Article

High density lipoprotein mediated lipid efflux from retinal pigment epithelial cells in culture.

Cardiovascular Research Institute, University of California, San Francisco, 94143, USA.
British Journal of Ophthalmology (Impact Factor: 2.81). 06/2006; 90(5):616-20. DOI: 10.1136/bjo.2005.085076
Source: PubMed

ABSTRACT [corrected] The transport of radiolabelled photoreceptor outer segments (POS) lipids was investigated by cultured retinal pigment epithelial cells (RPE). Phagocytosis of POS by the RPE is essential to maintain the health and function of the photoreceptors in vivo. POS are phagocytised at the apical cell surface of RPE cells. Phagocytised POS lipids may be either recycled to the photoreceptors for reincorporation into new POS or they may be transported to the basolateral surface for efflux into the circulation.
The authors have demonstrated that high density lipoprotein (HDL) stimulates efflux of radiolabelled lipids, of POS origin, from the basal surface of RPE cells in culture. Effluxed lipids bind preferentially to HDL species of low and high molecular weight. Effluxed radiolabelled phosphotidyl choline was the major phospholipid bound to HDL, with lesser amounts of phosphatidyl ethanolamine, phosphatidyl inosotol. Effluxed radiolabelled triglycerides, cholesterol, and cholesterol esters also bound to HDL. Lipid free apolipoprotein A-I (apoA-I) and apoA-I containing vesicles also stimulate lipid efflux.
The findings suggest a role for HDL and apoA-I in regulating lipid and cholesterol transport from RPE cells that may influence the pathological lipid accumulation associated with age related macular degeneration.

0 Followers
 · 
80 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: More details about the distribution of esterified and unesterified cholesterol (EC, UC), abundant druse components, would inform models of druse biogenesis and new technologies for ocular imaging. From donors with grossly normal maculas (n=10, 66-86years), whose eyes were preserved in paraformaldehyde within 6h of death, extra-macular drusen encased with retinal pigment epithelium (RPE) were isolated manually. Cryosections of pelleted drusen, stained with filipin for UC and EC, were used to investigate filipin staining patterns within single drusen (n=193) and to quantify fluorescence (n=146). From lipid extracts of other drusen/RPE and RPE samples, total cholesterol (TC) and UC were determined by enzymatic fluorimetry. Drusen contained cores, basally located regions that were intensely bright when stained for UC or deeply dark when stained for EC; many were surrounded by concentric lamellae. Within the same cores, the EC-poor regions were significantly smaller (13.0mum) than UC-rich regions (17.1mum). Drusen with highly fluorescent EC-rich shells lacked UC-rich shells. Small spots representing lakes were visible only in drusen stained for EC. Some drusen had small, refractive spherical inclusions lacking both UC and EC. Of drusen examined, 32% had a UC-rich core, 35% had an EC-poor core, 31% had an EC-rich shell, 25% had EC-rich lakes, and 4-5% had UC-, EC-poor inclusions. Shells and cores occurred in significantly non-overlapping druse populations. The percentage of TC that was esterified ranged from 32-66% for drusen/RPE and 5-21% for RPE. The disposition of cholesterol in cores may reflect the activity of invading cellular process. The greater size of UC-rich cores relative to EC-poor cores may reflect a declining gradient of enzymatic activity with increased radial distance from the putative invaders. The relative sizes of sub-domains defined by cholesterol composition are compared to sub-domains detected in drusen by in vivo imaging methods.
    Experimental Eye Research 09/2007; 85(2):192-201. DOI:10.1016/j.exer.2007.04.002 · 3.02 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The retinal pigment epithelium (RPE) maintains retinal function as the metabolic gatekeeper between photoreceptors (PRs) and the choriocapillaries. The RPE and Bruch's membrane (BM) suffer cumulative damage over lifetime, which is thought to induce age-related macular degeneration (AMD) in susceptible individuals. Unlike palliative pharmacologic treatments, replacement of the RPE has a curative potential for AMD. This article reviews mechanisms leading to RPE dysfunction in aging and AMD, laboratory studies on RPE transplantation, and surgical techniques used in AMD patients. Future strategies using ex vivo steps prior to transplantation, BM prosthetics, and stem cell applications are discussed. The functional peculiarity of the macular region, epigenetic phenomena leading to an age-related shift in protein expression, along with the accumulation of lipofuscin may affect the metabolism in the central RPE. Thickening of BM with age decreases its hydraulic conductivity. Drusen are deposits of extracellular material and formed in part by activation of the alternative complement pathway in individuals carrying a mutant allele of complement factor H. AMD likely represents an umbrella term for a disease entity with multifactorial etiology and manifestations. Presently, a slow progressing (dry) non-neovascular atrophic form and a rapidly blinding neovascular (wet) form are discerned. No therapy is currently available for the former, while RPE transplantation and promising (albeit non-causal) anti-angiogenic therapies are available for the latter. The potential of RPE transplantation was demonstrated in animal models. Rejection of allogeneic homologous transplants in patients focused further studies on autologous sources. In vitro studies elucidated cell adhesion and wound healing mechanisms on aged human BM. Currently, autologous RPE, harvested from the midperiphery, is being transplanted as a cell suspension or a patch of RPE and choroid in AMD patients. These techniques have been evaluated from several groups. Autologous RPE transplants may have the disadvantage of carrying the same genetic information that may have led to AMD manifestation. An intermittent culturing step would allow for in vitro therapy of the RPE, its rejuvenation and prosthesis of BM to improve the success RPE transplants. Recent advances in stem cell biology when combined with lessons learned from studies of RPE transplantation are intriguing future therapeutic modalities for AMD patients.
    Progress in Retinal and Eye Research 10/2007; 26(5):516-54. DOI:10.1016/j.preteyeres.2007.02.002 · 9.90 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Il existe des liens indiscutables entre des anomalies qualitatives et quantitatives des lipoprotéines, qu’elles soient primaires ou secondaires (en particulier dans l’insuffisance rénale), la genèse et le développement des complications microvasculaires chez les diabétiques de type 1 et de type 2. Leur place mérite d’être précisée dans l’histoire naturelle de la micro-angiopathie (dès la phase initiale ?). L’interprétation des études d’intervention thérapeutique par statines et fibrates restent encore controversée, ne permettant pas de séparer leurs effets sur les lipoprotéines per se des effets pleïotropes. Le faisceau d’argument existant légitime néanmoins une prise en charge agressive des dyslipidémies chez le patient diabétique, tant sur le plan macro- que microvasculaire.
    Médecine des Maladies Métaboliques 01/2008; 2(1). DOI:10.1016/S1957-2557(08)70005-1

Preview

Download
0 Downloads
Available from