Fibroblast growth factor (FGF)-2 mediates cell attachment through interactions with two FGF receptor-1 isoforms and extracellular matrix or cell-associated heparan sulfate proteoglycans

Stimulation of wound healing by PU/hydrogel composites containing fibroblast growth factor-2

Histological examination of wound repair in each group on day 2 after initial wounding. The arrows indicate the vascularization formation.

A complex role for FGF-2 in self-renewal, survival, and adhesion of human embryonic stem cells

The transcription program that is responsible for the pluripotency of human ESCs (hESCs) is believed to be comaintained by exogenous fibroblast growth factor-2 (FGF-2), which activates FGF receptors (FGFRs) and stimulates the mitogen-activated protein kinase (MAPK) pathway. However, the same pathway is stimulated by insulin receptors, insulin-like growth factor 1 receptors, and epidermal growth factor receptors. This mechanism is further complicated by intracrine FGF signals. Thus, the molecular mechanisms by which FGF-2 promotes the undifferentiated growth of hESCs are unclear. Here we show that, in undifferentiated hESCs, exogenous FGF-2 stimulated the expression of stem cell genes while suppressing cell death and apoptosis genes. Inhibition of autocrine FGF signaling caused upregulation of differentiation-related genes and downregulation of stem cell genes. Thus, exogenous FGF-2 reinforced the pluripotency maintenance program of intracrine FGF-2 signaling. Consistent with this hypothesis, expression of endogenous FGF-2 decreased during hESC differentiation and FGF-2 knockdown-induced hESC differentiation. In addition, FGF-2 signaling via FGFR2 activated MAPK kinase/extracellular signal-regulated kinase and AKT kinases, protected hESC from stress-induced cell death, and increased hESC adhesion and cloning efficiency. This stimulation of self-renewal, cell survival, and adhesion by exogenous and endogenous FGF-2 may synergize to maintain the undifferentiated growth of hESCs. Stem Cells2009;27:1847–1857

Long-term multilayer adherent network (MAN) expansion, maintenance, and characterization, chemical and genetic manipulation, and transplantation of human fetal forebrain neural stem cells

Human neural stem/precursor cells (hNSC/hNPC) have been targeted for application in a variety of research models and as prospective candidates for cell-based therapeutic modalities in central nervous system (CNS) disorders. To this end, the successful derivation, expansion, and sustained maintenance of undifferentiated hNSC/hNPC in vitro, as artificial expandable neurogenic micro-niches, promises a diversity of applications as well as future potential for a variety of experimental paradigms modeling early human neurogenesis, neuronal migration, and neurogenetic disorders, and could also serve as a platform for small-molecule drug screening in the CNS. Furthermore, hNPC transplants provide an alternative substrate for cellular regeneration and restoration of damaged tissue in neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. Human somatic neural stem/progenitor cells (NSC/NPC) have been derived from a variety of cadaveric sources and proven engraftable in a cytoarchitecturally appropriate manner into the developing and adult rodent and monkey brain while maintaining both functional and migratory capabilities in pathological models of disease. In the following unit, we describe a new procedure that we have successfully employed to maintain operationally defined human somatic NSC/NPC from developing fetal, pre-term post-natal, and adult cadaveric forebrain. Specifically, we outline the detailed methodology for in vitro expansion, long-term maintenance, manipulation, and transplantation of these multipotent precursors.

Laser-layered microfabrication of spatially patterned functionalized tissue-engineering scaffolds

