基于脂源性Nrg4特异性表达和调控模式研究早期营养对肝脏脂代谢的影响和作用机制

The postnatal overfeeding induced by small rearing (SL) promoted the early onset and exaggeration of high-fat diet-induced obesity and NAFLD. It has estimated that the brown fat-enriched secreted factor neuregulin 4(Nrg4 ) preserves metabolic homeostasis through attenuation of hepatic lipogenesis and browning adipocytes are induced to develop in white adipose tissue in response to certain stimuli. Thus, we hypothesis that depot-specific expression and regulation of Nrg4 in adipose tissue is key machanism of early nuritional programmin induced hepatic lipogenesis disorder. In this study, we will obsevere that Nrg4 expression level in subcutaneous and omental adipose tissue and its associated with age or BMI in children and adolescents. Moreover,with animal model by small litter rats and dietary intervention by different fatty acids at weaning, we will observe the early nutrition environments on hepaticlipid synthesis , ACC and SREBP1c, and relationship with white, brown or browning markers in adipose tissue and Nrg4 expression. Furthermore, in vitro study, we investigated the regulation effect of ω3 PUFA on preadipocytes differenciation by obsevration of adipocytes size and beige selective marker, and confirm that molecular pathway of induced preadipocyte to beige adipocytes via a PPARγ- PRDM16 formation. Finially, we will confirm that transfenic expression of Nrg4 prevents postnatal overfeeding induced hepatic lipogenesis disorder. These results obtained are benefit for us to explore the regulation mechanism of Nrg4 and may provide the molecular target and method for early nutritional progamming intervention.

早期过度营养导致肝脏脂合成代谢程序化改变，增加高脂诱导的肥胖和NAFLD。基于脂肪组织来源的Nrg4对NAFLD的保护作用以及脂肪组织棕色变可能性，本研究假设，脂肪组织特异性表达和调控Nrg4是早期营养影响肝脏脂合成代谢改变的重要机制。本研究将观察儿童青少年脂肪组织中Nrg4的表达与年龄/BMI关系，通过小窝组饲养诱导哺乳期过度营养以及断乳后不同膳食脂肪酸干预，观察大鼠成年期肝脏脂代谢结局，脂肪组织棕色样变特异性标志和Nrg4表达水平，及其与肝脏脂代谢相关酶ACC和SREBP1c的关系。进一步，通过前脂肪细胞诱导分化，从细胞形态、分子标志证ω3 PUFA通过PPARγ-PRDM16途径促进前脂肪细胞棕色样变，调控Nrg4表达和分泌的机制。最后，应用Nrg4过表达小鼠，证明脂源性Nrg4对哺乳期过度营养诱导的肝脏脂代谢的保护作用。研究结果为NAFLD早期预防和治疗提供确切靶点和新的思路。

通过临床，动物模型和细胞培养方法，研究脂源性细胞因子神经调节蛋白4（neuregulin4， Nrg4）在儿童时期脂肪组织中的表达模式和早期不同营养环境对脂肪组织Nrg4表达的作用、机制以及与肥胖和非酒精性脂肪肝（NAFLD）的关系进行深入探讨。结果证明,儿童脂肪组织Nrg4的表达和分泌水平随儿童BMI及腰围的增加而下降，血清Nrg4水平是预测儿童NAFLD发生风险的特异性指标。进一步，应用生后小窝组喂养诱导的早期过度营养动物模型，证明早期过度营养抑制大鼠脂肪组织（BAT，WAT和beigeAT）棕色化、Nrg4表达水平以及线粒体功能相关基因（Nrf1、Tfam，Mfn1、Dnm1，SIRT1 et al.）表达，Nrg4水平的下降与其肥胖、NAFLD、肝脏脂合成代谢相关基因(SREBP-1c、ACC、SCD1)水平密切相关。断乳后高脂喂养则加剧小窝喂养大鼠成年后的不良结局，而断乳后富含ω3 PUFA膳食可促进早期过度营养大鼠白色脂肪细胞UCP1, PGC1α，ADRB3等棕色样细胞标志基因表达水平、提高线粒体数目和功能基因表达并增加脂肪组织Nrg4表达水平，恢复肝脏正常的脂代谢。体外研究显示，ω3 PUFA通过PPARγ途径促进脂肪细胞棕色样变，改善线粒体代谢功能（如增加白色脂肪细胞线粒体数目，提高白色脂肪细胞线粒体基础呼吸），从脂肪细胞形态、棕色样变化的功能和分子标志水平阐明增加Nrg4表达和分泌的机制。通过重组的Nrg4蛋白作用已发生脂肪变的HepG2细胞，证明Nrg4通过抑制脂合成基因SREBP-1c、ACC、SCD1等肝细胞脂合成酶的表达降低肝脂肪变性。研究结果为探寻NAFLD儿童早期预防的手段和确切的分子靶点提供科学依据。.