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Type: Thesis
Title: The Role of Vitamin D Autocrine Activity and Signalling in Osteoclast Formation and Activity
Author: Reinke, Daniel Christopher
Issue Date: 2020
School/Discipline: Adelaide Medical School
Abstract: The role of Vitamin D receptor (VDR) signalling within the osteoclast is not fully elucidated, with even the presence of VDR in the osteoclast debated. However, the presence of the enzyme, 25-hydroxyvitamin D 1α hydroxylase (CYP27B1) responsible for the final conversion step of the Vitamin D pro-hormone into active Vitamin D, within the osteoclasts, osteoblast and osteocytes, and the potential for modified activity and maturation within the bone cells under the effects of Vitamin D has been established. The aim of the studies within this thesis were to examine through the use of genetic knock out models (KO) the role(s) vitamin D plays in osteoclast proliferation, maturation, activity and the underlying potential genetic mechanisms. Experimental work first optimised osteoclast maturation from wild type (WT) littermate matched splenocytes and then focused on osteoclastogenesis from genetic KO models, Cyp27b1KO and VdrKO with the aim of identifying the role of autocrine vitamin D. This was expanded into the role of the V-ATPase pump as a compensatory mechanism for loss of autocrine function and the effect of vitamin D on mature osteoclasts through the Ctsk-Cre.Vdr(fl/fl) mouse model in co-culture. The deletion of the Cyp27b1 and Vdr genes and the subsequent impairment of the vitamin D metabolic pathway resulted in changes in TRAP-positive multinucleated cells (MNC) as well as per cell increase in osteoclast resorptive activity. Osteoclast related gene expression was significantly reduced in both gene KO models and deranged in the V-ATPase subunits. It is worth mentioning that several genes from both Cyp27b1 and VdrKO cultures had almost identical patterns of gene expression, reinforcing the notion that the effects seen were mediated through the loss of the vitamin D metabolic pathway. Ctsk-Cre.Vdr(fl/fl) osteoclast cultures indicated that mature WT osteoclasts resorptive activity is suppressed by the presence of the vitamin D receptor. The loss of VDR in mature osteoclasts in cocultures resulted in a deregulated increase in resorptive activity and aberrant maturation. Overall, the findings of this thesis establish that there is a role for autocrine vitamin D activity within the osteoclast lineage. The loss of the vitamin D metabolic pathway in the case of Cyp27b1KO and VdrKO, result in significant changes to osteoclast maturation, proliferation, activity and gene expression and it is evident that there are compensatory mechanisms present that help minimise the impact. Further experimentation is warranted to further elucidate the effects of vitamin D activity in the osteoclast lineage and to overall fully understand how vitamin D works in human bone and aging.
Advisor: Atkins, Gerald J.
Anderson, Paul
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 2020
Keywords: Osteoclasts
vitamin D
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
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