SIAE-Mediated Loss of Sialic Acid Acetylation Contributes to Ulcerative Colitis

Background: Ulcerative colitis (UC) disrupts the colon’s protective mucus layer, exposing the epithelium to bacteria and triggering inflammation. This barrier, crucial for intestinal health, depends on complex glycosylation, notably sialic acid modifications. However, the precise role of sialic acid acetylation and the enzyme SIAE (sialic acid acetylesterase) in UC pathogenesis remains unclear. This study investigates the role of glycosylation changes, specifically sialic acid de-acetylation, in UC progression. Methods: Tissue samples were obtained from patients with ulcerative colitis (UC) and colorectal cancer at the Second Affiliated Hospital of Soochow University. HT-29 cells were utilized to investigate the molecular mechanisms of SIAE in UC pathogenesis. Mass spectrometry was performed to analyze differences in protein and glycoprotein expression. Western blot (WB) and immunohistochemistry (IHC) were used to examine SIAE protein expression changes during inflammation. Furthermore, polymerase chain reaction (PCR) and immunofluorescence were employed to determine the effects of SIAE on sialic acid levels and mucosal immunity. Results: In this study, we characterized proteins and glycoproteins from patient tissues with UC, finding that sialic acid acetylesterase (SIAE) is upregulated in UC. HT-29 cells exposed to TNF-α induced an inflammatory response with a 5-fold increased expression of SIAE and NEU1 when TNF-α was at a concentration of 100 ng/mL. Mass spectrometry analysis revealed a reduction in acetylation on glycans and glycoproteins, while confocal microscopy confirmed a decrease in sialic acid on the cell surface. Gene expression analysis showed that CDH1, CTNND1 , and ITGA8 were significantly downregulated in HT-29 cells stimulated by TNF-α, suggesting a reduction in cell-cell adhesion. SNA lectin-confocal microscopy revealed a reduction of sialic acid on HT-29 cells in TNF-α-induced UC cell models. Conclusion: This study demonstrates that SIAE is significantly upregulated in ulcerative colitis (UC) tissues and TNF-α-stimulated HT-29 cells, leading to a marked reduction in sialic acid acetylation and cell surface sialic acid levels. These changes correlate with decreased expression of cell adhesion molecules, suggesting a disruption of the mucosal barrier integrity. Consequently, SIAE-mediated sialic acid de-acetylation emerges as a critical factor in UC pathogenesis, potentially serving as both a valuable biomarker and a promising therapeutic target. Plain Language Summary: Ulcerative colitis (UC) is a disease where the lining of the large intestine becomes inflamed. This inflammation can damage the protective mucus layer, allowing bacteria to enter and trigger more inflammation. In this study, researchers found that a protein called SIAE is increased in UC patients. This protein breaks down sialic acid, a sugar molecule that helps protect the lining. When sialic acid levels decrease, the protective barrier weakens, leading to more inflammation and potentially worsening UC. Keywords: glycan, sialic acid, sialic acid acetylesterase, ulcerative colitis, inflammation bowel disease, mass spectrometry