Objective    To study the anti-apoptotic effect of melatonin in megakaryocytic cells and its molecular mechanism.     Methods    The apoptosis of human megakaryocytic cell line CHRF-288-11 was induced by serum deprivation. CHRF-288-11 cells were cocultured with 10% FBS

0.5% FBS

0.5% FBS+melatonin (20

50

100

200 and 500 nmol/L) or 0.5% FBS+TPO (50 ng/ml) for 72 h. Apoptotic cells were examined by Annexin V-FITC/PI

Caspase 3-FITC and JC-1 assays. To study the anti-apoptotic mechanism of melatonin

phospho-Akt and ERK1/2 were examined by flowcytometry with monoclonal antibodies.     Results    Melatonin (200 nmol/L) significantly protected CHRF cells from apoptosis. The population of Annexin V-positive cells

the activity of Caspase-3 and the cell rate in R2 region were significantly decreased from 42.9%

29.5%

47.7% to 31.7% (n=4

P0.05)

21.8% (n=4

P0.05)

37.2% (n=4

P0.05) respectively. The cell population positive for phospho-AKT and ERK1/2 was significantly increased from (5.9%±0.1%)

(6.1%±0.4)% to (9.5%±0.1%) (n=4

P0.05) and (9.3%±0.5%) (n=4

P0.05) respectively after 200 nmol/L melatonin treatment.     Conclusion    Melatonin protects megakaryocyte from apoptosis

and AKT and ERK1/2 signal pathways might be involved.