The Oxysterol 27-Hydroxycholesterol Increases B-Amyloid and Oxidative

The Oxysterol 27-Hydroxycholesterol Increases B-Amyloid and Oxidative

Dasari et al. BMC Ophthalmology 2010, 10:22 http://www.biomedcentral.com/1471-2415/10/22 RESEARCH ARTICLE Open Access The oxysterol 27-hydroxycholesterol increases b-amyloid and oxidative stress in retinal pigment epithelial cells Bhanu Dasari1, Jaya RP Prasanthi1, Gurdeep Marwarha1, Brij B Singh2, Othman Ghribi1* Abstract Background: Alzheimer’s disease (AD) and age-related macular degeneration (AMD) share several pathological features including b-amyloid (Ab) peptide accumulation, oxidative damage, and cell death. The causes of AD and AMD are not known but several studies suggest disturbances in cholesterol metabolism as a culprit of these diseases. We have recently shown that the cholesterol oxidation metabolite 27-hydroxycholesterol (27-OHC) causes AD-like pathology in human neuroblastoma SH-SY5Y cells and in organotypic hippocampal slices. However, the extent to which and the mechanisms by which 27-OHC may also cause pathological hallmarks related to AMD are ill-defined. In this study, the effects of 27-OHC on AMD-related pathology were determined in ARPE-19 cells. These cells have structural and functional properties relevant to retinal pigmented epithelial cells, a target in the course of AMD. Methods: ARPE-19 cells were treated with 0, 10 or 25 μM 27-OHC for 24 hours. Levels of Ab peptide, mitochondrial and endoplasmic reticulum (ER) stress markers, Ca2+ homeostasis, glutathione depletion, reactive oxygen species (ROS) generation, inflammation and cell death were assessed using ELISA, Western blot, immunocytochemistry, and specific assays. Results: 27-OHC dose-dependently increased Ab peptide production, increased levels of ER stress specific markers caspase 12 and gadd153 (also called CHOP), reduced mitochondrial membrane potential, triggered Ca2+ dyshomeostasis, increased levels of the nuclear factor B (NFB) and heme-oxygenase 1 (HO-1), two proteins activated by oxidative stress. Additionally, 27-OHC caused glutathione depletion, ROS generation, inflammation and apoptotic-mediated cell death. Conclusions: The cholesterol metabolite 27-OHC is toxic to RPE cells. The deleterious effects of this oxysterol ranged from Ab accumulation to oxidative cell damage. Our results suggest that high levels of 27-OHC may represent a common pathogenic factor for both AMD and AD. Background are composed of acute phase proteins, complement com- Age-related macular degeneration (AMD) is the most ponents, apolipoproteins, lipids, polysaccharides along common cause of irreversible vision loss in elderly popula- with various other molecules [3-5]. Intriguingly, AMD has tion [1]. This disease is characterized by a progressive cell many pathological features that are common to Alzhei- damage that targets the choroid, retinal pigment epithe- mer’s disease (AD), including the deposition of b-amyloid lium (RPE) and retina. Accumulation of drusen in the (Ab) peptide [6]. Ab is suggested to play a key role in AD extracellular compartment between the choroid and the pathogenesis by triggering oxidative stress, inflammation RPE is an early event in the course of AMD [2]. Drusen and cell death [7]. Ab accumulation has also been demon- strated to be associated with drusen in eyes from AMD * Correspondence: [email protected] patients [8-10], mice models for AMD [11] and in RPE 1Department of Pharmacology, Physiology and Therapeutics, University of cells [12]. Recent studies from our laboratory have shown North Dakota School of Medicine and Health Sciences, 501 North Columbia that the oxysterol 27-hydroxycholesterol (27-OHC) causes Road, Grand Forks, North Dakota, 58202, USA Full list of author information is available at the end of the article AD-like pathology by increasing Ab production and © 2010 Dasari et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dasari et al. BMC Ophthalmology 2010, 10:22 Page 2 of 12 http://www.biomedcentral.com/1471-2415/10/22 triggers apoptotic cell death in human neuroblastoma SH- Methods SY5Y cells [13,14] and in organotypic slices from rabbit Cells and Treatments hippocampus [15,16]. However, the extent to which and ARPE-19 cells (American Type Culture Collection, the mechanisms by which 27-OHC may also cause Ab Manassas, VA) were grown in DMEM/F12 Glutamax accumulation and cell death in in vitro model that is rele- media with 10% FBS and standard antibiotics (100 IU/ vant to retinal pigment epithelial cells and AMD studies mL penicillin, and 100 μg/mL streptomycin, Sigma, are lacking. St. Louis, MO) in a 5% CO2, 37°C incubator. Cells were Similar to AD, the causes of AMD are not fully under- seeded in 75-cm2 flasks, 6-well plates or 96-well plates. stood. Several lines of evidence suggest that genetic pre- All cell culture reagents were obtained from Invitrogen, disposition and environmental as well as dietary factors Carlsbad, CA. 27-OHC was obtained from Medical Iso- may contribute to the pathogenesis of these two pro- topes Inc, Pelham, NH. Stock solutions of 27-OHC were gressive degenerative disorders. Recent epidemiological prepared in 100% ethanol and stored at -70°C. Working studies have demonstrated that high plasma cholesterol concentrations were prepared by dissolving 27-OHC levels are associated with a high risk for AD [17]. Like- stock solution in media. When cells reached confluency, wise, high intake