Background: Hypothalamus is a constellation of nuclei, each of which controls an aspect of “internal milieu,” including satiety and energy homeostasis. Here we address molecular signature of each energy-regulating hypothalamic nucleus and its dynamism in diet-induced obesity (DIO).
Methods: We micro-dissected arcuate (ARC), paraventricular (PVN) and lateral (LH) hypothalamic nuclei from mice and verified by the expression of nucleus-specific genes. High fat diet (60%kcal)-fed and control B6 mice (3days, 2, 6 and 16weeks after the start of diets) and 9-week-old ob/ob mice were used. RNA was extracted for RNA-Seq analysis. GO analysis by David.
Results: ARC-specific genes were associated with GO terms: “neuropeptide,” “cilia,” while PVN with “neurogenesis” and LH with “ion channel,” “cell junction.” Among ∼6000 genes whose expression is altered in one or more of 3 nucleus x 4 timepoint = 12 settings in DIO were clustered into 13 groups with one big group of genes suppressed throughout (from 3d to 16w) and 12 groups of upregulated genes, each corresponding to 3 nucleus x 4 timepoint conditions. Genes in each group were specifically upregulated only in one condition and significantly associated with distinct GO terms, suggesting a nucleus x timepoint-specific pathology during the development of DIO. Among altered genes, we selected those with expression highly associated with leptin resistance in ARC, id est, upregulated at 6weeks and thereafter when leptin resistance is fully developed, and downregulated in ob/ob mice, a leptin-sensitive model. Among these was X that encodes a secreted protein whose expression and induction in DIO was confined to ARC. Recombinant X protein induced leptin resistance both in in vitro and in vivo leptin sensitivity assays.
Conclusion: By a comparative transcriptomic approach, “Stages” of DIO can now be defined by nucleus and timepoint-specific gene clusters with specific functions. We further identified a gene with a potential pathogenetic role in leptin resistance in obesity.
T. Tanaka: Research Support; Self; Japan Society for the Promotion of Science. Speaker's Bureau; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Daiichi Sankyo Company, Limited, Kissei Pharmaceutical Co., Ltd., Kowa Pharmaceutical Europe Co. Ltd., Mitsubishi Tanabe Pharma Corporation, Novartis Pharmaceuticals Corporation, Taisho Toyama Pharmaceutical Co. Ltd., Takeda Pharmaceutical Company Limited.
Japan Society for the Promotion of Science, Takeda Pharmaceutical Co. Ltd.