June 2023
Volume 64, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2023
Elevated levels of Glypican-4 (GPC4) in the aqueous humor of POAG patients, and the role of GPC4 in trabecular meshwork biology
Author Affiliations & Notes
  • Vasantha Rao
    Ophthalmology, Pharmacology and cancer Biology, Duke University School of Medicine, Durham, North Carolina, United States
  • Levi Lankford
    Ophthalmology, Duke University School of Medicine, Durham, North Carolina, United States
  • Pratap Challa
    Ophthalmology, Duke University School of Medicine, Durham, North Carolina, United States
  • Robin Vann
    Ophthalmology, Duke University School of Medicine, Durham, North Carolina, United States
  • Rupalatha Maddala
    Ophthalmology, Duke University School of Medicine, Durham, North Carolina, United States
  • Footnotes
    Commercial Relationships   Vasantha Rao None; Levi Lankford None; Pratap Challa None; Robin Vann None; Rupalatha Maddala None
  • Footnotes
    Support  NIH R01EY018590, R01EY028823 and P30EY005722.
Investigative Ophthalmology & Visual Science June 2023, Vol.64, 2430. doi:
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      Vasantha Rao, Levi Lankford, Pratap Challa, Robin Vann, Rupalatha Maddala; Elevated levels of Glypican-4 (GPC4) in the aqueous humor of POAG patients, and the role of GPC4 in trabecular meshwork biology. Invest. Ophthalmol. Vis. Sci. 2023;64(8):2430.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Our earlier investigations have demonstrated that the levels of glypican-4 (GPC4), a cell surface heparan sulfate proteoglycan and crucial regulator of Wnt signaling, are elevated in trabecular meshwork (TM) cells treated with dexamethasone (Dex) and TGF-β2. The role of GPC4 in TM biology or homeostasis of intraocular pressure (IOP) however, is not known. This study addresses the role of GPC4 in regulation of TM actin cytoskeletal organization and cell adhesion, and IOP.

Methods : The levels of GPC4 in aqueous humor (AH) samples from POAG and age and gender matched non-glaucoma (cataract) patients, and in conditioned media from cultured human TM cells were analyzed by ELISA and immunoblot analyses, respectively. The effects of recombinant human GPC4, Wnt5a, and their respective siRNAs, on actin cytoskeletal organization, cell adhesion and activation of JNK and MYPT1 (substrate of Rho kinase) in human TM cells were determined by immunofluorescence and immunoblot analyses. IOP changes in GPC4 null mice were evaluated using a rebound tonometer.

Results : GPC4 levels were significantly elevated (by > 4 fold, P<0.0001; Mann Whitney test; N=21) in the AH of POAG patients compared to cataract patients. GPC4 was readily detectable in conditioned media from TM cells. While treatment of TM cells with GPC4 siRNA led to decreased actin stress fibers, focal adhesions, and levels of p-JNK, p-paxillin, p-MYPT1 and Wnt5a in association with altered cell morphology, stimulation with GPC4 and Wnt5a had contrasting effects on these cellular and biochemical characteristics. IOP was found to be unaltered under basal conditions in GPC4 null mice (n=4), and investigations are underway to determine whether TGF-β2 has differential effects on IOP in GPC4 null mice.

Conclusions : The results of this study uncover a critical role for GPC4 in regulation of TM cell actin cytoskeletal organization and cell adhesive interactions by activating the non-canonical Wnt/planar cell polarity signaling pathway. These findings are directly relevant to the pathobiology of ocular hypertension since GPC4 is induced by glucocorticoids and TGF-β2 in TM cells and the levels of this protein have been found to be robustly elevated in the AH of POAG patients.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

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