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

Acute kidney injury in the elderly: pathogenesis, diagnosis and therapy

Elderly patients, especially those with chronic kidney disease, are at least a 3.5-fold higher risk for the development of acute kidney injury (AKI). With aging, renal functional reserve is lower owing to specific cellular changes that affect function. Molecular studies are elucidating these cellular changes and offer the prospect of designing novel therapeutics. The spectrum of AKI in elderly patients is wide but is over-represented by prerenal and postrenal (obstructive) etiologies. This reflects potentially nephrotoxic clinical variables, such as combordid states, impaired baseline renal function, polypharmacy and an increase in high-risk procedures. In this population, the development of AKI can lead to longer hospital stays, higher mortality rates and an increased risk for the development of chronic kidney disease and end-stage renal disease. Careful attention to clinical risk factors, avoidance of nephrotoxic insults and meticulous supportive care for patients who develop AKI is critical in alleviating the burden of this problem.

Aldosterone induces apoptosis in rat podocytes: role of PI3-K/Akt and p38MAPK signaling pathways

BACKGROUND

Podocytes play a critical role in the pathogenesis of glomerulosclerosis. Increasing evidence suggests that aldosterone (ALD) is involved in the initiation and progression of glomerular damage. It is, however, unknown whether there is a direct injurious effect of ALD on podocytes. Therefore, in the present study, we evaluated the effect of ALD on podocyte apoptosis and studied the role of phosphatidylinositol 3-kinase/Akt (PI3-K/Akt) and p38 mitogen-activated protein kinase (p38MAPK) signaling pathways in this process.

METHODS

Podocytes were incubated in media containing either buffer or increasing concentrations of ALD (10(-9) approximately 10(-5)M) for variable time periods. The cells were also treated with either wortmannin (inhibitor of PI3-K, 100 nM), SB202190 (SB20, inhibitor of p38MAPK, 10 microM) or buffer. All treatments were performed with or without ALD (10(-7)M) for 24 h. At the end of the incubation period, apoptosis was evaluated by cell nucleus staining and flow cytometric analyses. Activation of PI3-K/Akt and p38MAPK phosphorylation of cultured rat podocytes was evaluated by performing Akt kinase assay and Western blot, respectively.

RESULTS

Apoptosis of cultured rat podocytes was induced by ALD in a dose- and time-dependent manner. ALD inhibited the activity of PI3-K/Akt and increased the activation of p38MAPK. PI3-K/Akt activity was further inhibited by the addition of wortmannin to the cells in the presence of ALD. This was accompanied by a significant increase in apoptosis. ALD-induced p38MAPK phosphorylation and apoptosis were inhibited when the cells were pretreated with SB20. Furthermore, treatment with spironolactone not only attenuated the proapoptotic effect of ALD, but also significantly reversed its effects on PI3-K/Akt and p38MAPK signaling pathways.

CONCLUSION

ALD induces apoptosis in rat podocytes through inhibition of PI3-K/Akt and stimulation of p38 MAPK signaling pathways. Spironolactone attenuates ALD-induced podocyte apoptosis, thereby positioning this compound as a potential promising target of intervention in human renal damage.

Accelerating stem cell proliferation by down-regulation of cell cycle regulator p21

BACKGROUND

Tissue engineering is often limited by the time required for culture expansion of cells necessary for scaffold seeding. Cell cycle regulators control entry and exit into the cell cycle and as such regulate cellular proliferation rates. The authors hypothesized that transient alteration in cell cycle regulators can be utilized as a means to accelerate stem cell proliferation.

METHODS

Mesenchymal stem cells were harvested from wild-type mice and mice deficient in the cell cycle regulator p21. Wild-type cells were treated with small interfering RNA against p21 in two- or three-dimensional cultures in vitro. Cellular proliferation and the potential for cellular differentiation into the bone or fat lineage were assessed.

RESULTS

Mesenchymal stem cells treated with small interfering RNA targeting p21 demonstrated a significant decrease in p21 protein and mRNA expression 96 hours after treatment. They also proliferated significantly faster than control cells (2.5 to three times) in both two- and three-dimensional culture. Similarly, cells harvested from p21-deficient mice demonstrated a significant acceleration in cellular proliferation. Inhibition of p21 expression was not associated with significant changes in spontaneous cellular differentiation. However, transient p21 inhibition promoted both osteoblastic and adipogenic differentiation when cells were exposed to differentiation medium.

