基于MicroPET心肌动态显像技术研究棕色脂肪移植对糖尿病小鼠心肌糖代谢异常的作用及机制

The abnormality in myocardial energy substrate metabolism is the key mechanism for the occurrence of diabetic heart failure, in which the abnormality in myocardial glucose metabolism is closely associated with both diabetic ventricular remodeling and cardiac function abnormality. Active brown adipose tissue (BAT) plays important roles in maintaining stable glucose and lipid metabolisms as well as improving insulin sensitivity and endocrine regulation. BAT transplant is a new way to activate endogenous BAT. Therefore, we hypothesize that BAT transplant could improve abnormality of myocardial glucose metabolism in diabetic subjects, reverse left ventricular remodeling, and promote cardiac function. To this end, we selected diabetic mice as the study objectives and applied noninvasive imaging techniques including 18F labeled deoxyglucose microPET myocardial dynamic imaging and cardiac ultrasound to observe the in vivo effects of BAT transplant, transplanting different amount of BAT and BAT transplanting time on myocardial glucose metabolisms, left ventricular structure and cardiac functions with the hope to reveal whether BAT transplant is an effective method for improving myocardial glucose metabolism abnormalities in diabetic mice. Moreover, we further compared and analyzed the changes in various metabolism-related indexes of blood plasmas, changes in myocardial tissue pathology, as well as changes in myocardial glucose metabolism, insulin signal pathway, and expressions of key proteins regulating energy metabolisms after BAT transplant of these diabetic mice to reveal the mechanism of BAT transplant on improvement of myocardial glucose metabolism abnormities in diabetic mice.

心肌能量底物代谢异常是糖尿病心衰发生的关键机制，其中心肌糖代谢异常与糖尿病心室重构、心功能异常密切相关。活性棕色脂肪（BAT）有维持糖、脂代谢的稳态、改善胰岛素敏感性和内分泌调节的作用，其移植是新型的内源性BAT激活方式。我们设想：通过BAT移植改善糖尿病心肌糖代谢异常，逆转左室重构、改善心功能。基于上述设想：课题组将以糖尿病小鼠为研究对象，运用无创影像技术（18F标记脱氧葡萄糖microPET心肌动态显像和心脏超声），在体观察和比较是否移植BAT、移植不同质量的BAT、BAT移植后不同时间心肌葡萄糖代谢的变化及差异、左室结构和心功能的改变，揭示BAT移植可能是改善糖尿病心肌糖代谢异常有效的方法；比较BAT移植后血浆中各代谢相关指标的变化、心肌组织病理学改变、心肌糖代谢、胰岛素信号通路和能量代谢调节关键蛋白的变化，揭示BAT移植改善糖尿病心肌糖代谢异常的作用机制。

中国糖尿病患病人数已高居全球第一位，疾病负担日趋加重。糖尿病患者易发心衰，严重影响了糖尿病患者的预后，但目前尚缺乏无创、早期、准确反映糖尿病心肌病变、预警糖尿病心衰早期阶段的技术手段，也缺乏有效的干预措施和方法。本项目首先通过临床研究发现糖尿病患者普遍存在心肌葡萄糖代谢异常，运用回归分析男性、胰岛素抵抗指数（HOMA-IR）和非酒精性脂肪肝（NAFLD）是心肌FDG摄取差的独立危险因素，行关联分析发现，胰岛素抵抗（IR）的风险随心肌SUVmax的减低而逐渐增加，二者近似线性负相关。本项目以无创影像技术（microPET、心脏超声）为主要研究手段，以量化的方式、在体动态观察糖尿病小鼠心肌糖代谢的动态变化及与心室重构和心功能的相互关系，发现糖尿病小鼠心肌SUVmean与E/e’呈显著负相关（r=-0.618，P=0.014），与e’呈显著正相关（r=-0.618，P=0.004），阐明了心肌糖代谢异常是糖尿病左室心功能异常和心衰的关键环节。与此同时，本项目发现心肌胰岛素抵抗、胰岛素信号通路选择性转录障碍、葡萄糖跨膜转运蛋白（Glut-1和Glut-4）表达减低可能是糖尿病小鼠心肌糖代谢异常的可能机制。本项目将4周龄db/+小鼠肩胛间aBAT（0.216±0.159）g种植于糖尿病小鼠（db/db小鼠）肩胛间皮下。研究发现，移植后8周，与假手术组（db/db小鼠）比较，移植组小鼠体重、随机血糖显著减低，糖耐量及胰岛素耐量改善，心脏舒张功能及心肌糖代谢水平显著高于假手术组；行Western blot检测发现，BAT移植改善心肌糖代谢异常的机制可能与糖尿病整体代谢异常的改善、心肌胰岛素信号通路（PI3K/AKT通路和p38 MAPK/ERK通路）选择性转录障碍减轻，Glut4表达增加有关。本项目以糖尿病心衰过程中心肌能量代谢底物的异常-葡萄糖利用减低为着眼点，以无创影像技术（microPET、心超）为主要研究手段，拓宽了microPET心肌糖代谢显像的应用领域及范围，为该影像技术在代谢性疾病中的应用和推广奠定了基础；也阐明了BAT的激活有望成为改善糖尿病心肌糖代谢异常的新的靶点，为新型心肌能量底物代谢调节剂的研发提供了依据。