Replicative senescence in organ transplantation-mechanisms and significance

Risk Factors for Adverse Outcomes in Kidney Transplants From Donors After Circulatory Death With Normothermic Regional Perfusion: A Systematic Analysis

BACKGROUND

This study examined 1071 adult primary kidney transplants from the French-controlled donation after the circulatory determination of death (cDCD) program, which uses normothermic regional perfusion (NRP), and involves short cold ischemia times (CIT) and constrained asystole times differing by donor age.

METHODS

Logistic regression identified risk factors for primary nonfunction (PNF), delayed graft function (DGF), and graft failure.

RESULTS

Risk factors for PNF included donor hypertension, admission for ischemic vascular stroke, and HLA DR mismatches. Risk factors for DGF included functional warm ischemia time >40 min, dialysis >2 y, recipient body mass index of 30 kg/m2 or higher, recipient diabetes, and CIT >10 h. Risk factors for 1-y graft failure included donor hypertension, donor lung recovery, ostial calcification, recipient cardiovascular comorbidities, and HLA DR mismatches. A high donor estimated glomerular filtration rate protected against DGF and graft failure at 1-y. After adjustment restricted to recipient and graft factors and donor age, the risks of PNF, DGF, and graft failure increased with donor age up to 65 y and then remained stable.

CONCLUSIONS

The study suggests that cDCD kidney transplants are highly successful, but also that its outcomes are influenced by lung recovery, poor HLA DR matching, and warm ischemia times differing with donor age. Our study identified several risk factors for kidney transplantation failure after cDCD with systematic use of NRP and some of them seem as modifiable variables associated with cDCD transplant outcome.

In Vitro Impact of Pro-Senescent Endothelial Microvesicles on Isolated Pancreatic Rat Islets Function

BACKGROUND

Ischemia-driven islet isolation procedure is one of the limiting causes of pancreatic islet transplantation. Ischemia-reperfusion process is associated with endothelium dysfunction and the release of pro-senescent microvesicles. We investigated whether pro-senescent endothelial microvesicles prompt islet senescence and dysfunction in vitro.

MATERIAL AND METHODS

Pancreatic islets were isolated from male young rats. Replicative endothelial senescence was induced by serial passaging of primary porcine coronary artery endothelial cells, and microvesicles were isolated either from young passage 1 (P1) or senescent passage 3 (P3) endothelial cells. Islet viability was assessed by fluorescence microscopy, apoptosis by flow cytometry, and Western blot. Function was assessed by insulin secretion and islet senescence markers p53, p21, and p16 by Western blot. Microvesicles were stained by the PKH26 lipid fluorescent probe and their islet integration assessed by microscopy and flow cytometry.

RESULTS

Regardless of the passage, half microvesicles were integrated in target islets after 24 hours incubation. Insulin secretion significantly decreased after treatment by senescent microvesicles (P3: 1.7 ± 0.2 vs untreated islet: 2.7 ± 0.2, P < .05) without altering the islet viability (89.47% ± 1.69 vs 93.15% ± 0.97) and with no significant apoptosis. Senescent microvesicles significantly doubled the expression of p53, p21, and p16 (P < .05), whereas young microvesicles had no significant effect.

CONCLUSION

Pro-senescent endothelial microvesicles specifically accelerate the senescence of islets and alter their function. These data suggest that islet isolation contributes to endothelial driven islet senescence.

Complement component C5a induces aberrant epigenetic modifications in renal tubular epithelial cells accelerating senescence by Wnt4/βcatenin signaling after ischemia/reperfusion injury

Epigenetic mechanisms, such as DNA methylation, affect tubular maladaptive response after Acute Kidney Injury (AKI) and accelerate renal aging. Upon ischemia/reperfusion (I/R) injury, Complement activation leads to C5a release that mediates damage; however, little is known about the effect of C5a-C5a Receptor (C5aR) interaction in Renal Tubular Epithelial Cells (RTEC).

