Biomedical subjects

Wen-Cheng Xiong

Publications and source records attributed to Wen-Cheng Xiong.

16 recordsLinked to original sources

PubMed2006

Regulation of osteoclast function and bone mass by RAGE.

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily that has multiple ligands and is implicated in the pathogenesis of various diseases, including diabetic complications, neurodegenerative disorders, and inflammatory responses. However, the role of RAGE in normal physiology is largely undefined. Here, we present evidence for a role of RAGE in osteoclast maturation and function, which has consequences for bone remodeling. Mice lacking RAGE had increased bone mass and bone mineral density and decreased bone resorptive activity in vivo. In vitro-differentiated RAGE-deficient osteoclasts exhibited disrupted actin ring and sealing zone structures, impaired maturation, and reduced bone resorptive activity. Impaired signaling downstream of alphavbeta3 integrin was observed in RAGE(-/-) bone marrow macrophages and precursors of OCs. These results demonstrate a role for RAGE in osteoclast actin cytoskeletal reorganization, adhesion, and function, and suggest that the osteosclerotic-like phenotype observed in RAGE knockout mice is due to a defect in osteoclast function.

Actins↗

PubMed2006

MuSK signaling at the neuromuscular junction.

The neuromuscular junction (NMJ) is a peripheral cholinergic synapse that conveys signals from motor neurons to muscle cells (Sanes and Lichtman, 1999; Sanes and Lichtman, 2001). The formation of the NMJ requires communication between motoneurons and muscle fibers. Three molecules are essential for NMJ formation: agrin, MuSK, and rapsyn. MuSK appears to be involved in every aspect of NMJ development and maintenance. The paper reviews agrin-MuSK cascades and its potential cross talk with Wnt signaling pathways.

Agrin↗

PubMed2006

Mitochondrial amyloid-beta peptide: pathogenesis or late-phase development?

Mitochondrial and metabolic dysfunction have been linked to Alzheimer's disease for some time. Key questions regarding this association concern the nature and mechanisms of mitochondrial dysfunction, and whether such changes in metabolic properties are pathogenic or secondary, with respect to neuronal degeneration. In terms of mitochondria and Alzheimer's, altered function could reflect intrinsic properties of this organelle, potentially due to mutations in mitochondrial DNA, or extrinsic changes secondary to signal transduction mechanisms activated in the cytosol. This review presents data relevant to these questions, and considers the implication of recent findings demonstrating the presence of amyloid-beta peptide in mitochondria, as well as intra-mitochondrial molecular targets with which it can interact. Regardless of the underlying mechanism(s), it is likely that mitochondrial dysfunction contributes to oxidant stress which is commonly observed in brains of patients with Alzheimer's and transgenic models of Alzheimer's-like pathology.

Alzheimer Disease↗

PubMed2005

DCC-dependent phospholipase C signaling in netrin-1-induced neurite elongation.

Netrins, a family of secreted molecules, play important roles in axon pathfinding during nervous system development. Although phosphatidylinositol signaling has been implicated in this event, how netrin-1 regulates phosphatidylinositol signaling remains poorly understood. Here we provide evidence that netrin-1 stimulates phosphatidylinositol bisphosphate hydrolysis in cortical neurons. This event appears to be mediated by DCC (deleted in colorectal cancer), but not neogenin or Unc5h2. Netrin-1 induces phospholipase Cgamma (PLCgamma) tyrosine phosphorylation. Inhibition of PLC activity attenuates netrin-1-induced cortical neurite outgrowth. These results suggest that netrin-1 regulates phosphatidylinositol turnover and demonstrate a crucial role of PLC signaling in netrin-1-induced neurite elongation.

Animals↗

PubMed2005

Estrogen-induced mitochondrial reactive oxygen species as signal-transducing messengers.

We report here evidence in support of the role of 17beta-estradiol- (E2-) induced mitochondrial (mt) reactive oxygen species (ROS) as signal-transducing messengers. On the basis of monitoring the oxidation of 2',7'-dichlorofluorescin by spectrofluorometry, flow cytometry, and confocal microscopy, we have identified that exposure of E2 triggers the immediate rapid production of intracellular ROS ranging from a 1- to severalfold increase in a variety of cells. E2-stimulated ROS production does not correlate with the activity of the estrogen receptor (ER) in the cells. The ROS is most likely hydrogen peroxide based on its inhibition by antioxidants and catalase and lack of any effects of E2 on O(2)(*)(-) or NO(*) formation. Confocal microscopy showed that ROS is localized in the perinuclear mitochondria. E2 through anchorage- and integrin-dependent signaling to mitochondria increased ROS generation. Increased intracellular ROS formation identified here for the first time may explain the mechanism of previously reported oxidative damage and subsequent genetic alterations including mutations produced by elevated concentrations of estrogens. The functional consequences of E2-induced ROS formation included the enhanced cell motility as shown by the increase in cdc42 and activation of Pyk2 and the increased phosphorylation of signaling proteins c-jun and CREB. E2-induced ROS activated the binding of three oxidant-sensitive transcription factors: AP-1, CREB, and nuclear respiratory factor 1. In addition to ERs as signaling molecules, our findings further revealed that E2-induced mt ROS also act as signal transducing messengers and suggest new targets for the development of antioxidant-based drugs or antioxidant gene therapy for the prevention and treatment of estrogen-dependent cancer.

