title: Exchange protein activated by cyclic adenosine monophosphate regulates the switch between adipogenesis and osteogenesis of human mesenchymal stem cells through increasing the activation of phosphatidylinositol 3-kinase.
abstract: Epac, exchange protein activated by cyclic adenosine monophosphate (cAMP), could regulate the trans-differentiation between adipogenesis and osteogenesis of human mesenchymal stem cells (hMSCs). Epac activated by 8-pCPT-2'-O-Me-cAMP, a cAMP analog preferentially activating Epac, resulted in the increase of adipogenic gene expression and the decrease of osteogenic gene expression. The pro-adipogenic and anti-osteogenic effect of 8-pCPT-2'-O-Me-cAMP was attributed to that 8-pCPT-2'-O-Me-cAMP led to the activation of protein kinase B (PKB) and cAMP response element-binding protein (CREB) as well as the inhibition of Ras homolog gene family member A (RhoA), focal adhesion kinase (FAK), extracellular-signal-regulated kinase (ERK) and runt-related transcription factor 2 (Runx2) activities. Inhibition of Epac by a dominant-negative form of Epac1 resulted in the decrease of phosphatidylinositol 3-kinase (PI3K), PKB and CREB activities as well as down-regulation of peroxisome proliferator activated receptor-γ (PPARγ) expression. Inhibition of PI3K by a specific inhibitor or inhibition of Arf and Rho GAP adapter protein 3 (ARAP3, a phosphatidylinositol (PtdIns)(3,4,5)P(3) binding protein) by ARAP3 siRNA led to the recovery of RhoA and FAK activities. RhoA-V14, a constitutively active form of RhoA, could activate the MEK/ERK/Runx2 signaling. Therefore, we conclude that PI3K activated by Epac leads to the activation of PKB/CREB signaling and the up-regulation of PPARγ expression, which in turn activate the transcription of adipogenic genes; whereas osteogenesis is driven by Rho/FAK/MEK/ERK/Runx2 signaling, which can be inhibited by Epac via PI3K. These results should be helpful to provide new targets for treatment of osteoporosis and related bone-wasting diseases.
authors.affiliation: Institute of Cell and Development Biology, College of Life Sciences, Zhejiang University, Hangzhou 310058, PR China.
authors.forename: Zihua
authors.initials: Z
authors.lastname: Tang
authors.forename: Dongyan
authors.initials: D
authors.lastname: Shi
authors.forename: Bingbing
authors.initials: B
authors.lastname: Jia
authors.forename: Jiarong
authors.initials: J
authors.lastname: Chen
authors.forename: Chen
authors.initials: C
authors.lastname: Zong
authors.forename: Dan
authors.initials: D
authors.lastname: Shen
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zheng
authors.forename: Jinfu
authors.initials: J
authors.lastname: Wang
authors.forename: Xiangming
authors.initials: X
authors.lastname: Tong
mesh_terms: D050156:Adipogenesis; D002454:Cell Differentiation; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation; D015870:Gene Expression; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000378:metabolism*; D010012:Osteogenesis; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism*; D010766:Phosphorylation; D015398:Signal Transduction; D014162:Transfection
chemical_list: C473217:8-(4-chloro-phenylthio)-2'-O-methyladenosine-3'-5'-cyclic monophosphate; D020662:Guanine Nucleotide Exchange Factors; C116122:RAPGEF3 protein, human; D000242:Cyclic AMP; D058539:Phosphatidylinositol 3-Kinase