Interphotoreceptor matrix

These data suggest that one of possible mechanisms of carotenoid delivery to the neural retina may involve lipoprotein uptake from the basal side of the RPE followed by its retro-endocytosis on the apical site (Lorenzi et al., 2008). Alternatively, the endocytosed lipoprotein may be degraded in the RPE followed by secretion of certain lipophilic components from the lipoprotein at the apical site. Due to low solubility of carotenoids in aqueous solutions, it may be suggested that they are secreted already bound to a protein or that an acceptor protein is available in the interphotoreceptor matrix and/or POS. 

Adler, AJ and Edwards, RB, 2000. Human interphotoreceptor matrix contains serum albumin and retinolbinding protein. Exp Eye Res 70, 227-234. 

Figure 2. The rod phototransduction cascade and human diseases associated with mutations in GC1 and GCAP1. The main proteins of the cascade are shown in gray. GC1 and GCAP1 represent the main components of the Ca2+-regulated GC in rods and cones responsible for cGMP synthesis. IPM = Interphotoreceptor Matrix (See Colour Plate 7)...

The interstitial space between RPE and photoreceptors contains a sticky interphotoreceptor matrix consisting of glycoproteins, proteoglycans, and hyaluronic acid that helps the retina adhere to the back of the eye. Retinal adhesion is also promoted by extrusion of water from the RPE to choroid. Basolateral Cl channels and apical Na/K/2C1 transporters are particularly important for water transport out of the RPE. Because photoreceptors are not physically bound to the RPE, the retina can detach from the RPE with a strong blow to the eye, fluid build-up behind the retina (rhegmatogenous... 

Hewitt, A. T. Adler, R. In The Retinal Pigment Eptithelium and Interphotoreceptor Matrix Structure and Specialized Functions in Retina, 2nd ed. Ryan, S. J., Ed. Mosby-Year Book St. Louis, 1994, pp. 58-71. 

Figure 1 Schematic diagram of the eye in horizontal section indicating each ocular component, a, corneal epithelium b, keratocyte c, corneal endothelium d, aqueous humor e, conjunctiva /, sclera g, trabecular meshwork h, iris i, lens /, ciliary zonule and body k, vitreous /, retina m, interphotoreceptor matrix n, retinal pigment epithelium o, Bruch s membrane p, choroid q, optic nerve head r, lamina cribrosa extraocular muscles and tissues. The candidate glycosaminoglycans involved in the ocular components of each eye disease described in this chapter are as follows macular corneal dystrophy (b, c KS, CS/DS, HA), glaucoma (d HA g CS/DS, HS, HA q, r CS, HS, HA), cataract r. CS/DS, HS, HA), diabetic retinopathy (fc HA / HS), retinal detach-ment/proliferative vitreoretinopathy k, I, m, n CS/DS, HS, HA), myopia (f, p CS), thyroid eye disease (s CS, HA), pseudoexfoliation syndrome (c, d, g, h, i, j KS, CS/DS, HA). KS, keratan sulfate CS/DS, chondroitin sulfate/dermatan sulfate HS, heparan sulfate HA, hyaluronan.

Chen, Y. and Noy, N (1996) Docosahexaenoic acid modulates the interactions of the interphotoreceptor matrix retinoid-bindmg protein with 1 l-m-retinal J Biol. Ghem. 271,20,507-20,515... 

Fig. 3. Visual cycle retinoids and localion of retinoid-binding proteins in the pigment epithelium, interphotoreceptor matrix and distal retina. Key AT, ali-trans configuration M. Milller cell—a glial cell that spans the retina from the vitreous surface to the external limiting membrane. This membrane is formed by the Muller cell ciliary processes that project into the space filled with...

Although there is often close contact between the RPE processes and the rod outer segment surfaces, much of the retinol is probably delivered to the RPE via the subretinal space rather than by direct membrane-membrane transfer (but see Rando and Bangerter, 1982). It has been estimated that the subretinal space occupies 0.01-0.02 ml in human eyes and 0.03-0.10 ml in cattle eyes. It is filled with an interphotoreceptor matrix (IPM) (Feeney, 1973 Berman 1982) that contains proteoglycans (Adler and Severin, 1981 Adler and Klucznik, 1982). The ratio of protein to proteoglycans (measured as glycosaminoglycans) is greater than 50 1. Over 90% of the IPM remains with the retina when this tissue is separated from the RPE. 

Fig. 11. High-performance size-exclusion chromatography of bovine interphotoreceptor matrix on Bio-Rad TSK-400 and TSK-2S0 columns connected in series. The effluent was monitored by its absorbance at 280 nm (42so< upper trace) or the fluorescence due to its endogenous retinol (F, lower trace). Because fluorescence was monitored after absorbance, the fluorescence peak was slightly displaced with respect to the corresponding absorbance peak (arrowed). Protein standards A, thy-roglobulin (M, 669,(XX3) B, IgG (W, 150,000) C, ovalbumin (Af, 43,000) D, cyanocobalamin (M, 1,3SS). Fractions were collected, numbered, and analyzed by SDS-PAGE. (From Liou etal., 1982c.)...

Interstitial retinol-binding protein may correspond to a 7-8 S receptor for exogenous [ HJretinol assigned to bovine retina cytosol and brain by Wiggert et al. (1978), to bovine ROS by Lee and Wiggert (1982), and to the interphotoreceptor matrix by Lai et al. (1982). For further discussion, see Liou et al. (1982c). 

Fig. 17. SDS-PAGE analysis of proteins from retinitis pigmentosa-affected and normal ocular tissue. Tracks I and 2, normal retina cytosol (two loading levels) track 3, normal interphotoieceptor matrix track 4, combined retina cytosol, interphotoieceptor matrix, RPE, and choroid cytosol from RPI79 track S, choroid cytosol from RP179 track 6, normal interphotoreceptor matrix tracks 7 and 8, normal RPE cytosol (two loading levels) track s, protein standards (from the top, they correspond to W, = 210,(XX), 130,000.94.000,68,000,43.000,29,000,21,000, and 14,300, respectively). See Liou et al. (1982c) for methods.

The cause or causes of retinitis pigmentosa are yet to be found and at present a possible role for vitamin A in this condition has not been established. However, the above studies have enabled us to eliminate some possibilities and to identify others. The retinitis pigmentosa eye was normal in its ability to store retinoid, to esterify retinol, and to convert the all-trans isomer to 11-cis. A major abnormality was the absence of interstitial retinol-binding protein. It has not been established whether this is a selective loss, or whether other components of the interphotoreceptor matrix are also involved. Clearly, much more woric is needed before we arrive at an insight into the causes of chorioretinal binding diseases. 

Baranov, P., Michaelson, A., Kundu, J., Carrier, R. L., Young, M. (2014). Interphotoreceptor matrix-poly(s-caprolactone) composite scaffolds for human photoreceptor differentiation. Journal of Tissue Engineering, 5, 1—8. 

Interphotoreceptor retinoid binding protein (IRBP) occupies the space between the RPE and the rod outer segment (ROS), the interphotoreceptor matrix, and binds both llcROH and llcRCHO. Retinoids do not require IRBP for transfer between the two membranes, however, because IRBP null mice show no gross abnormalities of the visual cycle, even though they have severe retinal abnormalities. Although retinoids have very limited solubility in the aqueous phase, membranes of the RPE and ROS transfer retinoids between them in the absence of IRBP. 

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