title: Gas6/Axl-PI3K/Akt pathway plays a central role in the effect of statins on inorganic phosphate-induced calcification of vascular smooth muscle cells.
abstract: 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.
authors.affiliation: Department of Geriatric Medicine, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.
authors.forename: Bo-Kyung
authors.initials: BK
authors.lastname: Son
authors.forename: Koichi
authors.initials: K
authors.lastname: Kozaki
authors.forename: Katsuya
authors.initials: K
authors.lastname: Iijima
authors.forename: Masato
authors.initials: M
authors.lastname: Eto
authors.forename: Toru
authors.initials: T
authors.lastname: Nakano
authors.forename: Masahiro
authors.initials: M
authors.lastname: Akishita
authors.forename: Yasuyoshi
authors.initials: Y
authors.lastname: Ouchi
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis; D002114:Calcinosis / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation; D005229:Fatty Acids, Monounsaturated / Q000494:pharmacology; D000077340:Fluvastatin; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D015513:Oncogene Proteins / Q000378:metabolism*; D010710:Phosphates / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017035:Pravastatin / Q000494:pharmacology; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D000077191:Wortmannin; D051025:bcl-Associated Death Protein / Q000378:metabolism; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6
chemical_list: D000730:Androstadienes; D053148:Caspase 3; D005229:Fatty Acids, Monounsaturated; D000077340:Fluvastatin; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D007211:Indoles; D036341:Intercellular Signaling Peptides and Proteins; D015513:Oncogene Proteins; D010710:Phosphates; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017035:Pravastatin; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D020794:Receptor Protein-Tyrosine Kinases; D000077191:Wortmannin; D051025:bcl-Associated Death Protein; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6; C494819:BAD protein, human; C000722289:AXL protein, human