Downregulation of intrinsic apoptosis pathway in erythroblasts contributes to excessive erythrocytosis of chronic mountain sickness.

Chronic mountain sickness (CMS) has a higher incidence in the plateau region and is characterized by excessive erythrocytosis and hypoxemia. Bcl-2 family plays an important role in the process of erythropoiesis and the regulation of apoptosis. This study aimed to examine the change in apoptosis of erythroblasts in CMS patients and explore the involvement of Bcl-2 family. Bone marrow mononuclear cells (BMMNCs) were isolated by density gradient centrifugation from 18 CMS patients and 17 control participants. The apoptotic rate, mitochondrial membrane potential (MMP), the protein expression of caspase-3, TNFR, Fas, Bcl-2, Bax and Cyt-C were examined by flow cytometry, and mRNA expression was determined by real-time PCR. The results showed that apoptotic rate of erythroblasts was lower and MMP was higher in CMS group than in control group. The mRNA and protein expression levels of Bcl-2 were higher while Bax level was lower in CMS group than in control group. In CMS group, the apoptosis rate of CD71+ erythroblasts was negatively correlated with the ratio of CD71+ cells in BMMNCs and positively correlated with hemoglobin level. In conclusion, erythroblasts apoptosis is decreased due to the regulation of the expression of Bcl-2 family members in the erythroblasts of CMS patients.