Low methyl-esterified ginseng homogalacturonan pectins promote longevity of Caenorhabditis elegans via impairing insulin/IGF-1 signalling

Panax ginseng C. A. Meyer (ginseng) is a medicinal plant widely used for promoting longevity. Recently, homogalacturonan (HG) domain-rich pectins purified from some plants have been reported to have anti-aging-related activities, leading us to explore the longevity-promoting activity of the HG pectins from ginseng. In this study, we discovered that two of low methyl-esterified ginseng HG pectins (named as WGPA-2-HG and WGPA-3-HG), whose degree of methyl-esterification (DM) was 16 % and 8 % respectively, promoted longevity in Caenorhabditis elegans. Results showed that WGPA-2-HG/WGPA-3-HG impaired insulin/insulin-like growth factor 1 (IGF-1) signalling (IIS) pathway, thereby increasing the nuclear accumulation of transcription factors SKN-1/Nrf2 and DAF-16/FOXO and enhancing the expression of relevant anti-aging genes. BLI and ITC analysis showed that the insulin-receptor binding, the first step to activate IIS pathway, was impeded by the engagement of WGPA-2-HG/WGPA-3-HG with insulin. By chemical modifications, we found that high methyl-esterification of WGPA-2-HG/WGPA-3-HG was detrimental for their longevity-promoting activity. These findings provided novel insight into the precise molecular mechanism for the longevity-promoting effect of ginseng pectins, and suggested a potential to utilize the ginseng HG pectins with appropriate DM values as natural nutrients for increasing human longevity.