Interferon-γ Attenuates the Survival Activity of G-CSF through PI3K/Akt Signaling Pathway in Mouse Multipotent Progenitor Cells.

Aplastic anemia (AA) is characterized by cytopenias caused by loss of stem cell and immunological relevance. We found out that impaired stem cell could be caused by excess of interferon-gamma (IFN-γ) in the serum or hypersensitivity to IFN-γ in patients with AA, notably severe AA. However, it is not clear how IFN-γ works in terms of the etiology of AA, as it exhibits diverse biological effects on cells. Thus, we investigated the essential role and the mechanism for the apoptotic function of IFN-γ against hematopoietic stem and/or progenitor cells. Although G-CSF augmented the surviving, proliferative, and differentiating activity in 32D cells, mouse multipotent progenitor cells, those effects of G-CSF were abolished by IFN-γ and they were susceptible to apoptosis with IFN-γ treatment. We focused on Akt, which was associated with the control of stem cell fate. IFN-γ did not affect the expression of Akt in 32D cells treated with G-CSF. Intriguingly, although Akt was strongly phosphorylated at Ser473 with G-CSF, IFN-γ attenuated phospho-Akt expression in dose- and time-dependent manner. As Akt is known to be phosphorylated through phosphatidylinositol-3-kinase (PI3K) pathway, we analyzed whether wortmannin, a specific inhibitor of PI3K, might have any synergistic effect on Akt phosphorylation in conjunction with IFN-γ. Wortmannin enhanced the inhibitory effect on Akt phosphorylated by G-CSF in collaboration with IFN-γ, suggesting that the activity of IFN-γ might converge on PI3K pathway. Next, to explore the downstream molecule of Akt, we examined the expression of BAD and NF-kB, which work downstream of Akt. IFN-γ increased the BAD protein reduced by G-CSF. Regardless of addition of IFN-γ, there was no alteration of NF-kB expression. IFN-γ exerted apoptosis against 32D cells through the caspase pathway. Taken together, these results suggest that IFN-γ could exert the inhibitory action on stem cells and/or progenitors by the interference of the PI3K / Akt signaling pathway in AA patients. Our findings may provide a suggestion of the treatment potential for AA such as anti-IFN-γ antibody and contribute the further understanding of AA in terms of immunological aberration.