Involvement of Rel/nuclear factor-kappaB transcription factors in keratinocyte senescence

[Sorting of senescent cells by flow cytometry: Specificities and pitfalls to avoid]

Cells can be reprogrammed into senescence to adapt to a variety of stresses, most often affecting the genome integrity. Senescent cells accumulate with age or upon various insults in almost all tissues, and contribute to the development of several age-associated pathologies. Studying the molecular pathways involved in senescence induction, maintenance, or escape is challenged by the heterogeneity in the level of commitment to senescence, and by the pollution of senescent cell populations by proliferating pre- or post-senescent cells. We coped with these difficulties by developing a protocol for sorting senescent cells by flow cytometry, based on three major senescence markers : the SA-β-Galactosidase activity, the size of the cells, and their granularity reflecting the accumulation of aggregates, lysosomes, and altered mitochondria. We address the issues related to sorting senescent cells, the pitfalls to avoid, and propose solutions for sorting viable cells expressing senescent markers at different extents.

Sustained activation of NF-κB through constitutively active IKKβ leads to senescence bypass in murine dermal fibroblasts

Although the transcription factor nuclear factor κB (NF-κB) plays a central role in the regulation of senescence-associated secretory phenotype (SASP) acquisition, our understanding of the involvement of NF-κB in the induction of cellular senescence is limited. Here, we show that activation of the canonical NF-κB pathway suppresses senescence in murine dermal fibroblasts. IκB kinase β (IKKβ)-depleted dermal fibroblasts showed ineffective NF-κB activation and underwent senescence more rapidly than control cells when cultured under 20% oxygen conditions, as indicated by senescence-associated β-galactosidase (SA-β-gal) staining and p16INK4a mRNA levels. Conversely, the expression of constitutively active IKKβ (IKKβ-CA) was sufficient to drive senescence bypass. Notably, the expression of a degradation-resistant form of inhibitor of κB (IκB), which inhibits NF-κB nuclear translocation, abolished senescence bypass, suggesting that the inhibitory effect of IKKβ-CA on senescence is largely mediated by NF-κB. We also found that IKKβ-CA expression suppressed the derepression of INK4/Arf genes and counteracted the senescence-associated loss of Ezh2, a catalytic subunit of the Polycomb repressive complex 2 (PRC2). Moreover, pharmacological inhibition of Ezh2 abolished IKKβ-CA-induced senescence bypass. We propose that NF-κB plays a suppressive role in the induction of stress-induced senescence through sustaining Ezh2 expression.

RSK3 switches cell fate: from stress-induced senescence to malignant progression

BACKGROUND

TGFβ induces several cell phenotypes including senescence, a stable cell cycle arrest accompanied by a secretory program, and epithelial-mesenchymal transition (EMT) in normal epithelial cells. During carcinogenesis cells lose the ability to undergo senescence in response to TGFβ but they maintain an EMT, which can contribute to tumor progression. Our aim was to identify mechanisms promoting TGFβ-induced senescence escape.

METHODS

In vitro experiments were performed with primary human mammary epithelial cells (HMEC) immortalized by hTert. For kinase library screen and modulation of gene expression retroviral transduction was used. To characterize gene expression, RNA microarray with GSEA analysis and RT-qPCR were used. For protein level and localization, Western blot and immunofluorescence were performed. For senescence characterization crystal violet assay, Senescence Associated-β-Galactosidase activity, EdU staining were conducted. To determine RSK3 partners FLAG-baited immunoprecipitation and mass spectrometry-based proteomic analyses were performed. Proteosome activity and proteasome enrichment assays were performed. To validate the role of RSK3 in human breast cancer, analysis of METABRIC database was performed. Murine intraductal xenografts using MCF10DCIS.com cells were carried out, with histological and immunofluorescence analysis of mouse tissue sections.

RESULTS

A screen with active kinases in HMECs upon TGFβ treatment identified that the serine threonine kinase RSK3, or RPS6KA2, a kinase mainly known to regulate cancer cell death including in breast cancer, reverted TGFβ-induced senescence. Interestingly, RSK3 expression decreased in response to TGFβ in a SMAD3-dependent manner, and its constitutive expression rescued SMAD3-induced senescence, indicating that a decrease in RSK3 itself contributes to TGFβ-induced senescence. Using transcriptomic analyses and affinity purification coupled to mass spectrometry-based proteomics, we unveiled that RSK3 regulates senescence by inhibiting the NF-κΒ pathway through the decrease in proteasome-mediated IκBα degradation. Strikingly, senescent TGFβ-treated HMECs display features of epithelial to mesenchymal transition (EMT) and during RSK3-induced senescence escaped HMECs conserve EMT features. Importantly, RSK3 expression is correlated with EMT and invasion, and inversely correlated with senescence and NF-κΒ in human claudin-low breast tumors and its expression enhances the formation of breast invasive tumors in the mouse mammary gland.

CONCLUSIONS

We conclude that RSK3 switches cell fate from senescence to malignancy in response to TGFβ signaling.

The role of Sirtuin 1 and its activators in age-related lung disease

Aging is a major driving factor in lung diseases. Age-related lung disease is associated with downregulated expression of SIRT1, an NAD⁺-dependent deacetylase that regulates inflammation and stress resistance. SIRT1 acts by inducing the deacetylation of various substrates and regulates several mechanisms that relate to lung aging, such as genomic instability, lung stem cell exhaustion, mitochondrial dysfunction, telomere shortening, and immune senescence. Chinese herbal medicines have many biological activities, exerting anti-inflammatory, anti-oxidation, anti-tumor, and immune regulatory effects. Recent studies have confirmed that many Chinese herbs have the effect of activating SIRT1. Therefore, we reviewed the mechanism of SIRT1 in age-related lung disease and explored the potential roles of Chinese herbs as SIRT1 activators in the treatment of age-related lung disease.

Longevity-Associated Core Gut Microbiota Mining and Effect of Mediated Probiotic Combinations on Aging Mice: Case Study of a Long-Lived Population in Guangxi, China

With an ageing population, healthy longevity is becoming an important scientific concern. The longevity phenomenon is closely related to the intestinal microflora and is highly complicated; it is challenging to identify and define the core gut microbiota associated with longevity. Therefore, in this study, 16S rRNA sequencing data were obtained from a total of 135 faecal samples collected as part of the latest sampling and pre-collection initiative in the Guangxi longevity area, and weighted gene co-expression network analysis (WGCNA) was used to find a mediumpurple3 network module significantly associated with the Guangxi longevity phenomenon. Five core genera, namely, Alistipes, Bacteroides, Blautia, Lachnospiraceae NK4A136 group, and Lactobacillus, were identified via network analysis and random forest (RF) in this module. Two potential probiotic strains, Lactobacillus fermentum and Bacteroides fragilis, were further isolated and screened from the above five core genera, and then combined and used as an intervention in naturally ageing mice. The results show a change in the key longevity gut microbiota in mice toward a healthy longevity state after the intervention. In addition, the results show that the probiotic combination effectively ameliorated anxiety and necrosis of hippocampal neuronal cells in senescent mice, improving their antioxidant capacity and reducing their inflammation levels. In conclusion, this longer-term study provides a new approach to the search for longevity hub microbiota. These results may also provide an important theoretical reference for the healthification of the intestinal microflora in the general population, and even the remodelling of the structure of the longevity-state intestinal microflora.

