Structural characterization and antidiabetic potential of a novel heteropolysaccharide from Grifola frondosa via IRS1/PI3K-JNK signaling pathways

A novel heteropolysaccharide from Grifola frondosa named GFP-W has been isolated and purified by DEAE Sephadex A-52 chromatography. Gas chromatography, fourier transform infrared spectroscopy, one-dimensional (1H- and 13C-) and two-dimensional (1H-1H COSY, 1H-13C HSQC, and 1H-13C HMBC) nuclear magnetic resonance spectroscopy were used to characterize its structure. The average molecular weight of GFP-W was 66.1 kDa. GFP-W mainly contained four kinds of linkage type units as β-D-GlcpA→, 1,2,6-α-Gal, →2)-α-Manp→, and →3)-α-L-Fucp-(1→. It could significantly increase the uptake of glucose in dexamethasone induced insulin resistant HepG2 cells by improving the mRNA and protein expression of insulin receptor substrate 1, phosphatidylinositol-3-kinase, and glucose transporter 4 upregulation and c-Jun N-terminal Kinase 1 downregulation. Moreover, antidiabetic activities of GFP-W were associated with significant changes in the extent of protein lysine acetylation, crotonylation, and succinylation levels. Our results provide a new hypoglycemic therapeutic role and an in-depth analysis on molecular mechanisms upon polysaccharides from G. frondosa.