Adaptor Proteins, Signal Transducing↗

PubMed2005

The marriage of glucose and blood vessels: it isn't all that sweet.

The secondary complications of diabetes are the major factors limiting quality of life and longevity in diabetic patients. Among these complications, cardiovascular disease is the major cause of morbidity and mortality. Based on a recent paper by Vikramadithyan et al. (2005), this preview addresses the role of aldose reductase as a contributor to the pathogenesis of diabetic macrovascular disease.

Aldehyde Reductase↗

PubMed2005

Phosphatidylinositol transfer protein-alpha in netrin-1-induced PLC signalling and neurite outgrowth.

Neurite extension is essential for wiring the nervous system during development. Although several factors are known to regulate neurite outgrowth, the underlying mechanisms remain unclear. Here, we provide evidence for a role of phosphatidylinositol transfer protein-alpha (PlTPalpha) in neurite extension in response to netrin-1, an extracellular guidance cue. PlTPalpha interacts with the netrin receptor DCC (deleted in colorectal cancer) and neogenin. Netrin-1 stimulates PlTPalpha binding to DCC and to phosphatidylinositol (5) phosphate [Pl(5)P], increases its lipid-transfer activity and elevates hydrolysis of phosphatidylinositol bisphosphate (PlP2). In addition, the stimulated PIP2 hydrolysis requires PlTPalpha. Furthermore, cortical explants of PlTPalpha mutant mice are defective in extending neurites in response to netrin-1. Commissural neurons from chicken embryos expressing a dominant-negative PlTPalpha mutant show reduced axon outgrowth. Morpholino-mediated knockdown of PlTPalpha expression in zebrafish embryos leads to dose-dependent defects in motor-neuron axons and reduced numbers of spinal-cord neurons. Taken together, these results identify a crucial role for PlTPalpha in netrin-1-induced neurite outgrowth, revealing a signalling mechanism for DCC/neogenin and PlTPalpha regulation.

Animals↗

PubMed2004

RANKL regulates Fas expression and Fas-mediated apoptosis in osteoclasts.

UNLABELLED: Osteoclast apoptosis is an influential determinant of osteoclast bone-resorbing activity. RANKL, a critical factor for osteoclastogenesis, is also important in osteoclast survival. However, the mechanisms by which RANKL prevents osteoclast apoptosis remain largely unknown. INTRODUCTION: Fas, a death receptor, mediates apoptosis in multiple types of cells including osteoclasts. Here we report that RANKL acts as a survival factor in osteoclasts by downregulating Fas-mediated apoptosis and Fas expression in mature osteoclasts. MATERIALS AND METHODS: RAW264.7 and mouse bone marrow macrophage/monocyte progenitors and progenitor-derived osteoclasts, in the presence of various concentrations of RANKL, were used in this study. Western blotting, semiquantitative RT-PCR, flow cytometry, nuclear staining, and a fluorescent caspase-3 activity assay were used to assess the effect of RANKL on Fas expression and Fas-mediated apoptosis. The involvement of NF-kappaB in the regulation of Fas by RANKL was analyzed by luciferase assay and EMSA. RESULTS: Mature osteoclasts generated in the presence of a high concentration of RANKL (3.33 nM) failed to respond to Fas-induced apoptosis. The lack of responsiveness in mature osteoclasts is caused by the low level of Fas expression, as detected by both semiquantitative PCR and Western blotting. Fas protein and mRNA expression are inhibited by RANKL in concentration-dependent manners. The downregulation of Fas expression by RANKL is not because of modulation of the stability of Fas protein or mRNA. The regulation of Fas expression by RANKL is biphasic. During the early stage of osteoclastogenesis (1 day) when Fas is expressed at a very low level, RANKL upregulates Fas promoter activity by 2.4 +/- 0.1-fold in a concentration-dependent manner and increases Fas mRNA and protein. This event correlates with regulation of the binding activity of NF-kappaB to the Fas promoter by RANKL, as detected by EMSA. In osteoclast precursors, the induction of Fas promoter activity by RANKL was dramatically reduced when NF-kappaB binding sites on the Fas promoter were mutated. CONCLUSION: RANKL upregulates Fas expression in osteoclast progenitors through NF-kappaB, making osteoclasts targets of Fas-stimulated apoptosis. In differentiated mature osteoclasts, RANKL reduces the levels of Fas expression and Fas-mediated apoptosis, acting as a survival factor.

