RESUMEN
Direct reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) provides a unique opportunity to derive patient-specific stem cells with potential applications in tissue replacement therapies and without the ethical concerns of human embryonic stem cells (hESCs). However, cellular senescence, which contributes to aging and restricted longevity, has been described as a barrier to the derivation of iPSCs. Here we demonstrate, using an optimized protocol, that cellular senescence is not a limit to reprogramming and that age-related cellular physiology is reversible. Thus, we show that our iPSCs generated from senescent and centenarian cells have reset telomere size, gene expression profiles, oxidative stress, and mitochondrial metabolism, and are indistinguishable from hESCs. Finally, we show that senescent and centenarian-derived pluripotent stem cells are able to redifferentiate into fully rejuvenated cells. These results provide new insights into iPSC technology and pave the way for regenerative medicine for aged patients.
Asunto(s)
Diferenciación Celular , Reprogramación Celular , Senescencia Celular/genética , Células Madre Pluripotentes Inducidas/citología , Rejuvenecimiento , Anciano , Anciano de 80 o más Años , Animales , Línea Celular , Células Cultivadas , Senescencia Celular/efectos de los fármacos , Humanos , Ratones , Ratones Endogámicos NOD , Ratones SCID , Mitocondrias/metabolismo , Telómero/genética , Telómero/metabolismo , Factores de Transcripción/farmacologíaRESUMEN
DNA replication is highly regulated, ensuring faithful inheritance of genetic information through each cell cycle. In metazoans, this process is initiated at many thousands of DNA replication origins whose cell type-specific distribution and usage are poorly understood. We exhaustively mapped the genome-wide location of replication origins in human cells using deep sequencing of short nascent strands and identified ten times more origin positions than we expected; most of these positions were conserved in four different human cell lines. Furthermore, we identified a consensus G-quadruplex-forming DNA motif that can predict the position of DNA replication origins in human cells, accounting for their distribution, usage efficiency and timing. Finally, we discovered a cell type-specific reprogrammable signature of cell identity that was revealed by specific efficiencies of conserved origin positions and not by the selection of cell type-specific subsets of origins.
Asunto(s)
G-Cuádruplex , Origen de Réplica/genética , Secuencia de Bases , Línea Celular , Mapeo Cromosómico , Secuencia de Consenso , Cartilla de ADN/genética , Replicación del ADN/genética , Genoma Humano , Células HeLa , Humanos , Motivos de NucleótidosRESUMEN
Senescence is triggered by various cellular stresses that result in genomic lesions and DNA damage response activation. However, the role of chromatin and DNA replication in senescence induction remains elusive. Here we show that downregulation of p300 histone acetyltransferase activity induces senescence by a mechanism that is independent of the activation of p53, p21(CIP1) and p16(INK4A). This inhibition leads to a global H3, H4 hypoacetylation, initiating senescence-associated heterochromatic foci formation during S phase, together with a global decrease in replication fork velocity, and alteration of DNA replication timing. This replicative stress occurs without DNA damage and checkpoint activation, but results in a robust G2/M cell cycle arrest, within only one cell cycle. These results provide new insights into the control of S-phase progression by p300, and identify an unexpected chromatin-dependent alternative mechanism for senescence induction, which could possibly be exploited to treat cancer by senescence induction without generating further DNA damage.