Through a whole-genome DNA methylation analysis in cultured RTEC, we found that C5a induced aberrant methylation, particularly in regions involved in cell cycle control, DNA damage and Wnt signaling. The most represented genes were BCL9, CYP1B1 and CDK6. C5a stimulation of RTEC led to up-regulation of SA-β Gal and cell cycle arrest markers such as p53 and p21. C5a increased also IL-6, MCP-1 and CTGF gene expression, consistent with SASP development. In accordance, in a swine model of renal I/R injury, we found the increased expression of Wnt4 and βcatenin correlating with SA-β Gal, p21, p16 and IL-6 positivity. Administration of Complement Inhibitor (C1-Inh), antagonized SASP by reducing SA-β Gal, p21, p16, IL-6 and abrogating Wnt4/βcatenin activation.

Thus, C5a affects the DNA methylation of genes involved in tubular senescence. Targeting epigenetic programs and Complement may offer novels strategies to protect tubular cells from accelerated aging and to counteract progression to Chronic Kidney Disease

Regulation of aging and oxidative stress pathways in aged pancreatic islets using alpha-lipoic acid

Oxidative stress has been involved in the aging process and the pathogenesis of type-2 diabetes, which is a serious health problem worldwide. This study investigates the anti-aging, anti-apoptotic, and antioxidant properties of alpha-lipoic acid (ALA), aiming to improve aged rat pancreatic cells. In this regard, half maximal effective concentration (EC₅₀) of ALA based on the survival of aged pancreatic islet cells was determined as 100 µM. Following this, p38 and p53 genes expression as key factors in aging, oxidative stress biomarkers, insulin secretion, and Pdx1 protein expression were evaluated using real-time PCR, ELISA reader, and fluorescence microscope. It was revealed that ALA reduces and controls the effects of aging on beta cells mainly by suppressing p38 and p53 at the gene level (P < 0.001 and P < 0.01), respectively, reducing reactive oxygen species (P < 0.001) and enhancing levels of thiols (P < 0.05) compared with the aged islets. Furthermore, both qualitative and quantitative investigations of insulin secretion have shown that ALA can improve aged cells' function and increase insulin secretion specially in the stimulating concentration of glucose. Also, the expression of Pdx1 was considerably increased by ALA in comparison to the aged pancreatic islets (P < 0.001). As far as the authors of the present study are concerned, this is the first study, which evaluated aging associated with p38 and p53 pathways, oxidative stress parameters, and the expression of insulin in beta cells of an aged rat and reaffirmed the fact that ALA has a significant antioxidant role in reducing the aging process.

Increased Telomere Attrition After Renal Transplantation-Impact of Antimetabolite Therapy

Background

The uremic milieu exposes chronic kidney disease (CKD) patients to premature ageing processes. The impact of renal replacement therapy (dialysis and renal transplantation [RTx]) or immunosuppressive treatment regimens on ageing biomarkers has scarcely been studied.

Methods

In this study telomere length in whole blood cells was measured in 49 dialysis patients and 47 RTx patients close to therapy initiation and again after 12 months. Forty-three non-CKD patients were included as controls.

Results

Non-CKD patients had significantly (P ≤ 0.01) longer telomeres than CKD patients. Telomere attrition after 12 months was significantly greater in RTx patients compared to dialysis patients (P = 0.008). RTx patients receiving mycophenolate mofetil (MMF) had a greater (P = 0.007) degree of telomere attrition compared to those treated with azathioprine. After 12 months, folate was significantly higher in RTx patients than in dialysis patients (P < 0.0001), whereas the opposite was true for homocysteine (P < 0.0001). The azathioprine group had lower levels of folate after 12 months than the MMF group (P = 0.003).

Conclusions

The associations between immunosuppressive therapy, telomere attrition, and changes in folate indicate a link between methyl donor potential, immunosuppressive drugs, and biological ageing. The hypothesis that the increased telomere attrition, observed in the MMF group after RTx, is driven by the immunosuppressive treatment, deserves further attention.

Cellular senescence in aging and age-related disease: from mechanisms to therapy

Cellular senescence, a process that imposes permanent proliferative arrest on cells in response to various stressors, has emerged as a potentially important contributor to aging and age-related disease, and it is an attractive target for therapeutic exploitation. A wealth of information about senescence in cultured cells has been acquired over the past half century; however, senescence in living organisms is poorly understood, largely because of technical limitations relating to the identification and characterization of senescent cells in tissues and organs. Furthermore, newly recognized beneficial signaling functions of senescence suggest that indiscriminately targeting senescent cells or modulating their secretome for anti-aging therapy may have negative consequences. Here we discuss current progress and challenges in understanding the stressors that induce senescence in vivo, the cell types that are prone to senesce, and the autocrine and paracrine properties of senescent cells in the contexts of aging and age-related diseases as well as disease therapy.

