AGEs-RAGE axis causes endothelial-to-mesenchymal transition in early calcific aortic valve disease via TGF-β1 and BMPR2 signaling

Recent studies reported that advanced glycation end products (AGEs) and endothelial-to-mesenchymal transition (EndMT) were involved in the calcific aortic valve disease (CAVD). However, the roles of AGEs in EndMT in the development of CAVD have not been elucidated. In this study, six-week-old male Apoe(-/-) mice were divided into four groups based on the following feeding periods: 0, 2, 4, and 6 months. The latter three groups were further divided into three subgroups corresponding to the following diet treatments: normal diet, high-fat diet + normal saline injection, and high-fat diet + aminoguanidine injection. Weight gain was monitored weekly. Finally, heart echocardiographic assessments were performed, and serum lipid levels, the protein expression and the histological changes in the aortic valves were determined. Results showed that the AGE inhibitor aminoguanidine alleviated the transaortic valve velocity and decreased the total cholesterol and low-density lipoprotein cholesterol levels. Calcification and carboxymethyl-lysine deposition were firstly detected around the aortic valve surfaces, whereas aminoguanidine injection attenuated their accumulation. In the early stage, HFD-activated AGEs-RAGE signaling resulted in the alpha-smooth muscle actin (alpha-SMA) upregulation and the vascular endothelium cadherin (VE-cadherin) downregulation on the valve endothelial layer. The activation resulted in early the transforming growth factor-beta 1 (TGF-beta 1) and the alkaline phosphatase (ALP) upregulation, and simultaneously reduced the bone morphogenetic protein receptor type II (BMPR2) expression. However, aminoguanidine restricted these proteins changes by inhibiting the interaction of AGEs and RAGE. In addition, immunofluorescence images showed obvious double-positive staining of ALP and a-SMA on the valve surfaces, revealing the contribution of EndMT to the early calcification. Therefore, this study demonstrates that activation of the AGEs-RAGE axis induced EndMT, promoting the progression of the aortic valve calcification in the initial stage via the counteraction of BMPR2 and TGF-beta 1 signaling.