Mechanisms of autophagic programmed cell death escape during the very early stages of senescent cells neoplastic evolution

La senescence est un état d’arrêt prolifératif mis en place par les cellules en réponse à différents stress (raccourcissement des télomères, stress oxydant, ou activation d’oncogènes). Bien que la sénescence soit considérée comme irréversible, nous avons récemment montré, en utilisant des kératinocytes humains normaux d’épiderme, que certaines cellules sénescentes réactivent spontanément le processus mitotique pour générer des cellules proliférantes, baptisées émergentes post-sénescence, qui sont transformées et tumorigènes en souris nude. Nous avons montré dans la première partie de ce travail que les cellules sénescentes qui ne génèrent pas de cellules émergentes meurent. La mort engagée à la sénescence n’est ni apoptotique ni nécrotique, mais implique l’élimination par macroautophagie de nombreux composés cellulaires vitaux. Nous avons ensuite démontré que le stress oxydant, via les dommages qu’il crée, notamment aux niveaux nucléaire et mitochondrial, est responsable de l’activation de la mort cellulaire programmée par macroautophagie. Les cellules sénescentes progénitrices des cellules néoplasiques génèrent quant à elle moins d’espèces réactives de l’oxygène (ROS) que le reste des cellules sénescentes, ce qui leur permet d’échapper à la mort. Cependant, pour générer les cellules émergentes, elles doivent maintenir une activité macroautophagique de ménage. L’ensemble de ces travaux démontre donc que le devenir des kératinocytes sénescents dépend de leur niveau de ROS. Un haut niveau de ROS induirait une activité macroautophagique élevée et létale, alors qu’un niveau plus bas induirait une activité trop faible pour induire la mort, mais suffisante pour éliminer les composés cellulaires oxydés. Dans cette situation, les cellules deviendraient permissives à l’évolution néoplasique si les dommages oxydants touchent l’ADN et affectent des oncogènes, suppresseurs de tumeurs, ou d’autres régulateurs fondamentaux.Senescence is a non proliferative state that occurs in response to telomere shortening, oxidative stress or oncogenic activation. Whereas senescence is generally considered as an irreversible growth arrest, we recently reported, using Normal Human Epidermal Keratinocytes (NHEKs), that few senescent cells can spontaneously reactivate a mitotic process to generate so-called post-senescence emergent cells which are transformed and able to form skin hyperplasia in nude mice. In the first part of this work, we have investigated the outcome of the majority of senescent cells that do not generate emergent cells. We highlighted that senescent cells massively die during the growth arrest. Interestingly, the death is not associated with apoptotic or necrotic features but involves the elimination of numerous vital cells components by macroautophagy. We next investigated the mechanism that activates the autophagic programmed cell death in senescent keratinocytes. We show that oxidative stress occuring during senescence causes numerous cellular damages, notably to nucleus and mitochondria, that activate the macroautophagic process to ultimately lead to the death. In the last part of this work, we have investigated the relationship between oxidative stress and macroautophagy during the generation of post-senescence emergent cells. We show that progenitors of these neoplastic cells display less reactive oxygen species (ROS) production than other senescent keratinocytes, and hence escape autophagic cell death. However, in order to generate PS emergent cells, they have to maintain an housekeeping autophagic activity. Taken together, these results indicate that the outcome of a senescent cell is driven by its ROS level. A high ROS level induces a high and lethal activation of autophagy. At a lower ROS level, the cell activates a moderated autophagy that fails to induce death but favors the elimination of oxidized proteins and organelles. By this way, this cell becomes permissive to neoplastic evolution consecutively to the putative oxidative alteration of oncogenes, tumor suppressor genes or other crucial cell regulators

Mechanisms of autophagic programmed cell death escape during the very early stages of senescent cells neoplastic evolution

