Fig. 4

Reduced spermidine in ApoE4-TR mice following nerve injury. (A) Heatmap displaying the relative abundance of metabolites in the dorsal horn of the spinal cord in ApoE3-TR and ApoE4-TR mice 14 days after SNI. (B) PLS-DA of metabolites was conducted in ApoE3-TR and ApoE4-TR mice measured by both electrospray ionization in positive mode (ESI⁺) and negative mode (ESI⁻). (C) The Volcano plot of spinal dorsal horn metabolomics comparing ApoE3-TR and ApoE4-TR mice. (D) KEGG chord plot showing the relationship between the selected pathways and their corresponding metabolites. (E) ELISA measurement of spermidine levels in ApoE3-TR and ApoE4-TR mice before and 14 days after the SNI surgery. n = 3 biologically independent samples. (F, G) Representative HPLC chromatograms showing the levels of spermidine in the spinal dorsal horn of ApoE3-TR (F) and ApoE4-TR (G) mice after SNI. The peak area indicated by yellow arrowheads corresponds to spermidine. The x-axis represents retention time (min), while the y-axis represents absorbance (mAU). (H) Quantification of spermidine levels in ApoE3-TR and ApoE4-TR mice after the SNI. n = 3 biologically independent samples. (I) ELISA measurement of spermidine levels in primary astrocytes from ApoE3 and ApoE4 mice. n = 3 biologically independent samples. All data are expressed as mean ± SEM. Statistical comparisons were conducted with one-way ANOVA followed by Tukey’s post hoc test (E); and unpaired Student’s t-test (H, I). *P < 0.05, and **P < 0.01