Fibroblast Growth Factor-4 Enhances Proliferation of Mouse Embryonic Stem Cells via Activation of c-Jun Signaling

Abstract

Fibroblast growth factor-4 (FGF4) is expressed in embryonic stages and in adult tissues, where it plays critical roles in modulating multiple cellular functions. However, the exact roles of FGF4 on proliferation and differentiation of embryonic stem cells (ESCs) are not completely understood. Exogenous addition of FGF4 stimulated proliferation of mouse ESCs (mESCs), as proven by the increases in DNA synthesis and cell cycle regulatory protein induction. These increases were almost completely inhibited by pre-treating cells with anti-FGF4 antibody. FGF4 also activated c-Jun N-terminal kinase (JNK) and extracellular-signal regulated kinase (ERK) signaling, but not p38 kinase. Blockage of JNK signaling by SP600125 or by transfection with its specific siRNA significantly inhibited FGF4-stimulated cell proliferation through the suppression of c-Jun induction and activator protein-1 (AP-1) activity. However, ERK or p38 kinase inhibitor did not affect FGF4-stimulated proliferation in mESCs. FGF4 suppressed osteogenic differentiation of mESCs by inhibiting expression of transcription factors involved in bone formation. Further, exogenous FGF4 addition stimulated proliferation of human periodontal ligament stem cells (hPDLSCs) and bone marrow mesenchymal stem cells (BMMSCs) via activation of ERK signaling. FGF4 also augmented mineralization of hPDLSCs, but not of BMMSCs. Collectively, it is suggested that FGF4 triggers proliferation of stem cells by activating MAPK-mediated signaling, while it affects differently osteogenic differentiation according to the origins of stem cells.

Microgravity Reduces the Differentiation and Regenerative Potential of Embryonic Stem Cells

“…As EBs differentiated at 1xg exhibited significantly increased expression of most terminal lineage markers that failed to appear to the same extent in μg samples, decreased expression of CDKN1A/p21 in μg samples compared with 1xg controls may be further evidence for decreased differentiation of EBs in μg. FGF1, which inhibits apoptosis and cell cycle arrest and also plays a role in embryonic development, was downregulated in μg samples, while FGF4, which promotes proliferation of mESCs [ 28 ], exhibited increased expression in μg-differentiated EBs compared with 1xg-differentiated EBs. Collectively, these gene expression data provide evidence for the hypothesis that cell cycle arrest occurs in EBs exposed to μg without the corresponding cell differentiation, possibly causing accumulation of partially differentiated cells ready for differentiation upon reloading.…”

Small Players Ruling the Hard Game: siRNA in Bone Regeneration

“…RNAi, particularly siRNAs, have been utilized as investigational tools to understand the biological role of specific genes by observing the consequences of knocking down that gene in vitro or in vivo. Similar to other tissues, several bone‐specific pathways and genes have been elucidated using this technique …”

Bidirectional Regulation of Mouse Embryonic Stem Cell Proliferation by Nicotine Is Mediated Through Wnt Signaling Pathway

“…This assay was performed using a BrdU incorporation assay kit (Cell Signaling, Danvers, Massachusetts) as described previously. 21 Briefly, 48 hours after nicotine treatment, mESCs were treated with 10 mM BrdU for 4 hours and incubated with anti-BrdU peroxidase conjugate for 90 minutes before adding a tetramethylbenzidine substrate. Incorporated BrdU was measured by an enzyme-linked immunosorbent assay reader, and data were represented as fold change compared to control group.…”

“…DNA synthesis rate was measured using tritium update assay as described previously. 21 Briefly, 48 hours after nicotine treatment, 0.5 mCi of [methyl- 3 H] thymidine deoxyribose (TdR; Amersham Pharmacia Biotech Inc, Piscataway, New Jersey) was added to each well of 96-well plates for 16 hours. The 3 H-TdR-incorporated cells were analyzed with a liquid scintillation counter (Packard Instrument Co) by measuring β emission for 1 minute.…”