Cryptochrome 1 is modulated by blue light in human keratinocytes and exerts positive impact on human hair growth

Photoactivation of cryptochrome‐family proteins by blue light is a well‐established reaction regulating physiology of plants, fungi, bacteria, insects and birds, while impact of blue light on cryptochrome synthesis and/or activity in human non‐visual cells remains unknown. Here, we show that 453 nm blue light induces cryptochrome 1 (CRY1) accumulation in human keratinocytes and the hair follicle. CRY1 is prominently expressed in the human anagen hair follicle, including epithelial stem cells. Specific silencing of CRY1 promotes catagen, while stimulation of CRY1 by KL001 prolongs anagen ex vivo by altering the expression of genes involved in apoptosis and proliferation. Together, our study identifies a role for CRY1 in sustaining human hair growth. Previously, we demonstrated positive effects of 453 nm blue light on hair growth ex vivo. Taken all together, our study suggests that CRY1 might mediate blue light‐dependent positive effects on hair growth.