Blood N-glycomic signature of fibrosis in MASLD shows low levels of global α2,3-sialylation

Background & AimsAlterations in the glycosylation of blood proteins affect protein functionality and have been linked to various diseases. Metabolic dysfunction- associated steatotic liver disease (MASLD) is a silent disease, of which progression to advanced disease stages including metabolic dysfunction-associated steatohepatitis (MASH), fibrosis and cirrhosis often goes unnoticed. As current non- invasive diagnostic tests lack specificity, the purpose of this work was to study total blood protein N-glycosylation in individuals with MASLD and various degrees of fibrosis as compared to healthy controls. MethodsIn two independent cross-sectional cohort studies, blood N-glycosylation analysis was performed by mass spectrometry on released glycans of overall 132 MASLD patients and 99 age- and sex-matched healthy controls. Relationships between glycosylation traits and the disease spectrum of MASLD including fibrotic MASLD were investigated in comparison to healthy controls. Furthermore, publicly available transcriptomics datasets were used to explore glycosyltransferase expression in patients with MASLD. ResultsGlobally lower 2,3-sialylation distinguished MASLD from healthy controls (OR [CI]=0.36; [0.18-0.67]; p-value=0.019, and 0.11 [0.04-0.24]; p-value<0.000001), as well as non-fibrotic MASLD from its fibrotic counterparts (OR: 0.13 [0.06-0.26]; p- value<0.0001), but showed no association with steatohepatitis activity. Hepatic ST3GAL6, a sialyltransferase responsible for N-glycan 2,3-sialylation, negatively associated with fibrosis progression, similar to the observed glycomic signature. Both glycomic and transcriptomic signatures were replicated in independent cohorts. ConclusionsFibrotic MASLD is characterized by a global decrease of blood protein 2,3-sialylation and according decrease in hepatic 2,3-sialyltransferase expression, associating with disease progression. These findings suggest alterations in the N- glycan biosynthetic pathway and are potentially useful in the early diagnosis of fibrosis in MASLD. Lay SummaryNon-invasive markers of fibrotic MASLD perform suboptimal. This research identified that changes in blood protein glycosylation coincide with fibrosis development, offering blood-based markers that could potentially replace a liver biopsy. What You Need to KnowO_ST_ABSBACKGROUND AND CONTEXTC_ST_ABSThe majority of the plasma glycoproteins is synthesized in the liver and changes to their glycosylation are known to affect their function and to associate with liver disorders. NEW FINDINGSMASLD patients exhibit lower 2,3-sialylation on the complete range of their blood protein N-glycans, which coincides with the histological appearance of fibrosis, mediated likely via downregulation of hepatic ST3GAL6. LIMITATIONSWhile the findings of this study has could have implications for diagnosing fibrotic MASLD, the identified glycomic signature needs to be confirmed in a larger, ideally prospective patient cohort. CLINICAL RESEARCH RELEVANCEBy identifying specific signatures in the blood protein N-glycome, this research offers potential non-invasive markers for early diagnosis and monitoring of fibrosis in MASLD. Non-invasive diagnosis could potentially lessen the need for liver biopsies, and allow for timely intervention and improved disease management, ultimately leading to improvement of patient outcomes and the reduction of liver-related morbidity and mortality. BASIC RESEARCH RELEVANCEThe observed glycomic and transcriptomic signatures offer molecular-level insights into fibrosis development in MASLD. This paves the way for future research at the intersection of glycoscience and hepatology, that will offer deeper insights into the pathophysiology of this liver disease.