Thrombopoietin Protects Neural Cells and Endothelial Cells from Apoptosis Via PI3K/AKT Pathway

Background: Thrombopoietin (TPO) is a hematopoietic growth factor that regulates the production of platelets and stimulates production and differentiation. The expression of TPO and TPO receptor (c-mpl) in the central nervous system (CNS) has been identified. However, the role of TPO in neural cells and endothelial cells were not clear.

Methods: C17.2 and human umbilical vein endothelial (HUVEC) cells were treated with CoCl₂, TPO, or TPO + CoCl₂. TPO was added into the culture medium 48 h before CoCl₂ treatment. The cell viability and apoptosis of each group were tested by Cell Counter Kit 8 (CCK-8) assay and flow cytometry. The expression of Caspase-3 and mitochondrial membrane potential (MMP) were then determined by flow cytometry with Caspase-3-PE and JC-1. The effect of TPO in the PI3K/AKT pathway was detected by using Western blot.

Results: TPO has a dose-dependent effect on the growth of C17.2 cells. LY-294002 pretreatment suppressed the TPO-induced AKT activation and abolished the prosurvival effect of TPO. Via the Bcl-2/BAX signaling pathway, TPO exerted an anti-apoptotic effect by suppressing mitochondria membrane potentials. We also investigated the protective effect of TPO on human endothelial cells. The cell viability of HUVECs decreased gradually with the enhancement of CoCl₂ at a gradient of chemical concentrations (r= -0.997). CoCl₂ dramatically increased apoptosis of HUVECs, whereas pre-treatment with TPO rescued cell apoptosis induced by CoCl₂ (P<0.01). Further investigation found that TPO decreased the expression of Caspase-3 and inhibited the reduction of MMP induced by CoCl₂ (P<0.05). TPO increased the activation of PI3K/AKT pathway in HUVECs.

Conclusion: TPO has a protective effect against apoptosis of neural cells and endothelial cells through activating the PI3K/AKT pathway, thus decreasing the expression of apoptosis protease Caspase-3 and inhibiting the reduction of MMP.