Generation of sarcolipin heart-specific transgenic mice and molecular mechanism of atrial chamber-specific expression

体内超声心动图和血流动力学研究表明，与年龄匹配的对照组小鼠相比，肌肉磷脂（SLN）心脏特异性转基因小鼠的心功能，尤其是舒张功能受损。虽然SIN心脏特异性转基因小鼠没有表现出心肌肥厚或扩张，但心肌肥厚的分子标志物如ANF和BNP上调，提示SLN心脏特异性转基因小鼠心脏重构被掩盖。这些数据表明，SLN通过调节SERCA2a活性在心房功能中发挥重要作用。小鼠肌磷脂启动子及其转录调控分析我们克隆了一个包含小鼠SLN基因5'侧区的2.3千碱基对DNA片段，并检测了维甲酸对其启动子活性的影响。用f1荧光素酶（-2237到+62个核苷酸）瞬时转染H9C2后，启动子活性增加了40倍。瞬时转染f1荧光素酶的一系列5‘→3’缺失构建体表明，SLN启动子活性完全激活的最小区域位于-326个核苷酸，RA的负调控元件位于-2237至-326个核苷酸之间。目前的数据表明，SLN mRNA的表达可能在转录水平上受到视黄酸的调节，至少在一定程度上是如此。此外，我们发现压力超载、视黄酸和甲状腺激素下调了SLN mrna的表达。

I. Cardiac dysfunction sarcolipin heart-specific transgenic miceIn vivo echocardiography and hemodynamic study demonstrated that cardiac function, especially diastolic function was impaired in sarcolipin (SLN) heart-specific transgenic mice when compared with those in age-matched control mice. Although SIN heart-specific transgenic mice did not exhibited either cardiac hypertrophy or dilation, molecular markers of cardiac hypertrophy such as ANF and BNP were up regulated, suggesting masked cardiac remodeling in SLN heart-specific transgenic mine. These data indicate that SLN play an important role in atrial function via regulation of SERCA2a activity.II. Anaiysisi of mouse sarcolipin promoter and its transcriptional regulationWe cloned a 2.3-kilobase pair DNA fragment encompassing the 5'-flanking region of the mouse SLN gene and examined the effect of retinoic acid on its promoter activity. Transient transfection of H9C2 with F1-luciferase (-2237 to +62 nucleotides) yielded a 40-fold increase in promoter activity. Transient transfection of a series of 5'→3' deletion constructs of F1-luciferase suggested that the minimal region for full activation of the SLN promoter activity is located up to -326 nucleotides and that negative regulatory elements of RA were located between -2237 and -326 nucleotides. The present data indicate that the expression of SLN mRNA is likely regulated by retinoic acid, at least in part, at transcriptional level. In addition, we found that pressure overload, retinoic acid and thyroid hormono down-regulated the expression of SLN mRNAs.