title: Transcription, translation, and function of lubricin, a boundary lubricant, at the ocular surface.
abstract: OBJECTIVE
  Lubricin may be an important barrier to the development of corneal and conjunctival epitheliopathies that may occur in dry eye disease and contact lens wear.
  
  
  OBJECTIVE
  To test the hypotheses that lubricin (ie, proteoglycan 4 [PRG4 ]), a boundary lubricant, is produced by ocular surface epithelia and acts to protect the cornea and conjunctiva against significant shear forces generated during an eyelid blink and that lubricin deficiency increases shear stress on the ocular surface and promotes corneal damage.
  
  
  METHODS
  Human, porcine, and mouse tissues and cells were processed for molecular biological, immunohistochemical, and tribological studies, and wild-type and PRG4 knockout mice were evaluated for corneal damage.
  
  
  RESULTS
  Our findings demonstrate that lubricin is transcribed and translated by corneal and conjunctival epithelial cells. Lubricin messenger RNA is also present in lacrimal and meibomian glands, as well as in a number of other tissues. Absence of lubricin in PRG4 knockout mice is associated with a significant increase in corneal fluorescein staining. Our studies also show that lubricin functions as an effective friction-lowering boundary lubricant at the human cornea-eyelid interface. This effect is specific and cannot be duplicated by the use of hyaluronate or bovine serum albumin solutions.
  
  
  CONCLUSIONS
  Our results show that lubricin is transcribed, translated, and expressed by ocular surface epithelia. Moreover, our findings demonstrate that lubricin presence significantly reduces friction between the cornea and conjunctiva and that lubricin deficiency may play a role in promoting corneal damage.
authors.affiliation: Faculty of Kinesiology, Human Performance Laboratory Schulich School of Engineering, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Tannin A
authors.initials: TA
authors.lastname: Schmidt
authors.forename: David A
authors.initials: DA
authors.lastname: Sullivan
authors.forename: Erich
authors.initials: E
authors.lastname: Knop
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Richards
authors.forename: Nadja
authors.initials: N
authors.lastname: Knop
authors.forename: Shaohui
authors.initials: S
authors.lastname: Liu
authors.forename: Afsun
authors.initials: A
authors.lastname: Sahin
authors.forename: Raheleh Rahimi
authors.initials: RR
authors.lastname: Darabad
authors.forename: Sheila
authors.initials: S
authors.lastname: Morrison
authors.forename: Wendy R
authors.initials: WR
authors.lastname: Kam
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Sullivan
mesh_terms: D000818:Animals; D003228:Conjunctiva / Q000378:metabolism*; D003941:Diagnostic Techniques, Ophthalmological; D004847:Epithelial Cells / Q000378:metabolism*; D019573:Epithelium, Corneal / Q000378:metabolism* / Q000473:pathology; D019793:Fluorescein; D005456:Fluorescent Dyes; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D007765:Lacrimal Apparatus / Q000378:metabolism; D008537:Meibomian Glands / Q000378:metabolism; D051379:Mice; D057507:Mice, 129 Strain; D018345:Mice, Knockout; D011509:Proteoglycans / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013552:Swine; D014158:Transcription, Genetic; D000099158:Proteoglycan 4
chemical_list: D019793:Fluorescein; D005456:Fluorescent Dyes; D006023:Glycoproteins; D011509:Proteoglycans; D012333:RNA, Messenger; D000099158:Proteoglycan 4; C419197:PRG4 protein, human; C498837:Prg4 protein, mouse