Hypophosphorylation of aqueous humor sCD44 and primary open-angle glaucoma

Paul A. Knepper*, Adam M. Miller, John Choi, Robert D. Wertz, Michael J. Nolan, William Goossens, Susan Whitmer, Beatrice Y.J.T. Yue, Robert Ritch, Jeffrey M. Liebmann, R. Rand Allingham, John R. Samples

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

Abstract

PURPOSE. The ectodomain of CD44, the principal receptor for hyaluronic acid (HA), is shed as a 32-kDa fragment-soluble CD44 (sCD44)-which is cytotoxic to trabecular meshwork (TM) cells and retinal ganglion cells (RGCs) in culture. The purpose of this study was to characterize sCD44 further by determining the phosphorylation of aqueous humor sCD44 in normal and primary open-angle glaucoma (POAG). METHODS. Aqueous humor samples of patients were subjected to CD44 enzyme-linked immunosorbent assay (ELISA) and two-dimensional (2-D) polyacrylamide gel electrophoresis, followed by Western blot analysis with anti-CD44, anti-serine/threonine, and anti-tyrosine phosphospecific antibodies, to determine sCD44 concentration, isoelectric point (pI), and phosphorylation, respectively. The bioactivity of hypophosphorylated sCD44 was tested in cell culture and HA affinity columns. RESULTS. Two-dimensional Western blot analysis revealed that the representative pI of the 32-kDa sCD44 was 6.96 ± 0.07 in POAG versus 6.38 ± 0.08 in normal (P < 0.0004). Enzymatic dephosphorylation of sCD44 resulted in a basic shift in the pI. The normal aqueous humor sCD44 was positive for serine-threonine phosphorylation; however, POAG sCD44 was hypophosphorylated. Hypophosphorylated sCD44 was more toxic to TM and RGC cells than standard sCD44, and hypophosphorylated sCD44 had decreased affinity to HA, particularly with increased pressure. CONCLUSIONS. POAG aqueous is characterized by posttranslational change in the pI of sCD44 and hypophosphorylation, which clearly distinguished POAG from normal aqueous humor. The high toxicity and low HA-binding affinity of hypophosphorylated sCD44 may represent specific pathophysiologic features of the POAG disease process.

Original languageEnglish (US)
Pages (from-to)2829-2837
Number of pages9
JournalInvestigative Ophthalmology and Visual Science
Volume46
Issue number8
DOIs
StatePublished - 2005

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems
  • Cellular and Molecular Neuroscience

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