Chitosan-affected gene expression profiles in brain and stomach. Mus musculus

Chitosan has been widely used in food industry as a weight-loss aid and a cholesterol-lowering agent. Previous studies have shown that chitosan affects metabolic responses and contributes to anti-diabetic, hypocholestermic, and blood glucose-lowering effects; however, the in vivo targeting sites and mechanisms of chitosan remain to be clarified. In this study, we constructed transgenic mice which carried the luciferase genes driven by peroxisome proliferator-activated receptor (PPAR), a key regulator of fatty acid and glucose metabolism. Bioluminescent imaging of PPAR transgenic mice was applied to report the organs that chitosan acted on, and gene expression profiles of chitosan-targeted organs were further analyzed to elucidate the mechanisms of chitosan. Bioluminescent imaging showed that constitutive PPAR activities were detected in brain and gastrointestinal tract. Administration of chitosan significantly activated the PPAR activities in brain and stomach. Microarray analysis of brain and stomach showed that several pathways involved in lipid and glucose metabolism were regulated by chitosan. Moreover, the expression levels of metabolism-associated genes like apolipoprotein B (apoB) and ghrelin genes were down-regulated by chitosan. In conclusion, these findings suggested the feasibility of PPAR bioluminescent imaging-guided transcriptomic analysis on the evaluation of chitosan-affected metabolic responses in vivo. Moreover, we newly identified that downregulated expression of apoB and ghrelin genes were novel mechanisms for chitosan-affected metabolic responses in vivo . Overall design: Mice (6 to 8 weeks old) were subcutaneously injected saline or 0.2 g/kg chitosan. Chitosan oligosaccharide lactate (MW=4000-6000, >90% deacetylation) was purchased from Sigma-Aldrich (St. Louis, MO, USA) and dissolved in DDW. For rosiglitazone treatment, mice were orally administered 50 mg/kg rosiglitazone. Mice were then imaged for the luciferase activity or sacrificed for microarray analysis at indicated periods.

壳聚糖（chitosan）已作为减重助剂与降胆固醇剂，被广泛应用于食品工业领域。既往研究表明，壳聚糖可调控机体代谢反应，兼具抗糖尿病、降胆固醇及降血糖的功效；然而，壳聚糖在体内的作用靶点与调控机制仍有待阐明。
本研究构建了携带有由过氧化物酶体增殖物激活受体（peroxisome proliferator-activated receptor, PPAR）——脂肪酸与葡萄糖代谢的关键调控因子——驱动的荧光素酶基因的转基因小鼠。通过对PPAR转基因小鼠开展生物发光成像，可示踪壳聚糖的作用靶器官，并进一步分析壳聚糖靶器官的基因表达谱，以阐明壳聚糖的作用机制。
生物发光成像结果显示，组成型PPAR活性可在脑与胃肠道中被检测到。壳聚糖给药可显著激活脑与胃部的PPAR活性。对脑与胃部组织进行基因芯片分析表明，多条参与脂质与葡萄糖代谢的通路均受壳聚糖调控。此外，载脂蛋白B（apolipoprotein B, apoB）与饥饿素（ghrelin）等代谢相关基因的表达水平可被壳聚糖下调。
综上，本研究结果证实，采用PPAR生物发光成像引导的转录组分析，可用于评估壳聚糖在体内介导的代谢反应，该方法具备可行性。此外，本研究首次发现，载脂蛋白B与饥饿素基因的表达下调，是壳聚糖在体内调控代谢反应的全新机制。
实验设计：选取6~8周龄的小鼠，经皮下注射生理盐水或0.2 g/kg的壳聚糖。乳酸壳寡糖（分子量4000~6000，脱乙酰度>90%）购自西格玛奥德里奇（Sigma-Aldrich，美国密苏里州圣路易斯市），并溶于双蒸水（DDW）中。罗格列酮（rosiglitazone）处理组小鼠则予以口服给药50 mg/kg的罗格列酮。在指定时间点，对小鼠进行荧光素酶活性成像，或处死小鼠以开展基因芯片分析。