PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Senescent fibroblasts”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 1,009 records · Page 56Linked to original sources
PubMed2000

Stress-induced premature senescence as alternative toxicological method for testing the long-term effects of molecules under development in the industry.

No alternative in vitro method exists for detecting the potential long-term genotoxic effects of molecules at subcytotoxic concentrations, in terms of days and weeks after exposure(s) to the molecule tested. A theoretical model of cellular senescence led to the concept that subcytotoxic stresses under any molecules at subcytotoxic doses, such as molecules under development in the pharmaceutical, cosmetics and food industry, might lead human fibroblasts into a state closely related to in vitro senescence. This concept was then experimentally confirmed in vitro: many biomarkers of replicative senescence of human fibroblasts were found 72 h after their exposure to various kinds of stressors used at non-cytotoxic concentrations. This phenomenon has been termed stress-induced premature senescence (SIPS). Moreover, proteomics studies have revealed that, besides their effects on the appearance of the biomarkers of senescence, sublethal stresses under a variety of stressors also lead to long-term specific changes in the expression level of proteins which are stress-specific. These changes have been coined the molecular scars of stress. The proteins corresponding to these molecular scars may be identified using the latest developments in mass spectrometry. This model of stress-induced premature senescence may be applied to the toxicological sciences when testing for the potential irreversible long-term effects of molecules on the cell fate.

Aging, Premature↗
PubMed2006

Induction of transcriptionally active Jun proteins regulates drug-induced senescence.

The drug hydroxyurea (HU) is used for cancer therapy and treatment of sickle cell anemia. It inhibits cell cycle progression by blocking DNA synthesis and drives cells to undergo apoptosis or enter senescence. We demonstrate here that HU induces the expression of two AP-1 proteins, c-Jun and JunB, which exert antagonistic effects on the cell cycle. Moreover, the induction of c-Jun is observed following treatment with two other drugs that inhibit the cell cycle in S phase, aphidicolin and camptothecin. The induction of c-Jun, which promotes cell cycle progression, up-regulates expression of cyclin D after exposure of cells to HU. Deficiency in c-jun prevents elevation of cyclin D expression and extends entrance into HU-induced senescence but also renders cells more resistant to HU-dependent apoptosis. The induction of c-Jun is independent of JNK activity, and additionally, of c-Jun autoregulatory activity but is inhibited upon inhibition of protein kinase C activity. Therefore, we suggest that c-Jun activity prevents drug-induced senescence. Conversely, the JunB target gene, tumor suppressor p16(INK4a), a cyclin-dependent kinase inhibitor essential for the induction of drug-induced senescence, is also up-regulated by HU in a JunB-dependent manner. Constitutive expression of JunB up-regulates p16(INK4a) and increases the sensitivity of mouse fibroblasts to drug-induced-senescence. Thus, we suggest that in contrast to c-Jun, JunB drives cells to enter HU-dependent senescence. The effect of HU treatment, which regulates the intricate web of AP-1 transcription, depends on the balance between c-Jun and JunB activities.

Aging↗
PubMed1998

Molecular mechanisms for the senescent cell cycle arrest.

Normal human diploid fibroblasts (HDF) have a finite proliferative life-span at the end of which they are arrested with a G1 phase DNA content regardless of the culture conditions. Serum stimulated senescent HDF fail to phosphorylate their retinoblastoma protein (pRb) and consequently do not express a large cohort of late G1 phase genes whose products are necessary for entry into S phase. Because pRb is believed to be phosphorylated sequentially in G1 phase by cyclin D-CDK4/6 and cyclin E-CDK2 complexes, we and others have investigated the status of these complexes in senescent HDF. There is little or no cyclin E-associated kinase activity in senescent IMR90 even though potentially active cyclin E-CDK2 complexes are present, suggesting the presence of an inhibitor. Likewise, cyclin D is complexed with its catalytic partners CDK4 and CDK6 in senescent HDF, but it is not known whether these complexes are active. p21Sdi1,Cip1,Waf1, a ubiquitous inhibitor of the activity of cyclin-CDK complexes, increases progressively throughout the life-span of HDF, but then declines again after the cells become senescent. In contrast, p16Ink4a, which binds monomeric CDK4 and CDK6 thereby preventing their binding to cyclin D, is increased dramatically at the time of senescence and remains high for at least 2 mo. Thus, it is possible that increased p21 initiates the senescent cell cycle arrest in normal cells, but p16 is important for the long-term maintenance of that arrest.