Systems approaches to investigate the role of NF-κB signaling in aging

The nuclear factor-κB (NF-κB) signaling pathway is one of the most well-studied pathways related to inflammation, and its involvement in aging has attracted considerable attention. As aging is a complex phenomenon and is the result of a multi-step process, the involvement of the NF-κB pathway in aging remains unclear. To elucidate the role of NF-κB in the regulation of aging, different systems biology approaches have been employed. A multi-omics data-driven approach can be used to interpret and clarify unknown mechanisms but cannot generate mechanistic regulatory structures alone. In contrast, combining this approach with a mathematical modeling approach can identify the mechanistics of the phenomena of interest. The development of single-cell technologies has also helped clarify the heterogeneity of the NF-κB response and underlying mechanisms. Here, we review advances in the understanding of the regulation of aging by NF-κB by focusing on omics approaches, single-cell analysis, and mathematical modeling of the NF-κB network.

Novel small molecule inhibition of IKK/NF-κB activation reduces markers of senescence and improves healthspan in mouse models of aging

Constitutive NF-κB activation is associated with cellular senescence and stem cell dysfunction and rare variants in NF-κB family members are enriched in centenarians. We recently identified a novel small molecule (SR12343) that inhibits IKK/NF-κB activation by disrupting the association between IKKβ and NEMO. Here we investigated the therapeutic effects of SR12343 on senescence and aging in three different mouse models. SR12343 reduced senescence-associated beta-galactosidase (SA-β-gal) activity in oxidative stress-induced senescent mouse embryonic fibroblasts as well as in etoposide-induced senescent human IMR90 cells. Chronic administration of SR12343 to the Ercc1-/∆ and Zmpste24-/- mouse models of accelerated aging reduced markers of cellular senescence and SASP and improved multiple parameters of aging. SR12343 also reduced markers of senescence and increased muscle fiber size in 2-year-old WT mice. Taken together, these results demonstrate that IKK/NF-κB signaling pathway represents a promising target for reducing markers of cellular senescence, extending healthspan and treating age-related diseases.

Extracellular matrix and cellular senescence in venous leg ulcers

High prevalence of non-healing chronic wounds contributes to a huge healthcare burden across the world. Early treatment interventions for non-healing wounds are vital. It was previously shown that accumulation of 15% or more of senescent cells in a chronic wound edge is an indicator that the wound is unlikely to heal. However, determining the presence of senescent cells would require invasive procedures such as tissue biopsies to be taken. In this study, we found a strong correlation between decreased collagen area and presence of senescent cells in human chronic wounds i.e. venous leg ulcer (VLU), diabetic foot ulcer (DFU) and pressure ulcer (PRU). We also report that the lowest collagen levels were found in VLU patients less than 60 years of age, with a persistent wound of > 24 months. Elevated levels of senescent cells were also found in VLU of males. Second harmonic imaging of collagen at the edge of chronic wounds with a handheld multiphoton device could be used to predict the number of senescent cells, indicating if the wound is on a healing trajectory or not. Our data support the use of collagen imaging in cutaneous wound assessment for a faster and non-invasive method to predict cellular senescence and determining wound trajectory of healing.

Metformin reverses the effects of high glucose on human dermal fibroblasts of aged skin via downregulating RELA/p65 expression

Metformin has been successfully used as an anti-aging agent but exact molecular mechanisms of metformin in anti-aging remain unknown. Hyperglycemia during skin aging not only causes oxidative damage to cellular macromolecules, like dermal collagen, but also modulates the activation of transcription factor nuclear factor kappa B (NF-kB). We aimed to investigate in vitro effects of high glucose (HG) and metformin treatment on proliferation and apoptosis of human primary dermal fibroblasts (HDFs), and the expression of COL1A1, COL3A1, and RELA/p65 genes. Effects of normal glucose (5.5 mM) and HG concentration (50 mM HG) on HDFs, with two doses of metformin (50 μM and 500 μM), were investigated by immunostaining. Apoptotic levels were analyzed by flow cytometry. Expression of COL1A1, COL3A1, and RELA/p65 genes was measured by quantitative real-time PCR. The proliferation of HDFs was decreased significantly (P < 0.01) and expression of COL1A1 was downregulated by HG without metformin, whereas proliferation was elevated and expression was upregulated with 500 μM metformin + HG compared to 5.5 mM glucose (P < 0.05). The expression of COL3A1 and RELA/p65 were upregulated (P < 0.01 for COL3A1), and percentage of late apoptotic cells increased significantly by HG without metformin (P < 0.001) while it decreased in two concentrations of metformin dramatically compared with 5.5 mM glucose (P < 0.01 for expressions and < 0.001 for apoptosis). Metformin not only significantly downregulated RELA/p65 expression, but also inhibited the apoptosis of HDFs from aged human skin at toxic glucose concentrations which could be inversely mediated via COL1A1 and COL3A1 expression.

Control of Mesenchymal Stromal Cell Senescence by Tryptophan Metabolites

Cellular senescence contributes to aging and age-related disorders. High glucose (HG) induces mesenchymal stromal/stem cell (MSC) senescence, which hampers cell expansion and impairs MSC function. Intracellular HG triggers metabolic shift from aerobic glycolysis to oxidative phosphorylation, resulting in reactive oxygen species (ROS) overproduction. It causes mitochondrial dysfunction and morphological changes. Tryptophan metabolites such as 5-methoxytryptophan (5-MTP) and melatonin attenuate HG-induced MSC senescence by protecting mitochondrial integrity and function and reducing ROS generation. They upregulate the expression of antioxidant enzymes. Both metabolites inhibit stress-induced MSC senescence by blocking p38 MAPK signaling pathway, NF-κB, and p300 histone acetyltransferase activity. Furthermore, melatonin upregulates SIRT-1, which reduces NF-κB activity by de-acetylation of NF-κB subunits. Melatonin and 5-MTP are a new class of metabolites protecting MSCs against replicative and stress-induced cellular senescence. They provide new strategies to improve the efficiency of MSC-based therapy for diverse human diseases.

GATA6 regulates aging of human mesenchymal stem/stromal cells

Cellular reprogramming forcing the expression of pluripotency markers can reverse aging of cells, but how molecular mechanisms through which reprogrammed cells alter aging-related cellular activities still remains largely unclear. In this study, we reprogrammed human synovial fluid-derived mesenchymal stem cells (MSCs) into induced pluripotent stem cells (iPSCs) using six reprogramming factors and reverted the iPSCs back to MSCs, as an approach to cell rejuvenation. Using the parental and reprogrammed MSCs as control nonrejuvenated and rejuvenated cells, respectively, for comparative analysis, we found that aging-related activities were greatly reduced in reprogrammed MSCs compared with those in their parental lines, indicating reversal of cell aging. Global transcriptome analysis revealed differences in activities of regulatory networks associated with inflammation and proliferation. Mechanistically, we demonstrated that, compared with control cells, the expression of GATA binding protein 6 (GATA6) in reprogrammed cells was attenuated, resulting in an increase in the activity of sonic hedgehog signaling and the expression level of downstream forkhead box P1 (FOXP1), in turn ameliorating cellular hallmarks of aging. Lower levels of GATA6 expression were also found in cells harvested from younger mice or lower passage cultures. Our findings suggest that GATA6 is a critical regulator increased in aged MSCs that controls the downstream sonic hedgehog signaling and FOXP1 pathway to modulate cellular senescence and aging-related activities.

