Adipose tissue is now recognised as much more than an excess energy storage depot but is in fact a metabolically active organ [1].  Several adipokines signal to other tissues to help coordinate physiological processes including energy homeostasis [1].  Imbalanced adipokine production is thought to contribute to the pathogenesis of obesity related Type 2 diabetes and cardiovascular disease (CVD) complications [2]. Adipokines upregulated in obesity, including adiponectin and apelin, can exert anti-inflammatory and cardio-protective effects [3], whereas others impair cardiovascular function [3].

This project will focus on apelin, which is known to exist in various isoforms (processed from a larger apelin-77 precursor), including apelin-36, apelin-17, (pGlu)apelin-13 and apelin-13. Apelin-13 has multiple biological actions mediated through its cognate APJ receptor. There is growing interest in the role of apelin in metabolic diseases including T2DM, obesity and CVD [4,5]. A recent meta-analysis showed low circulating apelin concentrations are associated with a higher risk of hypertension [6].  Coronary heart disease subjects were reported to have lower apelin concentrations compared to healthy controls [7,8].  Despite this, relatively little is known about the role of apelin in the pathophysiology of obesity and diabetes.  Some studies show that circulating apelin concentrations are elevated in T2DM and obesity, but others suggest that it is lower [9].

Experimental Design:

The current research study will improve our understanding of the pathophysiology of apelin, while assessing its utility as a disease biomarker in stratified human clinical samples by quantifying various apelin isoforms in plasma samples under a variety of conditions. A HPLC method with MS verification will be used to examine peptide recovery from mouse plasma samples.

*Examining the stability and half-life of natural isoforms of apelin (e.g. apelin-36, (pGlu)apelin-13 and apelin-13) in mouse plasma in vitro using a HPLC based assay with peptide identification by mass spectrometry.

*To determine the recovery of apelin isoforms following sample spiking to determine assay recovery, variability and sensitivity.

*Measurement of apelin isoforms in human subjects at risk of diabetes (e.g. pre-diabetes and obese populations BMI>25 kg/m2) or during the time course of an OGTT (e.g. DexLife Study).


A reversed phase HPLC method will be used to examine peptide recovery from mouse plasma samples following spiking with synthetic forms of the naturally occurring peptides. An ELISA assay apelin-13 will be used to measure apelin in human plasma/serum samples.  LC-MS and MALDI-TOF mass spectrometry techniques will be developed to look at the quantification of various isoforms using spiked plasma samples.

Skills required of applicant:

The applicant should ideally have good practical laboratory, computer and communication skills and show enthusiasm and commitment to work diligently on all aspects the research project. A background in biomedical sciences, biochemistry, pharmacology or a related subject would be desirable.


[1]    Fantuzzi G. Adipose tissue, adipokines, and inflammation. J Allergy Clin Immunol 2005;115:911-920.

[2]    Shibata R, et al. The role of adipokines in cardiovascular disease. J Cardiol 2017;70(4):329-334.

[3]    Smekal A, et al. Adipokines and cardiovascular disease: A comprehensive review. Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub 2017;161:31– 40.

[4]    Cudnoch Jedrzejewska A, et al. The role of apelin in pathogenesis of Cardiovascular diseases and metabolic disorders].  
Kardiol Pol 2011;69 Suppl 3:89 –93.

[5]    Castan-Laurell I, et al. Apelin, diabetes, and obesity. Endocrine 2011;40:1–9.

[6]    Xie H, et al. Lowered circulating apelin is significantly associated with an increased risk for hypertension: a meta-analysis. Clin Exp Hypertens 2017;39:435– 440.

[7]   Chen T, et al. Association of apelin and apelin receptor with the risk of coronary artery disease:  A meta-analysis of observational studies. Oncotarget 2015;8(34).

[8]   Zhang BH, et al. Cardioprotective effects of adipokine apelin on myocardial infarction. Heart Vessels 2014;29:679 – 689.

[9]   Castan-Laurell I, et al. Apelin, a novel adipokine over-produced in obesity: Friend or foe? Mol Cell Endocrinol 2005;245:7–9

[10]  O'Harte FPM, et al. Acylated apelin-13 amide analogues exhibit enzyme resistance and prolonged insulin releasing, glucose lowering and anorexic properties. Biochem Pharmacol 2017;15;146:165-17

Essential criteria

  • To hold, or expect to achieve by 15 August, an Upper Second Class Honours (2:1) Degree or equivalent from a UK institution (or overseas award deemed to be equivalent via UK NARIC) in a related or cognate field.

The Doctoral College at Ulster University


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