OBJECTIVETo investigate the effect of PD0332991 (C24H29N7O2) on cell cycle, apoptosis, differentiation and self-renewal of hematopoietic stem cells (HSC) in mice.

METHODSThe self renewal ability of HSCs was measured by cobblestone forming cell assay (CAFC). The colony-forming cell (CFC) assay was used to quantify the changes of numbers and functions of HPC after the treatment of the compound. The expressions of self-renewal regulation genes, cell cycle-related genes, apoptosis-related genes were measured by real-time PCR. The cell cycle status and apoptosis of HSC and HPC were analyzed by flow cytometry.

RESULTSThere were obvious changes in cell cycle regulation between control and PD0332991 groups. HSCs in G1 phase increased significantly from 76.3% to 89.5% after treatment of PD0332991 (P<0.05) while cells in S, G2 and M phase reduced from 20.5% to 7.3% (P<0.05). HPCs in G1 phase also increased from 74% to 87.4% after treatment of PD0332991 (P<0.05) while cells in S, G2 and M phase reduced from 25.54% to 11.6% (P<0.05). The apoptotic fractions between control and PD0332991 groups had no statistical difference (P>0.05). After cultured with PD0332991, the expression levels of cell cycle genes CDK1, CyclinA2, CyclinF, p18, p19 and p27 decreased by 58.77%, 66.35%, 56.33%, 62.18%, 32.28% and 36.53% respectively, while expression of CDK7 increased by 27.27% (P<0.05). No visible expression difference was observed in apoptosis and self-renew related genes. After treatment of PD0332991, the self-renewal ability of HSC decreased significantly. There were almost no CFCs in PD0332991 group in CAFC assay. Similarly, the frequency of CFCs was dramatically lower in PD0332991 group.

CONCLUSIONThese results suggested that PD0332991 affected HSC/HPC from mice mainly through inhibiting the cell cycle rather than apoptosis. It also suggested that CDK4/6 might play a key role in the regulation of HSC/HPC.