Noncanonical Notch signaling modulates cytokine responses of dendritic cells to inflammatory stimuli.

Dendritic cell (DC)-derived cytokines play a key role in specifying adaptive immune responses tailored to the type of pathogen encountered and the local tissue environment. However, little is known about how DCs perceive the local environment. We investigated whether endogenous Notch signaling could affect DC responses to pathogenic stimuli. We demonstrate that concurrent Notch and TLR stimulation results in a unique cytokine profile in mouse bone-marrow derived DCs characterized by enhanced IL-10 and IL-2, and reduced IL-12 expression compared with TLR ligation alone. Unexpectedly, modulation of cytokine production occurred through a noncanonical Notch signaling pathway, independent of γ-secretase activity. Modulation required de novo protein synthesis, and PI3K, JNK, and ERK activity were necessary for enhanced IL-2 expression, whereas modulation of IL-10 required only PI3K activity. Further, we show that this γ-secretase-independent Notch pathway can induce PI3K activity. In contrast, expression of the canonical Notch target gene Hes1 was suppressed in DCs stimulated with Notch and TLR ligands simultaneously. Thus, our data suggest that Notch acts as an endogenous signal that modulates cytokine expression of DCs through a noncanonical pathway and therefore has the potential to tailor the subsequent adaptive immune response in a tissue- and/or stage-dependent manner.

Epithelial cell TGFß signaling induces acute tubular injury and interstitial inflammation.

TGFß signaling plays a central role in the development of acute and chronic kidney diseases. Previous in vivo studies involved systemic alteration of TGFß signaling, however, limiting conclusions about the direct role of TGFß in tubular cell injury. Here, we generated a double transgenic mouse that inducibly expresses a ligand-independent constitutively active TGFß receptor type 1 (TßR1) kinase specifically in tubular epithelial cells, with expression restricted by the Pax8 promoter. In this model, activation of TGFß signaling in the tubular epithelium alone was sufficient to cause AKI characterized by marked tubular cell apoptosis and necrosis, oxidative stress, dedifferentiation and regenerative cell proliferation, reduced renal function, and interstitial accumulation of inflammatory cells. This tubular injury was associated with mitochondrial-derived generation of reactive oxygen species (ROS), but cell damage and apoptosis were partially independent of mitochondrial-derived ROS. TßR1 signaling-induced tubular injury also associated with significant leukocyte infiltration consisting of F4/80(+) macrophages, CD11c(+) F4/80(+) dendritic cells, CD11c(+) F4/80(-) Ly6C(high) dendritic cells/monocytes, and T cells. Inhibition of mitochondrial-derived ROS significantly reduced accumulation of CD11c(+) F4/80(+) dendritic cells and T cells, suggesting a role for ROS in the activation and recruitment of the adaptive immune response to tubular injury. Taken together, these results suggest that TGFß signaling in the tubular epithelium alone is sufficient to cause acute tubular injury and inflammation; therefore, TGFß may be a mechanistic link between acute injury and chronic progression of kidney disease.

Cutting edge: Notch signaling induces a distinct cytokine profile in dendritic cells that supports T cell-mediated regulation and IL-2-dependent IL-17 production.

Recently it has been shown that dendritic cells (DC) express both Notch and Notch ligands, allowing for the possibility that Notch signaling may influence their maturation. We show that although both Jagged (Jgd) and Delta-like (DlL) ligands were able to activate the canonical Notch pathway in mouse DC, only Jgd1 could induce the production of certain cytokines. Maturation of DC via Jgd1 resulted in an entirely different maturation program from that induced through TLR (via LPS) signaling, promoting the production of high levels of IL-2 and IL-10. DC matured by Jgd1 (Jgd1-conditioned DC) promoted the survival and proliferation of CD4(+)CD25(+) regulatory T cells that were able to suppress efficiently the proliferation of CD25(-) cells. Further, CD25(+) cells cultured with Jgd1-conditioned DC produced very high levels of IL-17 in an IL-2-dependent fashion. Our data suggest a new and important role for the Notch pathway in the regulation of the DC phenotype.

Target pattern recognition by complement proteins of the classical and alternative pathways.

The complement system is a major component of the innate defence of animals against invading microorganisms, and is also essential for the recognition and clearance of damaged or structurally-altered host cells or macromolecules. The system is activated by three different pathways, each of which responds, using different recognition molecules, to a very wide range of activators. The recognition protein of the complement classical pathway, C1q is described in detail here, with comparisons to the alternative pathway.

BAMBI regulates angiogenesis and endothelial homeostasis through modulation of alternative TGFß signaling.

BACKGROUND: BAMBI is a type I TGFß receptor antagonist, whose in vivo function remains unclear, as BAMBI(-/-) mice lack an obvious phenotype. METHODOLOGY/PRINCIPAL FINDINGS: Identifying BAMBI's functions requires identification of cell-specific expression of BAMBI. By immunohistology we found BAMBI expression restricted to endothelial cells and by electron microscopy BAMBI(-/-) mice showed prominent and swollen endothelial cells in myocardial and glomerular capillaries. In endothelial cells over-expression of BAMBI reduced, whereas knock-down enhanced capillary growth and migration in response to TGFß. In vivo angiogenesis was enhanced in matrigel implants and in glomerular hypertrophy after unilateral nephrectomy in BAMBI(-/-) compared to BAMBI(+/+) mice consistent with an endothelial phenotype for BAMBI(-/-) mice. BAMBI's mechanism of action in endothelial cells was examined by canonical and alternative TGFß signaling in HUVEC with over-expression or knock-down of BAMBI. BAMBI knockdown enhanced basal and TGFß stimulated SMAD1/5 and ERK1/2 phosphorylation, while over-expression prevented both. CONCLUSIONS/SIGNIFICANCE: Thus we provide a first description of a vascular phenotype for BAMBI(-/-) mice, and provide in vitro and in vivo evidence that BAMBI contributes to endothelial and vascular homeostasis. Further, we demonstrate that in endothelial cells BAMBI interferes with alternative TGFß signaling, most likely through the ALK 1 receptor, which may explain the phenotype observed in BAMBI(-/-) mice. This newly described role for BAMBI in regulating endothelial function has potential implications for understanding and treating vascular disease and tumor neo-angiogenesis.