Animals↗

PubMed2004

Focal adhesion kinase in netrin-1 signaling.

Netrins are a family of secreted molecules that are important for axonal outgrowth and guidance in the developing nervous system. However, the signaling mechanisms that lie immediately downstream of netrin receptors remain poorly understood. Here we report that the netrin receptor DCC (deleted in colorectal cancer) interacts with the focal adhesion kinase (FAK), a kinase implicated in regulating cell adhesion and migration. FAK was expressed in developing brains and was localized with DCC in cultured neurons. Netrin-1 induced FAK and DCC tyrosine phosphorylation. Disruption of FAK signaling abolished netrin-1-induced neurite outgrowth and attractive growth cone turning. Taken together, these results indicate a new signaling mechanism for DCC, in which FAK is activated upon netrin-1 stimulation and mediates netrin-1 function; they also identify a critical role for FAK in axon navigation.

Animals↗

PubMed2004

Thrombospondin induces RhoA inactivation through FAK-dependent signaling to stimulate focal adhesion disassembly.

Cells utilize dynamic interactions with the extracellular matrix to adapt to changing environmental conditions. Thrombospondin 1 (TSP1) induces focal adhesion disassembly and cell migration through a sequence (hep I) in its heparin-binding domain signaling through the calreticulin-low density lipoprotein receptor-related protein receptor complex. This involves the Galphai-dependent activation of ERK and phosphoinositide (PI) 3-kinase, both of which are required for focal adhesion disassembly. Focal adhesion kinase (FAK) regulates adhesion dynamics, acting in part by modulating RhoA activity, and FAK is implicated in ERK and PI 3-kinase activation. In this work, we sought to determine the role of FAK in TSP1-induced focal adhesion disassembly. TSP1/hep I does not stimulate focal adhesion disassembly in FAK knockout fibroblasts, whereas re-expressing FAK rescues responsiveness. Inhibiting FAK signaling through FRNK or FAK Y397F expression in endothelial cells also abrogates this response. TSP1/hep I stimulates a transient increase in FAK phosphorylation that requires calreticulin and Galphai, but not ERK or PI 3-kinase. Hep I does not activate ERK or PI 3-kinase in FAK knockout fibroblasts, suggesting activation occurs downstream of FAK. TSP1/hep I stimulates RhoA inactivation with kinetics corresponding to focal adhesion disassembly in a FAK, ERK, and PI 3-kinase-dependent manner. Furthermore, hep I does not stimulate focal adhesion disassembly in cells expressing constitutively active RhoA, suggesting that RhoA inactivation is required for this response. This is the first work to illustrate a connection between FAK phosphorylation in response to a soluble factor and RhoA inactivation, as well as the first report of PI 3-kinase and ERK in FAK regulation of RhoA activity.

Animals↗

PubMed2004

Mitochondrial signals initiate the activation of c-Jun N-terminal kinase (JNK) by hypoxia-reoxygenation.

C-Jun N-terminal kinase (JNK) is part of the mitogen-activated protein kinase (MAPK) family of signaling pathways that are induced in response to extracellular stimuli. JNK is primarily a stress-response pathway and can be activated by proinflammatory cytokines and growth factors coupled to membrane receptors or through non-receptor pathways by stimuli such as heat shock, UV irradiation, protein synthesis inhibitors, and conditions that elevate the levels of reactive oxygen intermediates (ROI). The molecular initiators of MAPKs by non-receptor stimuli have not been described. Ischemia followed by reperfusion or hypoxia with reoxygenation represents a condition of high oxidative stress where JNK activation is associated with elevated ROI. We show here that the activation of JNK by this condition is initiated in the mitochondria and requires coupled electron transport, ROI generation, and calcium flux. These signals cause the selective, sequential activation of the calcium-dependent, proline-rich kinase Pyk2 and the small GTP binding factors Rac-1 and Cdc42. Interruption of these interactions with inactivated dominant negative mutant proteins, blocking calcium flux, or inhibiting electron transport through mitochondrial complexes II, III, or IV prevents JNK activation and results in a proapoptotic phenotype that is characteristic of JNK inhibition in this model of ischemia-reperfusion. The signaling pathway is unique for the reoxygenation stimulus and provides a framework for other non-receptor-mediated pathways of MAPK activation.

Animals↗

PubMed2003

Neuronal repellent Slit2 inhibits dendritic cell migration and the development of immune responses.

