The observation that the T-bet transcription factor allows tissue-specific upregulation of intracellular osteopontin (Opn-i) in plasmacytoid dendritic cells (pDCs) suggests that Opn might contribute to the expression of interferon-α (IFN-α) in those cells. Here we show that Opn deficiency substantially reduced Toll-like receptor 9 (TLR9)-dependent IFN-α responses but spared expression of transcription factor NF-κB-dependent proinflammatory cytokines. Shortly after TLR9 engagement, colocalization of Opn-i and the adaptor molecule MyD88 was associated with induction of transcription factor IRF7-dependent IFN-α gene expression, whereas deficient expression of Opn-i was associated with defective nuclear translocation of IRF7 in pDCs. The importance of the Opn-IFN-α pathway was emphasized by its essential involvement in crosspresentation in vitro and in anti-herpes simplex virus 1 IFN-α response in vivo. The finding that Opn-i selectively coupled TLR9 signaling to expression of IFN-α but not to that of other proinflammatory cytokines provides new molecular insight into the biology of pDCs.Increasing evidence that innate immune responses can determine both the type and intensity of adaptive immune responses has stimulated great interest in the underlying regulatory mechanisms. The recognition phase of innate responses depends on a series of patternrecognition receptors, including Toll-like receptors (TLRs) expressed by dendritic cells (DCs), which detect a wide range of pathogen-associated molecules carried by bacteria and viruses 1 . Engagement of the TLR9 family of endosomal receptors by microbe-derived DNA triggers the production of large amounts of interferons α and β (IFN-αβ) 2 , key mediators that regulate the development of both innate and adaptive immunity [3][4][5][6] . However, the pathway initiated by TLR9 engagement that culminates in IFN-αβ production is not fully understood.

BackgroundPeroxisome proliferator-activated receptor gamma (PPARγ) agonists are clinically used to counteract hyperglycemia. However, so far experienced unwanted side effects, such as weight gain, promote the search for new PPARγ activators.MethodsWe used a combination of in silico, in vitro, cell-based and in vivo models to identify and validate natural products as promising leads for partial novel PPARγ agonists.ResultsThe natural product honokiol from the traditional Chinese herbal drug Magnolia bark was in silico predicted to bind into the PPARγ ligand binding pocket as dimer. Honokiol indeed directly bound to purified PPARγ ligand-binding domain (LBD) and acted as partial agonist in a PPARγ-mediated luciferase reporter assay. Honokiol was then directly compared to the clinically used full agonist pioglitazone with regard to stimulation of glucose uptake in adipocytes as well as adipogenic differentiation in 3T3-L1 pre-adipocytes and mouse embryonic fibroblasts. While honokiol stimulated basal glucose uptake to a similar extent as pioglitazone, it did not induce adipogenesis in contrast to pioglitazone. In diabetic KKAy mice oral application of honokiol prevented hyperglycemia and suppressed weight gain.ConclusionWe identified honokiol as a partial non-adipogenic PPARγ agonist in vitro which prevented hyperglycemia and weight gain in vivo.General significanceThis observed activity profile suggests honokiol as promising new pharmaceutical lead or dietary supplement to combat metabolic disease, and provides a molecular explanation for the use of Magnolia in traditional medicine.

No abstract