Altered gene expression related to fuel use and sensory capacity in tanycytes throughout the hibernation season in the golden hamster
Hibernation is a physiological and behavioural adaptation that permits survival during periods of reduced food availability and extreme environmental temperatures. This is achieved through cycles of metabolic depression which results in reduced body temperature (torpor) and rewarming (arousal). This cannot be achieved without extensive preparative physiological changes prior to the hibernation season. Dramatic changes in body temperature set-point observed over the hibernation season, pointing towards the hypothalamus, and several lines of evidence implicate a specialised glial cell type, the tanycyte, in hypothalamic control mechanisms linked to metabolic regulation. To investigate changes in tanycytic cell phenotype over the course of the hibernation season, we exposed golden hamsters (Mesocricetus auratus) to short photoperiod (SP) and reduced ambient temperature (8?C) and then LASER capture microdissected the tanycytic region from animals at physiologically defined points across the season. RNAseq followed by combined hierarchical clustering and pathway analysis defined major changes in the tanycytic transcriptome linked to physiological status. Our analysis revealed a marked reduction in the expression of genes linked to ciliary assembly and GPCR-signalling during the hibernation season, as well as evidence for a shift towards increased glycolytic metabolism. These aspects all spontaneously reversed in refractory animals which have ceased to express torpor despite continued exposure to SP 8?C. Tanycytes sampled mid-torpor show increased expression of immediate-early genes compared to the interbout euthermic state, while genes linked to RNA processing and translation show the reverse. The putative involvement of tanycytes in hibernation control are discussed. Overall design: Three months old male golden hamsters (Mesocricetus auratus) were housed under long photoperiod (LP, 14 hr of light/24 hrs) and an ambient temperature of 22°C. At the start of the experiment, one group were kept on LP at 22°C and were sampled immediately prior to the photoperiodic switch and at the end of the experiment (LP). The remaining animals were transferred to short photoperiod (SP, 10 hr of light/24 hrs) and an ambient temperature of 8°C to initiate hibernation. Animals were sampled 4 weeks after transfer to SP (pre-hibernation), after 8-12 weeks of SP prior to intiating T-A cycling (late pre-hibernation), or after three T-A cycles either when interbout euthermic (IBE) or torpid. The average IBE duration in this experiment was approximately 24 hours, animals were sampled late in their interbout euthermia phase (23 hours). Torpid animals were sampled at their mid-point of torpor, which in this experiment was 13 hours. After approximately 20 weeks of SP exposure, animals spontaneously stopped hibernating and were sampled at least 2 weeks after the last torpor bout (refractory).   Brain were collected and laser capture microdissection of the ependymal region of the hypothalamus, to enrich for tancytes was undertaken. RNAseq analysis was performed.