Background: Disturbances in metabolic homeostasis, resulting in cardiovascular disease, are the major cause of morbidity and mortality in patients with chronic kidney disease (CKD). Mineral deposition in the vascular smooth muscle cell (VSMC)-rich medial layer of the vessel wall is a prominent driver of mortality in these patients. Vascular calcification (VC) is now recognized as an important predictor and independent risk factor for all-cause and cardiovascular mortality in patients with advanced CKD. Prolonged impairment in kidney functions, characteristic of chronic CKD, results in marked changes in blood biochemistry, namely elevated circulating levels of inorganic phosphate (Pi) and calcium. These changes in circulating mineral content trigger osteogenic transdifferentiation and apoptosis of the VSMCs, subsequently leading to VC. In addition to kidney-related metabolic changes, chronic inflammation and liver disease are also associated with increased VC. T-cell death-associated gene 51 (TDAG51) and growth differentiation factor 10 (GDF10) have been previously reported to contribute to metabolic regulation in conditions of atherogenic VC, osteogenesis, and adipogenesis. However their role in medial VC and associated morbidities remains unknown. Methods and Results: Using a combination of in vitro, ex vivo and in vivo models findings presented in this thesis demonstrate that TDAG51 is an important modulator of VC, and as such is upregulated by conditions of hyperphosphatemia. I show that VSMCs from TDAG51-/- mice exhibit reduced expression and activity of key driver of osteogenic transdifferentiation, Runt-related transcription factor 2 (Runx2). To explain these observations, I demonstrate reduced expression of type III sodium-dependent Pi transporter, Pit-1, as well as intracellular Pi in these cells. Additionally, GDF10, an established inhibitor of osteogenesis, was identified to be significantly upregulated in TDAG51-/- VSMCs and mice. In line with these observations, knockdown of human homologue of TDAG51, pleckstrin homology-like domain, family A, member 1, resulted in increased expression of GDF10. Consistent with the anti-osteogenic role of GDF10, treatment with recombinant human GDF10 reduced Pi-mediated hydroxyapatite deposition, Runx2 expression and activity in primary mouse VSMCs. Interestingly, GDF10-/- mice develop severe adiposity, hepatic lipid accumulation, injury and inflammation. To explain this phenotype, a marked increase in the expression and activity of established driver of adipogenesis, peroxisome-proliferator-activated receptor γ (PPAR γ) in the livers of GDF10-/- mice was demonstrated. Complementary experiments in cultured hepatocytes demonstrate that treatment with recombinant human GDF10 attenuates nuclear PPAR γ expression and subsequent lipid accumulation, inflammation and fibrosis in these cells. Conclusion: This work highlights TDAG51 as an important regulator of Pi-mediated VC through downregulation of Pit-1, Runx2, and GDF10. Additionally, GDF10 has been described as a novel systemic inhibitor and a potential diagnostic marker for VC. Lastly, this work further characterizes GDF10 as an adipokine important in the regulation of hepatic lipid levels, which can indirectly affect vascular health. / Thesis / Doctor of Philosophy (Medical Science)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/26056 |
| Date | January 2020 |
| Creators | Platko, Khrystyna |
| Contributors | Austin, Richard, Medical Sciences (Blood and Cardiovascular) |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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