Q-FISH measurement of hepatocyte telomere lengths in donor liver and graft after pediatric living-donor liver transplantation: donor age affects telomere length sustainability

Along with the increasing need for living-donor liver transplantation (LDLT), the issue of organ shortage has become a serious problem. Therefore, the use of organs from elderly donors has been increasing. While the short-term results of LDLT have greatly improved, problems affecting the long-term outcome of transplant patients remain unsolved. Furthermore, since contradictory data have been reported with regard to the relationship between donor age and LT/LDLT outcome, the question of whether the use of elderly donors influences the long-term outcome of a graft after LT/LDLT remains unsettled. To address whether hepatocyte telomere length reflects the outcome of LDLT, we analyzed the telomere lengths of hepatocytes in informative biopsy samples from 12 paired donors and recipients (grafts) of pediatric LDLT more than 5 years after adult-to-child LDLT because of primary biliary atresia, using quantitative fluorescence in situ hybridization (Q-FISH). The telomere lengths in the paired samples showed a robust relationship between the donor and grafted hepatocytes (r = 0.765, p = 0.0038), demonstrating the feasibility of our Q-FISH method for cell-specific evaluation. While 8 pairs showed no significant difference between the telomere lengths for the donor and the recipient, the other 4 pairs showed significantly shorter telomeres in the recipient than in the donor. Multiple regression analysis revealed that the donors in the latter group were older than those in the former (p = 0.001). Despite the small number of subjects, this pilot study indicates that donor age is a crucial factor affecting telomere length sustainability in hepatocytes after pediatric LDLT, and that the telomeres in grafted livers may be elongated somewhat longer when the grafts are immunologically well controlled.

Prostatic fibrosis, lower urinary tract symptoms, and BPH

Lower urinary tract symptoms (LUTS)--constituting a spectrum disorder that encompasses weak stream, nocturia, and sensations of incomplete emptying and intermittent or hesitant urination--are indicative of lower urinary tract dysfunction (LUTD). LUTD is a progressive disease that can lead to bladder dysfunction if left untreated or treated ineffectively. Sequelae include urinary retention, recurrent UTI, bladder calculi, and, eventually, renal impairment. LUTD involving the prostate is associated with both ageing and inflammation. Tissue inflammation resulting from ageing, infection, or other inflammatory disease processes (for example, type 2 diabetes mellitus) is epidemiologically associated with the subsequent development of tissue fibrosis in multiple organ systems, including the prostate. Recent studies show that tissue fibrosis in the lower urinary tract is associated with LUTD, and suggest that fibrosis might be a previously unrecognized pathobiology that contributes to LUTD. Thus, antifibrotic therapeutic agents should be considered as a new approach to efficaciously treating men with LUTD, especially those who don't experience durable responses to 5α-reductase inhibitors or α-adrenergic receptor antagonists.

CXC-type chemokines promote myofibroblast phenoconversion and prostatic fibrosis

Recent studies from our group suggest that extracellular matrix (ECM) deposition and fibrosis characterize the peri-urethral prostate tissues of some men suffering from Lower Urinary Tract Symptoms (LUTS) and that fibrosis may be a contributing factor to the etiology of LUTS. Fibrosis can generally be regarded as an errant wound-healing process in response to chronic inflammation, and several studies have shown that the aging prostate tissue microenvironment is rich with inflammatory cells and proteins. However, it is unclear whether these same inflammatory proteins, particularly CXC-type chemokines, can mediate myofibroblast phenoconversion and the ECM deposition necessary for the development of prostatic tissue fibrosis. To examine this, immortalized and primary prostate stromal fibroblasts treated with TGF-β1, CXCL5, CXCL8, or CXCL12 were evaluated morphologically by microscopy, by immunofluorescence and qRT-PCR for αSMA, collagen 1, vimentin, calponin, and tenascin protein and transcript expression, and by gel contraction assays for functional myofibroblast phenoconversion. The results of these studies showed that that immortalized and primary prostate stromal fibroblasts are induced to express collagen 1 and 3 and αSMA gene transcripts and proteins and to undergo complete and functional myofibroblast phenoconversion in response to CXC-type chemokines, even in the absence of exogenous TGF-β1. Moreover, CXCL12-mediated myofibroblast phenoconversion can be completely abrogated by inhibition of the CXCL12 receptor, CXCR4. These findings suggest that CXC-type chemokines, which comprise inflammatory proteins known to be highly expressed in the aging prostate, can efficiently and completely mediate myofibroblast phenoconversion and may thereby promote fibrotic changes in prostate tissue architecture associated with the development and progression of male lower urinary tract dysfunction.

