Involvement of Pkcε And Stat3 in Apoptosis of Hematopoietic Cells from Patients with Aplastic Anemia

Aplastic anemia (AA) is characterized by peripheral cytopenias in the setting of marrow hypoplasia. Recent reports have indicated that apoptosis plays an important role in injure to the stem and progenitor compartments in these patients. We previously revealed that impaired stem cells could be caused by excess IFN-γ in the serum or hypersensitivity to IFN-γ in the patients. To investigate the molecular mechanism of the apoptotic function of the serum from the patients against hematopoietic stem and/or progenitors, the apoptosis of CD34⁺ cells was assayed with flow cytometry 24 hr after incubation with the serum of normal controls, patients with non severe AA and severe AA. The CD34⁺ progenitors from the cord blood sample of healthy donors contained a significantly greater proportion of apoptotic cells after incubation with serum from SAA patients than incubated with serum from normal controls and NSAA. Moreover, the percent apoptosis of CD34⁺ cells after 24hr incubation with serum from NSAA was slight higher than that of normal controls. To further explore the mechanism of increased apoptosis induced by the serum of AA patients, the expression of phosphorylated protein kinase Cε(pPKCε) and phosphorylated signal transducer and activator of transcription 3 (pstat3) were measured after incubation with serum from the normal controls and AA patients using western blot. After incubation with serum from the AA patients, both pPKCε and pstat3 were overexpressed, correlating with the increased apoptosis induced by the same serum from AA patients. In addition, RT-PCR results shown that the stats gene expression had no difference after incubation with serum from AA patient. Together, these results implicate pPKCε and pstat3 may be involved in the apoptosis of CD34⁺ cells induced by sera from patients with aplastic anemia. Our findings may contribute to understanding the decreased number of stem cells characteristic of AA.