[Effects of small RNA interference targeting mammalian target of rapamycin on paraquat-induced pulmonary fibrosis in rats].

Objective: To investigate the effects of small RNA interference targeting mammalian target of rapamycin (mTOR) expression on paraquat-induced pulmonary fibrosis in rats.
Methods: Human embryonic kidney cells HEK-293 were cultured in vitro. The mTOR small interfering RNA (mTOR-siRNA) expression plasmid transfection lentivirus was constructed, and non-specific sequence plasmid with no homology to mTOR gene was set as the control. Seventy-two healthy male Sprague-Dawley (SD) rats were randomly divided into normal saline (NS) control group, paraquat model group, mTOR unrelated sequence group, and mTOR-siRNA group, with 18 rats in each group. Paraquat poisoning animal model was reproduced by intraperitoneally injecting 20% paraquat solution 15 mg/kg, while the NS control group was intraperitoneally injected the same volumes of NS. Rats in the mTOR unrelated sequence group and mTOR-siRNA group were injected 1×10 ⁹ TU/mL lentivirus solution 50 μL into the airway, respectively, while in the NS control group and paraquat model group were injected the same volumes of NS. At 7, 14 and 28 days after treatment, 6 rats in each group were sacrificed respectively for lung tissue, the pathological changes and fibrosis of lung tissues were observed under light microscope. The levels of hydroxyproline (HYP) in lung tissues were determined by alkaline hydrolysis. The mRNA and protein expressions of mTOR in lung tissues were determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western Blot.
Results: Under light microscope, there was no obvious pathological changes in the lung tissues in the NS control group, while in the paraquat model group and mTOR unrelated sequence group, lung tissue in rats were damaged, there were a lot of inflammatory cell infiltration, a large number of matrix collagen and fibrous tissues hyperplasia, and gradually increased with time, and it was consistent with paraquat-induced lung tissue fibrosis process. The pathological and fibrotic changes in lung tissue of mTOR-siRNA group were obviously reduced after silencing mTOR gene. The levels of HYP and the expression levels of mTOR mRNA and mTOR protein of lung tissues in the paraquat model group and mTOR unrelated sequence group were continuously increased in time-dependent manner, and they were significantly higher than those in the NS control group at all of the time points, but no significant difference was found between mTOR unrelated sequence group and paraquat model group. In mTOR-siRNA group, silencing mTOR gene could inhibit paraquat poisoning induced HYP increase in lung tissue, and the expressions increase in mTOR mRNA and mTOR protein, the values were close to the levels of NS control group, and the significant difference was found as compared with paraquat model group at 7 days or 14 days, and the change was maintained to 28 days [7 days: HYP (μg/mg) was 1.13±0.06 vs. 1.25±0.07; 14 days: HYP (μg/mg) was 1.19±0.09 vs. 1.29±0.12, mTOR mRNA (2 ^{-Δ ΔCt} ) was 0.99±0.11 vs. 1.94±0.12, mTOR protein (gray value) was 0.39±0.08 vs. 0.75±0.09; 28 days: HYP (μg/mg) was 1.28±0.06 vs. 1.40±0.05, mTOR mRNA (2 ^{-Δ ΔCt} ) was 1.15±0.13 vs. 2.85±0.15, mTOR protein (gray value) was 0.45±0.10 vs. 0.86±0.12, all P < 0.05].
Conclusions: Lentivirus-mediated mTOR-siRNA could effectively inhibit the expressions of mTOR in lung tissues of paraquat-poisoned rats, and reduce the damage and fibrosis of lung tissues caused by paraquat.