Non‑invasive proteome‑wide quantification of skin barrier‑related proteins using label‑free LC‑MS/MS analysis.

A number of epidermal proteins are closely related to skin barrier function, the abnormalities of which can lead to specific skin diseases. These proteins must be quantified to further investigate the changes in the skin barrier between healthy and disease states. However, the noninvasive and proteomewide quantification of skin proteins without any labelling steps remains a challenge. In this study, 3M medical adhesive tapes were used to obtain skin samples from volunteers. Proteins were extracted from fresh skin samples and digested with trypsin. Each tryptic peptide was analysed in three replicates using liquid chromatography with tandem mass spectrometry analysis and labelfree quantification. The data were searched against the Human Universal Protein Resource (UniProt) to match with known proteins. Using this method, 1,157 skin proteins recorded in the UniProt were quantified. A total of 50 identical proteins were identified in the three replicate analyses of all samples with no significant differences in abundance. The results provided an objective metric for further study of skin ageing and various skin diseases. Specifically, the noninvasive proteomewide method used in this study can be applied to future studies of skin diseases related to barrier destruction by monitoring the changes in the levels of epidermal proteins.