Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Senescence”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed2005

The ability of E1A to rescue ras-induced premature senescence and confer transformation relies on inactivation of both p300/CBP and Rb family proteins.

In primary cells, oncogenic ras induces a stable growth arrest known as premature senescence. Ras-induced premature senescence is considered as a tumor-suppressing defense response that needs to be bypassed before oncogenic potential ras can be revealed. To gain insights into the mechanism of senescence bypass during oncogenic transformation, we dissected the activities of an adenoviral oncoprotein E1A, which is capable of overcoming ras-induced senescence. Our results have indicated that the senescence bypassing activity resides in the NH2 terminus and requires both Rb-binding and p300/CBP-binding functions of E1A. Although interference with the p16(INK4A)/Rb pathway or inactivation of p300/CBP alone did not lead to senescence bypass, these two types of genetic alterations complemented the Rb-binding defective and the p300/CBP-binding defective mutants of E1A, respectively, to rescue premature senescence. Therefore, genetic alterations disrupting the p16(INK4A)/Rb pathway or the p300/CBP functions both contribute to the bypass of senescence. We further showed that p300/CBP were essential for ras-induced p53 activity, providing a potential mechanism underlying the important role of p300/CBP in senescence. Furthermore, p300/CBP inactivation led to cellular transformation in cooperation with the p300/CBP-binding defective E1A mutants, MDM2 and Ha-RasV12. These results have shown that p300 and CBP are integral components of the pathway that mediates ras-induced senescence. The critical role of p300 and CBP in the senescence response that limits the oncogenic potential of ras has provided a mechanistic basis for the tumor-suppressing function of these proteins.

Adenovirus E1A Proteins↗
PubMed2006

Vascular smooth muscle cells undergo telomere-based senescence in human atherosclerosis: effects of telomerase and oxidative stress.

Although human atherosclerosis is associated with aging, direct evidence of cellular senescence and the mechanism of senescence in vascular smooth muscle cells (VSMCs) in atherosclerotic plaques is lacking. We examined normal vessels and plaques by histochemistry, Southern blotting, and fluorescence in situ hybridization for telomere signals. VSMCs in fibrous caps expressed markers of senescence (senescence-associated beta-galactosidase [SAbetaG] and the cyclin-dependent kinase inhibitors [cdkis] p16 and p21) not seen in normal vessels. In matched samples from the same individual, plaques demonstrated markedly shorter telomeres than normal vessels. Fibrous cap VSMCs exhibited markedly shorter telomeres compared with normal medial VSMCs. Telomere shortening was closely associated with increasing severity of atherosclerosis. In vitro, plaque VSMCs demonstrated morphological features of senescence, increased SAbetaG expression, reduced proliferation, and premature senescence. VSMC senescence was mediated by changes in cyclins D/E, p16, p21, and pRB, and plaque VSMCs could reenter the cell cycle by hyperphosphorylating pRB. Both plaque and normal VSMCs expressed low levels of telomerase. However, telomerase expression alone rescued plaque VSMC senescence despite short telomeres, normalizing the cdki/pRB changes. In vivo, plaque VSMCs exhibited oxidative DNA damage, suggesting that telomere damage may be induced by oxidant stress. Furthermore, oxidants induced premature senescence in vitro, with accelerated telomere shortening and reduced telomerase activity. We conclude that human atherosclerosis is characterized by senescence of VSMCs, accelerated by oxidative stress-induced DNA damage, inhibition of telomerase and marked telomere shortening. Prevention of cellular senescence may be a novel therapeutic target in atherosclerosis.

Atherosclerosis↗
PubMed2004

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.

Animals↗
PubMed1999

Senescence of the retinal pigment epithelium.

