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Rakshit T, Senapati S, Parmar VM, Sahu B, Maeda A, Park PSH. Adaptations in rod outer segment disc membranes in response to environmental lighting conditions. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017. [PMID: 28645515 DOI: 10.1016/j.bbamcr.2017.06.013] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The light-sensing rod photoreceptor cell exhibits several adaptations in response to the lighting environment. While adaptations to short-term changes in lighting conditions have been examined in depth, adaptations to long-term changes in lighting conditions are less understood. Atomic force microscopy was used to characterize the structure of rod outer segment disc membranes, the site of photon absorption by the pigment rhodopsin, to better understand how photoreceptor cells respond to long-term lighting changes. Structural properties of the disc membrane changed in response to housing mice in constant dark or light conditions and these adaptive changes required output from the phototransduction cascade initiated by rhodopsin. Among these were changes in the packing density of rhodopsin in the membrane, which was independent of rhodopsin synthesis and specifically affected scotopic visual function as assessed by electroretinography. Studies here support the concept of photostasis, which maintains optimal photoreceptor cell function with implications in retinal degenerations.
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Affiliation(s)
- Tatini Rakshit
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Subhadip Senapati
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Vipul M Parmar
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Bhubanananda Sahu
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Akiko Maeda
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Paul S-H Park
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA.
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Son SH, Goo YH, Choi M, Saha PK, Oka K, Chan LCB, Paul A. Enhanced atheroprotection and lesion remodelling by targeting the foam cell and increasing plasma cholesterol acceptors. Cardiovasc Res 2015; 109:294-304. [PMID: 26487692 DOI: 10.1093/cvr/cvv241] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Accepted: 10/06/2015] [Indexed: 11/13/2022] Open
Abstract
AIMS Atherosclerosis development can be ameliorated by promoting reverse cholesterol transport (RCT) from arteries. The process involves cholesterol efflux from foam cells to extracellular acceptors such as apolipoprotein A-I (apoA-I) and high-density lipoprotein (HDL) that mediate transport to the liver. Perilipin-2 (PLIN2) is a lipid droplet (LD)-associated protein that in macrophages facilitates cholesterol storage and prevents efflux. We hypothesized that atheroprotection would be enhanced by concurrently targeting PLIN2 to increase the efflux capacity of foam cells and increasing plasma apoA-I and HDL. METHODS AND RESULTS PLIN2-knockout and wild-type mice lacking apolipoprotein E (PLIN2(-/-)/apoE(-/-) and PLIN2(+/+)/apoE(-/-)) were treated with a helper-dependent adenoviral vector encoding human apoA-I (HDAd-AI) or with control empty vector. Treatment with HDAd-AI increased hepatic apoA-I production, plasma apoA-I and HDL-cholesterol (HDL-C), and apoA-I deposition in lesions to a similar extent in PLIN2(-/-)/apoE(-/-) and PLIN2(+/+)/apoE(-/-) mice. However, atherosclerosis development at the aortic sinus was considerably lower in HDAd-AI-treated PLIN2(-/-)/apoE(-/-) mice. A more stable lesion phenotype, with increased collagen content, was primarily associated to treatment with HDAd-AI, but was enhanced under PLIN2 deficiency. PLIN2 deficiency and apoA-I cumulatively reduced LDs and cholesterol ester content in cultured macrophages. Neutral lipid in atheroma was significantly reduced in HDAd-AI-treated PLIN2(-/-)/apoE(-/-) mice, and RCT from macrophages to feces was enhanced in PLIN2(-/-) macrophages. CONCLUSION These studies demonstrate a mutually beneficial relationship between PLIN2 deficiency and elevated apoA-I/HDL-C in preventing atherosclerosis development. The data support that targeting foam cell components to mobilize cholesterol may be a promising strategy to enhance the atheroprotection of plasma cholesterol acceptors.
