Long-term growth arrest of PUVA-treated fibroblasts in G2/M in the absence of p16INK4a, p21CIP1or p53

Primary high-grade serous ovarian cancer cells are sensitive to senescence induced by carboplatin and paclitaxel in vitro

BACKGROUND

Various types of normal and cancer cells undergo senescence in response to carboplatin and paclitaxel, which are considered the gold standard treatments in ovarian cancer management. Surprisingly, the effect of these drugs on ovarian cancer cell senescence remained unknown.

METHODS

The experiments were conducted on primary high-grade serous ovarian cancer cells. Molecular markers of senescence were evaluated using cytochemistry and immunofluorescence. Cell cycle distribution was analyzed using flow cytometry. Expression of cyclins and signaling pathways was tested using western blot. Telomere length and telomerase activity were measured using qPCR, and the colocalization of telomeres with DNA damage foci using immuno-FISH. Oxidative stress-related parameters were quantified using appropriate fluorescence probes. Production of cancerogenic agents was analyzed using qPCR and ELISA.

RESULTS

Carboplatin applied with paclitaxel induces senescence of ovarian cancer cells in vitro. This activity was reflected by permanent G2/M growth arrest, a high fraction of cells expressing senescence biomarkers (SA-β-Gal and γ-H2A.X), upregulated expression of p16, p21, and p53 cell cycle inhibitors, and decreased expression of cyclin B1. Neither telomere length nor telomerase activity changed in the senescent cells, and the majority of DNA damage was localized outside telomeres. Moreover, drug-treated cancer cells exhibited increased production of STAT3 protein, overproduced superoxide and peroxides, and increased mitochondrial mass. They were also characterized by upregulated ANG1, CCL11, IL-6, PDGF-D, TIMP-3, TSP-1, and TGF-β1 at the mRNA and/or protein level.

CONCLUSIONS

Our findings imply that conventional chemotherapy may elicit senescence in ovarian cancer cells, which may translate to the development of a cancer-promoting phenotype, despite the inability of these cells to divide.

Membrane damage by betulinic acid provides insights into cellular aging

BACKGROUND

Cell senescence is a process of central importance to the understanding of aging as well as to the development of new drugs. It is related with genomic instability, which has been shown to occur in the presence of autophagy deficiency. Yet, the mechanism that triggers genomic instability and senescence from a condition of autophagy deficiency remains unknown. By analyzing the consequences of treating human keratinocytes (HaCaT) with the pentacyclic triterpenoid Betulinic Acid (BA) we were able to propose that cell senescence can develop as a response to parallel damage in the membranes of mitochondria and lysosome.

METHODS

We performed biochemical, immunocytochemical and cytometric assays after challenging HaCaT cells with BA. We also evaluated membrane leakage induced by BA in liposomes and giant unilamellar vesicles.

RESULTS

By destabilizing lipid bilayers of mitochondria and lysosomes, BA triggers the misbalance in the mitochondrial-lysosomal axis leading to perceived autophagy impairment, lipofuscinogenesis, genomic instability and cell senescence. The progressive accumulation of mitochondria and lipofuscin, which comes from imperfect mitophagy triggered by BA, provides a continuous source of reactive species further damaging lysosomes and leading to cell aging.

CONCLUSIONS

This work reveals that the initial trigger of cell senescence can be the physical damage in the membranes of lysosomes and mitochondria.

GENERAL SIGNIFICANCE

This concept will help in the search of new drugs that act as senescence-inductors. BA is under evaluation as chemotherapeutic agent against several types of tumors and induction of cell senescence should be considered as one of its main mechanisms of action.

UV, stress and aging

Skin is a model of choice in studies on aging. Indeed, skin aging can be modulated by internal and external factors, reflecting its complexity. Two types of skin aging have been identified: intrinsic, mainly genetically determined and extrinsic—also called "photo-aging"—resulting on the impact of environmental stress and more precisely of UV rays. Simplified in vitro models, based on cellular senescence, have been developed to study the relationship between UV and aging. These models vary on the cell type (fibroblasts or keratinocytes, normal or immortalized) and the type of UV used (UVA or UVB).

