Danitza Rebolledo-Mira

Thrombotic cardiovascular diseases are frequent side effects of cancer therapy with cytotoxic drugs such as Doxorubicin. Endothelial cell senescence is emerging as a critical mechanism underlying endothelial dysfunction in this context. Senescent cells, although unable to proliferate, secrete bioactive molecules that alter the tissue microenvironment, a feature known as the senescence-associated secretory phenotype (SASP). Besides soluble molecules, senescent cells also release extracellular vesicles (EVs). Previous studies indicate that senescent endothelial cells produce a secretome that promotes platelet activation; however, the contribution of EVs remains unclear. Here, we show that human microvascular endothelial cells (HMEC-1) exposed to Doxorubicin undergo senescence, display endothelial dysfunction, and release EVs. We found no differences in the concentration or size distribution of EVs from senescent and non-senescent cells. Nevertheless, EVs from senescent HMEC-1 promoted platelet activation more strongly than EVs from control cells. Notably, EVs alone did not induce platelet aggregation, suggesting that soluble factors are also required to support platelet-dependent hemostasis. These findings reveal that EVs from senescent endothelial cells contribute to platelet activation, a process that may favor thrombosis in patients receiving Doxorubicin-based chemotherapy.

Despite not dividing, senescent cells acquire the ability to synthesize and secrete a plethora of bioactive molecules, a feature known as the senescence-associated secretory phenotype (SASP). In addition, senescent cells often upregulate autophagy, a catalytic process that improves cell viability in stress-challenged cells. Notably, this “senescence-related autophagy” can provide free amino acids for the activation of mTORC1 and the synthesis of SASP components. However, little is known about the functional status of mTORC1 in models of senescence induced by CDK4/6 inhibitors (e.g., Palbociclib), or the effects that the inhibition of mTORC1 or the combined inhibition of mTORC1 and autophagy have on senescence and the SASP. Herein, we examined the effects of mTORC1 inhibition, with or without concomitant autophagy inhibition, on Palbociclib-driven senescent AGS and MCF-7 cells. We also assessed the pro-tumorigenic effects of conditioned media from Palbociclib-driven senescent cells with the inhibition of mTORC1, or with the combined inhibition of mTORC1 and autophagy. We found that Palbociclib-driven senescent cells display a partially reduced activity of mTORC1 accompanied by increased levels of autophagy. Interestingly, further mTORC1 inhibition exacerbated the senescent phenotype, a phenomenon that was reversed upon autophagy inhibition. Finally, the SASP varied upon inhibiting mTORC1, or upon the combined inhibition of mTORC1 and autophagy, generating diverse responses in cell proliferation, invasion, and migration of non-senescent tumorigenic cells. Overall, variations in the SASP of Palbociclib-driven senescent cells with the concomitant inhibition of mTORC1 seem to depend on autophagy.