Abstract
Interphotoreceptor retinoid-binding protein (IRBP), also known as retinol binding protein 3 (RBP3), is a lipophilic glycoprotein specifically secreted by photoreceptors. Enriched in the interphotoreceptor matrix (IPM) and recycled by the retinal pigment epithelium (RPE), IRBP is essential for the vision of all vertebrates as it facilitates the transfer of retinoids in the visual cycle. It also helps to transport lipids between the RPE and photoreceptors. The thiol-dependent antioxidant activity of IRBP maintains the delicate redox balance in the normal retina. Thus, its dysfunction is suspected to play a role in many retinal diseases. We have reviewed here the latest research on IRBP in both retinal health and disease, including the function and regulation of IRBP under retinal stress in both animal models and the human retina. We have also explored the therapeutic potential of targeting IRBP in retinal diseases. Although some technical barriers remain, it is possible that manipulating the expression of IRBP in the retina will rescue or prevent photoreceptor degeneration in many retinal diseases.
Highlights
A Brief History of IRBPInterphotoreceptor retinoid-binding protein (IRBP)Interphotoreceptor retinoid-binding protein (IRBP), known as retinol binding protein 3(RBP3), was first discovered in soluble proteins extracted from the bovine interphotoreceptor matrix (IPM), which is located between the neural retina and the retinal pigment epithelium (RPE)(Adler and Severin, 1981)
A study investigated the autoimmune condition of a girl with a rare triad of retinitis pigmentosa (RP), Coats disease and uveitis, and found that her peripheral lymphocytes had a specific anamnestic response to IRBP (Solomon et al, 1999), indicating that autoimmunity toward IRBP might play a role in the degeneration of photoreceptors
IRBP is required to maintain the normal functions of the retina, and its downregulation is a common phenomenon at the early stages of photoreceptor degeneration
Summary
A Brief History of IRBPInterphotoreceptor retinoid-binding protein (IRBP), known as retinol binding protein 3(RBP3), was first discovered in soluble proteins extracted from the bovine interphotoreceptor matrix (IPM), which is located between the neural retina and the retinal pigment epithelium (RPE)(Adler and Severin, 1981). IRBP can traffick retinoid, a class of Vitamin A derivatives that includes retinol and retinal, between photoreceptors and RPE cells (Kusakabe et al, 2009). Applying IRBP protein to the culture medium of rod photoreceptors reduced the level of all-trans-retinal and retinol in outer segments, preventing the formation of light-induced lipofuscin precursor (Chen et al, 2017).
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