Knockdown of paraoxonase 1 expression influences the ageing of human dermal microvascular endothelial cells

Skin is one of the most commonly studied tissues for microcirculation research owing to its close correlation of cutaneous vascular function, ageing and age-related cardiovascular events. To elucidate proteins that determine this correlation between endothelial cell function and ageing in the vascular environment of the skin, we performed a proteomic analysis of plasma samples from six donors in their 20s (young) and six donors in their 60s (old). Among identified proteins, paraoxonase 1 (PON1) was selected in this study. To elucidate the role of PON1 on skin ageing and determine how it controls cellular senescence, the characteristics of PON1 in human dermal microvascular endothelial cells (HDMECs) were determined. When the expression of endogenous PON1 was knocked-down by small interfering RNA (siRNA) targeting PON1, HDMECs showed characteristic features of cellular senescence such as increases in senescence-associated β-galactosidase stained cells and enlarged and flattened cell morphology. At 48 h post-transfection, the protein expression of p16 in PON1 siRNA-treated HDMECs was higher than that in scrambled siRNA-treated HDMECs. In addition, the expressions of moesin and rho GTP dissociation inhibitor, additional age-related candidate biomarkers, were decreased by PON1 knock-down in HDMECs. In conclusion, these results suggest that PON1 functions as an ageing-related protein and plays an important role in the cellular senescence of HDMECs.

Age-related changes in proliferation, the numbers of mast cells, eosinophils, and cd45-positive cells in human dermis

Skin aging is an extremely important medical and social problem in the modern world. Therefore, a goal of the present work was to estimate changes in the numbers of fibroblast-like cells, proliferating cells nuclear antigen-positive cells, CD45-positive cells, mast cells, and eosinophils in human dermis at different ages. Skin specimens from human fetuses that died antenatally from 20 to 40 weeks of pregnancy and humans who died from different causes from 1 day to 85 years of life were used for the study. Results showed a decrease in a total number and the number of proliferating cells nuclear antigen-positive fibroblast-like cells in dermis with progression of age. The numbers of CD45-positive cells and mast cells are gradually increased with aging. Eosinophils are almost absent in dermis independently on age. Mast cells are probably a main factor that potentially can be involved in tissue damage and aging changes in skin. Mast cells should be regarded as an important target for anti-aging therapy.

Histopathological changes seen in mycosis fungoides patients after phototherapy

Early stage (IA, IB, IIA) mycosis fungoides (MF) has long been treated with various agents including oral psoralen plus UVA (PUVA), broadband and narrowband. The histopathological changes seen after phototherapy have not been clearly described. Twenty-three skin biopsy specimens of MF patients treated with phototherapy both UVA and UVB were evaluated before and 3 months after phototherapy. The clinical and histomorphological response were evaluated. Various types of epidermotropism: such as single cells, haloed cells, linearly arranged single cells, pagetoid spread, and Pautrier microabscesses were noted. Stratum corneum was classified as normal, hyperkeratotic, and parakeratotic. The epidermal thickness was noted as normal, atrophic, and hypertrophic. Spongiotic microvesiculation, presence of dilated dermal vessels, was investigated. Papillary dermis fibrosis, the presence of plasma cells, eosinophils, and extravasated erythrocytes were also examined. Epidermal hyperplasia, dermal fibrosis, loss of parakeratotic pattern, and inflammatory infiltrate were frequently observed after therapy. After phototherapy, the atypical cells rarely formed "Pautrier microabscess" or made a "linear pattern" at the base of epidermis. The cells other than lymphocytes (plasma cells, eosinophils, and erythrocytes) should also be considered regarding the phototherapy effect. A pathology report of a MF patient who has undergone successful phototherapy would describe changes resulting from phototherapy-such as fibrosis or "lack of dermal inflammation" and the absence of active epidermal cellular changes such as "Pautrier microabscess" or "linearly arranged cells."

