Canonical and non canonical Wnt

Canonical and non-canonical Wnt signaling pathways play essential roles in various cellular activities, including cell fate determination, proliferation, migration and gene expression [57]. The canonical Wnt pathway (β-catenin dependent pathway), is activated by the binding of Wnt ligands, leading to the stabilization of cytosolic β-catenin which translocates to the nucleus and binds to T-cell factor/lymphoid enhancer binding factor (TCF/LEF) jak kinase in promoters of target genes [58]. Recently, some studies have reported that crosstalk between Wnt/β-catenin and estrogen receptor signaling synergistically promotes osteogenic differentiation of bone related cells [59], [60]. And crosstalk between Wnt/β-catenin and fatty acids has been shown in many studies [61], [62], [63]. However, very few studies have demonstrated a direct relationship between estrogen, fatty acids, Wnt/β-catenin and osteogenesis. Previous studies have suggested that GPR40 protects from bone loss via inhibition of osteoclasts. Wittrant et al. used GPR40 knock-out mice and primary osteoclasts to investigate the role of GPR40 on bone remodelling. Their results in primary osteoclast cultures and the RAW264.7 cell line showed that GPR40 significantly inhibited osteoclastic differentiation by modulating Rank/OPG. Furthermore, they performed in vivo experiments to investigate whether GPR40 protects from bone loss and suggested that GW9508 gavage protected ovariectomized mice from bone loss. However, gavage of the drug may affect the entire body endocrinology, which could indirectly change bone mass or density. To avoid these problems, we performed marrow cavity injection of increasing concentrations of GW9508 into the femur of ovariectomized (OVX) mice to further dig the direct effect of GPR40 on bone metabolism.
Conflict of interest
Acknowledgment This work was supported by the Ministry of Science and Technology of China (2011CB964703), National High Technology Research and Development Program 863 (2012AA020502) and National Natural Science Foundation of China (81472043), and and the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT13051). No benefits in any form have been or will be received from a commercial party directly or indirectly by the authors of this manuscript.
Introduction Free fatty acids (FFAs) are essential dietary nutrients and act as an important energy source. FFAs mediate a variety of cellular functions with FFA receptors (FFARs) which are identified as G-protein-coupled receptors (GPCRs). Activation of the individual FFARs is dependent on the carbon chain length of FFAs [1], [2], [3]. Since FFARs are widely expressed in several tissues and closely related with metabolic functions, it is considered that FFARs are potent target molecules for the control of obesity, diabetes and cardiovascular diseases [1], [4], [5], [6], [7]. FFA receptor 1 (FFA1) and FFA4 are a member of GPCRs and activated by the binding of medium- and long-chain FFAs [1], [2], [3]. Recently, it has been suggested that FFA1 and FFA4 are involved in the pathogenesis of cancer cells. The expression of FFA4 was significantly higher in human colorectal carcinomas than in adjacent non cancerous tissues, associating with tumor progression [8]. Moreover, activation of FFA4 induced the cell migration and angiogenesis in colon cancer cells which unexpressed FFA1 [8]. In pancreatic cancer cells, FFA4 positively and FFA1 negatively regulated the cell motility, invasion and tumorigenicity [9]. FFA1 reduced the cell motile and invasive activities of　fibrosarcoma cells [10]. In contrast, FFA4 inhibited and FFA1 promoted the cellular functions of lung cancer cells [11]. Our recent studies indicated that anticancer drug treatment changed the expression levels of FFAR1 and FFAR4 genes in lung cancer and fibrosarcoma cells [10], [11]. In this study, to assess an involvement of FFA1 and FFA4 in the regulation of cellular functions during tumor progression in colon cancer cells, the long-term anticancer drug treated cells were generated from DLD1 cells which endogenously expressed FFAR1 and FFAR4 genes [12]. In addition, we established highly migratory DLD1 cells.