetical scenarios for interactive association of kidney diseases and cell senescence, both culminating in progressive deterioration of renal function. Persistence of senescent cells is considered as a critical contributor to this association; and the mechanisms explaining persistence, such as activation of cell cycle regulators, anti-apoptotic stimuli, metabolic aberrations, and their interactions, are discussed. The mutual encroachment of underlying kidney disease and cell senescence bring about the conclusion that both entities merge along the natural history of the disease. This putative interpretation of vicarious relation between cell senescence and CKD may expand the arsenal of pharmacotherapy to include the judicious use of senotherapeutics in the management of renal disease.

Inhibition of the H3K4 methyltransferase MLL1/WDR5 complex attenuates renal senescence in ischemia reperfusion mice by reduction of p16INK4a

Renal function declines with aging and is pathologically characterized by chronic inflammation and fibrosis. Renal senescence is induced not only by aging but also by various stimuli, including ischemia reperfusion injury. Recently, the accumulation of p16^INK4a-positive cells in the kidney has been considered a molecular feature of renal senescence, with the p16^INK4a gene reportedly regulated by mixed-lineage leukemia 1 (MLL1)/WD-40 repeat protein 5 (WDR5)-mediated histone 3 lysine 4 trimethylation (H3K4me3). Here, we determined whether inhibition of MLL1/WDR5 activity attenuates renal senescence, inflammation, and fibrosis in mice with ischemia reperfusion injury and in cultured rat renal fibroblasts. MM-102 or OICR-9429, both MLL1/WDR5 protein-protein interaction inhibitors, and small interfering RNA (siRNA) for MLL1 or WDR5 suppressed the expression of p16^INK4a in mice with ischemia reperfusion injury, accompanied by downregulation of H3K4me3 expression. MM-102 attenuated renal fibrosis and inflammation in the kidney of mice with ischemia reperfusion injury. Moreover, in vitro study showed that transforming growth factor-β1 induced the expression of MLL1, WDR5, H3K4me3, and p16^INK4a. Finally, chromatin immunoprecipitation identified the p16^INK4a promoter at an H3K4me3 site in renal fibroblasts. Thus, our findings show that H3K4me3 inhibition ameliorates ischemia reperfusion-induced renal senescence along with fibrosis and inflammation.

Rejuvenation: Turning back the clock of aging kidney

Aging is inevitable in life. It is defined as impaired adaptive capacity to environmental or internal stresses with growing rates of disease and death. Aging is also an important risk factor for various kidney diseases such as acute kidney injury and chronic kidney disease. Patients older than 65 years have nearly 28% risk of failing recovery of kidney function when suffering from acute kidney injury. It is reported that more than a third of population aged 65 years and older have chronic kidney disease in Taiwan, and the occurrence of multiple age-related disorders is predicted to increase in parallel. Renal aging is a complex, multifactorial process characterized by many anatomical and functional changes. Several factors are involved in renal aging, such as loss of telomeres, cell cycle arrest, chronic inflammation, activation of renin-angiotensin system, decreased klotho expression, and development of tertiary lymphoid tissues. These changes can also be observed in many other different types of renal injury. Recent studies suggested that young blood may rejuvenate aged organs, including the kidneys. In order to develop new therapeutic strategies for renal aging, the mechanisms underlying renal aging and by which young blood can halt or reverse aging process warrants further study.

Genetic Susceptibility to Chronic Kidney Disease - Some More Pieces for the Heritability Puzzle

Chronic kidney disease (CKD) is a major global health problem with an increasing prevalence partly driven by aging population structure. Both genomic and environmental factors contribute to this complex heterogeneous disease. CKD heritability is estimated to be high (30-75%). Genome-wide association studies (GWAS) and GWAS meta-analyses have identified several genetic loci associated with CKD, including variants in UMOD, SHROOM3, solute carriers, and E3 ubiquitin ligases. However, these genetic markers do not account for all the susceptibility to CKD, and the causal pathways remain incompletely understood; other factors must be contributing to the missing heritability. Less investigated biological factors such as telomere length; mitochondrial proteins, encoded by nuclear genes or specific mitochondrial DNA (mtDNA) encoded genes; structural variants, such as copy number variants (CNVs), insertions, deletions, inversions and translocations are poorly covered and may explain some of the missing heritability. The sex chromosomes, often excluded from GWAS studies, may also help explain gender imbalances in CKD. In this review, we outline recent findings on molecular biomarkers for CKD (telomeres, CNVs, mtDNA variants, sex chromosomes) that typically have received less attention than gene polymorphisms. Shorter telomere length has been associated with renal dysfunction and CKD progression, however, most publications report small numbers of subjects with conflicting findings. CNVs have been linked to congenital anomalies of the kidney and urinary tract, posterior urethral valves, nephronophthisis and immunoglobulin A nephropathy. Information on mtDNA biomarkers for CKD comes primarily from case reports, therefore the data are scarce and diverse. The most consistent finding is the A3243G mutation in the MT-TL1 gene, mainly associated with focal segmental glomerulosclerosis. Only one GWAS has found associations between X-chromosome and renal function (rs12845465 and rs5987107). No loci in the Y-chromosome have reached genome-wide significance. In conclusion, despite the efforts to find the genetic basis of CKD, it remains challenging to explain all of the heritability with currently available methods and datasets. Although additional biomarkers have been investigated in less common suspects such as telomeres, CNVs, mtDNA and sex chromosomes, hidden heritability in CKD remains elusive, and more comprehensive approaches, particularly through the integration of multiple -"omics" data, are needed.

