title: Hemoglobin expression and regulation in glaucoma: insights into retinal ganglion cell oxygenation.
abstract: OBJECTIVE
  To determine expression, cellular distribution, and regulation of hemoglobin (Hb) in normal and glaucomatous tissues.
  
  
  METHODS
  Proteomic analysis of Hb expression was conducted on protein samples from ocular hypertensive and control rat eyes and human donor eyes with or without glaucoma. Proteomic findings were validated by quantitative (q)RT-PCR, Western blot analysis, immunohistochemistry, and the analysis of new Hb synthesis in culture. Hypoxic regulation of Hb expression was also studied in primary cultures of rat RGCs and macroglia and after transfer of the glia-conditioned medium to RGCs. The role of erythropoietin (EPO) signaling in Hb induction and cell survival was determined by applying recombinant (r)EPO treatment and performing EPO neutralization experiments by using soluble EPO receptor treatment of hypoxic cultures.
  
  
  RESULTS
  In vivo findings revealed Hb expression in the retina and optic nerve head macroglia and RGCs, suggesting an approximately two-fold upregulation in ocular hypertensive rat eyes and glaucomatous human donor eyes relative to the control eyes. In vitro findings collectively supported that hypoxia boosts glial Hb expression through hypoxia-inducible EPO signaling in an autocrine manner. Based on passive transfer experiments, hypoxia-induced production of glial EPO was also found to upregulate Hb expression in RGCs in a paracrine manner, thereby increasing the hypoxic survival of these neurons.
  
  
  CONCLUSIONS
  Findings of this study provide new insights into tissue oxygen transport in the inner retina and optic nerve head through the regulated expression of Hb in macroglia and RGCs. Upregulation of Hb expression appears to be an intrinsic protective mechanism to facilitate cellular oxygenation and may also provide free radical scavenging.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA. gulgun.tezel@louisville.edu
authors.forename: Gülgün
authors.initials: G
authors.lastname: Tezel
authors.forename: Xiangjun
authors.initials: X
authors.lastname: Yang
authors.forename: Cheng
authors.initials: C
authors.lastname: Luo
authors.forename: Jian
authors.initials: J
authors.lastname: Cai
authors.forename: Angela D
authors.initials: AD
authors.lastname: Kain
authors.forename: David W
authors.initials: DW
authors.lastname: Powell
authors.forename: Markus H
authors.initials: MH
authors.lastname: Kuehn
authors.forename: William M
authors.initials: WM
authors.lastname: Pierce
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D002470:Cell Survival; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004921:Erythropoietin / Q000494:pharmacology / Q000502:physiology; D005136:Eye Proteins / Q000378:metabolism; D005901:Glaucoma / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D013058:Mass Spectrometry; D009798:Ocular Hypertension / Q000378:metabolism; D009898:Optic Disk / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011914:Rats, Inbred BN; D011994:Recombinant Proteins; D012160:Retina / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055542:alpha-Globins / Q000235:genetics; D055544:beta-Globins / Q000235:genetics
chemical_list: D005136:Eye Proteins; D006454:Hemoglobins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D055542:alpha-Globins; D055544:beta-Globins; D004921:Erythropoietin; D010100:Oxygen