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Species-specific biological effects of FGF-2 in articular cartilage: Implication for distinct roles within the FGF receptor familyExisting literature demonstrates that fibroblast growth factor-2 (FGF-2) exerts opposing, contradictory biological effects on cartilage homeostasis in different species. In human articular cartilage, FGF-2 plays a catabolic and anti-anabolic role in cartilage homeostasis, driving homeostasis toward degeneration and osteoarthritis (OA). In murine joints, however, FGF-2 has been identified as an anabolic mediator as ablation of the FGF-2 gene demonstrated increased susceptibility to OA. There have been no previous studies specifically addressing species-specific differences in FGF-2-mediated biological effects. In this study, we provide a mechanistic understanding by which FGF-2 exerts contradictory biological effects in human versus murine tissues. Using human articular cartilage (ex vivo) and a medial meniscal destabilization (DMM) animal model (in vivo), species-specific expression patterns of FGFR receptors (FGFRs) are elucidated between human and murine articular cartilage. In the murine OA model followed by intra-articular injection of FGF-2, we further correlate FGFR profiles to changes in behavioral pain perception, proteoglycan content in articular cartilage, and production of inflammatory (CD11b) and angiogenic (VEGF) mediators in synovium lining cells. Our results suggest that the fundamental differences in cellular responses between human and murine tissues may be secondary to distinctive expression patterns of FGFRs that eventually determine biological outcomes in the presence of FGF-2. The complex interplay of FGFRs and the downstream signaling cascades induced by FGF-2 in human cartilage should add caution to the use of this particular growth factor for biological therapy in the future. J. Cell. Biochem. (c) 2012 Wiley Periodicals, Inc.
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Novel functional interactions between Trk kinase and p75 neurotrophin receptor in neuroblastoma cellsTo understand the functional interactions between the TrkA and p75 nerve growth factor (NGF) receptors, we stably transfected LAN5 neuroblastoma cells with an expression vector for ET-R, a chimeric receptor with the extracellular domain of the epidermal growth factor receptor (EGFR), and the TrkA transmembrane and intracellular domains. EGF activated the ET-R kinase and induced partial differentiation. NGF, which can bind to endogenous p75, did not induce differentiation but enhanced the EGF-induced response, leading to differentiation of almost all cells. A mutated NGF, 3T-NGF, that binds to TrkA but not to p75 did not synergize with EGF. Enhancement of EGF-induced differentiation required at least nanomolar concentrations of NGF, consistent with the low-affinity p75 binding site. EGF may induce a limited number of neuronal cells because it also enhanced apoptosis. Both NGF and a caspase inhibitor reduced apoptosis and, thereby, enhanced differentiation. NGF seems to enhance survival through the phosphatidylinositol-3 kinase (PI3K) pathway. Consistent with this hypothesis, Akt, a downstream effector of the PI3K pathway, was hyperphosphorylated in the presence of EGF+NGF. These results demonstrate that TrkA kinase initiates differentiation, and p75 enhances differentiation by rescuing differentiating cells from apoptosis via the PI3K pathway. Even though both EGF and NGF are required for differentiation of LAN5/ET-R cells, only NGF is required for survival of the differentiated cells. In the absence of NGF, the cells die by an apoptotic mechanism, involving caspase-3. An anti-p75 antibody blocked the survival effect of NGF. Brain-derived neurotrophic factor also enhanced cell survival, indicating that in differentiated cells, NGF acts through the p75 receptor to prevent apoptosis.
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Analysis of differential gene regulation in adequate versus inadequate secretory-phase endometrial complementary deoxyribonucleic acid populations from the rhesus monkeyThe ability to create artificial menstrual cycles in the rhesus monkey provides a model for studies on the regulation of genes and gene networks by estradiol or progesterone (P) in the primate endometrium. This model allowed us to create both a normal level of secretory phase P or an inadequate level of secretory phase P, i.e. endometria that cannot support implantation. The objective of our present study focused on PCR analyses of genes for several factors that are believed to be important in the proper maturation of the endometrium. Complementary DNA (cDNA) populations were prepared from endometria harvested on day 13 (peak E level), days 21-23 of an adequate secretory phase (PcDNA) and days 21-23 of an inadequate secretory phase (IcDNA). Although placental protein 14, leukemia inhibitory factor and 17-beta hydroxysteroid dehydrogenase displayed highly upregulated levels in PcDNA (P-activated genes), there was little or no up-regulation in IcDNA. Transforming growth factor-beta 2 and its receptor and insulin growth factor-I and its receptor were up-regulated in PcDNA, whereas little or no expression was observed in IcDNA. Regulators of the cell cycle and transcription, such as retinoblastoma, c-fos, and c-jun genes, were also greatly underexpressed in IcDNA compared with PcDNA. Interestingly, one gene that we studied, keratinocyte growth factor, that was up-regulated by P (peak E levels vs. PcDNA) was more highly expressed in IcDNA. This latter result suggests that low levels of circulating P are sufficient for expression of this gene, whereas high sustained P levels result in an autologous down-regulation. These data show that the regulation of genes that may play pivotal roles in endometrial maturation are differentially expressed in IcDNA vs. PcDNA and may, in part, characterize improper endometrial maturation.