Genetic susceptibility to delayed graft function following kidney transplantation: a systematic review of the literature

Delayed graft function (DGF) is defined as the need for dialysis within 7 days following kidney transplantation (KTx). DGF is associated with increased costs, higher risk for acute rejection and decreased long-term graft function. Renal ischaemia/reperfusion (I/R) injury plays a major role in DGF occurrence. Single nucleotide polymorphisms (SNPs) in certain genes may aggravate kidney susceptibility to I/R injury, thereby worsening post-transplant outcomes. The present article proposes an extensive review of the literature about the putative impact of donor or recipient SNPs on DGF occurrence in kidney transplant recipients (KTRs). Among 30 relevant PubMed reports, 16 articles identified an association between 18 SNPs and DGF. These polymorphisms concern 14 different well-known genes and one not-yet-identified gene located on chromosome 18. They have been categorized into five groups according to the role of the corresponding proteins in I/R cascade: (i) oxidative stress, (ii) telomere shortening, (iii) chemokines, (iv) T-cell homeostasis and (v) metabolism of anti-inflammatory molecules. The remaining 14 studies failed to demonstrate any association between the studied SNPs and the occurrence of DGF. A better understanding of the genetic susceptibility to renal I/R injury may help prevent DGF and improve clinical outcomes in KTRs.

The age of heterozygous telomerase mutant parents influences the adult phenotype of their offspring irrespective of genotype in zebrafish

Background: Mutations in proteins involved in telomere maintenance lead to a range of human diseases, including dyskeratosis congenita, idiopathic pulmonary fibrosis and cancer. Telomerase functions to add telomeric repeats back onto the ends of chromosomes, however non-canonical roles of components of telomerase have recently been suggested.

Methods: Here we use a zebrafish telomerase mutant which harbours a nonsense mutation in tert to investigate the adult phenotypes of fish derived from heterozygous parents of different ages. Furthermore we use whole genome sequencing data to estimate average telomere lengths.

Results: We show that homozygous offspring from older heterozygotes exhibit signs of body wasting at a younger age than those of younger parents, and that offspring of older heterozygous parents weigh less irrespective of genotype. We also demonstrate that tert homozygous mutant fish have a male sex bias, and that clutches from older parents also have a male sex bias in the heterozygous and wild-type populations. Telomere length analysis reveals that the telomeres of younger heterozygous parents are shorter than those of older heterozygous parents.

Conclusions: These data indicate that the phenotypes observed in offspring from older parents cannot be explained by telomere length. Instead we propose that Tert functions outside of telomere length maintenance in an age-dependent manner to influence the adult phenotypes of the next generation.

Concepts of Genomics in Kidney Transplantation

Purpose of review

Identification of genetic variants to aid in individualized treatment of solid organ allograft recipients would improve graft survival. We will review the current state of knowledge for associations of variants with transplant outcomes.

Recent findings

Many studies have yet to exhibit robust and reproducible results, however, pharmacogenomic studies focusing on cytochrome P450 (CYP) enzymes, transporters and HLA variants have shown strong associations with outcomes and have relevance towards drugs used in transplant. Genome wide association study data for the immunosuppressant tacrolimus have identified multiple variants in the CYP3A5 gene associated with trough concentrations. Additionally, APOL1 variants had been shown to confer risk to the development of end stage renal disease in African Americans.

Summary

The field is rapidly evolving and new technology such as next generation sequencing, along with larger cohorts, will soon be commonly applied in transplantation to understand genetic association with outcomes and personalized medicine.

