The weakness of senescent dermal fibroblasts.

Skin is the largest human organ with easily noticeable biophysical manifestations of aging. As human tissues age, there is chronological accumulation of biophysical changes due to internal and environmental factors. Skin aging leads to decreased elasticity and the loss of dermal matrix integrity via degradation. The mechanical properties of the dermal matrix are maintained by fibroblasts, which undergo replicative aging and may reach senescence. While the secretory phenotype of senescent fibroblasts is well studied, little is known about changes in the fibroblasts biophysical phenotype. Therefore, we compare biophysical properties of young versus proliferatively aged primary fibroblasts via fluorescence and traction force microscopy, single-cell atomic force spectroscopy, microfluidics, and microrheology of the cytoskeleton. Results show senescent fibroblasts have decreased cytoskeletal tension and myosin II regulatory light chain phosphorylation, in addition to significant loss of traction force. The alteration of cellular forces is harmful to extracellular matrix homeostasis, while decreased cytoskeletal tension can amplify epigenetic changes involved in senescence. Further exploration and detection of these mechanical phenomena provide possibilities for previously unexplored pharmaceutical targets against aging.