Senescence of human cells has largely been studied as an in vitro phenomenon resulting from replicative exhaustion. The literature contains many studies of retinal pigment epithelium (RPE) cells which document replicative senescence. Several studies by Burke and others illustrate the relationship between donor age and replicative lifespan, the relationship between geographical location of RPE in the posterior pole and replicative lifespan, and the phenomena of altered cellular morphology and decreased culture saturation density for senescent RPE cells. Other studies have focused on the alterations of the expression of specific genes or the alteration of enzymatic activities during the senescence of RPE cells in vitro. Recently, a technique utilizing a histochemical staining procedure for beta galactosidase has been developed which identifies senescent cells. Normal beta galactosidase histochemistry which identifies the lysosomal form of the enzyme is performed at pH 4.0, while senescence-associated beta galactosidase activity is observed at pH 6.0 and is observed in the cytoplasm. We have studied the replicative senescence of human RPE cells in vitro using this procedure and have also measured the length of chromosomal telomeres to identify the aging of cultures in vitro. Our results show that RPE cultures accumulate beta galactosidase positive cells as a function of the number of population doublings and that these data correlate with the shortening of chromosomal telomeres to a functional limit observed for many human cell types at senescence. We have also recently extended this work to the development of a senescence-associated beta galactosidase procedure for observing senescent RPE cells in vivo. Basically, the same histochemical procedure is used with a post-staining bleaching step to clearly visualize staining in the RPE. Our first studies were performed on globes from Rhesus monkeys at a variety of ages from 1 year to 29 years of age. The results show the accumulation of beta galactosidase positive cells in the older monkey eyes. We have also examined several human eyes in an attempt to observe whether any relationship exists between beta galactosidase staining and age, pathology (diabetes, basal laminar deposits), and geographical location (macula vrs. periphery). These studies represent a first effort to determine if senescent RPE are present in vivo. It will be important to extend these studies so that these data might be expressed on a quantitative bases.

Aging↗
PubMed2000

Reduction of UV-induced cell death in the human senescent fibroblasts.

We studied mechanisms by which senescent cells acquire resistance to UV-induced cellular insults. Human primary foreskin fibroblast culture was used since it undergoes cellular senescence in vitro after a limited number of passages. Senescence was induced by a brief treatment of the early passage cells with 100 microM of H2O2 for 1 h, and subsequent culture for 3 weeks. Hydrogen peroxide-treated cells showed an enhancement of senescence-associated beta-galactosidase activity. In the senescent cells, DNA fragmentation in response to UV-irradiation was found to decrease significantly compared with that in the young cells. The SAPK/JNK activation by UV irradiation was reduced in both non-treated senescent cells and the hydrogen peroxide-induced senescent cells, suggesting that a reduced DNA fragmentation by UV-irradiation in the senescent cells is closely related to the decreased SAPK/JNK activity. Since a cell cycle inhibitor, p21Waf1, has been implicated in protecting cells against apoptotic cell death, we determined p21Waf1 to assess whether its elevation has any impact on the reduction of UV-induced activation of SAPK/JNK in the senescent cells. The expression of p21Waf1 increased in both the nontreated and the hydrogen peroxide-treated senescent cells. Our study also revealed that the blockage of SAPK/JNK activation in the senescent cells was closely related to the increased level of p21Waf1. Our observation might provide clues about molecular mechanism of resistance to DNA fragmentation and the consequent cell death by UV-irradiation.

Cell Culture Techniques↗
PubMed2003

Tumor cell senescence in cancer treatment.

Cell senescence is broadly defined as the physiological program of terminal growth arrest, which can be triggered by alterations of telomeres or by different forms of stress. Neoplastic transformation involves events that inhibit the program of senescence, and tumor cells were believed until recently to have lost the ability to senesce. It has now become apparent, however, that tumor cells can be readily induced to undergo senescence by genetic manipulations or by treatment with chemotherapeutic drugs, radiation, or differentiating agents. Treatment-induced senescence, which has both similarities with, and differences from, replicative senescence of normal cells, was shown to be one of the key determinants of tumor response to therapy in vitro and in vivo. Although senescent cells do not proliferate, they remain metabolically active and produce secreted proteins with both tumor-suppressing and tumor-promoting activities. Expression of tumor-promoting factors by senescent cells is mediated, at least in part, by senescence-associated cyclin-dependent kinase inhibitors such as p21(Waf1/Cip1/Sdi1). Clinical and preclinical studies indicate that expression of different biological classes of senescence-associated growth-regulatory genes in tumor cells has significant prognostic implications. Elucidation of the genes and regulatory mechanisms that determine different aspects of tumor senescence makes it possible to design new therapeutic approaches to improving the efficacy and to decreasing the side effects of cancer therapy.

