叶酸缺乏对斑马鱼胚胎心脏发育影响的实验研究

Effects of folic acid on the development of heart of zebrafish

目的 构建叶酸缺乏斑马鱼模型,观察叶酸缺乏胚胎的心血管发育异常表型,探寻预防叶酸缺乏导致心脏发育异常的最佳补充叶酸时期,并初步探讨叶酸缺乏导致心脏发育异常的机制.方法 利用二氢叶酸还原酶抑制剂甲氨蝶呤（MTX）以及使二氢叶酸还原酶基因（dhfr）表达阻抑两种方法 构建叶酸缺乏斑马鱼模型.并进行四氢叶酸挽救实验.在叶酸缺乏组胚胎发育不同阶段给予叶酸.观察并统计胚胎的心脏发育异常百分比、心脏发育异常表型、心率、心室收缩指数（VSF） 利用荧光显微造影的方法 探查心脏流出道发育状况.采用原位杂交以及Real-time PCR的方法 检测各组胚胎vmhc、amhc、tbx5和nppa的表达情况.结果 与对照组相比,（78.00±3.74）%的MTX处理组胚胎以及（68.00±6.32）%的dhfr表达阻抑组胚胎存在心脏发育异常,包括心脏形态异常、心率和VSF下降以及心脏流出道发育畸形.给予四氢叶酸可挽救叶酸缺乏组胚胎的异常表型.在受精后8～12 h给予叶酸后,MTX处理组（20.20%±3.77%）以及dhfr表达阻抑组（43.40%±4.51%）胚胎的心脏发育异常百分比降低最显著,心脏发育异常状况改善最明显.MTX处理组胚胎以及dhfr表达阻抑组胚胎的vmhc和amhc表达水平正常 tbx5及nppa的表达水平明显下降.给予外源性叶酸后,tbx5和nppa的表达在MTX处理组胚胎以及dhfr表达阻抑组胚胎中增强.结论 本实验构建的叶酸缺乏模型中存在四氢叶酸水平下降.在胚胎发育早期中段给予补充适量的叶酸可以最有效预防叶酸缺乏导致的心脏发育异常.叶酸缺乏对心室以及心房肌球蛋白的分化无干扰作用.叶酸缺乏导致胚胎心脏发育异常与tbx5和nppa的表达水平下调有关.

Objective To construct the folic acid deficient model in zebrafish and observe the abnormal cardiac phenotypes, to find the optimal period for supplementing folic acid that can most effectively prevent the heart malformation induced by folic acid deficiency, and to investigate the possible mechanisms by which folic acid deficiency induces malformations of heart. Method The folic acid deficient zebrafish model was constructed by using both the folic acid antagonist methotrexate （MTX） and knocking-down dhfr （ dihydrofolate reductase gene）. Exogenous tetrahydrofolic acid rescue experiment was performed. Folic acid was given to folic acid deficient groups in different periods. The percent of cardiac malformation, the cardiac phenotypes,the heart rate and the ventricular shortening fraction （VSF） were recorded. The out flow tract （OFT） was observed by using fluorescein micro-angiography. Whole-mount in situ hybridization and realtime PCR were performed to detect vmhc, amhc, tbx5 and nppa expressions. Result About （78.00 ±3. 74 ） % embryos in MTX treated group and （ 68. 00 ± 6. 32 ） % embryos in dhfr knocking-down group had heart malformations, including the abnormal cardiac shapes, the hypogenesis of OFT and the reduced heart rate and VSF. Giving exogenous tetrahydrofolic acid rescued the above abnormalities. Given the folic acid on 8-12 hours post-fertilization （hpf）, both the MTX treated group （20. 20% ± 3. 77% ） and dhfr knockingdown group（43.40% ±4.51% ） showed the most significantly reduced percent of cardiac malformation and the most obviously improved cardiac development. In folic acid deficient group, the expressions of tbx5 and nppa were reduced while the expressions of vmhc and amhc appeared normal. After being given folic acid to MTX treated group and dhfr knocking-down group, the expressions of tbx5 and nppa were increased.Conclusions The synthesis of tetrahydrofolic acid was decreased in our folic acid deficient model. Giving folic acid in the middle period, which is the early developmental stage, can best prevent the abnormal developments of hearts induced by folic acid deficiency. Folic acid deficiency did not disrupt the differentiations of myosins in ventricle and atrium. The cardiac malformations caused by folic acid deficiency were related with the reduced expressions of tbx5 and nppa.