Acellular Mechanisms of Extracellular Matrix Degradation

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Abstract

Exposure of the skin to ultraviolet radiation (UVR) results clinically in the formation of deep wrinkles and mottled pigmentation and histologically, in a vast remodelling of the dermal extracellular matrix (ECM), in particular the elastic fibre network. Fibrillin microfibrils and fibulin-5 are early biomarkers of photoageing, where a loss of these fibres from the dermal epidermal junction is apparent. A study by our group showed that isolated fibrillin microfibrils and fibronectin which are rich in amino acids which absorb energy from UVR (UV-chromophores) are susceptible to UVR-induced damage, whilst UV-chromophore poor collagen type I is not. This research, with other earlier studies, indicates that acellular mechanism may work in tandem with cell-mediated up-regulation of matrix metalloproteinases (MMPs) in the progression of photoageing. This thesis aims to: i) test whether acellular mechanisms of photoageing are a result of direct photon absorption and/or the photodynamic production of reactive oxygen species (ROS); ii) assess the functional consequences of UVB degradation on the susceptibility of fibrillin microfibrils to MMPs and; iii) assay whether ECM proteins are differentially susceptible to solar simulated radiation (SSR) or UVA (315-400nm) alone using physiologically relevant doses of irradiation.Isolated proteins were exposed to UVB (280-315nm) in depleted-O2 conditions and in the presence of deuterium oxide. Depleted-O2 conditions decreased and deuterium oxide conditions increased UVR-induced degradation. Isolated proteins also show a similar pattern of degradation when exposed to H2O2 as an exogenous source of ROS. These results indicate that ROS play an important role in the differential degradation of dermal proteins.MMPs-3 and -9 are both upregulated in the skin after exposure to UVR and have the ability to degrade elastic fibre components. After exposure to UVB, damaged fibrillin microfibrils become more susceptible to degradation by both MMPs-3 and -9.Chromophore-rich fibrillin microfibrils and fibronectin are susceptible to degradation by both SSR and UVA alone, whereas chromophore-poor collagens type I and VI and tropoelastin are not. These results support our previous findings that amino acid composition of proteins is a good indicator of their relative susceptibility to UV-induced damage with a physiologically relevant irradiation system.In conclusion this work shows that ROS are an important mediator of acellular mechanisms of photoageing and that amino acid composition is a good indication of relative susceptibility of proteins to both ROS and UVR. The ability to predict ROS-susceptible proteins also has wider implications for human ageing as a whole.

Keyword(s)

Dermatology; Fibrillin Microfibrils; Photoageing; Ultraviolet Radiation

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