The age of heterozygous telomerase mutant parents influences the adult phenotype of their offspring irrespective of genotype in zebrafish

Background: Mutations in proteins involved in telomere maintenance lead to a range of human diseases, including dyskeratosis congenita, idiopathic pulmonary fibrosis and cancer. Telomerase functions to add telomeric repeats back onto the ends of chromosomes, however non-canonical roles of components of telomerase have recently been suggested.Methods: Here we use a zebrafish telomerase mutant which harbours a nonsense mutation intertto investigate the adult phenotypes of fish derived from heterozygous parents of different ages. Furthermore we use whole genome sequencing data to estimate average telomere lengths.Results: We show that homozygous offspring from older heterozygotes exhibit signs of body wasting at a younger age than those of younger parents, and that offspring of older heterozygous parents weigh less irrespective of genotype. We also demonstrate thatterthomozygous mutant fish have a male sex bias, and that clutches from older parents also have a male sex bias in the heterozygous and wild-type populations. Telomere length analysis reveals that the telomeres of younger heterozygous parents are shorter than those of older heterozygous parents.Conclusions: These data indicate that the phenotypes observed in offspring from older parents cannot be explained by telomere length. Instead we propose that Tert functions outside of telomere length maintenance in an age-dependent manner to influence the adult phenotypes of the next generation.

Identification of the activating cytotoxicity receptor NKG2D as a senescence marker in zero-hour kidney biopsies is indicative for clinical outcome

The definition of biological donor organ age rather than chronological age seems obvious for the establishment of a valid pre-transplant risk assessment. Therefore, we studied gene expression for candidate markers in 60 zero-hour kidney biopsies. Compared with 29 younger donors under age 55, 31 elderly donors age 55 and older had significant mRNA expression for immunoproteasome subunits (PSMB8, PSMB9 and PSMB10), HLA-DRB, and transcripts of the activating cytotoxicity receptor NKG2D. Gene expression was validated in an independent donor cohort consisting of 37 kidneys from donors 30 years and under (Group I), 75 kidneys from donors age 31-54 years (Group II) and 75 kidneys from donors age 55 and older (Group III). Significant gene induction was confirmed in kidneys from Group III for PSMB9 and PSMB10. Strikingly, transcripts of NKG2D had the significantly highest gene induction in Group III versus Group II and Group I. Similar results were obtained for CDKN2A, but not for telomere length. Both NKG2D and CDKN2A mRNA expression were significantly correlated with creatinine levels at 24 months after transplantation. Univariate regression analysis showed significant predictive power regarding graft function at 6 and 12 months for NKG2D and CDKN2A. However, only NKG2D remained significantly predictive in the multivariate model at 12 months. Thus, our results reveal novel candidate markers in aged renal allografts, which could be helpful in the assessment of organ quality.

Telomere Length Assessment for Prediction of Organ Transplantation Outcome. Future or Failure: A Review of the Literature

Telomeres are located at each end of eukaryotic chromosomes. Their functional role is genomic stability maintenance. The protective role of telomeres depends on various factors, including number of nucleotides repeats, telomere-binding proteins, and telomerase activity. Organ transplantation is the preferred replacement therapy in the case of chronic kidney disease and the only possibility of sustaining recipients’ life in the case of advanced liver failure. While the prevalence of acute rejection is constantly decreasing, prevention of transplanted organ long-term function loss is still challenging. It has been demonstrated that post-transplant stressors accelerate aging of the allografts manifested through telomere shortening.

The aim of this paper was to evaluate the importance of telomere length assessment for prediction of organ transplantation outcome. Literature review included the 10 most important studies regarding linkage between allograft function and telomere erosion, including 2 of our own reports.

Telomere length assessment is useful to predict organ transplantation outcome. The importance of telomere length as a prediction marker depends on the analyzed material. To obtain reliable results, both graft cells (donor material) and lymphocytes (recipient material) should be examined. In the case of kidney transplantation, assessment of telomere length in the early post-transplant period allows prediction of the long-term function of the transplanted organ. To increase the accuracy of transplantation outcome prediction, telomere length assessment should be combined with evaluation of other aging biomarkers, like CDKN2A (p16). Large-scale clinical studies regarding telomere length measurement, including genome wide association analysis introducing relevant genetic factors, are needed for the future.

Renal Aging: Causes and Consequences

Individuals age >65 years old are the fastest expanding population demographic throughout the developed world. Consequently, more aged patients than before are receiving diagnoses of impaired renal function and nephrosclerosis-age-associated histologic changes in the kidneys. Recent studies have shown that the aged kidney undergoes a range of structural changes and has altered transcriptomic, hemodynamic, and physiologic behavior at rest and in response to renal insults. These changes impair the ability of the kidney to withstand and recover from injury, contributing to the high susceptibility of the aged population to AKI and their increased propensity to develop subsequent progressive CKD. In this review, we examine these features of the aged kidney and explore the various validated and putative pathways contributing to the changes observed with aging in both experimental animal models and humans. We also discuss the potential for additional study to increase understanding of the aged kidney and lead to novel therapeutic strategies.