Animals↗
PubMed2004

Reflections on an unsolved problem of biology: the evolution of senescence and death.

The evolutionary theory of senescence is based largely on principles first outlined by Williams in 1957, and consists of two relatively independent parts. The first part builds on ideas first put forward by Medawar, Haldane and others, to explain how something as negative as senescence could have been positively selected in evolution, particularly since most animals in the wild do not reach an age where senescence is expressed. Williams proposed that the genes responsible for the negative effects of senecence (senescence effector genes) were fixed in evolution by a process he called antagonistic pleiotropy, wherein a subset of genes selected because they confer a reproductive advantage early in life may have harmful effects in the post-reproductive period; negative selection against these harmful effects fails because, as pointed out by Medawar, the force of natural selection declines with age. The evolutionary history of senescence-causing genes is seen as a nondirected accumulation of genes selected on a basis independent of senescence per se. In the second portion of his paper, Williams made a series of predictions about how the age of organisms at reproductive maturity, fecundity, lifespan and the timing of the onset of senescence would all interact in the life history of a species. These latter predictions, which do not depend at all on details of the mechanisms of selection of senescence effector genes, have been validated by numerous experiments over the past several decades. On the other hand, it has become increasingly evident that the senescence effector genes did not, as would be predicted by antagonistic pleiotropy, accumulate in a random, non-directed fashion in various species over evolutionary time. Rather, everything we know about these genes suggests they were present in eukaryotic founder cells shortly after, or even congruent with, the emergence of eukaryotes from their prokaryotic ancestors, and have been stringently conserved ever since. Complicated explanations of how so-called "death genes" may have evolved in eukaryotes are thus not required. It is suggested that the evolutionary theory of senescence should be focused on those evolutionary principles that have been validated experimentally, and that the notion of antagonistic pleiotropy--which cannot be experimentally validated--be dropped from our thinking about the evolution of senescence.

Aging↗
PubMed2004

Interactions of abscisic acid and sugar signalling in the regulation of leaf senescence.

Leaf senescence can be triggered by a high availability of carbon relative to nitrogen or by external application of abscisic acid (ABA). Most Arabidopsis mutants with decreased sugar sensitivity during early plant development are either ABA insensitive (abi mutants) or ABA deficient (aba mutants). To analyse the interactions of carbon, nitrogen and ABA in the regulation of senescence, wild-type Arabidopsis thaliana (L.) Heynh. and aba and abi mutants were grown on medium with varied glucose and nitrogen supply. On medium containing glucose in combination with low, but not in combination with high nitrogen supply, senescence was accelerated and sucrose, glucose and fructose accumulated strongly. In abi mutants that are not affected in sugar responses during early development (abi1-1 and abi2-1), we observed no difference in the sugar-dependent regulation of senescence compared to wild-type plants. Similarly, senescence was not affected in the sugar-insensitive abi4-1 mutant. In contrast, the abi5-1 mutant did exhibit a delay in senescence compared to its wild type. As ABA has been reported to induce senescence and ABA deficiency results in sugar insensitivity during early development, we expected senescence to be delayed in aba mutants. However, the aba1-1 and aba2-1 mutants showed accelerated senescence compared to their wild types on glucose-containing medium. Our results show that, in contrast to sugar signalling in seedlings, ABA is not required for the sugar-dependent induction of leaf senescence. Instead, increased sensitivity to osmotic stress could have triggered early senescence in the aba mutants.

Abscisic Acid↗
PubMed2001

Effects of age, sex and density on body weight of Norwegian red deer: evidence of density-dependent senescence.

