Thy-1 binds to integrin beta(3) on astrocytes and triggers formation of focal contact sites

Phenotypic and functional characteristics of spermatogonial stem cells in rats

Spermatogonial stem cells (SSCs) are at the foundation of the highly productive spermatogenic process that continuously produces male gametes throughout postnatal life. However, experimental evaluation of SSCs in postnatal testes is complicated because these cells are extremely rare and few defining morphology or biochemical characteristics are known. In this study, we used the spermatogonial transplantation functional assay, combined with fluorescence-activated cell sorting (FACS) analysis to identify cellular, biochemical and surface antigenic characteristics of SSCs in rat testes during development. Our results demonstrated that forward scatter (FSc)(hi), side scatter (SSc)(hi), mitochondria membrane potential (DeltaPsim)(lo), Ep-CAM(+), Thy-1(+), beta3-integrin(+) stem cells in neonate rat testes become SSc(lo), DeltaPsim(hi), Ep-CAM(+), Thy-1(lo), beta3-integrin(-) stem cells in pup rat testes. Furthermore, prospective identification of rat testis cell populations (Ep-CAM(+)), highly enriched for SSCs (1 in 13 for neonate; 1 in 8.5 for pup) enabled us to predict the Thy-1 and beta3-integrin status of stem cells in neonate and pup testes, which was subsequently confirmed by transplantation analyses. Systematic characterization of SSCs enabled the production of testis cell populations highly enriched (up to 120-fold) for SSCs and will facilitate future investigations of functional and genomic characteristics.

Distinct ontogenic and regional expressions of newly identified Cajal-Retzius cell-specific genes during neocorticogenesis

Cajal-Retzius (CR) cells are early-generated transient neurons and are important in the regulation of cortical neuronal migration and cortical laminar formation. Molecular entities characterizing the CR cell identity, however, remain largely elusive. We purified mouse cortical CR cells expressing GFP to homogeneity by fluorescence-activated cell sorting and examined a genome-wide expression profile of cortical CR cells at embryonic and postnatal periods. We identified 49 genes that exceeded hybridization signals by >10-fold in CR cells compared with non-CR cells at embryonic day 13.5, postnatal day 2, or both. Among these CR cell-specific genes, 25 genes, including the CR cell marker genes such as the reelin and calretinin genes, are selectively and highly expressed in both embryonic and postnatal CR cells. These genes, which encode generic properties of CR cell specificity, are eminently characterized as modulatory composites of voltage-dependent calcium channels and sets of functionally related cellular components involved in cell migration, adhesion, and neurite extension. Five genes are highly expressed in CR cells at the early embryonic period and are rapidly down-regulated thereafter. Furthermore, some of these genes have been shown to mark two distinctly different focal regions corresponding to the CR cell origins. At the late prenatal and postnatal periods, 19 genes are selectively up-regulated in CR cells. These genes include functional molecules implicated in synaptic transmission and modulation. CR cells thus strikingly change their cellular phenotypes during cortical development and play a pivotal role in both corticogenesis and cortical circuit maturation.

Thy-1: More than a Mouse Pan-T Cell Marker

Thy-1 (CD90) is a small GPI-anchored protein that is particularly abundant on the surface of mouse thymocytes and peripheral T cells. T cell proliferation and cytokine synthesis in response to Thy-1 cross-linking by specific mAb suggests a role for Thy-1 in mouse T lymphocyte activation. However, a physiological ligand or counterreceptor for murine Thy-1 in the lymphoid compartment has not yet been identified. Thy-1 cross-linking, in the context of strong costimulatory signaling through CD28, results in an activating signal that can at least partially substitute for TCR signaling during mouse T cell activation. Remarkably, Thy-1 cross-linking also results in the potent costimulation of T cells activated through the TCR. This novel dual signaling capacity suggests a possible role for Thy-1 in the maintenance of T cell homeostasis in the absence of TCR triggering, as well as potentiating Ag-induced T cell responses.

