p16INK4A expression induces paracrine senescence via small extracellular vesicles

Senescent cells are characterized by the expression of the cell cycle inhibitor and biomarker of aging, p16INK4A, and the capacity to modify the microenvironment through the senescence-associated secretory phenotype (SASP). Senescent cells accumulate in physiological and pathological conditions, including aging. In spite of this, fibroblasts ectopically expressing p16INK4A do not release a SASP nor communicate with the microenvironment. Here, we find that human primary fibroblasts expressing p16INK4A release more small extracellular vesicles (sEV) as part of the SASP than proliferating cells. In addition, we show that sEV isolated from p16INK4A cells are able to mediate paracrine senescence by inducing a growth arrest and DNA damage response in proliferating cells albeit not stimulating the expression of IL-8. Furthermore, we show the transmission of paracrine senescence via sEV is conserved in two cellular models of ageing: expression of progerin, mimicking an accelerated form of ageing, and inducing telomere shortening using a dominant negative mutant. Importantly, sEV isolated from fibroblasts derived from old donors also induce paracrine senescence in fibroblasts derived from young donors. In conclusion, our data indicate that sEV released by senescent and aging cells are an important mechanism of intercellular communication and could potentially explain tissue dysfunction in aging.