Leukocyte Telomere Length in Relation to 17 Biomarkers of Cardiovascular Disease Risk: A Cross-Sectional Study of US Adults

BACKGROUND

Leukocyte telomere length (LTL) is a putative biological marker of immune system age, and there are demonstrated associations between LTL and cardiovascular disease. This may be due in part to the relationship of LTL with other biomarkers associated with cardiovascular disease risk. However, the strength of associations between LTL and adiposity, metabolic, proinflammatory, and cardiovascular biomarkers has not been systematically evaluated in a United States nationally representative population.

METHODS AND FINDINGS

We examined associations between LTL and 17 cardiovascular biomarkers, including lipoproteins, blood sugar, circulatory pressure, proinflammatory markers, kidney function, and adiposity measures, in adults ages 20 to 84 from the cross-sectional US nationally representative 1999-2002 National Health and Nutrition Examination Survey (NHANES) (n = 7,252), statistically adjusting for immune cell type distributions. We also examine whether these associations differed systematically by age, race/ethnicity, gender, education, and income. We found that a one unit difference in the following biomarkers were associated with kilobase pair differences in LTL: BMI -0.00478 (95% CI -0.00749--0.00206), waist circumference -0.00211 (95% CI -0.00325--0.000969), percentage of body fat -0.00516 (95% CI -0.00761--0.0027), high density lipoprotein (HDL) cholesterol 0.00179 (95% CI 0.000571-0.00301), triglycerides -0.000285 (95% CI -0.000555--0.0000158), pulse rate -0.00194 (95% CI -0.00317--0.000705), C-reactive protein -0.0363 (95% CI 0.0601--0.0124), cystatin C -0.0391 (95% CI -0.0772--0.00107). When using clinical cut-points we additionally found associations between LTL and insulin resistance -0.0412 (95% CI -0.0685--0.0139), systolic blood pressure 0.0455 (95% CI 0.00137-0.0897), and diastolic blood pressure -0.0674 (95% CI -0.126--0.00889). These associations were 10%-15% greater without controlling for leukocyte cell types. There were very few differences in the associations by age, race/ethnicity, gender, education, or income. Our findings are relevant to the relationships between these cardiovascular biomarkers in the general population but not to cardiovascular disease as a clinical outcome.

CONCLUSIONS

LTL is most strongly associated with adiposity, but is also associated with biomarkers across several physiological systems. LTL may thus be a predictor of cardiovascular disease through its association with multiple risk factors that are physiologically correlated with risk for development of cardiovascular disease. Our results are consistent with LTL being a biomarker of cardiovascular aging through established physiological mechanisms.

Telomere length, cardiovascular risk and arteriosclerosis in human kidneys: an observational cohort study

BACKGROUND

Replicative senescence, associated with telomere shortening, plays an important role in aging and cardiovascular disease. The relation between telomere length, cardiovascular risk, and renal disease is unknown.

METHODS

Our study consisted of a cohort of 257 kidney donors for transplantation, divided into a test and a validation cohort. We used quantitative RT-PCR to measure relative telomere length (log T/S ratio) in peripheral blood leucocytes, and in kidney biopsies performed prior to implantation. The association between leucocyte and intrarenal telomere length, cardiovascular risk factors, and renal histology, was studied using multiple regression models, adjusted for calendar age, gender and other donor demographics.

RESULTS

Subjects with intrarenal arteriosclerosis had significantly shorter leucocyte telomere length compared with patients without arteriosclerosis (log T/S ratio -0.3±0.4 vs. 0.1±0.2 with vs. without arteriosclerosis; p=0.0008). Intrarenal arteriosclerosis was associated with shorter telomere length, independent of gender, calendar age, history of hypertension and history of cardiovascular events. For each increase of one standard deviation of the log T/S ratio, the odds for intrarenal arteriosclerosis decreased with 64% (Odds ratio 0.36; 95% CI 0.17-0.77; p=0.02). In accordance with leucocyte telomere length, shorter intrarenal telomere length associated significantly with the presence of renal arteriosclerosis (log T/S ratio -0.04±0.06 vs. 0.08±0.01 with vs. without arteriosclerosis, p=0.007), and not with other histological lesions.

INTERPRETATION

We demonstrate that arteriosclerosis in smaller intrarenal arteries is associated with shorter telomere length. Our study suggests a central role of replicative senescence in the progression of renovascular disease, independent of calendar age.