Korean Red ginseng prevents endothelial senescence by downregulating the HO-1/NF-κB/miRNA-155-5p/eNOS pathway

Background

Korean Red ginseng extract (KRGE) has beneficial effects on the cardiovascular system by improving endothelial cell function. However, its pharmacological effect on endothelial cell senescence has not been clearly elucidated. Therefore, we examined the effect and molecular mechanism of KRGE on the senescence of human umbilical vein endothelial cells (HUVECs).

Methods

HUVECs were grown in normal or KRGE-supplemented medium. Furthermore, they were transfected with heme oxygenase-1 (HO-1) gene or treated with its inhibitor, a NF-κB inhibitor, and a miR-155-5p mimic or inhibitor. Senescence-associated characteristics of endothelial cells were determined by biochemical and immunohistochemical analyses.

Results

Treatment of HUVECs with KRGE resulted in delayed onset and progression of senescence-associated characteristics, such as increased lysosomal acidic β-galactosidase and decreased telomerase activity, angiogenic dysfunction, and abnormal cell morphology. KRGE preserved the levels of anti-senescent factors, such as eNOS-derived NO, MnSOD, and cyclins D and A: however, it decreased the levels of senescence-promoting factors, such as ROS, activated NF-κB, endothelial cell inflammation, and p21 expression. The beneficial effects of KRGE were due to the induction of HO-1 and the inhibition of NF-κB-dependent biogenesis of miR-155-5p that led to the downregulation of eNOS. Moreover, treatment with inhibitors of HO-1, NF-κB, and miR-155-5p abolished the anti-senescence effects of KRGE.

Conclusion

KRGE delayed or prevented HUVEC senescence through a signaling cascade involving the induction of HO-1, the inhibition of NF-κB-dependent miR-155-5p biogenesis, and the maintenance of the eNOS/NO axis activity, suggesting that it may protect against vascular diseases associated with endothelial senescence.

Extra Virgin Olive Oil Polyphenols: Modulation of Cellular Pathways Related to Oxidant Species and Inflammation in Aging

The olive-oil-centered Mediterranean diet has been associated with extended life expectancy and a reduction in the risk of age-related degenerative diseases. Extra virgin olive oil (EVOO) itself has been proposed to promote a "successful aging", being able to virtually modulate all the features of the aging process, because of its great monounsaturated fatty acids content and its minor bioactive compounds, the polyphenols above all. Polyphenols are mostly antioxidant and anti-inflammatory compounds, able to modulate abnormal cellular signaling induced by pro-inflammatory stimuli and oxidative stress, as that related to NF-E2-related factor 2 (Nrf-2) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which have been identified as important modulators of age-related disorders and aging itself. This review summarizes existing literature about the interaction between EVOO polyphenols and NF-κB and Nrf-2 signaling pathways. Reported studies show the ability of EVOO phenolics, mainly hydroxytyrosol and tyrosol, to activate Nrf-2 signaling, inducing a cellular defense response and to prevent NF-κB activation, thus suppressing the induction of a pro-inflammatory phenotype. Literature data, although not exhaustive, indicate as a whole that EVOO polyphenols may significantly help to modulate the aging process, so tightly connected to oxidative stress and chronic inflammation.

Methods to Quantify the NF-κB Pathway During Senescence

Nuclear factor κB (NF-κB) is a family of transcription factors important for regulating innate and adaptive immunity, cellular proliferation, apoptosis and senescence. The NF-κB family is comprised of five subunits, RelA/p65, RelB, C-Rel, p50 (p105/NF-κB1), and p52 (p100/NF-κB2). NF-κB activity goes up with age in multiple tissues. The two subunits RelA/p65 and p50 have been implicated in senescence and aging with genetic deletion of p65 and p50 reducing or increasing senescence respectively. Pharmacologic inhibition of NF-κB also extends health span and reduces senescence in mouse models of accelerated aging. In addition, NF-κB regulates expression of many of senescence associated secretory phenotype (SASP) factors released by certain types of senescent cells that drives loss of tissue homeostasis and secondary senescence. To measure NF-κB activity with aging in vivo, multiple methods can and need to be utilized including cellular localization of p65, EMSA analysis of NF-κB DNA binding, RNA in situ hybridization, and analysis of expression of NF-κB target genes. To colocalize NF-κB activation and senescence, p65 localization or transcriptional activity can be measured by immunostaining or RNA in situ hybridization for NF-κB regulated genes along with methods such as immunostaining for γH2AX or RNA in situ for senescence markers like p16^INK4a and p21. These and related methods will be described in this chapter.

Signal Transduction, Ageing and Disease

Ageing is defined by the loss of functional reserve over time, leading to a decreased tissue homeostasis and increased age-related pathology. The accumulation of damage including DNA damage contributes to driving cell signaling pathways that, in turn, can drive different cell fates, including senescence and apoptosis, as well as mitochondrial dysfunction and inflammation. In addition, the accumulation of cell autonomous damage with time also drives ageing through non-cell autonomous pathways by modulation of signaling pathways. Interestingly, genetic and pharmacologic analysis of factors able to modulate lifespan and healthspan in model organisms and even humans have identified several key signaling pathways including IGF-1, NF-κB, FOXO3, mTOR, Nrf-2 and sirtuins. This review will discuss the roles of several of these key signaling pathways, in particular NF-κB and Nrf2, in modulating ageing and age-related diseases.

Cockayne Syndrome Type A Protein Protects Primary Human Keratinocytes from Senescence

Defects in Cockayne syndrome type A (CSA), a gene involved in nucleotide excision repair, cause an autosomal recessive syndrome characterized by growth failure, progressive neurological dysfunction, premature aging, and skin photosensitivity and atrophy. Beyond its role in DNA repair, the CSA protein has additional functions in transcription and oxidative stress response, which are not yet fully elucidated. Here, we investigated the role of CSA protein in primary human keratinocyte senescence. Primary keratinocytes from three patients with CS-A displayed premature aging features, namely premature clonal conversion, high steady-state levels of reactive oxygen species and 8-OH-hydroxyguanine, and senescence-associated secretory phenotype. Stable transduction of CS-A keratinocytes with the wild-type CSA gene restored the normal cellular sensitivity to UV irradiation and normal 8-OH-hydroxyguanine levels. Gene correction was also characterized by proper restoration of keratinocyte clonogenic capacity and expression of clonal conversion key regulators (p16 and p63), decreased NF-κB activity and, in turn, the expression of its targets (NOX1 and MnSOD), and the secretion of senescence-associated secretory phenotype mediators. Overall, the CSA protein plays an important role in protecting cells from senescence by facilitating DNA damage processing, maintaining physiological redox status and keratinocyte clonogenic ability, and reducing the senescence-associated secretory phenotype-mediated inflammatory phenotype.

