Ginsenoside-Rb1 promotes adipogenesis through regulation of PPARγ and microRNA-27b.

Ginsenoside-Rb1 (Rb1), one of the bioactive components in ginseng extract, is recently reported to be able to promote adipogenesis and peroxisome proliferator-activated receptor gamma (PPARγ) expression. Meanwhile, microRNA-27b (miR-27b) is also identified to regulate adipogenesis by targeting PPARγ2. In the present study, we attempted to link up the Rb1-promoted adipogenesis with PPARγ binding and miR-27b regulation. First, we demonstrated that GW9662, an antagonist of PPARγ, could block Rb1-induced 3T3-L1 differentiation with little toxicity towards cell proliferation. Then, expression levels for both of miR-27b and its primary transcript, pri-mir-27b, were found to decrease upon Rb1 treatment. Again, GW9662 could attenuate the inhibitory effect of Rb1 on both miR-27 and pri-mir-27b expression. Since Rb1 was demonstrated to have binding activity towards PPARγ, we thus speculate that Rb1 may act though PPARγ to downregulate mir-27b gene transcription and mature miR-27b activity, which in turn promotes PPARγ expression and adipogenesis. Enhancement on adipogenesis of adipose tissues is expected to prevent lipotoxicty in nonadipose tissues. Our data may give a better illustration to explain the antidiabetic effect of Rb1 and provide a hint on treatment of lipid related metabolic diseases in the future.

Analysis of the action of euxanthone, a plant-derived compound that stimulates neurite outgrowth.

We have investigated the neurite growth-stimulating properties of euxanthone, a xanthone derivative isolated from the Chinese medicinal plant Polygala caudata. Euxanthone was shown to exert a marked stimulatory action on neurite outgrowth from chick embryo dorsal root ganglia explanted in collagen gels, in the absence of added neurotrophins. It was also shown to promote cell survival in explanted chick embryo ganglia, and to stimulate neurite outgrowth from isolated adult rat primary sensory neurons in vitro. The further finding that euxanthone stimulates neurite outgrowth from explants of chick embryo retina and ventral spinal cord suggests an action on signaling pathways downstream of neuronal receptors for specific neurotrophic factors. Consistent with this, euxanthone did not promote neurite outgrowth from non-transfected PC12 cells, or from PC12 cells transfected with TrkB or TrkC, under conditions in which these cells extended neurites in response to, respectively, the neurotrophins nerve growth factor, brain-derived neurotrophic factor and neurotrophin 3. Western blot analysis of euxanthone-stimulated dorsal root ganglion explants showed that expression of phospho-mitogen-activated protein (MAP) kinase was up-regulated after 1 h of euxanthone-treatment. Inhibition of the MAP kinase pathway using PD98059, a specific inhibitor of MAP kinase kinase, blocked all euxanthone-stimulated neurite outgrowth. However, analysis of phospho-Akt expression indicated that the phosphatidylinositol-3 kinase-Akt pathway, another major signaling pathway engaged by neurotrophins, is not significantly activated by euxanthone. These results suggest that euxanthone promotes neurite outgrowth by selectively activating the MAP kinase pathway.