Cudrania tricuspidata leaf extracts and its components, chlorogenic acid, kaempferol, and quercetin, increase claudin 1 expression in human keratinocytes, enhancing intercellular tight junction capacity

Dysfunction of tight junctions and their components can cause diverse skin diseases. Here, we investigated the expression of claudin 1, a major tight junction protein, and changes of tight junction capacity upon treatment of the extracts of Cudrania tricuspidata (C. tricuspidata) and its components, chlorogenic acid, kaempferol, and quercetin. The effects of ethanol extracts of C. tricuspidata (EECT) and water extracts of C. tricuspidata (WECT) on the viability of human keratinocyte HaCaT cells were assessed by cell proliferation assay. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was conducted to measure the expression of claudin 1 mRNA. The protein expression of claudin 1 was analyzed by western blot and its tight junctional distribution was observed with immunofluorescence microscopy analysis. The tight junction capacity was analyzed by dispase assay. Upon treatment of WECT to HaCaT cells, the mRNA and protein expressions of claudin 1 were increased. In addition, chlorogenic acid, kaempferol, and quercetin increased claudin 1 protein expression levels in a dose-dependent manner. WECT and these three compounds enhanced the tight junction capacity of HaCaT cells in dispase assay. WECT, and its components, such as chlorogenic acid, kaempferol, and quercetin, upregulates both mRNA and protein expressions of claudin 1, which leads to the enhancement of tight junction capacity. Thus, WECT could be a therapeutic approach for treating tight junction-disrupted conditions such as atopic dermatitis and psoriasis.