Citation: Lei Y, Stamer WD, Wu J, Sun X. Endothelial nitric oxide synthaserelated mechanotransduction changes in aged porcine angular aqueous plexus cells. Invest Ophthalmol Vis Sci. 2014;55:8402-8408. DOI: 10.1167/iovs.14-14992 PURPOSE. To investigate effects of aging on endothelial nitric oxide synthase (eNOS) expression and signaling in angular aqueous plexus (AAP) (functional equivalent to human Schlemm's canal) cells subjected to shear stress.
METHODS.The AAP cells were isolated differentially from porcine outflow tissues using puromycin selection. Cell aging was induced by culturing cells in hyperoxia condition (40% oxygen and 5% carbon dioxide) for 14 days. The AAP cells grown in chamber slides were exposed to a shear stress of 8 dynes/cm 2 for 24 hours. Expression of eNOS, eNOS-phospho Thr495, eNOS-phospho Ser1177, and Akt-phospho was tested by Western blot analysis and immunofluorescence staining. Nitric oxide (NO) levels were measured using the Griess assay.
RESULTS.Compared with control, eNOS levels in aged cells were significantly reduced by 60% (P < 0.05; n Œ 6). Phosphorylation of eNOS at Ser1177 and Akt at Ser473 was 63% and 80% lower in aged cells, respectively, whereas phosphorylation of the eNOS inhibition site (Thr495) increased by 6.1-fold (P < 0.05; n Œ 6). Shear stress (8 dynes/cm 2 for 24 hours) increased eNOS abundance (total protein and at cell borders) and phosphorylation at Ser1177 by 1.7-fold and 1.8-fold, respectively (P < 0.05; n Œ 6), whereas aged cells were unresponsive. In control cells exposed to shear stress, the NO concentration was 1.8-fold higher than in the static group (P < 0.05; n Œ 4); however, aged cells were unresponsive to shear stress (mean 6 SD, 4.3 6 1.3 vs. 4.1 6 1.4 lM).CONCLUSIONS. Aged AAP cells appear compromised in their mechanotransduction machinery involving eNOS, the protein product of the gene, NOS3, polymorphisms of which impart a risk for the development of glaucoma.Keywords: aging, Schlemm's canal, eNOS G laucoma comprises a group of complex and heterogeneous blinding diseases, affecting almost 60 million people worldwide. 1 Clinically, glaucoma is characterized by cupping of the optic nerve head and visual field loss. Elevated IOP is the primary risk factor for glaucomatous optic nerve damage, and reducing pressure remains the only treatable end point that slows or stops disease progression. The risk of developing POAG also clearly increases with age. 2-8 Primarily, IOP is determined by changes in aqueous humor outflow resistance, which is thought to reside mainly in the juxtacanalicular region, where the trabecular meshwork (TM) and the inner wall of Schlemm's canal (SC) cells interact. 9,10 The endothelial cells of the inner wall of SC are important in regulating outflow resistance and thus IOP.
11,12Nitric oxide (NO) regulation appears to have a role in POAG. Family association studies [13][14][15] show a relationship between NOS3 gene polymorphisms, which encode for endothelial NO synthase (eNOS), and POAG. These recent findings are consistent wit...