Insulin resistance and lipodystrophy in mice lacking ribosomal S6 kinase 2

The p90 ribosomal S6 kinase 2 (RSK2) is a serine/threonine kinase with high expression levels in adipose tissue. Numerous in vitro studies show that RSK2 is activated by a broad number of cellular stimuli and suggest that RSK2 is involved in the regulation of a variety of cellular processes. However, the physiological role of RSK2 still remains elusive. We therefore generated rsk2 knockout (KO) mice to better understand the function of RSK2 in vivo. Birth weights of RSK2 KO mice are normal, but the body weight is reduced with age, as compared with wild-type littermates. We found that the difference in body weight was largely caused by a specific loss of white adipose tissue that is accompanied by reduced serum levels of the adipocyte-derived peptide, leptin. KO mice also have impaired glucose tolerance and elevated fasting insulin and glucose levels that are restored following administration of low amounts of leptin, which do not affect food intake. We conclude that RSK2 plays a novel and an important role in regulation of adipose mass in mice and speculate that the reduction in fat tissue may negatively affect insulin sensitivity, as observed in human lipodystrophy, through reduced levels of adipocyte-derived factors, such as leptin.