myocardin在低氧诱导肺血管内皮向平滑肌样细胞转分化中的作用

目的探讨低氧条件下肺动脉内皮细胞(PAEC)向平滑肌样细胞的转分化及myocardin在其转分化过程中的作用。方法经免疫磁珠法(用血小板内皮细胞黏附分子1做免疫分选标记)纯化分离的原代肺动脉内皮细胞,用:RNA干扰(RNAi)技术构建psimyocardin RNA表达载体抑制myocardin基因的表达。细胞分为常氧组(含21％O2,5％CO2和74％N2)、低氧组(含1％O2,5％CO2, 94％N2)、常氧+myocardin抑制组和低氧+myocardin抑制组,分别培养1 d、4 d和7 d。用逆转录-聚合酶链反应法(RT-PCR)检测myocardin mRNA的表达;免疫荧光检测平滑肌特异性标志物α-平滑肌(α-SM)肌动蛋白的表达,结合形态学鉴定平滑肌样细胞的转分化。结果(1)免疫荧光检测PAEC中α-SM-肌动蛋白阳性率在低氧4 d组(0．96‰±0．08‰)明显低于7 d组(2．07‰±0．06‰,P< 0．01),阳性细胞呈梭形或多角形,而常氧组和低氧1 d组均未见α-SM-肌动蛋白的阳性表达;(2)RT- PCR显示myocardin mRNA的表达在低氧4 d组(0．14±0．01)明显低于低氧7 d组(0．23±0．03, P<0．01),常氧组和低氧1 d组均未检测出其表达。(3)RNAi沉默myocardin基因表达后,其mRNA水平明显低于对应的低氧4 d组(0．03±0．02)和低氧7 d组(0．05±0．01,P<0．01);平滑肌样细胞的转分化率也明显降低(0．19‰±0．07‰,0．21‰±0．04‰,P<0．01)。以上每组重复3次。结论PAEC中存在少数细胞具有转分化为平滑肌样细胞的潜能,低氧可明显促进其转分化,myocardin在此转分化过程中起重要作用。

The role of myocardin in hypoxia-induced transdifferentiation of pulmonary artery endothelial cells into smooth muscle-like cells

OBJECTIVE: To investigate the transdifferentiation of pulmonary artery endothelial cells (PAECs) into smooth muscle-like cells under hypoxia and the role of myocardin therein. METHODS: Recombinant plasmid psimyocardin (pSi), capable of silencing the expression of myocardin gene, was constructed by RNAi to be used to transfect the PAECs. Endothelial cells of adult pig pulmonary small arteries were purified by immunomagnetic purification technique, and divided into 4 groups: normoxia group (to be cultured in normoxic cell culture box containing 21% O(2), 5% CO2, and 74% N(2)), normoxia + pSi group, hypoxia group (to be cultured in cell box containing 1% O(2), 5% CO2, and 74% N(2)), and hypoxia + pSi group to be cultured for 1, 4, and 7 days respectively. Indirect fluorescence technique and morphological examination were used to identify the smooth muscle (SM) -like cells and the alpha-SM-actin positive cell ratio. RT-PCR was used to detect the mRNA expression of myocardin. RESULTS: Alpha-SM-actin positive cell could not be seen in the normoxia group and hypoxia 1 d group. The alpha-SM-actin positive cell rate of the hypoxia 7 days group was 2.07% +/- 0.06%, significantly higher than that of the hypoxia 4 d group (0.96% +/- 0.08%, P < 0.01). mRNA expression of myocardin gene could not be seen in the normoxia, normoxia + pSi, hypoxia 1 days, and hypoxia + pSi 1 days groups. The mRNA expression of myocardin gene of the hypoxia 7 days group was 0.23 +/- 0.03, significantly higher than that of the hypoxia 4 days group (0.14 +/- 0.01, P < 0.01). The mRNA expression levels of myocardin gene of the hypoxia + pSi 4 days and 7 days groups 0.03 +/- 0.02 and 0.05 +/- 0.01, both significantly lower than those of the hypoxia 4 days and 7 days groups respectively (0.14 +/- 0.01 and 0.23 +/- 0.03, both P < 0.01). The SM-like cell transdifferentiation rates of the hypoxia + pSi 4 days and 7 days groups were 0.19% +/- 0.07% and 0.21% +/- 0.04% respectively, both significantly lower than those of the corresponding hypoxia groups (0.96% +/- 0.08 and 2.07% +/- 0.06% respectively, both P < 0.01). CONCLUSION: Some PAECs have the potential to transdifferentiate into SM-like cells and may be one of the resources of muscularization of peripheral small vessels. Hypoxia remarkably promotes this transdifferentiation and myocardin may play an important role in this process.