CONCLUSIONS

Transient inhibition of the cell cycle regulator p21 results in significant acceleration of mesenchymal stem cell proliferation without promoting spontaneous cellular differentiation. Exposure to differentiation medium results in increased cellular differentiation toward the osteoblast and fat lineage. Manipulation of cell cycle regulators may represent a novel means by which stem cell proliferation can be accelerated, thereby decreasing the time required for scaffold synthesis in tissue engineering.

Senescent keratinocytes die by autophagic programmed cell death

Normal cells reach senescence after a specific time and number of divisions, leading ultimately to cell death. Although escape from this fate may be a requisite step in neoplastic transformation, the mechanisms governing senescent cell death have not been well investigated. We show here, using normal human epidermal keratinocytes, that no apoptotic markers appear with senescence. In contrast, the expression of several proteins involved in the regulation of macroautophagy, notably Beclin-1 and Bcl-2, was found to change with senescence. The corpses occurring at the senescence growth plateau displayed a large central area delimited by the cytokeratin network that contained a huge quantity of autophagic vacuoles, the damaged nucleus, and most mitochondria. 3-methyladenine, an inhibitor of autophagosome formation, but not the caspase inhibitor zVAD, prevented senescent cell death. We conclude that senescent cells do not die by apoptosis, but as a result of high macroautophagic activity that targets the primary vital cell components.

Accelerated senescence in the kidneys of patients with type 2 diabetic nephropathy

We examined the hypothesis that senescence represents a proximate mechanism by which the kidney is damaged in type 2 diabetic nephropathy (DN). As a first step, we studied whether the senescence-associated β-galactosidase (SA-β-Gal) and the cell cycle inhibitor p16INK4A are induced in renal biopsies from patients with type 2 DN. SA-β-Gal staining was approximately threefold higher ( P < 0.05) than in controls in the tubular compartment of diabetic kidneys and correlated directly with body mass index and blood glucose. P16INK4A expression was significantly increased in tubules ( P < 0.005) and in podocytes ( P = 0.04). Nuclear p16INK4A in glomeruli was associated with proteinuria ( P < 0.002), while tubular p16INK4A was directly associated with body mass index, LDL cholesterol, and HbA1c ( P < 0.001–0.05). In a parallel set of experiments, proximal tubule cells passaged under high glucose presented a limited life span and an approximately twofold increase in SA-β-Gal and p16INK4A protein. Mean telomere lengths decreased ∼20% as an effect of replicative senescence. In addition, mean telomere decreased further by ∼30% in cells cultivated under high glucose. Our results show that the kidney with type 2 diabetic nephropathy displays an accelerated senescent phenotype in defined renal cell types, mainly tubule cells and, to a lesser extent, podocytes. A similar senescent pattern was observed when proximal tubule cell cultures where incubated under high-glucose media. These changes are associated with shortening tubular telomere length in vitro. These findings indicate that diabetes may boost common pathways involving kidney cell senescence, thus reinforcing the role of the metabolic syndrome on biological aging of tissues.

The impact of aging on kidney repair

The process of normal aging affects organ homeostasis as well as responses to acute and chronic injury. In view of the rapid growth in the elderly population, it is increasingly important for us to develop a mechanistic understanding of how these age-dependent changes can impact the susceptibility and response of the kidney to injurious stimuli. In this overview, we focus on the current understanding of those mechanisms by reviewing how cellular changes in the aging kidney might lead to a diminished proliferative reserve, an increased tendency for apoptosis, alterations in growth factor profiles, and changes in potential progenitor and immune cell functions. A better understanding of these processes may help us to define new targets for studying kidney repair and could ultimately lead to new therapeutic strategies that are specifically tailored for treatment of the elderly population.

Changes in the level and distribution of Ku proteins during cellular senescence

Aging is associated with accumulation of genomic rearrangements consistent with aberrant repair of DNA breaks. We have shown previously that DNA repair by non-homologous end joining (NHEJ) becomes less efficient and more error-prone in senescent cells. Here, we show that the levels of Ku70 and Ku80 drop approximately twofold in replicatively senescent cells. Intracellular distribution of Ku also changes. In the young cells roughly half of Ku is located in the nucleus and half in the cytoplasm. In senescent cells the nuclear levels of Ku do not change, while the cytoplasmic Ku fraction disappears. Upon treatment with gamma-irradiation, in the young cells cytoplasmic Ku moved into the nuclear and membrane fractions, while no change in the Ku distribution occurred in senescent cells. Upon treatment with UVC Ku moved out of the nucleus in the young cells, while most Ku remained nuclear in senescent cells. This suggests that the nuclear Ku in senescent cells is unable to respond to DNA damage. We hypothesize that overall decline in Ku levels changes in Ku intracellular distribution, and the loss of appropriate response of Ku to DNA damage in senescent cells contribute to the decline of NHEJ and to age-related genomic instability.

