Journal club 26.05.15

Neuropsin, TRPV4 and intracellular calcium mediate intrinsic photosensitivity in corneal epithelial cells

Luka Lapajne ¹, Monika Lakk ², Christopher N Rudzitis ³, Shruti Vemaraju ⁴, Richard A Lang ⁴, Marko Hawlina ⁵, David Križaj ⁶

• ¹Department of Ophthalmology & Visual Sciences, University of Utah School of Medicine, Salt Lake City, UT, USA; Department of Ophthalmology, University Medical Center, Ljubljana, Slovenia.
• ²Department of Ophthalmology & Visual Sciences, University of Utah School of Medicine, Salt Lake City, UT, USA.
• ³Department of Ophthalmology & Visual Sciences, University of Utah School of Medicine, Salt Lake City, UT, USA; Interdepartmental Program in Neuroscience, University of Utah, USA.
• ⁴Department of Ophthalmology, College of Medicine, University of Cincinnati, Cincinnati, OH, USA.
• ⁵Department of Ophthalmology, University Medical Center, Ljubljana, Slovenia.
• ⁶Department of Ophthalmology & Visual Sciences, University of Utah School of Medicine, Salt Lake City, UT, USA; Interdepartmental Program in Neuroscience, University of Utah, USA; Department of Bioengineering, University of Utah, Salt Lake City, UT, USA; Department of Neurobiology, University of Utah, Salt Lake City, UT, USA. Electronic address: david.krizaj@hsc.utah.edu.

Abstract

Purpose: To investigate intrinsic phototransduction in the corneal epithelium and its role in intracellular and inflammatory signaling.

Methods: Optical imaging in isolated corneal epithelial cells (CECs) and debrided epithelia was combined with molecular, biochemical, pharmacological assays and gene deletion studies to track UVB-induced calcium signaling and release of cytokines, chemokines and matrix remodeling enzymes. Results from wild type mouse CECs were compared to data obtained from Opn5^-/- and Trpv4^-/- cells.

Results: UVB stimuli and TRPV4 activity induced epithelial release of IL-1β, IL-17, matrix metalloproteinases MMP-3/MMP-9, and thymic stromal lymphopoietin (TSLP). UVB stimuli evoked [Ca²⁺]_i elevations in dissociated mouse CECs that were partially reduced by inhibition of TRPV4 channels, Trpv4 knockdown and replacement of control saline with Ca²⁺-free saline. UVB-induced Ca²⁺ responses were significantly suppressed by OPN5 deletion and by inhibition of phospholipase C signaling, and responses were abrogated in cells with depleted intracellular Ca²⁺ stores.

Conclusions: Mammalian CECs are intrinsically and constitutively photosensitive. UVB photons are transduced by neuropsin, phospholipase C and CICR signaling, with mouse but not human CE transduction exhibiting a UVB-sensitive TRPV4 component. TRPV4 activity and UVB transduction are linked to cell-autonomous release of proinflammatory, matrix remodeling and nociceptive interleukins and MMPS. TRPV4-induced cytokine release may contribute to the pain induced by mechanical injury of the cornea and CEC photosensing may alert and protect the visual system from ultraviolet B (UVB) radiation -induced snow blindness, injury, vision loss and cancer.

Keywords: Corneal epithelium; Neuropsin; Phototransduction; Snow blindness; TRPV4.