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Affiliation(s)
- Se-Hee Son
- Center for Cardiovascular Sciences, Albany Medical College, 47 New Scotland Avenue, MC-8, Albany, NY 12208, USA
| | - Young-Hwa Goo
- Center for Cardiovascular Sciences, Albany Medical College, 47 New Scotland Avenue, MC-8, Albany, NY 12208, USA
| | - Mihyun Choi
- Center for Cardiovascular Sciences, Albany Medical College, 47 New Scotland Avenue, MC-8, Albany, NY 12208, USA
| | - Pradip K Saha
- Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX, USA
| | - Kazuhiro Oka
- Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX, USA
| | - Lawrence C B Chan
- Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX, USA
| | - Antoni Paul
- Center for Cardiovascular Sciences, Albany Medical College, 47 New Scotland Avenue, MC-8, Albany, NY 12208, USA
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Masihzadeh O, Lei TC, Domingue SR, Kahook MY, Bartels RA, Ammar DA. Third harmonic generation microscopy of a mouse retina. Mol Vis 2015; 21:538-47. [PMID: 25999681 PMCID: PMC4440497] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Accepted: 04/30/2015] [Indexed: 12/02/2022] Open
Abstract
PURPOSE To demonstrate lipid-specific imaging of the retina through the use of third harmonic generation (THG), a multiphoton microscopic technique in which tissue contrast is generated from optical inhomogeneities. METHODS A custom fiber laser and multiphoton microscope was constructed and optimized for simultaneous two-photon autofluorescence (TPAF) and THG retinal imaging. Imaging was performed using fixed-frozen sections of mouse eyes without the use of exogenous fluorescent dyes. In parallel experiments, a fluorescent nuclear stain was used to verify the location of the retinal cell nuclei. RESULTS Simultaneous THG and TPAF images revealed all retinal layers with subcellular resolution. In BALB/c strains, the THG signal stems from the lipidic organelles of the cellular and nuclear membranes. In the C57BL/6 strain, the THG signal from the RPE cells originates from the pigmented granules. CONCLUSIONS THG microscopy can be used to image structures of the mouse retina using contrast inherent to the tissue and without the use of a fluorescent dye or exogenously expressed recombinant protein.
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Affiliation(s)
- Omid Masihzadeh
- Department of Ophthalmology, University of Colorado Denver, Aurora, CO
| | - Tim C. Lei
- Department of Electrical Engineering, University of Colorado Denver, Denver, CO
| | - Scott R. Domingue
- Department of Electrical Engineering, Colorado State University, Fort Collins, CO
| | - Malik Y. Kahook
- Department of Ophthalmology, University of Colorado Denver, Aurora, CO
| | - Randy A. Bartels
- Department of Electrical Engineering, Colorado State University, Fort Collins, CO
| | - David A. Ammar
- Department of Ophthalmology, University of Colorado Denver, Aurora, CO
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Kevany BM, Zhang N, Jastrzebska B, Palczewski K. Animals deficient in C2Orf71, an autosomal recessive retinitis pigmentosa-associated locus, develop severe early-onset retinal degeneration. Hum Mol Genet 2015; 24:2627-40. [PMID: 25616964 DOI: 10.1093/hmg/ddv025] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 01/21/2015] [Indexed: 02/01/2023] Open
Abstract
Genetic mapping was recently used to identify the underlying cause for a previously uncharacterized cohort of autosomal recessive retinitis pigmentosa cases. Genetic mapping of affected individuals resulted in the identification of an uncharacterized gene, C2Orf71, as the causative locus. However, initial homology searches failed to reveal similarities to any previously characterized protein or domain. To address this issue, we characterized the mouse homolog, BC027072. Immunohistochemistry with a custom polyclonal antibody showed staining localized to the inner segments (IS) of photoreceptor cells, as well as the outer segments (OS) of cone cells. A knockout mouse line (BC(-/-)) was generated and demonstrated that loss of this gene results in a severe, early-onset retinal degeneration. Histology and electron microscopy (EM) revealed disorganized OS as early as 3 weeks with complete loss by 24 weeks of age. EM micrographs displayed packets of cellular material containing OS discs or IS organelles in the OS region and abnormal retinal pigmented epithelium cells. Analyses of retinoids and rhodopsin levels showed <20% in BC(-/-) versus wild-type mice early in development. Electroretinograms demonstrated that affected mice were virtually non-responsive to light by 8 weeks of age. Lastly, RNAseq analysis of ocular gene expression in BC(-/-) mice revealed clues to the causes of the progressive retinal degenerations. Although its function remains unknown, this protein appears essential for normal OS development/maintenance and vision in humans and mice. RNAseq data are available in the GEO database under accession: GSE63810.