A dual role of p21 in stem cell aging

A decline in adult stem cell function occurs during aging, likely contributing to the decline in organ homeostasis and regeneration with age. An emerging field in aging research is to analyze molecular pathways limiting adult stem cell function in response to macromolecular damage accumulation during aging. Current data suggest that the p21 cell cycle inhibitor has a dual role in stem cell aging: On one hand, p21 protects adult stem cells from acute genotoxic stress by preventing inappropriate cycling of acutely damaged stem cells. On the other hand, p21 activation impairs stem cell function and survival of aging telomere dysfunctional mice indicating that p21 checkpoint function is disadvantageous in the context of chronic and persistent damage, which accumulates during aging. This article focuses on these dual roles of p21 in aging stem cells.

Cellular senescence in the glaucomatous outflow pathway

The mechanisms responsible for the progressive malfunction of the trabecular meshwork (TM)-Schlemm's canal (SC) conventional outflow pathway tissue in primary open angle glaucoma (POAG) are still not fully understood. To determine whether POAG is characterized by an accumulation of senescent cells, similar to what has been described in other diseases, we have compared the levels of the senescence marker senescence-associated-beta-galactosidase (SA-beta-gal) in the outflow pathway cells of POAG and age-matched control donors. POAG donors demonstrated a statistically significant fourfold increase in the percentage of SA-beta-gal positive cells. These results suggest a potential role for cellular senescence in the pathophysiology of the outflow pathway.

Statin Monotherapy Attenuates Renal Injury in a Salt-Sensitive Hypertension Model of Renal Disease

BACKGROUND

Several salutary biological effects of statins have been described. We sought to investigate more closely the anti-inflammatory and antiproliferative effects of simvastatin (SIMV) in a model of hypertension and progressive renal disease, as well as its effects on the cyclin-cdk inhibitors p21 and p27.

METHODS

Munich-Wistar rats received the nitric oxide (NO) synthase inhibitor L-NAME (25 mg/kg/day p.o.) for 20 days accompanied by a high-salt diet (HS, 3% Na) and then were kept on HS for 60 days. Animals were then divided into two groups: vehicle (VH) or SIMV 2 mg/kg/day p.o. Albuminuria and tail-cuff pressure were determined at 30 and 60 days. RT-PCR was done to assess renal expression of TGF-beta1, collagen I and III, fibronectin, p27, p21 and monocyte chemoattractant protein-1 (MCP-1). Renal protein expression was assessed by Western blot (proliferating cell nuclear antigen (PCNA)) and immunostaining (macrophage, lymphocyte, PCNA).

RESULTS

SIMV did not prevent the development of severe hypertension or albuminuria. SIMV-treated animals had less severe renal interstitial inflammation and cell proliferation. MCP-1 expression was significantly diminished in the SIMV-treated animals (55.4 +/- 7.3 vs. 84.4 +/- 8.2 OD, p = 0.02). mRNA renal expression for p27 and TGF-beta did not change between groups, but p21 mRNA renal expression, highly induced in this model, significantly decreased with SIMV treatment (31.6 +/- 6.6 vs. 50.2 +/- 5.8 OD, p < 0.05). The interstitial fibrosis score significantly decreased with SIMV (2.46 +/- 0.40 vs. 4.07 +/- 0.38%, p < 0.01), which was confirmed by a decrease in renal collagen I and fibronectin expression. Serum cholesterol level did not change with SIMV.

CONCLUSION

SIMV attenuated interstitial fibrosis associated with this model of hypertensive renal disease. The mechanism involved MCP-1 downregulation. SIMV treatment was also associated with a p21 downregulation in the kidney, which might be involved in the protection of renal scarring.

