神经干细胞与RPE细胞的线粒体交换及其对RPE细胞增生和能量代谢的影响

Improvement of RPE cells growth and metabolism abilities by mitochondrial transfer of neural stem cells

背景 研究表明,干细胞可通过与损害靶细胞进行线粒体交换的方式修复受损细胞.视网膜色素变性疾病是以视网膜色素上皮（RPE）细胞凋亡为病理基础的眼病,干细胞是否能够通过上述机制进行治疗尚不清楚. 目的 研究神经干细胞（NSCs）能否通过线粒体交换机制改善RPE细胞的增生和能量代谢功能.方法 分离Long-Evans大鼠的视网膜进行RPE细胞的培养和传代,取第3代细胞用于实验,采用荧光显微镜检测RPE细胞中RPE65和Bestrophin蛋白的表达.小鼠NSCs C17.2细胞系和带绿色荧光蛋白（GFP）的C17.2细胞（GFP-C17.2细胞）进行培养和传代.分别采用线粒体特异性染色剂Mitotracker-green和Mitotracker-red标记RPE细胞和NSCs线粒体.将RPE细胞与小鼠NSCs进行共培养,用麦胚凝集素（WGA）标记隧道纳米管（TNT）,于激光扫描共焦显微镜下观察共培养的RPE细胞与小鼠NSCs间TNT中线粒体交换方式;采用流式细胞术检测RPE细胞与NSCs共培养前后的细胞周期改变;采用高效液相色谱（HPLC）技术检测共培养前后RPE细胞中ATP、ADP和AMP的质量分数. 结果 培养的第3代RPE细胞生长良好,RPE65和Bestrophin表达阳性细胞均＞85％.NSCs和RPE细胞中线粒体对Mitotracker-red标记的阳性率均＞95％.2种细胞共培养后24 h可见RPE细胞与NSCs间形成的膜性TNT结构,WGA染色呈蓝色荧光.随着时间的推移,NSCs中呈红色荧光的线粒体通过TNT进入呈绿色荧光的RPE细胞中.接受TNT线粒体后,处于G1期的RPE细胞比例较未进行线粒体交换的RPE细胞明显下降,差异有统计学意义（P=0.016）,S期细胞和G2/M期细胞比例分别增加了5％和2％,差异均无统计学意义（P=0.114、0.189）.HPLC检测结果显示,与NSCs共培养后,RPE细胞中ATP、ADP和AMP质量分数分别为（8.77 ±3.68）、（2.76±0.92）和（1.07±0.65） μg/mg,较共培养前的（11.29±2.29）、（3.12±0.95）和（1.59±1.22） μg/mg均有所下降,但差异均无统计学意义（P=0.370、0.668、0.553）.结论 NSCs通过建立的TNT能将线粒体单向传递给共培养的RPE细胞,线粒体交换可能是NSCs改善RPE细胞增生和代谢能力的机制之一.

Background Researches showed that stem cells can rescue damaged cells through mitochondrial transfer.This mode has been used to regenerative cell-based therapy.Retinal pigment degeneration is an eye disease of retinal pigment epithelial （RPE） cell apoptosis as pathogenetic mechanism.Whether stem cells can repair the target cells by above mechanism has not been clarified.Objective This study was to investigate the influence of mitochondrial transfer on the function of RPE cells.Methods The RPE cells of Long-Evans rats were isolated and cultured and the third generation of cells were used in sequential experiment.The cells were identified by detecting the expressions of RPE65 and Bestrophin proteins with immunofluorescence stain.Mouse neural stem cells （NSCs） （C17.2 strain） with green fluorescence protein （GFP） and without GFP were cultured.Mitotracker-green and Mitotracker-red staining were separately used to labeled the mitochondria of RPE cells and NSCs.RPE cells were cocultured with NSCs,and wheat germ agglutinin （WGA） was used to mark the tunneling nanotubes （TNT） between the two kinds of cells,and then the mitochondrial migration in TNT was exhibited by the laser scanning confocal microscope.The proportion of RPE cells in different cycles was assayed after marked with propidium iodide （PI） by flow cytometry.The contents of ATP,ADP and AMP in RPE cells were detected by high performance liquid chromatography （HPLC）.Results The third-generation of RPE cells grew well with the RPE65-and Bestrophinpositive rate 〉85%.The Mitotracker-red-labeled rates of NSCs and RPE cells were no less than 95%.TNT structure was seen to appear the blue fluorescence between RPE cells and NSCs 24 hours after co-cultured and the red dye mitochondria from NSCs migrated toward red dye mitochondria from RPEs with the lapse of time.The RPE cell proportion reduced in G1 phase and increased by 5% and 2% in the S phase and G2/M phase respectively after mitochondrial transfer than before （P=0.016,0.114,0.189）.The contents of ATP,ADP and AMP in the RPE cells were （8.77 ±3.68）,（2.76±0.92） and （1.07 ±0.65） μg/mg after cell co-culture,and those before co-culture were （11.29±2.29）,（3.12±0.95） and （1.59± 1.22） μg/mg,without significant differences between them （P =0.370,0.668,0.553）.Conclusions NSCs can transfer normal mitochondria to co-cultured RPEs via TNT structure.Mitochondrial exchange might be one of therapeutic mechanisms of NSCs recuing damaged RPE cells.