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Abdulaziz Alarifi, Suresh C Regmi, David A Hart, Tannin A Schmidt; Title: Quantification of Proteoglycan 4 (PRG4) / Lubricin in Human Vitreous Humor. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1096. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Proteoglycan 4 (PRG4) / lubricin is a mucin-like glycoprotein originally discovered in synovial fluid, and recently on the ocular surface. PRG4 is classically known to function as a boundary lubricant at articulating biointerfaces, both alone and in combination with hyaluronan (HA). In a recent mass spectrometry study, PRG4 was identified in human vitreous humor (VH). We have also recently shown by western blot the full-length protein is present in VH. However, both the functional role and concentration of PRG4 within human vitreous humor remain to be determined. The objective of this initial study was to quantify the PRG4 protein, along with HA, in human VH samples.
Methods: Human VH samples, from both left and right eyes, were obtained (N=12, 4 female and 8 male) through Southern Alberta Lions Eye Bank. The subjects’ ages varied from 61 to 77 years with a mean of 70.25, with diverse pathological medical histories. Samples were obtained within 8 hours of death, and were centrifuged prior to aliquoting and storage at -80°C. The concentration of PRG4 was determined via a competitive amplified luminescent proximity homogeneous assay using recombinant human PRG4 as the control. The concentration of HA was determined in select samples via a commercially available sandwich enzyme-linked immunosorbent assay.
Results: The mean +/- SD PRG4 concentration in VH was 20 ± 25 µg/mL, and values ranged from 2 – 95 µg/mL. Left and right samples from individual donors were within 31+/-20 % of each other. The HA concentration in two subjects, one high (12 µg/mL) and one low (2 µg/mL) in corresponding PRG4 content, were 52 and 208 µg/mL, respectively.
Conclusion: PRG4 was quantified in human VH for the first time. The reported values are approximately an order of magnitude lower than those reported for synovial fluid. Analysis is ongoing to establish any potential correlation between HA and PRG4 concentration. While there is no obvious load bearing surface in the vitreous humor for PRG4 to directly lubricate, it could contribute to the viscous properties of vitreous humor. Given PRG4’s recently described biological and anti-inflammatory properties (e.g. through TLR interaction), PRG4 could also have biological function(s) in the VH. Future studies are required to elucidate the role of PRG4 in the VH and its contributions to VH health and/or disease.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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