Tubular cell senescence and expression of TGF-beta1 and p21(WAF1/CIP1) in tubulointerstitial fibrosis of aging rats

Role of cellular senescence in inflammation and regeneration

Cellular senescence is the state in which cells undergo irreversible cell cycle arrest and acquire diverse phenotypes. It has been linked to chronic inflammation and fibrosis in various organs as well as to individual aging. Therefore, eliminating senescent cells has emerged as a potential target for extending healthy lifespans. Cellular senescence plays a beneficial role in many biological processes, including embryonic development, wound healing, and tissue regeneration, which is mediated by the activation of stem cells. Therefore, a comprehensive understanding of cellular senescence, including both its beneficial and detrimental effects, is critical for developing safe and effective treatment strategies to target senescent cells. This review provides an overview of the biological and pathological roles of cellular senescence, with a particular focus on its beneficial or detrimental functions among its various roles.

The Role of Collagen VIII in the Aging Mouse Kidney

The gradual loss of kidney function due to increasing age is accompanied by structural changes such as fibrosis of the tissue. The underlying molecular mechanisms are complex, but not yet fully understood. Non-fibrillar collagen type VIII (COL8) could be a potential factor in the fibrosis processes of the aging kidney. A pathophysiological significance of COL8 has already been demonstrated in the context of diabetic kidney disease, with studies showing that it directly influences both the development and progression of renal fibrosis occurring. The aim of this study was to investigate whether COL8 impacts age-related micro-anatomical and functional changes in a mouse model. The kidneys of wild-type (Col8-wt) and COL8-knockout (Col8-ko) mice of different age and sex were characterized with regard to the expression of molecular fibrosis markers, the development of nephrosclerosis and renal function. The age-dependent regulation of COL8 mRNA expression in the wild-type revealed sex-dependent effects that were not observed with collagen IV (COL4). Histochemical staining and protein analysis of profibrotic cytokines TGF-β1 (transforming growth factor) and CTGF (connective tissue growth factor) in mouse kidneys showed significant age effects as well as interactions of the factors age, sex and Col8 genotype. There were also significant age and Col8 genotype effects in the renal function data analyzed by urinary cystatin C. In summary, the present study shows, for the first time, that COL8 is regulated in an age- and sex-dependent manner in the mouse kidney and that the expression of COL8 influences the severity of age-induced renal fibrosis and function.

Effects of Multiwall Carbon Nanotubes on Premature Kidney Aging: Biochemical and Histological Analysis

Carbon nanotubes (CNTs) have gained much attention due to their superb properties, which make them promising options for the reinforcing composite materials with desirable mechanical properties. However, little is known about the linkage between lung exposure to nanomaterials and kidney disease. In this study, we compared the effects on the kidneys and aging for two different types of multiwall carbon nanotubes (MWCNTs): pristine MWCNTs (PMWCNTs) and acid-treated MWCNTs (TMWCNTs), with TMWCNTs being the preferred form for use as a composite material due to its superior dispersion properties. We used tracheal instillation and maximum tolerated dose (MTD) for both types of CNTs. MTD was determined as a 10% weight loss dose in a 3-month subchronic study, and the appropriate dosage for 1-year exposure was 0.1 mg/mouse. Serum and kidney samples were analyzed using ELISA, Western blot, and immunohistochemistry after 6 months and 1 year of treatment. PMWCNT-administered mice showed the activation of pathways for inflammation, apoptosis, and insufficient autophagy, as well as decreased serum Klotho levels and increased serum levels of DKK-1, FGF-23, and sclerostin, while TMWCNTs did not. Our study suggests that lung exposure to PMWCNTs can induce premature kidney aging and highlights a possible toxic effect of using MWCNTs on the kidneys in the industrial field, further highlighting that dispersibility can affect the toxicity of the nanotubes.

Glomerular endothelial cell senescence drives age-related kidney disease through PAI-1

The mechanisms underlying the development of glomerular lesions during aging are largely unknown. It has been suggested that senescence might play a role, but the pathophysiological link between senescence and lesion development remains unexplained. Here, we uncovered an unexpected role for glomerular endothelial cells during aging. In fact, we discovered a detrimental cross-talk between senescent endothelial cells and podocytes, through PAI-1. In vivo, selective inactivation of PAI-1 in endothelial cells protected glomeruli from lesion development and podocyte loss in aged mice. In vitro, blocking PAI-1 in supernatants from senescent endothelial cells prevented podocyte apoptosis. Consistently, depletion of senescent cells prevented podocyte loss in old p16 INK-ATTAC transgenic mice. Importantly, these experimental findings are relevant to humans. We showed that glomerular PAI-1 expression was predictive of poor outcomes in transplanted kidneys from elderly donors. In addition, we observed that in elderly patients, urinary PAI-1 was associated with age-related chronic kidney disease. Altogether, these results uncover a novel mechanism of kidney disease and identify PAI-1 as a promising biomarker of kidney dysfunction in allografts from elderly donors.

The Genomic Response to TGF-β1 Dictates Failed Repair and Progression of Fibrotic Disease in the Obstructed Kidney

Tubulointerstitial fibrosis is a common and diagnostic hallmark of a spectrum of chronic renal disorders. While the etiology varies as to the causative nature of the underlying pathology, persistent TGF-β1 signaling drives the relentless progression of renal fibrotic disease. TGF-β1 orchestrates the multifaceted program of kidney fibrogenesis involving proximal tubular dysfunction, failed epithelial recovery or re-differentiation, capillary collapse and subsequent interstitial fibrosis eventually leading to chronic and ultimately end-stage disease. An increasing complement of non-canonical elements function as co-factors in TGF-β1 signaling. p53 is a particularly prominent transcriptional co-regulator of several TGF-β1 fibrotic-response genes by complexing with TGF-β1 receptor-activated SMADs. This cooperative p53/TGF-β1 genomic cluster includes genes involved in cellular proliferative control, survival, apoptosis, senescence, and ECM remodeling. While the molecular basis for this co-dependency remains to be determined, a subset of TGF-β1-regulated genes possess both p53- and SMAD-binding motifs. Increases in p53 expression and phosphorylation, moreover, are evident in various forms of renal injury as well as kidney allograft rejection. Targeted reduction of p53 levels by pharmacologic and genetic approaches attenuates expression of the involved genes and mitigates the fibrotic response confirming a key role for p53 in renal disorders. This review focuses on mechanisms underlying TGF-β1-induced renal fibrosis largely in the context of ureteral obstruction, which mimics the pathophysiology of pediatric unilateral ureteropelvic junction obstruction, and the role of p53 as a transcriptional regulator within the TGF-β1 repertoire of fibrosis-promoting genes.