Current Understanding of the Pathogenesis of Progressive Chronic Kidney Disease in Cats

In cats with chronic kidney disease (CKD), the most common histopathologic finding is tubulointerstitial inflammation and fibrosis. However, these changes reflect a nonspecific response of the kidney to any inciting injury. The risk of developing CKD is likely to reflect the composite effects of genetic predisposition, aging, and environmental and individual factors that affect renal function over the course of a cat's life. However, there is still little information available to determine exactly which individual risk factors predispose a cat to develop CKD. Although many cats diagnosed with CKD have stable disease for years, some cats show overtly progressive disease.

Telomerase, Autophagy and Acute Kidney Injury

In humans, aging is associated with telomere shortening and increased susceptibility to acute kidney injury. Telomerase is essential to maintain telomere length. The fourth generation mice with telomerase deletion have progressive shortening of telomeres. Those mice delayed recovery from ischemia-reperfusion injury, due to an increase in tubule cell senescence and impairment of autophagy, the latter of which may be mediated in part by increased mTOR signaling. © 2016 S. Karger AG, Basel.

Sequence variation in telomerase reverse transcriptase (TERT) as a determinant of risk of cardiovascular disease: the Atherosclerosis Risk in Communities (ARIC) study

Background

Telomerase reverse transcriptase (TERT) maintains telomere ends during DNA replication by catalyzing the addition of short telomere repeats. The expression of telomerase is normally repressed in somatic cells leading to a gradual shortening of telomeres and cellular senescence with aging. Interindividual variation in leukocyte telomere length has been previously associated with susceptibility to cardiovascular disease. The aim of the present study was to determine whether six variants in the TERT gene are associated with risk of incident coronary heart disease, incident ischemic stroke, and mortality in participants in the biracial population-based Atherosclerosis Risk in Communities (ARIC) study, including rs2736100 that was found to influence mean telomere length in a genome-wide analysis.

Methods

ARIC is a prospective study of the etiology and natural history of atherosclerosis in 15,792 individuals aged 45 to 64 years at baseline in 1987–1989. Haplotype tagging SNPs in TERT were genotyped using a custom array containing nearly 49,000 SNPs in 2,100 genes associated with cardiovascular and metabolic phenotypes. Cox proportional hazards models were used to assess the association between the TERT polymorphisms and incident cardiovascular disease and mortality over a 20-year follow-up period in 8,907 whites and 3,022 African-Americans with no history of disease at the baseline examination, while individuals with prevalent cardiovascular disease were not excluded from the analyses of mortality.

Results

After adjustment for age and gender, and assuming an additive genetic model, rs2736122 and rs2853668 were nominally associated with incident coronary heart disease (hazards rate ratio = 1.20, p = 0.02, 95 % confidence interval = 1.03– 1.40) and stroke (hazards rate ratio = 1.17, p = 0.05, 95 % confidence interval = 1.00 - 1.38), respectively, in African-Americans. None of the variants was significantly associated with cardiovascular disease in white study participants or with mortality in either racial group.

Conclusions

Replication in additional population-based samples combined with genotyping of polymorphisms in other genes involved in maintenance of telomere length may help to determine whether genetic variants associated with telomere homeostasis influence the risk of cardiovascular disease in middle-aged adults.

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.

Telomerase deficiency delays renal recovery in mice after ischemia-reperfusion injury by impairing autophagy

The aged population suffers increased morbidity and higher mortality in response to episodes of acute kidney injury (AKI). Aging is associated with telomere shortening, and both telomerase reverse transcriptase (TerT) and RNA (TerC) are essential to maintain telomere length. To define a role of telomerase deficiency in susceptibility to AKI, we used ischemia/reperfusion injury in wild type mice or mice with either TerC or TerT deletion. Injury induced similar renal impairment at day 1 in each genotype, as assessed by azotemia, proteinuria, acute tubular injury score and apoptotic tubular epithelial cell index. However, either TerC or TerT knockout significantly delayed recovery compared to wild type mice. Electron microscopy showed increased autophagosome formation in renal tubular epithelial cells in wild type mice but a significant delay of their development in TerC and TerT knockout mice. There were also impeded increases in the expression of the autophagosome marker LC3 II, prolonged accumulation of the autophagosome protein P62, an increase of the cell cycle regulator p16, and greater activation of the mTOR pathway. The mTORC1 inhibitor, rapamycin, partially restored the ischemia/reperfusion-induced autophagy response, without a significant effect on either p16 induction or tubule epithelial cell proliferation. Thus, muting the maintenance of normal telomere length in mice impaired recovery from AKI, due to an increase in tubule cell senescence and impairment of mTOR-mediated autophagy.

What determines ageing of the transplanted liver?