Chronic renal allograft rejection: Pathophysiologic considerations

Chronic rejection is currently the most prevalent cause of renal transplant failure. Clinically, chronic rejection presents by chronic transplant dysfunction, characterized by a slow loss of function, often in combination with proteinuria and hypertension. The histopathology is not specific in most cases but transplant glomerulopathy and multilayering of the peritubular capillaries are highly characteristic. Several risk factors have been identified such as young recipient age, black race, presensitization, histoincompatability, and acute rejection episodes, especially vascular rejection episodes and rejections that occur late after transplantation. Chronic rejection develops in grafts that undergo intermittent or persistent damage from cellular and humoral responses resulting from indirect recognition of alloantigens. Progression factors such as advanced donor age, renal dysfunction, hypertension, proteinuria, hyperlipidemia, and smoking accelerate deterioration of renal function. At the tissue level, senescence conditioned by ischemia/reperfusion (I/R) may contribute to the development of chronic allograft nephropathy (CAN). The most effective option to prevent renal failure from chronic rejection is to avoid graft injury from both immune and nonimmune mechanism together with nonnephrotoxic maintenance immunosuppression.

Aging, tumor suppression and cancer: high wire-act!

Evolutionary theory holds that aging is a consequence of the declining force of natural selection with age. We discuss here the evidence that among the causes of aging in complex multicellular organisms, such as mammals, is the antagonistically pleiotropic effects of the cellular responses that protect the organism from cancer. Cancer is relatively rare in young mammals, owing in large measure to the activity of tumor suppressor mechanisms. These mechanisms either protect the genome from damage and/or mutations, or they elicit cellular responses-apoptosis or senescence--that eliminate or prevent the proliferation of somatic cells at risk for neoplastic transformation. We focus here on the senescence response, reviewing its causes, regulation and effects. In addition, we describe recent data that support the idea that both senescence and apoptosis may indeed be the double-edged swords predicted by the evolutionary hypothesis of antagonistic pleiotropy-protecting organisms from cancer early in life, but promoting aging phenotypes, including late life cancer, in older organisms.

Effects of donor age on proteasome activity and senescence in trabecular meshwork cells

The mechanisms involved in the progressive malfunction of the trabecular meshwork (TM) in glaucoma are not yet understood. To study age-related changes in human TM cells, we isolated primary TM cell cultures from young (ages 9, 14, and 25) and old (ages 66, 70, and 73) donors, and compared levels of oxidized proteins, autofluorescence, proteasome function, and markers for cellular senescence. TM cells from old donors showed a 3-fold increase in oxidized proteins and a 7.5-fold decrease of proteasome activity. Loss of proteasome function was not associated with decreased proteasome content but with partial replacement of the proteolytic subunit PSMB5 with the inducible subunit LMP7. Cells from old donors also demonstrated features characteristic of cellular senescence associated with phosphorylation of p38MAPK but only a modest increase in p53. These data suggest that age-related proteasome inhibition and cellular senescence could contribute to the pathophysiological alterations of the TM in glaucoma.

Role of Podocytes for Reversal of Glomerulosclerosis and Proteinuria in the Aging Kidney After Endothelin Inhibition

The cause of focal-segmental glomerulosclerosis as a consequence of physiological aging, which is believed to be inexorable, is unknown. This study investigated whether inhibition of endothelin-1, a growth-promoting peptide contributing to renal injury in hypertension and diabetes, affects established glomerulosclerosis and proteinuria in the aged kidney. We also determined the role of endothelin receptors for podocyte injury in vivo and in vitro. Aged Wistar rats, a model of spontaneous age-dependent glomerulosclerosis, were treated with the orally active endothelin subtype A (ET A ) receptor antagonist darusentan, and evaluation of renal histology, renal function studies, and expression analyses were performed. In vitro experiments using puromycin aminonucleoside to induce podocyte injury investigated the role of ET A receptor signaling for apoptosis, cytoskeletal injury, and DNA synthesis. In aged Wistar rats, established glomerulosclerosis and proteinuria were reduced by >50% after 4 weeks of darusentan treatment, whereas blood pressure, glomerular filtration rate, or tubulo-interstitial renal injury remained unaffected. Improvement of structural injury in glomeruli and podocytes was accompanied by a reduction of the expression of matrix metalloproteinase-9 and p21 Cip1/WAF1 . In vitro experiments blocking ET A receptors using specific antagonists or RNA interference prevented apoptosis and structural damage to podocytes induced by puromycin aminonucleoside. In conclusion, these results support the hypothesis that endogenous endothelin contributes to glomerulosclerosis and proteinuria in the aging kidney. The results further suggest that age-dependent glomerulosclerosis is not merely a “degenerative” but a reversible process locally confined to the glomerulus involving recovery of podocytes from previous injury.