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.

Cellular senescence and the senescence-associated secretory phenotype: Potential therapeutic targets for renal fibrosis

Renal fibrosis plays a crucial role in the progression of chronic kidney disease and end-stage renal disease. However, because the aetiology of this pathological process is complex and remains unclear, there is still no effective treatment. Cellular senescence and the senescence-associated secretory phenotype (SASP) have been reported to lead to renal fibrosis. This review first discusses the relationships among cellular senescence, the SASP and renal fibrosis. Then, the key role of the SASP in irreversible renal fibrosis, including fibroblast activation and abnormal extracellular matrix accumulation, is discussed, with the results of studies having indicated that inhibiting cellular senescence and the SASP might be a potential preventive and therapeutic strategy for renal fibrosis. Finally, we summarize promising therapeutic strategies revealed by existing research on senescent cells and the SASP, including emerging interventions targeting the SASP, caloric restriction and mimetics, and novel regeneration therapies with stem cells.

Effects of TRPC6 Inactivation on Glomerulosclerosis and Renal Fibrosis in Aging Rats

Canonical transient receptor potential 6 (TRPC6) channels have been implicated in familial and acquired forms of focal and segmental glomerulosclerosis (FSGS) in patients and animal models, as well as in renal fibrosis following ureteral obstruction in mice. Aging also evokes declines in renal function owing to effects on almost every renal compartment in humans and rodents. Here, we have examined the role of TRPC6 in driving inflammation and fibrosis during aging in Sprague-Dawley rats. This was assessed in rats with non-functional TRPC6 channels owing to CRISPR-Cas9 deletion of a portion of the ankyrin repeat domain required for the assembly of functional TRPC6 channels (Trpc6^del/del rats). Wild-type littermates (Trpc6^wt/wt rats) were used as controls. Animals were evaluated at 2 months and 12 months of age. There was no sign of kidney disease at 2 months of age, regardless of genotype. However, by 12 months of age, all rats examined showed declines in renal function associated with albuminuria, azotemia and increased urine excretion of β2-microglobulin, a marker for proximal tubule pathology. These changes were equally severe in Trpc6^wt/wt and Trpc6^del/del rats. We also observed age-related increases in renal cortical expression of markers of fibrosis (α-smooth muscle actin and vimentin) and inflammation (NLRP3 and pro-IL-1β), and there was no detectable protective effect of TRPC6 inactivation. Tubulointerstitial fibrosis assessed from histology also appeared equally severe in Trpc6^wt/wt and Trpc6^del/del rats. By contrast, glomerular pathology, blindly scored from histological sections, suggested a significant protective effect of TRPC6 inactivation, but only within the glomerular compartment.

[Molecular mechanisms of renal aging]

Chronic kidney disease (CKD) is characterized by the progressive decline of renal function, that occurs once a critical number of nephrons has been lost, regardless the etiology. CKD prevalence is constantly increasing, especially with age. Nevertheless, the molecular mechanisms underlying this progression are not very well known. With an increasing number of patients with CKD, especially elderly patients, it urges to better understand the pathophysiology of this progression to elaborate new therapeutic strategies. Recent works have highlighted the role of some cellular processes, such as senescence, during age-related kidney dysfunction. Senescence corresponds to a cellular state associated with a cell cycle blockade. Although the cell cannot proliferate, she is able to secrete a lot of proteins grouped under the term of senescence associated secretory phenotype (SASP). Identification of molecular mechansims involved in age related kidney dysfunction could help to determine new therapeutic targets.

Cellular senescence in vivo: From cells to tissues to pathologies

Senescent cells accumulate during aging in a variety of tissues. Although scarce, they could influence tissue function non-cell-autonomously via secretion of a range of factors in their neighborhood. Recent studies support a role of senescent cells in age-related morbidity, including neurodegenerative diseases, cardiovascular pathologies, cancers, aging-associated nephrological alterations, chronic pulmonary disease and osteoarthritis, indicating that senescent cells could represent an interesting target for therapeutic exploitation across a range of pathophysiological contexts. In this article, we review data available to indicate which cell types can undergo senescence within various mammalian tissue environments and how these processes may contribute to tissue-specific pathologies associated with old age. We also consider markers used to identify senescent cells in vitro and in vivo. The data discussed may serve as an important starting point for an extended definition of molecular and functional characteristics of senescent cells in different organs and may hence promote the development and refinement of targeting strategies aimed at removing senescent cells from aging tissues.

Long Non-Coding RNA (LncRNA)-ATB Promotes Inflammation, Cell Apoptosis and Senescence in Transforming Growth Factor-β1 (TGF-β1) Induced Human Kidney 2 (HK-2) Cells via TGFβ/SMAD2/3 Signaling Pathway

Background

Renal fibrosis occurs in the end-stage of all chronic kidney disease. Transforming growth factor-β1 (TGF-β1) is a central contributor in fibrosis. Identifying effective biomarkers that targets TGF-β1 is necessary for the development of therapeutic agents for kidney disease. In this study, we investigated the effects and mechanism of long non-coding RNA (LncRNA)-ATB in TGF-β1 induced human kidney 2 (HK-2) cells.

Material/Methods

We investigated the effects of either overexpression or knockdown of LncRNA-ATB on inflammation, cell apoptosis, and senescence in TGF-β1 induced HK-2 cells. TGF-β1 induced HK-2 cells served as the cell model. The gene level was evaluated by quantitative real-time polymerase chain reaction (qRT-PCR) and protein expressions by western blot. Cell Counting Kit-8 (CCK-8) assay was performed for assessment of cell viability. Flow cytometry was applied for detection of cell apoptosis. Tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were measured by corresponding kits.

Results

LncRNA-ATB was highly expressed in TGF-β1 induced HK-2 cells. Inflammation, cell apoptosis, and senescence were enhanced by TGF-β1 and these effects were all reduced by knockdown of LncRNA-ATB. Whereas overexpression of LncRNA-ATB had the opposite effects with knockdown of LncRNA-ATB. The TGFβ/SMAD2/3 signaling pathway was activated by TGF-β1 and this effect was further enhanced by LncRNA-ATB overexpression. Silencing LncRNA-ATB inhibited the TGFβ/SMAD2/3 signaling pathway in TGF-β1 induced cells. The effects of LncRNA-ATB overexpression aforementioned in TGF-β1 induced cells were abolished by blockage of the TGFβ/S0MAD2/3 signaling pathway.

