Objective To observe the effects of 3-methyladenine (3-MA) and rapamycin on autophagy activity and cell apoptosis of dust exposed rat pulmonary macrophages.
Methods A total of 120 male Wistar rats were administered with 50 mg/mL SiO2 dust by indotracheal intubation and divided into control, 3-MA, and rapamycin groups. The 3-MA and rapamycin groups were intraperitoneally injected with 1.5 mg/(kg& #183;d) 3-MA and 2 μg/(kg& #183;d) rapamycin every other day, for 28 d. Then the rats were neutralized on day 7, 14, 28, 60, and 90 to collect lung lavage followed by determining apoptosis rate of macrophages after centrifugation. Western blotting was used to detect the expression of autophagy protein light chain 3 (LC3) and autophagy regulatory protein Beclin1.
Results In the rapamycin group, the LC3 protein expressions at various time points were highter as compared with the control group; the early apoptosis rates of pulmonary macrophage sampled at five selected time points were lower for the former four time points but higher for the latter time point than the corresponding values in the control group (1.74& #177;0.73)%, (1.25& #177; 0.35)%, (1.44& #177;1.24)%, (3.70& #177;1.51)% and (36.98& #177;11.91)% vs.(5.63& #177;1.01)%, (4.95& #177;0.63)%, (4.10& #177;0.43)%, (6.75& #177;4.19)%, and (30.23& #177;11.05)%, respectively, all Ps < 0.0.5 except for day 90. In the 3-MA group, the LC3 protein expression levels were lower than those of the control group during exposure, but increased when the drug stopped, and returned to the level of the control group on day 90. In the 3-MA group, the early apoptosis rates of pulmonary macrophage were (2.86& #177;1.13)%, (8.80& #177;0.28)%, (6.84& #177;1.29)%, (2.54& #177;1.65)%, and (37.22& #177;16.22)%, the lowest value was found on day 7; the apoptosis rates were higher than those of the control group on day 14 and 28 (P < 0.05), lowered again on day 60, and showed no significant difference from the control group on day 90.
Conclusion The findings suggest that 3-MA or rapamycin interventions could induce pulmonary macrophage autophagy activity to varied degrees and in negative association with the apoptosis rate of pulmonary macrophages.
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