Age-related accumulation of ploidy changes is associated with decreased expression of genes controlling chromosome segregation and cohesin functions. To determine the consequences of whole chromosome instability (W-CIN) we down-regulated the spindle assembly checkpoint component BUB1 and the mitotic cohesin SMC1A, and used four-color-interphase-FISH coupled with BrdU incorporation and analyses of senescence features to reveal the fate of W-CIN cells. We observed significant correlations between levels of not-diploid cells and senescence-associated features (SAFs). W-CIN induced DNA double strand breaks and elevated oxidative stress, but caused low apoptosis. SAFs of W-CIN cells were remarkably similar to those induced by replicative senescence but occurred in only 13 days versus 4 months. Cultures enriched with not-diploid cells acquired a senescence-associated secretory phenotype (SASP) characterized by IL1B, CXCL8, CCL2, TNF, CCL27 and other pro-inflammatory factors including a novel SASP component CLEC11A. These findings suggest that W-CIN triggers premature senescence, presumably to prevent the propagation of cells with an abnormal DNA content. Cells deviating from diploidy have the ability to communicate with their microenvironment by secretion of an array of signaling factors. Our results suggest that aneuploid cells that accumulate during aging in some mammalian tissues potentially contribute to age-related pathologies and inflammation through SASP secretion.

Chromosomal aneuploidy, the gain or loss of whole chromosomes, is a hallmark of pathological conditions and a causal factor of birth defects and cancer. A number of studies indicate that aneuploid cells are present at a high frequency in the brain of mice and humans, suggesting that mosaic aneuploidies are compatible with normal brain function and prompting the question about their consequences. To explore the possible contribution of aneuploidy to functional decline and loss of cognitive functions during aging, we used a quantitative, dual-labeling interphase-fluorescence in situ hybridization approach to compare aneuploidy levels of chromosomes 1, 7, 14, 15, 16, 18, 19 and Y in the cerebral cortex of 4- and 28-month-old mice. We show that aneuploidy accumulates with age in a chromosome-specific manner, with chromosomes 7, 18 and Y most severely affected, i.e. up to 9.8% of non-neuronal brain nuclei in 28-month-old animals for chromosome 18. While at early age, both neuronal and glial cells are affected equally, the age-related increase was limited to the non-neuronal nuclei. No age-related increase in aneuploidy was observed in the cerebellum or in the spleen of the same animals. Extrapolating the average frequencies of aneuploidy from the average over 8 chromosomes to all 20 mouse chromosomes would indicate an almost 50% aneuploidy frequency in aged mouse brain. Such high levels of genome instability could well be a factor in age-related neurodegeneration.