Investigation of the cAMP-mediated inhibitory mechanism on the signalling pathways of 2 cytokines: IL-6 and leptin in endothelial cells

Woolson, Hayley D. (2009) Investigation of the cAMP-mediated inhibitory mechanism on the signalling pathways of 2 cytokines: IL-6 and leptin in endothelial cells. PhD thesis, University of Glasgow.

Abstract

There is a wealth of evidence to support the anti-inflammatory properties of the prototypical second messenger cyclic-AMP (cAMP), notably with regard to endothelial function. Many studies have shown that cAMP can limit vascular permeability by enhancing barrier function and reducing pro-inflammatory effects of cytokines. Although the protective effects of cAMP elevation on limiting endothelial dysfunction have been well documented, the exact molecular mechanisms remain unclear.
Using two endothelial cell types, namely human umbilical vein endothelial cells (HUVECs) and a novel human endothelial angiosarcoma-derived cell line (AS-M), this study has further characterised the cAMP-mediated inhibitory mechanism on the signalling pathways of two cytokines; interleukin-6 (IL-6) and leptin. Both cytokines have been implicated in the regulation of the immune response and both have been shown to play important pathological roles in various inflammatory diseases.
In preliminary studies, cAMP elevation was shown to induce suppressor of cytokine signalling 3 (SOCS3) in HUVECs. Further investigation of this SOCS protein in the context of IL-6 and leptin signalling in endothelial cells would be of interest in terms of possibly elucidating the molecular mechanisms underlying the protective effects of cAMP. Results from this study demonstrated a cAMP-mediated inhibition of soluble IL-6Rα (sIL-6R)/IL-6-stimulated extracellular regulated mitogen-activated protein kinase 1, 2 (ERK1,2) and signal transducer and activator of transcription 3 (STAT3) activation in HUVECs, which was independent of cAMP-dependent protein kinase A (PKA). Instead, results demonstrated the involvement of the other major cAMP sensor; exchange protein activated by cAMP 1 (Epac1). Moreover, this inhibition was shown to be SOCS3-dependent. There also appeared to be a requirement for ERK1,2 activation in the cAMP-mediated inhibition of sIL-6R/IL-6-stimulated STAT3 activation in HUVECs. In contrast to these findings, cAMP-mediated inhibition of leptin-stimulated STAT3 activation in HUVECs was shown to occur via a SOCS3-independent mechanism. The responses to cAMP elevation on sIL-6R/IL-6- and leptin-stimulated ERK1,2 activation in AS-Ms were variable, since basal levels of ERK1,2 activation were high. Furthermore, the responses to cAMP elevation on sIL-6R/IL-6- and leptin-stimulated STAT3 activation in AS-Ms were either very modest or showed no effect, respectively. SOCS3 was not shown to be involved in the cAMP-mediated inhibition of sIL-6R/IL-6-stimulated ERK1,2 and STAT3 activation in AS-Ms.
In conclusion, this study further characterised the cAMP-mediated inhibitory mechanism in HUVECs and AS-Ms, with a particular focus on the ERK1,2 signalling pathway of IL-6 and leptin. Despite varying results between both cell types, this study also identified AS-Ms as a useful and tractable cell model to study in the context of endothelial biology. Thus, a potentially new pathway has been identified which inhibits cytokine receptor activation of ERK1,2 and STAT3 in endothelial cells. A better understanding of this mechanism could contribute towards new therapeutics in the area of chronic inflammatory diseases, such as atheroscleriosis.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: cAMP, endothelial cells, ERK1/2, STAT3, SOCS3, Epac1, PKA, IL-6, Leptin, HUVECs
• Subjects: Q Science > QR Microbiology; Q Science > QP Physiology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Molecular Biosciences
• Supervisor's Name: Palmer, Dr. Tim
• Date of Award: 2009
• Depositing User: Miss Hayley D Woolson
• Unique ID: glathesis:2009-648
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 24 Mar 2009
• Last Modified: 10 Dec 2012 13:20
• URI: https://theses.gla.ac.uk/id/eprint/648