There are only a few recent studies that have demonstrated senescence in ungulates and nothing is known regarding how patterns of senescence may vary as a function of density Senescence in general is linked to the cost of reproduction, which probably increases with density in ungulates and may differ between the sexes. Further, senescence in ungulates is also regarded to be a function of tooth wear rates. As density dependence and sexual differences in food choice have been well documented, this may lead to different tooth wear rates and, thus, possibly density-dependent and sex-specific patterns of senescence. We therefore investigated the effects of age, sex, density and their possible interactions on the variability of body weight in 29,047 red deer harvested during 1965-1998 from Norway, out of which 380 males and 1452 females were eight years or older. There was clear evidence that spatio-temporal variation in density correlated negatively with body weights. In addition, there was evidence of senescence in both male and female red deer. Age at onset of senescence in females was after 20 years of age and independent of population density. In males, the onset and rate of senescence increased with increasing population density. The onset of senescence for males was at ca. 12 years of age at low density, but decreased to approximately ten years of age at high density. The pattern of density-dependent senescence in males, but not that in females, can be explained if (i) the cost of reproduction increases with density more strongly in male than in female red deer, and/or (ii) tooth wear rates are density dependent in males, but not in females. We discuss the ability of these two different, not mutually exclusive hypotheses in explaining the observed pattern of senescence.

Aging↗
PubMed2005

Characterization of markers to determine the extent and variability of leaf senescence in Arabidopsis. A metabolic profiling approach.

Comparison of the extent of leaf senescence depending on the genetic background of different recombinant inbred lines (RILs) of Arabidopsis (Arabidopsis thaliana) is described. Five RILs of the Bay-0 x Shahdara population showing differential leaf senescence phenotypes (from early senescing to late senescing) were selected to determine metabolic markers to discriminate Arabidopsis lines on the basis of senescence-dependent changes in metabolism. The proportion of gamma-aminobutyric acid, leucine, isoleucine, aspartate, and glutamate correlated with (1) the age and (2) the senescence phenotype of the RILs. Differences were observed in the glycine/serine ratio even before any senescence symptoms could be detected in the rosettes. This could be used as predictive indicator for plant senescence behavior. Surprisingly, late-senescing lines appeared to mobilize glutamine, asparagine, and sulfate more efficiently than early-senescing lines. The physiological basis of the relationship between leaf senescence and flowering time was analyzed.

Amino Acids↗
PubMed2006

A novel nuclear-localized CCCH-type zinc finger protein, OsDOS, is involved in delaying leaf senescence in rice.

Leaf senescence is a developmentally programmed degeneration process, which is fine tuned by a complex regulatory network for plant fitness. However, molecular regulation of leaf senescence is poorly understood, especially in rice (Oryza sativa), an important staple crop for more than half of the world population. Here, we report a novel nuclear-localized CCCH-type zinc finger protein, Oryza sativa delay of the onset of senescence (OsDOS), involved in delaying leaf senescence in rice. The expression of OsDOS was down-regulated during natural leaf senescence, panicle development, and pollination, although its transcripts were accumulated in various organs. RNAi knockdown of OsDOS caused an accelerated age-dependent leaf senescence, whereas its overexpression produced a marked delay of leaf senescence, suggesting that it acts as a negative regulator for leaf senescence. A genome-wide expression analysis further confirmed its negative regulation for leaf senescence and revealed that, in particular, the jasmonate (JA) pathway was found to be hyperactive in the OsDOS RNAi transgenic lines but impaired in the OsDOS overexpressing transgenic lines, indicating that this pathway is likely involved in the OsDOS-mediated delaying of leaf senescence. Furthermore, methyl JA treatments of both seeds and detached leaves from the RNAi and the overexpressing transgenic lines showed hyper- and hyporesponses, respectively, consistent with the negative regulation of the JA pathway by OsDOS. Together, these results indicate that OsDOS is a novel nuclear protein that delays leaf senescence likely, at least in part, by integrating developmental cues to the JA pathway.

Amino Acid Sequence↗
PubMed1997

Increases in Cytosolic Ca2+ in Parsley Mesophyll Cells Correlate with Leaf Senescence.

