title: Possible involvement of AMP-activated protein kinase in PGE1-induced synthesis of osteoprotegerin in osteoblasts.
abstract: AMP-activated protein kinase (AMPK) is firmly established as a central regulator of cellular energy homeostasis. We have previously reported that prostaglandin E1(PGE1) stimulates the synthesis of osteoprotegerin through p38 mitogen-activated protein (MAP) kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells. The present study investigated the involvement of AMPK in PGE1-induced osteoprotegerin synthesis in MC3T3-E1 cells. The levels of osteoprotegerin were measured using an enzyme-linked immunosorbent assay, while the phosphorylation of AMPK, acetyl-CoA carboxylase, p38 MAP kinase and SAPK/JNK were analyzed by western blotting. In addition, the mRNA expression levels of osteoprotegerin were determined by a reverse transcription-quantitative polymerase chain reaction. It was revealed that PGE1significantly induced the phosphorylation of the α and β subunits of AMPK in a time-dependent manner (P<0.05). In addition, acetyl-CoA carboxylase, a direct substrate of AMPK, was significantly phosphorylated by PGE1(P<0.05). Compound C, an AMPK inhibitor, was revealed to suppress the phosphorylation of acetyl-CoA carboxylase, which significantly reduced the release and mRNA expression levels of PGE1-stimulated osteoprotegerin (P<0.05). However, the PGE1-induced phosphorylation of p38 MAP kinase and SAPK/JNK were not affected by compound C. The results of the present study indicated that AMPK may positively regulate PGE1-stimulated osteoprotegerin synthesis in osteoblasts; thus providing novel insight into the regulatory mechanisms underlying bone metabolism.
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi 467-8601, Japan; Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Kainuma
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi 467-8601, Japan.
authors.forename: Takanobu
authors.initials: T
authors.lastname: Otsuka
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi 467-8601, Japan; Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Gen
authors.initials: G
authors.lastname: Kuroyanagi
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi 467-8601, Japan; Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Naohiro
authors.initials: N
authors.lastname: Yamamoto
authors.affiliation: Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Matsushima-Nishiwaki
authors.affiliation: Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Kozawa
authors.affiliation: Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan; Department of Clinical Laboratory, National Center for Geriatrics and Gerontology, Obu, Aichi 474-8511, Japan.
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Tokuda
keywords: AMP-activated protein kinase; osteoblasts; osteoprotegerin; prostaglandin E1