·To investigate the effects of low-dose decitabine on the biological behaviors of proliferation and apoptosis of bone marrow mesenchymal stem cells (MSC) derived from the patients with primary immune thrombocytopenia (ITP).

·Ten patients with ITP onset who were outpatients or inpatients in the Department of Hematology, Renji Hospital, Shanghai Jiao Tong University School of Medicine, from April 2020 to October 2021 were included, and 10 non-ITP patients without bone marrow abnormalities were included as controls (normal control, NC). The bone marrow aspiration specimens were collected, MSCs were isolated, and flow cytometry was used to detect their surface antigenic markers. Differences in MSC proliferation levels between the ITP patients (MSC-ITP) and the controls (MSC-NC) were detected by using the CCK-8 kit and the EdU cell proliferation assay kit, and the changes in cell morphology were detected by using microtubule fluorescent probes. Apoptosis was observed by using Hoechst 33258 staining, and the level of apoptosis was detected by using Annexin V-FITC/PI apoptosis double-staining kit. The optimal concentration and treatment time of decitabine to promote the proliferation of MSC-ITP were explored by treatment with different concentrations and different durations. Western blotting was performed to detect the expression of apoptosis-related proteins and the effect of decitabine.

·Compared with MSC-NC, MSC-ITP showed abnormal morphology, more nuclear fragmentation and crinkling, reduced proliferation level in vitro, and increased basal apoptosis rate. The optimal working concentration of decitabine to stimulate MSC-ITP proliferation was 2.5 μmol/L, and the optimal treatment time was 24 h. After 2.5 μmol/L decitabine treating MSC-ITP for 24 h, cell nuclear morphology was improved, nuclei fragmentation and coalescence were reduced, and apoptosis rate was significantly decreased (P<0.05). Western blotting results showed that BAX, a mitochondrial apoptosis pathway-related protein, cystatin protease 3 (caspase3) and cleaved-caspase3 were reduced in MSC-ITP after treatment with decitabine (P<0.05).

·The MSCs originating from ITP patients' bone marrow have abnormal morphology, reduced proliferation level and increased basal apoptosis rate in vitro; low-dose decitabine can promote the proliferation and inhibit the apoptosis of the cells, which may be mediated through the mitochondrial apoptosis pathway.