La senescence est un état d’arrêt prolifératif mis en place par les cellules en réponse à différents stress (raccourcissement des télomères, stress oxydant, ou activation d’oncogènes). Bien que la sénescence soit considérée comme irréversible, nous avons récemment montré, en utilisant des kératinocytes humains normaux d’épiderme, que certaines cellules sénescentes réactivent spontanément le processus mitotique pour générer des cellules proliférantes, baptisées émergentes post-sénescence, qui sont transformées et tumorigènes en souris nude. Nous avons montré dans la première partie de ce travail que les cellules sénescentes qui ne génèrent pas de cellules émergentes meurent. La mort engagée à la sénescence n’est ni apoptotique ni nécrotique, mais implique l’élimination par macroautophagie de nombreux composés cellulaires vitaux. Nous avons ensuite démontré que le stress oxydant, via les dommages qu’il crée, notamment aux niveaux nucléaire et mitochondrial, est responsable de l’activation de la mort cellulaire programmée par macroautophagie. Les cellules sénescentes progénitrices des cellules néoplasiques génèrent quant à elle moins d’espèces réactives de l’oxygène (ROS) que le reste des cellules sénescentes, ce qui leur permet d’échapper à la mort. Cependant, pour générer les cellules émergentes, elles doivent maintenir une activité macroautophagique de ménage. L’ensemble de ces travaux démontre donc que le devenir des kératinocytes sénescents dépend de leur niveau de ROS. Un haut niveau de ROS induirait une activité macroautophagique élevée et létale, alors qu’un niveau plus bas induirait une activité trop faible pour induire la mort, mais suffisante pour éliminer les composés cellulaires oxydés. Dans cette situation, les cellules deviendraient permissives à l’évolution néoplasique si les dommages oxydants touchent l’ADN et affectent des oncogènes, suppresseurs de tumeurs, ou d’autres régulateurs fondamentaux.Senescence is a non proliferative state that occurs in response to telomere shortening, oxidative stress or oncogenic activation. Whereas senescence is generally considered as an irreversible growth arrest, we recently reported, using Normal Human Epidermal Keratinocytes (NHEKs), that few senescent cells can spontaneously reactivate a mitotic process to generate so-called post-senescence emergent cells which are transformed and able to form skin hyperplasia in nude mice. In the first part of this work, we have investigated the outcome of the majority of senescent cells that do not generate emergent cells. We highlighted that senescent cells massively die during the growth arrest. Interestingly, the death is not associated with apoptotic or necrotic features but involves the elimination of numerous vital cells components by macroautophagy. We next investigated the mechanism that activates the autophagic programmed cell death in senescent keratinocytes. We show that oxidative stress occuring during senescence causes numerous cellular damages, notably to nucleus and mitochondria, that activate the macroautophagic process to ultimately lead to the death. In the last part of this work, we have investigated the relationship between oxidative stress and macroautophagy during the generation of post-senescence emergent cells. We show that progenitors of these neoplastic cells display less reactive oxygen species (ROS) production than other senescent keratinocytes, and hence escape autophagic cell death. However, in order to generate PS emergent cells, they have to maintain an housekeeping autophagic activity. Taken together, these results indicate that the outcome of a senescent cell is driven by its ROS level. A high ROS level induces a high and lethal activation of autophagy. At a lower ROS level, the cell activates a moderated autophagy that fails to induce death but favors the elimination of oxidized proteins and organelles. By this way, this cell becomes permissive to neoplastic evolution consecutively to the putative oxidative alteration of oncogenes, tumor suppressor genes or other crucial cell regulators

Détermination des mécanismes d'échappement à la mort par autophagie lors des étapes très précoces de transformation de cellules sénescentes en cellules tumorales

La senescence est un état d arrêt prolifératif mis en place par les cellules en réponse à différents stress (raccourcissement des télomères, stress oxydant, ou activation d oncogènes). Bien que la sénescence soit considérée comme irréversible, nous avons récemment montré, en utilisant des kératinocytes humains normaux d épiderme, que certaines cellules sénescentes réactivent spontanément le processus mitotique pour générer des cellules proliférantes, baptisées émergentes post-sénescence, qui sont transformées et tumorigènes en souris nude. Nous avons montré dans la première partie de ce travail que les cellules sénescentes qui ne génèrent pas de cellules émergentes meurent. La mort engagée à la sénescence n est ni apoptotique ni nécrotique, mais implique l élimination par macroautophagie de nombreux composés cellulaires vitaux. Nous avons ensuite démontré que le stress oxydant, via les dommages qu il crée, notamment aux niveaux nucléaire et mitochondrial, est responsable de l activation de la mort cellulaire programmée par macroautophagie. Les cellules sénescentes progénitrices des cellules néoplasiques génèrent quant à elle moins d espèces réactives de l oxygène (ROS) que le reste des cellules sénescentes, ce qui leur permet d échapper à la mort. Cependant, pour générer les cellules émergentes, elles doivent maintenir une activité macroautophagique de ménage. L ensemble de ces travaux démontre donc que le devenir des kératinocytes sénescents dépend de leur niveau de ROS. Un haut niveau de ROS induirait une activité macroautophagique élevée et létale, alors qu un niveau plus bas induirait une activité trop faible pour induire la mort, mais suffisante pour éliminer les composés cellulaires oxydés. Dans cette situation, les cellules deviendraient permissives à l évolution néoplasique si les dommages oxydants touchent l ADN et affectent des oncogènes, suppresseurs de tumeurs, ou d autres régulateurs fondamentaux.Senescence is a non proliferative state that occurs in response to telomere shortening, oxidative stress or oncogenic activation. Whereas senescence is generally considered as an irreversible growth arrest, we recently reported, using Normal Human Epidermal Keratinocytes (NHEKs), that few senescent cells can spontaneously reactivate a mitotic process to generate so-called post-senescence emergent cells which are transformed and able to form skin hyperplasia in nude mice. In the first part of this work, we have investigated the outcome of the majority of senescent cells that do not generate emergent cells. We highlighted that senescent cells massively die during the growth arrest. Interestingly, the death is not associated with apoptotic or necrotic features but involves the elimination of numerous vital cells components by macroautophagy. We next investigated the mechanism that activates the autophagic programmed cell death in senescent keratinocytes. We show that oxidative stress occuring during senescence causes numerous cellular damages, notably to nucleus and mitochondria, that activate the macroautophagic process to ultimately lead to the death. In the last part of this work, we have investigated the relationship between oxidative stress and macroautophagy during the generation of post-senescence emergent cells. We show that progenitors of these neoplastic cells display less reactive oxygen species (ROS) production than other senescent keratinocytes, and hence escape autophagic cell death. However, in order to generate PS emergent cells, they have to maintain an housekeeping autophagic activity. Taken together, these results indicate that the outcome of a senescent cell is driven by its ROS level. A high ROS level induces a high and lethal activation of autophagy. At a lower ROS level, the cell activates a moderated autophagy that fails to induce death but favors the elimination of oxidized proteins and organelles. By this way, this cell becomes permissive to neoplastic evolution consecutively to the putative oxidative alteration of oncogenes, tumor suppressor genes or other crucial cell regulators.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

