从SNX3-Retromer复合体对STAT3的调控角度研究心肌肥大的病理机制

The intracellular transportation and subcellular localization of signal protein is the basis of their physiological function. SNXs-Retromer complex are anchored in the endosome membrane, directly bind to and recruit different signal protein, mediating their intracellular recycle and regulating cellular functions. Pathological myocardial hypertrophy is an important precursor lesion in heart failure. Recently, we have successfully observed early manifestations of cardiac injury in the heart specific SNX3 transgenic mice. SNX3 knockdown ameliorated abdominal aortic coarctation (AAC)-induced cardiac hypertrophy in SD rats. Further screening found that STAT3 (signal transduction and transcriptional activator 3), a transcription factor which is closely related to myocardial hypertrophy, was one of the target protein of SNX3. The modification of tyrosine phosphorylation is stimulative but unnecessary for the nuclear import of STAT3. Based on the above foundation, we proposed a hypothesis of SNX3-Retromer-STAT3 complex. We will focus on the following two questions: whether (1) the cytoplasmic STAT3 is recruited by SNX3-Retromer complex to the early endosome which acts as a platform, thereby facilitating the interaction of kinase JAK2 with STAT3, promoting the phosphorylation of STAT3 and then resulting in its nuclear translocation? (2) Whether the SNX3-Retromer complex carries STAT3 into nucleus through nuclear membrane, And whether the Retromer complex itself fused with the nuclear membrane, or dissociated from STAT3 in the nuclear? The implementation of this project will provide a direct evidence for the involvement of transcription factors in the endosomal recycle, and provide new insights into the mechanism of STAT3 participating in pathological myocardial hypertrophy.

信号蛋白的胞内转运及定位是其发挥生理功能的基础。分选连接蛋白（SNXs）-Retromer复合体锚定在内体膜，直接结合并募集不同的信号蛋白，介导其胞内循环，调节细胞功能。病理性心肌肥大是心衰的前驱病变，我们观察到心脏特异性SNX3转基因小鼠的心功能出现早期损伤表现，敲低SNX3可减轻腹主动脉缩窄所致心肌肥大。经筛查发现与心肌肥大密切相关的转录因子STAT3为其分选的靶蛋白之一。STAT3的磷酸化修饰有助于其入核，但非必需条件，本课题提出SNX3-Retromer-STAT3复合体假说，将重点研究SNX3是否：①通过特定结构域，募集胞质STAT3至早期内体“平台”上，便利激酶JAK2对其进行磷酸化修饰后诱导入核？②携带STAT3透过核膜转位入核？其本身是与核膜融合还是与STAT3共同入核后解离？本课题的实施将提供转录因子参与内体循环的直接证据，并为STAT3参与心肌肥大的机制提出新的见解。

信号蛋白的胞内转运及定位是其发挥生理功能的基础。分选连接蛋白（SNXs）-Retromer复合体锚定在内体膜，直接结合并募集不同的信号蛋白，介导其胞内循环，调节细胞功能。其中，SNX3是该家族中结构最简单的亚型，仅含有PX基本结构域，但其与心血管疾病特别是心脏疾病的关系尚未见报道。.病理性心肌肥大是心衰的前驱病变。通过实验研究，我们发现：1）在病理性心肌肥大及心衰模型下，SNX3显著上调；2）利用心脏特异性敲除SNX3（SNX3-cKO）小鼠、心脏特异性转基因小鼠（SNX3-cTg），发现SNX3加剧病理性心肌肥大向心衰的发展进程；3）在心肌细胞中，SNX3-retromer复合体与STAT3直接结合并促进STAT3磷酸化后入核，从而导致心肌损伤。.多柔比星（Dox）是临床上广泛用于治疗多种肿瘤的化疗药，但其严重的心脏毒副作用，限制了其临床应用。为了更加全面研究SNX3在心脏疾病中的作用，我们在整体动物及心肌细胞水平上，建立Dox心肌毒性模型，研究SNX3在该疾病模型下的作用。结果提示：1）在Dox诱导的心肌毒性模型中，SNX3显著下降，这与病理性肥大模型不同，提示SNX3在不同心肌损伤模型中可能发挥着不同的作用；2）在整体动物及细胞水平上，SNX3加重Dox心肌损伤；3）在心肌细胞水平上，SNX3结合并促进Cyt-C的线粒体释放，Cyt-C可能是SNX3-retromer的靶蛋白，且共定位于线粒体中。.本项目围绕SNX3介导的靶蛋白的细胞内转运调节，重点研究了SNX3对靶蛋白STAT3的细胞核方向转运在病理性心肌肥大中的作用，以及SNX3对靶蛋白Cyt-C线粒体释放在Dox心肌毒性中的作用，为防治心脏疾病提供新的理论依据。