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

Abstract

Background: 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 proosteogenic activity in AVICs. Materials and methods: 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. Results: 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. Conclusions: 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.

Upregulated Autophagy in Calcific Aortic Valve Stenosis Confers Protection of Valvular Interstitial Cells

“…In the preset study, inhibition of the degradation step of autophagy by bafilomycin A1 led to a decrease in VIC viability, which could explain the increase in calcification observed by Deng et al [15], especially since a decrease in autophagy may increase VIC cell death, thus serving as nucleating structures for calcification [22]. Moreover, we show here that acute high phosphate treatment increased autophagic flux in VICs when the recycling of the autophagosome was inhibited by bafilomycin, implying that an upregulation in autophagy might precede VIC calcification.…”

“…In line with this data, inhibition of autophagy by bafilomycin and knock down of Atg7 in VICs resulted in an increase of both calcification and of the pro-osteogenic molecules bone morphogenic protein 2 (BMP-2) and alkaline phosphatase (ALP). Additionally, induction of autophagy in VICs by rapamycin led to a decrease of both ALP and BMP-2; however, whether this translated to a reduction of calcification in VICs was not explored [15].…”

“…Recently, autophagy has been implicated in vascular calcification, specifically, as a mechanism safeguarding vascular smooth muscle cells (VSMCs) from hyperphosphatemia [14]. These findings may be extrapolated to valve calcification, since VIC autophagy has been shown to inhibit pro-osteogenic signaling [15]. Taken together, these findings suggest that autophagy serves as a protective mechanism in VICs.…”

Aortic Valve Stenosis and Mitochondrial Dysfunctions: Clinical and Molecular Perspectives

“…Modulation of autophagy by the use of the inhibitor 3-methyladenine (3-MA) and the activator rapamycin highlighted the protective role of autophagy in inhibiting BMP and ALP expression and calcium deposits. Thus, autophagy inhibits pro-osteogenic activity in HAVICs [ 144 ]. This work shows discrepancies with that of Somers et al [ 143 ].…”

miR-503 suppresses the proliferation and metastasis of esophageal squamous cell carcinoma by triggering autophagy via PKA/mTOR signaling

“…Autophagy is a highly conserved catabolic process through which proteins and organelles are recycled to generate intracellular nutrients and energy, to ultimately promote cell survival ( 7 , 8 ). It is well established that autophagy plays dual roles in tumorigenesis, playing either a suppressive or promoting role ( 9 , 10 ).…”