Alterations in Extracellular Matrix Composition during Aging and Photoaging of the Skin

Human skin is composed of the cell-rich epidermis, the extracellular matrix (ECM) rich dermis, and the hypodermis. Within the dermis, a dense network of ECM proteins provides structural support to the skin and regulates a wide variety of signaling pathways which govern cell proliferation and other critical processes. Both intrinsic aging, which occurs steadily over time, and extrinsic aging (photoaging), which occurs as a result of external insults such as UV radiation, cause alterations to the dermal ECM. In this study, we utilized both quantitative and global proteomics, alongside single harmonic generation (SHG) and two-photon autofluorescence (TPAF) imaging, to assess changes in dermal composition during intrinsic and extrinsic aging. We find that both intrinsic and extrinsic aging result in significant decreases in structural ECM integrity, evidenced by decreasing collagen abundance and increasing fibril fragmentation, and ECM-supporting proteoglycans. Intrinsic aging also produces changes distinct from those produced by photoaging, including reductions in elastic fiber and crosslinking enzyme abundance. In contrast, photoaging is primarily defined by increases in elastic fiber-associated protein and pro-inflammatory proteases. Changes induced by photoaging are evident even in comparisons of young underarm and forearm skin, indicating that photoexposure experienced by an individual’s mid-20s is sufficient for large-scale proteomic alterations and that molecular-level changes due to photoaging are evident well before clinical indications are present. GO term enrichment revealed that both intrinsic aging and photoaging share common features of chronic inflammation.