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Affiliation(s)
- Brian M Kevany
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Ning Zhang
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Beata Jastrzebska
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Krzysztof Palczewski
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA
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Palczewski K. Chemistry and biology of the initial steps in vision: the Friedenwald lecture. Invest Ophthalmol Vis Sci 2014; 55:6651-72. [PMID: 25338686 DOI: 10.1167/iovs.14-15502] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Visual transduction is the process in the eye whereby absorption of light in the retina is translated into electrical signals that ultimately reach the brain. The first challenge presented by visual transduction is to understand its molecular basis. We know that maintenance of vision is a continuous process requiring the activation and subsequent restoration of a vitamin A-derived chromophore through a series of chemical reactions catalyzed by enzymes in the retina and retinal pigment epithelium (RPE). Diverse biochemical approaches that identified key proteins and reactions were essential to achieve a mechanistic understanding of these visual processes. The three-dimensional arrangements of these enzymes' polypeptide chains provide invaluable insights into their mechanisms of action. A wealth of information has already been obtained by solving high-resolution crystal structures of both rhodopsin and the retinoid isomerase from pigment RPE (RPE65). Rhodopsin, which is activated by photoisomerization of its 11-cis-retinylidene chromophore, is a prototypical member of a large family of membrane-bound proteins called G protein-coupled receptors (GPCRs). RPE65 is a retinoid isomerase critical for regeneration of the chromophore. Electron microscopy (EM) and atomic force microscopy have provided insights into how certain proteins are assembled to form much larger structures such as rod photoreceptor cell outer segment membranes. A second challenge of visual transduction is to use this knowledge to devise therapeutic approaches that can prevent or reverse conditions leading to blindness. Imaging modalities like optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) applied to appropriate animal models as well as human retinal imaging have been employed to characterize blinding diseases, monitor their progression, and evaluate the success of therapeutic agents. Lately two-photon (2-PO) imaging, together with biochemical assays, are revealing functional aspects of vision at a new molecular level. These multidisciplinary approaches combined with suitable animal models and inbred mutant species can be especially helpful in translating provocative cell and tissue culture findings into therapeutic options for further development in animals and eventually in humans. A host of different approaches and techniques is required for substantial progress in understanding fundamental properties of the visual system.
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Affiliation(s)
- Krzysztof Palczewski
- Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, United States
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Submembrane assembly and renewal of rod photoreceptor cGMP-gated channel: insight into the actin-dependent process of outer segment morphogenesis. J Neurosci 2014; 34:8164-74. [PMID: 24920621 DOI: 10.1523/jneurosci.1282-14.2014] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The photoreceptor outer segment (OS) is comprised of two compartments: plasma membrane (PM) and disk membranes. It is unknown how the PM renewal is coordinated with that of the disk membranes. Here we visualized the localization and trafficking process of rod cyclic nucleotide-gated channel α-subunit (CNGA1), a PM component essential for phototransduction. The localization was visualized by fusing CNGA1 to a fluorescent protein Dendra2 and expressing in Xenopus laevis rod photoreceptors. Dendra2 allowed us to label CNGA1 in a spatiotemporal manner and therefore discriminate between old and newly trafficked CNGA1-Dendra2 in the OS PM. Newly synthesized CNGA1 was preferentially trafficked to the basal region of the lateral OS PM where newly formed and matured disks are also added. Unique trafficking pattern and diffusion barrier excluded CNGA1 from the PM domains, which are the proposed site of disk membrane maturation. Such distinct compartmentalization allows the confinement of cyclic nucleotide-gated channel in the PM, while preventing the disk membrane incorporation. Cytochalasin D and latrunculin A treatments, which are known to disrupt F-actin-dependent disk membrane morphogenesis, prevented the entrance of newly synthesized CNGA1 to the OS PM, but did not prevent the entrance of rhodopsin and peripherin/rds to the membrane evaginations believed to be disk membrane precursors. Uptake of rhodopsin and peripherin/rds coincided with the overgrowth of the evaginations at the base of the OS. Thus F-actin is essential for the trafficking of CNGA1 to the ciliary PM, and coordinates the formations of disk membrane rim region and OS PM.
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Carr RM, Peralta G, Yin X, Ahima RS. Absence of perilipin 2 prevents hepatic steatosis, glucose intolerance and ceramide accumulation in alcohol-fed mice. PLoS One 2014; 9:e97118. [PMID: 24831094 PMCID: PMC4022498 DOI: 10.1371/journal.pone.0097118] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 04/14/2014] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Perilipin 2 (Plin2) is a lipid droplet protein that has roles in both lipid and glucose homeostasis. An increase in Plin2 in liver is associated with the development of steatosis, glucose intolerance, and ceramide accumulation in alcoholic liver disease. We investigated the role of Plin2 on energy balance and glucose and lipid homeostasis in wildtype and Plin2 knockout (Plin2KO) mice chronically fed a Lieber-DeCarli liquid ethanol or control diet for six weeks. METHODS We performed in vivo measurements of energy intake and expenditure; body composition; and glucose tolerance. After sacrifice, liver was dissected for histology and lipid analysis. RESULTS We found that neither genotype nor diet had a significant effect on final weight, body composition, or energy intake between WT and Plin2KO mice fed alcohol or control diets. Additionally, alcohol feeding did not affect oxygen consumption or carbon dioxide production in Plin2KO mice. We performed glucose tolerance testing and observed that alcohol feeding failed to impair glucose tolerance in Plin2KO mice. Most notably, absence of Plin2 prevented hepatic steatosis and ceramide accumulation in alcohol-fed mice. These changes were related to downregulation of genes involved in lipogenesis and triglyceride synthesis. CONCLUSIONS Plin2KO mice chronically fed alcohol are protected from hepatic steatosis, glucose intolerance, and hepatic ceramide accumulation, suggesting a critical pathogenic role of Plin2 in experimental alcoholic liver disease.