Is cellular senescence important in pediatric kidney disease?

Somatic cellular senescence (SCS) describes the limited ability of cells to divide. Normally, SCS is associated with physiological aging, but evidence suggests that it may play a role in disease progression, even in young patients. Stressors such as acute injury or chronic inflammation may induce SCS, which in turn exhausts organ regenerative potential. This review summarizes what is known about SCS in the kidney with aging and disease. As most patients with chronic kidney disease (CKD) also develop cardiovascular complications, a second focus of this review deals with the role of SCS in cardiovascular disease. Also, as SCS seems to accelerate CKD and cardiovascular disease progression, developing strategies for new treatment options that overcome SCS or protect a patient from it represents an exciting challenge.

Chemokines and BPH/LUTS

A wealth of published studies indicate that a variety of chemokines are actively secreted by the prostatic microenvironment consequent to disruptions in normal tissue homeostasis due to the aging process or inflammatory responses. The accumulation of senescent stromal fibroblasts, and, possibly, epithelial cells, may serve as potential driving forces behind chemokine secretion in the aging and enlarged human prostate. Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) and histological inflammation may also potentially serve as rich sources of chemokine secretion in the prostate. Once bound to their cognate receptors, chemokines can stimulate powerful pro-proliferation signal transduction pathways and thus function as potent growth factors in the development and progression of Benign Prostatic Hyperplasia (BPH) and lower urinary tract symptoms (LUTS). These functions have been amply demonstrated experimentally and particularly point to robust Mitogen Activated Protein Kinase (MAPK) and phosphoinositide 3-kinase (PI3K) signaling, as well as global transcriptional responses, which mediate chemokine-stimulated cellular proliferative responses. A small body of literature also suggests that chemokine-mediated angiogenesis may comprise a contributing factor to BPH/LUTS development and progression. Thus, the observed low-level secretion of multiple chemokines within the aging prostatic microenvironment may promote a concomitant low-level, but cumulative, over-proliferation of both stromal fibroblastic and epithelial cell types associated with increased prostatic volume. Though the accumulated evidence is far from complete and suffers from some rather extensive gaps in knowledge, it argues favorably for the conclusion that chemokines can, and likely do, promote prostatic enlargement and the associated lower urinary tract symptoms, and justifies further investigations examining chemokines as potential therapeutic targets to delay or ablate BPH/LUTS initiation and progression.

Transition of kidney tubule cells to a senescent phenotype in early experimental diabetes

Diabetic nephropathy is the commonest cause of end-stage renal disease. Inordinate kidney growth and glomerular hyperfiltration at the very early stages of diabetes are putative antecedents to this disease. The kidney is the only organ that grows larger with the onset of diabetes mellitus, yet there remains confusion about the mechanism and significance of this growth. Here we show that kidney proximal tubule cells in culture transition to senescence in response to oxidative stress. We further determine the temporal expression of G(1) phase cell cycle components in rat kidney cortex at days 4 and 10 of streptozotocin diabetes to evaluate changes in this growth response. In diabetic rats we observe increases in kidney weight-to-body weight ratios correlating with increases in expression of the growth-related proteins in the kidney at day 4 after induction of diabetes. However, at day 10 we find a decrease in this profile in diabetic animals coincident with increased cyclin-dependent kinase inhibitor expressions. We observe no change in caspase-3 expression in the diabetic kidneys at these early time points; however, diabetic animals demonstrate reduced kidney connexin 43 and increased plasminogen activator inhibitor-1 expressions and increased senescence-associated beta-galactosidase activity in cortical tubules. In summary, diabetic kidneys exhibit an early temporal induction of growth phase components followed by their suppression concurrent with the induction of cyclin-dependent kinase inhibitors and markers of senescence. These data delineate a phenotypic change in cortical tubules early in the pathogenesis of diabetes that may contribute to further downstream complications of the disease.