The SCN9A channel and plasma membrane depolarization promote cellular senescence through Rb pathway

Oncogenic signals lead to premature senescence in normal human cells causing a proliferation arrest and the elimination of these defective cells by immune cells. Oncogene‐induced senescence (OIS) prevents aberrant cell division and tumor initiation. In order to identify new regulators of OIS, we performed a loss‐of‐function genetic screen and identified that the loss of SCN9A allowed cells to escape from OIS. The expression of this sodium channel increased in senescent cells during OIS. This upregulation was mediated by NF‐κB transcription factors, which are well‐known regulators of senescence. Importantly, the induction of SCN9A by an oncogenic signal or by p53 activation led to plasma membrane depolarization, which in turn, was able to induce premature senescence. Computational and experimental analyses revealed that SCN9A and plasma membrane depolarization mediated the repression of mitotic genes through a calcium/Rb/E2F pathway to promote senescence. Taken together, our work delineates a new pathway, which involves the NF‐κB transcription factor, SCN9A expression, plasma membrane depolarization, increased calcium, the Rb/E2F pathway and mitotic gene repression in the regulation of senescence. This work thus provides new insight into the involvement of ion channels and plasma membrane potential in the control of senescence.

Global mapping of transcription factor motifs in human aging

Biological aging is a complex process dependent on the interplay of cell autonomous and tissue contextual changes which occur in response to cumulative molecular stress and manifest through adaptive transcriptional reprogramming. Here we describe a transcription factor (TF) meta-analysis of gene expression datasets accrued from 18 tissue sites collected at different biological ages and from 7 different in-vitro aging models. In-vitro aging platforms included replicative senescence and an energy restriction model in quiescence (ERiQ), in which ATP was transiently reduced. TF motifs in promoter regions of trimmed sets of target genes were scanned using JASPAR and TRANSFAC. TF signatures established a global mapping of agglomerating motifs with distinct clusters when ranked hierarchically. Remarkably, the ERiQ profile was shared with the majority of in-vivo aged tissues. Fitting motifs in a minimalistic protein-protein network allowed to probe for connectivity to distinct stress sensors. The DNA damage sensors ATM and ATR linked to the subnetwork associated with senescence. By contrast, the energy sensors PTEN and AMPK connected to the nodes in the ERiQ subnetwork. These data suggest that metabolic dysfunction may be linked to transcriptional patterns characteristic of many aged tissues and distinct from cumulative DNA damage associated with senescence.

Epithelial cell senescence: an adaptive response to pre-carcinogenic stresses?

Senescence is a cell state occurring in vitro and in vivo after successive replication cycles and/or upon exposition to various stressors. It is characterized by a strong cell cycle arrest associated with several molecular, metabolic and morphologic changes. The accumulation of senescent cells in tissues and organs with time plays a role in organismal aging and in several age-associated disorders and pathologies. Moreover, several therapeutic interventions are able to prematurely induce senescence. It is, therefore, tremendously important to characterize in-depth, the mechanisms by which senescence is induced, as well as the precise properties of senescent cells. For historical reasons, senescence is often studied with fibroblast models. Other cell types, however, much more relevant regarding the structure and function of vital organs and/or regarding pathologies, are regrettably often neglected. In this article, we will clarify what is known on senescence of epithelial cells and highlight what distinguishes it from, and what makes it like, replicative senescence of fibroblasts taken as a standard.

Blockade of the LRP16-PKR-NF-κB signaling axis sensitizes colorectal carcinoma cells to DNA-damaging cytotoxic therapy

Acquired therapeutic resistance by tumors is a substantial impediment to reducing the morbidity and mortality that are attributable to human malignancies. The mechanisms responsible for the dramatic shift between chemosensitivity and chemoresistance in colorectal carcinoma have not been defined. Here, we report that LRP16 selectively interacts and activates double-stranded RNA-dependent kinase (PKR), and also acts as scaffolds to assist the formation of a ternary complex of PKR and IKKβ, prolonging the polymers of ADP-ribose (PAR)-dependent nuclear factor kappa B (NF-κB) transactivation caused by DNA-damaging agents and confers acquired chemoresistance. We also identified a small molecule, MRS2578, which strikingly abrogated the binding of LRP16 to PKR and IKKβ, converting LRP16 into a death molecule and forestalling colon tumorigenesis. Inclusion of MRS2578 with etoposide, versus each drug alone, exhibited synergistic antitumor cytotoxicity in xenografts. Our combinatorial approach introduces a strategy to enhance the efficacy of genotoxicity therapies for the treatment of tumors.

Proteome oxidative carbonylation during oxidative stress-induced premature senescence of WI-38 human fibroblasts

Accumulation of oxidatively damaged proteins is a hallmark of cellular and organismal ageing, and is also a phenotypic feature shared by both replicative senescence and stress-induced premature senescence of human fibroblasts. Moreover, proteins that are building up as oxidized (i.e. the "Oxi-proteome") during ageing and age-related diseases represent a restricted set of cellular proteins, indicating that certain proteins are more prone to oxidative carbonylation and subsequent intracellular accumulation. The occurrence of specific carbonylated proteins upon oxidative stress induced premature senescence of WI-38 human fibroblasts and their follow-up identification have been addressed in this study. Indeed, it was expected that the identification of these proteins would give insights into the mechanisms by which oxidatively damaged proteins could affect cellular function. Among these proteins, some are belonging to the cytoskeleton while others are mainly involved in protein quality control and/or biosynthesis as well as in redox and energy metabolism, the impairment of which has been previously associated with cellular ageing. Interestingly, the majority of these carbonylated proteins were found to belong to functional interaction networks pointing to signalling pathways that have been implicated in the oxidative stress response and subsequent premature senescence.

Analysis of Gene Expression in Human Dermal Fibroblasts Treated with Senescence-Modulating COX Inhibitors

We have previously reported that NS-398, a cyclooxygenase-2 (COX-2)-selective inhibitor, inhibited replicative cellular senescence in human dermal fibroblasts and skin aging in hairless mice. In contrast, celecoxib, another COX-2-selective inhibitor, and aspirin, a non-selective COX inhibitor, accelerated the senescence and aging. To figure out causal factors for the senescence-modulating effect of the inhibitors, we here performed cDNA microarray experiment and subsequent Gene Set Enrichment Analysis. The data showed that several senescence-related gene sets were regulated by the inhibitor treatment. NS-398 up-regulated gene sets involved in the tumor necrosis factor β receptor pathway and the fructose and mannose metabolism, whereas it down-regulated a gene set involved in protein secretion. Celecoxib up-regulated gene sets involved in G2M checkpoint and E2F targets. Aspirin up-regulated the gene set involved in protein secretion, and down-regulated gene sets involved in RNA transcription. These results suggest that COX inhibitors modulate cellular senescence by different mechanisms and will provide useful information to understand senescence-modulating mechanisms of COX inhibitors.

