Sylvie Mémet

Nod1 responds to peptidoglycan delivered by the Helicobacter pylori cag pathogenicity island.

Epithelial cells can respond to conserved bacterial products that are internalized after either bacterial invasion or liposome treatment of cells. We report here that the noninvasive Gram-negative pathogen Helicobacter pylori was recognized by epithelial cells via Nod1, an intracellular pathogen-recognition molecule with specificity for Gram-negative peptidoglycan. Nod1 detection of H. pylori depended on the delivery of peptidoglycan to host cells by a bacterial type IV secretion system, encoded by the H. pylori cag pathogenicity island. Consistent with involvement of Nod1 in host defense, Nod1-deficient mice were more susceptible to infection by cag pathogenicity island–positive H. pylori than were wild-type mice. We propose that sensing of H. pylori by Nod1 represents a model for host recognition of noninvasive pathogens.

NF-kappaB regulates spatial memory formation and synaptic plasticity through protein kinase A/CREB signaling.

ABSTRACT Synaptic activity-dependent de novo gene transcription is crucial for long-lasting neuronal plasticity and long-term memory. In a forebrain neuronal conditional NF-κB-deficient mouse model, we demonstrate here that the transcription factor NF-κB regulates spatial memory formation, synaptic transmission, and plasticity. Gene profiling experiments and analysis of regulatory regions identified the α catalytic subunit of protein kinase A (PKA), an essential memory regulator, as a new NF-κB target gene. Consequently, NF-κB inhibition led to a decrease in forskolin-induced CREB phosphorylation. Collectively, these results disclose a novel hierarchical transcriptional network involving NF-κB, PKA, and CREB that leads to concerted nuclear transduction of synaptic signals in neurons, accounting for the critical function of NF-κB in learning and memory.

Listeriolysin O‐dependent activation of endothelial cells during infection with Listeria monocytogenes: activation of NF‐κB and upregulation of adhesion molecules and chemokines

The facultative intracellular bacterium Listeria monocytogenes is an invasive pathogen that crosses the vascular endothelium and disseminates to the placenta and the central nervous system. Its interaction with endothelial cells is crucial for the pathogenesis of listeriosis. By infecting in vitro human umbilical vein endothelial cells (HUVEC) with L. monocytogenes, we found that wild‐type bacteria induced the expression of the adhesion molecules (ICAM‐1 and E‐selectin), chemokine secretion (IL‐8 and monocyte chemotactic protein‐1) and NF‐κB nuclear translocation. The activation of HUVEC required viable bacteria and was abolished in prfA‐deficient mutants of L. monocytogenes, suggesting that virulence genes are associated with endothelial cell activation. Using a genetic approach with mutants of virulence genes, we found that listeriolysin O (LLO)‐deficient mutants inactivated in the hly gene did not induce HUVEC activation, as opposed to mutants inactivated in the other virulence genes. Adhesion molecule expression, chemokine secretion and NF‐κB activation were fully restored by a strain of Listeria innocua transformed with the hly gene encoding LLO. The relevance in vivo of endothelial cell activation for listerial pathogenesis was investigated in transgenic mice carrying an NF‐κB‐responsive lacZ reporter gene. NF‐κB activation was visualized by a strong lacZ expression in endothelial cells of capillaries of mice infected with a virulent haemolytic strain, but was not seen in those infected with a non‐haemolytic isogenic mutant. Direct evidence that LLO is involved in NF‐κB activation in transgenic mice was provided by injecting intravenously purified LLO, thus inducing stimulation of NF‐κB in endothelial cells of blood capillaries. Our results demonstrate that functional listeriolysin O secreted by bacteria contributes as a potent inflammatory stimulus to inducing endothelial cell activation during the infectious process.

Toll-like receptor 4 in lymphatic endothelial cells contributes to LPS-induced lymphangiogenesis by chemotactic recruitment of macrophages.

The lymphatic vessel is a major conduit for immune cell transport; however, little is known about how lymphatic vessels regulate immune cell trafficking and how lymphatic vessels themselves respond to inflammation. Toll-like receptor 4 (TLR4) plays a central role in lipopolysaccharide (LPS)-induced inflammation, but the role of TLR4 in lymphatic endothelial cells (LECs) is poorly understood. Here, we found that LECs express high amounts of TLR4 in the intracellular region, and that the TLR4 of LECs is the main mediator of nuclear factor-kappaB (NF-kappaB) activation by LPS. LPS-TLR4 signaling in LECs resulted in the production of various chemokines for chemotaxis of macrophage. In addition, TLR4 in LECs actively contributed to the recruitment of macrophages to the draining lymphatic vessel. Furthermore, the macrophages that infiltrated into the lymphatic vessel induced lymphangiogenesis by secreting lymphangiogenic growth factors. These phenomena were largely attenuated not only in the mice defective in TLR4 signaling but also in the chimeric mice defective in TLR4 signaling that were recipients for bone marrow transplantation from normal TLR4-signaling mice. In conclusion, TLR4 in LECs plays an essential role in LPS-induced inflammatory lymphangiogenesis by chemotactic recruitment of macrophages.

