Role of calcium-phosphate deposition in vascular smooth muscle cell calcification
Abstract
In this work we are studying whether calcium phosphate deposition (CPD) during vascular calcification is a passive or a cell-mediated mechanism. Passive CPD was studied in fixed vascular smooth muscle cells (VSMC), which calcify faster than live cells in the presence of 1.8 mM Ca2+ and 2 mM P i. CPD seems to be a cell-independent process that depends on the concentration of calcium, phosphate, and hydroxyl ions, but not on Ca X P i concentration products, given that deposition is obtained with 2 X 2 and 4 X 1 Ca X Pi mM2 but not with 2 X 1 or 1 X 4 Ca X Pi mM2. Incubation with 4 mM Pi without CPD (i.e., plus 1 mM Ca) does not induce osteogene expression. Increased expression of bone markers such as Bmp2 and Cbfa1 is only observed concomitantly with CPD. Hydroxyapatite is the only crystalline phase in both lysed and live cells. Lysed cell deposits are highly crystalline, whereas live cell deposits still contain large amounts of amorphous calcium. High-resolution transmission electron microscopy revealed a nanostructure of rounded crystallites of 5-10 nm oriented at random in lysed cells, which is compatible with spontaneous precipitation. The nanostructure in live cells consisted of long fiber crystals, 10-nm thick, embedded in an amorphous matrix. This structure indicates an active role of cells in the process of hydroxyapatite crystallization. In conclusion, our data suggest that CPD is a passive phenomenon, which triggers the osteogenic changes that are involved in the formation of a well organized, calcified crystalline structure. Copyright © 2011 the American Physiological Society. ; This work was supported by a grant from the Spanish Ministry of Science and Innovation (BFU2009-12763/BFI to V. Sorribas), research grant MAT2007-61621 from the Spanish CICYT Project Consolider-Ingenio in Molecular Nanoscience CSD2007-00010 from the Spanish Ministry of Science, and a predoctoral fellowship from the Government of Aragón, Spain (B086/2007 to R. Villa-Bellosta). ; Peer Reviewed
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