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Affiliation(s)
- Rotonya M. Carr
- University of Pennsylvania, Perelman School of Medicine, Department of Medicine, Gastroenterology Division, Philadelphia, Pennsylvania, United States of America
- * E-mail:
| | - Giselle Peralta
- University of Pennsylvania, Perelman School of Medicine, Institute for Diabetes, Obesity and Metabolism, Philadelphia, Pennsylvania, United States of America
| | - Xiaoyan Yin
- University of Pennsylvania, Perelman School of Medicine, Institute for Diabetes, Obesity and Metabolism, Philadelphia, Pennsylvania, United States of America
| | - Rexford S. Ahima
- University of Pennsylvania, Perelman School of Medicine, Institute for Diabetes, Obesity and Metabolism, Philadelphia, Pennsylvania, United States of America
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Two-photon microscopy reveals early rod photoreceptor cell damage in light-exposed mutant mice. Proc Natl Acad Sci U S A 2014; 111:E1428-37. [PMID: 24706832 DOI: 10.1073/pnas.1317986111] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Atrophic age-related and juvenile macular degeneration are especially devastating due to lack of an effective cure. Two retinal cell types, photoreceptor cells and the adjacent retinal pigmented epithelium (RPE), reportedly display the earliest pathological changes. Abca4(-/-)Rdh8(-/-) mice, which mimic many features of human retinal degeneration, allowed us to determine the sequence of light-induced events leading to retinal degeneration. Using two-photon microscopy with 3D reconstruction methodology, we observed an initial strong retinoid-derived fluorescence and expansion of Abca4(-/-)Rdh8(-/-) mouse rod cell outer segments accompanied by macrophage infiltration after brief exposure of the retina to bright light. Additionally, light-dependent fluorescent compounds produced in rod outer segments were not transferred to the RPE of mice genetically defective in RPE phagocytosis. Collectively, these findings suggest that for light-induced retinopathies in mice, rod photoreceptors are the primary site of toxic retinoid accumulation and degeneration, followed by secondary changes in the RPE.
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Valapala M, Wilson C, Hose S, Bhutto IA, Grebe R, Dong A, Greenbaum S, Gu L, Sengupta S, Cano M, Hackett S, Xu G, Lutty GA, Dong L, Sergeev Y, Handa JT, Campochiaro P, Wawrousek E, Zigler JS, Sinha D. Lysosomal-mediated waste clearance in retinal pigment epithelial cells is regulated by CRYBA1/βA3/A1-crystallin via V-ATPase-MTORC1 signaling. Autophagy 2014; 10:480-96. [PMID: 24468901 PMCID: PMC4077886 DOI: 10.4161/auto.27292] [Citation(s) in RCA: 92] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
In phagocytic cells, including the retinal pigment epithelium (RPE), acidic compartments of the endolysosomal system are regulators of both phagocytosis and autophagy, thereby helping to maintain cellular homeostasis. The acidification of the endolysosomal system is modulated by a proton pump, the V-ATPase, but the mechanisms that direct the activity of the V-ATPase remain elusive. We found that in RPE cells, CRYBA1/βA3/A1-crystallin, a lens protein also expressed in RPE, is localized to lysosomes, where it regulates endolysosomal acidification by modulating the V-ATPase, thereby controlling both phagocytosis and autophagy. We demonstrated that CRYBA1 coimmunoprecipitates with the ATP6V0A1/V0-ATPase a1 subunit. Interestingly, in mice when Cryba1 (the gene encoding both the βA3- and βA1-crystallin forms) is knocked out specifically in RPE, V-ATPase activity is decreased and lysosomal pH is elevated, while cathepsin D (CTSD) activity is decreased. Fundus photographs of these Cryba1 conditional knockout (cKO) mice showed scattered lesions by 4 months of age that increased in older mice, with accumulation of lipid-droplets as determined by immunohistochemistry. Transmission electron microscopy (TEM) of cryba1 cKO mice revealed vacuole-like structures with partially degraded cellular organelles, undigested photoreceptor outer segments and accumulation of autophagosomes. Further, following autophagy induction both in vivo and in vitro, phospho-AKT and phospho-RPTOR/Raptor decrease, while pMTOR increases in RPE cells, inhibiting autophagy and AKT-MTORC1 signaling. Impaired lysosomal clearance in the RPE of the cryba1 cKO mice also resulted in abnormalities in retinal function that increased with age, as demonstrated by electroretinography. Our findings suggest that loss of CRYBA1 causes lysosomal dysregulation leading to the impairment of both autophagy and phagocytosis.
