Cortical neurons develop a senescence-like phenotype promoted by dysfunctional autophagy.

Senescent cells accumulate in various tissues and organs with aging altering surrounding tissue due to an active secretome, and at least in mice their elimination extends healthy lifespan and ameliorates several chronic diseases. Whether all cell types senesce, including post-mitotic cells, has been poorly described mainly because cellular senescence was defined as a permanent cell cycle arrest. Nevertheless, neurons with features of senescence have been described in old rodent and human brains. In this study we characterized an in vitro model useful to study the molecular basis of senescence of primary rat cortical cells that recapitulates senescent features described in brain aging. We found that in long-term cultures, rat primary cortical neurons displayed features of cellular senescence before glial cells did, and developed a functional senescence-associated secretory phenotype able to induce paracrine premature senescence of mouse embryonic fibroblasts but proliferation of rat glial cells. Functional autophagy seems to prevent neuronal senescence, as we observed an autophagic flux reduction in senescent neurons both in vitro and in vivo, and autophagy impairment induced cortical cell senescence while autophagy stimulation inhibited it. Our findings suggest that aging-associated dysfunctional autophagy contributes to senescence transition also in neuronal cells.

The secretory phenotype of senescent astrocytes isolated from Wistar newborn rats changes with anti-inflammatory drugs, but does not have a short-term effect on neuronal mitochondrial potential.

In the central nervous system (CNS), senescent astrocytes have been associated with neurodegeneration. Senescent cells secrete a complex mixture of pro-inflammatory factors, which are collectively called Senescence Associated Secretory Phenotype (SASP). The SASP components can vary depending on the cell type, senescence inducer and time. The SASP has been mainly studied in fibroblasts and epithelial cells, but little is known in the context of the CNS. Here, the SASP profile in senescent astrocytes isolated from Wistar newborn rats induced to senescence by oxidative stress or by proteasome inhibition was analyzed. Senescent astrocytes secreted predominantly chemokines and IL-1α, but no IL-6. The effect of the anti-inflammatory drugs, sulforaphane (SFN) and dehydroepiandrosterone (DHEA), on the SASP profile was evaluated. Our results showed that SFN and DHEA decreased IL-1α secretion while increasing IL-10, thus modifying the SASP to a less anti-inflammatory profile. Primary neurons were subjected to the conditioned media obtained from drug-treated senescent astrocytes, and their mitochondrial membrane potential was evaluated.

Cellular Senescence, Neurological Function, and Redox State.

SIGNIFICANCE: Cellular senescence, characterized by permanent cell cycle arrest, has been extensively studied in mitotic cells such as fibroblasts. However, senescent cells have also been observed in the brain. Even though it is recognized that cellular energetic metabolism and redox homeostasis are perturbed in the aged brain and neurodegenerative diseases (NDDs), it is still unknown which alterations in the overall physiology can stimulate cellular senescence induction and their relationship with the former events. Recent Advances: Recent findings have shown that during prolonged inflammatory and pathologic events, the blood-brain barrier could be compromised and immune cells might enter the brain; this fact along with the brain's high oxygen dependence might result in oxidative damage to macromolecules and therefore senescence induction. Thus, cellular senescence in different brain cell types is revised here. CRITICAL ISSUES: Most information related to cellular senescence in the brain has been obtained from research in glial cells since it has been assumed that the senescent phenotype is a feature exclusive to mitotic cells. Nevertheless, neurons with senescence hallmarks have been observed in old mouse brains. Therefore, although this is a controversial topic in the field, here we summarize and integrate the observations from several studies and propose that neurons indeed senesce. FUTURE DIRECTIONS: It is still unknown which alterations in the overall metabolism can stimulate senescence induction in the aged brain, what are the mechanisms and signaling pathways, and what is their relationship to NDD development. The understanding of these processes will expose new targets to intervene age-associated pathologies.-Antioxid. Redox Signal. 28, 1704-1723.

[Cellular senescence as a common denominator in age-related diseases]. / La senescencia celular como denominador común de enfermedades asociadas a la edad.

