Igf2bp2 deletion ameliorates aging-associated myeloid-biased HSC expansion and myeloid skewing in PB. Fluorescence-activated cell sorting (FACS) analysis of the frequencies of CD150⁺ (high and low) HSCs (CD150⁺CD34⁻LSK) (A-C), myeloid-restricted HSCs (CD41⁺CD150⁺CD34⁻LSK) (D-F), and myeloid-biased (CD150^highCD34⁻LSK) (G-H) vs balanced HSCs (CD150^lowCD34⁻LSK) in total BM cells from Igf2bp2^+/+ and Igf2bp2^−/− mice at young (range: 3-6 months), middle (range: 9-15 months), and old (range: 18-27 months) age. (A,D,G) Graphs show the number of HSCs per 10⁶ total BM cells. Data points represent 6 to 24 individual mice per group. (B,E,I) Representative FACS plots. (C,F) Scatter plots depict the number of HSCs per 10⁶ total BM cells. The slopes were analyzed by linear regression; group-wise (dis)agreement of models was determined with a Wald test (C), regression coefficients R² = 0.7517 for Igf2bp2^+/+ male mice, R² = 0.7174 for Igf2bp2^−/− male mice; R² = 0.709 for Igf2bp2^+/+ female mice, and R² = 0.8576 for Igf2bp2^−/− female mice; (F) R² = 0.851 for Igf2bp2^+/+ male mice, R² = 0.8504 for Igf2bp2^−/− male mice R² = 0.6363 for Igf2bp2^+/+ female mice, and R² = 0.5988 for Igf2bp2^−/− female mice. (H) Ratio of myeloid-biased HSCs to balanced HSCs of mice of the indicated age group, sex, and genotype. (J-K) The frequency of myeloid cells (including Gr1⁺ cells and CD11b⁺ cells) and lymphoid cells (including B220⁺, CD4⁺, and CD8⁺ cells) in PB of the indicated genotypes of male (J) and female (K) mice at young (range: 3-6 months) and old (range: 22-27 months) ages. Data points represent 6 to 17 mice per genotype per age. (A,D,G-H,J-K) Statistics were calculated by 2-way analysis of variance on log-transformed data (A,D,G), on logit-transformed data (H), or on original data (J-K), followed by Sidak’s test for multiple comparisons. The y-axes of panels A, D, and G are in log scale. (L) HSCs from young (range: 3-6 months) or old (27 months) donors were transplanted along with competitor total BM cells (CD45.1). Analysis of myeloid cells (including Gr1⁺ and CD11b⁺ cells) vs lymphoid cells (including B220⁺, CD4⁺, and CD8⁺ cells) in donor-derived cells in PB 16 or 20 weeks after transplantation. Lineage composition in donor-derived PB of recipients of CD150⁺ (high and low) HSCs from young and old donors (4-5 mice per group; left). Lineage composition in donor-derived PB of recipients of myeloid-biased HSCs (right; CD150^high) from young donors (9-10 mice per group; right). Note the myeloid skewing in transplantation of CD150⁺ (high and low) HSCs from old donors was rescued by Igf2bp2 depletion. Statistical significance of genotype-dependent differences between young and old donors was calculated by Welch’s t test. Data are expressed as the mean ± SD. ns, nonsignificant.