• Few articles published to date on the effects of IRA radiation on photoaging of the epidermis.
• Article concludes that IRA inhibits proliferation of human skin keratinocytes and clarifies its putative mechanism.
• Prevention of IRA penetration into skin may contribute to maintaining the proliferative activity of human skin keratinocytes and epidermal turnover rate, which is considered to play an important role in maintaining a healthy and youthful appearance skin.

Otsuka Pharmaceutical Co., Ltd. (Otsuka) has published an article in the peer-reviewed scientific journal, Photochemistry and Photobiology entitled 'Infrared-A Irradiation-induced Inhibition of Human Keratinocyte Proliferation and Potential Mechanisms'.

This article describes for the first time that IRA radiation inhibits human epidermal keratinocyte proliferation and clarifies its inhibitory mechanism, by focusing on the regulatory mechanism for the activation of mTOR complex 1 (mTORC1).

The human epidermis has a self-renewing ability known as epidermal turnover, which is mediated by the proliferation of keratinocytes. It has been recognized that intrinsic aging and other factors suppress the proliferative activity, resulting in the retardation of epidermal turnover rate. Photoaging, which is both qualitatively and quantitatively different from chronological aging, is known to be associated with inhibition of keratinocyte proliferation. However, the molecular mechanisms involved in the inhibitory effect are incompletely understood.

Otsuka believes that maintaining epidermal turnover rate is important for healthy skin and has been investigating the effects of sunlight on the proliferative activity of keratinocytes. The authors have demonstrated that IRA, which is known to promote photoaging of the dermis, inhibits the activity of mTORC1, an intracellular signaling molecule that plays a critical role in regulating cell cycle progression, and thereby inhibits cell proliferation of keratinocytes. Furthermore, it was revealed that there are at least two pathways by which the molecular mechanism inhibits the activity of mTORC1 upon IRA irradiation.

These findings suggest that prevention of IRA radiation from sunlight may contribute to preserve epidermal cell proliferation activity, leading to the maintenance of epidermal turnover rate that is required to maintain a healthy and youthful appearance skin. We believe that these findings provide new insights into the mechanisms of photoaging.

The full text of the article can be found here：https://doi.org/10.1111/php.13248

About Otsuka

Otsuka Pharmaceutical Co., Ltd. is a global healthcare company with the corporate philosophy: "Otsuka-people creating new products for better health worldwide." Otsuka researches, develops, manufactures and markets innovative products, with a focus on pharmaceutical products for the treatment of diseases and nutraceutical products for the maintenance of everyday health.