[NIX-mediated mitochondrial autophagy in pathogenesis of myelodysplastic syndrome anemia]

Objective: To investigate the change of NIX level of bone marrow nucleated red blood cells in anemia patients with myelodysplastic syndromes (MDS), to explore the significance of NIX-mediated mitochondrial autophagy in the pathogenesis of MDS anemia. Methods: A total of 54 patients with MDS diagnosed in the Department of Hematology of General Hospital, Tianjin Medical University from July 2015 to July 2016 were enrolled into the MDS group, 33 cases of immune thrombocytopenia or idiopathic leukopenia as controls.The level of NIX, the number of mitochondria, mitochondrial membrane potential, the level of reactive oxygen species (ROS) in GlycoA(+) nucleated red blood cells were measured by flow cytometry; the level of NIX mRNA was measured by PCR. Results: (1) The expression of NIX in GlycoA(+) nucleated red blood cells in high-risk MDS patients (0.61±0.24) was significantly lower than that in controls (0.79±0.16, P=0.027), and lower than that in low-risk MDS patients (0.81±0.15, P=0.011), while there was no significant difference between the controls and low-risk MDS patients. The expression of NIX mRNA in GlycoA(+) nucleated red blood cells in high-risk MDS group (0.36±0.09) was lower than that in the controls (1.44±0.41, P=0.027) and that in the low-risk group (1.02±0.22, P=0.012); there was no significant difference between the controls and the low-risk group. (2) The number of mitochondria in GlycoA(+) nucleated red blood cells in high-risk MDS patients (937.17±707.85) was significantly higher than that in the controls (513.49±372.33, P=0.019) and that in low-risk MDS patients (461.74±438.02, P=0.008); while there was no significant difference between low-risk MDS patients and the controls. (3) The level of mitochondrial membrane potential in GlycoA(+) nucleated red blood cells in high-risk MDS patients (0.33±0.18) was significantly lower than that in the controls (0.61±0.32, P=0.001) and that in low-risk MDS patients (0.61±0.34, P=0.001); with no significant difference between low-risk MDS patients and the controls. (4)The level of ROS in GlycoA(+) nucleated red blood cells in high-risk MDS patients (438.65±322.83) was significantly higher than that in the controls (242.77±136.87, P=0.006), and higher than that in low-risk MDS patients (197.40±95.07, P=0.001); no significantly different between low-risk MDS patients and the controls. (5) The number of mitochondria in GlycoA(+) nucleated red blood cell was positively correlated with the percentage of ring sideroblast (r=0.457, P=0.028) in the MDS patients.(6) The number of mitochondria in GlycoA(+) nucleated red blood cells was negatively correlated with the concentration of hemoglobin (r=-0.521, P=0.009) in high-risk MDS patients, but not correlated with the concentration of hemoglobin in low-risk MDS patients. Conclusion: NIX level is reduced in nucleated red blood cells of high-risk MDS patients, which leads to impaired mitochondrial autophagy, increased damaged mitochondria and apoptosis of nucleated red blood cells, thus related with anemia.