Alterations in extracellular matrix composition during aging and photoaging of the skin

Abstract

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 solar 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 ECM-supporting proteoglycans and structural ECM integrity, evidenced by decreasing collagen abundance and increasing fibril fragmentation. 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 associated with photoaging are evident even in young (mid 20s) sun-exposed forearm skin, indicating that proteomic evidence of photoaging is present decades prior to clinical signs of photoaging. GO term enrichment revealed that both intrinsic aging and photoaging share common features of chronic inflammation. The proteomic data has been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the data set identifier PXD015982.

Evaluation and refinement of sample preparation methods for extracellular matrix proteome coverage

“…For optimal ECM coverage, the Gnd-HCl/HA extraction protocol is recommended as it produces the greatest number of PSMs and highest sequence coverage of core matrisome proteins. Disease progression and aging have been shown to increase the resistance of the insoluble ECM to extraction, 44 increasing the necessity of effectively extracting the insoluble ECM via chemical digestion. Additionally, the Gnd-HCl/HA extraction produces two separate ECM fractions which can be analyzed independently, further increasing ECM identifications and allowing for assessment of ECM solubility.…”

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing

“…Several studies have shown that downregulation of LOX in the context of ageing is not restricted to the lung. For instance, LOX expression is reduced with age in human, rat and monkey skin ( 153 , 214 , 215 ), in urogenital tissues of female mice ( 216 ) and in rat aorta ( 217 ). Notably, loss of function mutations in LOX predispose to aortic aneurysms and age is the most important risk factor for aortic aneurysms ( 158 , 159 ), supporting the concept that loss of LOX upon ageing may have direct effects on ECM integrity and tissue stiffness.…”

“…An immunohistochemical study of human lungs found an age-dependent increase of TIMP2 + cells, but not MMP2 + cells, in the lung ( 249 ), providing some evidence for decreased MMP-mediated collagen degradation in the aged lung. Notably, in a recent pioneering study of human skin ageing, the authors correlated matrisome changes with the assessment of ECM integrity by single harmonic generation and two-photon autofluorescence imaging ( 214 ). Among other changes, they found decreased MMP2 and increased TIMP3 levels in aged skin.…”

Evaluation and Refinement of Sample Preparation Methods for Extracellular Matrix Proteome Coverage

“…For optimal ECM coverage, the Gnd-HCl/HA extraction protocol is recommended as it produces the greatest number of PSMs and highest sequence coverage of core matrisome proteins. Disease progression and aging have been shown to increase the resistance of the insoluble ECM to extraction ( 46 ), increasing the necessity of effectively extracting the insoluble ECM via chemical digestion. Additionally, the Gnd-HCl/HA extraction produces two separate ECM fractions, which can be analyzed independently, further increasing ECM identifications and allowing for assessment of ECM solubility.…”