title: Ultrastructural changes associated with dexamethasone-induced ocular hypertension in mice.
abstract: OBJECTIVE
  To determine whether dexamethasone (DEX)-induced ocular hypertension (OHT) in mice mimics the hallmarks of steroid-induced glaucoma (SIG) in humans, including reduced conventional outflow facility (C), increased extracellular matrix (ECM), and myofibroblasts within the outflow pathway.
  
  
  METHODS
  Osmotic mini-pumps were implanted subcutaneously into C57BL/6J mice for systemic delivery of DEX (3-4 mg/kg/d, n = 31 mice) or vehicle (n = 28). IOP was measured weekly by rebound tonometry. After 3 to 4 weeks, mice were euthanized and eyes enucleated for ex vivo perfusion to measure C, for electron microscopy to examine the trabecular meshwork (TM) and Schlemm's canal (SC), or for immunohistochemistry to examine type IV collagen and α-smooth muscle actin. The length of basement membrane material (BMM) was measured along the anterior-posterior extent of SC by electron microscopy. Ultrastructural changes in BMM of DEX-treated mice were compared against archived human SIG specimens.
  
  
  RESULTS
  Dexamethasone increased IOP by 2.6 ± 1.6 mm Hg (mean ± SD) over 3 to 4 weeks and decreased C by 52% ± 17% versus controls. Intraocular pressure elevation correlated with decreased C. Dexamethasone treatment led to increased fibrillar material in the TM, plaque-like sheath material surrounding elastic fibers, and myofibroblasts along SC outer wall. The length of BMM underlying SC was significantly increased in mice with DEX and in humans with SIG, and in mice decreased C correlated with increased BMM.
  
  
  CONCLUSIONS
  Dexamethasone-induced OHT in mice mimics hallmarks of human SIG within 4 weeks of DEX treatment. The correlation between reduced C and newly formed ECM motivates further study using DEX-treated mice to investigate the pathogenesis of conventional outflow obstruction in glaucoma.
authors.affiliation: Department of Bioengineering, Imperial College London, London, United Kingdom.
authors.forename: Darryl R
authors.initials: DR
authors.lastname: Overby
authors.affiliation: Department of Bioengineering, Imperial College London, London, United Kingdom.
authors.forename: Jacques
authors.initials: J
authors.lastname: Bertrand
authors.affiliation: Department of Anatomy II, University of Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Ozan-Yüksel
authors.initials: OY
authors.lastname: Tektas
authors.affiliation: Department of Bioengineering, Imperial College London, London, United Kingdom.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Boussommier-Calleja
authors.affiliation: Department of Anatomy II, University of Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Schicht
authors.affiliation: Department of Bioengineering, Imperial College London, London, United Kingdom Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States.
authors.forename: C Ross
authors.initials: CR
authors.lastname: Ethier
authors.affiliation: Department of Biological Sciences, Allergan, Inc., Irvine, California, United States.
authors.forename: David F
authors.initials: DF
authors.lastname: Woodward
authors.affiliation: Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina, United States.
authors.forename: W Daniel
authors.initials: WD
authors.lastname: Stamer
authors.affiliation: Department of Anatomy II, University of Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Elke
authors.initials: E
authors.lastname: Lütjen-Drecoll
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003315:Cornea / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D003907:Dexamethasone / Q000493:pharmacokinetics / Q000633:toxicity*; D004195:Disease Models, Animal; D005500:Follow-Up Studies; D005938:Glucocorticoids / Q000493:pharmacokinetics / Q000633:toxicity; D006801:Humans; D007150:Immunohistochemistry; D007429:Intraocular Pressure / Q000187:drug effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D009798:Ocular Hypertension / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology*; D010865:Pilot Projects
chemical_list: D000199:Actins; D005938:Glucocorticoids; C544013:alpha-smooth muscle actin, mouse; D003907:Dexamethasone
keywords: basement membrane; steroid glaucoma; trabecular meshwork