An aged immune system drives senescence and ageing of solid organs

Ageing of the immune system, or immunosenescence, contributes to the morbidity and mortality of the elderly1,2. To define the contribution of immune system ageing to organism ageing, here we selectively deleted Ercc1, which encodes a crucial DNA repair protein3,4, in mouse haematopoietic cells to increase the burden of endogenous DNA damage and thereby senescence5-7 in the immune system only. We show that Vav-iCre+/-;Ercc1-/fl mice were healthy into adulthood, then displayed premature onset of immunosenescence characterized by attrition and senescence of specific immune cell populations and impaired immune function, similar to changes that occur during ageing in wild-type mice8-10. Notably, non-lymphoid organs also showed increased senescence and damage, which suggests that senescent, aged immune cells can promote systemic ageing. The transplantation of splenocytes from Vav-iCre+/-;Ercc1-/fl or aged wild-type mice into young mice induced senescence in trans, whereas the transplantation of young immune cells attenuated senescence. The treatment of Vav-iCre+/-;Ercc1-/fl mice with rapamycin reduced markers of senescence in immune cells and improved immune function11,12. These data demonstrate that an aged, senescent immune system has a causal role in driving systemic ageing and therefore represents a key therapeutic target to extend healthy ageing.

Tissue specificity of senescent cell accumulation during physiologic and accelerated aging of mice

Senescent cells accumulate with age in vertebrates and promote aging largely through their senescence‐associated secretory phenotype (SASP). Many types of stress induce senescence, including genotoxic stress. ERCC1‐XPF is a DNA repair endonuclease required for multiple DNA repair mechanisms that protect the nuclear genome. Humans or mice with reduced expression of this enzyme age rapidly due to increased levels of spontaneous, genotoxic stress. Here, we asked whether this corresponds to an increased level of senescent cells. p16^Ink4a and p21^Cip1 mRNA were increased ~15‐fold in peripheral lymphocytes from 4‐ to 5‐month‐old Ercc1^−/∆ and 2.5‐year‐old wild‐type (WT) mice, suggesting that these animals exhibit a similar biological age. p16^Ink4a and p21^Cip1 mRNA were elevated in 10 of 13 tissues analyzed from 4‐ to 5‐month‐old Ercc1^−/∆ mice, indicating where endogenous DNA damage drives senescence in vivo. Aged WT mice had similar increases of p16^Ink4a and p21^Cip1 mRNA in the same 10 tissues as the mutant mice. Senescence‐associated β–galactosidase activity and p21^Cip1 protein also were increased in tissues of the progeroid and aged mice, while Lamin B1 mRNA and protein levels were diminished. In Ercc1^−/Δ mice with a p16^Ink4a luciferase reporter, bioluminescence rose steadily with age, particularly in lung, thymus, and pancreas. These data illustrate where senescence occurs with natural and accelerated aging in mice and the relative extent of senescence among tissues. Interestingly, senescence was greater in male mice until the end of life. The similarities between Ercc1^−/∆ and aged WT mice support the conclusion that the DNA repair‐deficient mice accurately model the age‐related accumulation of senescent cells, albeit six‐times faster.