Elucidation of Arvcf-dependent mechanisms required for lens function

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Abstract: The function of the lens requires the maintenance of its transparency and refractive properties throughout its lifespan but those mechanisms responsible are not well understood. While important cellular functions and pathways such as cell adhesion or GTPase signaling have long been hypothesized to play a role in preserving these functions the removal of genes associated with these cellular functions often severely disrupt the lens making the contribution of them challenging to interpret. We have overcome this barrier with the discovery that mice lacking the Arvcf gene develop bilateral, age- dependent cortical cataracts. Arvcf is a member of the p120-catenin subfamily of catenins that bind to a specific intracellular domain of cadherins and regulate Rho-GTPases and junctional protein dynamics and stability. We have additionally found that Arvcf is highly enriched within lens fiber cell junctional structures and is required for the recruitment of several proteins to the cadherin complex, normal lens refraction, preservation of fiber cell morphology, organization of the F-actin architecture, and the normal biomechanical properties of the lens. We propose three aims to address the central question: What molecular functions lie downstream of Arvcf to maintain lens transparency, refraction, cell morphology, and biomechanical properties? In the first aim we will determine which of these properties, precede, follow, or are simultaneous with cadherin complex and adherens junction instability in Arvcf deficient lenses. We will test the hypothesis that the initiating event is the reduction of cadherin complex proteins in fiber cell membranes through a combination of biophysical property measurements of whole lenses and fluorescent/electron microscopy of lens fiber cells. Our early investigations also found that Aquaporin 0 (AQP0) depends on Arvcf to associate with the cadherin complex and novel quantitative analysis of super-resolution microscopy images of interlocking protrusions demonstrated a significant reduction of AQP0 from the distal tips of these structures. Therefore, in the second Aim of this proposal we plan to test the hypothesis that Arvcf recruits AQP0 to the tips of interlocking protrusions to facilitate cell adhesion and water transport by determining whether AQP0 and the Arvcf/N-cadherin protein complex function together in adhesion and water transport. In the third aim we will test the hypothesis that altered GTPase signaling downstream of Arvcf contributes to lens function. The GTPase regulation domain of Arvcf and candidate GTPase regulatory proteins will be genetically altered to determine their contribution to Arvcf function, lens fiber cell biology, and lens transparency. Together, these project aims will identify functional mechanisms of a previously untested and important protein required for lens transparency and lens fiber cell function. Furthermore, they will elucidate mechanisms underlying the etiology of age-dependent cortical cataracts. Because of the association of murine Arvcf with cortical cataracts and the human ARVCF gene with genetic disorders, neurological diseases, and cancer, the advances made on this proposal will also have a broad impact.