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Affiliation(s)
- Mallika Valapala
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Christine Wilson
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Stacey Hose
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Imran A Bhutto
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Rhonda Grebe
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Aling Dong
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Seth Greenbaum
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Limin Gu
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA; Department of Ophthalmology of Shanghai Tenth People's Hospital and Tongji Eye Institute; Tongji University School of Medicine; Shanghai, China
| | - Samhita Sengupta
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Marisol Cano
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Sean Hackett
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Guotong Xu
- Department of Ophthalmology of Shanghai Tenth People's Hospital and Tongji Eye Institute; Tongji University School of Medicine; Shanghai, China
| | - Gerard A Lutty
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Lijin Dong
- National Eye Institute; National Institutes of Health; Bethesda, MD USA
| | - Yuri Sergeev
- National Eye Institute; National Institutes of Health; Bethesda, MD USA
| | - James T Handa
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Peter Campochiaro
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Eric Wawrousek
- National Eye Institute; National Institutes of Health; Bethesda, MD USA
| | - J Samuel Zigler
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Debasish Sinha
- Wilmer Eye Institute; Johns Hopkins University School of Medicine; Baltimore, MD USA
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Affiliation(s)
| | | | - Krzysztof Palczewski
- Department of Pharmacology, School of Medicine, Case
Western Reserve University, 2109 Adelbert Road, Cleveland, Ohio 44106-4965,
United States
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11
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Kohjima M, Tsai TH, Tackett BC, Thevananther S, Li L, Chang BHJ, Chan L. Delayed liver regeneration after partial hepatectomy in adipose differentiation related protein-null mice. J Hepatol 2013; 59:1246-54. [PMID: 23928401 PMCID: PMC4001732 DOI: 10.1016/j.jhep.2013.07.025] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 07/19/2013] [Accepted: 07/22/2013] [Indexed: 12/04/2022]
Abstract
BACKGROUND & AIMS Adult hepatocytes undergo cell cycle progression and proliferation in response to partial hepatectomy (PH). Transient lipid accumulation within hepatocytes preceding the peak proliferative phase is a characteristic feature of regenerating livers. However, the molecular mediators and mechanisms responsible for lipid accumulation in regenerating livers are not well understood. Adipose differentiation related protein (ADRP; Plin2) regulates hepatic triglyceride storage and Plin2-deficient (Plin2(-/-)) mice have significantly reduced triglyceride (TG) content in the liver. We sought to determine the functional significance of PLIN2 in liver regeneration in response to PH and toxic liver injury and examined whether absence of Plin2 expression modulates hepatocyte proliferation and liver regeneration. METHODS We subjected wild-type (WT) and Plin2(-/-) mice to 70% PH or acute carbon tetrachloride (CCL4) treatment and examined the hepatic lipid content, the expression profile of lipid metabolism-related genes, the rate of cellular proliferation and the dynamics of liver regeneration in the treated animals. RESULTS In response to PH, Plin2(-/-) mice showed decreased hepatic triglyceride accumulation and delayed cell cycle progression, which was associated with impaired liver regeneration. Fatty acid (FA) synthesis and lipid transfer gene expression profile were comparable between Plin2(-/-) and wild-type mice, while VLDL secretion rate was higher in the Plin2(-/-) mice. Downregulated β-oxidation and reduced cytosolic FA level in Plin2(-/-) mice may have contributed to the attenuation of the liver regeneration capacity in these animals. In parallel experiments, we also observed attenuated hepatic lipid accumulation and proliferation in response to CCl4-mediated acute toxic liver injury in Plin2(-/-) mice. CONCLUSIONS We conclude that PLIN2-mediated lipid accumulation and utilization by the liver is important for efficient liver regeneration in response to PH and toxic liver injury.