Conclusions

LncRNA-ATB overexpression have promoting effects on inflammation, cell apoptosis and senescence in TGF-β1 induced HK-2 cells via activating the TGFβ/SMAD2/3 signaling pathway. LncRNA-ATB act as a key downstream mediator via activating the TGFβ/SMAD2/3 signaling pathway and silencing LncRNA-ATB might be a new strategy for chronic kidney disease treatment.

Local and transient inhibition of p21 expression ameliorates age-related delayed wound healing

Nonhealing chronic wounds in the constantly growing elderly population represent a major public health problem with high socioeconomic burden. Yet, the underlying mechanism of age-related impairment of wound healing remains elusive. Here, we show that the number of dermal cells expressing cyclin-dependent kinase inhibitor p21 was elevated upon skin injury, particularly in aged population, in both man and mouse. The nuclear expression of p21 in activated wound fibroblasts delayed the onset of the proliferation phase of wound healing in a p53-independent manner. Further, the local and transient inhibition of p21 expression by in vivo delivered p21-targeting siRNA ameliorated the delayed wound healing in aged mice. Our results suggest that the increased number of p21⁺ wound fibroblasts enforces the age-related compromised healing, and targeting p21 creates potential clinical avenues to promote wound healing in aged population.

Cellular Senescence and the Kidney: Potential Therapeutic Targets and Tools

Chronic kidney disease (CKD) is an increasing health burden (affecting approximately 13.4% of the population). Currently, no curative treatment options are available and treatment is focused on limiting the disease progression. The accumulation of senescent cells has been implicated in the development of kidney fibrosis by limiting tissue rejuvenation and through the secretion of pro-fibrotic and pro-inflammatory mediators termed as the senescence-associated secretory phenotype. The clearance of senescent cells in aging models results in improved kidney function, which shows promise for the options of targeting senescent cells in CKD. There are several approaches for the development of “senotherapies”, the most rigorous of which is the elimination of senescent cells by the so-called senolytic drugs either newly developed or repurposed for off-target effects in terms of selectively inducing apoptosis in senescent cells. Several chemotherapeutics and checkpoint inhibitors currently used in daily oncological practice show senolytic properties. However, the applicability of such senolytic compounds for the treatment of renal diseases has hardly been investigated. A serious concern is that systemic side effects will limit the use of senolytics for kidney fibrosis. Specifically targeting senescent cells and/or targeted drug delivery to the kidney might circumvent these side effects. In this review, we discuss the connection between CKD and senescence, the pharmacological options for targeting senescent cells, and the means to specifically target the kidney.

Connective Tissue and Age-Related Diseases

We begin this chapter by describing normal characteristics of several pertinent connective tissue components, and some of the basic changes they undergo with ageing. These alterations are not necessarily tied to any specific disease or disorders, but rather an essential part of the normal ageing process. The general features of age-induced changes, such as skin wrinkles, in selected organs with high content of connective or soft tissues are discussed in the next part of the chapter. This is followed by a section dealing with age-related changes in specific diseases that fall into at least two categories. The first category encompasses common diseases with high prevalence among mostly ageing populations where both genetic and environmental factors play roles. They include but may not be limited to atherosclerosis and coronary heart disease, type II diabetes, osteopenia and osteoporosis, osteoarthritis, tendon dysfunction and injury, age-related disorders of spine and joints. Disorders where genetics plays the primary role in pathogenesis and progression include certain types of progeria, such as Werner syndrome and Hutchinson-Gilford progeria belong to the second category discussed in this chapter. These disorders are characterized by accelerated signs and symptoms of ageing. Other hereditary diseases or syndromes that arise from mutations of genes encoding for components of connective tissue and are less common than diseases included in the first group will be discussed briefly as well, though they may not be directly associated with ageing, but their connective tissue undergoes some changes compatible with ageing. Marfan and Ehlers-Danlos syndromes are primary examples of such disorders. We will probe the role of specific components of connective tissue and extracellular matrix if not in each of the diseases, then at least in the main representatives of these disorders.

Diabetic gut microbiota dysbiosis as an inflammaging and immunosenescence condition that fosters progression of retinopathy and nephropathy

The increased prevalence of type 2 diabetes mellitus (T2DM) and life expectancy of diabetic patients fosters the worldwide prevalence of retinopathy and nephropathy, two major microvascular complications that have been difficult to treat with contemporary glucose-lowering medications. The gut microbiota (GM) has become a lively field research in the last years; there is a growing recognition that altered intestinal microbiota composition and function can directly impact the phenomenon of ageing and age-related disorders. In fact, human GM, envisaged as a potential source of novel therapeutics, strongly modulates host immunity and metabolism. It is now clear that gut dysbiosis and their products (e.g. p-cresyl sulfate, trimethylamine‑N‑oxide) dictate a secretory associated senescence phenotype and chronic low-grade inflammation, features shared in the physiological process of ageing ("inflammaging") as well as in T2DM ("metaflammation") and in its microvascular complications. This review provides an in-depth look on the crosstalk between GM, host immunity and metabolism. Further, it characterizes human GM signatures of elderly and T2DM patients. Finally, a comprehensive scrutiny of recent molecular findings (e.g. epigenetic changes) underlying causal relationships between GM dysbiosis and diabetic retinopathy/nephropathy complications is pinpointed, with the ultimate goal to unravel potential pathophysiological mechanisms that may be explored, in a near future, as personalized disease-modifying therapeutic approaches.

Accelerated Glomerular Cell Senescence in Experimental Lupus Nephritis

BACKGROUND The aim of this study was to determine whether senescence in renal glomeruli is involved in lupus nephritis (LN); the expression of senescence-associated β-galactosidase (SA-β-Gal) and its association with glomerular lesions were investigated in a mouse model of LN. MATERIAL AND METHODS Eighteen MRL/lpr mice with severe proteinuria were randomly divided into 2 equal groups and intraperitoneally injected with dexamethasone (DEX) or saline; 4 age-matched mice with mild proteinuria served as controls. Serum creatinine and urinary protein levels were analyzed, and kidney histological changes were observed by periodic acid-Schiff and Sirius Red staining. SA-β-Gal was detected via histochemistry. Glomerular expression of collagen IV, α-SMA, and nephrin was analyzed by immunohistochemistry, and glomerular complement C3 deposition was tested by immunofluorescence. The relationships between SA-β-Gal expression and renal function or glomerular lesion markers were determined by Spearman's correlation analysis. RESULTS Mice with severe proteinuria exhibited glomerular segmental sclerosis and endothelial cell proliferation. DEX administration suppressed these lesions but had no significant effect on 24-hour urinary protein levels. The elevated glomerular expression of SA-β-Gal in proteinuric mice was attenuated by DEX treatment. In addition, DEX treatment markedly downregulated glomerular C3 deposition and collagen IV and α-SMA expression, while significantly increasing nephrin expression. Furthermore, SA-β-Gal expression was positively correlated with urinary protein levels and expression of α-SMA. CONCLUSIONS Accelerated senescence of glomerular cells may contribute to glomerular injury in LN.

