Predicting the differential susceptibility of dermal extracellular matrix proteins to photodegradation by solar-simulated radiation

Bioscience, University Sydney, AUPhotoaged skin is characterised by profound remodelling of the extracellular matrix (ECM). We have previously shown that UV chromophore (Cys, His, Phe, Trp and Tyr)-rich proteins are differentially degraded by UV radiation (UVR). We tested the hypothesises that; (i) UV-mediated ECM degradation occurs via reactive oxygen species (ROS), by exposing chromophore-rich fibronectin and chromophore-poor tropoelastin to UVR in depleted-O2 and D2O environments and (ii) exogenous ROS mediates differential degradation of the same proteins. As the photodynamic production of ROS can be inhibited in depleted-O2 environments we exposed purified fibronectin to a broadband UVB (TL-12: 50 and 500mJ/cm2) in ambient and depleted-O2 conditions by bubbling with N2. Solutions were analysed by reducing SDS-PAGE. Irradiation of fibronectin in ambient-O2 (50 and 500mJ/cm2) caused dose-dependent aggregation (5 and 83 fold changes in the optical density (OD) of the aggregate at 50 and 500mJ/cm2 respectively), fibronectin aggregation was abrogated (68 fold lower OD) in the depleted-O2 compared with ambient-O2. Conversely, fibronectin aggregation was increased 4 fold in D2O compared with H2O environments. UV-mediated changes to the molecular weight (Mw) of fibronectin were recapitulated by exposure to H2O2 (40mM for 2 hrs). In contrast, UVB irradiation in both H2O and D2O had no observable effect on the Mw of tropoelastin. Therefore, ROS may play an important role in the selective degradation of long-lived UV chromophore-rich ECM in both UV-exposed and protected ageing tissues. Research supported by Alliance Boots.