Differentiation and apoptosis in UVA-irradiated cells treated with furocoumarin derivatives

In this review we summarize the structure and biological effects of linear and angular psoralens. These compounds exhibit interesting biological effects on the cell cycle, apoptosis and differentiation. These molecules should be considered promising drugs in the therapy of several diseases, including psoriasis, mycosis fungoides and cancer. Also, preclinical data demonstrate a possible use of these molecules for the treatment of beta-thalassemia and other hematological disorders.

Increased levels of a particular phosphatidylcholine species in senescent human dermal fibroblasts in vitro

Plasma membranes are essential components of living cells, and phospholipids are major components of cellular membranes. Here, we used liquid chromatography/mass spectrometry to investigate changes in the membrane phospholipid content that occur in association with aging. Our results indicate that the levels of a particular species of phosphatidylcholine comprised of stearic acid and arachidonic acid increased with age. To determine the reason for the increased levels of this particular phosphatidylcholine, we examined the effect of highly unsaturated fatty acids, such as arachidonic acid and eicosapentaenoic acid, on cellular aging. Applied arachidonic acid was incorporated into phosphatidylcholine molecules, but neither arachidonic acid nor other related unsaturated fatty acids had any effect. We conclude that increased levels of this distinctive phosphatidylcholine are a result of in vitro senescence.

Contributions of DNA interstrand cross-links to aging of cells and organisms

Impaired DNA damage repair, especially deficient transcription-coupled nucleotide excision repair, leads to segmental progeroid syndromes in human patients as well as in rodent models. Furthermore, DNA double-strand break signalling has been pinpointed as a key inducer of cellular senescence. Several recent findings suggest that another DNA repair pathway, interstrand cross-link (ICL) repair, might also contribute to cell and organism aging. Therefore, we summarize and discuss here that (i) systemic administration of anti-cancer chemotherapeutics, in many cases DNA cross-linking drugs, induces premature progeroid frailty in long-term survivors; (ii) that ICL-inducing 8-methoxy-psoralen/UVA phototherapy leads to signs of premature skin aging as prominent long-term side effect and (iii) that mutated factors involved in ICL repair like ERCC1/XPF, the Fanconi anaemia proteins, WRN and SNEV lead to reduced replicative life span in vitro and segmental progeroid syndromes in vivo. However, since ICL-inducing drugs cause damage different from ICL and since all currently known ICL repair factors work in more than one pathway, further work will be needed to dissect the actual contribution of ICL damage to aging.

The gene expression profile of psoralen plus UVA-induced premature senescence in skin fibroblasts resembles a combined DNA-damage and stress-induced cellular senescence response phenotype

After a finite number of population doublings, normal human cells undergo replicative senescence accompanied by growth arrest. We previously described a model of stress-induced premature senescence by treatment of dermal fibroblasts with psoralen plus UVA, a common photodermatological therapy. Psoralen photoactivation has long been used as a therapy for hyperproliferative skin disorders. The repetitive therapeutical treatment is accompanied by premature aging of the skin. Treatment of fibroblasts in vitro with 8-methoxypsoralen (8-MOP) and subsequent ultraviolet A (UVA) irradiation results in growth arrest with morphological and functional changes reminiscent of replicative senescence. For gene expression profiling in two strains of human skin fibroblasts after PUVA treatment, we used a low-density DNA array representing 240 genes involved in senescence and stress response. Twenty-nine genes were differentially expressed after PUVA treatment in the two strains of human skin fibroblasts. These genes are involved in growth arrest, stress response, modification of the extracellular matrix and senescence. This study contributes further to the elucidation of the PUVA model and its validation as a useful stress-induced premature senescence model aiming to characterize the premature senescence of fibroblasts and to identify biomarkers that could be applied in vivo.

