Claudin reduction may relate to an impaired skin barrier in rosacea.

Rosacea is a chronic inflammatory skin disorder whose pathophysiological mechanism remains largely unknown. Although recent studies have revealed the hypersensitivity of the skin towards chemical, thermal and biological stimuli, there is no direct molecular evidence suggesting the skin barrier is impaired in rosacea. In this study, we demonstrated that the mRNA levels of most claudins (CLDN), the main components of tight junctions determining the major barrier of the paracellular pathway between epithelial cells, were lowered in lesional skin of rosacea patients, especially with erythematotelangiectatic (ETR) and papulopustular (PPR) subtypes. Immunohistochemical analysis showed a significant decrease in the expression of CLDN1, CLDN3, CLDN4 and CLDN5 in the epidermis of ETR and PPR patients. However, the expression of other skin barrier genes, such as filaggrin, loricrin and keratin 10, was not altered. In vitro, various rosacea trigger factors reduced the protein levels of CLDN1, CLDN3 and CLDN5 in keratinocytes. Taken together, our results demonstrate a significant decrease in the expression of CLDN rather than other skin barrier genes, which may be associated with an impaired skin barrier responsible for the development of rosacea.