IκBα/IκBε deficiency reveals that a critical NF-κB dosage is required for lymphocyte survival

In most cells, the NF-κB transcription factor is sequestered in the cytoplasm by interaction with inhibitory proteins, the IκBs. Here, we show that combined IκBα/IκBε deficiency in mice leads to neonatal death, elevated κB binding activity, overexpression of NF-κB target genes, and disruption of lymphocyte production. In IκBα/IκBε-deficient fetuses, B220+IgM+ B cells and single-positive T cells die by apoptosis. In adults, IκBα-/-IκBε-/- reconstituted chimeras exhibit a nearly complete absence of T and B cells that is not rescued by cotransfer with wild-type bone marrow. These findings demonstrate that IκBs tightly control NF-κB activity in vivo and that increased NF-κB activity intrinsically impairs lymphocyte survival. Because reduction or rise of NF-κB activity leads to similar dysfunction, they also reveal that only a narrow window of NF-κB activity is tolerated by lymphocytes.

Regrowing the Adult Brain: NF-κB Controls Functional Circuit Formation and Tissue Homeostasis in the Dentate Gyrus

Cognitive decline during aging is correlated with a continuous loss of cells within the brain and especially within the hippocampus, which could be regenerated by adult neurogenesis. Here we show that genetic ablation of NF-κB resulted in severe defects in the neurogenic region (dentate gyrus) of the hippocampus. Despite increased stem cell proliferation, axogenesis, synaptogenesis and neuroprotection were hampered, leading to disruption of the mossy fiber pathway and to atrophy of the dentate gyrus during aging. Here, NF-κB controls the transcription of FOXO1 and PKA, regulating axogenesis. Structural defects culminated in behavioral impairments in pattern separation. Re-activation of NF-κB resulted in integration of newborn neurons, finally to regeneration of the dentate gyrus, accompanied by a complete recovery of structural and behavioral defects. These data identify NF-κB as a crucial regulator of dentate gyrus tissue homeostasis suggesting NF-κB to be a therapeutic target for treating cognitive and mood disorders.

Sleep deprivation increases the activation of nuclear factor kappa B in lateral hypothalamic cells

Sleep deprivation increases sleep propensity in rats and mice as well as the production of several sleep-regulatory substances. Nuclear factor kappa B (NF-kappa B) is a transcription factor implicated in the activation of many of these sleep-promoting substances. A unique population of neurons immunoreactive for the p65 subunit of NF-kappa B was previously localized within the caudal dorsolateral hypothalamus of rats. Therefore, we evaluated the effect of sleep deprivation on NF-kappa Bp65-immunoreactivity (IR) in cells of this region in rats as well as its nuclear translocation in a kappa B-lacZ transgenic mouse line. In rats after 6 h of sleep deprivation beginning at light onset, the number of neurons with NF-kappa Bp65-IR increased significantly in the caudal lateral hypothalamus, specifically the magnocellular lateral hypothalamus adjacent to the subthalamus. Sleep deprivation also significantly increased the number of cells expressing NF-kappa B-dependent beta-galactosidase in the magnocellular lateral hypothalamus, zona incerta dorsal, as well as the adjacent subthalamus in the transgenic mice. These results suggest that NF-kappa B expressing cells within the lateral hypothalamus may be important in the maintenance of the sleep-wake cycle.

NF-κB activation in endothelial cells is critical for the activity of angiostatic agents

In tumor cells, the transcription factor NF-κB has been described to be antiapoptotic and proproliferative and involved in the production of angiogenic factors such as vascular endothelial growth factor. From these data, a protumorigenic role of NF-κB has emerged. Here, we examined in endothelial cells whether NF-κB signaling pathway is involved in mediating the angiostatic properties of angiogenesis inhibitors. The current report describes that biochemically unrelated agents with direct angiostatic effect induced NF-κB activation in endothelial cells. Our data showed that endostatin, anginex, angiostatin, and the 16-kDa N-terminal fragment of human prolactin induced NF-κB activation in endothelial cells in both cultured human endothelial cells and in vivo in a mouse tumor model. It was also found that NF-κB activity was required for the angiostatic activity, because inhibition of NF-κB in endothelial cells impaired the ability of angiostatic agents to block sprouting of endothelial cells and to overcome endothelial cell anergy. Therefore, activation of NF-κB in endothelial cells can result in an unexpected antitumor outcome. Based on these data, the current approach of systemic treatment with NF-κB inhibitors may therefore be revisited because NF-κB activation specifically targeted to endothelial cells might represent an efficient strategy for the treatment of cancer. [Mol Cancer Ther 2009;8(9):2645–54]

