Gas6/Axl-PI3K/Akt pathway plays a central role in the effect of statins on inorganic phosphate-induced calcification of vascular smooth muscle cells.

Apoptosis is essential for the initiation and progression of vascular calcification. Recently, we showed that 3-hydroxy-3-methylglutaryl (HMG) CoA reductase inhibitors (statins) have a protective effect against vascular smooth muscle cell calcification by inhibiting apoptosis, where growth arrest-specific gene 6 (Gas6) plays a pivotal role. In the present study, we clarified the downstream targets of Gas6-mediated survival signaling in inorganic phosphate (Pi)-induced apoptosis and examined the effect of statins. We found that fluvastatin and pravastatin significantly inhibited Pi-induced apoptosis and calcification in a concentration-dependent manner in human aortic smooth muscle cells (HASMC), as was found with atorvastatin previously. Gas6 and its receptor, Axl, expression were downregulated in the presence of Pi, and recombinant human Gas6 (rhGas6) significantly inhibited apoptosis and calcification in a concentration-dependent manner. During apoptosis, Pi suppressed Akt phosphorylation, which was reversed by rhGas6. Wortmannin, a specific phosphatidylinositol 3-OH kinase (PI3K) inhibitor, abolished the increase in Akt phosphorylation by rhGas6 and eliminated the inhibitory effect of rhGas6 on both Pi-induced apoptosis and calcification, suggesting that PI3K-Akt is a downstream signal of the Gas6-mediated survival pathway. Pi reduced phosphorylation of Bcl2 and Bad, and activated caspase 3, all of which were reversed by rhGas6. The inhibitory effect of statins on Pi-induced apoptosis was accompanied by restoration of the Gas6-mediated survival signal pathway: upregulation of Gas6 and Axl expression, increased phosphorylation of Akt and Bcl2, and inhibition of Bad and caspase 3 activation. These findings indicate that the Gas6-mediated survival pathway is the target of statins' effect to prevent vascular calcification.