JAM-A Acts via C/EBP-α to Promote Claudin-5 Expression and Enhance Endothelial Barrier Function

Abstract

Rationale: Intercellular tight junctions are crucial for correct regulation of the endothelial barrier. Their composition and integrity are affected in pathological contexts, such as inflammation and tumour growth. 'Junctional adhesion molecule-A' (JAM-A) is a transmembrane component of tight junctions with a role in maintenance of endothelial barrier function, although how this is accomplished remains elusive. Objective: We aimed to understand the molecular mechanisms through which JAM-A expression regulates tight-junction organisation to control endothelial permeability, with potential implications under pathological conditions. Methods and Results: Genetic deletion of JAM-A in mice significantly increased vascular permeability. This was associated with significantly decreased expression of claudin-5 in the vasculature of various tissues, including brain and lung. We observed that 'CCAAT/enhancer-binding protein'-α (C/EBP-α) can act as a transcription factor to trigger the expression of claudin-5 downstream of JAM-A, to thus enhance vascular barrier function. Accordingly, gain-of-function for C/EBP-α increased claudin-5 expression and decreased endothelial permeability, as measured by the passage of FITC-dextran through endothelial monolayers. Conversely, C/EBP-α loss-of-function showed the opposite effects, of decreased claudin-5 levels and increased endothelial permeability. Mechanistically, JAM-A promoted C/EBP-α expression through suppression of b-catenin transcriptional activity, and also through activation of 'Exchange protein directly activated by cAMP' (EPAC). C/EBP-α then directly binds the promoter of claudin-5, to thereby promote its transcription. Finally, JAM-A-C/ EBP-α-mediated regulation of claudin-5 was lost in blood vessels from tissue biopsies from patients with glioblastoma and ovarian cancer. Conclusions: We describe here a novel role for the transcription factor C/EBP-α that is positively modulated by JAM-A, a component of tight junctions that acts through EPAC to up-regulate the expression of claudin-5, to thus decrease endothelial permeability. Overall, these data unravel a regulatory molecular pathway through which tight junctions limit vascular permeability. This will help in the identification of further therapeutic targets for diseases associated with endothelial barrier dysfunction.

Exercise-induced angiogenesis is dependent on metabolically primed ATF3/4+ endothelial cells

“…ATF4 functions in heterodimers with other bZIP TFs and also co-regulates many of its target genes together with other TFs ( Kilberg et al., 2009 ). Many of those bZIP TFs, such as cMYC ( Wilhelm et al., 2016 ), C/EBP ( Kakogiannos et al., 2020 ; Loinard et al., 2012 ; Min et al., 2017 ), JunD ( Gerald et al., 2004 ), and others ( Hamik et al., 2006 ), have been linked to endothelial biology before. Also, ATF3/4 have been previously shown to stabilize P53 ( Yan et al., 2005 ), a known regulator of angiogenesis ( Gogiraju et al., 2015 ).…”

Endothelial Control of Cerebral Blood Flow

“…76 Recently, it was found that JAM-A acts through activation of the cAMP-regulated guanine nucleotide exchange factor I to up-regulate the expression of claudin-5 and limit vascular permeability. 77 In the setting of cerebral inflammation, JAM-A relocalizes to the endothelial apical membrane and promotes leukocyte adhesion. 78 Endothelial cells also express adherens junctions that contain transmembrane proteins, cadherins, of which VEcadherin is most important for adhesion between cells.…”

The region‐selective regulation of endothelial claudin‐5 expression and signaling in brain health and disorders

“…In this sense, the CLDN5–ERα signaling loop may be attributed to the recent finding showing that a weak association of the CLDN5 variant rs10314 with schizophrenia only in female subjects of 22q11.2 DS (Guo et al, 2020). As other transcription factors, such as SOX18 and CCAAT/enhancer‐binding proteinα (C/EBPα), are also known to induce CLDN5 expression (Fontijn et al, 2008; Kakogiannos et al, 2020; Roudnicky et al, 2020), it would be intriguing to validate whether the positive CLDN5–SOX18 and CLDN5–C/EBPα signaling loop contribute to control of the region‐selective endothelial barrier.…”