Hypothalamic Transcriptional Profiling and Quantitative Proteomics of Mice under 24-Hour Fasting

Abstract

Energy balance includes energy intake and energy expenditure. Either excessive food intake or insufficient physical activity will increase the body mass and cause obesity, a worldwide health problem. In the US, more than two-thirds of people are obesity or overweight. Conversely, it is well accepted that reducing energy intake can increase the life span and the resistance to age-related diseases. MicroRNAs are highly conserved non-coding RNA molecules with a length of 21-23 nucleotides. Recent studies show that numerous microRNAs are associated with the regulation of oxidative stress, inflammation, insulin signaling, apoptosis, and angiogenesis that relate to obesity. However, the role of microRNAs in the regulation of energy balance in central nervous system remains unknown, especially within the hypothalamus, a primary site of energy balance control. In this project, microRNA, and mRNA were profiled using microarray technology. Furthermore, quantitative proteomics were used to identify differential protein levels during fasting, and in a genetically obese mouse model, Mice were given either a 24-hour fast, or ad libitum access to food. Hypothalamic RNA and microRNA samples were analyzed by microarray, using both the Affymetrix and Toray 3D mRNA and microRNA platforms. No microRNAs were found to be differentially expressed between two treatments, whereas numerous mRNAs were significantly regulated by fasting, including 7 cell cycle related genes. Hypothalamic protein samples from WT and N2KO mice treated either to ad lib feeding or 24-hour fasting were analyzed by MSE quantitative proteomics. Over 650 proteins were identified with some proteins showing significantly different abundances between or among the four groups. Between ad lib fed WT and N2KO mice, 53 proteins were differentially expressed, with some of these linked to neurodegeneration, NAD synthesis, and the citrate acid cycle (TCA). Overall, the results of this study suggest that while microRNA-mediated mechanisms are not significant modulators of hypothalamic gene expression upon a 24 hour fast, cell cycle gene expression changes represent a major contributor to the fasting response. Moreover, Nlhl2 might play an important role in the neurodegeneration and mitochondrial metabolism.