Platelet depletion leads to the activation of HSCs and MPP2. (A) Platelet numbers in peripheral blood after a single injection of antiplatelet serum (control [Ctrl.], n = 4-12; depletion [Depl.], n = 3-12). The P values were calculated using 2-tailed unpaired Student t tests. (B) Mk numbers per field at 2 hours and 24 hours after platelet depletion (data points are Mk numbers per area from Ctrl. [n = 4] and Depl. [n = 7] mice). Cell cycle analysis of HSCs (LSK CD48⁻ CD150⁺) and MPP2 (LSK CD48⁺ CD150⁺) at 12 hours (Ctrl., n = 14; Depl., n = 17) (C) and at 24 hours (Ctrl., n = 8; Depl., n = 7) (D) after platelet depletion. Number of cells at 24 hours (Ctrl., n = 7; Depl., n = 5) (E) and at 48 hours (Ctrl., n = 7-8; Depl., n = 5-7) (F) after platelet depletion in 2 femur and 2 tibia. (G) Single CD41⁻ and CD41⁺ HSCs were sorted at 24 hours after platelet depletion and cultivated in liquid culture media supplemented with murine SCF, murine TPO, murine IL-3, and human Epo. Cell composition was analyzed after 14 days using May-Grünwald–Giemsa staining (number of analyzed colonies: CD41⁻ HSCs: 34 Ctrl. and 65 Depl.; CD41⁺ HSCs: 46 Ctrl. and 72 Depl.).