Alternation between short- and long photoperiod reveals hypothalamic gene regulation linked to seasonal body weight changes in Djungarian hamsters (Phodopus sungorus)

Djungarian hamsters are able to reduce their body weight by more than 30% in anticipation of the winter season. This particular adaptation to extreme environmental conditions is primarily driven by a natural reduction in day length and conserved under laboratory conditions. We used this animal model to investigate hypothalamic gene expression linked to body weight regulation behind this physiological phenomenon. After an initial collective short photoperiod (SP) adaptation for 14 weeks from a preceding long photoperiod (LP), hamsters were re-exposed to LP for either six or 14 weeks, followed by a second re-exposure to SP for eight weeks. Our data showed that re-exposure to LP led to an increase in body weight. In the hypothalamus Dio2, Vimentin, Crbp1 and Grp50 expression increased, but expression of Dio3, Mct8 and Srif decreased. The changes in body weight and gene expression were reversible in most hamsters after a further re-exposure to SP following six or 14 weeks in LP. Interestingly, body weight loss was pronounced in six hamsters re-exposed to SP after 14 weeks in LP, while five hamsters did not respond to SP. In non-responding hamsters, a different gene expression pattern was manifested, with the exception of Dio2 which was reduced not only in SP re-exposed hamsters but also hamsters maintained in LP. Together these data suggest that body weight regulation seems to be tightly linked to a co-ordinated regulation of several genes in the hypothalamus including those involved in thyroid hormone metabolism.