The Eye, Oxidative Damage and Polyunsaturated Fatty Acids

Polyunsaturated fatty acids (PUFA) are known to have numerous beneficial effects, owing to their anti-inflammatory and antioxidant properties. From a metabolic standpoint, the mitochondria play a fundamental role in cellular homeostasis, and oxidative stress can affect their functioning. Indeed, the mitochondria are the main source of ROS, and an imbalance between ROS and antioxidant defenses leads to oxidative stress. In addition, aging, the decline of cellular functions, and continual exposure to light underlie many diseases, particularly those of the eye. Long-term exposure to insults, such as UV light, visible light, ionizing radiation, chemotherapeutics, and environmental toxins, contribute to oxidative damage in ocular tissues and expose the aging eye to considerable risk of pathological consequences of oxidative stress. Ample antioxidant defenses responsible for scavenging free radicals are essential for redox homeostasis in the eye, indeed, eye tissues, starting from the tear film, which normally are exposed to high oxygen levels, have strong antioxidant defenses that are efficient for protecting against ROS-related injuries. On the contrary, instead, the trabecular meshwork is not directly exposed to light and its endothelial cells are poorly equipped with antioxidant defenses. All this makes the eye a target organ of oxidative damage. This review focuses on the role of the polyunsaturated fatty acids in the human eye, particularly in such pathologies as dry eye, glaucoma, and macular degeneration, in which dietary PUFA supplementation can be a valid therapeutic aid.

Wnt9a Promotes Renal Fibrosis by Accelerating Cellular Senescence in Tubular Epithelial Cells

Cellular senescence is associated with renal disease progression, and accelerated tubular cell senescence promotes the pathogenesis of renal fibrosis. However, the underlying mechanism is unknown. We assessed the potential role of Wnt9a in tubular cell senescence and renal fibrosis. Compared with tubular cells of normal subjects, tubular cells of humans with a variety of nephropathies and those of several mouse models of CKD expressed high levels of Wnt9a that colocalized with the senescence-related protein p16^INK4A Wnt9a expression level correlated with the extent of renal fibrosis, decline of eGFR, and expression of p16^INK4A Furthermore, ectopic expression of Wnt9a after ischemia-reperfusion injury (IRI) induced activation of β-catenin and exacerbated renal fibrosis. Overexpression of Wnt9a exacerbated tubular senescence, evidenced by increased detection of p16^INK4A expression and senescence-associated β-galactosidase activity. Conversely, shRNA-mediated knockdown of Wnt9a repressed IRI-induced renal fibrosis in vivo and impeded the growth of senescent tubular epithelial cells in culture. Notably, Wnt9a-induced renal fibrosis was inhibited by shRNA-mediated silencing of p16^INK4A in the IRI mouse model. In a human proximal tubular epithelial cell line and primary renal tubular cells, Wnt9a remarkably upregulated levels of senescence-related p16^INK4A, p19^ARF, p53, and p21 and decreased the phosphorylation of retinoblastoma protein. Wnt9a also induced senescent tubular cells to produce TGF-β1, which promoted proliferation and activation in normal rat kidney fibroblasts. Thus, Wnt9a drives tubular senescence and fibroblast activation. Furthermore, the Wnt9a-TGF-β pathway appears to create a reciprocal activation loop between senescent tubular cells and activated fibroblasts that promotes and accelerates the pathogenesis of renal fibrosis.

Targeting Senescent Cells in Fibrosis: Pathology, Paradox, and Practical Considerations

PURPOSE OF THE REVIEW

Senescent cells have the capacity to both effect and limit fibrosis. Senotherapeutics target senescent cells to improve aging conditions. Here, we review the contexts in which senescent cells mediate wound healing and fibrotic pathology and the potential utility of senotherapeutic drugs for treatment of fibrotic disease.

RECENT FINDINGS

Multi-action and temporal considerations influence deleterious versus beneficial actions of senescent cells. Acutely generated senescent cells can limit proliferation, and the senescence-associated secretory phenotype (SASP) contains factors that can facilitate tissue repair. Long-lived senescent cells that evade clearance or are generated outside of programmed remodeling can deplete the progenitor pool to exhaust regenerative capacity and through the SASP, stimulate continual activation, leading to disorganized tissue architecture, fibrotic damage, sterile inflammation, and induction of bystander senescence. Senescent cells contribute to fibrotic pathogenesis in multiple tissues, including the liver, kidney, and lung. Senotherapeutics may be a viable strategy for treatment of a range of fibrotic conditions.

The role of cellular senescence in aging through the prism of Koch-like criteria

Since Hayflick's discovery of cellular senescence (CS), a great volume of knowledge in the field has been accumulated and intensively discussed. Here, we attempted to organize the evidence "for" and "against" the hypothesized causal role of CS in aging. For that purpose, we utilized robust Koch-like logical criteria, based on the assumption that some quantitative relationships between the accumulation of senescent cells and aging rate should exist. If so, it could be expected that (i) the "CS load" would be greater in the premature aging phenotype and lesser in longevity phenotype; (ii) CS would promote age-related diseases, and (iii) the interventions that modulate the levels of senescent cells should also modulate health/lifespan. The analysis shows that CS can be considered a causal factor of aging and an important player in various age-related diseases, though its contribution may greatly vary across species. While the relative impact of senescent cells to aging could overall be rather limited and their elimination is hardly expected to be the "fountain of youth", the potential benefits of the senolytic strategy seems a promising option in combating age-related diseases and extending healthspan.

Cellular senescence in the aging and diseased kidney

The program of cellular senescence is involved in both the G1 and G2 phase of the cell cycle, limiting G1/S and G2/M progression respectively, and resulting in prolonged cell cycle arrest. Cellular senescence is involved in normal wound healing. However, multiple organs display increased senescent cell numbers both during natural aging and after injury, suggesting that senescent cells can have beneficial as well as detrimental effects in organismal aging and disease. Also in the kidney, senescent cells accumulate in various compartments with advancing age and renal disease. In experimental studies, forced apoptosis induction through the clearance of senescent cells leads to better preservation of kidney function during aging. Recent groundbreaking studies demonstrate that senescent cell depletion through INK-ATTAC transgene-mediated or cell-penetrating FOXO4-DRI peptide induced forced apoptosis, reduced age-associated damage and dysfunction in multiple organs, in particular the kidney, and increased performance and lifespan. Senescence is also involved in oncology and therapeutic depletion of senescent cells by senolytic drugs has been studied in experimental and human cancers. Although studies with senolytic drugs in models of kidney injury are lacking, their dose limiting side effects on other organs suggest that targeted delivery might be needed for successful application of senolytic drugs for treatment of kidney disease. In this review, we discuss (i) current understanding of the mechanisms and associated pathways of senescence, (ii) evidence of senescence occurrence and causality with organ injury, and (iii) therapeutic strategies for senescence depletion (senotherapy) including targeting, all in the context of renal aging and disease.

