Topical ocular sodium 4-phenylbutyrate rescues glaucoma in a myocilin mouse model of primary open-angle glaucoma.
OBJECTIVE
Mutations in the myocilin gene (MYOC) are the most common known genetic cause of primary open-angle glaucoma (POAG). The purpose of this study was to determine whether topical ocular sodium 4-phenylbutyrate (PBA) treatment rescues glaucoma phenotypes in a mouse model of myocilin-associated glaucoma (Tg-MYOC(Y437H) mice).


METHODS
Tg-MYOC(Y437H) mice were treated with PBA eye drops (n = 10) or sterile PBS (n = 8) twice daily for 5 months. Long-term safety and effectiveness of topical PBA (0.2%) on glaucoma phenotypes were examined by measuring intraocular pressure (IOP) and pattern ERG (PERG), performing slit lamp evaluation of the anterior chamber, analyzing histologic sections of the anterior segment, and comparing myocilin levels in the aqueous humor and trabecular meshwork of Tg-MYOC(Y437H) mice.


RESULTS
Tg-MYOC(Y437H) mice developed elevated IOP at 3 months of age when compared with wild-type (WT) littermates (n = 24; P < 0.0001). Topical PBA did not alter IOP in WT mice. However, it significantly reduced elevated IOP in Tg-MYOC(Y437H) mice to the level of WT mice. Topical PBA-treated Tg-MYOC(Y437H) mice also preserved PERG amplitudes compared with vehicle-treated Tg-MYOC(Y437H) mice. No structural abnormalities were observed in the anterior chamber of PBA-treated WT and Tg-MYOC(Y437H) mice. Analysis of the myocilin in the aqueous humor and TM revealed that PBA significantly improved the secretion of myocilin and reduced myocilin accumulation as well as endoplasmic reticulum (ER) stress in the TM of Tg-MYOC(Y437H) mice. Furthermore, topical PBA reduced IOP elevated by induction of ER stress via tunicamycin injections in WT mice.


CONCLUSIONS
Topical ocular PBA reduces glaucomatous phenotypes in Tg-MYOC(Y437H) mice, most likely by reducing myocilin accumulation and ER stress in the TM. Topical ocular PBA could become a novel treatment for POAG patients with myocilin mutations.
Howard Hughes Medical Institute, University of Iowa, Iowa City, Iowa, USA.
Gulab S
GS
Zode
Kevin E
KE
Bugge
Kabhilan
K
Mohan
Sinisa D
SD
Grozdanic
Joseph C
JC
Peters
Demelza R
DR
Koehn
Michael G
MG
Anderson
Randy H
RH
Kardon
Edwin M
EM
Stone
Val C
VC
Sheffield
D060433:Administration, Ophthalmic; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001082:Aqueous Humor / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004195:Disease Models, Animal; D005123:Eye / Q000187:drug effects; D005136:Eye Proteins / Q000378:metabolism; D005260:Female; D005902:Glaucoma, Open-Angle / Q000188:drug therapy* / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007429:Intraocular Pressure / Q000187:drug effects; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009798:Ocular Hypertension / Q000188:drug therapy; D009883:Ophthalmic Solutions / Q000008:administration & dosage*; D010654:Phenylbutyrates / Q000008:administration & dosage*; D014415:Tunicamycin / Q000494:pharmacology; D000099179:Myocilin
D000900:Anti-Bacterial Agents; D003598:Cytoskeletal Proteins; D005136:Eye Proteins; D006023:Glycoproteins; D009883:Ophthalmic Solutions; D010654:Phenylbutyrates; D014415:Tunicamycin; D000099179:Myocilin; C075773:4-phenylbutyric acid