Expression of CD18, CD49b, CD49c and CD49e on lens anterior capsules in human cataracts

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.

Conditional deletion of beta1-integrin from the developing lens leads to loss of the lens epithelial phenotype

Beta1-integrins are cell surface receptors that participate in sensing the cell's external environment. We used the Cre-lox system to delete beta1-integrin in all lens cells as the lens vesicle transitions into the lens. Adult mice lacking beta1-integrin in the lens are microphthalmic due to apoptosis of the lens epithelium and neonatal disintegration of the lens fibers. The first morphological alterations in beta1-integrin null lenses are seen at 16.5 dpc when the epithelium becomes disorganized and begins to upregulate the fiber cell markers beta- and gamma-crystallins, the transcription factors cMaf and Prox1 and downregulate Pax6 levels demonstrating that beta1-integrin is essential to maintain the lens epithelial phenotype. Furthermore, beta1-integrin null lens epithelial cells upregulate the expression of alpha-smooth muscle actin and nuclear Smad4 and downregulate Smad6 suggesting that beta1-integrin may brake TGFbeta family signaling leading to epithelial-mesenchymal transitions in the lens. In contrast, beta1-integrin null lens epithelial cells show increased E-cadherin immunoreactivity which supports the proposed role of beta1-integrins in mediating complete EMT in response to TGFbeta family members. Thus, beta1-integrin is required to maintain the lens epithelial phenotype and block inappropriate activation of some aspects of the lens fiber cell differentiation program.

Extracellular matrix and integrin signaling in lens development and cataract

During development of the vertebrate lens there are dynamic interactions between the extracellular matrix (ECM) of the lens capsule and lens cells. Disruption of the ECM causes perturbation of lens development and cataract. Similarly, changes in cell signaling can result in abnormal ECM and cataract. Integrins are key mediators of ECM signals and recent studies have documented distinct repertoires of integrin expression during lens development, and in anterior subcapsular cataract (ASC) and posterior caspsule opacification (PCO). Increasingly, studies are being directed to investigating the signaling pathways that integrins modulate and have identified Src, focal adhesion kinase (FAK) and integrin-linked kinase (ILK) as downstream kinases that mediate proliferation, differentiation and morphological changes in the lens during development and cataract formation.

Development of an accommodating intra-ocular lens--in vitro prevention of re-growth of pig and rabbit lens capsule epithelial cells

Cataract surgery is routinely performed to replace the clouded lens by a rigid polymeric intra-ocular lens unable to accommodate. By implanting a silicone gel into an intact capsular bag the accommodating properties of the natural lens can be maintained or enhanced. The implantation success of accommodating lenses is hampered by the occurrence of capsular opacification (PCO) due to lens epithelial cell (LEC) growth. In order to prevent LEC proliferation, a treatment regime using actinomycin D, cycloheximide and water was developed. The effectiveness of treatment was analyzed using an in vitro, MTT-based cell culture system and an ex vivo pig eye model in which the implanted lens-in-the-bag is cultured as a whole. LEC were exposed to treatment solutions for 5 min, then the cells were allowed to recover and to re-colonize the substratum. MTT conversion by cells was transiently inhibited by cycloheximide dissolved in water and by water alone. Exposure to actinomycin D resulted in a lasting inhibition of MTT conversion and consequently cell proliferation. These in vitro data could not be fully reproduced in the ex vivo pig eye model due to essential differences between both models. Treatment with actinomycin D containing solutions, however, resulted in a nearly complete absence of cells on the capsular wall. The pig eye model is a promising approach to further evaluate the effects of peri-surgical treatment during the accommodating intra-ocular lens implantation.