Leptin promotes osteoblast differentiation and mineralization of primary cultures of vascular smooth muscle cells by inhibiting glycogen synthase kinase (GSK)-3β.
In this study, we begin to investigate the underlying mechanism of leptin-induced vascular calcification. We found that treatment of cultured bovine aortic smooth muscle cells (BASMCs) with leptin (0.5-4 μg/ml) induced osteoblast differentiation in a dose-dependent manner. Furthermore, we found that leptin significantly increased the mRNA expression of osteopontin and bone sialoprotein, while down-regulating matrix gla protein (MGP) expression in BASMCs. Key factors implicated in osteoblast differentiation, including members of the Wnt signaling pathway, were examined. Exposure to leptin enhanced phosphorylation of GSK-3β on serine-9 thereby inhibiting activity and promoting the nuclear accumulation of β-catenin. Transfection of BASMCs with an adenovirus that expressed constitutively active GSK-3β (Ad-GSK-3β S9A) resulted in a >2-fold increase in GSK-3β activity and a significant decrease in leptin-induced alkaline phosphatase (ALP) activity. In addition, qRT-PCR analysis showed that GSK-3β activation resulted in a significant decrease in the expression of osteopontin and bone sialoprotein, but a marked increase in MGP mRNA expression. When taken together, our results suggest a mechanism by which leptin promotes osteoblast differentiation and vascular calcification in vivo.
Department of Medicine, McMaster University, Hamilton, ON, Canada.
Melec G
MG
Zeadin
Martin K
MK
Butcher
Stephen G
SG
Shaughnessy
Geoff H
GH
Werstuck
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D002113:Calcification, Physiologic / Q000187:drug effects*; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors; D002417:Cattle; D002454:Cell Differentiation / Q000187:drug effects*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D016326:Extracellular Matrix Proteins / Q000037:antagonists & inhibitors; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D058574:Integrin-Binding Sialoprotein / Q000096:biosynthesis; D020738:Leptin / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects*; D053495:Osteopontin / Q000096:biosynthesis; D051176:beta Catenin / Q000378:metabolism; D000097568:Matrix Gla Protein
D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D058574:Integrin-Binding Sialoprotein; D020738:Leptin; D053495:Osteopontin; D051176:beta Catenin; D000097568:Matrix Gla Protein; C000605506:GSK3B protein, human