Lymphatic vessel density and function in experimental bladder cancer

BackgroundThe lymphatics form a second circulatory system that drains the extracellular fluid and proteins from the tumor microenvironment, and provides an exclusive environment in which immune cells interact and respond to foreign antigen. Both cancer and inflammation are known to induce lymphangiogenesis. However, little is known about bladder lymphatic vessels and their involvement in cancer formation and progression.MethodsA double transgenic mouse model was generated by crossing a bladder cancer-induced transgenic, in which SV40 large T antigen was under the control of uroplakin II promoter, with another transgenic mouse harboring a lacZ reporter gene under the control of an NF-κB-responsive promoter (κB-lacZ) exhibiting constitutive activity of β-galactosidase in lymphatic endothelial cells. In this new mouse model (SV40-lacZ), we examined the lymphatic vessel density (LVD) and function (LVF) during bladder cancer progression. LVD was performed in bladder whole mounts and cross-sections by fluorescent immunohistochemistry (IHC) using LYVE-1 antibody. LVF was assessed by real-time in vivo imaging techniques using a contrast agent (biotin-BSA-Gd-DTPA-Cy5.5; Gd-Cy5.5) suitable for both magnetic resonance imaging (MRI) and near infrared fluorescence (NIRF). In addition, IHC of Cy5.5 was used for time-course analysis of co-localization of Gd-Cy5.5 with LYVE-1-positive lymphatics and CD31-positive blood vessels.ResultsSV40-lacZ mice develop bladder cancer and permitted visualization of lymphatics. A significant increase in LVD was found concomitantly with bladder cancer progression. Double labeling of the bladder cross-sections with LYVE-1 and Ki-67 antibodies indicated cancer-induced lymphangiogenesis. MRI detected mouse bladder cancer, as early as 4 months, and permitted to follow tumor sizes during cancer progression. Using Gd-Cy5.5 as a contrast agent for MRI-guided lymphangiography, we determined a possible reduction of lymphatic flow within the tumoral area. In addition, NIRF studies of Gd-Cy5.5 confirmed its temporal distribution between CD31-positive blood vessels and LYVE-1 positive lymphatic vessels.ConclusionSV40-lacZ mice permit the visualization of lymphatics during bladder cancer progression. Gd-Cy5.5, as a double contrast agent for NIRF and MRI, permits to quantify delivery, transport rates, and volumes of macromolecular fluid flow through the interstitial-lymphatic continuum. Our results open the path for the study of lymphatic activity in vivo and in real time, and support the role of lymphangiogenesis during bladder cancer progression.

NF-κB is developmentally regulated during spermatogenesis in mice

To analyze NF‐κB activity in the testis, we used murine transgenic lines carrying a LacZ reporter gene under the control of a NF‐κB‐responsive promoter (Schmidt‐Ullrich et al. [ 1996 ] Dev 122:2117–2128). We constructed three independent lines containing the promoter of the gene encoding p105, the precursor of the p50 subunit. This promoter contains three NF‐κB‐binding sites in its proximal part. Our results show that in adult mice, the β‐galactosidase activity which reflects nuclear NF‐κB activity, is first detected in spermatocytes at the pachytene stage and remains activated in the following steps of germ cell differentiation and maturation. Using transgenic mice carrying a p105nlslacZ construct with the 3 NF‐κB sites mutated in the p105 promoter, we found a significant reduction in the transgene activity, confirming the important role of NF‐κB in the activation of the transgene. To confirm the stage of induction during spermatogenesis, we analysed the β‐galactosidase activity in the testes from prepuberal mice in which cells synchrouneously enter meiosis. We detected the transgene activity at 18 days after birth, corresponding to the pachytene stage in spermatocytes. In nuclear extracts prepared from prepuberal mice, we found a peak of NF‐κB DNA‐binding activity made of p50 and p65 subunits at day 18 after birth, which remains high in the later stages. Further analysis showed that IκBα and β, but not ϵ are expressed in the testes. Altogether, these data suggest that NF‐κB factors are stage specifically controlled and may play a role during the development of sperm cells.