Understanding cell behavior inside complex, three-dimensional (3D) microenvironments with controlled spatiotemporal patterning of physical and biochemical factors would provide significant insights into the basic biology of organ development and tissue functions. One of the fundamental limitations in studying such behavior has been the inability to create patterned microenvironments within 3D scaffold structures. Here a simple, layer-by-layer stereolithography (SL) method that can precisely pattern ligands, extracellular-matrix (ECM) components, and growth factors, as well as controlled release particles inside a single scaffold, has been developed. The process also allows fabrication of predesigned internal architectures and porosities. Photocrosslinkable poly(ethylene glycol) dimethacrylate (PEGDMA) was used as the basic structural component of these microfabricated scaffolds. PEG acrylates, covalently modified with the cell adhesive peptide arginine-glycine-aspartic acid (RGD) or the ECM component heparan sulfate, was incorporated within the scaffolds to facilitate cell attachment and to allow spatial sequestration of heparan-binding growth factors. Fluorescently labeled polymer microparticles and basic fibroblast growth factor (FGF-2) were chosen to illustrate the capability of SL to spatiotemporally pattern scaffolds. The results demonstrate that a precise, predesigned distribution of single or multiple factors within a single 3D structure can be created, and specific internal architectures can be fabricated. Functionalization of these scaffolds with RGD is demonstrated, and heparan sulfate allows efficient cell attachment and spatial localization of growth factors. Such patterned scaffolds might provide effective systems to study cell behavior in complex microenvironments and could eventually lead to engineering of complex, hybrid tissue structures through predesigned, multilineage differentiation of a single stem-cell population.

Dickkopf-1 regulates gastrulation movements by coordinated modulation of Wnt/beta catenin and Wnt/PCP activities, through interaction with the Dally-like homolog Knypek

Dickkopf-1 (Dkk1) is a secreted protein that negatively modulates the Wnt/beta catenin pathway. Lack of Dkk1 function affects head formation in frog and mice, supporting the idea that Dkk1 acts as a "head inducer" during gastrulation. We show here that lack of Dkk1 function accelerates internalization and rostral progression of the mesendoderm and that gain of function slows down both internalization and convergence extension, indicating a novel role for Dkk1 in modulating these movements. The motility phenotype found in the morphants is not observed in embryos in which the Wnt/beta catenin pathway is overactivated, and that dominant-negative Wnt proteins are not able to rescue the gastrulation movement defect induced by absence of Dkk1. These data strongly suggest that Dkk1 is acting in a beta catenin independent fashion when modulating gastrulation movements. We demonstrate that the glypican 4/6 homolog Knypek (Kny) binds to Dkk1 and that they are able to functionally interact in vivo. Moreover, Dkk1 regulation of gastrulation movements is kny dependent. Kny is a component of the Wnt/planar cell polarity (PCP) pathway. We found that indeed Dkk1 is able to activate this pathway in both Xenopus and zebrafish. Furthermore, concomitant alteration of the beta catenin and PCP activities is able to mimic the morphant accelerated cell motility phenotype. Our data therefore indicate that Dkk1 regulates gastrulation movement through interaction with LRP5/6 and Kny and coordinated modulations of Wnt/beta catenin and Wnt/PCP pathways.

Prostate cells express two isoforms of fibroblast growth factor receptor 1 with different affinities for fibroblast growth factor-2

BACKGROUND

Fibroblast growth factor receptor 1 (FGFR1) mRNA can be alternatively spliced to generate isoforms containing (FGFR1alpha) or lacking (FGFR1beta) the first immunoglobulin-like domain. We examined which isoforms are expressed by cultured prostate cells, their affinities for FGF-2, and the effect of heparin on FGF-2 binding.

METHODS

FGFR1 isoform expression was examined by RT-PCR. FGFR1alpha and FGFR1beta were expressed in CHO cells mutant in heparan sulfate synthesis, and their affinities for FGF-2, FGF-1, FGF-4, and FGF-6 were determined in the presence and absence of heparin.

RESULTS

FGFR1alpha was expressed in luminal epithelial cells, whereas FGFR1beta was expressed in basal epithelial and smooth muscle cells. FGFR1beta bound FGF-2 with three-fourfold higher affinity than FGFR1alpha both in the presence and absence of heparin. Heparin increased affinity of both receptor isoforms for FGF-2 approximately four-fivefold.

CONCLUSIONS

Prostate smooth muscle and basal epithelial cells are likely to be more sensitive than luminal epithelial cells to the low concentrations of FGFs present in vivo.

