A Model of early vitamin deficiency in a hibernator, the 13-lined ground squirrel
Sprenger, Ryan J.
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Hibernators, such as the 13-lined ground squirrel (Ictidomys tridecemlineatus), undergo dramatic changes in adipose tissue mass during their circannual cycle. Retinoic acid (RA), the biologically active derivative of vitamin A, plays key roles in the development and growth of adipose tissue. We developed a model of early vitamin A deficiency in juvenile ground squirrels to determine RA’s effects on the ability to adequately build adipose mass prior to the first season of hibernation. Deficient squirrels (VAD) were maintained on the diet until 8 weeks of age when severe symptoms of hypovitaminosis were observed, including stunted growth and limb weakness. Liver retinoid analysis showed that these animals had essentially no retinoid stores. Even when placed on a normal diet, the VAD squirrels never reached the retinoid stores of controls. Control retinoid stores were high compared to other rodents, but in the normal range for the species. Serum retinol binding protein (RBP) was not affected by diet, although decreased levels were found in torpid hibernators. Early deficiency was associated with decreased mass of white (WAT) and brown (BAT) adipose tissue depots, decreased expression of resistin, altered seasonal expression of the RXR-β retinoid receptor and increased expression of BAT uncoupling protein. Our results suggest that ground squirrels require high levels of retinoids for normal function and are especially susceptible to deficiency as it affects the seasonal accumulation of adipose tissue.