IGF-1 acts independent of TPO signal pathway to promote thrombopoiesis. (A) Peripheral platelet counts in C57BL/6J-Mpl^hlb219/J and WT mice injected with saline or rhIGF-1 for 7 days. (B) Fold induction of platelet counts on days 3 and 7 in C57BL/6J-Mpl^hlb219/J and WT mice after rhIGF-1 injection. Each group contained 6 to 7 mice. (C-D) Number of c-kit⁺ cells (C) and CD41⁺CD42b⁺ expression on c-kit⁺ cells (D) after stimulation with or without 100 ng/mL rhIGF-1 for 3 and 7 days. (E-F) Proplatelet-forming MKs (E) and culture-derived platelets (F) from c-kit⁺ cells cultured with or without 100 ng/mL rhIGF-1 for 8 days, c-kit⁺ cells were isolated from C57BL/6J-Mpl^hlb219/J or WT mice and were then cultured in the presence of 10 ng/mL rmIL-3. (G) western blot analysis of ERK1/2 and Akt phosphorylation in mouse-derived MKs from WT C57BL/6 mice after exposure to rhIGF-1 or rhTPO for 15 minutes. (H-I) Proplatelet-forming cells (H) and culture-derived platelets (I) from WT mouse-derived MKs cultured with rhIGF-1 or rhTPO for 3 days. Mouse-derived MKs were cultured from WT c-kit⁺ cells stimulated with rhTPO for 5 days in the presence of 10 ng/mL rmIL-3. *P < .05, **P < .01.