BACKGROUND

Liver transplantation is used to treat patients with irreversible liver failure from a variety of causes. Long-term survival has been reported, particularly in the paediatric population, with graft survival longer than 20 years now possible. The goal for paediatric liver transplantation is to increase the longevity of grafts to match the normal life expectancy of the child. This paper reviews the literature on the current understanding of ageing of the liver and biomarkers that may predict long-term survival or aid in utilization of organs.

METHODS

Scientific papers published from 1950 to 2013 were sought and extracted from the MEDLINE, PubMed and University of Melbourne databases.

RESULTS

Hepatocytes appear resistant to the ageing process, but are affected by both replicative senescence and stress-related senescence. These processes may be exacerbated by the act of transplantation. The most studied biomarkers are telomeres and SMP-30.

CONCLUSION

There are many factors that play a role in the ageing of the liver. Further studies into biomarkers of ageing and their relationship to the chronological age of the liver are required to aid in predicting long-term graft survival and utilization of organs.

Effect of delayed graft function, acute rejection and chronic allograft dysfunction on kidney allograft telomere length in patients after transplantation: a prospective cohort study

BACKGROUND

The outcome of kidney allograft transplantation is associated with numerous donor-dependent and recipient-dependent immunological and non-immunological factors. Studies on genetic factors affecting the non-immunological aspects, like ageing of the kidney allograft and patient outcome are still lacking. The aim of this study was the analysis of relative telomere length (RTL; T/S ratio) in the biopsy specimens of the transplanted kidney allograft and its correlation with the delayed graft function (DGF), acute rejection (AR) and chronic allograft dysfunction (CAD).

METHODS

The study enrolled 119 Caucasian kidney allograft recipients (64 M/55 F, mean age 47.32 ± 14.03; transplantation performed between 2001 and 2012). Organs were harvested from cadaveric donors (59.8 M/40.2 F, mean age 45.99 ± 14.62).

RESULTS

There were significant differences in RTL assessed in kidney allograft biopsy specimens collected 3-6 months after transplantation between patients with DGF and without DGF (181.8 ± 82.0 vs. 284.6 ± 149.6; p < 0.05) and in RTL of kidney allograft biopsy specimens collected 18-60 months after transplantation between patients with AR and without AR (188.1 ± 162.1 vs. 263.3 ± 134.7; p = 0.047). There were significant differences in RTL assessed in kidney allograft biopsy specimens collected 12-24 months after transplantation between patients with CAD and without CAD (168.0 ± 120.0 vs. 282.1 ± 158.4; p = 0.038).

CONCLUSIONS

Duration of dialysis before transplantation and PRA influence the kidney allograft ageing. Telomere length assessed in biopsy specimens collected in the peri-transplant period predicts the long-term kidney allograft function. Complications of kidney transplantation, like DGF, AR and CAD are linked with the telomere length and thus, graft ageing.

Proteins induced by telomere dysfunction are associated with human IgA nephropathy

Aging is one of the contributing risk factors for kidney diseases. Accumulating evidence prompts the view that telomere length in kidney tissue cells is an indicator for organismal aging. Previously identified aging markers (cathelin-related antimicrobial peptide (CRAMP), stathmin, elongation factor-1α (EF-1α), and chitinase) were associated not only with telomere driven aging in mice but also with human aging and chronic diseases. This study focuses on the relationship between these biomarkers and IgA nephropathy (IgAN) progression in the Chinese population. For 260 individuals, the four markers are determined in blind datasets using direct enzyme-linked immunosorbent assay (ELISA) and immunofluorescence staining. The expression levels of CRAMP and chitinase increased in blood plasma, urine, and kidney tissues during human IgAN progression. And for the other nephropathy, such as systemic lupus erythematosus (SLE), diabetic nephropathy (DN), and focal segmental glomerulosclerosis (FSGS), there is no protein upregulation with telomere shortening. Moreover, a combination of CRAMP and chitinase can distinguish patients with IgAN from healthy individuals with 88.2%/92.5% (plasma) and 74.3%/84.2% (urine) sensitivity/specificity. These data provide the experimental evidence that telomere shortening and related inflammatory proteins are associated with human IgAN, and it could be a new direction for the disease progression study.

The aging kidney: increased susceptibility to nephrotoxicity

Three decades have passed since a series of studies indicated that the aging kidney was characterized by increased susceptibility to nephrotoxic injury. Data from these experimental models is strengthened by clinical data demonstrating that the aging population has an increased incidence and severity of acute kidney injury (AKI). Since then a number of studies have focused on age-dependent alterations in pathways that predispose the kidney to acute insult. This review will focus on the mechanisms that are altered by aging in the kidney that may increase susceptibility to injury, including hemodynamics, oxidative stress, apoptosis, autophagy, inflammation and decreased repair.

