Can Violet Light Speed Up Wound Healing?

Let's continue exploring the effects of light on the eyes and metabolism. My interest focuses mainly on effects associated with the photoreceptors OPN3, OPN4, and OPN5. The first two are sensitive to blue light, while OPN5 is sensitive to near-ultraviolet light, that is, UV-A.

It appears that OPN5 is an important component of the mechanisms involved in healing mechanical tissue injuries. Here, we'll look at an interesting study investigating the healing of corneal injuries. Genetic suppression of OPN5 (Opn5-/-) leads to impaired healing of corneal injuries and a loss of light sensitivity in the healing process.

Perhaps we can quote a few paragraphs here.

The non-visual opsins, OPN3, OPN4, and OPN5, are opsinfamily receptors that are activated by light but that subserve non-visual functions. We have previously shown that the local molecular circadian clocks in cells of the murine retina and skin display an Opn5-dependent violet-light-induced photo-entrainment, which is independent of the phase of behavioral rhythms. A similar photoentrainment of the local molecular circadian clocks is observed within the cornea. Interestingly, Opn5 is not constitutively expressed in healthy mouse corneas in vivo but is induced upon tissue culture. In addition to the regulation of local circadian clocks, Opn5 expression in the retina is necessary for violet-light-dependent suppression of defocus-induced myopia, influences the regulation of body temperature, and, in conjunction with Opn4, regulates the light-dependent timing of vascular development. Opn4 has also been identified in the trigeminal sensory neurons that innervate the cornea, and it plays a role in photo-oculodynia.

OPN5 integrates light cues over relatively long timescales (minutes or longer) compared with the millisecond-level responses required for visual signaling. In addition to neural expression in the retina, OPN5 and the other non-visual opsins are also expressed in several non-neuronal cell types. We have identified Opn5 in epithelial cells and keratocytes in the cultured murine cornea and in melanocytes of dermal hair follicles. Opn4 and Opn3 have also been identified in cultured mammalian melanocytes. Opn3 is also expressed in white adipocytes of scapular and inguinal fat pads, where it performs a role in lightinduced lipolysis. While the diverse roles of non-visual opsins are still being defined, their expression in non-neural cell types appears to involve slow light response kinetics and often the release of paracrine factors.

End of quote

The authors of this study demonstrate the importance of light that specifically activates OPN5 for healing the cornea, the outer protective layer of the eye, following mechanical injury. Throughout our lives, the eye's outer layer, the epithelium, is constantly being worn away. It must be replaced with new cells, and activation of the OPN5 photoreceptors significantly shortens healing time. Light sensitivity is greatest about 12 hours after injury and then gradually decreases. Interestingly, before an injury occurs, the cornea lacks these photoreceptors. They develop only in response to the injury and disappear once healing is complete.

The authors also investigated whether other photoreceptors, such as the visual or nonvisual photoreceptors OPN3 and OPN4, might be involved, but they ruled out this possibility. The observed effect was caused exclusively by OPN5 photoreceptors. It appears that these photoreceptors are generally important for wound healing, even in complete darkness. This brings me back once again to the extensive discussion of the virtually unknown ultraviolet mitogenic radiation, which apparently is ubiquitous. Take a look at the link.

In addition to in vivo studies, meaning studies conducted on living mice, an ex vivo experiment was also performed using tissue samples taken from monkey eyes. Violet light at wavelengths of both 400 and 412 nm was effective and activated several enzymes involved in wound healing. It can therefore be assumed that the human cornea functions in a very similar way and also requires near-ultraviolet light to better activate the healing process. Thus, unlike narrowband blue light, which disables the antioxidant protection of the cornea via OPN3, near-ultraviolet light has the exact opposite effect and may help heal the eyes.


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Zdroje:

Opsin 5 mediates violet light-accelerated wound healing in mammalian corneas

The Hidden Harms of Modern Lighting and the Fight to Bring Back Incandescent Bulbs


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