Development of metabolic inflammation late in the active season of thirteen-lined ground squirrels

Obesity is a worldwide pandemic with significant comorbidities. Several laboratory models of obesity exist, but seasonal models such as hibernators may be valuable for understanding the pathogenesis of obesity. As part of their annual cycle, obligate hibernators, like the 13-lined ground squirrel (Ictidomys tridecemlineatus), undergo a rapid shift from a lean to obese state in order to store energy in the form of fat for their prolonged winter fast. Inflammation of metabolic tissues, such as liver, adipose and skeletal muscle, often develops prior to and along with obesity and insulin resistance. We therefore examined changes in adiposity and metabolic tissue cytokines in ground squirrels throughout their active season. In visceral adipose, we found increases in adipocyte size, TNF-alpha and IL-6 levels. IL-6 levels also increased in liver and muscle late in the active season. These data suggest metabolic inflammation develops along with obesity late in the squirrels active season.