单纯性先天性心脏病中TBX5基因表达异常的机制

为探讨人类单纯性先天性心脏病患者中TBX5基因表达下调的可能原因, 应用变性高效液相色谱(DHPLC)方法检测100例单纯性先天性心脏病患者中TBX5基因上游1 200 bp调控区的突变情况; 应用甲基化敏感性限制性内切酶(MS-RE)法检测50例单纯性先天性心脏病患者和5例非先天性心脏病患者心肌组织TBX5基因启动子区两个CpG岛(转录起始点上游-49~-188 bp和-247~-464 bp处)的甲基化情况; 应用P-match软件预测小鼠Tbx5基因上游转录因子Nkx2-5的结合位点, 构建Nkx2-5表达载体转染小鼠H9C2(2-1)心肌细胞, RT-PCR及Western blotting检测Tbx5基因表达, 凝胶阻滞实验(EMSA)验证Nkx2-5和Tbx5基因的作用。结果在100例单纯性先天性心脏病患者中, 未检测到TBX5基因上游1 200 bp调控区突变; 非先天性心脏病患者和单纯性先天性心脏病患者在两个CpG岛存在相同的甲基化; 小鼠Tbx5基因转录起始点上游-312~-315 bp可能存在Nkx2-5的结合位点, 转染Nkx2-5表达载体后Tbx5基因在mRNA及蛋白质水平均有表达增高趋势, Nkx2-5在体外可以与Tbx5基因上游-312~-315 bp序列相结合。以上结果提示TBX5基因调控区突变和两个CpG岛的甲基化不是单纯性先天性心脏病患者心肌组织中TBX5基因表达下调的原因, TBX5基因表达下调可能由于NKX2-5的表达异常引起。

The mechanism of TBX5 abnormal expression in simple con-genital heart disease

To explore the mechanism of TBX5 abnormal expression in simple congenital heart disease (CHD), 100 CHD venous blood, 50 CHD heart tissues, and 5 non-CHD heart tissues were involved in this study. The mutation and methyla-tion in the 1 200 bp region upstream of TBX5 gene were detected by high-performance liquid chromatography (DHPLC) and methylation-sensitive restriction endonuclease (MS-RE), respectively. The binding site of NKX2-5 to Tbx5 predicted by P-MATCH software was validated by EMSA (Electrophoretic mobility shift assay). Tbx5 gene expression in mouse cardiac muscle cell H9C2(2-1) transfected with NKX2-5 expression vector was evaluated. No mutation was found in all patients. Both non-CHD and CHD heart tissues had the same methylation in the two CpG islands. Exogenous Nkx2-5 efficiently activated the transcription of the endogenous Tbx5 gene in H9C2 (2-1) cells. EMSA showed that the special binding band appeared when Nkx2-5 existed. These results indicates that the down expression of TBX5 might not be caused by mutation and methylation in the 1 200 bp region upstream of gene, and might be regulated by abnormal expression of NKX2-5 gene in heart muscle of CHD.