Functional Genomics of Mammalian Hibernation

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PROJECT SUMMARY Mammalian hibernation is an integrative organismal adaptation involving a coordinated orchestration of systems physiology that results in a seasonally expressed change in behavioral state. As body temperature declines from euthermic values of 36-38°C to 2°C or lower in the ground squirrel, heart rate drops from 200- 300 beats/min to 7-10 beats/min, respiration rates fall from 100-150 breaths/min to 1-2 breaths/min, and metabolism declines to 1/30 to 1/100 of euthermic values. The mechanisms that underlie the entrance into, and arousal from, hibernation are poorly understood. However, the molecular, neurobiological, and endocrine adaptations underlying these dramatic arousal state changes are likely to have significance for human health in understanding metabolic homeostasis and aging, as well as for strategies to enhance organ preservation. Transcriptomic and proteomic studies have begun to describe the molecular landscape that underlies these changes in arousal state. To date, published studies have primarily focused on one organ system at a time, with little effort at integration across systems. In this proposal, we will exploit a bank of 12 dissected brain regions and 10 peripheral tissues collected from the golden-mantled ground squirrel (Callospermophilus lateralis) at 12 time points across the 5 major phases of the hibernation cycle to create a public database of transcriptomic information from the same individuals. In Aim 1, genome sequencing and de novo assembly of the C. lateralis genome will be conducted by a contractor who has previously assembled the genome of the 13- lined ground squirrel; the resultant genome will be annotated in collaboration with colleagues at the National Library of Medicine. These efforts will provide the necessary scaffold to enable Aim 2, whose goal is to conduct RNAseq analyses of multiple brain regions sampled across the hibernation cycle and to establish a public database of transcriptomic information. Our studies will initially focus on basal forebrain, hypothalamus, pons, and cerebral cortex because of their distinct roles in arousal state regulation. This RNAseq data will enrich the genome annotation conducted in Aim 1. The RNAseq data will be visualized and made available for mining through a publicly available database similar to CircaDB (http://circadb.hogeneschlab.org), a gene expression database widely used in circadian biology, that we will create in Aim 2b. The database will be extensible, enabling addition of transcriptomic and proteomic data from other brain regions and peripheral organs by our group as well as others. Collectively, this information will fuel hypothesis testing and organism-wide interrogation of the molecular bases of the dynamic changes in physiology that occur across the hibernation cycle and may provide insights into the adaptations that enable metabolic suppression and those that prevent hibernators from experiencing stroke, apnea, muscle atrophy and memory loss.