The ability to maintain the cytoplasmic Ca2+ concentration ([Ca2+]cyt) at homeostatic levels has been examined during leaf senescence in detached parsley (Petroselinum crispum) leaves. Fluorescence ratiometric imaging of mesophyll cells isolated from parsley leaves at various senescence stages and loaded with the Ca2+ indicator fura-2 has revealed a distinct elevation of [Ca2+]cyt, which was positively correlated with the progress of leaf senescence. This initial increase of [Ca2+]cyt, which was first observed in cells isolated from 3-d-senescent leaves, occurred 1 d before or in parallel with changes in two established senescence parameters, chlorophyll loss and lipid peroxidation. However, the [Ca2+]cyt elevation followed by 2 d the initial increase in the senescence-associated proteolysis. Whereas the [Ca2+]cyt of nonsenescent cells remained at the basal level, the elevated [Ca2+]cyt of the senescent cells was a long-lasting effect. Experimental retardation of senescence processes, achieved by pretreatment of detached leaves with the cytokinin benzyladenine, resulted in maintenance of homeostatic levels of [Ca2+]cyt in cells isolated from 3-d-senescent leaves. These observations demonstrate for the first time to our knowledge a correlation between elevated [Ca2+]cyt and the process of senescence in parsley leaves. Such senescence-associated elevation of [Ca2+]cyt, which presumably results from a loss of the cell's capability to extrude Ca2+, may serve as a signal inducing subsequent deteriorative processes.

Journal Article↗
PubMed1979

Ethylene as a regulator of senescence in tobacco leaf discs.

The regulatory role of ethylene in leaf senescence was studied with excised tobacco leaf discs which were allowed to senesce in darkness. Exogenous ethylene, applied during the first 24 hours of senescence, enhanced chlorophyll loss without accelerating the climacteric-like pattern of rise in both ethylene and CO(2), which occurred in the advanced stage of leaf senescence. Rates of both ethylene and CO(2) evolution increased in the ethylene-treated leaf discs, especially during the first 3 days of senescence. The rhizobitoxine analog, aminoethoxy vinyl glycine, markedly inhibited ethylene production and reduced respiration and chlorophyll loss. Pretreatment of leaf discs with Ag(+) or enrichment of the atmosphere with 5 to 10% CO(2) reduced chlorophyll loss, reduced rate of respiration, and delayed the climacteric-like rise in both ethylene and respiration. Ag(+) was much more effective than CO(2) in retarding leaf senescence. Despite their senescence-retarding effect, Ag(+) and CO(2), which are known to block ethylene action, stimulated ethylene production by the leaf discs during the first 3 days of the senescing period; Ag(+) was more effective than CO(2). The results suggest that although ethylene production decreases prior to the climacteric-like rise during the later stages of senescence, endogenous ethylene plays a considerable role throughout the senescence process, presumably by interacting with other hormones participating in leaf senescence.

Journal Article↗
PubMed1980

Mechanism of monocarpic senescence in rice.

During grain formation stage (90 to 110 days), the youngest flag leaf of rice (Oryza sativa L. cv. Jaya) remained metabolically most active (as indicated by cellular constituents and enzyme activities) and the third leaf the least active. At the grain development stage (110 to 120 days) the above pattern of age-related senescence of the flag leaf completely changed and it senesced at a faster rate than the second leaf which remained metabolically active even up to grain maturation time (120 to 130 days), when both the flag and the third leaf partially senesced. Removal of any leaf temporarily arrested senescence of the remaining attached leaves, that of flag leaf did not hasten senescence of the second leaf, while that of either the second or the third accelerated senescence of the flag. Removal of the inflorescence after emergence or foliar treatment of intact plant with kinetin equally delayed senescence and produced an age-related, sequential mode of senescence or leaves. Both translocation and retention of (32)P by the flag leaf were maximum at the time of grain formation and that by the second leaf was maintained even up to grain maturation time. The induction of senescence of the flag leaf was preceded by a plentiful transport of (32)P to the grains. Kinetin treatment decreased the transport of (32)P, prolonged its duration, and almost equally involved all of the leaves in this process. The pattern of senescence of isolated leaf tips was similar to that of attached leaves. The level of endogenous abscisic acid-like substance(s) maintained a close linearity with the senescence behavior of the leaves of intact and defruited plants during aging, and the rise in abscisic acid in the flag leaf was also preceded by higher (32)P transport to the grains.

Journal Article↗
PubMed1992

Physiological changes accompanying senescence in the ephemeral daylily flower.