MnSOD upregulation induces autophagic programmed cell death in senescent keratinocytes.

Senescence is a state of growth arrest resulting mainly from telomere attrition and oxidative stress. It ultimately leads to cell death. We have previously shown that, in keratinocytes, senescence is induced by NF-kappaB activation, MnSOD upregulation and H(2)O(2) overproduction. We have also shown that senescent keratinocytes do not die by apoptosis but as a result of high macroautophagic activity that targets the primary vital cell components. Here, we investigated the mechanisms that activate this autophagic cell death program. We show that corpses occurring at the senescence plateau display oxidatively-damaged mitochondria and nucleus that colocalize with autophagic vacuoles. The occurrence of such corpses was decreased by specifically reducing the H(2)O(2) level with catalase, and, conversely, reproduced by overexpressing MnSOD or applying subtoxic doses of H(2)O(2). This H(2)O(2)-induced cell death did occur through autophagy since it was accompanied by an accumulation of autophagic vesicles as evidenced by Lysotracker staining, LC3 vesiculation and transmission electron microscopy. Most importantly, it was partly abolished by 3-methyladenine, the specific inhibitor of autophagosome formation, and by anti-Atg5 siRNAs. Taken together these results suggest that autophagic cell death is activated in senescent keratinocytes because of the upregulation of MnSOD and the resulting accumulation of oxidative damages to nucleus and mitochondria

L'expression de s-SHIP identifie une sous-population de cellules souches prostatiques néonatales chez la souris

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Senescent Fibroblasts Enhance Early Skin Carcinogenic Events via a Paracrine MMP-PAR-1 Axis

<div><p>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.</p></div

Activation of type 3 innate lymphoid cells and interleukin 22 secretion in the lungs during streptococcus pneumoniae infection

Mucosal sites are continuously exposed to pathogenic microorganisms and are therefore equipped to control respiratory infections. Type 3 innate lymphoid cells (ILC3) are key players in antimicrobial defense in intestinal mucosa, through interleukin 17 and interleukin 22 (IL-22) production. The present study aimed at analyzing the distribution and function of ILC3 in the respiratory tract. We first observed that lung mucosa harbors a discrete population of ILC3 expressing CD127, CD90, CCR6, and the transcriptional factor RORγt. In addition, lung ILC3 were identified as a major source of IL-22 in response to interleukin 23 stimulation. During Streptococcus pneumoniae infection, ILC3 rapidly accumulated in the lung tissue to produce IL-22. In response to S. pneumoniae, dendritic cells and MyD88, an important adaptor of innate immunity, play critical functions in IL-22 production by ILC3. Finally, administration of the Toll-like receptor 5 agonist flagellin during S. pneumoniae challenge exacerbated IL-22 production by ILC3, a process that protects against lethal infection. In conclusion, boosting lung ILC3 might represent an interesting strategy to fight respiratory bacterial infections. © The Author 2014

Senescence-associated oxidative DNA damage promotes the generation of neoplastic cells

Studies on human fibroblasts have led to viewing senescence as a barrier against tumorigenesis. Using keratinocytes, we show here that partially transformed and tumorigenic cells systematically and spontaneously emerge from senescent cultures. We show that these emerging cells are generated from senescent cells, which are still competent for replication, by an unusual budding-mitosis mechanism. We further present data implicating reactive oxygen species that accumulate during senescence as a potential mutagenic motor of this post-senescence emergence. We conclude that senescence and its associated oxidative stress could be a tumor-promoting state for epithelial cells, potentially explaining why the incidence of carcinogenesis dramatically increases with advanced age. ©2009 American Association for Cancer Research.SCOPUS: ar.jinfo:eu-repo/semantics/publishe