Bone Morphogenetic Protein Signaling Is Required for Aortic Valve Calcification

Abstract

Objective Calcific Aortic Valve Disease (CAVD) is the most prevalent type of heart valve disease, affecting ~2% of the US population. CAVD is characterized by the presence of calcific nodules resulting in aortic valve (AoV) stenosis; however, the underlying mechanisms driving disease remain unknown. Studies of human diseased AoV provide initial evidence that BMP signaling, essential for normal bone formation, is activated during CAVD. Mice deficient in Klotho, an FGF23 transmembrane co-receptor, exhibit premature aging and develop AoV calcific nodules as occurs in human CAVD. The role of BMP signaling in the development of CAVD was examined in porcine aortic valve interstitial cells (VICs) and Klotho−/− mice. Approach & Results We show that activation of BMP signaling, as indicated by pSmad1/5/8 expression, precedes and later localizes with AoV calcification in Klotho−/− mice. In addition, cellular and ECM changes resembling features of normal bone formation are accompanied by increased osteochondrogenic gene induction in calcified Klotho−/− AoV. Likewise, osteogenic media (OM) treatment of porcine VICs results in BMP pathway activation, increased osteochondrogenic gene induction and formation of calcific nodules in vitro. We demonstrate that genetic inactivation of the Bmpr1a receptor in Klotho−/− aortic VICs, as well as BMP pathway inhibition of OM-treated aortic VICs in vitro, results in the inhibition of AoV calcification. Discussion BMP signaling and osteochondrogenic gene induction are active in calcified Klotho−/− AoV in vivo and calcified porcine aortic VICs in vitro. Importantly, BMP signaling is required for the development of AoV calcification in vitro and in vivo.

Klotho suppresses high phosphate-induced osteogenic responses in human aortic valve interstitial cells through inhibition of Sox9

“…The Klotho −/− mouse model, which exhibits premature aging associated with hyperphosphatemia and low vitamin D, has been used to study age-related diseases, including CKD and vascular calcification. Klotho −/− mice exhibit aortic valve calcification at the hinge region of the fibrosa side [16], a pathological change similar to human CAVD. Reduced expression of this protein has been observed in patients with CKD, and this may be one of the factors underlying the aortic valve calcification in CKD.…”

“…Klotho levels in the kidney and blood were lower in patients with CKD [15]. Klotho-deficient mice suffer from a wide variety of age-related disorders as well as tissue calcification, including aortic valve calcification [16, 17]. However, it remains unknown whether Klotho suppresses high Pi-induced osteogenic responses in human AVICs.…”

Genetic basis of aortic valvular disease

“…It has been well established that BMP2, BMP4 and pSMAD1/5/8 are associated with aortic valve calcification [33], but a recent study by Gomez-Stallons et al demonstrated that BMP signaling is also required for aortic valve calcification in the Klotho −/− mouse model, which exhibits CAVD and premature aging associated with hyperphosphatemia. It was found that BMP signaling precedes and localizes with calcification in the aortic valve, and inhibition of BMP in VICs in vitro and in vivo prevents calcification [48]. Additional recent studies have further support the role of cadherin signaling in CAVD.…”

BMP2 expression in the endocardial lineage is required for AV endocardial cushion maturation and remodeling

“…However, a recent paper has shown that deletion of Bmpr1a with a PostnCre (Lindsley et al ., 2007) mesenchymal lineage driver line do not cause aortic or mitral valve defects at PD1 (Gomez-Stallons et al ., 2016). In the present study, we demonstrate that Bmp2 cKO Endo mice consistently exhibit membranous VSDs (Fig.…”