Kidney graft function in long-term cyclosporine and tacrolimus treatment: comparative study with nephrotoxicity markers

Calcineurin inhibitors improve kidney allograft survival in the posttransplantation period; however, they may cause nephrotoxicity. The objective of this study was to compare the effect of cyclosporine (CsA) and tacrolimus (Tac) treatment on the transplanted kidney. The study included 219 patients aged 21 to 65 years. Of these, 120 (39 women and 81 men) were treated with CsA and 99 (38 women and 61 men) were treated with Tac. Patients were divided into 4 groups depending on the time since kidney transplantation. We evaluated urine markers of nephrotoxicity: proximal tubular cells lysosomal enzymes (N-acetyl-beta-d-glucosaminidase [NAG] and its isoform NAG-B, beta-d-galactosidase, and beta-glucouronidase) and brush border enzymes (alanyl aminopeptidase and gamma-glutamyl transpeptidase). Urine activities of nephrotoxicity markers were compared in CsA- and Tac-treated patients groups depending on the duration of treatment and allograft function as measured by serum creatinine concentration. Correlation studies between CsA and Tac levels and enzyme activities were performed in both groups and in the entire patient cohort. NAG and its isoform NAG-B seemed to be the most reliable markers of nephrotoxicity. Despite the significant correlation between NAG urine activity and serum creatinine concentration in the CsA group, there were no significant differences in NAG or NAG-B activities between CsA- and Tac-treated graft recipients.

Strategies for future histocompatible stem cell therapy

Stem cell therapy based on the safe and unlimited self-renewal of human pluripotent stem cells is envisioned for future use in tissue or organ replacement after injury or disease. A gradual decline of regenerative capacity has been documented among the adult stem cell population in some body organs during the aging process. Recent progress in human somatic cell nuclear transfer and inducible pluripotent stem cell technologies has shown that patient-derived nuclei or somatic cells can be reprogrammed in vitro to become pluripotent stem cells, from which the three germ layer lineages can be generated, genetically identical to the recipient. Once differentiation protocols and culture conditions can be defined and optimized, patient-histocompatible pluripotent stem cells could be directed towards virtually every cell type in the human body. Harnessing this capability to enrich for given cells within a developmental lineage, would facilitate the transplantation of organ/tissue-specific adult stem cells or terminally differentiated somatic cells to improve the function of diseased organs or tissues in an individual. Here, we present an overview of various experimental cell therapy technologies based on the use of patient-histocompatible stem cells, the pending issues needed to be dealt with before clinical trials can be initiated, evidence for the loss and/or aging of the stem cell pool and some of the possible uses of human pluripotent stem cell-derivatives aimed at curing disease and improving health.

Aging and induced senescence as factors in the pathogenesis of lung emphysema

Classically, the development of emphysema in chronic obstructive pulmonary disease is believed to involve inflammation induced by cigarette smoke and leukocyte activation, including oxidant-antioxidant and protease-antiprotease imbalances. While there is substantial evidence for this, additional aspects have been suggested by a number of clinical and experimental observations. Smokers exhibit signs of premature aging, particularly obvious in the skin. The link between aging and chronic disease is well-known, e.g., for the brain and musculoskeletal or cardiovascular system, as well as the clinical link between malnutrition and emphysema, and the experimental link to caloric restriction. Interestingly, this intervention also increases lifespan, in parallel with alterations in metabolism, oxidant burden and endocrine signaling. Of special interest is the observation that, even in the absence of an inflammatory environment, lung fibroblasts from patients with emphysema show persistent alterations, possibly based on epigenetic mechanisms. The importance of these mechanisms for cellular reprogramming and response patterns, individual risk profile and therapeutic options is becoming increasingly recognized. The same applies to cellular senescence. Recent findings from patients and experimental models open novel views into the arena of gene-environment interactions, including the role of systemic alterations, cellular stress, telomeres, CDK inhibitors such as p16, p21, pRb, PI3K, mTOR, FOXO transcription factors, histone modifications, and sirtuins. This article aims to outline this emerging picture and to stimulate the identification of challenging questions. Such insights also bear implications for the long-term course of the disease in relation to existing or future therapies and the exploration of potential lung regeneration.

