Hematopoietic PI3Kδ deficiency aggravates murine atherosclerosis through impairment of Tregs.

Chronic activation of the adaptive immune system is a hallmark of atherosclerosis. As PI3Kδ is a key regulator of T and B cell differentiation and function, we hypothesized that alleviation of adaptive immunity by PI3Kδ inactivation may represent an attractive strategy counteracting atherogenesis. As expected, lack of hematopoietic PI3Kδ in atherosclerosis-prone Ldlr-/- mice resulted in lowered T and B cell numbers, CD4+ effector T cells, Th1 response, and immunoglobulin levels.

Smooth muscle cell specific NEMO deficiency inhibits atherosclerosis in ApoE mice.

The development of atherosclerotic plaques is the result of a chronic inflammatory response coordinated by stromal and immune cellular components of the vascular wall. While endothelial cells and leukocytes are well-recognised mediators of inflammation in atherosclerosis, the role of smooth muscle cells (SMCs) remains incompletely understood. Here we aimed to address the role of canonical NF-κB signalling in SMCs in the development of atherosclerosis.

A20 prevents inflammasome-dependent arthritis by inhibiting macrophage necroptosis through its ZnF7 ubiquitin-binding domain.

Deficiency in the deubiquitinating enzyme A20 causes severe inflammation in mice, and impaired A20 function is associated with human inflammatory diseases. A20 has been implicated in negatively regulating NF-κB signalling, cell death and inflammasome activation; however, the mechanisms by which A20 inhibits inflammation in vivo remain poorly understood. Genetic studies in mice revealed that its deubiquitinase activity is not essential for A20 anti-inflammatory function.

Innate Sensing through Mesenchymal TLR4/MyD88 Signals Promotes Spontaneous Intestinal Tumorigenesis.

MyD88, an adaptor molecule downstream of innate pathways, plays a significant tumor-promoting role in sporadic intestinal carcinogenesis of the Apc model, which carries a mutation in the Apc gene. Here, we show that deletion of MyD88 in intestinal mesenchymal cells (IMCs) significantly reduces tumorigenesis in this model. This phenotype is associated with decreased epithelial cell proliferation, altered inflammatory and tumorigenic immune cell infiltration, and modified gene expression similar to complete MyD88 knockout mice.

Differential role of MyD88 and TRIF signaling in myeloid cells in the pathogenesis of autoimmune diabetes.

Type 1 diabetes (T1D) is caused by the autoimmune destruction of the insulin-producing pancreatic beta cells. While the role of adaptive immunity has been extensively studied, the role of innate immune responses and particularly of Toll- like Receptor (TLR) signaling in T1D remains poorly understood. Here we show that myeloid cell-specific MyD88 deficiency considerably protected mice from the development of streptozotocin (STZ)-induced diabetes.

Kinase-independent functions of RIPK1 regulate hepatocyte survival and liver carcinogenesis.

The mechanisms that regulate cell death and inflammation play an important role in liver disease and cancer. Receptor-interacting protein kinase 1 (RIPK1) induces apoptosis and necroptosis via kinase-dependent mechanisms and exhibits kinase-independent prosurvival and proinflammatory functions. Here, we have used genetic mouse models to study the role of RIPK1 in liver homeostasis, injury, and cancer.

Kinase Activities of RIPK1 and RIPK3 Can Direct IFN-β Synthesis Induced by Lipopolysaccharide.

The innate immune response is a central element of the initial defense against bacterial and viral pathogens. Macrophages are key innate immune cells that upon encountering pathogen-associated molecular patterns respond by producing cytokines, including IFN-β. In this study, we identify a novel role for RIPK1 and RIPK3, a pair of homologous serine/threonine kinases previously implicated in the regulation of necroptosis and pathologic tissue injury, in directing IFN-β production in macrophages.

RIPK1 counteracts ZBP1-mediated necroptosis to inhibit inflammation.

Receptor-interacting protein kinase 1 (RIPK1) regulates cell death and inflammation through kinase-dependent and -independent functions. RIPK1 kinase activity induces caspase-8-dependent apoptosis and RIPK3 and mixed lineage kinase like (MLKL)-dependent necroptosis. In addition, RIPK1 inhibits apoptosis and necroptosis through kinase-independent functions, which are important for late embryonic development and the prevention of inflammation in epithelial barriers.

