| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000)
Fiscal Year 2012: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2011: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2010: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
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| Research Abstract |
Vascular calcification is the most important cause of cardiovascular disease in patients with chronic kidney disease (CKD). Medial layer vascular calcification, which is recognized to be an active process (i.e., the transformation of vascular smooth muscle cells into osteoblast-like cells), is common in CKD patients. We have recently reported the possibility of an interaction between elastin degradation and medial layer vascular calcification. Matrix metalloproteinase-2 (MMP-2), which induces the degradation of elastin, has been implicated in the elastic calcification in arteries of dialysis patients. However, the precise mechanisms by which elastin degradation interacts with the development of vascular calcification remain to be studied. To clarify the mechanisms by which elastin degradation is involved in the development of medial layer vascular calcification in the uremic milieu, we induced aortic medial layer calcification in 5/6 nephrectomized uremic rats (male Sprague-Dawley rats
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) fed a diet containing high phosphate (1.2%) and lactate (20%). After 10 weeks, the rats were euthanized for the measurement of serum chemistry profiles and histological analyses. The uremic rats showed significant increases in blood pressure, serum creatinine, phosphate, and parathyroid hormone levels compared with normal rats. von Kossa staining showed medial layer aortic calcification in the uremic rats. In calcified lesions, thin elastic lamellae were observed by elastin staining, indicating that elastin degradation could occur in the area. Furthermore, MMP-2 expression determined by immunohistochemistry was also observed in the same area. Elastin degradation accompanied by MMP-2 expression might be involved in the development of medial layer vascular calcification in uremic rats. In the next step we focused on anti-inflammatory effect of vitamin D receptor activators (VDRAs) on vascular smooth muscle cell (VSMC) mineralization induced by phosphate and TNF-α since inflammatory cytokines induce MMP-2 which contributes to elastin degradation.Human VSMCs were treated with either vehicle, maxacalcitol (10^<-9> M to 10^<-7> M), or calcitriol (10^<-9> M to 10^<-7> M) in 2.5 mM of phosphate media with TNF-α (1 ng/ml) for 9 days. VSMC mineralization was determined and expression of genes associated with the osteogenic process was examined by real-time RT-PCR. Expression of matrix metalloproteinase-2 (MMP-2) mRNA in VSMCs and MMP-2 protein in media were also analyzed. Vehicle-treated VSMCs exhibited massive mineralization, which was inhibited by maxacalcitol in a concentration-dependent manner. Calcitriol also inhibited the mineralization. While vehicle-treated VSMCs exhibited increased mRNA expression of genes associated with the osteogenic process (Cbfa1/Runx2 and osteocalcin) compared with VSMCs grown in normal media without TNF-α (control), maxacalcitol and calcitriol suppressed the increase in mRNA species. Furthermore, vehicle-treated VSMCs exhibited increased MMP-2 mRNA and protein in the media that were suppressed notably by maxacalcitol. Both of the VDRAs abrogated the acceleration of the osteogenic process induced by phosphate and TNF-α in VSMCs, which was linked to inhibition of mineralization in VSMCs. MMP-2 blockade by VDRAs may contribute to an inhibitory effect on vascular calcification. Less
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