Autophagy negatively regulates pro-osteogenic activity in human aortic valve interstitial cells

Autophagy is a physiological process that plays an important role in maintaining cellular functions. When aortic valve interstitial cells (AVICs) are stimulated with inflammatory or mechanical stress, one response is elevated pro-osteogenic activity. We hypothesized that autophagy is important in the prevention or regulation of this pro-osteogenic activity in AVICs.

AVICs were isolated. Autophagy activity was examined and its role in AVIC's pro-osteogenic activity was determined using chemical inhibitors and genetic techniques. The pro-osteogenic biomarker bone morphogenetic protein 2 (BMP-2) and alkaline phosphatase (ALP) were analyzed by immunoblotting and calcium deposition assay.

Human AVICs from normal aortic valve donors displayed significantly higher autophagic activity than those from calcified aortic valve donors as indicated by lower protein levels of light chain 3-II. Suppression of autophagy by 3-methyladenine, bafilomycin, or knockdown of Atg7 gene induced the expression of BMP-2 and ALP, increased ALP activity, and calcium deposit formation in normal AVICs. Conversely, upregulation of autophagy with rapamycin or overexpression of Atg7 gene decreased the levels of BMP-2 and ALP in diseased AVICs.

Our data showed that autophagy negatively regulates the pro-osteogenic activity in human AVICs, suggesting that upregulation of autophagy may prevent the progression of calcific aortic valve disease.