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Affiliation(s)
- Motoyuki Kohjima
- Diabetes and Endocrinology Research Center and Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Tsung-Huang Tsai
- Diabetes and Endocrinology Research Center and Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Bryan C. Tackett
- Diabetes and Endocrinology Research Center and Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
- Department of Pediatrics, Section of Gastroenterology, Hepatology and Nutrition, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Sundararajah Thevananther
- Diabetes and Endocrinology Research Center and Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
- Department of Pediatrics, Section of Gastroenterology, Hepatology and Nutrition, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Lan Li
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Benny Hung-Junn Chang
- Diabetes and Endocrinology Research Center and Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Lawrence Chan
- Diabetes and Endocrinology Research Center and Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
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Charvet CD, Saadane A, Wang M, Salomon RG, Brunengraber H, Turko IV, Pikuleva IA. Pretreatment with pyridoxamine mitigates isolevuglandin-associated retinal effects in mice exposed to bright light. J Biol Chem 2013; 288:29267-80. [PMID: 23970548 DOI: 10.1074/jbc.m113.498832] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The benefits of antioxidant therapy for treating age-related macular degeneration, a devastating retinal disease, are limited. Perhaps species other than reactive oxygen intermediates should be considered as therapeutic targets. These could be lipid peroxidation products, including isolevuglandins (isoLGs), prototypical and extraordinarily reactive γ-ketoaldehydes that avidly bind to proteins, phospholipids, and DNA and modulate the properties of these biomolecules. We found isoLG adducts in aged human retina but not in the retina of mice kept under dim lighting. Hence, to test whether scavenging of isoLGs could complement or supplant antioxidant therapy, we exposed mice to bright light and found that this insult leads to retinal isoLG-adduct formation. We then pretreated mice with pyridoxamine, a B6 vitamer and efficient scavenger of γ-ketoaldehydes, and found that the levels of retinal isoLG adducts are decreased, and morphological changes in photoreceptor mitochondria are not as pronounced as in untreated animals. Our study demonstrates that preventing the damage to biomolecules by lipid peroxidation products, a novel concept in vision research, is a viable strategy to combat oxidative stress in the retina.
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Masihzadeh O, Ammar DA, Kahook MY, Lei TC. Coherent anti-stokes Raman scattering (CARS) microscopy: a novel technique for imaging the retina. Invest Ophthalmol Vis Sci 2013; 54:3094-101. [PMID: 23580484 DOI: 10.1167/iovs.13-11642] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To image the cellular and noncellular structures of the retina in an intact mouse eye without the application of exogenous fluorescent labels using noninvasive, nondestructive techniques. METHODS Freshly enucleated mouse eyes were imaged using two nonlinear optical techniques: coherent anti-Stokes Raman scattering (CARS) and two-photon autofluorescence (TPAF). Cross sectional transverse sections and sequential flat (en face) sagittal sections were collected from a region of sclera approximately midway between the limbus and optic nerve. Imaging proceeded from the surface of the sclera to a depth of ∼60 μm. RESULTS The fluorescent signal from collagen fibers within the sclera was evident in the TPAF channel; the scleral collagen fibers showed no organization and appeared randomly packed. The sclera contained regions lacking TPAF and CARS fluorescence of ∼3 to 15 μm in diameter that could represent small vessels or scleral fibroblasts. Intense punctate CARS signals from the retinal pigment epithelial layer were of a size and shape of retinyl storage esters. Rod outer segments could be identified by the CARS signal from their lipid-rich plasma membranes. CONCLUSIONS CARS microscopy can be used to image the outer regions of the mammalian retina without the use of a fluorescent dye or exogenously expressed recombinant protein. With technical advancements, CARS/TPAF may represent a new avenue for noninvasively imaging the retina and might complement modalities currently used in clinical practice.
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Affiliation(s)
- Omid Masihzadeh
- Department of Ophthalmology, University of Colorado Denver, Aurora, Colorado, USA
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Transient scrotal hyperthermia induces lipid droplet accumulation and reveals a different ADFP expression pattern between the testes and liver in mice. PLoS One 2012; 7:e45694. [PMID: 23056214 PMCID: PMC3464254 DOI: 10.1371/journal.pone.0045694] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2012] [Accepted: 08/24/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND In most mammals, the testes provide a stable environment for spermatogenesis, which depends on a lower temperature than the core body temperature. It has been reported that mild testicular heating safely and reversibly suppresses spermatogenesis, and is under consideration for its potential application as a male contraceptive. Previously, we focused on the molecular mechanism of germ cell apoptosis and anti-apoptotic factors induced by heat treatment in humans and mice. However, the recovery process remains under investigation. RESULTS In this study, we found that lipid droplets in mouse testes are dramatically increased after a brief period of scrotal hyperthermia, and gradually dissipate following temperature normalization. Analysis of the human testis proteome revealed nine proteins associated with lipid droplets. Two of them, ADFP (also known as ADRP and PLIN2) and TIP47 (also known as PLIN3) may participate in acute lipid droplet formation in mammalian testes. We show that Adfp expression is upregulated after scrotal heat treatment in mice. Surprisingly, we find Adfp lacking its 5'-UTR is observed in Adfp(Δ1/Δ1) mouse testes, but is not detectable in liver. CONCLUSIONS These results reveal testis Adfp transcriptional regulation is tissue-specific, and is associated with lipid droplet accumulation induced by heat. The results also indicate that the testes could retain functional proteins through testes-specific transcriptional regulation.