Distinct Cell Stress Responses Induced by ATP Restriction in Quiescent Human Fibroblasts

Quiescence is the prevailing state of many cell types under homeostatic conditions. Yet, surprisingly little is known about how quiescent cells respond to energetic and metabolic challenges. To better understand compensatory responses of quiescent cells to metabolic stress, we established, in human primary dermal fibroblasts, an experimental ‘energy restriction’ model. Quiescence was achieved by short-term culture in serum-deprived media and ATP supply restricted using a combination of glucose transport inhibitors and mitochondrial uncouplers. In aggregate, these measures led to markedly reduced intracellular ATP levels while not compromising cell viability over the observation period of 48 h. Analysis of the transcription factor (TF) landscape induced by this treatment revealed alterations in several signal transduction nodes beyond the expected biosynthetic adaptations. These included increased abundance of NF-κB regulated TFs and altered TF subsets regulated by Akt and p53. The observed changes in gene regulation and corresponding alterations in key signaling nodes are likely to contribute to cell survival at intracellular ATP concentrations substantially below those achieved by growth factor deprivation alone. This experimental model provides a benchmark for the investigation of cell survival pathways and related molecular targets that are associated with restricted energy supply associated with biological aging and metabolic diseases.

Screening of a kinase library reveals novel pro-senescence kinases and their common NF-κB-dependent transcriptional program

Cellular senescence results in proliferation arrest and acquisition of hallmarks such as the Senescence-Associated Secretory Phenotype (SASP). Senescence is involved in regulating numerous physio-pathological responses, including embryonic development, cancer, and several aging-related diseases. Only a few kinases, centered on the RAS signaling pathway, have been identified as inducing premature senescence. About possible other senescence-regulating kinases and signaling pathways, practically little is known. By screening a library of activated kinases, we identified 33 kinases whose constitutive expression decreases cell proliferation and induces expression of senescence markers; p16 and SASP components. Focusing on some kinases showing the strongest pro-senescence effects, we observed that they all induce expression of SASP-component genes through activation of an NF-κB-dependent transcriptional program. Furthermore, inhibition of the p53 or Rb pathway failed to prevent the SASP-inducing effect of pro-senescence kinases. Inhibition of the NF-κB, p53, or Rb pathway proved insufficient to prevent kinase-triggered cell cycle arrest. We have thus identified a repertoire of novel pro-senescence kinases and pathways. These results will open new perspectives in the understanding on the role of cellular senescence in various physio-pathological responses.

A novel role for DNA single-strand breaks in senescence and neoplastic escape of epithelial cells

In contrast to fibroblasts, epithelial cells spontaneously escape from senescence and develop clones of mutated, transformed, and tumorigenic cells. Recently, we revealed that accumulation of unrepaired DNA single-strand breaks is a trigger of the p16 (CDKN2)-dependent cell cycle arrest pathway in senescent epithelial cells and also the mutagenic motor of post-senescence neoplastic escape.

Defective DNA single-strand break repair is responsible for senescence and neoplastic escape of epithelial cells

The main characteristic of senescence is its stability which relies on the persistence of DNA damage. We show that unlike fibroblasts, senescent epithelial cells do not activate an ATM-or ATR-dependent DNA damage response (DDR), but accumulate oxidative-stress-induced DNA single-strand breaks (SSBs). These breaks remain unrepaired because of a decrease in PARP1 expression and activity. This leads to the formation of abnormally large and persistent XRCC1 foci that engage a signalling cascade involving the p38MAPK and leading to p16 upregulation and cell cycle arrest. Importantly, the default in SSB repair also leads to the emergence of post-senescent transformed and mutated precancerous cells. In human-aged skin, XRCC1 foci accumulate in the epidermal cells in correlation with a decline of PARP1, whereas DDR foci accumulate mainly in dermal fibroblasts. These findings point SSBs as a DNA damage encountered by epithelial cells with aging which could fuel the very first steps of carcinogenesis.

Loss of Nfkb1 leads to early onset aging

NF-κB is a major regulator of age-dependent gene expression and the p50/NF-κB1 subunit is an integral modulator of NF-κB signaling. Here, we examined Nfkb1-/- mice to investigate the relationship between this subunit and aging. Although Nfkb1-/- mice appear similar to littermates at six months of age, by 12 months they have a higher incidence of several observable age-related phenotypes. In addition, aged Nfkb1-/- animals have increased kyphosis, decreased cortical bone, increased brain GFAP staining and a decrease in overall lifespan compared to Nfkb1+/+. In vitro, serially passaged primary Nfkb1-/- MEFs have more senescent cells than comparable Nfkb1+/+ MEFs. Also, Nfkb1-/- MEFs have greater amounts of phospho-H2AX foci and lower levels of spontaneous apoptosis than Nfkb1+/+, findings that are mirrored in the brains of Nfkb1-/- animals compared to Nfkb1+/+. Finally, in wildtype animals a substantial decrease in p50 DNA binding is seen in aged tissue compared to young. Together, these data show that loss of Nfkb1 leads to early animal aging that is associated with reduced apoptosis and increased cellular senescence. Moreover, loss of p50 DNA binding is a prominent feature of aged mice relative to young. These findings support the strong link between the NF-κB pathway and mammalian aging.

The role of the ubiquitin-editing enzyme A20 in diseases of the central nervous system and other pathological processes

In recent years, the ubiquitin-editing enzyme A20 has been shown to control a large set of molecular pathways involved in the regulation of protective as well as self-directed immune responses. Here, we assess the current and putative roles of A20 in inflammatory, vascular and degenerative diseases of the central nervous system and explore future directions of research.

The unfolded protein response and cellular senescence. A review in the theme: cellular mechanisms of endoplasmic reticulum stress signaling in health and disease

The endoplasmic reticulum (ER) is a multifunctional organelle critical for the proper folding and assembly of secreted and transmembrane proteins. Perturbations of ER functions cause ER stress, which activates a coordinated system of transcriptional and translational controls called the unfolded protein response (UPR), to cope with accumulation of misfolded proteins and proteotoxicity. It results in ER homeostasis restoration or in cell death. Senescence is a complex cell phenotype induced by several stresses such as telomere attrition, DNA damage, oxidative stress, and activation of some oncogenes. It is mainly characterized by a cell enlargement, a permanent cell-cycle arrest, and the production of a secretome enriched in proinflammatory cytokines and components of the extracellular matrix. Senescent cells accumulate with age in tissues and are suspected to play a role in age-associated diseases. Since senescence is a stress response, the question arises of whether an ER stress could occur concomitantly with senescence and participate in the onset or maintenance of the senescent features. Here, we described the interconnections between the UPR signaling and the different aspects of the cellular senescence programs and discuss the implication of UPR modulations in this context.

