364 Mechanical forces of human dermal fibroblasts significantly decrease with age

Abstract

With age, skin undergoes chronological, intrinsic aging and extrinsic aging due to environmental factors. Young skin is characterized by a thick epidermis and an extensive dermis composed of a structured matrix synthesized by fibroblasts, conferring elasticity and tone. During injury, young skin rapidly heals due to the efficient response and metabolic activity of dermal fibroblasts. In contrast, mature skin is characterized by a decrease in tissue depth, a loss of collagen and other structural fibers promoting the appearance of visible signs of skin aging such as wrinkles, and defects in healing. Our comparison of the proteome of fibroblasts from young and mature skin revealed significant differences in proteins associated with the actin cytoskeleton and the extracellular matrix. The present work aims to deepen these data, by comparing the mechanical properties of fibroblasts cultured from the skin of young (<35 y.o., n=6) or mature (>55 y.o., n=6) women. Mechanical stress was exerted on these two sets of fibroblasts using rectangle-shaped patterns on different stiffnesses of polyacrylamide gel (1-30kPa), thus mimicking the stiffness of the skin during different stages of healing and aging. The cellular energy produced in response to these mechanical stresses was measured by Traction Force Microscopy (TFM). It was significantly reduced by a 1000 factor in mature fibroblasts compared to young fibroblasts. The modulation by siRNA transfection of several actin-related proteins demonstrated their involvement in the mechanical capacities of fibroblasts, as well as in cell migration and contraction capacities. Altogether, our study evidences an alteration in fibroblast forces which are linked to fibroblast cytoskeleton and aging. This reveals new potent proteins that could be targeted in order to improve the texture and regeneration of mature skin.