Animals↗
PubMed2025

Intrinsic changes in cell differentiation and identity drive impaired wound healing in aged female murine skin.

Cellular and molecular mechanisms that drive a perturbed wound microenvironment and impaired healing in aged skin have not been fully delineated. To obtain a comprehensive understanding of cell-intrinsic changes acquired during ageing that impact early responses to injury, we performed single-cell RNA sequencing in young and aged intact female murine skin and wounds 3 days post-injury. We observed that substantial changes in the mean proportional distribution and transcriptomic state of skin resident subpopulations in aged, but not young, tissues accompany a global increase in basal inflammation. This is driven by an altered signalling environment leading to impaired keratinocyte differentiation, loss of fibroblast identity and defective macrophage function. Further, we show that ageing-induced changes in skin resident cells persist after injury, resulting in increased expression of senescence-related genes in wound fibroblasts and aberrant monocyte-to-macrophage transitioning coupled to an enhanced inflammatory signature and defective intercellular signalling in comparison to wounds in young mice. In summary, our data highlights a contribution of both cell-intrinsic changes and an altered tissue microenvironment to poor wound healing responses in aged mice.

Animals↗
PubMed1999

Replicative senescence in human uroepithelial cells.

PURPOSE: Normal human uroepithelial cells (HUCs) proliferate rapidly in culture during early passage and then spontaneously undergo replicative senescence. We previously reported that the cyclin D1-CDK4/6 inhibitor, p16INK4a, is elevated at senescence in HUCs. Hence, we proposed that p16INK4a may play a critical role in mediating senescence in this cell type. In the current study, we further characterized the senescent state in HUCs. We also tested the possible roles of changes in other cell cycle proteins, including p53, p21WAF1, pRb, and cyclin D1 in HUC senescence. METHODS: Normal HUCs cultured from explants of ureteral mucosa were used for these studies. Senescence associated-beta-galactosidase activity (SA-beta-gal) was used to identify cells in senescence. Flow cytometric analysis was used to determine changes in cell cycle distribution at senescence. Response of cells to serum stimulation was determined by Northern analysis of c-fos. Western analysis was used to assess changes in p53, p21WAF, p16INK4a, cyclin D1 and plasminogen activator inhibitor-1 (PAI-1) levels at senescence. RESULTS: beta-gal-positive HUCs were blocked at G1/S in senescence and failed to show c-fos induction in response to serum stimulation. As previously reported, senescent HUCs also showed elevated p16INK4a. However, unlike human fibroblasts, neither p53 nor p21WAF1 elevation accompanied HUCs senescence. PAI-1 levels were also not elevated in HUC senescence. CONCLUSION: These findings support a model in which elevation of p16INK4a, but not p53 or p21WAF1 plays a critical role in HUC replicative senescence. These findings elucidate the tumor suppressor mechanism of p16INK4a and the frequent loss of either p16INK4a or pRb in invasive human bladder tumors.

Cell Cycle Proteins↗
PubMedDate not supplied

Insights on immunological aging derived from the T lymphocyte cellular senescence model.

A human T cell culture system has been developed to study cellular senescence in a manner analogous to that used for fibroblasts. Using this system, several markers of replicative senescence have been identified. Evidence is provided to show that new insights into the immune deficiency of aging as well as HIV infection have emerged from the in vitro model. The culture model is now being exploited to dissect the basic mechanisms underlying the senescence program in T cells.

Animals↗
PubMed2006

Klotho RNAi induces premature senescence of human cells via a p53/p21 dependent pathway.

Klotho has recently emerged as a regulator of aging. To investigate the role of Klotho in the regulation of cellular senescence, we generated stable MRC-5 human primary fibroblast cells knockdown for Klotho expression by RNAi. Downregulation of Klotho dramatically induces premature senescence with a concomitant upregulation of p21. The upregulation of p21 is associated with cell cycle arrest at G1/S boundary. Knockdown of p53 in the Klotho attenuated MRC-5 cells restores normal growth and replicative potential. These results demonstrate that Klotho normally regulates cellular senescence by repressing the p53/p21 pathway. Our findings implicate Klotho as a regulator of aging in primary human fibroblasts.

