TRPV1-dependent NKCC1 Activation in Mouse Lens Involves Integrin and the Tubulin Cytoskeleton

Previously we showed hyperosmotic solution caused TRPV1-dependent NKCC1 activation in the lens by a mechanism that involved ERK1/2 signaling. In various tissues, integrins and the cytoskeletal network play a role in responses to osmotic stress. Here, we examined the association between integrins and TRPV1-dependent activation of NKCC1 in mouse lens epithelium. Wild-type (WT) lenses exposed to the integrin agonist leukadherin-1 (LA-1) for 10 min displayed a ~33% increase in the bumetanide-sensitive rate of Rb uptake indicating NKCC activation. Paclitaxel, a microtubule stabilizing agent, abolished the Rb uptake response. In primary cultured lens epithelium LA-1 caused a robust ERK1/2 activation response that was almost fully suppressed by paclitaxel. The TRPV1 agonist capsaicin caused a similar ERK1/2 activation response. Consistent with an association between integrins and TRPV1, the TRPV1 antagonist A889425 prevented the Rb uptake response to LA-1 as did the ERK inhibitor U0126. LA-1 did not increase Rb uptake by lenses from TRPV1 knockout mice. In cells exposed to a hyperosmotic stimulus, both the ERK1/2 activation and Rb uptake responses were prevented by paclitaxel. Taken together, the findings suggest TRPV1 activation is associated with integrins and the tubulin cytoskeleton. This aligned with the observation that LA-1 elicited a robust cytoplasmic calcium rise in cells from WT lenses but failed to increase calcium in cells from TRPV1 knockout lenses. The results are consistent with the notion that integrin activation by LA-1, or a hyperosmotic stimulus, causes TRPV1 channel opening and the consequent downstream activation of the ERK1/2 and NKCC1 responses.