Reduction in disialyl-T antigen levels in mice deficient for both St6galnac3 and St6galnac4 results in blood filling of lymph nodes.

Sialic acid (SA) is present at the terminal ends of carbohydrate chains in glycoproteins and glycolipids and is involved in various biological phenomena. The biological function of the disialyl-T (SAα2-3Galß1-3(SAα2-6)GalNAcα1-O-Ser/Thr) structure is largely unknown. To elucidate the role of disialyl-T structure and determine the key enzyme from the N-acetylgalactosaminide α2,6-sialyltransferase (St6galnac) family involved in its in vivo synthesis, we generated St6galnac3- and St6galnac4-deficient mice. Both single-knockout mice developed normally without any prominent phenotypic abnormalities. However, the St6galnac3::St6galnact4 double knockout (DKO) mice showed spontaneous hemorrhage of the lymph nodes (LN). To identify the cause of bleeding in the LN, we examined podoplanin, which modifies the disialyl-T structures. The protein expression of podoplanin in the LN of DKO mice was similar to that in wild-type mice. However, the reactivity of MALII lectin, which recognizes disialyl-T, in podoplanin immunoprecipitated from DKO LN was completely abolished. Moreover, the expression of vascular endothelial cadherin was reduced on the cell surface of high endothelial venule (HEV) in the LN, suggesting that hemorrhage was caused by the structural disruption of HEV. These results suggest that podoplanin possesses disialyl-T structure in mice LN and that both St6galnac3 and St6galnac4 are required for disialyl-T synthesis.

Global Loss of Core 1-Derived O-Glycans in Mice Leads to High Mortality Due to Acute Kidney Failure and Gastric Ulcers.

The core 1 structure is the major constituent of mucin-type O-glycans, which are added via glycosylation-a posttranslational modification present on membrane-bound and secretory proteins. Core 1 ß1,3-galactosyltransferase (C1galt1), an enzyme that synthesizes the core 1 structure, requires Cosmc, a C1galt1-specific molecular chaperone, for its enzymatic activity. Since Cosmc-knockout mice exhibit embryonic lethality, the biological role of core 1-derived O-glycans in the adult stage is not fully understood. We generated ubiquitous and inducible CAGCre-ERTM/Cosmc-knockout (iCAG-Cos) mice to investigate the physiological function of core 1-derived O-glycans. The iCAG-Cos mice exhibited a global loss of core 1-derived O-glycans, high mortality, and showed a drastic reduction in weights of the thymus, adipose tissue, and pancreas 10 days after Cosmc deletion. They also exhibited leukocytopenia, thrombocytopenia, severe acute pancreatitis, and atrophy of white and brown adipose tissue, as well as spontaneous gastric ulcers and severe renal dysfunction, which were considered the causes underlying the high mortality of the iCAG-Cos mice. Serological analysis indicated the iCAG-Cos mice have lower blood glucose and total blood protein levels and higher triglyceride, high-density lipoprotein, and total cholesterol levels than the controls. These data demonstrate the importance of core 1-derived O-glycans for homeostatic maintenance in adult mice.