Cell Differentiation↗
PubMed2002

Induction of the Cdk inhibitor p21 by LY83583 inhibits tumor cell proliferation in a p53-independent manner.

Using microarray analysis, we have detected downregulation of several components of the cGMP signaling pathway during replicative senescence of primary human diploid fibroblasts (HDFs). Therefore, the effect of pharmacological inhibition of cGMP synthesis was analyzed in HDFs. Treatment with 6-anilino-5,8-quinolinequinone (LY83583, referred to as LY hereafter), a previously described inhibitor of guanylate cyclase, induced cellular senescence. Microarray analysis revealed that LY treatment induced the Cdk inhibitor p21(WAF1/SDI/CIP1). In colorectal cancer cells, transcription of p21 was induced by LY in a p53-independent manner. Furthermore, p21, but not p53, was required for inhibition of proliferation by LY. The lack of p53 involvement suggests that LY does not induce DNA damage. Growth inhibition was also observed in malignant melanoma and breast cancer cell lines. Functional inactivation of the retinoblastoma tumor-suppressor protein, an effector of p21-mediated cell-cycle inhibition, converted LY-induced growth arrest to apoptosis. These results suggest that LY, or derivatives, may be useful therapeutic agents for the treatment of tumors.

Aminoquinolines↗
PubMed2006

Role of 2-5A-dependent RNase-L in senescence and longevity.

Senescence is a permanent growth arrest that restricts the lifespan of primary cells in culture, and represents an in vitro model for aging. Senescence functions as a tumor suppressor mechanism that can be induced independent of replicative crisis by diverse stress stimuli. RNase-L mediates antiproliferative activities and functions as a tumor suppressor in prostate cancer, therefore, we examined a role for RNase-L in cellular senescence and aging. Ectopic expression of RNase-L induced a senescent morphology, a decrease in DNA synthesis, an increase in senescence-associated beta-galactosidase activity, and accelerated replicative senescence. In contrast, senescence was retarded in RNase-L-null fibroblasts compared with wild-type fibroblasts. Activation of endogenous RNase-L by 2-5A transfection induced distinct senescent and apoptotic responses in parental and Simian virus 40-transformed WI38 fibroblasts, respectively, demonstrating cell type specific differences in the antiproliferative response to RNase-L activation. Replicative senescence is a model for in vivo aging; therefore, genetic disruption of senescence effectors may impact lifespan. RNase-L-/- mice survived 31.7% (P<0.0001) longer than strain-matched RNase-L+/+ mice providing evidence for a physiological role for RNase-L in aging. These findings identify a novel role for RNase-L in senescence that may contribute to its tumor suppressive function and to the enhanced longevity of RNase-L-/- mice.

Aging↗
PubMed2001

Mammalian prohibitin proteins respond to mitochondrial stress and decrease during cellular senescence.

The two prohibitin proteins, Phb1p and Phb2p(BAP37), have been ascribed various functions, including cell cycle regulation, apoptosis, assembly of mitochondrial respiratory chain enzymes, and aging. We show that the mammalian prohibitins are present in the inner mitochondrial membrane and are always bound to each other, with no free protein detectable. They are coexpressed during development and in adult mammalian tissues, and expression levels are indicative of a role in mitochondrial metabolism, but are not compatible with roles in the regulation of cellular proliferation or apoptosis. High level expression of the proteins is consistently seen in primary human tumors, while cellular senescence of human and chick fibroblasts is accompanied by heterogeneous decreases in both proteins. The two proteins are induced by metabolic stress caused by an imbalance in the synthesis of mitochondrial- and nuclear-encoded mitochondrial proteins, but do not respond to oxidative stress, heat shock, or other cellular stresses. The gene promoter sequences contain binding sites for the Myc oncoprotein and overexpression of Myc induces expression of the prohibitins. The data support conserved roles for the prohibitins in regulating mitochondrial respiratory activity and in aging.

Animals↗
PubMed1998

A telomere-independent senescence mechanism is the sole barrier to Syrian hamster cell immortalization.

