Astrocyte IKKß/NF-κB signaling is required for diet-induced obesity and hypothalamic inflammation.

OBJECTIVE: Obesity and high fat diet (HFD) consumption in rodents is associated with hypothalamic inflammation and reactive gliosis. While neuronal inflammation promotes HFD-induced metabolic dysfunction, the role of astrocyte activation in susceptibility to hypothalamic inflammation and diet-induced obesity (DIO) remains uncertain. METHODS: Metabolic phenotyping, immunohistochemical analyses, and biochemical analyses were performed on HFD-fed mice with a tamoxifen-inducible astrocyte-specific knockout of IKKß (GfapCreERIkbkbfl/fl, IKKß-AKO), an essential cofactor of NF-κB-mediated inflammation. RESULTS: IKKß-AKO mice with tamoxifen-induced IKKß deletion prior to HFD exposure showed equivalent HFD-induced weight gain and glucose intolerance as Ikbkbfl/fl littermate controls. In GfapCreERTdTomato marker mice treated using the same protocol, minimal Cre-mediated recombination was observed in the mediobasal hypothalamus (MBH). By contrast, mice pretreated with 6 weeks of HFD exposure prior to tamoxifen administration showed substantially increased recombination throughout the MBH. Remarkably, this treatment approach protected IKKß-AKO mice from further weight gain through an immediate reduction of food intake and increase of energy expenditure. Astrocyte IKKß deletion after HFD exposure-but not before-also reduced glucose intolerance and insulin resistance, likely as a consequence of lower adiposity. Finally, both hypothalamic inflammation and astrocytosis were reduced in HFD-fed IKKß-AKO mice. CONCLUSIONS: These data support a requirement for astrocytic inflammatory signaling in HFD-induced hyperphagia and DIO susceptibility that may provide a novel target for obesity therapeutics.

Direction of microtubule movement is an intrinsic property of the motor domains of kinesin heavy chain and Drosophila ncd protein.

The kinesin heavy chain and the ncd (non-claret disjunctional) gene product of Drosophila are microtubule-associated motor proteins related by sequence similarity within an approximately 340-aa domain. Despite the sequence similarity, the kinesin heavy chain and ncd protein move in opposite directions on microtubules. To investigate the molecular basis for direction of movement, we created a series of truncated kinesin heavy chain and ncd proteins. We found that the conserved domain of both proteins has microtubule motor activity, although the efficiency with which ATP hydrolysis is coupled to microtubule movement declines dramatically with increasing truncation. Further, the direction of movement is intrinsic to the conserved motor domains, rather than being a consequence of domain organization or adjacent sequences.