Telomere length of recipients and living kidney donors and chronic graft dysfunction in kidney transplants

BACKGROUND

A biological marker that would allow clinicians to determine the length of time an allograft will remain functional after transplantation would greatly aid the ability to stratify donors by risk and to use biologically "young" allografts in young recipients, maximizing the use of this rare resource. Telomere length (TL) has been proposed to be such a marker to determine the biological age of a tissue.

METHODS

We genotyped DNA from 1805 recipients and 1038 living kidney donors for TL to determine the association of TL with acute rejection (AR), chronic graft dysfunction (CGD), and graft failure of kidney allografts. DNA was isolated from peripheral blood white blood cells and TL was measured in DNA using the multiplexed monochrome quantitative polymerase chain reaction assay.

RESULTS

As has been previously shown, we found a significant association between log-transformed TL and donor age (P=3.8×10) and recipient age (P=5.6×10). Univariate and multivariate analysis did not show any significant associations between log-transformed TL in donor or recipient DNA with AR, CGD, or graft failure, although we did observe an association between donor chronological age and CGD (P=0.018).

CONCLUSION

Although older allografts have been shown to be at greater risk for AR and CGD, this does not appear to be associated with shorter TL. Different markers will need to be identified to determine how biological age impacts transplant outcome, such as age-related fibrosis or tubular atrophy and tubular loss.

The aging kidney revisited: a systematic review

As for the whole human body, the kidney undergoes age-related changes which translate in an inexorable and progressive decline in renal function. Renal aging is a multifactorial process where gender, race and genetic background and several key-mediators such as chronic inflammation, oxidative stress, the renin-angiotensin-aldosterone (RAAS) system, impairment in kidney repair capacities and background cardiovascular disease play a significant role. Features of the aging kidney include macroscopic and microscopic changes and important functional adaptations, none of which is pathognomonic of aging. The assessment of renal function in the framework of aging is problematic and the question whether renal aging should be considered as a physiological or pathological process remains a much debated issue. Although promising dietary and pharmacological approaches have been tested to retard aging processes or renal function decline in the elderly, proper lifestyle modifications, as those applicable to the general population, currently represent the most plausible approach to maintain kidney health.

In vivo and in vitro analysis of age-associated changes and somatic cellular senescence in renal epithelial cells

Acute kidney injury is a major clinical problem and advanced age is associated with ineffective renal regeneration and poor functional outcome. Data from kidney injury models suggest that a loss of tubular epithelial proliferation contributes to a decrease in renal repair capacity with aging, but aging can also lead to a higher severity of inflammation and damage which may influence repair. In this study we tested intrinsic age-dependent changes in tubular epithelial proliferation in young and old mice, by injecting low-dose lead acetate as a non-injurious mitogen. In parallel, we explored in vitro techniques of studying cellular senescence in primary tubular epithelial cells (PTEC). Lead acetate induced tubular epithelial proliferation at a significantly higher rate in young as compared to old mice. Old kidneys showed significantly more senescence as demonstrated by increased p16 (INK4a), senescence associated β-galactosidase, and γH2AX(+)/Ki-67(-) cells. This was paralleled in old kidneys by a higher number of Cyclin D1 positive tubular cells. This finding was corroborated by a positive correlation between Cyclin D1 positivity and age in human renal biopsies. When tubular cells were isolated from mouse kidneys they rapidly lost their age-associated differences under culture conditions. However, senescence was readily induced in PTEC by γ-irradiation representing a future model for study of cellular senescence in the renal epithelium. Together, our data indicate that the tubular epithelium of aged kidney has an intrinsically reduced proliferative capacity probably due to a higher load of senescent cells. Moreover, stress induced models of cellular senescence are preferable for study of the renal epithelium in vitro. Finally, the positive correlation of Cyclin D1 with age and cellular senescence in PTEC needs further evaluation as to a functional role of renal epithelial aging.