Reactivation of telomerase and stabilization of telomeres occur simultaneously during human cell immortalization in vitro and the vast majority of human cancers possess high levels of telomerase activity. Telomerase repression in human somatic cells may therefore have evolved as a powerful resistance mechanism against immortalization, clonal evolution and malignant progression. The comparative ease with which rodent cells immortalize in vitro suggests that they have less stringent controls over replicative senescence than human cells. Here, we report that Syrian hamster dermal fibroblasts possess substantial levels of telomerase activity throughout their culture life-span, even after growth arrest in senescence. In our studies, telomerase was also detected in uncultured newborn hamster skin, in several adult tissues, and in cultured fibroblasts induced to enter the post-mitotic state irreversibly by serum withdrawal. Transfection of near-senescent dermal fibroblasts with a selectable plasmid vector expressing the SV40 T-antigen gene resulted in high-frequency single-step immortalization without the crisis typically observed during the immortalization of human cells. Collectively, these data provide an explanation for the increased susceptibility of rodent cells to immortalization (and malignant transformation) compared with their human equivalents, and provide evidence for a novel, growth factor-sensitive, mammalian senescence mechanism unrelated to telomere maintenance.

Animals↗
PubMed2005

The concept of telomeric non-reciprocal recombination (TENOR) applied to human fibroblasts grown in serial cultures: concordance with genealogical data.

Since the discovery of the limited life span of human fibroblasts some 50 years ago, many genealogical studies have been undertaken to describe growth kinetics of fibroblasts in serial cultures by their individual division behavior. It is now accepted that proliferation capacities of human fibroblasts strongly depend on their telomere lengths and integrity. Telomeres shorten with each replication round, and there is a direct correlation between cell division capacity and telomere lengths; that is, the consumption of disposable telomeric DNA repeats during cell divisions progresses until critically short telomeres determining the replicative senescence of the cells are present. Recently, we have suggested that telomeres in fibroblasts can also become elongated during DNA replication by telomeric non-reciprocal recombination (TENOR). Here we discuss genealogical data collected over the last decades as well as more recent findings on the telomere-driven replicative senescence process, and we summarize both to give an integrated picture.

Animals↗
PubMed2004

Acrogeria with decreased gene expression of alpha1 (I) and alpha1 (III) collagen in cultured dermal fibroblasts.

We report a case of acrogeria. A 47-year-old Japanese man presented with micrognathism, thin lips, radial wrinkles around his month, atrophy of skin and subcutaneous tissue, and mottled hyperpigmentation on his extremities. A biopsy of the lesional skin showed flat epidermis and atrophy of the dermal layer. The in vitro life span of the patient's fibroblasts (18+/-2.2 PDL) was significantly shorter than that of control fibroblasts (42+/-3.5 PDL). The early-passage fibroblasts from the patient showed abnormal morphology which was also seen in the late-passage (in vitro aging) of normal fibroblasts. In northern blotting analysis of cultured dermal fibroblasts, mRNA levels of alpha1 (I) collagen and alpha1 (III) collagen were markedly reduced. These results revealed that patient fibroblasts might be in severe senescence in vitro and contribute to the phenotypes of this premature aging syndrome.

Biopsy, Needle↗
PubMed2004

c-Jun-deficient cells undergo premature senescence as a result of spontaneous DNA damage accumulation.

Mouse embryo fibroblasts deficient for the c-Jun proto-oncogene (c-Jun-/- MEF) undergo p53-dependent premature senescence in conventional culture. This phenotype becomes evident only after several cell divisions, suggesting that senescence may result from exposure to unknown environmental factors. Here, we show that c-Jun-/- MEF can proliferate successfully in low oxygen (3% O2), indicating that premature senescence under conventional culture conditions is a consequence of hyperoxic stress. c-Jun-/- MEF exhibit higher basal levels of DNA damage compared to normal fibroblasts in high but not low oxygen, implying that senescence results from chronic accumulation of spontaneous DNA damage. This accumulation may be attributable, at least in part, to inefficient repair, since DNA damage induced by gamma ionizing radiation and H2O2 persists for longer in c-Jun-/- MEF than in wild-type MEF. Unexpectedly, p53 expression, phosphorylation, and transcriptional activity are largely unaffected by oxygen exposure, indicating that the accumulation of spontaneous DNA damage does not result in chronic activation of p53 as judged by conventional criteria. Finally, we find that c-Jun associates with nuclear foci containing gammaH2AX and ATM following irradiation, suggesting a potential role for c-Jun in DNA repair processes per se.

