Diacylglycerol kinase zeta in hypothalamus interacts with long form leptinreceptor - 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 n atural variants, Ob-Ra, results in severe obesity in rodents. We demonstrat e here that diacylglycerol kinase zeta (DGK zeta) interacts, via its ankyri n repeats, with the cytoplasmic portion of Ob-Rb in yeast two-hybrid system s, in protein precipitation experiments in vitro and in vivo, It does not i nteract, however, with the short form, Ob-Ra, which mediates the entry of l eptin into the brain. Furthermore, we show by in situ hybridization that DG K zeta is expressed in neurons of hypothalamic nuclei known to synthesize O b-Rb and to participate in energy homeostasis, The mutant ob-/ab- and db-/d b- mice exhibit increased hypothalamic DGK zeta mRNA level compared with th eir wild-type controls, suggesting a role for the leptin/ OB-Rb system in r egulating DGK zeta expression. Further experiments show that hypothalamic D GK 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 in bred mice that become obese on a high-fat diet compared with their lean cou nterparts. In fact, it is strongly, negatively correlated with both body fa t and circulating levels of leptin. Taken together, our evidence suggests t hat DGK zeta constitutes a downstream component of the leptin signaling pat hway and that reduced hypothalamic DGK zeta' mRNA, and possibly activity, i s associated with obesity.