Interorgan coordination of the murine adaptive response to fasting

The effects of fasting have been studied extensively, predominantly on isolated processes, within a specific organ. No comprehensive study of the adaptations was available for different organs, let alone interrelating them, which left the understanding of the body's orchestration of fasting response limited. The gene expression profiles of brain, small intestine, kidney, liver and skeletal muscle were therefore studied in mice subjected to short, moderate and prolonged fasting. Functional category enrichment, network, and text-mining analyses were employed to scrutinize the overall adaptive response, aiming to identify responsive pathways, processes and networks, and their regulation. The implicated processes did not follow the accepted carbohydrate-lipid-protein succession of energy substrates expenditure. Instead, they were activated simultaneously in different organs during the whole duration of fasting. The most prominent changes occurred in lipid and steroid metabolism, especially in the liver and kidney, which showed biochemically similar, orchestrated responses. They were accompanied by suppression of the immune response and cell turnover, particularly in the small intestine, tied in with increased proteolysis in the muscle. Enhanced defence against oxidative damage, obvious in all the organs, was the top reaction of the brain, otherwise shown to be extremely well protected from starvation. The major transcription regulators of fasting response in different organs were FoxO transcription factors, AP-1, p53, cMyc, Sp1, EGF and HNF4alpha. The revealed interorgan interactions between metabolic, inflammatory and cell turnover responses are essential when designing strategies to treat the starvation affected individuals, while stressing the significance of using complimentary bioinformatics tools in the high-throughput data analysis. 6 week-old male FVB mice were fasted for 0, 12, 24, 48 or 72 hours before sacrifice (N = 5 per group). From each mouse total RNA was isolated from five organs - liver, small intestine, kidney, brain, and calf muscle. Five microarrays per experimental condition (five tissues, five timepoints) were performed. We used a common reference design. The single common-reference sample was a pool of equal amounts of RNA from all the samples investigated, including additional samples from 5 mice that were fasted for 48 hours and supplemented with vitamin B complex after 24 and 36 hours of fasting.禁食的效应已被广泛研究，但绝大多数仅聚焦于单一器官内的孤立生物学过程。目前尚无针对不同器官的禁食适应性的系统性研究，更遑论对器官间交互关联的探讨，这使得学界对机体如何协同调控禁食应答的认知极为有限。为此，本研究针对经历短期、中度及长期禁食的小鼠，对其脑、小肠、肾、肝与骨骼肌的基因表达谱展开分析。研究采用功能类别富集分析、网络分析及文本挖掘手段，对整体适应性应答进行细致解析，旨在明确受调控的应答通路、生物学过程及其调控网络。本研究揭示的生物学过程并未遵循学界公认的糖-脂-蛋白供能底物消耗顺序。相反，在整个禁食周期内，这些过程在不同器官中被同步激活。最为显著的变化出现在脂质与类固醇代谢通路中，尤以肝和肾最为突出，二者呈现出生化特性相似的协同应答。与此同时，免疫应答与细胞更新过程受到抑制，这一现象在小肠中尤为明显，同时伴随肌肉组织中蛋白水解作用的增强。所有器官均出现了抗氧化损伤防御能力的增强，而这一反应在脑中最为显著——此前学界曾认为脑组织在饥饿状态下受到了极好的保护。调控不同器官禁食应答的主要转录因子包括FoxO转录因子（FoxO transcription factors）、AP-1、p53、cMyc、Sp1、表皮生长因子（EGF）以及肝细胞核因子4α（HNF4α）。本研究揭示的代谢、炎症与细胞更新应答间的器官间交互作用，对于设计针对饥饿相关个体的治疗策略至关重要；同时也凸显了在高通量数据分析中整合互补生物信息学工具的重要性。本研究选用6周龄雄性FVB小鼠（FVB mice），将其分别禁食0、12、24、48或72小时后实施安乐死（每组n=5）。从每只小鼠的肝、小肠、肾、脑及腓肠肌中提取总RNA。每个实验条件（对应5种组织与5个时间点）均开展5次微阵列实验。本研究采用通用参考样本设计，单一通用参考样本为所有待测样本的等比例RNA混合池，额外包含5只禁食48小时、并在禁食24小时与36小时后补充复合维生素B的小鼠的RNA样本。