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Elmendorf JS. Fretting about fat: a new look at the lipid droplet surface and the roundabout role of Plin2 in cellular lipid storage: focus on "Direct interaction of Plin2 with lipids on the surface of lipid droplets: a live cell FRET analysis". Am J Physiol Cell Physiol 2012; 303:C713-4. [PMID: 22855294 DOI: 10.1152/ajpcell.00250.2012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Orban T, Palczewska G, Palczewski K. Retinyl ester storage particles (retinosomes) from the retinal pigmented epithelium resemble lipid droplets in other tissues. J Biol Chem 2011; 286:17248-58. [PMID: 21454509 DOI: 10.1074/jbc.m110.195198] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Levels of many hydrophobic cellular substances are tightly regulated because of their potential cytotoxicity. These compounds tend to self-aggregate in cytoplasmic storage depots termed lipid droplets/bodies that have well defined structures that contain additional components, including cholesterol and various proteins. Hydrophobic substances in these structures become mobilized in a specific and regulated manner as dictated by cellular requirements. Retinal pigmented epithelial cells in the eye produce retinyl ester-containing lipid droplets named retinosomes. These esters are mobilized to replenish the visual chromophore, 11-cis-retinal, and their storage ensures proper visual function despite fluctuations in dietary vitamin A intake. But it remains unclear whether retinosomes are structures specific to the eye or similar to lipid droplets in other organs/tissues that contain substances other than retinyl esters. Thus, we initially investigated the production of these lipid droplets in experimental cell lines expressing lecithin:retinol acyltransferase, a key enzyme involved in formation of retinyl ester-containing retinosomes from all-trans-retinol. We found that retinosomes and oleate-derived lipid droplets form and co-localize concomitantly, indicating their intrinsic structural similarities. Next, we isolated native retinosomes from bovine retinal pigmented epithelium and found that their protein and hydrophobic small molecular constituents were similar to those of lipid droplets reported for other experimental cell lines and tissues. These unexpected findings suggest a common mechanism for lipid droplet formation that exhibits broad chemical specificity for the hydrophobic substances being stored.
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Affiliation(s)
- Tivadar Orban
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA
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Sakami S, Maeda T, Bereta G, Okano K, Golczak M, Sumaroka A, Roman AJ, Cideciyan AV, Jacobson SG, Palczewski K. Probing mechanisms of photoreceptor degeneration in a new mouse model of the common form of autosomal dominant retinitis pigmentosa due to P23H opsin mutations. J Biol Chem 2011; 286:10551-67. [PMID: 21224384 DOI: 10.1074/jbc.m110.209759] [Citation(s) in RCA: 201] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rhodopsin, the visual pigment mediating vision under dim light, is composed of the apoprotein opsin and the chromophore ligand 11-cis-retinal. A P23H mutation in the opsin gene is one of the most prevalent causes of the human blinding disease, autosomal dominant retinitis pigmentosa. Although P23H cultured cell and transgenic animal models have been developed, there remains controversy over whether they fully mimic the human phenotype; and the exact mechanism by which this mutation leads to photoreceptor cell degeneration remains unknown. By generating P23H opsin knock-in mice, we found that the P23H protein was inadequately glycosylated with levels 1-10% that of wild type opsin. Moreover, the P23H protein failed to accumulate in rod photoreceptor cell endoplasmic reticulum but instead disrupted rod photoreceptor disks. Genetically engineered P23H mice lacking the chromophore showed accelerated photoreceptor cell degeneration. These results indicate that most synthesized P23H protein is degraded, and its retinal cytotoxicity is enhanced by lack of the 11-cis-retinal chromophore during rod outer segment development.