Animals↗
PubMedDate not supplied

A proton magnetic resonance spectroscopy study of aging and transformed human fibroblasts.

Proton magnetic resonance spectroscopy (1H MRS) has been used to monitor changes occurring during aging and transformation in human lung fibroblasts. Aging was studied in MRC-5 cells from nonsenescent (early passage) to presenescent (late passage) and senescence. Nonsenescent cells infected with SV40 virus (pretransformed) were monitored through crisis and subsequent immortalization. Aging changes were observed with one- and two-dimensional MR spectra. Cholesterol and lipid resonances were significantly increased from nonsenescent cultures to senescence. These changes could be caused by chemical or structural changes in the plasma membrane or in intracellular lipid pools. In contrast, choline levels rose from nonsenescent to presenescent cells but at senescence dropped to that of nonsenescent cells. Increased choline levels are often associated with increased cellular proliferation. After SV40 infection of MRC-5 cells there was an increase of cholesterol and lipid levels that peaked at crisis. Newly immortalized cells exhibited a drop in cholesterol and lipid to nonsenescent cell levels, but these rose again in established immortalized cells. In contrast to presensescent cultures, the levels of choline gradually increased from pretransformed to crisis phase but still continued to rise after immortalization. Thus, 1H MRS illustrates similarities in lipid behavior at senescence and crisis, whereas the choline levels are different.

Cell Line, Transformed↗
PubMed2004

Functional genetic screen for genes involved in senescence: role of Tid1, a homologue of the Drosophila tumor suppressor l(2)tid, in senescence and cell survival.

We performed a genetic suppressor element screen to identify genes whose inhibition bypasses cellular senescence. A normalized library of fragmented cDNAs was used to select for elements that promote immortalization of rat embryo fibroblasts. Fragments isolated by the screen include those with homology to genes that function in intracellular signaling, cellular adhesion and contact, protein degradation, and apoptosis. They include mouse Tid1, a homologue of the Drosophila tumor suppressor gene l(2)tid, recently implicated in modulation of apoptosis as well as gamma interferon and NF-kappaB signaling. We show that GSE-Tid1 enhances immortalization by human papillomavirus E7 and simian virus 40 T antigen and cooperates with activated ras for transformation. Expression of Tid1 is upregulated upon cellular senescence in rat and mouse embryo fibroblasts and premature senescence of REF52 cells triggered by activated ras. In accordance with this, spontaneous immortalization of rat embryo fibroblasts is suppressed upon ectopic expression of Tid1. Modulation of endogenous Tid1 activity by GSE-Tid1 or Tid1-specific RNA interference alleviates the suppression of tumor necrosis factor alpha-induced NF-kappaB activity by Tid1. We also show that NF-kappaB sequence-specific binding is strongly downregulated upon senescence in rat embryo fibroblasts. We therefore propose that Tid1 contributes to senescence by acting as a repressor of NF-kappaB signaling.

Animals↗
PubMed2003

Duration of senescent cell survival in vitro as a characteristic of organism longevity, an additional to the proliferative potential of fibroblasts.

More than 40 years have passed since the original publication by Hayflick and Moorhead led to the concept of the 'Hayflick limit' of the maximum number of divisions which somatic cells undergo in vitro. This concept is still regarded as a fundamental characteristic of species longevity. Here we want to emphasize another characteristic of somatic cells, namely, the duration of their survival in vitro in the non-dividing state after cessation of proliferation. This is suggested on the basis of results of recent experiments with so-called Japanese accelerated senescent mice. Results of these experiments reveal a good correlation between the longevity of the mice, the number of duplications of their fibroblasts in vitro, and the survival time of these cells in the non-dividing state. In routine culture conditions, cell survival time may be very long, as much as a few years. However, when the cells are grown under conditions of oxidative stress, cellular longevity is markedly shortened. This new test may serve as an additional marker of organismic longevity. The comparative value of both tests, the classical 'Hayflick limit' and the new test, is discussed.

Animals↗