Cigarette Smoke Induces Senescence in Alveolar Epithelial Cells

Cellular senescence is a state of irreversible growth arrest induced either by telomere shortening (replicative senescence) or by telomere-independent signals (stress-induced senescence). The alveolar epithelium is often injured by a variety of inhaled toxins, including cigarette smoke (CS). In the present study, we investigated whether exposure to CS induces senescence of alveolar epithelial cells. In vitro experiments showed that exposure of A549 cells or normal human alveolar epithelial cells to sublethal concentrations of aqueous CS extracts induced cellular senescence. The senescence was characterized by a dose- and time-dependent increase in senescence-associated beta-galactosidase activity, senescence-associated changes in cell morphology, an increase in cell size and lysosomal mass, accumulation of lipofuscin, overexpression of p21(CIP1/WAF1/Sdi1) protein, and irreversible growth arrest. In vivo experiments in Institute for Cancer Research mice showed that inhalation of CS for 2 wk induced increases in senescence-associated beta-galactosidase activity, lipofuscin accumulation, and p21(CIP1/WAF1/Sdi1) protein expression in alveolar epithelial cells. These results suggest that CS induces a phenotype that is indistinguishable from that of senescence in alveolar epithelial cells. The induction of cellular senescence by CS may contribute to impaired re-epithelialization, leading to CS-related chronic lung diseases.

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.

DNA end joining becomes less efficient and more error-prone during cellular senescence

Accumulation of somatic mutations is thought to contribute to the aging process. Genomic instability has been shown to increase during aging, suggesting an aberrant function of DNA double-strand break (DSB) repair. Surprisingly, DSB repair has not been examined with respect to cellular senescence. Therefore, we have studied the ability of young, presenescent, and senescent normal human fibroblasts to repair DSBs in transfected DNA by using a fluorescent reporter substrate. We have found that the efficiency of end joining is reduced up to 4.5 fold in presenescent and senescent cells, relative to young cells. Sequence analysis of end junctions showed that the frequency of precise ligation was higher in young cells, whereas end joining in old cells was associated with extended deletions. These results indicate that end joining becomes inefficient and more error-prone during cellular senescence. Furthermore, the ability to use microhomologies for end joining was compromised in senescent cells, suggesting that young and senescent cells may use different end joining pathways. We hypothesize that inefficient and aberrant end joining is a likely mechanism underlying the age-related genomic instability and higher incidence of cancer in the elderly.

Influence of age and vitamin E on post-ischemic acute renal failure

The aging process causes progressive deterioration in kidney structure and function. Aberrant generation of reactive oxygen species has been implicated in both age-related and ischemia-related tissue injury. Vitamin E (VE), one of the most powerful and effective exogenous antioxidants, prevents lipid peroxidation and protects against the effects of oxidative stress. The objective of this study was to determine the influence of age and VE on post-ischemic acute renal failure (ARF). Young adult, middle-aged and aged male Wistar rats were maintained on three different 30-day diets: Normal, VE absent and VE supplemented. On day 30, urinary protein and serum cholesterol and VE were measured. On day 31, rats were subjected to 60' clamping of the left renal artery plus right nephrectomy. Inulin clearance (InCl) was performed 48 h after renal ischemia. Malondialdehyde (MDA) was measured in the cortex of normal and 48-h post-ischemic kidneys. Urinary protein and serum cholesterol were higher in aged rats than in other rats. With aging, InCl decreased progressively. Vitamin E deficiency aggravated ARF. In middle-aged and aged rats, VE supplementation protected against ARF. In the absence of VE, MDA increased with age. In conclusion, our data suggest that ARF becomes more severe with age and that ischemia/reperfusion injury is exacerbated when antioxidant-scavenging ability of the kidney is impaired by VE deficiency. Supplementation with VE is essential for protecting aging kidneys against ischemic ARF.

Cell senescence in rat kidneys in vivo increases with growth and age despite lack of telomere shortening

BACKGROUND

Somatic cells in vitro have a finite life expectancy before entering a state of senescence, but it is unclear whether this state occurs in vivo in kidney development, growth, and aging. We previously showed that human kidney cortex displays telomere shortening with age. In this study, we compared the structural and functional changes in rat kidney with age to phenomena associated with cellular senescence in vitro.