The aging kidney and the nephrotoxic effects of mercury

Owing to advances in modern medicine, life expectancies are lengthening and leading to an increase in the population of older individuals. The aging process leads to significant alterations in many organ systems, with the kidney being particularly susceptible to age-related changes. Within the kidney, aging leads to ultrastructural changes such as glomerular and tubular hypertrophy, glomerulosclerosis, and tubulointerstitial fibrosis, which may compromise renal plasma flow (RPF) and glomerular filtration rate (GFR). These alterations may reduce the functional reserve of the kidneys, making them more susceptible to pathological events when challenged or stressed, such as following exposure to nephrotoxicants. An important and prevalent environmental toxicant that induces nephrotoxic effects is mercury (Hg). Since exposure of normal kidneys to mercuric ions might induce glomerular and tubular injury, aged kidneys, which may not be functioning at full capacity, may be more sensitive to the effects of Hg than normal kidneys. Age-related renal changes and the effects of Hg in the kidney have been characterized separately. However, little is known regarding the influence of nephrotoxicants, such as Hg, on aged kidneys. The purpose of this review was to summarize known findings related to exposure of aged and diseased kidneys to the environmentally relevant nephrotoxicant Hg.

Mechanism of ginsenoside Rg1 renal protection in a mouse model of d-galactose-induced subacute damage

Context Ginseng is a widely used herbal medicine in China but its mechanism of action remains unclear. Objective The objectives of this work were to study the protective effect of ginsenoside Rg1 on subacute murine renal damage induced by d-galactose and its mechanism. Materials and methods C57BL/6J mice were injected with 120 mg/kg/d (sc) d-galactose for 1 week, followed by a combined treatment of Rg1 20 mg/kg/d (ip) and 120 mg/kg/d d-galactose (sc) for 5 weeks. Mice were injected with the 0.9% saline 0.2 mL/d (sc) and 120 mg/kg/d d-galactose (sc) for 6 weeks in the control group and the d-galactose group, respectively. After 6 weeks, urea, creatinine, uric acid, cystatin (Cys-C), senescence-associated β-galactosidase (SA-β-gal) staining positive kidney cells, superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), malondialdehyde (MDA), glycation end products (AGEs) and 8-hydroxy-2 deoxyguanosine (8-OH-dG) were measured. Results Treatment with Rg1 ameliorated kidney function and aging state (urea from 17.19 ± 1.09 to 15.77 ± 1.22 mmol·L (-) (1), creatinine from 29.40 ± 5.72 to 22.60 ± 3.97 μmol·L (-) (1), uric acid from 86.80 ± 5.97 to 72.80 ± 10.61 μmol·L (-) (1), Cys-C from 0.23 ± 0.03 to 0.18 ± 0.05 mg·L (-) (1), ROD of SA-β-gal from 56.32 ± 10.48 to 26.78 ± 7.34, SOD from 150.22 ± 19.07 to 190.56 ± 15.83 U·(mg·prot) (-1), MDA from 9.28 ± 1.59 to 3.17 ± 0.82 nmol·(mg·prot) (-1), GSH-PX from 15.68 ± 2.11 to 20.32 ± 2.96 U·(mg·prot) (-1) as well as regulated glomerulus morphology (glomerulus diameter from 775.77 ± 18.41 to 695.04 ± 14.61 μm, renal capsule width from 39.56 ± 3.51 to 31.42 ± 2.70 μm, glomerulus basement membrane from 206.03 ± 16.22 to 157.27 ± 15.70 nm, podocyte slit from 55.21 ± 8.55 to 37.63 ± 6.65 nm). Conclusions Ginsenoside Rg1 can antagonise d-galactose subacute renal damage in mice and this may occur due to alleviating oxidative stress injury.

From DNA damage to functional changes of the trabecular meshwork in aging and glaucoma

Glaucoma is a degenerative disease of the eye. Both the anterior and posterior segments of the eye are affected, extensive damage being detectable in the trabecular meshwork and the inner retina-central visual pathway complex. Oxidative stress is claimed to be mainly responsible for molecular damage in the anterior chamber. Indeed, oxidation harms the trabecular meshwork, leading eventually to endothelial cell decay, tissue malfunction, subclinical inflammation, changes in the extracellular matrix and cytoskeleton, altered motility, reduced outflow facility and (ultimately) increased IOP. Moreover, free radicals are involved in aging and can be produced in the brain (as well as in the eye) as a result of ischemia, leading to oxidation of the surrounding neurons. Glaucoma-related cell death occurs by means of apoptosis, and apoptosis is triggered by oxidative stress via (a) mitochondrial damage, (b) inflammation, (c) endothelial dysregulation and dysfunction, and (d) hypoxia. The proteomics of the aqueous humor is significantly altered in glaucoma as a result of oxidation-induced trabecular damage. Those proteins whose aqueous humor levels are increased in glaucoma are biomarkers of trabecular meshwork impairment. Their diffusion from the anterior to the posterior segment of the eye may be relevant in the cascade of events triggering apoptosis in the inner retinal layers, including the ganglion cells.

MTOR regulates the pro-tumorigenic senescence-associated secretory phenotype by promoting IL1A translation

The TOR (target of rapamycin) kinase limits longevity by poorly understood mechanisms. Rapamycin suppresses the mammalian TORC1 complex, which regulates translation, and extends lifespan in diverse species, including mice. We show that rapamycin selectively blunts the pro-inflammatory phenotype of senescent cells. Cellular senescence suppresses cancer by preventing cell proliferation. However, as senescent cells accumulate with age, the senescence-associated secretory phenotype (SASP) can disrupt tissues and contribute to age-related pathologies, including cancer. MTOR inhibition suppressed the secretion of inflammatory cytokines by senescent cells. Rapamycin reduced IL6 and other cytokine mRNA levels, but selectively suppressed translation of the membrane-bound cytokine IL1A. Reduced IL1A diminished NF-κB transcriptional activity, which controls much of the SASP; exogenous IL1A restored IL6 secretion to rapamycin-treated cells. Importantly, rapamycin suppressed the ability of senescent fibroblasts to stimulate prostate tumour growth in mice. Thus, rapamycin might ameliorate age-related pathologies, including late-life cancer, by suppressing senescence-associated inflammation.

