Genome-wide effects of acute progressive feed restriction in liver and white adipose tissue. Rattus norvegicus

Acute progressive feed restriction (APFR) represents a specific form of caloric restriction in which feed availability is increasingly curtailed over a period of a few days to a few weeks. It is often used for control animals in toxicological and pharmacological studies on compounds causing body weight loss to equalize weight changes between experimental and control groups and thereby, intuitively, to also set their metabolic states to the same phase. However, scientific justification for this procedure is lacking. In the present study, we analyzed by DNA microarrays the impact on hepatic gene expression in rats of two APFR regimens that caused identical diminution of body weight (19%) but differed slightly in duration (4 vs. 10 days). In addition, white adipose tissue (WAT) was also subjected to the transcriptomic analysis on day-4. The data revealed that the two regimens led to distinct patterns of differentially expressed genes in liver, albeit some major pathways of energy metabolism were similarly affected (particularly fatty acid and amino acid catabolism). The reason for the divergence appeared to be entrainment by the longer APFR protocol of peripheral oscillator genes, which resulted in derailment of circadian rhythms and consequent interaction of altered diurnal fluctuations with metabolic adjustments in gene expression activities. WAT proved to be highly unresponsive to the 4-day APFR as only 17 mRNA levels were influenced by the treatment. This study demonstrates that body weight is a poor proxy of metabolic state and that the customary protocols of feed restriction can lead to rhythm entrainment. Keywords: physiological state comparison Overall design: Thirteen feed restricted and thirteen control animals, each hybridized to a single array. Pre-processing was performed by group: all WAT samples together in one group, all four-day liver samples in a second group, and all ten-day liver samples in a third.

急性渐进性限饲（Acute Progressive Feed Restriction, APFR）是一类特定的热量限制方式，指在数天至数周的周期内逐步减少饲料供给量。该方法常被应用于针对可导致体重下降的化合物开展的毒理学与药理学研究中的对照动物处理，用以平衡实验组与对照组的体重变化，从而直观上使二者的代谢状态处于同一阶段。然而，该操作目前尚缺乏科学依据。
本研究通过DNA微阵列（DNA microarrays）技术，分析了两种APFR方案对大鼠肝脏基因表达的影响：两种方案均导致相同幅度的体重下降（19%），但持续时长存在细微差异（4天与10天）。此外，本研究还在处理第4天对白色脂肪组织（White Adipose Tissue, WAT）开展了转录组学分析。
数据分析结果显示，尽管两条核心能量代谢通路（尤其是脂肪酸与氨基酸分解代谢）受到了相似的影响，但两种限饲方案在肝脏中诱导出了截然不同的差异基因表达模式。这种表达模式差异的成因，似乎是更长时长的APFR方案同步了外周生物钟基因，进而引发昼夜节律紊乱，使得日间波动的代谢变化与基因表达活性的代谢调节产生相互作用。
实验还发现，白色脂肪组织对4天APFR处理的响应极弱，仅17个mRNA的表达水平受到该处理的影响。
本研究证实，体重无法很好地作为代谢状态的替代指标，而常规限饲方案可能会引发节律同步效应。
关键词：生理状态比较
整体实验设计：13只限饲动物与13只对照动物，每只样本均单独杂交至一张微阵列芯片。预处理按分组进行：所有白色脂肪组织样本归为一组，所有4天肝脏样本归为第二组，所有10天肝脏样本归为第三组。