Molecular-level insights into aging processes of skin elastin.

Skin aging is characterized by different features including wrinkling, atrophy of the dermis and loss of elasticity associated with damage to the extracellular matrix protein elastin. The aim of this study was to investigate the aging process of skin elastin at the molecular level by evaluating the influence of intrinsic (chronological aging) and extrinsic factors (sun exposure) on the morphology and susceptibility of elastin towards enzymatic degradation. Elastin was isolated from biopsies derived from sun-protected or sun-exposed skin of differently aged individuals. The morphology of the elastin fibers was characterized by scanning electron microscopy. Mass spectrometric analysis and label-free quantification allowed identifying differences in the cleavage patterns of the elastin samples after enzymatic digestion. Principal component analysis and hierarchical cluster analysis were used to visualize differences between the samples and to determine the contribution of extrinsic and intrinsic aging to the proteolytic susceptibility of elastin. Moreover, the release of potentially bioactive peptides was studied. Skin aging is associated with the decomposition of elastin fibers, which is more pronounced in sun-exposed tissue. Marker peptides were identified, which showed an age-related increase or decrease in their abundances and provide insights into the progression of the aging process of elastin fibers. Strong age-related cleavage occurs in hydrophobic tropoelastin domains 18, 20, 24 and 26. Photoaging makes the N-terminal and central parts of the tropoelastin molecules more susceptible towards enzymatic cleavage and, hence, accelerates the age-related degradation of elastin.