IFNγ induces oxidative stress, DNA damage and tumor cell senescence via TGFβ/SMAD signaling-dependent induction of Nox4 and suppression of ANT2

Cellular senescence provides a biological barrier against tumor progression, often associated with oncogene-induced replication and/or oxidative stress, cytokine production and DNA damage response (DDR), leading to persistent cell-cycle arrest. While cytokines such as tumor necrosis factor-alpha (TNFα) and interferon gamma (IFNγ) are important components of senescence-associated secretome and induce senescence in, for example, mouse pancreatic β-cancer cell model, their downstream signaling pathway(s) and links with oxidative stress and DDR are mechanistically unclear. Using human and mouse normal and cancer cell models, we now show that TNFα and IFNγ induce NADPH oxidases Nox4 and Nox1, reactive oxygen species (ROS), DDR signaling and premature senescence. Unlike mouse tumor cells that required concomitant presence of IFNγ and TNFα, short exposure to IFNγ alone was sufficient to induce Nox4, Nox1 and DDR in human cells. siRNA-mediated knockdown of Nox4 but not Nox1 decreased IFNγ-induced DDR. The expression of Nox4/Nox1 required Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling and the effect was mediated by downstream activation of transforming growth factor-beta (TGFβ) secretion and consequent autocrine/paracrine activation of the TGFβ/Smad pathway. Furthermore, the expression of adenine nucleotide translocase 2 (ANT2) was suppressed by IFNγ contributing to elevation of ROS and DNA damage. In contrast to mouse B16 cells, inability of TC-1 cells to respond to IFNγ/TNFα by DDR and senescence correlated with the lack of TGFβ and Nox4 response, supporting the role of ROS induced by NADPH oxidases in cytokine-induced senescence. Overall, our data reveal differences between cytokine effects in mouse and human cells, and mechanistically implicate the TGFβ/SMAD pathway, via induction of NADPH oxidases and suppression of ANT2, as key mediators of IFNγ/TNFα-evoked genotoxicity and cellular senescence.

Controlled induction of DNA double-strand breaks in the mouse liver induces features of tissue ageing

DNA damage has been implicated in ageing, but direct evidence for a causal relationship is lacking, owing to the difficulty of inducing defined DNA lesions in cells and tissues without simultaneously damaging other biomolecules and cellular structures. Here we directly test whether highly toxic DNA double-strand breaks (DSBs) alone can drive an ageing phenotype using an adenovirus-based system based on tetracycline-controlled expression of the SacI restriction enzyme. We deliver the adenovirus to mice and compare molecular and cellular end points in the liver with normally aged animals. Treated, 3-month-old mice display many, but not all signs of normal liver ageing as early as 1 month after treatment, including ageing pathologies, markers of senescence, fused mitochondria and alterations in gene expression profiles. These results, showing that DSBs alone can cause distinct ageing phenotypes in mouse liver, provide new insights in the role of DNA damage as a driver of tissue ageing.

Accumulation of DNA damage is a hallmark of cellular ageing but cause and effect are unclear. Here White et al. induce clean DNA double-strand breaks in the liver of mice using a modified restriction enzyme and demonstrate that DNA damage alone is sufficient to recapitulate some aspects of tissue ageing.

Renal fibrosis in feline chronic kidney disease: known mediators and mechanisms of injury

Chronic kidney disease (CKD) is a common medical condition of ageing cats. In most cases the underlying aetiology is unknown, but the most frequently reported pathological diagnosis is renal tubulointerstitial fibrosis. Renal fibrosis, characterised by extensive accumulation of extra-cellular matrix within the interstitium, is thought to be the final common pathway for all kidney diseases and is the pathological lesion best correlated with function in both humans and cats. As a convergent pathway, renal fibrosis provides an ideal target for the treatment of CKD and knowledge of the underlying fibrotic process is essential for the future development of novel therapies. There are many mediators and mechanisms of renal fibrosis reported in the literature, of which only a few have been investigated in the cat. This article reviews the process of renal fibrosis and discusses the most commonly cited mediators and mechanisms of progressive renal injury, with particular focus on the potential significance to feline CKD.

Senescent cells: SASPected drivers of age-related pathologies

The progression of physiological ageing is driven by intracellular aberrations including telomere attrition, genomic instability, epigenetic alterations and loss of proteostasis. These in turn damage cells and compromise their functionality. Cellular senescence, a stable irreversible cell-cycle arrest, is elicited in damaged cells and prevents their propagation in the organism. Under normal conditions, senescent cells recruit the immune system which facilitates their removal from tissues. Nevertheless, during ageing, tissue-residing senescent cells tend to accumulate, and might negatively impact their microenvironment via profound secretory phenotype with pro-inflammatory characteristics, termed senescence-associated secretory phenotype (SASP). Indeed, senescent cells are mostly abundant at sites of age-related pathologies, including degenerative disorders and malignancies. Interestingly, studies on progeroid mice indicate that selective elimination of senescent cells can delay age-related deterioration. This suggests that chronic inflammation induced by senescent cells might be a main driver of these pathologies. Importantly, senescent cells accumulate as a result of deficient immune surveillance, and their removal is increased upon the use of immune stimulatory agents. Insights into mechanisms of senescence surveillance could be combined with current approaches for cancer immunotherapy to propose new preventive and therapeutic strategies for age-related diseases.

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.

Cellular senescence: from physiology to pathology

Recent discoveries are redefining our view of cellular senescence as a trigger of tissue remodelling that acts during normal embryonic development and upon tissue damage. To achieve this, senescent cells arrest their own proliferation, recruit phagocytic immune cells and promote tissue renewal. This sequence of events - senescence, followed by clearance and then regeneration - may not be efficiently completed in aged tissues or in pathological contexts, thereby resulting in the accumulation of senescent cells. Increasing evidence indicates that both pro-senescent therapies and antisenescent therapies can be beneficial. In cancer and during active tissue repair, pro-senescent therapies contribute to minimize the damage by limiting proliferation and fibrosis, respectively. Conversely, antisenescent therapies may help to eliminate accumulated senescent cells and to recover tissue function.

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.

