Polyunsaturated fatty acids and seasonal acclimatization

Many small mammals cope with cold and limited feed supply during winter by abandoning the energetically costly maintenance of a high body temperature (Tb) and entering hibernation or daily torpor. We found similar reactions in several non-hibernating ungulates, except that Tb changes were substantial only in peripheral body parts. Hibernators prepare for life at low Tb by changing the fatty acid composition of cellular membranes, i.e. increased incorporation of omega-6 linoleic acid, an essential polyunsaturated fatty acid, into phospholipids. In such an environment works the membrane- bound calcium pump SERCA faster, an essential protein for muscular function. This attenuates the cold-induced retardation of SERCA and maintains pumping power required for normal muscle function at low Tb. In contrast, high contents of highly unsaturated omega-3 fatty acids in phospholipids slow SERCA activity down, but boost that of key enzymes of supplying energy to the cell in form of ATP. In summary, profound changes of metabolic rate and Tb seem to be ubiquitous among birds and mammals living in seasonal environments, as is associated membrane remodelling. However, specific effects of polyunsaturated fatty acids suggest trade-offs determining a seasonally changing fatty acid composition of membranes that is largely independent of direct dietary intake. The proposed study shall investigate effects of PUFA on seasonal acclimatization in red deer, a model species for large seasonal non-hibernating mammals. We will for the first time disentangle experimentally the role of dietary and photoperiodic origin of changes in membrane PL composition and its effect on membrane-bound enzymes. We expect to find profound consequences of seasonal acclimatization at this molecular level on thermoregulation and energetics of the whole organism. Our approach is a longitudinal study on a herd of red deer kept under close to natural conditions, but subjected to a feeding experiment manipulating availability of food, of dietary supply of polyunsaturated fatty acids, and of photoperiodic control of seasonal acclimatization. Analyses of the fatty acid composition of membranes, expression and activity of key membrane enzymes in muscle cells sampled repeatedly from winter and summer acclimatized deer will be combined with continuous measurement of heart rate as an indicator of metabolic rate, core and peripheral Tb, and locomotor activity of the deer with an approved telemetry system.