Tumor necrosis factor (TNF) is key to the pathogenesis of various arthritic diseases and inflammatory bowel disease (IBD). Anti-TNF therapies have proved successful in the clinical treatment of these diseases, but a mechanistic understanding of TNF function is still lacking. We have investigated early cellular mechanisms of TNF function in these diseases using an established TNF transgenic model, which develops a spondyloarthritis-like disease characterized by peripheral joint arthritis, sacroiliitis, enthesitis, and Crohn's-like IBD. Bone marrow grafting experiments demonstrated that development of arthritis requires TNF receptor I (TNFRI) expression in the radiation-resistant compartment, which is also known to be a sufficient target of TNF in the development of Crohn's-like IBD in the same model. Early activation of synovial fibroblasts and intestinal myofibroblasts could also be demonstrated by perturbed expression of matrix metalloproteases and their inhibitors. Notably, selective Cre/loxP-mediated TNFRI expression in mesenchymal cells resulted in a fully arthritic–spondyloarthritic and intestinal phenotype, indicating that mesenchymal cells are primary and sufficient targets of TNF in these pathologies. Our results offer a novel mechanistic perspective for TNF function in gut and joint pathologies and indicate early common cellular pathways that may also explain the often observed synovial–gut axis in human disease.

Abstract-As the most successful cryptocurrency to date, Bitcoin constitutes a target of choice for attackers. While many attack vectors have already been uncovered, one important vector has been left out though: attacking the currency via the Internet routing infrastructure itself. Indeed, by manipulating routing advertisements (BGP hijacks) or by naturally intercepting traffic, Autonomous Systems (ASes) can intercept and manipulate a large fraction of Bitcoin traffic.This paper presents the first taxonomy of routing attacks and their impact on Bitcoin, considering both small-scale attacks, targeting individual nodes, and large-scale attacks, targeting the network as a whole. While challenging, we show that two key properties make routing attacks practical: (i) the efficiency of routing manipulation; and (ii) the significant centralization of Bitcoin in terms of mining and routing. Specifically, we find that any network attacker can hijack few (<100) BGP prefixes to isolate ∼50% of the mining power-even when considering that mining pools are heavily multi-homed. We also show that on-path network attackers can considerably slow down block propagation by interfering with few key Bitcoin messages.We demonstrate the feasibility of each attack against the deployed Bitcoin software. We also quantify their effectiveness on the current Bitcoin topology using data collected from a Bitcoin supernode combined with BGP routing data.The potential damage to Bitcoin is worrying. By isolating parts of the network or delaying block propagation, attackers can cause a significant amount of mining power to be wasted, leading to revenue losses and enabling a wide range of exploits such as double spending. To prevent such effects in practice, we provide both short and long-term countermeasures, some of which can be deployed immediately.

Recent clinical evidence demonstrated the importance of tumor necrosis factor (TNF) in the development of Crohn's disease. A mouse model for this pathology has previously been established by engineering defects in the translational control of TNF mRNA (Tnf Δ AREmouse). Here, we show that development of intestinal pathology in this model depends on Th1-like cytokines such as interleukin 12 and interferon γ and requires the function of CD8+ T lymphocytes. Tissue-specific activation of the mutant TNF allele by Cre/loxP-mediated recombination indicated that either myeloid- or T cell–derived TNF can exhibit full pathogenic capacity. Moreover, reciprocal bone marrow transplantation experiments using TNF receptor–deficient mice revealed that TNF signals are equally pathogenic when directed independently to either bone marrow–derived or tissue stroma cell targets. Interestingly, TNF-mediated intestinal pathology was exacerbated in the absence of MAPKAP kinase 2, yet strongly attenuated in a Cot/Tpl2 or JNK2 kinase–deficient genetic background. Our data establish the existence of redundant cellular pathways operating downstream of TNF in inflammatory bowel disease, and demonstrate the therapeutic potential of selective kinase blockade in TNF-mediated intestinal pathology.