Level of macroautophagy drives senescent keratinocytes into cell death or neoplastic evasion

Senescence is a non-proliferative state reached by normal cells in response to various stresses, including telomere uncapping, oxidative stress or oncogene activation. In previous reports, we have highlighted that senescent human epidermal keratinocytes have two opposite outcomes: either they die by autophagic programmed cell death or they evade in the form of neoplastic postsenescence emergent (PSNE) cells. Herein, we show that partially reducing macroautophagy in senescent keratinocytes using 3-methyl adenine or anti-Atg5 siRNAs increases the PSNE frequency, suggesting that senescent keratinocytes have to escape autophagic cell death to generate PSNE cells. However, totally inhibiting macroautophagy impairs PSNE and leads to a huge accumulation of oxidative damages, indicating that senescent keratinocytes need to achieve quality-control macroautophagy for PSNE to occur. In accordance, we demonstrate that the progenitors of PSNE cells display a level of macroautophagy slightly lower than that of the average senescent population, which is directly dictated by their level of reactive oxygen species, their level of upregulation of MnSOD, their level of activation of NF-κB transcription factors and their level of dysfunctional mitochondria. Macroautophagy thus has antagonistic roles during senescence, inducing cell death or promoting neoplastic transformation, depending on its level of activation. Taken together, these data suggest that levels of oxidative damages and ensuing macroautophagic activity could be two main determinants of the very initial phases of neoplastic transformation by senescence evasion.

A drug-induced accelerated senescence (DIAS) is a possibility to study aging in time lapse

Currently, the oxidative stress (or free radical) theory of aging is the most popular explanation of how aging occurs at the molecular level. Accordingly, a stress-induced senescence-like phenotype of human dermal fibroblasts can be induced in vitro by the exposure of human diploid fibroblasts to subcytotoxic concentrations of hydrogen peroxide. However, several biomarkers of replicative senescence e.g. cell cycle arrest and enlarged morphology are abrogated 14 days after treatment, indicating that reactive oxygen species (ROS) rather acts as a trigger for short-term senescence (1-3 days) than being responsible for the maintenance of the senescence-like phenotype. Further, DNA-damaging factors are discussed resulting in a permanent senescent cell type. To induce long-term premature senescence and to understand the molecular alterations occurring during the aging process, we analyzed mitomycin C (MMC) as an alkylating DNA-damaging agent and ROS producer. Human dermal fibroblasts (HDF), used as model for skin aging, were exposed to non-cytotoxic concentrations of MMC and analyzed for potential markers of cellular aging, for example enlarged morphology, activity of senescence-associated-ß-galactosidase, cell cycle arrest, increased ROS production and MMP1-activity, which are well-documented for HDF in replicative senescence. Our data show that mitomycin C treatment results in a drug-induced accelerated senescence (DIAS) with long-term expression of senescence markers, demonstrating that a combination of different susceptibility factors, here ROS and DNA alkylation, are necessary to induce a permanent senescent cell type.

Photodynamic therapy mediated antiproliferative activity of some metal-doped ZnO nanoparticles in human liver adenocarcinoma HepG2 cells under UV irradiation

Photodynamic therapy (PDT) is a promising new modality for the treatment of cancer through generation of reactive oxygen species (ROS). In this work, human liver adenocarcinoma cells HepG2 were treated with zinc oxide nanoparticles (ZnO-NPs), metal-doped-ZnO-NPs: Fe-ZnO-NPs Ag-ZnO-NPs, Pb-ZnO-NPs, and Co-ZnO-NPs, Silica-coated ZnO-NPs, titanium dioxide nanoparticles (TiO2-NPs), titanium dioxide nano-tubes (TiO2-NTs) and ZnO-NPs/TiO2-NTs nanocomposite under UV irradiation. Doxorubicin was used as a standard drug. The results demonstrated that the ZnO-NPs, Fe-ZnO-NPs, Ag-ZnO-NPs, Pb-ZnO-NPs, and Co-ZnO-NPs showed cytotoxicity against HepG2 cells, with the median growth inhibitory concentrations (IC50) 42.60, 37.20, 45.10, 77.20 and 56.50 μg/ml, respectively, as compared to doxorubicin (IC50: 20.10 μg/ml). Treatment of the cancer cells with ZnO-NPs, Fe-ZnO-NPs, Ag-ZnO-NPs, Pb-ZnO-NPs, and Co-ZnO-NPs resulted in a significant increase in the activity of SOD and the levels of H2O2 and NO than those of control, accompanied with a significant decrease in the activity of CAT and GSH-Px. Also, depletion of reduced GSH, total protein and nucleic acids levels was observed. In conclusion, metal-doped ZnO-NPs may induce antiproliferative effect on HepG2 cells under UV-irradiation due to generation of ROS. Therefore, they could be included in modern clinical trials after in vivo more investigations, using photodynamic therapy technique.

Caveolin-1/PTRF upregulation constitutes a mechanism for mediating p53-induced cellular senescence: implications for evidence-based therapy of delayed wound healing in diabetes

A heightened state of oxidative stress and senescence of fibroblasts constitute potential therapeutic targets in nonhealing diabetic wounds. Here, we studied the underlying mechanism mediating diabetes-induced cellular senescence using in vitro cultured dermal fibroblasts and in vivo circular wounds. Our results demonstrated that the total antioxidant capacity and mRNA levels of thioredoxinreductase and glucose-6-phosphate dehydrogenase as well as the ratio of NADPH/NADP were decreased markedly in fibroblasts from patients with type 2 diabetes (DFs). Consistent with this shift in favor of excessive reactive oxygen species, DFs also displayed a significant increase in senescence-associated β-galactosidase activity and phospho-γ-histone H2AX (pH2AX) level. Moreover, the ability of PDGF to promote cell proliferation/migration and regulate the phosphorylation-dependent activation of Akt and ERK1/2 appears to be attenuated as a function of diabetes. Mechanistically, we found that diabetes-induced oxidative stress upregulated caveolin-1 (Cav-1) and PTRF expression, which in turn sequestered Mdm2 away from p53. This process resulted in the activation of a p53/p21-dependent pathway and the induction of premature senescence in DFs. Most of the aforementioned oxidative stress and senescence-based features observed in DFs were recapitulated in a 10-day-old diabetic wound. Intriguingly, we confirmed that the targeted depletion of Cav-1 or PTRF using siRNA- or Vivo-Morpholino antisense-based gene therapy markedly inhibited diabetes/oxidative stress-induced premature senescence and also accelerated tissue repair in this disease state. Overall, our data illuminate Cav-1/PTRF-1 as a key player of a novel signaling pathway that may link a heightened state of oxidative stress to cellular senescence and impaired wound healing in diabetes.

Mesenchymal stroma: primary determinant and therapeutic target for epithelial cancer

Multifocal and recurrent epithelial tumors, originating from either dormant or de novo cancer cells, are major causes of morbidity and mortality. The age-dependent increase of cancer incidence has long been assumed to result from the sequential accumulation of cancer-driving or -facilitating mutations with induction of cellular senescence as a protective mechanism. However, recent evidence suggests that the initiation and development of epithelial cancer results from a close interplay with its altered tissue microenvironment, with chronic inflammation, stromal senescence, autophagy, and the activation of cancer-associated fibroblasts (CAFs) playing possible primary roles. We will discuss recent progress in these areas, and highlight how this understanding may be used for devising novel preventive and therapeutic approaches to the epithelial cancer problem.

