The expression of opsins in the human skin and its implications for photobiomodulation: A Systematic Review

Abstract

Background Skin is the organ most extensively exposed to light of a broad range of wavelengths. Several studies have reported that skin expresses photoreceptive molecules called opsins. However, the identity and functional role of opsins in the human skin remain elusive. We aim to summarize current scientific evidence on the types of opsins expressed in the skin and their biological functions. Methods A primary literature search was conducted using PubMed to identify articles on dermal opsins found in nonhuman animals and humans. Results Twenty‐two articles, representing, however, a non‐exhaustive selection of the scientific papers published in this specific field, met the inclusion criteria. In nonhuman animals, opsins and opsin‐like structures have been detected in the skin of fruit fly, zebrafish, frog, octopus, sea urchin, hogfish, and mouse, and they mediate skin color change, light avoidance, shadow reflex, and circadian photoentrainment. In humans, opsins are present in various skin cell types, including keratinocytes, melanocytes, dermal fibroblasts, and hair follicle cells. They have been shown to mediate wound healing, melanogenesis, hair growth, and skin photoaging. Conclusion Dermal opsins have been identified across many nonhuman animals and humans. Current evidence suggests that opsins have biological significance beyond light reception. In nonhuman animals, opsins are involved in behaviors that are critical for survival. In humans, opsins are involved in various functions of the skin although the underlying molecular mechanisms remain unclear. Future investigation on elucidating the mechanism of dermal opsins will be crucial to expand the therapeutic benefits of photobiomodulation for various skin disorders.

Photobiomodulation promotes hair regeneration in injured skin by enhancing migration and exosome secretion of dermal papilla cells

“…Photoreceptors expressed in skin including cytochrome c oxidase, cryptochromes, opsins and so on, can response to specific light parameters and trigger different molecular mechanisms. For example, UV‐blue light can activate Opsin 1‐SW, Opsin 2, Opsin 3, Opsin 4 and Opsin 5 receptors and red light can activate cytochrome c oxidase 38–41 . The activation of cytochrome c oxidase can produce reactive oxygen species, 42 leading to the activation of Akt/GSK‐3β/β‐catenin pathway 21 .…”

Impact of visible light on skin health: The role of antioxidants and free radical quenchers in skin protection

“…1,6,25 Opsins (OPNs) are a large group of light-sensitive, G proteinecoupled receptors responsible for triggering signaling cascades when activated by various wavelengths of light, including VL, resulting in VL phototransduction. 6,[36][37][38] Identified skin OPN's activation wavelengths range from 380 to 400 nm (OPN4, OPN5) to as high as 557 to 560 nm (OPN-1-LW). Various cell types in the epidermis and dermis, including melanocytes, keratinocytes, fibroblasts, and hair follicle stem cells, have been shown to have opsin receptors.…”

“…Various cell types in the epidermis and dermis, including melanocytes, keratinocytes, fibroblasts, and hair follicle stem cells, have been shown to have opsin receptors. 6,36,[38][39][40][41][42][43] The group of carotenoids in human skin includes a-carotene, g-carotene, ß-carotene, lycopene, lutein, and zeaxanthin and their isomers. 44,45 The distribution of carotenoids in human skin depends on the areas of skin examined and significantly varies from individual to individual.…”

The circadian clock and diseases of the skin

“…Selective expression of Bmal1 only in the epidermis does not disturb the skin diurnal rhythm as long as the mice experience regular light-dark cycles [17], indicating that the epidermal clock does not require the SCN clock or clocks in other tissues. Possible contributors to the maintenance of such diurnality are light-sensitive opsin proteins present in various skin cell types (such as melanocytes, keratinocytes, fibroblasts, and hair follicle cells) that may be able to entrain the skin circadian clock [18,19].…”