FMT effectively modulated the gut microbiome in the recipient aged mice. (A) α-diversity (Chao1 index and Shannon index) of bacterial communities in antibiotics-treated, aged, FMT-AA, FMT-YA, and young mice (n = 6 per group). (B-C) Principal component analysis (PCA) plot and UniFrac distance of microbial composition (n = 6 per group). (D) Average relative abundance of prevalent microbiota at the phylum level among the 5 groups. (E) Average relative abundance of prevalent microbiota at the genus level among the 5 groups (n = 6 per group). (F) Bar graph showing the differential microbiota between FMT-AA and FMT-YA mice at the gene level (n = 6 per group). (G) The flowchart of microbiota interventions. Specific pathogen-free (SPF) aged mice were given phosphate-buffered saline (PBS), Lachnospiraceae, or Clostridium by gavage for 4 weeks, after treatment with antibiotics for 3 days. Then, colony-forming unit (CFU) assay and transplantation assay were performed to assess the cellular function of purified LT-HSCs. (H) Absolute numbers of HSPCs in BM in PBS group vs Lachnospiraceae group (n = 5 per group). (I) BrdU incorporation in LT-HSCs (n = 5 per group). (J) Number of total colonies measured for LT-HSCs in methylcellulose (n = 5 per group). (K) Donor-derived CD45.2⁺ reconstitution in CD45.1⁺ mice at 16 weeks after HSC transplantation (n = 5 per group). (L) Absolute cell number of donor-derived HSPCs in BM from recipient mice in HSC transplantation assay (n = 5 per group). (M) Intestinal permeability measured by FITC-dextran in blood (n = 5 per group). Graphs show mean ± SEM, with statistical significance determined by Student t test. ∗P < .05, ∗∗P < .01.