IKKβ regulates endothelial thrombomodulin in a Klf2-dependent manner

BACKGROUND

Endothelial thrombomodulin (TM) is critically involved in anticoagulation, anti-inflammation, cytoprotection and normal fetal development. Tumor necrosis factor alpha (TNFα) suppresses TM expression.

OBJECTIVE

TNFα has been shown to down-regulate TM partly via activation of nuclear factor kappa B (NF-κB). However, because the TM promoter lacks an NF-κB binding site, the direct involvement of NF-κB has been controversial. We investigated the role of the upstream regulatory serine kinase, inhibitory kappa-B kinase-β (IKKβ), in TM expression and function with or without TNFα treatment.

METHODS

Inhibition of IKKβ was achieved by specific chemical inhibitors, siRNA or shRNA. TM expression was assessed by qRT-PCR, Western blot, flow cytometry, luciferase reporter assay and chromatin immune-precipitation (ChIP) assay. TM function was estimated by generation of activated protein C (APC). NF-κB activation was determined by immunocytochemistry.

RESULTS AND CONCLUSIONS

IKKβ inhibition increased TM expression and function, and attenuated TNFα-mediated TM down-regulation. In contrast, inhibition of downstream canonical NF-κB protein family members p50 and p65 (RelA) failed to up-regulate TM expression and did not affect IKKβ inhibition-mediated TM over-expression. However, knockdown of cRel and RelB, family members of the canonical and non-canonical NF-κB pathway, respectively, resulted in TM over-expression. IKKβ inhibition caused over-expression, increased promoter activity and enhanced binding of Krüppel-like factor 2 (Klf2) to the TM promoter, which positively regulates TM expression. Finally, knockdown of Klf2 completely attenuated IKKβ inhibition-mediated TM up-regulation. We conclude that IKKβ regulates TM in a Klf2-dependent manner.

Increased Abeta1-42 production sensitizes neuroblastoma cells for ER stress toxicity

Alzheimer's disease (AD) is characterized by the aggregation and subsequent deposition of misfolded beta-amyloid (Abeta) peptide. The unfolded protein response (UPR) is activated by misfolded protein stress in the endoplasmic reticulum (ER). In previous studies we demonstrated mild activation of the UPR by extracellularly applied oligomeric but not fibrillar Abeta1-42. In addition, we showed that oligomeric Abeta1-42 is internalized by cells, whereas fibrillar Abeta1-42 remains on the outside of the cell. Inhibition of Abeta uptake specifically inhibits toxicity of Abeta1-42 oligomers, underscoring the toxic potential of intracellular Abeta. Therefore, in the present study, we investigated the connection between intracellularly produced Abeta and the ER stress response, using human neuroblastoma cells overexpressing either wild type APP695 (APPwt) or APP695V717F (APPmut). Both cell lines secrete higher levels of Abeta1-40 and Abeta1-42 compared to the parental line. In addition, APPmut produces more Abeta1-42 than APPwt. Whereas the basal levels of UPR markers are not different, we find augmented UPR induction in response to ER stress in both APP overproducing cell lines compared to the parental cell line, with the strongest UPR activation in APPmut cells. In addition, ER stress toxicity was highest in APPmut cells, strongly suggesting a connection with the production of Abeta1-42. The difference in ER stress mediated toxicity between the APPwt and APPmut cell lines is alleviated by pretreatment with gamma-secretase inhibitor, indicating that it is dependent on Abeta production and in particular on Abeta1-42. Our data indicate that increased Abeta1-42 production sensitizes neuroblastoma cells for ER stress toxicity.

Always Around, Never the Same: Pathways of Amyloid Beta Induced Neurodegeneration Throughout the Pathogenic Cascade of Alzheimers Disease

There is an increasing amount of evidence showing the importance of intermediate aggregation species of amyloid beta (Abeta) in the pathogenic cascade of Alzheimer's disease (AD). Different Abeta assembly forms may mediate diverse toxic effects at different stages of the disease. Mouse models for AD suggest that intraneuronal accumulation of Abeta oligomers might be involved in AD pathogenesis at a very early stage of the disease. The detrimental effect of oligomeric Abeta on synaptic efficacy is suggested to be an early event in the pathogenic cascade. Also early neuronal responses as activation of the unfolded protein response are processes likely to be associated with the increased occurrence of oligomeric or low fibrillar Abeta in AD pathology. In later stages of AD pathology, the fibrillarity of Abeta increases, concomitantly with a neuroinflammatory response, followed by tau related neurofibrillary changes in end stage pathology. We will review recent findings in in vitro cell models, in vivo mouse models, and post mortem AD brain tissue in view of the effects of different Abeta peptide species on neurodegeneration during AD pathogenesis. Insight into the role of different Abeta species during AD pathogenesis is essential for the development of disease modifying drugs and therapeutical strategies.