METHODS

We assessed the changes in Fischer 344 rat kidneys from age 1 to 9 months to define growth and development and from age 9 to 24 months to define aging.

RESULTS

Rat kidney telomeres were approximately 35 to 40 kb long and did not shorten significantly. Expression of mRNA for p16INK4a, a characteristic senescence gene in vitro, was undetectable in most young rats but rose 27 fold during growth and a further 72-fold during aging. p16INK4a protein was localized to the nucleus and increased with age. p16INK4a mRNA also increased in other tissues. Lipofuscin and senescence-associated beta-galactosidase increased in epithelium with growth and aging and their occurrence was significantly associated with each other. Lipofuscin was particularly found in atrophic nephrons.

CONCLUSION

We conclude that cell senescence occurs in both growth and aging in rat kidney and may contribute to the age-related pathology. These changes are not due to telomere shortening, but may reflect cumulative environmental stress.

Cancer and aging: a model for the cancer promoting effects of the aging stroma

The incidence of cancer rises exponentially with age in humans and many other mammalian species. Malignant tumors are caused by an accumulation of oncogenic mutations. In addition, malignant tumorigenesis requires a permissive tissue environment in which mutant cells can survive, proliferate, and express their neoplastic phenotype. We propose that the age-related increase in cancer results from a synergy between the accumulation of mutations and age-related, pro-oncogenic changes in the tissue milieu. Most age-related cancers derive from the epithelial cells of renewable tissues. An important element of epithelial tissues is the stroma, the sub-epithelial layer composed of extracellular matrix and several cell types. The stroma is maintained, remodeled and repaired by resident fibroblasts, supports and instructs the epithelium, and is essential for epithelial function. One change that occurs in tissues during aging is the accumulation of epithelial cells and fibroblasts that have undergone cellular senescence. Cellular senescence irreversibly arrests proliferation in response to damage or stimuli that put cells at risk for neoplastic transformation. Senescent cells secrete factors that can disrupt tissue architecture and/or stimulate nearby cells to proliferate. We therefore speculate that their presence may create a pro-oncogenic tissue environment that synergizes with oncogenic mutations to drive the rise in cancer incidence with age. Recent evidence lends support to this idea, and suggests that senescent stromal fibroblasts may be particularly adept at creating a tissue environment that can promote the development of age-related epithelial cancers.

Angiotensin II induces apoptosis in rat glomerular epithelial cells

ANG II has been shown to modulate kidney cell growth and contribute to the pathobiology of glomerulosclerosis. Glomerular visceral epithelial cell (GEC) injury or loss is considered to play a pivotal role in the initiation and progression of glomerulosclerosis. In the present study, we investigated the effect of ANG II on GEC apoptosis. Rat GECs were incubated with increasing doses of ANG II for variable time periods. Apoptosis was evaluated by cell nucleus staining and DNA fragmentation assay. ANG II induced GEC apoptosis in a dose- and time-dependent manner. The proapoptotic effect was attenuated by the ANG II receptor type 1 antagonist losartan or the ANG II receptor type 2 antagonist PD-123319 and was completely blocked by incubation with the combined antagonists. Moreover, ANG II stimulated transforming growth factor (TGF)-beta1 production as measured by ELISA. GECs exposed to TGF-beta1 demonstrated a dose- and time-dependent increase in apoptosis. ANG II-induced apoptosis was significantly inhibited by addition of anti-TGF-beta1 antibody. ANG II also upregulated the expression of Fas, FasL, and Bax and downregulated the expression of Bcl-2 in GECs. These studies suggest that ANG II induces GEC apoptosis by a mechanism involving TGF-beta1 expression that may, importantly, contribute to the pathogenesis of glomerulosclerosis.

Markers of senescence?

The specific identification of cellular senescence in clinical material has important implications for determining the role of senescence in age-related pathologies and in neoplasia in certain tumours. One suggested marker of senescence is the histochemical identification of a specific beta-galactosidase enzyme operative at pH 6.0. However, recent data indicate that this enzyme may not be specific for senescence in all tissues and probably represents the expression of endogenous lysosomal acid beta-galactosidase, which is expressed by a variety of differentiated cell types.