The daylily flower, Hemerocallis hybrid cv Cradle Song, develops from the opening bud to full senescence in 36 hours. Unlike other ephemeral flowers studied to date, it does not respond to ethylene, but other senescence phenomena are similar. There was a small respiration climacteric coinciding with early flower senescence, and it was also observed in isolated petals and petal slices. Cycloheximide abolished the climacteric and delayed senescence in all three systems. Petal apparent free space increased from 30% at bud opening to 38% at the onset of senescence, and sugar efflux increased from 0.2 to 2.8 milligrams per gram of fresh weight per hour during the same period. A sharp increase in ion efflux from 0.8 to 4.0 micromoles of NaCl equivalents per gram of fresh weight per hour, coinciding with the climacteric, was abolished by cycloheximide. Uptake of radiolabeled inorganic phosphate by petal slices from 100 micromolar solution increased during onset of senescence from 6 to 10 nmoles per gram of fresh weight per hour. Half was esterified; of this, 14% went into ATP, and the cellular energy charge remained high at 0.86 during senescence. The proportion incorporated into phospholipid (2.2%) did not change during senescence, but the proportion in phosphatidyl choline increased and in phosphatidyl glycerol decreased during senescence. The general phosphate ester pattern in presenescent slices closely resembled that in other plant tissues except that phospholipid precursors were more prominent (approximately 20% of total organic (32)P versus 5%). In senescent slices, the proportion of hexose phosphates decreased from 40 to 15% of total organic (32)P and that of phospholipid precursors increased to approximately 50%, suggesting that phospholipid synthesis was blocked early in senescence.

Journal Article↗
PubMed1992

Changes in Cytosolic Glutamine Synthetase Polypeptide and its mRNA in a Leaf Blade of Rice Plants during Natural Senescence.

Changes in the levels of cytosolic glutamine synthetase (GS1) and chloroplastic glutamine synthetase (GS2) polypeptides and of their corresponding mRNAs have been investigated in segments of the 13th leaf of hydroponically grown rice (Oryza sativa L.) plants during natural senescence. The leaf blade on the main stem at early (0 day), middle (15 days), and late (25 days) stages of senescence was harvested and cut into 18 or 19 segments, 2 centimeters in length from the base to the tip. The amount of GS1 polypeptide, detected with specific antibody for the GS1, was greatest near the middle of the leaf blade (segments 11-13). There was little difference in the GS1 content between corresponding leaf segments obtained at the early and middle stages of senescence. At the late senescence stage, all segments had lost some GS1 polypeptide, but more than 50% of GS1 detected at both the early and middle stages was still detectable in segments. The relative content of mRNA for GS1 in the total RNA in all segments was very low during early senescence but increased in all leaf segments during later senescence. At the late stage of senescence, GS1 mRNA in the total RNA increased about 4.2- to 4.6-fold in segments 12 to 16 in the day-25 samples compared with those in the early stage. The content of the GS2 polypeptide, as well as ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein, was highest in segment 17 in the 0-day samples. During senescence, this peak became lower and broader, and finally disappeared, i.e. approximately 80% of GS2 polypeptide and Rubisco protein in segment 17 were lost by day 25. In contrast with GS2 polypeptide, the relative level of GS2 mRNA increased 1.8- to 2.9-fold in individual segments at the middle stage of senescence. Even at the late stage, the transcript signals remained slightly higher than those at the early stage in all segments. Thus, GS1 and GS2 polypeptides and corresponding mRNAs responded in a different manner within an attached rice leaf during natural senescence. The contents of GS1 and GS2 polypeptides were not simply determined by the abundance of their corresponding mRNAs in the rice leaf blades during natural senescence.

Journal Article↗
PubMed1996

Altered regulation of inducible nitric oxide synthase expression in macrophages from senescent mice.

