Bone as an endocrine organ: the biological role and mechanisms of action of osteocalcin in the vasculature

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The mini project will address two aims; (1) what are the direct vascular effects of osteocalcin in human mesenteric arteries, and (2) what are the effects of osteocalcin on endothelial cells. (1) Using wire myography (O'Sullivan et al., 2004; 2005; 2006; 2009) in human mesenteric arteries we will examine whether osteocalcin causes vasorelaxation of pre-constricted arteries or causes vasoconstriction of arteries when applied to baseline tone. We will also examine physiologically the effect of physiologically-relevant concentrations of osteocalcin on subsequent vasodilator function by exposing arteries to osteocalcin, pre-constricting pharmacologically and then performing concentration responses curves to endothelium-dependent and independent vasorelaxants. The effect of osteocalcin on vasoconstrictor responses to noradrenaline, angiotensin II and endothelin-1 will also be examined. (2) No studies to date have examined the effects of osteocalcin on endothelial cells, although a recent study suggested that osteocalcin, via hypoxia-inducible factor 1 signalling, stimulates expression of osteochondrogenic transcription factors in VSMCs (Idelevich et al., 2011). Students will investigate the effects of osteocalcin on a human endothelial cell line to establish whether osteocalcin affects a number of features of endothelial cell function, including endothelial cell proliferation (MTT assay), cytotoxicity (LDH assay), the expression of vascular adhesion molecule, vCAM (by ELISA), and markers of calcification (ALP content or calcium staining).