RIPK1 and RIPK3 Kinases Promote Cell-Death-Independent Inflammation by Toll-like Receptor 4.

Macrophages are a crucial component of the innate immune system in sensing pathogens and promoting local and systemic inflammation. RIPK1 and RIPK3 are homologous kinases, previously linked to activation of necroptotic death. In this study, we have described roles for these kinases as master regulators of pro-inflammatory gene expression induced by lipopolysaccharide, independent of their well-documented cell death functions.

NEMO Prevents RIP Kinase 1-Mediated Epithelial Cell Death and Chronic Intestinal Inflammation by NF-κB-Dependent and -Independent Functions.

Intestinal epithelial cells (IECs) regulate gut immune homeostasis, and impaired epithelial responses are implicated in the pathogenesis of inflammatory bowel diseases (IBD). IEC-specific ablation of nuclear factor κB (NF-κB) essential modulator (NEMO) caused Paneth cell apoptosis and impaired antimicrobial factor expression in the ileum, as well as colonocyte apoptosis and microbiota-driven chronic inflammation in the colon. Combined RelA, c-Rel, and RelB deficiency in IECs caused Paneth cell apoptosis but not colitis, suggesting that NEMO prevents colon inflammation by NF-κB-independent functions.

NEMO Prevents Steatohepatitis and Hepatocellular Carcinoma by Inhibiting RIPK1 Kinase Activity-Mediated Hepatocyte Apoptosis.

IκB kinase/nuclear [corrected] factor κB (IKK/NF-κB) signaling exhibits important yet opposing functions in hepatocarcinogenesis. Mice lacking NEMO in liver parenchymal cells (LPC) spontaneously develop steatohepatitis and hepatocellular carcinoma (HCC) suggesting that NF-κB prevents liver disease and cancer. Here, we show that complete NF-κB inhibition by combined LPC-specific ablation of RelA, c-Rel, and RelB did not phenocopy NEMO deficiency, but constitutively active IKK2-mediated NF-κB activation prevented hepatocellular damage and HCC in NEMO(LPC-KO) mice.

TLR-independent anti-inflammatory function of intestinal epithelial TRAF6 signalling prevents DSS-induced colitis in mice.

Objective: The gut microbiota modulates host susceptibility to intestinal inflammation, but the cell types and the signalling pathways orchestrating this bacterial regulation of intestinal homeostasis remain poorly understood. Here, we investigated the function of intestinal epithelial toll-like receptor (TLR) responses in the dextran sodium sulfate (DSS)-induced mouse model of colitis.

Design: We applied an in vivo genetic approach allowing intestinal epithelial cell (IEC)-specific deletion of the critical TLR signalling adaptors, MyD88 and/or TIR-domain-containing adapter-inducing interferon-β (TRIF), as well as the downstream ubiquitin ligase TRAF6 in order to reveal the IEC-intrinsic function of these TLR signalling molecules during DSS colitis.

Hematopoietic RIPK1 deficiency results in bone marrow failure caused by apoptosis and RIPK3-mediated necroptosis.

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is recruited to the TNF receptor 1 to mediate proinflammatory signaling and to regulate TNF-induced cell death. RIPK1 deficiency results in postnatal lethality, but precisely why Ripk1(-/-) mice die remains unclear. To identify the lineages and cell types that depend on RIPK1 for survival, we generated conditional Ripk1 mice.

RIPK1 maintains epithelial homeostasis by inhibiting apoptosis and necroptosis.

Necroptosis has emerged as an important pathway of programmed cell death in embryonic development, tissue homeostasis, immunity and inflammation. RIPK1 is implicated in inflammatory and cell death signalling and its kinase activity is believed to drive RIPK3-mediated necroptosis. Here we show that kinase-independent scaffolding RIPK1 functions regulate homeostasis and prevent inflammation in barrier tissues by inhibiting epithelial cell apoptosis and necroptosis.

Cutting edge: RIPK1 Kinase inactive mice are viable and protected from TNF-induced necroptosis in vivo.