Differential properties of adult rat and mouse brain-derived neural stem/progenitor cells

Adult neurogenesis from neural stem/progenitor cells occurs in discrete regions of the central nervous system of all mammals, but the mechanisms regulating endogenous neurogenesis are poorly understood. Advances in understanding the neurogenesis depend on knowing their intrinsic properties and responses to environmental signals that control their behavior. Before these issues can be addressed, it is necessary to know whether there are significant species-specific differences in the properties of the stem/progenitor cells derived from CNS of two commonly studied model systems, mouse and rat. We found major differences between rat and mouse stem/progenitor cell proliferation in response to various substrates, mitogenic growth factors and heparin and to the influence of differentiation factors on generation of neurons and glia. Thus, extrapolation of cell properties from one species to another based on studies of these cells should be made with caution.

Xylosyltransferase I acceptor properties of fibroblast growth factor and its fragment bFGF (1-24)

Human basic fibroblast growth factor (bFGF) is a heparin-binding growth factor containing a G-S-G-motif which is a potential recognition sequence of xylosyltransferase I (XT-I). Here, we show that the recombinant human bFGF was xylosylated in vitro by human XT-I and that the fragment bFGF (1-24) is a good XT-I acceptor (K(m) = 20.8 microM for native XT-I and K(m) = 22.3 microM for recombinant XT-I). MALDI and MALDI-PSD time-of-flight mass spectrometric analyses of the xylosylated bFGF protein demonstrate the transfer of xylose to the serine residue of the G-S-G-motif in the amino terminal end of bFGF. The peptide bFGF (1-24) is well suitable as an acceptor substrate for XT-I and can be used in a radiochemical assay to measure the XT-I activity in cell culture supernatant and human body fluids, respectively. Furthermore, we could demonstrate that the XT-I interacts strongly with heparin and that this glycosaminoglycan is a predominantly non-competitive inhibitor of the enzyme using the fragment bFGF (1-24) as xylose acceptor.

Expression and potential role of fibroblast growth factor 2 and its receptors in human embryonic stem cells

Although the detection of several components of the fibroblast growth factor (FGF) signaling pathway in human embryonic stem cells (hESCs) has been reported, the functionality of that pathway and effects on cell fate decisions are yet to be established. In this study we characterized expression of FGF-2, the prototypic member of the FGF family, and its receptors (FGFRs) in undifferentiated and differentiating hESCs; subsequently, we analyzed the effects of FGF-2 on hESCs, acting as both exogenous and endogenous factors. We have determined that undifferentiated hESCs are abundant in several molecular-mass isoforms of FGF-2 and that expression pattern of these isoforms remains unchanged under conditions that induce hESC differentiation. Significantly, FGF-2 is released by hESCs into the medium, suggesting an autocrine activity. Expression of FGFRs in undifferentiated hESCs follows a specific pattern, with FGFR1 being the most abundant species and other receptors showing lower expression in the following order: FGFR1 --> FGFR3 --> FGFR4 --> FGFR2. Initiation of differentiation is accompanied by profound changes in FGFR expression, particularly the upregulation of FGFR1. When hESCs are exposed to exogenous FGF-2, extracellular signal-regulated kinases are phosphorylated and thereby activated. However, the presence or absence of exogenous FGF-2 does not significantly affect the proliferation of hESCs. Instead, increased concentration of exogenous FGF-2 leads to reduced outgrowth of hESC colonies with time in culture. Finally, the inhibitor of FGFRs, SU5402, was used to ascertain whether FGF-2 that is released by hESCs exerts its activities via autocrine pathways. Strikingly, the resultant inhibition of FGFR suppresses activation of downstream protein kinases and causes rapid cell differentiation, suggesting an involvement of autocrine FGF signals in the maintenance of proliferating hESCs in the undifferentiated state. In conclusion from our data, we propose that this endogenous FGF signaling pathway can be implicated in self-renewal or differentiation of hESCs.