α7nAChR-HIF1α-VEGF通路介导脂肪血管生成在母体尼古丁暴露致子代肥胖易感中的作用及机制

An array of statistical information provide a close reciprocal connection between maternal smoking and obese offsprings in their adulthood. However, the underlying fundamental mechanism remains to be investigated. Current approaches for characterizing obesity development focus on studying adipocytes; while recent studies have revealed that adipose vascular microenvironment plays an essential role in the modulation of obesity. Hypoxia inducible factor 1α(HIF1α) and vascular endothelial growth factor (VEGF) actively participate in the process of angiogenesis. Nicotine can enhance the expression of VEGF to facilitate angiogenesis in tumor through specifically acting on α7-nicotinic acetylcholine receptor (α7nAChR) . It has been reported that both the expression of HIF1α and VEGF is elevated in obese mice and the high level of VEGF in adipose tissue contributes to angiogenesis and adipogenesis. In our recent study, it was found that the expression of VEGF, HIF1α and CD34 in adipose tissue was upregulated and obesity susceptibility was also increased by maternal nicotine exposure. Theoretically, it is speculated that nicotine can be combined with α7nAChR in fetal adipose tissueto activate HIF1α-VEGF passway, promote angiogenesis and hyperplasia of adipocytes, and then increase child obesity susceptibility. Therefore, this project is designed to investigate the role of α7nAChR-HIF1α-VEGF signal passway—mediated adipose tissue angiogenesis in offspring's obesity susceptibility induced by maternal nicotine exposure, and explore the links of “maternal smoking—abnormal expression of α7nAChR-HIF1α-VEGF pathway—increae of adipose angiogenesis—hyperplasia of adipocytes—obesity susceptibility”. This study has important significance in elucidating the developmental origin of obesity caused by maternal nicotine exposure and in searching for early intervention approches for it.

资料显示母体吸烟与子代肥胖关系密切，但机制不清。传统肥胖研究多关注脂肪细胞，新进展提示脂肪血管微环境在肥胖发生中至关重要。已知HIF1α、VEGF参与血管生成；尼古丁通过α7nAChR上调VEGF表达，促进肿瘤血管生成；肥胖鼠脂肪高表达HIF1α及VEGF；脂肪高表达VEGF促进血管及脂肪增生。我们发现母体尼古丁暴露增加子代脂肪HIF1α、VEGF和CD34表达及肥胖易感并提出假说：尼古丁与胎脂肪α7nAChR结合，激活HIF1α-VEGF通路，促进血管及脂肪增生，增加子代肥胖易感。为此，本项目拟研究α7nAChR-HIF1α-VEGF通路介导脂肪血管生成在母体尼古丁暴露致子代肥胖易感中的关键作用，探讨 “母体尼古丁暴露—子代脂肪α7nAChR-HIF1α-VEGF通路异常—血管增生—脂肪细胞增生—肥胖易感”间联系。该研究对阐明母体吸烟致子代肥胖发生机制，探寻肥胖早期干预靶标具有重要意义。

肥胖是全球性公共卫生问题。孕期及哺乳期母体尼古丁摄入可致子代肥胖及代谢综合征易感性增加，但机制研究甚少。本项目旨在揭示脂肪组织血管生成在发育早期母体尼古丁暴露子代大鼠肥胖中的作用及机制。建立孕期及哺乳期母体尼古丁暴露致子代大鼠成年后肥胖易感模型，并检测代谢及脂肪血管生成相关指标、α7nAChR-Egr1-FGF2信号通路基因/蛋白表达。尼古丁分别处理不同细胞（3T3-L1、C3H10T1/2和HUVECs），检测脂肪细胞成脂分化、血管生成因子和α7nAChR-Egr1-FGF2信号通路表达，油红O染色观察脂滴形成，成管实验观察内皮细胞血管生成。结果显示，出生后5周开始，尼古丁组雌性子代（NIC组）体重显著高于对照组。出生后4周及12周，NIC组血糖、血脂水平升高；出生后26周，NIC组白色脂肪量显著增加且出现糖代谢异常。本研究还发现，母体尼古丁暴露引起雌性子代皮下及性腺白色脂肪组织微血管数目增多、血管生成因子表达增加，脂肪血管密度在发育早期（4周龄）时变化最明显。进一步发现性腺周围白色脂肪中α7nAChR-Egr1-FGF2信号通路在不同阶段均有明显上调，而皮下白色脂肪中该通路仅在发育早期明显上调。出生后4周和26周母体尼古丁暴露可显著降低棕色脂肪中微血管密度，且出生后26周多个血管生成因子基因表达下调。细胞实验发现，尼古丁促进3T3-L1细胞成脂分化和血管生成相关基因表达，促进HUVECs血管生成相关基因表达和成管。尼古丁处理3T3-L1细胞和HUVECs均促进α7nAChR-Egr1-FGF2信号通路基因和蛋白表达。α7nAChR抑制剂可拮抗尼古丁促成管和上调α7nAChR-Egr1-FGF2信号通路的作用，而降低HUVECs血管生成因子表达。综上，母体尼古丁暴露可通过α7nAChR-Egr1-FGF2信号通路，增加子代白色脂肪组织中早期血管生成、减少棕色脂肪中血管生成，导致成年后肥胖易感、脂代谢紊乱和胰岛素抵抗。此外，结果也表明母体尼古丁暴露可致子代大鼠白色脂肪组织瘦素抵抗、棕色脂肪结构和功能改变及米色表型改变是其他重要机制。本研究从脂肪组织血管生成角度深刻阐明母体尼古丁暴露导致子代肥胖易感发生机制，有助于深入揭示尼古丁的毒性及肥胖的发育起源。