Feline chronic kidney disease is associated with shortened telomeres and increased cellular senescence

Telomeres are protective structures at the ends of chromosomes that have important implications for aging. To address the question of whether telomeres contribute to feline chronic kidney disease (CKD), we evaluated kidney, liver, and skin samples from 12 cats with naturally occurring CKD, 12 young normal cats, and 6 old normal cats. Telomere length was assessed using standard telomere fluorescent in situ hybridization (TEL-FISH) combined with immunohistochemistry (TELI-FISH) to identify proximal (PTEC) and distal tubular epithelial cells (DTEC), whereas senescence-associated β-galactosidase (SABG) staining was used to evaluate senescence. Results revealed statistically significant decreases in the average telomere fluorescence intensity (TFI) of PTEC in CKD cats compared with young and geriatric normal cats, and in the DTEC of CKD cats compared with young normal cats. When histograms of individual TFI were compared, statistically significant decreases in the PTEC and DTEC of CKD cats were observed compared with young and geriatric normal cats. Concomitantly, a statistically significant increase in SABG staining was seen in CKD kidney samples compared with young normal cats. CKD cats tended to have increased SABG staining in the kidney compared with normal geriatric cats, but this did not reach statistical significance. No significant telomere shortening in liver or skin from any group was observed. Real-time quantitative telomeric repeat amplification protocol assessment of renal telomerase activity revealed comparable low levels of telomerase activity in all groups. Our results suggest that shortened telomeres and increased senescence in the kidneys of CKD cats may represent novel targets for interventional therapy.

Aging phenotypes in cultured normal human mammary epithelial cells are correlated with decreased telomerase activity independent of telomere length

Background

Shortening of telomeres, which are essential for maintenance of genomic integrity, is a mechanism commonly associated with the aging process. Here we ascertained whether changes in telomere lengths or telomerase activity correlated with age in normal human mammary epithelial cells (HMEC), or with phenotypes of aging in breast. Accordingly, flow cytometry fluorescence in situ hybridization (flowFISH) was used to determine relative telomere lengths (RTL), and telomerase activity was measured by the telomeric repeat amplification protocol (TRAP), in a collection of 41 primary HMEC strains established from women aged 16 to 91 years.

Results

RTL measurements of HMEC strains that were heterogeneous with respect to lineage composition revealed no significant associations between telomere length with age, maximum observed population doublings, or with lineage composition of the strains. However, within strains, luminal epithelial and cKit-expressing epithelial progenitor cells that were flow cytometry-enriched from individual HMEC strains exhibited significantly shorter telomeres relative to isogenic myoepithelial cells (P < 0.01). In unsorted strains, detectable telomerase activity did not correlate with RTL. Telomerase activity declined with age; the average age of strains that exhibited TRAP activity was 29.7 ± 3.9y, whereas the average age of strains with no detectable TRAP activity was 49.0 ± 4.9y (P < 0.01). Non-detectable TRAP activity also was correlated with phenotypes of aging previously described in HMEC strains; increased proportions of CD227-expressing luminal epithelial cells (P < 0.05) and cKit-expressing progenitor cells (P < 0.05).

Conclusions

Telomere shortening did not correlate with the chronological ages of HMEC strains, whereas decreased telomerase activity correlated with age and with lineage distribution phenotypes characteristic of aging.

Applications of physiological bases of ageing to forensic sciences. Estimation of age-at-death

Age-at-death estimation is one of the main challenges in forensic sciences since it contributes to the identification of individuals. There are many anthropological techniques to estimate the age at death in children and adults. However, in adults this methodology is less accurate and requires population specific references. For that reason, new methodologies have been developed. Biochemical methods are based on the natural process of ageing, which induces different biochemical changes that lead to alterations in cells and tissues. In this review, we describe different attempts to estimate the age in adults based on these changes. Chemical approaches imply modifications in molecules or accumulation of some products. Molecular biology approaches analyze the modifications in DNA and chromosomes. Although the most accurate technique appears to be aspartic acid racemization, it is important to take into account the other techniques because the forensic context and the human remains available will determine the possibility to apply one or another methodology.

From cellular senescence to age-associated diseases: the miRNA connection

Cellular senescence has evolved from an in-vitro model system to study aging in vitro to a multifaceted phenomenon of in-vivo importance as senescent cells in vivo have been identified and their removal delays the onset of age-associated diseases in a mouse model system. From the large emerging class of non-coding RNAs, miRNAs have only recently been functionally implied in the regulatory networks that are modified during the aging process. Here we summarize examples of similarities between the differential expression of miRNAs during senescence and age-associated diseases and suggest that these similarities might emphasize the importance of senescence for the pathogenesis of age-associated diseases. Understanding such a connection on the level of miRNAs might offer valuable opportunities for designing novel diagnostic and therapeutic strategies.

New insights on molecular mechanisms of renal aging

Long-term transplant outcome is importantly influenced by the age of the organ donor. The mechanisms how age carries out its pathophysiological impact on graft survival are still not understood. One major contributing factor for the observed poor performance of old donor kidneys seems in particular the age-related loss in renal regenerative capacity. In this review, we will summarize recent findings about the molecular basis of renal aging with specific focus on the potential role of somatic cellular senescence and mitochondrial aging in renal transplant outcome.