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B. D. Sullivan, S. M. Richards, D. Talbot, T. A. Schmidt, D. A. Sullivan; Proteoglycan 4 mRNA Expression in Human Corneal and Conjunctival Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):795.
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Proteoglycan 4 (PRG4) may play a critical role as a boundary lubricant in articulating joints. This secreted glycoprotein, which is also called lubricin and superficial zone protein, protects cartilaginous surfaces against frictional forces, cell adhesion and protein deposition. We hypothesize that PRG4 may serve an analogous role on the ocular surface and protect the cornea and conjunctiva against significant shear forces generated during an eyelid blink. We also hypothesize that PRG4 is synthesized by corneal and conjunctival epithelial cells and secreted onto the ocular surface. The purpose of this study was to determine whether ocular surface cells express the gene for PRG4.
Human corneal epithelial cells were isolated from the corneoscleral rims of male and female donors. Cells were processed either directly (n = 8), or first cultured (n = 2). We also obtained bulbar conjunctivae during surgical procedures (n = 2), conjunctival impression cytology samples (n = 9), and immortalized human conjunctival epithelial cells after culture (n = 1). Samples were processed for the analysis of PRG4 mRNA by using primarily RT-PCR (n = 18), but also Affymetrix gene chips (n = 4). The PRG4 primers for PCR spanned over 1 kbp of intron sequences, in order to suppress amplification of contaminating chromosomal DNA. Amplified samples were screened for the presence of PRG4 products by using agarose gel electrophoresis and an Agilent 2100 Bioanalyzer. To confirm the identity of amplicons, PCR products from cornea samples (n = 2) and conjunctival epithelial cells (n = 1) were sequenced with a 3100 Genetic Analyzer and resulting data were analyzed with BLASTn searches.
Our findings demonstrate that PRG4 mRNA is present in all human corneal and conjunctival epithelial cell and impression cytology samples. The identity of PRG4 PCR products was confirmed by DNA sequence analysis.
Our results show that PRG4 is transcribed in human corneal and conjunctival epithelial cells. (The authors thank Sandra Michaud and Pablo Argueso for their assistance.)
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