Abstract
Cellular senescence is the permanent arrest of cell cycle, physiologically related to aging and aging-associated diseases. Senescence is also recognized as a mechanism for limiting the regenerative potential of stem cells and to protect cells from cancer development. The senescence program is realized through autocrine/paracrine pathways based on the activation of a peculiar senescence-associated secretory phenotype (SASP). We show here that conditioned media (CM) of senescent mesenchymal stem cells (MSCs) contain a set of secreted factors that are able to induce a full senescence response in young cells. To delineate a hallmark of stem cells SASP, we have characterized the factors secreted by senescent MSC identifying insulin-like growth factor binding proteins 4 and 7 (IGFBP4 and IGFBP7) as key components needed for triggering senescence in young MSC. The pro-senescent effects of IGFBP4 and IGFBP7 are reversed by single or simultaneous immunodepletion of either proteins from senescent-CM. The blocking of IGFBP4/7 also reduces apoptosis and promotes cell growth, suggesting that they may have a pleiotropic effect on MSC biology. Furthermore, the simultaneous addition of rIGFBP4/7 increased senescence and induced apoptosis in young MSC. Collectively, these results suggest the occurrence of novel-secreted factors regulating MSC cellular senescence of potential importance for regenerative medicine and cancer therapy.