Up-regulation of cell cycle regulatory genes after renal ischemia/reperfusion: differential expression of p16(INK4a), p21(WAF1/CIP1) and p27(Kip1) cyclin-dependent kinase inhibitor genes depending on reperfusion time

The aim of this study was to evaluate the influence of renal ischemia, cold preservation and reperfusion on the degree of renal kidney senescence. An experimental model of ex vivo renal hemoperfusion was used. Expression of p16(INK4a), p21(WAF1/CIP1) and p27(Kip1) cyclin-dependent kinase inhibitor genes (CDKIGs) was studied immunohistochemically in kidney biopsy samples at baseline and different time points after reperfusion. All three markers were up-regulated in kidney tissue after the reperfusion; however, their activation in different renal cells varied according to the reperfusion time. Expression of p16 was significantly increased in tubular cells at 180 min of reperfusion when compared with the baseline. Activation of p27 was detected in glomerular cells at 15 min and was significantly higher at 60, 120 and 180 min of reperfusion. The marker started increasing in tubular cells at 15 min and was elevated at every time point afterwards. p21 was significantly over-expressed in all renal cells after the reperfusion. It has been shown by the results of the current study that renal ischemia/reperfusion is associated with over-expression of CDKIGs indicating on substantial DNA damage and/or accelerated tissue senescence. For the first time it has been shown that tissue expression of CDKIGs is positively related with the reperfusion time.

Influence of ischaemia/reperfusion and LFA-1 inhibition on telomere lengths and CDKI genes in ex vivo haemoperfusion of primate kidneys

The telomere (T) length, p21(WAF1/CIP1) and p27(Kip1) cyclin-dependent kinase inhibitor (CDKI) genes are the markers of cell senescence and DNA damage. The aim of the study was to determine the influence of renal ischaemia/reperfusion (I/R) and anti-lymphocyte function-associated antigen-1 (LFA-1) monoclonal antibody (mAb) treatment on the value of the above-mentioned markers. Significantly higher levels of p21 and p27 were expressed by the glomeruli (P=0.001 and P=0.0001), tubules (P=0.0065 and P=0.0006), and interstitial cells (P=0.0017 and P=0.0022, respectively) of the xenoperfused kidneys. The mean T length of non-perfused renal specimens (5.56+/-0.60 kbp) was longer than that of the xenoperfused kidneys (5.46+/-0.36 kbp) [P= non-significant (NS)]. Addition of anti-LFA-1 mAb did not significantly influence the gene expression profile in the xenoperfused kidneys. The mean T length was longer in the kidneys with anti-LFA-1 mAb than in those without the medication (5.7+/-0.11 vs 5.13+/-0.31 kbp) (P=0.0661). Kidney I/R is associated with telomere shortening and an over-expression of p21 and p27 CDKIs, which indicates substantial DNA damage and/or accelerated tissue senescence. Although anti-LFA-1 mAb had some protective effect on the telomeres, it did not influence the gene expression profile in this study.

Telomere shortening and cellular senescence in a model of chronic renal allograft rejection

Cellular senescence has been suggested to play a role in the deterioration of renal graft function and has been linked to telomere shortening. We have investigated markers of cellular senescence in the F344 to LEW rat model of chronic renal transplant rejection. Syngeneic and LEW to F344 transplants were used as controls. Substantial telomere shortening was observed in all transplants, including allogeneic and syngeneic grafts from day 7 post-transplant onwards. Ischemia of native F344 kidneys was already sufficient to induce telomere shortening. It is known that shortened telomeres can activate cell cycle regulators, such as p21 and p16. Accordingly, all cases showed a transient p21 increase, with a maximum at day 7 and a sustained expression of p16. Importantly, senescence-associated beta-galactosidase staining, a cytological marker for senescence, was only observed in tubular epithelial cells of chronically rejecting F344 allografts from day 30 post-transplantation onwards. Long-term surviving LEW allografts or syngeneic F344 grafts were negative for senescence-associated beta-galactosidase. In conclusion, ischemia during transplantation results in telomere shortening and subsequent activation of p21 and p16, whereas senescence-associated beta-galactosidase staining is only present in chronically rejecting kidney grafts.