High Expression of the Pi-Transporter SLC20A1/Pit1 in Calcific Aortic Valve Disease Promotes Mineralization through Regulation of Akt-1

Diala El Husseini,Marie-Chloé Boulanger,Patrick Mathieu,Ablajan Mahmut,Dominique Fournier,Philippe Pibarot,Yohan Bossé,Ferenc Gallyas

doi:10.1371/journal.pone.0053393

Diala El Husseini, Marie-Chloé Boulanger + Show 6 more

Open Access

https://doi.org/10.1371/journal.pone.0053393

Copy DOI

Abstract

The regulation of phosphate (Pi) handling is crucial during calcification of the aortic valve. Gene profiling of Pi transporters revealed that VIC culture expresses SLC201A1/Pit1 and SLC20A2/Pit2. On exposure to a mineralizing medium (2 mM Pi), the expression of Pi transporters in VIC culture is increased several folds, with the highest magnitude for SLC20A1. By using siRNAs, we established that silencing SLC20A1 significantly reduced Pi-induced mineralization of VICs. In human pathological specimens, we found that the expression of SCL20A1 was increased in CAVD tissues compared to control non-mineralized aortic valves. Treatment of VIC culture with Pi promoted the loss of mitochondrial membrane potential (ΔΨm) and cytochrome c release within the cytosol, leading to apoptosis. Inhibition of Pi transporters with phosphonoformic acid (PFA) prevented Pi-mediated apoptosis of VICs. Moreover, we discovered that the level of the Akt-1 transcript is diminished in CAVD tissues compared with control valves. Accordingly, treatment with Pi caused a reduction of the Akt-1 transcript in VIC culture, and treatment with PFA or siRNA against SLC20A1 restored the level of Akt-1. Overexpression of Akt-1 (pCMVAkt-1) prevented both Pi-induced apoptosis and mineralization of VIC culture. These results strongly suggest that overexpression of SLC20A1 promotes apoptosis and mineralization by altering the level of Akt-1.

Highlights

Calcific aortic valve disease (CAVD) is a common disorder of the aging population [1]
Apoptosis levels were measured by using a TUNEL assay and we demonstrated that phosphonoformic acid (PFA) completely blocked phosphate handling (Pi)-induced apoptosis of valve interstitial cells (VICs) (Figure 3A)
We found that PFA impedes the Pi-mediated cytochrome c release within the cytosol of VICs (Figure 3D). These findings suggest that intracellular channelling of Pi promotes apoptosis of VIC culture by activating the mitochondrial pathway and the opening of the mitochondrial permeability transition pore (MTP)

Summary

Introduction

Calcific aortic valve disease (CAVD) is a common disorder of the aging population [1]. Despite the high prevalence of this condition, there is so far no medical treatment for CAVD To this effect, randomized trials with statins have indicated that a lipidlowering strategy in patients with CAVD is no more efficient than the placebo [2,3,4]. Different risk factors, such as age, male gender, diabetes, and hypertension, have been identified in CAVD [5]. Mineralization of the aortic valve is the major culprit in the development of CAVD. The key molecular processes leading to the mineralization of the aortic valve are just beginning to be understood, and this understanding is of utmost importance in devising novel medical therapies

Methods

Results

Discussion

Conclusion