Wounding Induces Facultative Opn5-Dependent Circadian Photoreception in the Murine Cornea

Jun 17, 2020Investigative ophthalmology & visual science

Wounding triggers a light-sensitive daily rhythm response in the mouse cornea dependent on Opn5

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Abstract

Corneal circadian rhythms become photosensitive after wounding, with Opn5 gene function necessary for this induced sensitivity.

In vivo corneal clocks align with behavioral rhythms, while ex vivo clocks respond to light cycles.
Wounding the cornea induces expression of the Opn5 in specific epithelial cells near the injury.
This induction leads to increased sensitivity of circadian clocks in the cornea to short-wavelength light.
Opn5 is essential for the light sensitivity that develops post-wounding, while Opn3 and Opn4 do not play a role.

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PURPOSE: Autonomous molecular circadian clocks are present in the majority of mammalian tissues. These clocks are synchronized to phases appropriate for their physiologic role by internal systemic cues, external environmental cues, or both. The circadian clocks of the in vivo mouse cornea synchronize to the phase of the brain's master clock primarily through systemic cues, but ex vivo corneal clocks entrain to environmental light cycles. We evaluated the underlying mechanisms of this difference.

METHODS: Molecular circadian clocks of mouse corneas were evaluated in vivo and ex vivo for response to environmental light. The presence of and effect of genetic deletion of opsins were evaluated for influence on circadian photoresponses. Opn5-expressing cells were identified using Opn5Cre;Ai14 mice and RT-PCR, and they were characterized using immunocytochemistry.

RESULTS: Molecular circadian clocks of the cornea remain in phase with behavioral circadian locomotor rhythms in vivo but are photoentrainable in tissue culture. After full-thickness incision or epithelial debridement, expression of the opsin photopigment Opn5 is induced in the cornea in a subset of preexisting epithelial cells adjacent to the wound site. This induction coincides with conferral of direct, short-wavelength light sensitivity to the circadian clocks throughout the cornea.

CONCLUSIONS: Corneal circadian rhythms become photosensitive after wounding. Opn5 gene function (but not Opn3 or Opn4 function) is necessary for induced photosensitivity. These results demonstrate that opsin-dependent direct light sensitivity can be facultatively induced in the murine cornea.

Key numbers

14.4 ± 4.3 cells/mm

Increase in tdTomato-positive cells

Comparison of wounded vs. nonwounded corneal areas after 24 hours.

4.6 ± 0.8 cells/mm

Decrease in tdTomato-positive cells

Observed in nonwounded areas of the cornea.

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Wounding Induces Facultative Opn5-Dependent Circadian Photoreception in the Murine Cornea

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