Cell Senescence-Independent Ageing of Human Skin
Skin ageing is defined in part by collagen depletion and fragmentation that leads to a loss of mechanical tension. This is currently believed to reflect, in part, the accumulation of senescent cells. We compared the expression of genes and proteins for components of the extracellular matrix (ECM) as well as their regulators and found that senescent cells produced more matrix metalloproteinases (MMPs) than proliferating cells from adult and neonatal donors. This was consistent with senescent cells contributing to increased matrix degradation with age; however, cells from adult donors proved significantly less capable of producing new collagen than neonatal or senescent cells, and they showed significantly lower myofibroblast activation as determined by the marker -SMA. Functionally, adult cells also showed slower migration than neonatal cells. We concluded that while increased collagen degradation with age might reflect senescent cell accumulation, the reduced collagen production that prevents the skin from maintaining homeostasis must reflect senescence-independent processes.