Substrate stiffness and viscoelasticity influence fibroblast senescence.

Senescent cell accumulation has been implicated in aging and fibrotic disease, which are both characterized by increased tissue stiffness. However, the direct connection between tissue mechanics and senescence induction remains disputed in the literature. Thus, this work investigates the influence of hydrogel stiffness and viscoelasticity in promoting fibroblast senescence both in combination with genotoxic stress and independently. We show that while lung fibroblast YAP signaling declines with senescence induction, senescent fibroblasts maintain their mechanosensing capabilities with increased YAP nuclear localization on higher stiffness hydrogels. Most notably, we find a unique role for hydrogel viscoelasticity in senescence induction with soft (2 kPa) viscoelastic substrates promoting both the onset and amplification of senescence, even in the absence of genotoxic stress. These changes are not associated with a decline in YAP activity, but instead with a decline in nuclear DAPI intensity, suggesting a role of nuclear organization in driving this phenotype. Overall, this work highlights the influence of mechanics on the induction of senescence and supports the key role of viscoelasticity.