Aging and the disposition and toxicity of mercury in rats

Progressive loss of functioning nephrons, secondary to age-related glomerular disease, can impair the ability of the kidneys to effectively clear metabolic wastes and toxicants from blood. Additionally, as renal mass is diminished, cellular hypertrophy occurs in functional nephrons that remain. We hypothesize that these nephrons are exposed to greater levels of nephrotoxicants, such as inorganic mercury (Hg(2+)), and thus are at an increased risk of becoming intoxicated by these compounds. The purpose of the present study was to characterize the effects of aging on the disposition and renal toxicity of Hg(2+) in young adult and aged Wistar rats. Paired groups of animals were injected (i.v.) with either a 0.5μmol·kg(-1) non-nephrotoxic or a 2.5μmol·kg(-1) nephrotoxic dose of mercuric chloride (HgCl2). Plasma creatinine and renal biomarkers of proximal tubular injury were greater in both groups of aged rats than in the corresponding groups of young adult rats. Histologically, evidence of glomerular sclerosis, tubular atrophy, interstitial inflammation and fibrosis were significant features of kidneys from aged animals. In addition, proximal tubular necrosis, especially along the straight segments in the inner cortex and outer stripe of the outer medulla was a prominent feature in the renal sections from both aged and young rats treated with the nephrotoxic dose of HgCl2. Our findings indicate 1) that overall renal function is significantly impaired in aged rats, resulting in chronic renal insufficiency and 2) the disposition of HgCl2 in aging rats is significantly altered compared to that of young rats.

Spironolactone prevents dietary-induced metabolic syndrome by inhibiting PI3-K/Akt and p38MAPK signaling pathways

OBJECTIVES

Aim of the study is to evaluate the impact of spironolactone (SPL) on indexes of metabolic syndrome (MS) and further investigate the mechanisms underlying its protective effects.

METHODS

A rat model of MS was established by administering a fat- and salt-enriched diet (FS diet). The occurrence of MS was examined by measurement of blood pressure (BP), aldosterone (ALD) content, blood lipid (BL), glucose and insulin levels. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. Pancreatic gland tissue injury was assessed by β-cell apoptosis. Mineralocorticoid receptor (MR) activity, phosphatidylinositol 3- kinase/Akt (PI3-K/Akt), and phosphorylation of p38MAPK (Pp38MAPK) in pancreatic gland tissue were evaluated by western blot analysis.

RESULTS

SPL prevented hypertension, and dyslipidemia during MS induced by the intake of FS diet, but had no effect on K+ and Na+ disturbances. Furthermore, SPL significantly attenuated ALD and MR expression levels after FS diet. Finally, SPL inhibited phosphorylation protein kinase B (p- PKB) activation in the pancreatic gland tissue, a downstream target of PI3-K, and phosphorylation of p38MAPK pathway, critical for cellular apoptosis.

CONCLUSIONS

This study demonstrates that SPL exerts a protective effect on hypertension and dyslipidemia. This protective effect may depend, at least in part, on MAPK and PI3-K pathways.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Sirtuin 6 (SIRT6) rescues the decline of homologous recombination repair during replicative senescence

Genomic instability is a hallmark of aging tissues. Genomic instability may arise from the inefficient or aberrant function of DNA double-stranded break (DSB) repair. DSBs are repaired by homologous recombination (HR) and nonhomologous DNA end joining (NHEJ). HR is a precise pathway, whereas NHEJ frequently leads to deletions or insertions at the repair site. Here, we used normal human fibroblasts with a chromosomally integrated HR reporter cassette to examine the changes in HR efficiency as cells progress to replicative senescence. We show that HR declines sharply with increasing replicative age, with an up to 38-fold decrease in efficiency in presenescent cells relative to young cells. This decline is not explained by a reduction of the number of cells in S/G(2)/M stage as presenescent cells are actively dividing. Expression of proteins involved in HR such as Rad51, Rad51C, Rad52, NBS1, and Sirtuin 6 (SIRT6) diminished with cellular senescence. Supplementation of Rad51, Rad51C, Rad52, and NBS1 proteins, either individually or in combination, did not rescue the senescence-related decline of HR. However, overexpression of SIRT6 in "middle-aged" and presenescent cells strongly stimulated HR repair, and this effect was dependent on mono-ADP ribosylation activity of poly(ADP-ribose) polymerase (PARP1). These results suggest that in aging cells, the precise HR pathway becomes repressed giving way to a more error-prone NHEJ pathway. These changes in the processing of DSBs may contribute to age-related genomic instability and a higher incidence of cancer with age. SIRT6 activation provides a potential therapeutic strategy to prevent the decline in genome maintenance.

Accelerated senescence of renal tubular epithelial cells is associated with disease progression of patients with immunoglobulin A (IgA) nephropathy

The aim of this study is to determine the potential correlation between the accelerated senescence of renal tubular epithelial cells (RTECs) and the disease progression of patients with immunoglobulin A nephropathy (IgAN). A total of 108 IgAN patients with different Lee's pathologic grades were enrolled. Additionally, 18 patients with renal resection were recruited as controls. Cellular senescence was evaluated by senescence-associated β-galactosidase (SA-β-gal) staining and an immunohistochemical analysis of p21 and p16 protein expression. The expression of type III collagen (Col III) and fibronectin (FN) in renal interstitium and the levels of serum total and low-density lipoprotein (LDL) cholesterol, serum creatinine concentration (SCr), and 24-h urinary protein excretion were evaluated also. SA-β-gal staining and the expression of p16 and p21 were increased significantly in renal biopsy specimens obtained from grades I-II IgAN patients compared with controls (P < 0.05). The expression of these senescence-associated markers increased gradually with disease progression and correlated with the renal morphologic changes and the expression of Col III and FN in renal interstitium in IgAN patients. A correlation analysis showed that the expressions of p16, p21, and SA-β-gal staining were associated significantly with blood pressure and renal function (P < 0.05), but not with patient age, body mass index (BMI), LDL cholesterol level, or 24-h urinary protein value (P > 0.05). Our results indicated that the RTECs in IgAN patients exhibited features of accelerated senescence, which were unrelated to mechanisms associated with normal aging. Cellular senescence was associated closely with IgAN disease progression, which suggested the accelerated senescence of RTECs may contribute to this progression.

