Xylooligosaccharide and Akkermansia muciniphila synergistically ameliorate insulin resistance by reshaping gut microbiota, improving intestinal barrier and regulating NKG2D/NKG2DL signaling in gestational diabetes mellitus mice

Abstract

Xylooligosaccharides (XOS) ameliorate insulin resistance (IR) in gestational diabetes mellitus (GDM) probably by propagating Akkermansia muciniphila (Akk). This study aimed to investigate the effects and mechanisms of XOS, Akk and combination on IR in GDM mice/pseudo-germ-free (PGF) mice. Female mice were fed with AIN-93 (n = 19) and high fat diet (HFD) (n = 206). After 4 weeks, HFD-fed mice were further allotted to HFD, GDM, GDM + XOS, GDM + Akk, GDM + XOS + Akk, GDM + PGF, GDM + PGF + XOS, GDM + PGF + Akk, and GDM + PGF + XOS + Akk groups (n ≥ 19). GDM was induced by intraperitoneally injecting streptozotocin and PGF was established by intragastrically administrating antibiotic cocktails. XOS (500 mg/kg·BW) or/and Akk (4 × 10⁸ CFU) were gavaged once a day for 10 days. Fasting blood glucose (FBG), insulin, oral glucose tolerance test (OGTT) and insulin signaling pathway were determined. Gut microbiota were detected by 16S rRNA sequencing and absolute quantities of Akk by qRT-PCR. Intestinal tissues were stained by Hematoxylin-Eosin and Periodic acid-Schiff-Alcian blue staining. Occludin and Zonula occludens-1 (ZO-1) in intestine, Natural killer group 2 member D (NKG2D) on intestinal epithelial lymphocytes (IELs) and NKG2D ligands (NKG2DL) on intestinal epithelial cells (IECs) were detected by Western blotting. In GDM mice, XOS, Akk and XOS + Akk reduced (p < 0.05) the area under the curve of OGTT (AUC), insulin and homeostasis model assessment of insulin resistance (HOMA-IR), and increased (p < 0.05) protein kinase B (Akt) phosphorylation in liver and insulin receptor substrate 1 (IRS-1) phosphorylation in muscle. Furthermore, XOS + Akk reduced (p < 0.05) FBG and increased (p < 0.05) Akt phosphorylation in muscle and IRS-1 phosphorylation in liver. XOS, Akk and XOS + Akk reshaped gut microbiota with XOS + Akk exhibiting the greatest effectiveness. XOS increased (p < 0.05) Akk and clearance of gut microbiota abolished such effect. XOS, Akk and XOS + Akk reduced (p < 0.05) the small intestine Chiu’s score and the colon Dieleman’s scores, increased (p < 0.05) ZO-1 and Occludin, and reduced (p < 0.05) NKG2D on IELs and NKG2DLs (H60, MULT-1, Rae-1ε) on IECs. Moreover, XOS + Akk reduced (p < 0.05) MULT-1 in duodenum. Collectively, XOS and Akk synergistically ameliorate IR by reshaping gut microbiota, improving intestinal barrier and regulating NKG2D/NKG2DL signaling in GDM mice.