of cholesterol and saturated fat is asso- they were incubated with 0, 10 or 25 μM27-OHCin ciated with increased AMD [18]. Cholesterol (free and culture media for 24 hrs, time by which 27-OHC esterified) is highly distributed in the human drusen increases Ab levels in SH-SY5Y cells [13]. Experiments [5,19,20]. The source of the cholesterol that accumulates were carried out in triplicate. The concentrations of the in the retina is suggested to derive from both local cells 27-OHCusedinthepresentstudyarethesameas and plasma origins [4,21-23]. Currently, the mechanisms thosewedemonstratedtocauseAD-likepathologyin by which cholesterol may increase the incidence of AD human neuroblastoma cells and in organotypic slices or AMD are not clear. Several lines of evidence suggest [13,15]. Joffre and colleagues have used concentrations that oxidized cholesterol metabolites (oxysterols) may be up to 50 μM of 7-ketocholesterol, 24-hydroxycholes- the link by which cholesterol contributes to the patho- terol, and 25-hydroxycholesterol [30]. genesis of AD [24]. The oxysterol pathway has also been proposed as a unifying hypothesis for the cause of AMD Quantification of Ab by Enzyme-Linked Immunosorbent [25-27]. Assay (ELISA) Oxysterols are oxidation products of cholesterol that Cells were treated with 27-OHC for 24 hrs. Spent media result from either autoxidation or enzymatic oxidation. was collected, protease and phosphatase inhibitors cock- While 7-ketocholesterol is the major oxysterol generated tail (Thermo Scientific, Rockford, IL) was added. The by autoxidation on the B hydrocarbon ring of choles- media was centrifuged at 16,000 × g for 5 min at 4°C. terol, 24-hydroxycholesterol, 25-hydroxycholesterol and 100 μL of supernatant was used for Ab1-42 and Ab1-40 27-hydroxycholesterol are major oxysterols produced by quantification by colorimetric sandwich ELISA (Cov- enzymatic oxidation on the lateral chain of the choles- ance, Denver, PA) according to the manufacturer’s terol structure. Oxysterols have diverse physiological instructions and as we have previously described [13]. and biochemical functions ranging from regulation of Ab1-42 and Ab1-40 levels were expressed in pg/mL. cholesterol homeostasis to regulation of nuclear recep- tors [26-28]. However, abnormal oxysterol levels can Western Blot Analysis cause oxidative stress, inflammation and apoptotic cell After 24 hrs treatment with 27-OHC, cells were har- death [25,28-32]. vested on ice and homogenized in a mammalian protein In this study, we determined in the human RPE cell extraction reagent (M-PER, Thermo Scientific, Rockford, line ARPE-19 the effects of 27-OHC on pathological IL) supplemented with protease and phosphatase inhibi- hallmarks that are common to both AMD and AD. We tors. Nuclear extracts for NFB were prepared by using have specifically determined levels of Ab and b-site of NE-PER extraction kit (Thermo Scientific, Rockford, IL). APP cleaving enzyme (BACE-1), which initiates Ab pro- Protein concentrations were determined with bicincho- duction, caspase 12 and gadd153 as markers of ER ninic acid (BCA) protein assay reagent. Proteins (10 μg) stress, mitochondrial membrane potential as a marker of were separated on SDS-PAGE gels followed by transfer mitochondrial stress, the nuclear factor B(NFB) and onto a polyvinylidene difluoride (PVDF) membrane heme-oxygenase 1 (HO-1) two proteins activated by oxi- (Biorad, Herculus, CA) and incubation with antibodies dative stress, ROS generation and glutathione depletion to BACE-1 (Mouse, 1:1000, Millipore, Bedford, MD), and TNF-a as marker of inflammation. Additionally, caspase 12 (Rat, 1:1000, Abcam, Cambridge, MA), calcium homeostasis, cytotoxicity and cell death assays gadd153 (Mouse, 1:1000, Abcam, Cambridge, MA), and were also carried out. HO-1(Mouse,1:500,AssayDesigns,AnnArbor,MI). Dasari et al. BMC Ophthalmology 2010, 10:22 Page 3 of 12 http://www.biomedcentral.com/1471-2415/10/22 b-actin (Mouse, 1:5000, Santa Cruz Biotechnology, Santa fluorescence was monitored at 510 nm with an Orka Cruz,CA)wasusedasagelloadingcontrol.5μgof imaging camera (Hamamatsu). The images of multiple nuclear extracts were used for NFB(NFBp65; cells collected at each excitation wavelength were pro- Mouse, 1:100, Santa Cruz Biotechnology, Santa Cruz, cessed using the Ca2+ imaging, PCI software (Compix CA) and lamin (Rabbit, 1:500, Cell Signaling Technol- Inc., Cranbery, PA) to provide ratios of Fura-2 fluores- ogy, Inc. Danvers, MA) was used as loading control. For cence from excitation at 340 nm to that of excitation at antibodies of mouse origin, goat anti-mouse secondary 380 nm (F340/F380).

View Full Text

Details

  • File Type
    pdf
  • Upload Time
    -
  • Content Languages
    English
  • Upload User
    Anonymous/Not logged-in
  • File Pages
    12 Page
  • File Size
    -

Download

Channel Download Status
Express Download Enable

Copyright

We respect the copyrights and intellectual property rights of all users. All uploaded documents are either original works of the uploader or authorized works of the rightful owners.

  • Not to be reproduced or distributed without explicit permission.
  • Not used for commercial purposes outside of approved use cases.
  • Not used to infringe on the rights of the original creators.
  • If you believe any content infringes your copyright, please contact us immediately.

Support

For help with questions, suggestions, or problems, please contact us