PURPOSE. To investigate the alteration of vitreal N-glycans in patients with proliferative diabetic retinopathy (PDR).
METHODS. Plasma and vitreous samples were collected from 17 patients (10 females and 7 males) with PDR (PDR group) and 17 nondiabetic patients (8 females and 9 males) with epiretinal membrane (ERM) and idiopathic macular hole (MH) (non-diabetes mellitus [DM] group). Profiles of N-glycans were analyzed by a glycoblotting-based high-throughput protocol that we recently developed. Human retinal microvascular endothelial cells (HRMECs) were cultivated with culture media containing either low glucose (5 mM) or high glucose (25 mM), and expression levels of sialyltransferases were analyzed by real-time PCR and ELISA.
RESULTS. Amount of N-glycans in the vitreous fluid of the PDR group was significantly higher than that of the non-DM group (495.5 +/- 37.4 vs. 142.7 +/- 30.8 pmol/100 mu g protein, P < 0.005), whereas there was no significant difference in the plasma samples between the PDR and the non-DM group. In addition, profile analysis showed that N-glycans with sialic acids increased in the vitreous of the PDR group (328.4 +/- 25.8 pmol/100 mu g protein) compared to the non-DM group (92.1 +/- 21.2 pmol/100 mu g protein, P < 0.0005). Expression levels of sialyltransferases ST3GAL1 and ST3GAL4 were upregulated in the HRMECs after high-glucose stimulation. Consistent with the real-time PCR data, high-glucose stimulation elevated the protein levels of ST3GAL1 (117.4 +/- 14.9 pg/mg, P < 0.01) and ST3GAL4 (6.1 +/- 0.9 pg/mg, P < 0.05) in the HRMECs compared with the cells cultured with low-glucose culture media (ST3GAL1, 64.4 +/- 5.8 pg/mg; ST3GAL4, 3.8 +/- 0.3 pg/mg).
CONCLUSIONS. Our data demonstrate distinct changes in the N-glycan profile and an increase in sialylated N-glycans in eyes with PDR.