Yu Xun

The melanocortin system centrally regulates energy homeostasis, with key components such as melanocortin-4 receptor (MC4R) and adenylyl cyclase 3 (ADCY3) in neuronal primary cilia. Mutations in MC4R and ADCY3 as well as ciliary dysfunction lead to obesity, but how melanocortin signaling works in cilia remains unclear. Using mouse random germline mutagenesis, we identified two missense mutations in G protein–coupled receptor 45 (Gpr45) that lead to obesity through hyperphagia. GPR45 was expressed in paraventricular nucleus of the hypothalamus (PVH), where it localized to cilia and recruited Gα _s to increase ciliary cyclic adenosine monophosphate (cAMP) via ADCY3. GPR45 colocalized with MC4R in PVH cilia and promoted ciliary MC4R activation. Loss of GPR45 in the PVH or MC4R ⁺ neurons caused obesity. These findings establish GPR45 as a key regulator of the ciliary melanocortin system, bridging MC4R and ADCY3.

Neuroglobin is an endogenous neuroprotective protein, but the underlying neuroprotective mechanisms remain to be elucidated. Our previous yeast two-hybrid screening study identified that Dishevelled-1, a key hub protein of Wnt/β-Catenin signaling, is an interaction partner of Neuroglobin. In this study, we further examined the role of Neuroglobin in regulating Dishevelled-1 and the downstream Wnt/β-Catenin and NFκB signaling pathway. We found that Neuroglobin directly interacts with Dishevelled-1 by co-immunoprecipitation, and the two proteins are co-localized in both cytoplasma and nucleus of SK-N-SH cells. Moreover, the ectopic expression of Neuroglobin promotes the degradation of exogenous and endogenous Dishevelled-1 through the proteasomal degradation pathway. Furthermore, our results showed that Neuroglobin significantly inhibits the luciferase activity of Topflash reporter and the expression of β-Catenin mediated by Dishevelled-1 in SK-N-SH cells. In addition, we also documented that Neuroglobin enhances TNF-α-induced NFκB activation via down-regulating Dishevelled-1. Finally, 3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyltetrazolium Bromide (MTT) assays showed that Neuroglobin is an important neuroprotectant that protects SK-N-SH cells from TNF-α-induced decrease in cell viability. Taken together, these findings demonstrated that Neuroglobin functions as an important modulator of the Wnt/β-Catenin and NFκB signaling pathway through regulating Dishevelled-1.