TL1-A can engage death receptor-3 and activate NF-kappa B in endothelial cells.

BACKGROUND: Death receptors (DRs) play an important role in renal pathology. We have shown that DR3 is inducibly expressed on renal tubular epithelial cells in the setting of inflammatory injuries. In this study we investigate the expression of DR3 in renal endothelial cells and their response to TL1A, the only known ligand of DR3. METHODS: We did RT-PCR, flow cytometry and subcellular immunoblotting to examine the expression and function of DR3 in cells in vitro. We did organ culture of human and mouse tissue to examine expression and signal of DR3 in vivo. RESULTS: DR3 is expressed in some interstitial vascular endothelial cells (EC) in human kidney in situ; these EC also respond to its ligand TL1A by activating NF-κB. Very low levels of DR3 can be detected on the cell surface of cultured human umbilical vein (HUV) EC, which do not respond to TL1A. HUVEC transfected to overexpress DR3 become responsive to TL1A, assessed by IκBα degradation and E-selectin induction, indicating that the signaling components needed for DR3 responsiveness are expressed. TL1A induces NF-κB activation in EC in renal and cardiac tissue from wild type but not DR3 knock-out mice. CONCLUSION: TL1A and DR3 activate NF-κB in vascular endothelial cells, and can be an important regulator of renal interstitial vascular injury.

DR3 signaling protects against cisplatin nephrotoxicity mediated by tumor necrosis factor.

The expression of death receptor 3 (DR3), a member of the tumor necrosis factor (TNF) receptor superfamily, is up-regulated in human tubular epithelial cells (TECs) during renal injury, but its function in this setting remains unknown. We used cisplatin to induce renal injury in wild-type (DR3(+/+)) or congenitally deficient DR3(-/-) mice to examine the in vivo role of DR3. Cisplatin induced the expression of DR3, its ligand, TNF-like ligand 1A (TL1A), and TNF in TECs, as observed in human renal injury. Cisplatin increased apoptotic death of DR3(-/-) TECs by twofold compared with DR3(+/+) TECs, whereas it reduced the number of tubules expressing phospho-NF-κBp65(Ser276) by 50% at 72 hours. Similar degrees of induction of DR3, TL1A, and TNF, and changes in apoptosis and phospho-NF-κBp65(Ser276), were obtained in mouse kidney organ cultures treated with cisplatin for 3 hours, suggesting a direct effect on TECs. TNF was implicated in mediating cisplatin-induced tubular damage given that the in vivo co-administration of GM6001, an inhibitor of TNF maturation and release, significantly reduced TNF production and tubular damage. Moreover, TNF exacerbated, whereas TL1A reduced, cisplatin-induced apoptosis in the DR3(+/+) mouse proximal tubule cell line, TKPTS. Our data demonstrate that cisplatin-induced nephrotoxicity is mitigated by DR3 signaling, suggesting that this occurs by antagonizing pro-apoptotic signals induced by TNF. Therefore, activating DR3 may be beneficial in reducing acute kidney injury.

The TNF-like protein 1A-death receptor 3 pathway promotes macrophage foam cell formation in vitro.

TNF-like protein 1A (TL1A), a TNF superfamily cytokine that binds to death receptor 3 (DR3), is highly expressed in macrophage foam cell-rich regions of atherosclerotic plaques, although its role in foam cell formation has yet to be elucidated. We investigated whether TL1A can directly stimulate macrophage foam cell formation in both THP-1 and primary human monocyte-derived macrophages with the underlying mechanisms involved. We demonstrated that TL1A promotes foam cell formation in human macrophages in vitro by increasing both acetylated and oxidized low-density lipoprotein uptake, by enhancing intracellular total and esterified cholesterol levels and reducing cholesterol efflux. This imbalance in cholesterol homeostasis is orchestrated by TL1A-mediated changes in the mRNA and protein expression of several genes implicated in the uptake and efflux of cholesterol, such as scavenger receptor A and ATP-binding cassette transporter A1. Furthermore, through the use of virally delivered DR3 short-hairpin RNA and bone marrow-derived macrophages from DR3 knockout mice, we demonstrate that DR3 can regulate foam cell formation and contributes significantly to the action of TL1A in this process in vitro. We show, for the first time, a novel proatherogenic role for both TL1A and DR3 that implicates this pathway as a target for the therapeutic intervention of atherosclerosis.

Age-dependent maintenance of motor control and corticostriatal innervation by death receptor 3.

Death receptor 3 is a proinflammatory member of the immunomodulatory tumor necrosis factor receptor superfamily, which has been implicated in several inflammatory diseases such as arthritis and inflammatory bowel disease. Intriguingly however, constitutive DR3 expression has been detected in the brains of mice, rats, and humans, although its neurological function remains unknown. By mapping the normal brain expression pattern of DR3, we found that DR3 is expressed specifically by cells of the neuron lineage in a developmentally regulated and region-specific pattern. Behavioral studies on DR3-deficient (DR3(ko)) mice showed that constitutive neuronal DR3 expression was required for stable motor control function in the aging adult. DR3(ko) mice progressively developed behavioral defects characterized by altered gait, dyskinesia, and hyperactivity, which were associated with elevated dopamine and lower serotonin levels in the striatum. Importantly, retrograde tracing showed that absence of DR3 expression led to the loss of corticostriatal innervation without significant neuronal loss in aged DR3(ko) mice. These studies indicate that DR3 plays a key nonredundant role in the retention of normal motor control function during aging in mice and implicate DR3 in progressive neurological disease.

Nuclear cytokine-activated IKKalpha controls prostate cancer metastasis by repressing Maspin.

Inflammation enhances tumour promotion through NF-kappaB-dependent mechanisms. NF-kappaB was also proposed to promote metastatogenesis through epithelial-mesenchymal transition. Yet a mechanistic link between inflammation and metastasis is missing. We identified a role for IkappaB kinase alpha (IKKalpha), activated by receptor activator of NF-kappaB (RANK/TNFRSF11A), in mammary epithelial proliferation during pregnancy. Owing to similarities between mammary and prostate epithelia, we examined IKKalpha involvement in prostate cancer and its progression. Here we show that a mutation that prevents IKKalpha activation slows down CaP growth and inhibits metastatogenesis in TRAMP mice, which express SV40 T antigen in the prostate epithelium. Decreased metastasis correlated with elevated expression of the metastasis suppressor Maspin, the ablation of which restored metastatic activity. IKKalpha activation by RANK ligand (RANKL/TNFSF11) inhibits Maspin expression in prostate epithelial cells, whereas repression of Maspin transcription requires nuclear translocation of active IKKalpha. The amount of active nuclear IKKalpha in mouse and human prostate cancer correlates with metastatic progression, reduced Maspin expression and infiltration of prostate tumours with RANKL-expressing inflammatory cells. We propose that tumour-infiltrating RANKL-expressing cells lead to nuclear IKKalpha activation and inhibition of Maspin transcription, thereby promoting the metastatic phenotype.