Total saponins of Panax ginseng (TSPG) promote erythroid differentiation of human CD34+ cells via EpoR-mediated JAK2/STAT5 signaling pathway

Ethnopharmacological relevance: Total saponins of Panax ginseng (TSPG), main constituents extracted from Panax ginseng, a highly valued traditional Chinese medicine, have been shown to be an effective agent on hematopoiesis. Objective: To investigate the effect and mechanism underlying in which TSPG promote human CD34(+) hematopoietic stem and progenitor cells to differentiate into erythroid-lineage cells. Materials and methods: The effect of TSPG on erythroid differentiation of purified CD34(+) cells derived from umbilical cord blood (UCB) was determined by methylcellulose assay system and colorimetry for hemoglobin content. The changes of EpoR expression in umbilical cord blood mononuclear cells (UCB-MNCs) and purified CD34(+) cells were detected with Western blotting and flow cytometry, respectively, and observed under laser scanning confocal microscope (LSCM). RT-PCR was performed to examine EpoR mRNA expression in CD34(+) cells. The effects of TSPG-pretreatment on Epo-induced JAK(2) and STAT(5) tyrosine phosphorylation were analyzed by immunoprecipitation. Results: The addition of TSPG (20-70 mg/L) increased the colony formation rate of BFU-E. TSPG (50 mg/L) alone used significantly increased the hemoglobin content, the addition of AG490 evidently reduced TSPG-induced elevation of hemoglobin content. TSPG increased the expression of EpoR on the surface membrane of CD34(+) cells but did not change the expression of EpoR in total UCB-MNCs. TSPG also increased the expression of EpoR mRNA in CD34(+) cells. TSPG markedly enhanced Epo-induced tyrosine phosphorylation of JAK(2) and STAT(5) in UCB-MNCs. Conclusion: These findings suggest that TSPG may enhance the erythroid differentiation of hematopoietic stem and progenitor cells via Epo/EpoR-mediated JAK(2)/STAT(5) signaling pathway. (C) 2009 Elsevier Ireland Ltd. All rights reserved.