Age-dependent renal cortical microvascular loss in female mice

Renal function and blood flow decline during aging in association with a decrease in the number of intrarenal vessels, but if loss of estrogen contributes to this microvascular, rarefaction remains unclear. We tested the hypothesis that the decreased renal microvascular density with age is aggravated by loss of estrogen. Six-month-old female C57/BL6 mice underwent ovariectomy (Ovx) or sham operation and then were allowed to age to 18-22 mo. Another comparable group was replenished with estrogen after Ovx (Ovx+E), while a 6-mo-old group served as young controls. Kidneys were then dissected for evaluation of microvascular density (by micro-computed tomography) and angiogenic and fibrogenic factors. Cortical density of small microvessels (20-200 μm) was decreased in all aged groups compared with young controls (30.3 ± 5.8 vessels/mm², P < 0.05), but tended to be lower in sham compared with Ovx and Ovx+E (9.9 ± 1.7 vs. 17.2 ± 4.2 and 18 ± 3.0 vessels/mm², P = 0.08 and P = 0.02, respectively). Cortical density of larger microvessels (200-500 μm) decreased only in aged sham (P = 0.04 vs. young control), and proangiogenic signaling was attenuated. On the other hand, renal fibrogenic mechanisms were aggravated in aged Ovx compared with aged sham, but blunted in Ovx+E, in association with downregulated transforming growth factor-β signaling and decreased oxidative stress in the kidney. Therefore, aging induced in female mice renal cortical microvascular loss, which was likely not mediated by loss of endogenous estrogen. However, estrogen may play a role in protecting the kidney by decreasing oxidative stress and attenuating mechanisms linked to renal interstitial fibrosis.

Glyoxalase I retards renal senescence

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

Kidney aging--inevitable or preventable?

The aging process affects all organs, including the kidneys. As part of this process, progressive scarring and a measurable decline in renal function occur in most people over time. The improved understanding of the processes that can lead to and/or hasten scarring and loss of renal function over time parallels advances in our understanding of the aging process. Clinical factors, including hypertension, diabetes mellitus, obesity, abnormal lipid levels and vitamin D deficiency, have been associated with increasing renal sclerosis with age. In addition, tissue factors such as angiotensin II, advanced glycation end products, oxidative stress and Klotho are associated with renal aging. These associations and possible interventions, including the control of blood pressure, blood sugar, weight, diet and calorie restriction might make renal aging more preventable than inevitable.

DNA repair deficiency in neurodegeneration

Deficiency in repair of nuclear and mitochondrial DNA damage has been linked to several neurodegenerative disorders. Many recent experimental results indicate that the post-mitotic neurons are particularly prone to accumulation of unrepaired DNA lesions potentially leading to progressive neurodegeneration. Nucleotide excision repair is the cellular pathway responsible for removing helix-distorting DNA damage and deficiency in such repair is found in a number of diseases with neurodegenerative phenotypes, including Xeroderma Pigmentosum and Cockayne syndrome. The main pathway for repairing oxidative base lesions is base excision repair, and such repair is crucial for neurons given their high rates of oxygen metabolism. Mismatch repair corrects base mispairs generated during replication and evidence indicates that oxidative DNA damage can cause this pathway to expand trinucleotide repeats, thereby causing Huntington's disease. Single-strand breaks are common DNA lesions and are associated with the neurodegenerative diseases, ataxia-oculomotor apraxia-1 and spinocerebellar ataxia with axonal neuropathy-1. DNA double-strand breaks are toxic lesions and two main pathways exist for their repair: homologous recombination and non-homologous end-joining. Ataxia telangiectasia and related disorders with defects in these pathways illustrate that such defects can lead to early childhood neurodegeneration. Aging is a risk factor for neurodegeneration and accumulation of oxidative mitochondrial DNA damage may be linked with the age-associated neurodegenerative disorders Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. Mutation in the WRN protein leads to the premature aging disease Werner syndrome, a disorder that features neurodegeneration. In this article we review the evidence linking deficiencies in the DNA repair pathways with neurodegeneration.

Cellular senescence: putting the paradoxes in perspective

Cellular senescence arrests the proliferation of potential cancer cells, and so is a potent tumor suppressive mechanism, akin to apoptosis. Or is it? Why did cells evolve an anti-cancer mechanism that arrests, rather than kills, would-be tumor cells? Recent discoveries that senescent cells secrete growth factors, proteases and cytokines provide a shifting view--from senescence as a cell autonomous suppressor of tumorigenesis to senescence as a means to mobilize the systemic and local tissue milieu for repair. In some instances, this mobilization benefits the organism, but in others it can be detrimental. These discoveries provide potential mechanisms by which cellular senescence might contribute to the diverse, and seemingly incongruent, processes of tumor suppression, tumor promotion, tissue repair, and aging.

MnSOD upregulation induces autophagic programmed cell death in senescent keratinocytes

Senescence is a state of growth arrest resulting mainly from telomere attrition and oxidative stress. It ultimately leads to cell death. We have previously shown that, in keratinocytes, senescence is induced by NF-kappaB activation, MnSOD upregulation and H₂O₂ overproduction. We have also shown that senescent keratinocytes do not die by apoptosis but as a result of high macroautophagic activity that targets the primary vital cell components. Here, we investigated the mechanisms that activate this autophagic cell death program. We show that corpses occurring at the senescence plateau display oxidatively-damaged mitochondria and nucleus that colocalize with autophagic vacuoles. The occurrence of such corpses was decreased by specifically reducing the H₂O₂ level with catalase, and, conversely, reproduced by overexpressing MnSOD or applying subtoxic doses of H₂O₂. This H₂O₂-induced cell death did occur through autophagy since it was accompanied by an accumulation of autophagic vesicles as evidenced by Lysotracker staining, LC3 vesiculation and transmission electron microscopy. Most importantly, it was partly abolished by 3-methyladenine, the specific inhibitor of autophagosome formation, and by anti-Atg5 siRNAs. Taken together these results suggest that autophagic cell death is activated in senescent keratinocytes because of the upregulation of MnSOD and the resulting accumulation of oxidative damages to nucleus and mitochondria.

Alterations in chromatin are associated with increases in collagen III expression in aging nephropathy

Aging nephropathy is a slowly progressive fibrotic process that affects all compartments of the kidney and eventually impairs kidney function; however, little is known about the mechanisms that contribute to this process. These studies examined the epigenetic control of expression of collagen III (Col3a1), a matrix protein that contributes to kidney fibrosis. Using real-time PCR, Western blotting, and chromatin immunoprecipitation assay of kidneys harvested from 4- and 24-mo-old ad libitum-fed F344 rats, we found increased transcription of Col3a1 that was associated with increased RNA polymerase II recruitment despite elevated posttranslational histone modification (H3K27me3) normally associated with gene silencing. A reduction in the density of another repressive modification (H3K9me3) at the Col3a1 locus in aged rats suggests that cooperation between Polycomb- and heterochromatin-mediated systems are required to maintain repression of the Col3a1 gene. These findings demonstrate alterations in epigenetic control of gene expression in association with the fibrosis of aging nephropathy.