Comparison of the effects of elevated inorganic phosphate on primary human vascular smooth muscle cells and the pre-osteoblastic cell line MC3T3-E1.

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandling

  • Lasse Ebdrup Pedersen, Danmark
Inorganic phosphate (Pi) plays a central role in biological mineralization. Mineralization physiologically takes place in bone and teeth; however, pathologically it can also take place in soft tissue such as the vasculature. Vascular mineralization, often also referred to as vascular calcification, is prevailing in patients suffering from diabetes and/or chronic kidney disease. Patients with chronic kidney disease have elevated levels of Pi in the blood (hyperphosphatemia), and hyperphosphatemia is a strong predictor of vascular mineralization and poor disease outcome. Research in the past decade into the role of Pi on vascular mineralization has revealed that vascular smooth muscle cells (VSMCs) mineralize in vitro when cultured in hyperphosphatemic media in a manner that is dependent on the type III sodium-dependent Pi transporter, PiT1, and that Pi causes regulation of gene expression, e.g., upregulation of the osteoblastic transcription factor Runx2, demonstrating that Pi is a signaling molecule. Other similarities with mineralizing osteoblasts have also often been observed in vascular mineralization. In addition, in the past two decades, a number of studies on knockout mice have demonstrated the existence of various inhibitors of vascular mineralization, which are expressed by VSMCs. Together these observations suggest that vascular mineralization is not a passive deposition of calcium-phosphate, as believed for many years, but that VSMCs play a role in the process. In this thesis, I have investigated the similarities of VSMC and osteoblast mineralization. My studies show that VSMC and pre-osteoblasts react similarly to elevated concentrations of Pi. They react by upregulating inhibitors of mineralization and by increasing Pi import and intracellular Pi concentration. We have also investigated the role of PiT1 in mesenchymal stem cell osteoblastic differentiation/mineralization and found that PiT1 is upstream of Runx2 expression in the osteoblastic differentiation also. While the role of PiT1 as a regulator of Pi-induced Runx2 expression in VSMCs has been interpreted as Pi causes an osteo-/chondro-genic phenotypic shift in VSMCs, my research, however, suggest that not to be the case. Thus, the exact role of VSMCs in vascular mineralization still requires more research.
ForlagAarhus Universitet
Antal sider236
StatusUdgivet - 10 feb. 2012

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