Substrate stiffness modulates the emergence and magnitude of senescence phenotypes

Cellular senescence is a major driver of aging and disease. Here we show that substrate stiffness modulates the emergence and magnitude of senescence phenotypes post induction. Using a primary dermal fibroblast model of senescence, we show that decreased substrate stiffness accelerates cell-cycle arrest during senescence development and regulate expression of conventional protein-based biomarkers of senescence. We found that the expression of these senescence biomarkers, namely p21 WAF1/CIP1 ( CDKN1a ) and p16 INK4a ( CDKN2a ) are mechanosensitive and are in-part regulated by myosin contractility through focal adhesion kinase (FAK)-ROCK signaling. Interestingly, at the protein level senescence-induced dermal fibroblasts on soft substrates (0.5 kPa) do not express p21 WAF1/CIP1 and p16 INK4a at comparable levels to induced cells on stiff substrates (4GPa). However, cells do express CDKN1a, CDKN2a, and IL6 at the RNA level across both stiff and soft substrates. When cells were transferred from soft to stiff substrates, senescent cells recover an elevated expression expressing p21 WAF1/CIP1 and p16 INK4a at levels comparable to senescence cells on stiff substrates, pointing to a mechanosensitive regulation of the senescence phenotypes. Together, our results indicate that the induction of senescence programs depends critically on the mechanical environments of cells and that senescent cells actively respond and adapt to changing mechanical cues.

Senescent stroma induces nuclear deformations in cancer cells via the inhibition of RhoA/ROCK/myosin II-based cytoskeletal tension

The presence of senescent cells within tissues has been functionally linked to malignant transformations. Here, using tension-gauge tethers technology, particle-tracking microrheology, and quantitative microscopy, we demonstrate that senescent-associated secretory phenotype (SASP) derived from senescent fibroblasts impose nuclear lobulations and volume shrinkage on malignant cells, which stems from the loss of RhoA/ROCK/myosin II-based cortical tension. This loss in cytoskeletal tension induces decreased cellular contractility, adhesion, and increased mechanical compliance. These SASP-induced morphological changes are, in part, mediated by Lamin A/C. These findings suggest that SASP induces defective outside-in mechanotransduction from actomyosin fibers in the cytoplasm to the nuclear lamina, thereby triggering a cascade of biophysical and biomolecular changes in cells that associate with malignant transformations.