We investigated the capacity of mouse macrophages obtained from senescent animals to respond in vitro to microbial stimuli. Significant hypersecretion of nitric oxide (NO) was observed in thioglycolate-elicited macrophages from senescent mice compared with those obtained from young mice in response to lipopolysaccharide (LPS). In contrast, both cell populations manifested equivalent responses to LPS with respect to tumor necrosis factor alpha secretion. Further, macrophages from senescent animals also showed potentiated responses to both zymosan and heat-killed Staphylococcus aureus, as assessed by NO production. Both cell populations were equivalently inhibited by a competitive inhibitor of NO synthase NG-monomethyl-L-arginine. Since endogenous beta interferon (IFN-beta) is recognized as an essential cofactor for LPS-induced NO production by macrophages, we investigated the role of IFN-beta in enhancing the capacity of both macrophage populations for LPS-induced NO production. Macrophages from young mice were minimally activated by LPS alone to express inducible NO synthase (iNOS), and the response was significantly potentiated by the addition of IFN-beta. These findings were confirmed by immunocytochemical staining of iNOS in which the frequency of iNOS-positive cells in response to LPS was enhanced in the presence of IFN-beta. Reverse transcription-PCR analyses revealed that macrophages from senescent animals produced larger amounts of iNOS mRNA in response to LPS. Further, exogenous IFN-beta potentiated iNOS mRNA expression in macrophages from young mice. In contrast, the frequency of LPS-activated macrophages for iNOS expression was markedly increased during senescence and addition of IFN-beta did not significantly change this frequency. These results correlated with reverse transcription PCR data showing high levels of iNOS mRNA in LPS-stimulated macrophages from senescent mice. LPS-induced NO production in macrophages from both young and senescent mice was inhibited by neutralizing antibody to either IFN-beta or IFN-gamma. Mixed cultures of macrophages from young and senescent mice stimulated with LPS manifested significantly enhanced NO production relative to that which would be predicted from an additive response of the two macrophage populations stimulated separately. The differential responsiveness of NO production observed with thioglycolate-elicited macrophages from young and senescent mice was also observed in resident macrophages but, interestingly, not in bone marrow culture-derived macrophages. These results suggest that environmental factors may be responsible for the potentiated NO responses of macrophages from senescent mice. Collectively, these data suggest that macrophages from senescent animals manifest an altered mechanism for regulation of macrophage function in NO production and iNOS expression by constitutive and/or induced expression of autoregulatory cytokines.

Aging↗
PubMed2004

N-methyl-N'-nitro-N-nitrosoguanidine-induced senescence-like growth arrest in colon cancer cells is associated with loss of adenomatous polyposis coli protein, microtubule organization, and telomeric DNA.

BACKGROUND: Cellular senescence is a state in which mammalian cells enter into an irreversible growth arrest and altered biological functions. The senescence response in mammalian cells can be elicited by DNA-damaging agents. In the present study we report that the DNA-damaging agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) is able to induce senescence in the HCT-116 colon cancer cell line. RESULTS: Cells treated with lower concentrations of MNNG (0-25 microM) for 50 h showed a dose-dependent increase in G2/M phase arrest and apoptosis; however, cells treated with higher concentrations of MNNG (50-100 microM) showed a senescence-like G0/G1 phase arrest which was confirmed by increased expression of beta-galactosidase, a senescence induced marker. The G2/M phase arrest and apoptosis were found to be associated with increased levels of p53 protein, but the senescence-like G0/G1 phase arrest was dissociated with p53 protein levels, since the p53 protein levels decreased in senescence-like arrested cells. We further, determined whether the decreased level of p53 was a transcriptional or a translational phenomenon. The results revealed that the decreased level of p53 protein in senescence-like arrested cells was a transcriptional phenomenon since p53 mRNA levels simultaneously decreased after treatment with higher concentrations of MNNG. We also examined the effect of MNNG treatment on other cell cycle-related proteins such as p21, p27, cyclin B1, Cdc2, c-Myc and max. The expression levels of these proteins were increased in cells treated with lower concentrations of MNNG, which supported the G2/M phase arrest. However, cells treated with higher concentrations of MNNG showed decreased levels of these proteins, and hence, may not play a role in cell cycle arrest. We then examined a possible association of the expression of APC protein and telomeric DNA signals with cellular senescence in MNNG-treated cells. We found that protein and mRNA levels of APC were drastically reduced in cells treated with higher concentrations of MNNG. The loss of APC expression might lead to chromosomal instability as well as microtubular disorganization through its dissociation with tubulin. In fact, the protein level of alpha-tubulin was also drastically decreased in senescence-like arrested cells treated with higher concentrations of MNNG. The levels of telomeric DNA also decreased in cells treated with higher concentrations of MNNG. CONCLUSIONS: These results suggest that in response to DNA alkylation damage the senescence-like arrest of HCT-116 cells was associated with decreased levels of APC protein, microtubular organization, and telomeric DNA.

Adenomatous Polyposis Coli Protein↗