The role of lipoproteins in vascular calcification and plaque stabilisation

Vascular calcification (VC) is a feature of atherosclerotic plaques and is associated with co-morbidities such as diabetes and chronic kidney disease. While its presence is used by cardiologists to identify higher risk patients, increasing data suggests that the morphology of calcification is also important to the stability of a plaque, whereby smaller growths, particularly in the fibrous cap, increase likelihood of rupture and larger sheets decrease likelihood. Although lipoproteins, namely high (HDL), low (LDL), very low (VLDL) density lipoproteins and lipoprotein (a) (Lp(a)), have been previously studied in their relationship to general plaque growth and progression, their roles in influencing plaque calcification are less understood due to experimental variations within the literature. This thesis therefore aims to study the roles of HDL, LDL, VLDL and their pro-atherogenic oxidised forms (ox) on atherosclerotic VC in vitro, in vivo and in human plasma samples ex vivo, and aims to assess these using standardised models. Using in vitro calcification assays developed in chapter 3, we observed that both oxVLDL and oxLDL increase vascular smooth muscle cell (VSMC) calcification, whereas native HDL reduces mineralisation. This effect of HDL however is not observed in reconstituted or oxidised species, showing a pro-calcification effect for oxidised lipoprotein species. PCR and western blot techniques identified raised Runx2, RANKL, RANK and lowered OPG as potential calcification molecules that may be influenced by lipoproteins in these cells, however further studies are needed to elucidate the full mechanisms and solidify these results. In vivo, modifying VLDL into a pro-atherogenic phenotype via apo CIII deletion on an Apo E knock out background had only minor effects on plaque characteristics when challenged with an atherogenic diet. Interestingly, triglyceride levels positively correlated with calcification markers both in vivo and ex vivo, suggesting a role for triglyceride rich lipoproteins in the stabilisation of plaques. Furthermore, the results for triglyceride involvement in VC carried into in vivo studies using pro-atherogenic Apo E knockout and pro-atherogenic/pro-calcification Apo E x OPG double knock out mice fed an atherogenic diet for 40 weeks and infused with HDL during the final 4 weeks of the study. Alongside the in vivo results, the triglyceride level in human plasma correlated with calcification markers in ex vivo human studies. While we expected to see changes in correlation with Lp(a) levels, none were detected in this thesis, prompting more precise investigation in the future when examining this particle. This thesis therefore shows roles for several lipoprotein forms in vascular calcification in standardised experiments, providing a starting point for comparison and further experimentation in the future. In continuing this research, a broader spectrum of markers will need to be analysed and further mechanistic studies would provide insight into molecules which may be therapeutically targeted for late-stage and culprit plaque stabilisation.

Author dc:creator

• Akers, Emma Jill

Advisors dc:contributor.advisor

• Nicholls, Stephen
• Di Bartolo, Belinda

• Atherosclerosis
• vascular calcification
• lipoproteins
• LDL
• HDL
• VLDL
• Lp(a)
• apolipoproteins
• valvular calcification
• calcification
• arterial

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2440/133847

OAI identifier oai:identifier

oai:digital.library.adelaide.edu.au:2440/133847