p38 mitogen-activated protein kinases (MAPKs) are activated primarily in response to inflammatory cytokines and cellular stress, and inhibitors which target the p38␣ and p38␤ MAPKs have shown potential for the treatment of inflammatory disease. Here we report the generation and initial characterization of a knockout of the p38␤ (MAPK11) gene. p38␤ ؊/؊ mice were viable and exhibited no apparent health problems. The expression and activation of p38␣, ERK1/2, and JNK in response to cellular stress was normal in embryonic fibroblasts from p38␤ ؊/؊ mice, as was the activation of p38-activated kinases MAPKAP-K2 and MSK1. The transcription of p38-dependent immediate-early genes was also not affected by the knockout of p38␤, suggesting that p38␣ is the predominant isoform involved in these processes. The p38␤ ؊/؊ mice also showed normal T-cell development. Lipopolysaccharide-induced cytokine production was also normal in the p38␤ ؊/؊ mice. As p38 is activated by tumor necrosis factor, the p38␤ ؊/؊ mice were crossed onto a TNF⌬ARE mouse line. These mice overexpress tumor necrosis factor, which results in development symptoms similar to rheumatoid arthritis and inflammatory bowel disease. The progression of these diseases was not however moderated by knockout of p38␤. Together these results suggest that p38␣, and not p38␤, is the major p38 isoform involved in the immune response and that it would not be necessary to retain activity against p38␤ during the development of p38 inhibitors.

TNF plays a crucial role in the pathogenesis of Crohn disease. Dysregulated TNF production in mice that bear the genetic deletion of the TNF AU-rich regulatory elements (ARE) (Tnf ΔARE/+ mice) results in TNF receptor I (TNFRI)-dependent spontaneous Crohn-like pathology. Current concepts consider intestinal epithelial cell (IEC) responses to TNF to be critical for intestinal pathology, but the potential contribution of IEC-derived TNF in disease pathogenesis has not been addressed. In this study we examined whether IEC are sufficient as cellular targets or sources of TNF in the development of intestinal pathology. Using IEC-specific reactivation of a hypomorphic TnfΔAREneo allele in mice, we show that selective chronic overproduction of TNF by IEC suffices to cause full development of Crohn-like pathology. Epithelial TNF overexpression leads to early activation of the underlying intestinal myofibroblast, a cell type previously identified as a sufficient target of TNF for disease development in the Tnf ΔARE model. By contrast, restricted TNFRI expression on IEC although sufficient to confer IEC apoptosis after acute exogenous TNF administration, fails to induce pathology following chronic specific targeting of IEC by endogenous TNF in Tnf ΔARE/+ mice. Our results argue against IEC being early and sufficient responders to chronic TNF-mediated pathogenic signals and suggest that proinflammatory aberrations leading to chronic TNF production by IEC may initiate pathology in Crohn disease.inflammatory bowel disease | ileitis | mucosal | mesenchymal I nflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract resulting from inappropriate and sustained activation of the mucosal immune system against the bacterial microflora of the gut (1). IBD is represented by two major forms: ulcerative colitis (UC), which is manifested in the colon, and Crohn disease (CD), which is manifested primarily in the ileum but also in the colon (2). Genome-wide association studies in patients with CD indicate a putative role for genes of the innate and adaptive immunity system and an emerging role for genes implicated in autophagy (3). Animal models of disease suggest that adaptive immune responses are required for disease manifestation and that the gut microflora appear to drive inflammation (4). However, the exact mechanisms underlying IBD pathogenesis and especially the early pathogenic events remain largely obscure.TNF is critically implicated in IBD pathophysiology, highlighted by the successful use of anti-TNF therapies for the treatment of patients who have CD (5). TNF is shown to exert pathogenic activities in several animal models of IBD (6), whereas protective roles have been described also (7,8). The crucial pathogenic role of TNF in CD has been verified experimentally in mice that bear the genetic deletion of the TNF AUrich regulatory elements (ARE) that leads to defective posttranscriptional regulation of tnf expression and chronic TNF overproduction (9). Tnf ΔARE/+ mice chronically overprodu...