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Affiliation(s)
- Sanae Sakami
- Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106, USA
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Noninvasive multiphoton fluorescence microscopy resolves retinol and retinal condensation products in mouse eyes. Nat Med 2010; 16:1444-9. [PMID: 21076393 PMCID: PMC3057900 DOI: 10.1038/nm.2260] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Accepted: 08/03/2010] [Indexed: 12/13/2022]
Abstract
Multi–photon excitation fluorescence microscopy (MPM) can image certain molecular processes in vivo. In the eye, fluorescent retinyl esters in sub–cellular structures called retinosomes mediate regeneration of the visual chromophore, 11–cis–retinal, by the visual cycle. But harmful fluorescent condensation products were also identified previously. We report that in wild type mice, excitation with λ ~730 nm identified retinosomes in the retinal pigment epithelium, whereas excitation with λ ~910 nm revealed at least one additional retinal fluorophore. The latter fluorescence was absent in eyes of genetically modified mice lacking a functional visual cycle, but accentuated in eyes of older WT mice and mice with defective clearance of all–trans–retinal, an intermediate in the visual cycle. MPM, a noninvasive imaging modality that facilitates concurrent monitoring of retinosomes along with potentially harmful products in aging eyes, has the potential to detect early molecular changes due to age–related macular degeneration and other defects in retinoid metabolism.
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Retinoids for treatment of retinal diseases. Trends Pharmacol Sci 2010; 31:284-95. [PMID: 20435355 DOI: 10.1016/j.tips.2010.03.001] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2010] [Revised: 03/10/2010] [Accepted: 03/11/2010] [Indexed: 12/31/2022]
Abstract
Knowledge about retinal photoreceptor signal transduction and the visual cycle required for normal eyesight has increased exponentially over the past decade. Substantial progress in human genetics has facilitated the identification of candidate genes and complex networks underlying inherited retinal diseases. Natural mutations in animal models that mimic human diseases have been characterized and advanced genetic manipulation can now be used to generate small mammalian models of human retinal diseases. Pharmacological repair of defective visual processes in animal models not only validates their involvement in vision, but also provides great promise for the development of improved therapies for millions who are progressing towards blindness or are almost completely robbed of their eyesight.
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Chang BHJ, Li L, Saha P, Chan L. Absence of adipose differentiation related protein upregulates hepatic VLDL secretion, relieves hepatosteatosis, and improves whole body insulin resistance in leptin-deficient mice. J Lipid Res 2010; 51:2132-42. [PMID: 20424269 DOI: 10.1194/jlr.m004515] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We previously showed that adipose differentiation related protein (Adfp)-deficient mice display a 60% reduction in hepatic triglyceride (TG) content. In this study, we investigated the role of ADFP in lipid and glucose homeostasis in a genetic obesity model, Lep(ob/ob) mice. We bred Adfp(-/-) mice with Lep(ob/ob) mice to create Lep(ob/ob)/Adfp(-/-) and Lep(ob/ob)/Adfp(+/+) mice and analyzed the hepatic lipids, lipid droplet (LD) morphology, LD protein composition and distribution, lipogenic gene expression, and VLDL secretion, as well as insulin sensitivity of the two groups of mice. Compared with Lep(ob/ob)/Adfp(+/+) mice, Lep(ob/ob)/Adfp(-/-) mice displayed an increased VLDL secretion rate, a 25% reduction in hepatic TG associated with improvement in fatty liver grossly and microscopically with a change of the size of LDs in a proportion of the hepatocytes and a redistribution of major LD-associated proteins from the cytoplasmic compartment to the LD surface. There was no detectable change in lipogenic gene expression. Lep(ob/ob)/Adfp(-/-) mice also had improved glucose tolerance and insulin sensitivity in both liver and muscle. The alteration of LD size in the liver of Lep(ob/ob)/Adfp(-/-) mice despite the relocation of other LDPs to the LD indicates a nonredundant role for ADFP in determining the size and distribution of hepatic LDs.
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Abstract
Vertebrate vision is maintained by the retinoid (visual) cycle, a complex enzymatic pathway that operates in the retina to regenerate the visual chromophore, 11-cis-retinal, a prosthetic group of rhodopsin that undergoes activation by light. Many different mutations in genes encoding retinoid cycle proteins can cause a variety of human blinding diseases. Two-photon microscopy is an evolving, non-invasive, and repetitive imaging technology that can be used to monitor biomolecules within the vertebrate retina at a subcellular resolution. This method has the great advantage of portraying endogenous retinoid fluorophores in their native state without the need for artificial staining. Such real-time retinal imaging permits rapid evaluation not only of various stages of retinal disease in live animal models of human retinopathies but also of the outcome from intended pharmacological therapies. Two-photon microscopy offers substantial potential for early detection of age- and disease-related changes in the eye, long before clinical or pathological manifestations become apparent.
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Affiliation(s)
- Yoshikazu Imanishi
- Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4965, USA
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