Dipeptidase-1 Is an Adhesion Receptor for Neutrophil Recruitment in Lungs and Liver.

A hallmark feature of inflammation is the orchestrated recruitment of neutrophils from the bloodstream into inflamed tissue. Although selectins and integrins mediate recruitment in many tissues, they have a minimal role in the lungs and liver. Exploiting an unbiased in vivo functional screen, we identified a lung and liver homing peptide that functionally abrogates neutrophil recruitment to these organs. Using biochemical, genetic, and confocal intravital imaging approaches, we identified dipeptidase-1 (DPEP1) as the target and established its role as a physical adhesion receptor for neutrophil sequestration independent of its enzymatic activity. Importantly, genetic ablation or functional peptide blocking of DPEP1 significantly reduced neutrophil recruitment to the lungs and liver and provided improved survival in models of endotoxemia. Our data establish DPEP1 as a major adhesion receptor on the lung and liver endothelium and identify a therapeutic target for neutrophil-driven inflammatory diseases of the lungs.

Renal immune surveillance and dipeptidase-1 contribute to contrast-induced acute kidney injury.

Radiographic contrast agents cause acute kidney injury (AKI), yet the underlying pathogenesis is poorly understood. Nod-like receptor pyrin containing 3-deficient (Nlrp3-deficient) mice displayed reduced epithelial cell injury and inflammation in the kidney in a model of contrast-induced AKI (CI-AKI). Unexpectedly, contrast agents directly induced tubular epithelial cell death in vitro that was not dependent on Nlrp3. Rather, contrast agents activated the canonical Nlrp3 inflammasome in macrophages. Intravital microscopy revealed diatrizoate (DTA) uptake within minutes in perivascular CX3CR1+ resident phagocytes in the kidney. Following rapid filtration into the tubular luminal space, DTA was reabsorbed and concentrated in tubular epithelial cells via the brush border enzyme dipeptidase-1 in volume-depleted but not euvolemic mice. LysM-GFP+ macrophages recruited to the kidney interstitial space ingested contrast material transported from the urine via direct interactions with tubules. CI-AKI was dependent on resident renal phagocytes, IL-1, leukocyte recruitment, and dipeptidase-1. Levels of the inflammasome-related urinary biomarkers IL-18 and caspase-1 were increased immediately following contrast administration in patients undergoing coronary angiography, consistent with the acute renal effects observed in mice. Taken together, these data show that CI-AKI is a multistep process that involves immune surveillance by resident and infiltrating renal phagocytes, Nlrp3-dependent inflammation, and the tubular reabsorption of contrast via dipeptidase-1.

TNFα regulates the localization of CD40 in lipid rafts of glioma cells.

Resistance of glioblastoma multiforme (GBM) to TNFα induced apoptosis is attributed to NFκB activation. As TNF-receptor family member CD40 regulates NFκB activation, we investigated the role of CD40 in NFκB activation in GBM. We observed elevated CD40 levels in human glioma samples as compared to the surrounding normal tissue. Treatment with TNFα elevated CD40 levels in glioma cells and inhibition of CD40 signaling failed to abrogate TNFα induced NFκΒ activity. While TNFα increased the interaction between TRAF2/6, IκBα, IKKα/ß in the CD40 signalosome, the level of CD40 in the signalosome remained unaffected upon TNFα treatment. Interestingly, TNFα decreased the spatial localization of CD40 and increased TRAF2/6 co-localization with lipid raft marker Caveolin. As localization of CD40 signalosome in lipid raft is crucial for NFκB activation, TNFα mediated decreased clustering of CD40 in lipid rafts could have possibly contributed to its non-involvement in NFκB activation.

Involvement of TNFα-induced TLR4-NF-κB and TLR4-HIF-1α feed-forward loops in the regulation of inflammatory responses in glioma.

The precise role of different toll-like receptor (TLR) superfamily members is just beginning to get elucidated in glioblastoma multiforme (GBM). In this study, we observed heightened TLR4 levels in GBM tumor samples as compared to adjacent normal tissue. Since the pro-inflammatory cytokine tumor necrosis factor (TNF)α induces NF-κB activation in GBM, and as several common signaling mediators are involved in TNFα and TLR4-mediated NF-κB activation, we investigated the role of TLR4 in the regulation of NF-κB activation and inflammatory responses in TNFα-treated glioma cells. TNFα elevated TLR4 expression and inhibition of TLR4 signaling by either signaling inhibitor, neutralizing antibody, or small interfering RNA (siRNA)-attenuated TNFα-induced NF-κB activation. TLR4-mediated NF-κB activation was independent of canonical myeloid differentiation factor 88 signaling but involved toll/IL-1R homology domain-containing adaptor protein-inducing interferon-ß. Inhibition of TLR4 signaling abrogated TNFα-induced increase in (1) transcription factors interferon (IFN) regulatory factor 3 and STAT-1 and (2) IFNß and inflammatory cytokines/chemokines expression. Furthermore, TNFα-induced TLR4-dependent increase in AKT activation and HIF-1α transcriptional activation suggested the existence of TLR4-AKT-HIF-1α axis. Importantly, TNFα-induced TLR4 was abrogated in cells transfected with dominant negative IκB and HIF-1α siRNA. Our studies indicate that TNFα triggered TLR4-HIF-1α and NF-κB-TLR4 feed-forward loops act in tandem to sustain inflammatory response in glioma.