Senescent fibroblasts enhance early skin carcinogenic events via a paracrine MMP-PAR-1 axis

The incidence of carcinoma increases greatly with aging, but the cellular and molecular mechanisms underlying this correlation are only partly known. It is established that senescent fibroblasts promote the malignant progression of already-transformed cells through secretion of inflammatory mediators. We investigated here whether the senescent fibroblast secretome might have an impact on the very first stages of carcinogenesis. We chose the cultured normal primary human epidermal keratinocyte model, because after these cells reach the senescence plateau, cells with transformed and tumorigenic properties systematically and spontaneously emerge from the plateau. In the presence of medium conditioned by autologous senescent dermal fibroblasts, a higher frequency of post-senescence emergence was observed and the post-senescence emergent cells showed enhanced migratory properties and a more marked epithelial-mesenchymal transition. Using pharmacological inhibitors, siRNAs, and blocking antibodies, we demonstrated that the MMP-1 and MMP-2 matrix metalloproteinases, known to participate in late stages of cancer invasion and metastasis, are responsible for this enhancement of early migratory capacity. We present evidence that MMPs act by activating the protease-activated receptor 1 (PAR-1), whose expression is specifically increased in post-senescence emergent keratinocytes. The physiopathological relevance of these results was tested by analyzing MMP activity and PAR-1 expression in skin sections. Both were higher in skin sections from aged subjects than in ones from young subjects. Altogether, our results suggest that during aging, the dermal and epidermal skin compartments might be activated coordinately for initiation of skin carcinoma, via a paracrine axis in which MMPs secreted by senescent fibroblasts promote very early epithelial-mesenchymal transition of keratinocytes undergoing transformation and oversynthesizing the MMP-activatable receptor PAR-1.

Chronic wounds - is cellular 'reception' at fault? Examining integrins and intracellular signalling

As with all physiologic processes, chronic wounds are associated with unique intracellular and cellular/extracellular matrix (ECM) receptor types and signalling messages. These cellular receptors mediate responses of the epidermis to provisional wound matrix and change in form and number in cases of impaired wound healing. Integrins are the major cell-surface receptors for cell adhesion and migration and epidermal keratinocytes express several integrins that bind ECM ligands in provisional wound ECM. Integrin receptors and more particularly integrin clusters and focal adhesion points appear to influence epidermal and dermal cell matrix interactions, cell motility, cell phenotype and ultimate healing trajectory. In chronic wounds, a variety of changes in receptors have been identified: decreased integrin α5β1 receptors affect the integration of fibronectin and subsequent keratinocyte migration; integrin αvβ6 stimulate transforming growth factor (TGF)-β and may increase the susceptibility to ulceration and fibrosis; however, TGF-β signal receptors have been found to be dysfunctional in many chronic wounds; additionally receptor interactions result in increased senescent cells including fibroblasts, myofibroblasts and even keratinocytes - this produces a degradative ECM and wound bed and corrosive chronic wound fluid. The activation or inhibition of integrin receptors by various agents may provide an excellent means of influencing wound healing. This process offers an earlier intervention into the wound healing cascade promoting intrinsic healing and elaboration of growth factors and ECM proteins, which may be more cost effective than the traditional attempts at extrinsic addition of these agents.

The frequency of 4 common gene polymorphisms in nonagenarians, centenarians, and average life span individuals

Single nucleotide polymorphisms of angiotensin-converting enzyme (ACE) such as rs1799752, nuclear factor kappa B (NFkB) such as rs28362491 and cholesteryl ester transport protein (CETP) such as rs708272 (TaqB1) and rs5882 (I405V) were evaluated in nonagenarians, centenarians, and average life span individuals (controls). The study population (n = 307; 190 nonagenarians, 12 centenarians and 105 middle-aged controls) was genotyped for ACE, NFkB, and CETP genetic variants. The age of nonagenarian and centenarian group ranged between 90 and 111 years; centenarians and controls age ranged from 99 to 111, and from 18 to 80 years, respectively. The I carriers of ACE I/D gene were fewer in nonagenarians compared to centenarians (37.6% vs 62.5%, P = .016). The I carriers of ACE gene were more frequent in centenarians compared to controls (62% vs 41%, P = .045). No differences in frequency of common NFkB and CETP genotypes between patients with exceptional longevity and middle-aged patients were observed.

Treatment-induced damage to the tumor microenvironment promotes prostate cancer therapy resistance through WNT16B

Acquired resistance to anticancer treatments is a substantial barrier to reducing the morbidity and mortality that is attributable to malignant tumors. Components of tissue microenvironments are recognized to profoundly influence cellular phenotypes, including susceptibilities to toxic insults. Using a genome-wide analysis of transcriptional responses to genotoxic stress induced by cancer therapeutics, we identified a spectrum of secreted proteins derived from the tumor microenvironment that includes the Wnt family member wingless-type MMTV integration site family member 16B (WNT16B). We determined that WNT16B expression is regulated by nuclear factor of κ light polypeptide gene enhancer in B cells 1 (NF-κB) after DNA damage and subsequently signals in a paracrine manner to activate the canonical Wnt program in tumor cells. The expression of WNT16B in the prostate tumor microenvironment attenuated the effects of cytotoxic chemotherapy in vivo, promoting tumor cell survival and disease progression. These results delineate a mechanism by which genotoxic therapies given in a cyclical manner can enhance subsequent treatment resistance through cell nonautonomous effects that are contributed by the tumor microenvironment.

Regenerative materials that facilitate wound healing

Wounds and damaged tissue become problematic when the tissue repair process does not proceed in a normal manner. Standard treatment of wounds entails topical dressings and devices in conjunction with good wound care practices. Good practices adequately support healing in most patients. Difficult, chronic, or recalcitrant wounds may require the use of more advanced technologies. Wounds that are full thickness or present with the absence of a matrix, may particularly benefit from regenerative materials. This article focuses on the use of cellular and acellular materials as well as chemical constructs to support granulation, tissue repair, and wound closure.

Rejuvenation of gene expression pattern of aged human skin by broadband light treatment: a pilot study

Studies in model organisms suggest that aged cells can be functionally rejuvenated, but whether this concept applies to human skin is unclear. Here we apply 3′-end sequencing for expression quantification (“3-seq”) to discover the gene expression program associated with human photoaging and intrinsic skin aging (collectively termed “skin aging”), and the impact of broadband light (BBL) treatment. We find that skin aging was associated with a significantly altered expression level of 2,265 coding and noncoding RNAs, of which 1,293 became “rejuvenated” after BBL treatment; i.e., they became more similar to their expression level in youthful skin. Rejuvenated genes (RGs) included several known key regulators of organismal longevity and their proximal long noncoding RNAs. Skin aging is not associated with systematic changes in 3′-end mRNA processing. Hence, BBL treatment can restore gene expression pattern of photoaged and intrinsically aged human skin to resemble young skin. In addition, our data reveal, to our knowledge, a previously unreported set of targets that may lead to new insights into the human skin aging process.

