## 3 Results
The effect of supplementation with NR on the relative abundance of gut microbiota at the class, order, family and species levels in CD- or HFD-fed ApoE/- mice are summarized in Table S2. In terms of SCFAs, both the HFD and HFD + NR groups resulted in lower concentrations of acetic acids and butyric acids in fecal samples than the CD and CD + NR groups (both _P-diet_ < 0.05) (Table S3), and supplementation with NR did not alter these concentrations. CD + NR resulted in higher concentrations of propionic acids than the CD, HFD and HFD + NR groups (_P-diet_\({}^{*}\)NR_ = 0.0220, _P-diet_ = 0.0357), and higher concentrations of isobutyric acids than the CD group (_P-diet_\({}^{*}\)NR_ = 0.0252, _P-NR_ = 0.0342) (Table S3). Correlations between the Relative Abundance of Gut Microbiota at Different Taxa Levels with Blood Biochemical Parameters, Gene Expressions in Cholesterol Metabolism, Atherosclerotic Lesions in the Aorta, and Fecal SCFAs Concentrations  
A total of 16 genera in 6 phyla levels had correlations with plasma biochemical parameters, hepatic and intestinal gene expressions in the cholesterol metabolism, atherosclerotic lesions in the aorta or SCFAs concentrations in fecal samples. The relative abundance of _Lactococcus_, which was lower in the CD + NR and HFD + NR groups than the CD and HFD groups, had positive correlations with fasting plasma TC: HDL-C and LDL-C: HDL-C ratios, and inverse correlations with the hepatic mRNA expression of HMGCR and CYP7A1 and fecal concentrations of acetic, propionic and butyric acids (all \(P\) < 0.05) (Figure 5). The relative abundance of _Bacteroides_, which was respectively lower in CD + NR and HFD + NR groups than the CD and HFD groups, had inverse correlations with fasting plasma concentrations of TC, HDL-C and non-HDL-C, and the percentage of atherosclerotic plaque in aorta and fecal concentrations of isobutyric acids (all \(P\) < 0.05) (Figure 5). The relative abundance of _Coriobacteraceae_UCG-002_, which was lower in the HFD + NR group than in the CD + NR and HFD groups, had positive correlations with the hepatic mRNA expression of PCSK9 and fecal concentrations of SCFAs, including acetic, propionic and isobutyric acids, and inverse correlations with the intestinal mRNA expressions of intestinal LXR-\(\alpha\) and hepatic ABCA1 and the percentage of atherosclerotic plaque in the aorta (all \(P\) < 0.05) (Figure 5). The relative abundance of the _Muribaculaceae_, _Alloprevtotulla_, _Alistipes_ or _Lachospiraceae_NKA136_group_, which were lower in both the HFD and HFD + NR groups compared to the CD and CD + NR groups, had positive correlations with the hepatic mRNA expression of HMGCR or fecal concentrations of acetic, propionic or butyric acids, and inverse correlations with fasting plasma concentrations of TC, HDL-C, non-HDL-C, glucose or TC: HDL-C and LDL-C: HDL-C ratios, and the percentage of atherosclerotic plaque in aorta or fecal concentrations of isobutyric acids (all \(P\) < 0.05) (Figure 5). The relative abundance of _Faecalibaculum_, which was higher in both the HFD and HFD + NR groups than the CD and CD + NR groups, had positive correlations with the percentage of atherosclerotic plaque in the aorta, and inverse correlations with the hepatic mRNA expressions of HMGCR and PCSK9 (all \(P\) < 0.05) (Figure 5). The relative abundance of the _[Eubacterium]_coprostanoligenes_group_, which was also higher in both the HFD and HFD + NR groups than the CD and CD + NR groups, had positive correlations with glucose concentrations (_P_ < 0.05) (Figure 5). Correlations between the relative abundance of gut microbiota at the class, order, family and species levels with other parameters were summarized and are presented in Tables S4 and S5, respectively.