妊娠心肌肥厚预适应现象的实验证明及FoxO3a对预适应心肌保护的贡献

Myocardial hypertrophy is one of the important etiologies for heart failure. We have provided first evidence for a phenomenon termed myocardial hypertrophic preconditioning (MHP). However, many issues on this phenomenon and potential mechanisms are still unknown，for example，whether physiologic myocardial hypertrophy, such as pregnancy-causing hypertrophy, has preconditioning effects？and if so what are the underlying mechanisms？ Our preliminary experimental results demonstrated that pregnancy-causing myocardial hypertrophy not only can render the heart to resist pathological myocardial hypertrophy after labor for some time, but also can slow the progression of heart failure. We further screened out three key proteins that potentially contribute to preconditioning effects: Forkhead box O3 (Foxo3a), Murf1 (Muscle specific RING-finger protein-1) and OTR (oxytocin receptor). According to the findings in our previous studies and other research literature, we hypothesized that the increasing of Ang II during pregnancy would generate functional and molecular memory in the process of physiological myocardial hypertrophy, in which the expressive levels and/or activity of myocardial Foxo3 and other proteins are changing at the same time to contribute to preconditioning effects. This process can be regulated by heart-failure-related pathophysiological processes such as autophagy, apoptosis, or oxidative stress, and consequently inhibiting the following pathological myocardial hypertrophy and slowing the heart failure process. This project will focus on investigating the following subjects from various experimental levels of animal, cell and molecular biology: (1): The characteristics of pregnant hypertrophy preconditioning in function, histology and molecular biology. (2): Ang II is the hypertrophy preconditioning factor. (3): The effects and mechanisms of Foxo3a in pregnant hypertrophic preconditioning. We believe that the finishiment of this project would contribute to provide new therapy approaches for heart failure.

心肌肥厚是心衰重要原因之一，我们首证了心肌肥厚预适应现象（Circulation. 2015），但妊娠引起的生理性心肌肥厚是否有预适应效应，如有，其机制如何，均属未知。预实验初示存在妊娠心肌肥厚预适应现象，并进一步筛选出三个重要分子：FoxO3a、MuRF1和催产素受体OTR。因此，我们假设妊娠期Ang II升高引起生理性心肌肥厚，伴随心肌FoxO3a等蛋白的改变将产生分子记忆，可能通过相应信号通路调控细胞生长和凋亡等病生过程从而抑制后续病理性心肌肥厚并延缓心衰进程。本项目拟从动物、细胞和分子生物学三个水平进行以下研究：1：妊娠肥厚预适应产生的时间窗，2：Ang II是否为肥厚预适应因子；3：FoxO3a在妊娠肥厚预适应中的作用。本项目的完成将首次验证妊娠心肌肥厚预适应现象及部分机制，为心衰干预治疗取得重取得重要进展。

研究背景：心肌肥厚是心衰重要原因之一，我们首证了心肌肥厚预适应现象，并在拓展研究中探索了运动作为生理性心肌肥厚预适应因子，可以发挥抑制病理性心肌肥厚及延缓心衰进展的作用。同为妊娠诱导的生理性心肌肥厚是否有预适应效应，如有，其机制如何，均属未知。本研究从动物、细胞和分子生物学等水平探索妊娠心肌肥厚预试验对病理性心肌肥厚和心力衰竭的影响及可能机制。.获得以下主要的结果和数据：.1.首次证明妊娠引起的生理性心肌肥厚可以抑制后续Ang II或TAC病理性刺激，表现为预适应组小鼠心肌细胞面积减少、心肌肥厚标志物水平下降。同样妊娠心肌肥厚预适应可以延缓TAC诱导的心力衰竭，表现为肺重/体重比值等指标降低，左室射血分数比值增加。2. 机制研究，首先检测小鼠分娩3周后心肌组织甲基化水平变化，发现和证实 FoxO3a、OTR等在分娩后母鼠心肌中的表达增加。进一步发现FoxO3a相关信号分子的变化，表现为预适应组小鼠心肌p-FoxO3a、p-GSK3β、β-Catenin、CyclinD-1的表达水平减少。3. 敲低FoxO3a增加p-FoxO3a、p-GSK3β、β-Catenin、CyclinD-1等蛋白表达。同样过表达FoxO3a则获得相反的结果。4.心脏敲低FoxO3a增加Ang II刺激或TAC引起的心肌肥厚，表现为心肌细胞面积增大，肥厚标志物表达上调。相反，过表达心肌FoxO3a则抑制Ang II刺激或TAC引起的心肌肥厚，表现为心肌细胞面积增大，肥厚标志物表达下调。心脏敲低FoxO3a增加TAC引起的心力衰竭，表现为小鼠肺重/体重比值增加、左室射血分数比值下降。相反，心脏过表达FoxO3a延缓TAC引起的心力衰竭，表现为小鼠肺重/体重比值下降、左室射血分数比值增加。.研究结论及意义：妊娠预适应通过下调FoxO3a基因甲基化水平，进而增加FoxO3a表达及作用GSK3β/β-Catenin/CyclinD-1通路发挥抑制心肌病理性肥厚及延缓心衰进展。研究结果丰富了心肌肥厚预适应理论，拓宽心衰研究视野，为病理性心肌肥厚及心力衰竭的防治提供新思路。此外，调节基因DNA甲基化水平及FoxO3a表达可能对心力衰竭的防治提供益处。