One of the essential functions of dendritic cells is to take up Ags in peripheral tissues and migrate into secondary lymphoid organs to present Ags to lymphocytes for the induction of immune responses. Although many studies have demonstrated that the migration of dendritic cells is closely associated with the development of immune responses, little is known about factors that inhibit dendritic cell migration and control the extent of immune responses to Ag stimulation. We show that Slit2, a neuronal repellent factor, is up-regulated in the skin by allergen sensitization and down-regulates the migration of Langerhans cells. The effect is mediated by direct interaction of Slit2 with cells that express a Slit-specific receptor, Robo1. Slit2-mediated inhibition of Langerhans cell migration results in suppression of contact hypersensitivity responses. These findings provide insights into a novel mechanism by which Slit2 functions as an anti-inflammatory factor for the initiation of immune responses.

Animals↗

PubMed2003

PYK2 and FAK in osteoclasts.

Integrin alpha(v)beta3 plays a pivotal role in osteoclastic bone resoprtion by mediating both osteoclast attachments on bone matrix and cytoskeleton reorganization. The focal adhesion kinase (FAK) family kinases including FAK and proline-rich tyrosine kinase 2 (PYK2) are major tyrosine kinases activated by integrin engagement. In osteoclasts, although FAK is expressed, PYK2 appears to be the predominant mediator of integrin alpha(v)beta3 signaling events that influence osteoclast physiology and pathology. Recent progress in the understanding of the role of PYK2/FAK kinases in the regulation of osteoclastic actin cytoskeletal organization, cell migration, and bone resorption will be discussed in this review.

Animals↗

PubMed2003

Roles of FAK family kinases in nervous system.

Focal adhesion kinase (FAK) and its related kinase, proline rich tyrosine kinase 2 (PYK2), are major kinases activated by cell-extracellular matrix adhesion. Although they are highly expressed in the nervous system, the functions of these two kinases in the nervous system remained unclear until recently. FAK and PYK2 appear to play an important role in developing nervous system as well as adult brain. Importantly the two kinases are activated by different extracellular stimuli and execute distinct regulatory effects on various aspects of neural developmental processes and neuronal function. This review summarizes the potential roles of FAK and PYK2 in axon path-finding and synaptic plasticity.

Animals↗

PubMed2003

Regulation of the formation of osteoclastic actin rings by proline-rich tyrosine kinase 2 interacting with gelsolin.

Osteoclast activation is important for bone remodeling and is altered in multiple bone disorders. This process requires cell adhesion and extensive actin cytoskeletal reorganization. Proline-rich tyrosine kinase 2 (PYK2), a major cell adhesion-activated tyrosine kinase in osteoclasts, plays an important role in regulating this event. The mechanisms by which PYK2 regulates actin cytoskeletal organization and osteoclastic activation remain largely unknown. In this paper, we provide evidence that PYK2 directly interacts with gelsolin, an actin binding, severing, and capping protein essential for osteoclastic actin cytoskeletal organization. The interaction is mediated via the focal adhesion-targeting domain of PYK2 and an LD motif in gelsolin's COOH terminus. PYK2 phosphorylates gelsolin at tyrosine residues and regulates gelsolin bioactivity, including decreasing gelsolin binding to actin monomer and increasing gelsolin binding to phosphatidylinositol lipids. In addition, PYK2 increases actin polymerization at the fibroblastic cell periphery. Finally, PYK2 interacts with gelsolin in osteoclasts, where PYK2 activation is required for the formation of actin rings. Together, our results suggest that PYK2 is a regulator of gelsolin, revealing a novel PYK2-gelsolin pathway in regulating actin cytoskeletal organization in multiple cells, including osteoclasts.

Actins↗

PubMed2003

Drosophila homeodomain protein REPO controls glial differentiation by cooperating with ETS and BTB transcription factors.

In Drosophila, cell-fate determination of all neuroectoderm-derived glial cells depends on the transcription factor Glial cells missing (GCM), which serves as a binary switch between the neuronal and glial cell fates. Because the expression of GCM is restricted to the early phase of glial development, other factors must be responsible for the terminal differentiation of glial cells. Expression of three transcription factors, Reversed Polarity (REPO), Tramtrack p69 (TTK69) and PointedP1 (PNTP1), is induced by GCM in glial cells. REPO is a paired-like homeodomain protein, expressed exclusively in glial cells, and is required for the migration and differentiation of embryonic glial cells. To understand how REPO functions in glial terminal differentiation, we have analyzed the mechanism of gene regulation by REPO. We show that REPO can act as a transcriptional activator through the CAATTA motif in glial cells, and define three genes whose expression in vivo depends on REPO function. In different types of glial cells, REPO can act alone, or cooperate with either TTK69 or PNTP1 to regulate different target genes. Coordination of target gene expression by these three transcription factors may contribute to the diversity of glial cell types. In addition to promoting glial differentiation, we found that REPO is also necessary to suppress neuronal development, cooperating with TTK69. We propose that REPO plays a key role in both glial development and diversification.

Animals↗