The serine/threonine kinase RIPK1 is recruited to TNFR1 to mediate proinflammatory signaling and to regulate TNF-induced cell death. A RIPK1 deficiency results in perinatal lethality, impaired NFκB and MAPK signaling, and sensitivity to TNF-induced apoptosis. Chemical inhibitor and in vitro-reconstitution studies suggested that RIPK1 displays distinct kinase activity-dependent and -independent functions.

Improved HSC reconstitution and protection from inflammatory stress and chemotherapy in mice lacking granzyme B.

The serine protease granzyme B (GzmB) is stored in the granules of cytotoxic T and NK cells and facilitates immune-mediated destruction of virus-infected cells. In this study, we use genetic tools to report novel roles for GzmB as an important regulator of hematopoietic stem cell (HSC) function in response to stress. HSCs lacking the GzmB gene show improved bone marrow (BM) reconstitution associated with increased HSC proliferation and mitochondrial activity.

Conditional targeting of tumor necrosis factor receptor-associated factor 6 reveals opposing functions of Toll-like receptor signaling in endothelial and myeloid cells in a mouse model of atherosclerosis.

Background: Previous studies implicated Toll-like receptor signaling as a critical pathogenic pathway in atherosclerosis, but the cell-specific mechanisms by which Toll-like receptors act to control atherosclerotic plaque development remain poorly understood.

Methods And Results: To study the cell-specific role of tumor necrosis factor receptor-associated factor 6 (TRAF6) in atherosclerosis, we generated ApoE(-/-) mice with endothelial cell- or myeloid cell-specific TRAF6 deficiency using Cre/LoxP-mediated gene targeting. Endothelial TRAF6 deficiency reduced atherosclerosis in female ApoE(-/-) mice by inhibiting nuclear factor-κB-dependent proinflammatory gene expression and monocyte adhesion to endothelial cells.

Hemodialysis removes uremic toxins that alter the biological actions of endothelial cells.

Chronic kidney disease is linked to systemic inflammation and to an increased risk of ischemic heart disease and atherosclerosis. Endothelial dysfunction associates with hypertension and vascular disease in the presence of chronic kidney disease but the mechanisms that regulate the activation of the endothelium at the early stages of the disease, before systemic inflammation is established remain obscure. In the present study we investigated the effect of serum derived from patients with chronic kidney disease either before or after hemodialysis on the activation of human endothelial cells in vitro, as an attempt to define the overall effect of uremic toxins at the early stages of endothelial dysfunction.

A Pleiotrophin C-terminus peptide induces anti-cancer effects through RPTPβ/ζ.

Background: Pleiotrophin, also known as HARP (Heparin Affin Regulatory Peptide) is a growth factor expressed in various tissues and cell lines. Pleiotrophin participates in multiple biological actions including the induction of cellular proliferation, migration and angiogenesis, and is involved in carcinogenesis. Recently, we identified and characterized several pleiotrophin proteolytic fragments with biological activities similar or opposite to that of pleiotrophin.

Endothelial cell-specific NF-kappaB inhibition protects mice from atherosclerosis.

Atherosclerosis is a progressive disorder of the arterial wall and the underlying cause of cardiovascular diseases such as heart attack and stroke. Today, atherosclerosis is recognized as a complex disease with a strong inflammatory component. The nuclear factor-kappaB (NF-kappaB) signaling pathway regulates inflammatory responses and has been implicated in atherosclerosis.

Characterization of heparin affin regulatory peptide signaling in human endothelial cells.

Heparin affin regulatory peptide (HARP) is an 18-kDa secreted growth factor that has a high affinity for heparin and a potent role on tumor growth and angiogenesis. We have previously reported that HARP is mitogenic for different types of endothelial cells and also affects cell migration and differentiation (12). In this study we examined the signaling pathways involved in the migration and tube formation on matrigel of human umbilical vein endothelial cells (HUVEC) induced by HARP.

Identification of heparin affin regulatory peptide domains with potential role on angiogenesis.

Heparin affin regulatory peptide (HARP) is a growth factor displaying high affinity for heparin. It is present in the extracellular matrix of many tissues, interacting with heparan sulfate and dermatan/chondroitin sulfate glycosaminoglycans. We have previously shown that HARP is implicated in the control of angiogenesis and its effects are mimicked, at least in part, by synthetic peptides that correspond to its N and C termini.