Activity of the glycosylating enzyme, core 2 GlcNAc (beta1,6) transferase, is higher in polymorphonuclear leukocytes from diabetic patients compared with age-matched control subjects: relevance to capillary occlusion in diabetic retinopathy.
The exact mechanism for capillary occlusion in diabetic retinopathy is still unclear, but increased leukocyte-endothelial cell adhesion has been implicated. We examined the possibility that posttranslational modification of surface O-glycans by increased activity of core 2 transferase (UDP-Glc:Galbeta1-3GalNAcalphaRbeta-N-acetylglucoaminyltr ansferase) is responsible for increased adhesion of leukocytes to vascular endothelium in diabetes. The mean activity of core 2 transferase in polymorphonuclear leukocytes isolated from type 1 and type 2 diabetic patients was higher compared with age-matched control subjects (1,638 +/- 91 [n = 42] vs. 249 +/- 35 pmol x h(-1) x mg(-1) protein [n = 24], P = 0.00013; 1,459 +/- 194 [n = 58] vs. 334 +/- 86 [n = 11], P = 0.01). As a group, diabetic patients with retinopathy had significantly higher mean activity of core 2 transferase compared with individuals with no retinopathy. There was a significant association between enzyme activity and severity of retinopathy in type 1 and type 2 diabetic patients. There was a strong correlation between activity of core 2 transferase and extent of leukocyte adhesion to cultured retinal capillary endothelial cells for diabetic patients but not for age-matched control subjects. Results from transfection experiments using human myelocytic cell line (U937) demonstrated a direct relationship between increased activity of core 2 transferase and increased binding to cultured endothelial cells. There was no relationship between activity of core 2 transferase and HbA(1c) (P = 0.8314), serum advanced glycation end product levels (P = 0.4159), age of the patient (P = 0.7896), and duration of diabetes (P = 0.3307). On the basis that branched O-glycans formed by the action of core 2 transferase participate in leukocyte adhesion, the present data suggest the involvement of this enzyme in increased leukocyte-endothelial cell adhesion and the pathogenesis of capillary occlusion in diabetic retinopathy.
Chibber
R
R
GKT Department of Ophthalmology, The Raynes Institute, St. Thomas' Hospital, London, UK.
Ben-Mahmud
B M
BM
Coppini
D
D
Christ
E
E
Kohner
E M
EM
D000328:Adult; D000375:Aging; D002196:Capillaries / Q000473:pathology; D002448:Cell Adhesion; D002478:Cells, Cultured; D003922:Diabetes Mellitus, Type 1 / Q000201:enzymology*; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology*; D003930:Diabetic Retinopathy / Q000201:enzymology* / Q000473:pathology; D004730:Endothelium, Vascular / Q000473:pathology; D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis; D017127:Glycation End Products, Advanced / Q000097:blood; D006031:Glycosylation; D006801:Humans; D008297:Male; D008875:Middle Aged; D017351:N-Acetylglucosaminyltransferases / Q000097:blood* / Q000235:genetics; D009504:Neutrophils / Q000201:enzymology* / Q000502:physiology; D012171:Retinal Vessels / Q000473:pathology; D014162:Transfection
D006442:Glycated Hemoglobin; D017127:Glycation End Products, Advanced; D017351:N-Acetylglucosaminyltransferases; C053024:beta-1,3-galactosyl-O-glycosyl-glycoprotein beta-1,6-acetylglucosaminyl transferase