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Nicholas Delamere, Amritlal Mandal, Mohammad Shahidullah; ERK1/2 and p38 activation linked to TRPV1 ion channels in the lens.. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3482.
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© ARVO (1962-2015); The Authors (2016-present)
We are interested in sensing and signaling mechanisms that enable function of the epithelium, a monolayer at the anterior surface, to integrate with the homeostatic needs of the entire lens. We previously showed evidence for a swelling-activated remote control mechanism dependent on TRPV4 ion channels. Studies here were carried out to determine the response of the lens to osmotic shrinkage and to examine functional role of a different ion channel, TRPV1.
Studies were carried out using intact porcine lenses. TRPV1 expression was examined by RTPCR. ERK1/2 and p38 MAP Kinase activation (phosphorylation) was determined by Western blot analysis. Data were analyzed by one-way ANOVA.
RTPCR studies revealed TRPV1 expression in porcine lens epithelium. Transient ERK1/2 and p38 activation was observed in the epithelium of intact lenses exposed to the TRPV1 agonist capsaicin (100 nM) for 1-15 min. Peak activation was observed at approximately 5 min, increasing ERK1/2 phosphorylation ~20 fold and p38 ~7 fold (n=3; p<0.001). A similar pattern of ERK1/2 and p38 activation was observed in the epithelium of lenses exposed to hyperosmotic solution (350 mOsm vs control conditions of 300 mOsm), increasing ERK1/2 and p38 by ~13 and ~3.5 fold respectively (n=3; p<0.001). The TRPV1 antagonist A889425 (1µM) inhibited the ERK1/2 and p38 responses to capsaicin and hyperosmotic solution by ~50% (n=3, p<0.01). To test for calcium-dependence, lenses were pre-incubated with a cytosolic calcium chelator BAPTA-AM before exposure to capsaicin or hyperosmotic solution. In BAPTA pre-treated lenses the ERK1/2 activation response to capsaicin as well as hyperosmotic treatment was inhibited by more than 50% (n=3, p<0.01).
The findings point to functional TRPV1 channels in the lens. TRPV1 channel opening and calcium entry seem to be involved in the rapid signaling response of the epithelium when the lens is subjected to a hyperosmotic (shrinkage) stimulus. It is noteworthy that TRPV1 channels appear to play a role in the shrinkage response while swelling activates TRPV4.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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