SIRT1 as a therapeutic target in inflammaging of the pulmonary disease

OBJECTIVE

Chronic inflammation and cellular senescence are intertwined in the pathogenesis of premature aging, which is considered as an important contributing factor in driving chronic obstructive pulmonary disease (COPD). Sirtuin1 (SIRT1), a nicotinamide adenine dinucleotide (NAD(+))-dependent protein/histone deacetylase, regulates inflammation, senescence/aging, stress resistance, and deoxyribonucleic acid (DNA) damage repair via deacetylating intracellular signaling molecules and chromatin histones. The present review describes the mechanism and regulation of SIRT1 by environmental agents/oxidants/reactive aldehydes and pro-inflammatory stimuli in lung inflammation and aging. The role of dietary polyphenols in regulation of SIRT1 in inflammaging is also discussed.

METHODS

Analysis of current research findings on the mechanism of inflammation and senescence/aging (i.e., inflammaging) and their regulation by SIRT1 in premature aging of the lung.

RESULTS

COPD is a disease of the lung inflammaging, which is associated with the DNA damage response, transcription activation and chromatin modifications. SIRT1 regulates inflammaging via regulating forkhead box class O 3, p53, nuclear factor kappa B, histones and various proteins involved in DNA damage and repair. Polyphenols and its analogs have been shown to activate SIRT1 although they have anti-inflammatory and antioxidant properties.

CONCLUSIONS

Targeting lung inflammation and cellular senescence as well as premature lung aging using pharmacological SIRT1 activators or polyphenols would be a promising therapeutic intervention for COPD/emphysema.

Acute activation of AMP-activated protein kinase prevents H2O2-induced premature senescence in primary human keratinocytes

We investigated the effects of AMPK on H₂O₂-induced premature senescence in primary human keratinocytes. Incubation with 50 µM H₂O₂ for 2 h resulted in premature senescence with characteristic increases in senescence-associated ß-galactosidase (SA-gal) staining 3 days later and no changes in AMPK or p38 MAPK activity. The increase in SA-gal staining was preceded by increases in both p53 phosphorylation (S15) (1 h) and transactivation (6 h) and the abundance of the cyclin inhibitor p21^CIP1 (16 h). Incubation with AICAR or resveratrol, both of which activated AMPK, prevented the H₂O₂-induced increases in both SA-Gal staining and p21 abundance. In addition, AICAR diminished the increase in p53 transactivation. The decreases in SA-Gal expression induced by resveratrol and AICAR were prevented by the pharmacological AMPK inhibitor Compound C, expression of a DN-AMPK or AMPK knock-down with shRNA. Likewise, both knockdown of AMPK and expression of DN-AMPK were sufficient to induce senescence, even in the absence of exogenous H₂O₂. As reported by others, we found that AMPK activation by itself increased p53 phosphorylation at S15 in embryonic fibroblasts (MEF), whereas under the same conditions it decreased p53 phosphorylation in the keratinocytes, human aortic endothelial cells, and human HT1080 fibrosarcoma cells. In conclusion, the results indicate that H₂O₂ at low concentrations causes premature senescence in human keratinocytes by activating p53-p21^CIP1 signaling and that these effects can be prevented by acute AMPK activation and enhanced by AMPK downregulation. They also suggest that this action of AMPK may be cell or context-specific.

NF-κB hyper-activation by HTLV-1 tax induces cellular senescence, but can be alleviated by the viral anti-sense protein HBZ

Activation of I-κB kinases (IKKs) and NF-κB by the human T lymphotropic virus type 1 (HTLV-1) trans-activator/oncoprotein, Tax, is thought to promote cell proliferation and transformation. Paradoxically, expression of Tax in most cells leads to drastic up-regulation of cyclin-dependent kinase inhibitors, p21^CIP1/WAF1 and p27^KIP1, which cause p53-/pRb-independent cellular senescence. Here we demonstrate that p21^CIP1/WAF1-/p27^KIP1-mediated senescence constitutes a checkpoint against IKK/NF-κB hyper-activation. Senescence induced by Tax in HeLa cells is attenuated by mutations in Tax that reduce IKK/NF-κB activation and prevented by blocking NF-κB using a degradation-resistant mutant of I-κBα despite constitutive IKK activation. Small hairpin RNA-mediated knockdown indicates that RelA induces this senescence program by acting upstream of the anaphase promoting complex and RelB to stabilize p27^KIP1 protein and p21^CIP1/WAF1 mRNA respectively. Finally, we show that down-regulation of NF-κB by the HTLV-1 anti-sense protein, HBZ, delay or prevent the onset of Tax-induced senescence. We propose that the balance between Tax and HBZ expression determines the outcome of HTLV-1 infection. Robust HTLV-1 replication and elevated Tax expression drive IKK/NF-κB hyper-activation and trigger senescence. HBZ, however, modulates Tax-mediated viral replication and NF-κB activation, thus allowing HTLV-1-infected cells to proliferate, persist, and evolve. Finally, inactivation of the senescence checkpoint can facilitate persistent NF-κB activation and leukemogenesis.

Transcription factors of the NF-κB/Rel family are critical for the proliferation of lymphocytes and the expression of genes that mediate inflammatory and immune responses. They are often aberrantly activated in human cancers, especially leukemia, where they confer survival and proliferation advantages. Through the study of the trans-activator/oncoprotein, Tax, of the human T-lymphotropic virus type 1 (HTLV-1), we have found that persistent and potentially oncogenic activation of NF-κB triggers a defense mechanism that commits cells into senescence, an irreversible state of cell cycle arrest. This checkpoint is turned on by hyper-activated p65/RelA and is mediated by two cyclin-dependent kinase inhibitors, p21 and p27, in a p53- and pRb-independent manner. It is often impaired in cancer cells with constitutively active NF-κB. Our results anticipate that the anti-sense protein of HTLV-1, HBZ, which down-regulates NF-κB and HTLV-1 trans-activation by Tax, would mitigate or prevent Tax-induced senescence. This prediction has been borne out experimentally. Thus, Tax promotes robust HTLV-1 replication, potent NF-κB activation and senescence, while HBZ attenuates Tax-driven viral replication and NF-κB activation to allow proliferation of infected cells and persistent infection. Finally, our data support the notion that inactivation of the senescence checkpoint facilitates chronic NF-κB hyper-activation, a critical step in leukemia development.

The biology of aging and frailty

In developing and validating the concept of frailty as a geriatric syndrome, it has been necessary to distinguish the clinical expression of frailty from normal age-related changes and other age-related disease pathologies. A framework for excluding potentially confounding disease and a working clinical tool to diagnose frailty have been provided. The associations between frailty and other pathophysiologies has also been shown. However, investigating the underlying biologic basis for the geriatric syndrome of frailty by studying basic homeostatic pathways and mechanisms has not proceeded at the same rate. The following article provides an overview of the homeostatic pathways emphasized in research on aging and explains how this science may help to stimulate frailty research.