Research on retinitis pigmentosa (RP) and age related macular degeneration (AMD) has significantly advanced knowledge into their genetic causes. Although such findings triggered exploration of numerous therapeutic paradigms, we still come short in our understanding of the cause of the late onset of visual loss although the mutant protein is present from birth. It is often proposed that these cells survive due to effects f neuroprotective factors that significantly prolong the life of the sick cell. However, it is not clar as to why the patient starts to encounter visual difficulties all of a sudden? Here we propose an additional contributing hypothesis for the delayed onset of visual loss based upon two related findings. The first is the identification of CFH and fibulin 5 as sulfated proteins. Besides being present in drusen, mutations in both proteins associate with AMD. Our second is that we observe modulations in levels and types of tyrosine-sulfated proteins during retinal degeneration in two well-studied animal models of RP, the VPP and the rds+/- mouse models. Since sulfation is a post-translational modification that occurs on secreted and membrane-associated extracellular matrix (ECM) proteins, we hypothesize that the slow death of cells will lead to gradual deterioration of ECM. However, when a critical number of ECM-maintaining cells are lost, a breaking point is reached, suddenly accelerating the degenerative process. We propose two specific aims to address our hypothesis.
In Aim 1, we are generating retina/RPE-specific conditional knockout mice for both of the enzymes responsible for protein sulfation, protein tyrosyl sulfotransferases 1 and 2. The double knockout (DKO) mice will be characterized functionally, structurally and biochemically from birth to 2 years of age for effects of lack of sulfation. To determine if the lack of sulfation of ECM proteins exacerbate the AMD phenotype, we plan to backcross these mice into an AMD transgenic model (cfhY402H). To address the effect of lack of sulfation of ECM proteins on the RP phenotype, we plan to backcross the DKO mice to two well-studied RP models representing the P23H mutation in the rhodopsin gene (VPP) and the haploinsufficiency of the retinal degeneration slow (rds+/-) protein.
In Aim 2, we will evaluate the role of sulfation in the function of CFH and fibulin 5. The identified sulfated tyrosine(s) will be mutated to phenylalanines and in vitro analyses of 1) ability of unsulfated CFH to bind CRP (C-reactive protein), 2) its ability to self-dimerize and 3) its interactions with polyanions. For fibulin 5, we will test the ability of the unsulfated protein to interact with interins and ECM super oxide dismutase (SOD) 3. Subsequently, we will generate and characterize retina/RPE-specific conditional knock-in mice expressing either sulfation-deficient CFH or fibulin 5. Accomplishment of the proposed studies will open a new window on the role of ECM in degenerative process and direct attention to development of new therapeutic approaches focusing on protection of the ECM to prolong vision in patients and widen the window for interventions. This is of significance to over 10 million US Citizens of all ages and races that suffer from RP and AMD.
According to the Foundation Fighting Blindness, over 10 million Americans suffer from age related macular degeneration (AMD) and retinitis pigmentosa (RP). This proposal focuses on understanding why these diseases manifest later in life although the genetic mutations are expressed much earlier. The overriding hypothesis is that the deterioration of the extracellular matrix (ECM) during the progression of the degenerative diseases exacerbates vision loss. The proposed studies will investigate changes in ECM during the degenerative process.
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|Kelley, Ryan A; Al-Ubaidi, Muayyad R; Naash, Muna I (2015) Retbindin is an extracellular riboflavin-binding protein found at the photoreceptor/retinal pigment epithelium interface. J Biol Chem 290:5041-52|
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