Aggregation of Integrins and RhoA Activation Are Required for Thy-1-induced Morphological Changes in Astrocytes

Thy-1, a cell adhesion molecule abundantly expressed in mammalian neurons, binds to a beta(3)-containing integrin on astrocytes and thereby stimulates the assembly of focal adhesions and stress fibers. Such events lead to morphological changes in astrocytes that resemble those occurring upon injury in the brain. Extracellular matrix proteins, typical integrin ligands, bind to integrins and promote receptor clustering as well as signal transduction events that involve small G proteins and cytoskeletal changes. Here we investigated the possibility that the cell surface protein Thy-1, when interacting with a beta(3)-containing integrin on astrocytes, could trigger signaling events similar to those generated by extracellular matrix proteins. DI-TNC(1) astrocytes were stimulated with Thy-1-Fc immobilized on beads, and increased RhoA activity was confirmed using an affinity precipitation assay. The effect of various inhibitors on the cellular response was also studied. The presence of Y-27632, an inhibitor of Rho kinase (p160ROCK), a key downstream effector of RhoA, significantly reduced focal adhesion and stress fiber formation induced by Thy-1. Similar effects were obtained when astrocytes were treated with C3 transferase, an inhibitor of RhoA. Alternatively, astrocytes were transfected with an expression vector encoding fusion proteins of enhanced green fluorescent protein with either the Rho-binding domain of Rhotekin, which blocks RhoA function, or the dominant-negative N19RhoA mutant. In both cases, Thy-1-induced focal adhesion formation was inhibited. Furthermore, we observed that RhoA activity after stimulation with soluble Thy-1-Fc molecule was augmented upon further cross-linking using protein A-Sepharose beads. The same was shown by cross-linking beta(3)-containing integrin with anti-beta(3) antibodies. Together, these results indicate that Thy-1-mediated astrocyte stimulation depended on beta(3) integrin clustering and the resulting increase in RhoA activity.

Integrin signaling to the actin cytoskeleton

Integrin engagement stimulates the activity of numerous signaling molecules, including the Rho family of GTPases, tyrosine phosphatases, cAMP-dependent protein kinase and protein kinase C, and stimulates production of PtdIns(4,5)P2. Integrins promote actin assembly via the recruitment of molecules that directly activate the actin polymerization machinery or physically link it to sites of cell adhesion.

Nuclear factor E2-related factor 2-dependent antioxidant response element activation by tert-butylhydroquinone and sulforaphane occurring preferentially in astrocytes conditions neurons against oxidative insult

Binding of the transcription factor nuclear factor E2-related factor 2 (Nrf2) to the antioxidant response element (ARE) in neural cells results in the induction of a battery of genes that can coordinate a protective response against a variety of oxidative stressors. In this study, tert-butylhydroquinone (tBHQ) and sulforaphane were used as activators of this pathway. Consistent with previous studies, treatment of primary cortical cultures from ARE reporter mice revealed selective promoter activity in astrocytes. This activation protected neurons from hydrogen peroxide and nonexcitotoxic glutamate toxicity. tBHQ treatment of cultures from Nrf2 knock-out animals resulted in neither ARE activation nor neuroprotection. By reintroducing Nrf2 via infection with a replication-deficient adenovirus (ad), both the genetic response and neuroprotection were rescued. Conversely, infection with adenovirus encoding dominant-negative (DN) Nrf2 (ad-DN-Nrf2) or pretreatment with the selective phosphatidylinositol-3 kinase inhibitor LY294002 inhibited the tBHQ-mediated promoter response and corresponding neuroprotection. Interestingly, the adenoviral infection showed a high selectivity for astrocytes over neurons. In an attempt to reveal some of the cell type-specific changes resulting from ARE activation, cultures were infected with adenovirus encoding green fluorescent protein (GFP) (ad-GFP) or ad-DN-Nrf2 (containing GFP) before tBHQ treatment. A glia-enriched population of GFP-infected cells was then isolated from a population of uninfected neurons using cell-sorting technology. Microarray analysis was used to evaluate potential glial versus neuron-specific contributions to the neuroprotective effects of ARE activation and Nrf2 dependence. Strikingly, the change in neuronal gene expression after tBHQ treatment was dependent on Nrf2 activity in the astrocytes. This suggests that Nrf2-dependent genetic changes alter neuron-glia interactions resulting in neuroprotection.

Thrombospondin-1-induced focal adhesion disassembly in fibroblasts requires Thy-1 surface expression, lipid raft integrity, and Src activation

The hep I peptide of thrombospondin-1 is known to induce the disassembly of focal adhesions, a critical step in regulating cellular adhesive changes needed for cell motility. Fibroblasts that are heterogeneous with respect to the surface expression of Thy-1 differ markedly in morphology, cytoskeletal organization, and migration, suggesting differential regulation of focal adhesion dynamics. Here we demonstrate that disassembly of focal adhesions mediated by both full-length thrombospondin-1 and the hep I peptide in fibroblasts requires the expression of Thy-1, although it does not appear to function as a stable member of the hep I receptor complex. Consistent with a known function of Thy-1 in regulating lipid raft-associated signaling, intact lipid rafts are necessary for hep I-mediated focal adhesion disassembly. Furthermore, we establish Src family kinase (SFK) activation as a novel component required for hep I-induced signaling leading to focal adhesion disassembly. hep I induces transient phosphorylation of SFKs in Thy-1-expressing fibroblasts only. Therefore, we conclude that Thy-1 surface expression is required for thrombospondin-1-induced focal adhesion disassembly in fibroblasts through an SFK-dependent mechanism. This represents a novel role for Thy-1 in the regulation of fibroblast-matrix interactions critical to tissue homeostasis and remodeling.

