Diacylglycerol kinase ζ in hypothalamus interacts with long form leptin receptor -: Relation to dietary fat and body weight regulation

Leptin and its long form receptor, Ob-Rb, in hypothalamic nuclei play a key role in regulating energy balance. The mutation of Ob-Rb into one of its natural variants, Ob-Ra, results in severe obesity in rodents. We demonstrate here that diacylglycerol kinase zeta (DGK zeta) interacts, via its ankyrin repeats, with the cytoplasmic portion of Ob-Rb in yeast two-hybrid systems, in protein precipitation experiments in vitro and in vivo, It does not interact, however, with the short form, Ob-Ra, which mediates the entry of leptin into the brain. Furthermore, we show by in situ hybridization that DGK zeta is expressed in neurons of hypothalamic nuclei known to synthesize Ob-Rb and to participate in energy homeostasis, The mutant ob-/ab- and db-/db- mice exhibit increased hypothalamic DGK zeta mRNA level compared with their wild-type controls, suggesting a role for the leptin/ OB-Rb system in regulating DGK zeta expression. Further experiments show that hypothalamic DGK zeta mRNA level is stimulated by the consumption of a high-fat diet. In addition, DGK zeta mRNA is statistically significantly lower in rats and inbred mice that become obese on a high-fat diet compared with their lean counterparts. In fact, it is strongly, negatively correlated with both body fat and circulating levels of leptin. Taken together, our evidence suggests that DGK zeta constitutes a downstream component of the leptin signaling pathway and that reduced hypothalamic DGK zeta' mRNA, and possibly activity, is associated with obesity.