Farquharson, Colin

Macrae, Victoria

Zhu, Dongxing

Biotechnology and Biological Sciences Research Council (BBSRC)

2014-04-29T15:29:22Z

2014-04-29T15:29:22Z

2013-11-29

Vascular calcification is prevalent in ageing, in atherosclerosis, and especially in patients with Chronic Kidney Disease (CKD), with associated increased morbidity and mortality. The phenotypic transition of Vascular Smooth Muscle Cells (VSMCs) into osteoblastic/chondrogenic-like cells is critical for the development of calcification in CKD patients. Osteocytes, terminally differentiated osteoblasts, have recently emerged as major regulators of calcification in bone. Recently, osteocytelike cells have been observed in human peripheral arteries with medial vascular calcification. However, it remains undetermined as to whether VSMCs can undergo osteocytic differentiation within a calcifying environment and the functional role of osteocyte formation in the development of medial vascular calcification. Initial studies have characterised the ectonucleotide pyrophosphatase/phosphodiesterase 1 knockout (Enpp1-/-) mouse as a valid model of medial vascular calcification, which is employed throughout this thesis. This thesis has compared VSMCs to osteoblasts undergoing osteocytic differentiation in vitro. VSMC in vitro calcification was accompanied by up-regulated expression of osteocyte markers, including Sost, E11, Dmp1, Phex, Mepe and Fgf23. Immunohistochemistry confirmed the appearance of sclerostin and E11 in calcified aortae from the Enpp1-/- mouse. Further studies have identified a direct inhibitory role for the osteocyte specific gene FGF23 in modulating vascular calcification. The inhibitory effect of FGF23 on VSMC calcification was mediated through the MAPK/ERK signalling pathway. This thesis has also determined the role of BMP9, a highly osteogenic bone morphogenic protein, in vascular calcification, which induces VSMC calcification through a Smad signalling mechanism. Furthermore, VSMC expression of the osteocytic marker Sost was markedly increased following BMP9 treatment. Intriguingly, BMP9 was markedly elevated in serum from dialysis patients and a significant correlation was observed between dialysis time and BMP9 concentration in patients receiving haemodialysis. The work described herein has demonstrated that vascular calcification is associated with an osteocyte phenotype, and reports a direct inhibitory effect of the osteocyte specific gene FGF23 on vascular calcification. Furthermore, this thesis has shown that BMP9 induces the expression of the osteocytic marker Sost in VSMCs, and appears to play a critical role in vascular calcification.

http://hdl.handle.net/1842/8765

en

The University of Edinburgh

Zhu D, Mackenzie NCW, Millán JL, Farquharson C, MacRae VE (2011). The appearance and modulation of osteocyte marker expression during calcification of vascular smooth muscle cells. PLoS One 6 (5), e19595

Mackenzie NCW, Zhu D, Milne EM, van 't Hof R, Martin A, Darryl Quarles L, et al. (2012). Altered bone development and an increase in FGF-23 expression in Enpp1-/- mice. PLoS One 7:e32177.

Zhu D, Mackenzie NCW, Millan JL, Farquharson C, Macrae VE (2013). A protective role for FGF-23 in local defence against disrupted arterial wall integrity? Mol Cell Endocrinol 372:1-11

2100-12-31

Medial vascular calcification

Osteocyte markers

Role of osteocyte markers in medial vascular calcification

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy

Restricted Access