Werner Syndrome (WS) fibroblasts enter replicative senescence after a reduced in vitro life span. Although this has been postulated as causal in the accelerated ageing seen in this disease, controversy remains as to whether WS is showing the acceleration of a normal cellular ageing mechanism, or instead the occurrence of a novel WS-specific process. To address this we analysed the signalling pathways responsible for senescence in WS fibroblasts. Cultured WS (AG05229) fibroblasts senesced after ~20 population doublings, with the majority of the cells having a 2N DNA content. This was associated with high levels of the CdkIs p16(INK4A) and p21(WAF1). Senescent WS cells re-entered the cell cycle following microinjection of a p53-neutralising antibody. Similarly, pre-senescent WS fibroblasts expressing the E6 and/or E7 oncoproteins by-passed M1 and ultimately reached a second proliferative life span barrier, which strongly resembled the second lifespan barriers found in normal cells for growth dynamics, cellular morphology, and expression of p16(INK4A) and p21(WAF1). The strong similarity between the signalling pathways triggering cell cycle arrest in WS and normal fibroblasts, and the observation that telomeres may shorten faster in WS cells, provides support for the defect in WS causing the acceleration of a normal ageing mechanism, and validates the use of WS as a model for some aspects of human ageing.
Cell cycle control