p16INK4A is a robust in vivo biomarker of cellular aging in human skin

The cell-cycle regulating gene, p16INK4A, encoding an inhibitor of cyclin-dependent kinases 4 and 6, is considered to play an important role in cellular aging and in premature senescence. Although there is an age-dependent increase of p16INK4A expression in human fibroblast senescence in vitro, no data are available regarding the age dependency of p16INK4A in vivo. To determine whether p16INK4A expression in human skin correlates with donor age, p16INK4A expression was analyzed by immunohistochemistry as well as the expression of the p16INK4A repressor BMI1. Samples from the age groups 0-20, 21-70, and 71-95 years were selected from a bank of healthy human skin. We show that the number of p16INK4A positive cells is significantly higher in elderly individuals compared to the younger age groups. The number of p16INK4A positive cells was found to be increased in both epidermis and dermis, compartments with strictly different proliferative activities. BMI1 gene expression was significantly down-regulated with increasing donor age, whereas no striking age differences were observed for Ki67. In immunofluorescence co-expression studies, Ki67-positive cells were negative for p16INK4A and BMI1-expressing cells also stained negatively for Ki67. In conclusion, we provide for the first time evidence that p16INK4A expression directly correlates with chronological aging of human skin in vivo. p16INK4A therefore is a biomarker for human aging in vivo. The data reported here suggest a model for changes in regulatory gene expression that drive aging in human skin.

Senescence of human fibroblasts after psoralen photoactivation is mediated by ATR kinase and persistent DNA damage foci at telomeres

Cellular senescence is a phenotype that is likely linked with aging. Recent concepts view different forms of senescence as permanently maintained DNA damage responses partially characterized by the presence of senescence-associated DNA damage foci at dysfunctional telomeres. Irradiation of primary human dermal fibroblasts with the photosensitizer 8-methoxypsoralen and ultraviolet A radiation (PUVA) induces senescence. In the present study, we demonstrate that senescence after PUVA depends on DNA interstrand cross-link (ICL) formation that activates ATR kinase. ATR is necessary for the manifestation and maintenance of the senescent phenotype, because depletion of ATR expression before PUVA prevents induction of senescence, and reduction of ATR expression in PUVA-senesced fibroblasts releases cells from growth arrest. We find an ATR-dependent phosphorylation of the histone H2AX (gamma-H2AX). After PUVA, ATR and gamma-H2AX colocalize in multiple nuclear foci. After several days, only few predominantly telomere-localized foci persist and telomeric DNA can be coimmunoprecipitated with ATR from PUVA-senesced fibroblasts. We thus identify ATR as a novel mediator of telomere-dependent senescence in response to ICL induced by photoactivated psoralens.

Photoaging as a consequence of natural and therapeutic ultraviolet irradiation—studies on PUVA-induced senescence-like growth arrest of human dermal fibroblasts

Premature aging of the skin is a prominent side effect of psoralen photoactivation, a therapy widely and successfully used for different skin disorders. Recently, we demonstrated that treatment of fibroblasts with 8-methoxypsoralen and ultraviolet A irradiation resulted in growth arrest with morphological and functional changes reminiscent of replicative senescence. In this minireview we will focus on the similarities between intrinsic and extrinsic aging and PUVA-induced senescence-like growth arrest both resulting in the loss of the structural integrity of the dermal connective tissue as a hallmark of intrinsic aging and photoaging (extrinsic aging) of the skin, and we will discuss the important role of oxidative stress related telomere attrition in the PUVA-induced phenotype of dermal fibroblasts. With the PUVA-induced growth arrest of fibroblasts a new model has been added to the growing number of in vitro models with longterm growth arrest upon exposure to sublethal stressors (i.e. hyperoxia, hydrogen peroxide, ethanol), which are characterized by morphological and functional changes common for cellular senescence. This model may be particularly suited for further studies addressing mechanisms of stress-induced senescence-like growth arrest in vitro and in vivo, since many dermatological patients are treated with PUVA allowing the analysis of putative stress-induced premature senescence in vivo.