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Published on: June 2, 2022
Calcium Overload Accelerates Phosphate-Induced Vascular Calcification Via Pit-1, but not the Calcium-Sensing Receptor
Asuka Masumoto1, Tomohiro Sonou1, Masaki Ohya1
1Division of Nephrology, Department of Internal Medicine, Wakayama Medical University.
Insights
High phosphate and calcium accelerate vascular calcification (VC) in rats by increasing Pit-1 protein. This study clarifies calcium
Area of Science:
- Biochemistry
- Nephrology
- Cardiovascular Biology
Background:
- Vascular calcification (VC) is a significant mortality risk factor in chronic kidney disease (CKD) patients.
- CKD-mineral and bone disorder involves abnormal serum phosphate and calcium, contributing to bone disease and cardiovascular issues.
- Hypercalcemia exacerbates VC in CKD, but intracellular calcium mechanisms remain unclear.
Purpose of the Study:
- To investigate the mechanisms of calcium-induced vascular calcification.
- To elucidate the role of Pit-1 and the calcium-sensing receptor in this process.
Main Methods:
- Rat aortic segments were cultured and exposed to high calcium (HiCa) and high phosphate (HPi) conditions.
- Phosphonoformic acid and R-568 were used to probe the involvement of Pit-1 and the calcium-sensing receptor.
- Vascular calcification and Pit-1 protein levels were quantified.
Main Results:
- High phosphate and high calcium (HPi+HiCa) significantly increased medial VC by 300% compared to HPi alone.
- HPi+HiCa medium upregulated Pit-1 protein expression.
- Phosphonoformic acid completely blocked the HPi+HiCa-induced increase in VC, while R-568 had no effect.
Conclusions:
- High phosphate and high calcium accelerate medial vascular calcification.
- This acceleration is mediated by the Pit-1 protein pathway.
- The calcium-sensing receptor is not directly involved in this calcium-induced VC mechanism.
Aim:
Vascular calcification (VC) is a risk factor of cardiovascular and all-cause mortality in patients with chronic kidney disease (CKD). CKD-mineral and bone metabolism disorder is an important problem in patients with renal failure. Abnormal levels of serum phosphate and calcium affect CKD-mineral and bone metabolism disorder and contribute to bone disease, VC, and cardiovascular disease. Hypercalcemia is a contributing factor in progression of VC in patients with CKD. However, the mechanisms of how calcium promotes intracellular calcification are still unclear. This study aimed to examine the mechanisms underlying calcium-induced calcification in a rat aortic tissue culture model.
Methods:
Aortic segments from 7-week-old male Sprague-Dawley rats were cultured in serum-supplemented medium for 10 days. We added high calcium (HiCa; calcium 3.0 mM) to high phosphate (HPi; phosphate 3.8 mM) medium to accelerate phosphate and calcium-induced VC. We used phosphonoformic acid and the calcimimetic R-568 to determine whether the mechanism of calcification involves Pit-1 or the calcium-sensing receptor.
Results:
Medial VC was significantly augmented by HPi+HiCa medium compared with HPi alone (300%, p＜0.05), and was associated with upregulation of Pit-1 protein. Pit-1 protein concentrations in HPi+HiCa medium were greater than those in HPi medium. Phosphonoformic acid completely negated the augmentation of medial VC induced by HPi+HiCa. R-568 had no additive direct effect on medial VC.
Conclusion:
These results indicated that exposure to HPi+HiCa accelerates medial VC, and this is mediated through Pit-1, not the calcium-sensing receptor.
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