Mechanisms of vascular inflammaging: TNF-α mediates endothelial CEACAM1 expression by NF-κB and β-Catenin in a biphasic manner

Chronic inflammation with progressive age, also called inflammaging, is a hallmark of the pathogenesis of cardiovascular diseases. Previously we have shown increased expression of the Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) in the vasculature of aged mice and humans that leads to a chronic pro-inflammatory milieu via mutual upregulation with TNF-α. Furthermore, CEACAM1 critically promotes vascular aging processes like collagen deposition, endothelial permeability as well as enhanced oxidative stress. Therefore, CEACAM1 is a main mediator of vascular inflammaging that may facilitate progress into cardiovascular diseases. In this study we identified the mechanisms that underly the upregulation of endothelial CEACAM1 expression by TNF-α in detail.

Immunohistochemical analyses of aortic sections from Wildtype (WT) and TNF-α knockout (Tnf^-/-) mice of different age revealed that TNF-α critically contributes to the aging-related upregulation of endothelial CEACAM1 expression in vivo. The mechanisms underlying TNF-α-dependent CEACAM1 upregulation were further analyzed in an endothelial cell culture model (EA.hy926). TNF-α upregulated CEACAM1 expression in a time-dependent manner in vitro.  In pharmacological experiments we identified an early NF-κB- and a delayed β-Catenin-mediated response. This finding was supported by time-matched nuclear translocation of NF-κB and β-Catenin. Furthermore, siRNA-mediated knockdown of the β-Catenin-targeted transcription factor TCF4 reduced TNF-α-mediated CEACAM1 upregulation.  Co-immunoprecipitation analyses show that β-Catenin is released by TNF-α-mediated adherens junctions disassembly. Furthermore, TNF-α enhanced activating phosphorylation of Akt kinase at Ser⁴⁷³. Akt kinase in turn increased phosphorylation of β-Catenin at Ser⁵⁵², a modification reported to augment its transcriptional activity. Additionally, Akt kinase facilitated β-Catenin signaling by inhibition of its degradation via phosphorylation of GSK3β at Ser⁹.

Taken together, this study identified the signaling mechanisms that underly the vascular upregulation of CEACAM1 with age. Our results directly link endothelial barrier impairment, an initial step in the pathogenesis of atherosclerosis, to CEACAM1 expression. Since CEACAM1 critically promotes vascular inflammaging and age-dependent vascular alterations this further emphasizes the potential of CEACAM1 as a novel target to prevent cardiovascular diseases.