Astragalus polysaccharides ameliorates experimental colitis by regulating memory B cells metabolism

It is well-established that the reduced Memory B cells (MBCs) play an important role in the pathogenesis of ulcerative colitis (UC), rendering them a potential therapeutic target for UC intervention. Astragalus polysaccharide (APS), a primary active constituent derived from the classic traditional Chinese medicine Astragalus membranaceus (AM), has been used for centuries in the treatment of UC in both human and animal subjects due to its renowned immunomodulatory properties. However, it is unknown whether APS can regulate MBCs to alleviate experimental colitis. In the present investigation, the murine colitis was successfully induced using dextran sulphate sodium (DSS) and subsequently treated with APS for a duration of 7 days. APS exhibited significant efficacy in reducing the disease activity index (DAI), colonic weight index, the index of colonic weight/colonic length. Furthermore, APS mitigated colonic pathological injuries, restored the colonic length, elevated the immunoglobulin A (IgA), transforming growth factor-β1 (TGF-β1) and interleukin (IL)-10 levels, while concurrently suppressing IgG, IgM, IL-6, tumor necrosis factor alpha (TNF-α) levels. Crucially, the quantities of MBCs, IgA+MBCs and forkhead box P3 (Foxp3+) MBCs were notably increased along with a concurrent decrease in IgG1+MBCs, IG2a+MBCs, IgG2b+MBCs after APS administration in colitis mice. Additionally, the Mitotracker red expressions of MBCs and their subgroups demonstrated a significantly up-regulation. Meanwhile, the transcriptomics analysis identified mitochondrial metabolism as the predominant and pivotal mechanism underlying APS-mediated mitigation of DSS-induced colitis. Key differentially expressed genes, including B-cell linker (BLNK), aldehyde dehydrogenase 1A1 (ALDH1A1), B-cell lymphoma 6 (BCL-6), B-lymphocyte-induced maturation protein 1 (Blimp-1), paired box gene 5 (PAX5), purinergic 2 × 7 receptor (P2X7R), B Cell activation factor (BAFF), B Cell activation factor receptor (BAFFR), CD40, nuclear factor kappa-B (NF-κB), IL-6 and so on were implicated in this process. These mRNA expressions were validated through quantitative polymerase chain reaction (qPCR) and immunohistochemistry. These findings revealed that APS effectively restored MBCs and their balance to ameliorate DSS-induced colitis, which was potentially realized via promoting mitochondrial metabolism to maintain MBCs activation.