Skeletal development and homeostasis is comprised of complex events characterized by the presence of cell specific regulators and markers. Aberrant expression of any of the regulating factors usually results in metabolic bone disease. Therefore understanding the mechanisms of skeletal homeostasis may disclose new therapies for treating these disorders. While the complete pathway that defines normal osteoblast differentiation remains indeterminate, several regulatory factors have already been identified and characterized. Using gene targeting technology, the importance of parathyroid hormone-related peptide (PTHrP) in skeletal biology has been well established, as PTHrP^-/- and PTHrP^+/- mice demonstrate skeletal abnormalities. Several lines of evidence from in vivo and in vitro studies suggest that PTHrP has unique roles in osteoblast biology, independent from its well-established roles in chondrocytes. The presence of an intronic variable number tandem repeat sequence (VNTR) in the human PTHrP gene has been proposed to provide a novel mechanism of transcriptional gene regulation in osteoblasts. A preliminary survey indicated that osteoporotic patients with low bone mineral density have the shortest allele of the VNTR. In this work, we set out to investigate the role of the minisatellite in PTHrP expression and as a potential predictor of decreased bone mineral density. However, in a large sample of osteoporotic patients, a correlation between bone mineral density and VNTR length was not apparent. Also, the presence of the VNTR, or its length, seemed not to affect PTHrP promoter activity in osteoblast-like cells. EMSA experiments demonstrated the ability of the VNTR to bind proteins whose natures remain unclear. We also studied the effect of the newly identified zinc-finger transcription factor, Osterix, on the GC-rich PTHrP promoter. Osx did not bind the promoter or affect its transcriptional activity. However, unexpectedly, we observed that the transcription factor Cbfal, the master regulator of osteoblast differentiation, decreases PTHrP gene expression, likely through a molecular intermediate. Our investigations have shed some light on the role of PTHrP in osteoblast differentiation, and its regulation in this process by polymorphic elements and transcription factors specific to osteoblasts. The potential role of these parameters in the homeostatic regulation of the skeleton and the development of metabolic bone diseases such as osteoporosis warrants further investigation.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.19451 |
| Date | January 2003 |
| Creators | Bukka, Prasanna L. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Human Genetics) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002010452, Theses scanned by McGill Library. |
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