Cellular senescence has been traditionally characterized by cell cycle arrest of pot-mitotic cells as a response to a cellular damage. Now is known that senescent cells secret a diverse array of cytokines, chemokines, growth factors and other that altogether are called senescence associates secretory phenotype (SASP), which might have beneficial or deleterious effects on neighbor cells. This review describes those effects as well as the relationship between the SASP and several age related diseases. We also analyze the direction that recent investigations are turning in order to modulate or avoid the effect of the SASP in those pathologies.

La senescencia celular es un fenómeno que tradicionalmente se ha caracterizado por la detención de la proliferación de células post-mitóticas como respuesta a algún tipo de daño. Ahora se sabe que las células senescentes secretan un conjunto de moléculas, entre las que se encuentran quimiocinas, citocinas, factores de crecimiento y otras que, en conjunto, han sido denominadas fenotipo secretor asociado a la senescencia (SASP). Estas moléculas pueden tener efectos benéficos o dañinos sobre las células vecinas a ellas. Esta revisión describe dichos efectos, así como la relación del SASP con diversas enfermedades asociadas a la edad. También se analiza el rumbo que han tomado las investigaciones recientes para tratar de modular o eliminar el efecto del SASP en dichas patologías.

[Involvement of phenotype secretor of senescent cells in the development of cancer, aging and the diseases associated with age]. / Participación del fenotipo secretor de las células senescentes en el desarrollo del cáncer, el envejecimiento y las enfermedades asociadas a la edad.

Cellular senescence is defined as the physiological program of terminal growth arrest; in mammals it is an important tumor-suppressor mechanism since it stops premalignant cell proliferation. However, senescence also contributes to the decline associated to aging and the development of several diseases. This is explained by the fact that senescent cells secrete diverse molecules, which compromise the cellular microenvironment, and altogether are referred as senescent-associated secretory phenotype (SASP). The SASP is composed by cytokines, chemokines, growth factors, proteases, etc., whose function is to maintain the antiproliferative state and promote senescent cell clearance by the immune system. Nevertheless, over time, and particularly during old age, SASP might stimulate proliferation and premalignant cell transformation. The multifunctional roles of SASP would depend on the cell type and their physiological nature. Therefore, relying on the biological context, SASP could be beneficial and participate in the repair and regeneration processes, or detrimental and induce degenerative pathologies and cancer.

Cell proliferation arrest and redox state status as part of different stages during senescence establishment in mouse fibroblasts.

Senescence phenotype can be achieved by multiple pathways. Most of them involve the activation of negative cell cycle regulators as well as a shift to an oxidative status. However, the exact participation of these events in senescence establishment and maintenance is not completely understood. In this study we investigated the content of three final cell cycle regulators, as well as the redox state in some critical points during the pre-senescent and the full-senescent states. Our results highlight the existence of a critical pre-phase in senescent phenotype establishment, in which cell proliferation stops with the participation of the cell cycle inhibitors, and a second maintenance stage where the exacerbated pro-oxidant state inside the cell induces the physiological decline characteristic in senescent cells.

Insertion of beta-alanine in model peptides for copper binding to His96 and His111 of the human prion protein.

The prion protein coordinates copper with high affinity in the regions encompassing residues 92-99 (GGGTHSQW) and 106-115 (KTNMKHMAGA). Cu(II) binding to these sites involves the coordination of the His96/His111 imidazole ring and backbone deprotonated amides that precede the His residue. Such a coordination arrangement involves the formation of hexa- and penta-membered cycles that provide further stabilization of the metal-peptide complex. The purpose of the present study is to introduce a methylene group in the peptide backbone, to evaluate the impact of increasing the size of these cycles in Cu(II) binding. Thus, a ß-alanine residue was inserted at different positions preceding the His residue in these prion fragments, and their Cu(II) coordination properties were assessed by UV-Visible absorption, circular dichroism, and electron paramagnetic resonance. Spectroscopic data show that the insertion of a methylene group leads to a completely different Cu(II) coordination that involves the His96/His111 imidazole ring and nitrogen or oxygen atoms provided by the peptide backbone towards the C-terminal. This study clearly shows that two main factors determine the nature of Cu(II)-peptide complexes involving an anchoring His residue and deprotonated amides from the backbone chain: i) the stabilization of Cu(II)-peptide complexes due to the formation of cyclic structures (i.e. chelate effect) and ii) the nature of the residues associated to the deprotonated amide groups that participate in metal ion coordination.