Human Thy-1 (CD90) on Activated Endothelial Cells Is a Counterreceptor for the Leukocyte Integrin Mac-1 (CD11b/CD18)

Leukocyte recruitment in response to inflammatory signals is in part governed by interactions between endothelial cell receptors belonging to the Ig superfamily and leukocyte integrins. In our previous work, the human Ig superfamily glycoprotein Thy-1 (CD90) was identified as an activation-associated cell adhesion molecule on human dermal microvascular endothelial cells. Furthermore, the interaction of Thy-1 with a corresponding ligand on monocytes and polymorphonuclear cells was shown to be involved in the adhesion of these leukocytes to activated Thy-1-expressing endothelial cells. In this study, we have identified the specific interaction between human Thy-1 and the leukocyte integrin Mac-1 (CD11b/CD18; alphaMbeta2) both in cellular systems and in purified form. Monocytes and polymorphonuclear cells were shown to adhere to transfectants expressing human Thy-1 as well as to primary Thy-1-expressing human dermal microvascular endothelial cells. Furthermore, leukocyte adhesion to activated endothelium as well as the subsequent transendothelial migration was mediated by the interaction between Thy-1 and Mac-1. This additional pathway in leukocyte-endothelium interaction may play an important role in the regulation of leukocyte recruitment to sites of inflammation.

Expression, purification, and characterization of avian Thy-1 from Lec1 mammalian and Tn5 insect cells

Structural studies of asparagine-linked glycoproteins are complicated by the oligosaccharide heterogeneity inherent to individual glycosylation sites. Herein, we report the cloning of a novel isoform of avian Thy-1 and the subsequent expression, purification, and characterization of a soluble form of Thy-1 from Lec1 mammalian and Tn5 insect cells. The novel isoform of Thy-1 differs from the previously reported chicken isoform by eight amino acid residues, but these changes do not alter the secondary structure content, the disulfide bond pattern, or the sites of glycosylation. The disulfide linkage pattern and glycoform distribution on each N-glycosylation site of recombinant chicken Thy-1 from both cell lines were determined by a combination of amino-terminal sequencing and mass spectrometry. The mass spectral data showed that the amino-terminal glutamine was modified to pyroglutamate. Recombinant Thy-1 from Lec1 cells contained (GlcNAc)(2)(Man)(5) on asparagine 60, whereas the oligosaccharides on asparagine 23 and 100 contained approximately 80% (GlcNAc)(2)(Man)(4) and approximately 20% (GlcNAc)(2)(Man)(5). The glycoforms on Thy-1 expressed in Tn5 cells were more heterogeneous, with the oligosaccharides ranging over (GlcNAc)(2)(Fuc)(0-2)(Man)(2-3) on each site. The ability to generate recombinant glycoproteins with restricted carbohydrate heterogeneity is the first step toward the systematic study of structure-function relationships in intact glycoproteins.

The journey of tetanus and botulinum neurotoxins in neurons

Anaerobic bacteria of the genus Clostridia are a major threat to human and animal health, being responsible for pathologies ranging from food poisoning to gas gangrene. In each of these, the production of sophisticated exotoxins is the main cause of disease. The most powerful clostridial toxins are tetanus and botulinum neurotoxins, the causative agents of tetanus and botulism. They are structurally organized into three domains endowed with distinct functions: high affinity binding to neurons, membrane translocation and specific cleavage of proteins controlling neuroexocytosis. Recent discoveries regarding the mechanism of membrane recruitment and sorting of these neurotoxins within neurons make them ideal tools to uncover essential aspects of neuronal physiology in health and disease.

Current perspective on the pathogenesis of Graves' disease and ophthalmopathy

Graves' disease (GD) is a very common autoimmune disorder of the thyroid in which stimulatory antibodies bind to the thyrotropin receptor and activate glandular function, resulting in hyperthyroidism. In addition, some patients with GD develop localized manifestations including ophthalmopathy (GO) and dermopathy. Since the cloning of the receptor cDNA, significant progress has been made in understanding the structure-function relationship of the receptor, which has been discussed in a number of earlier reviews. In this paper, we have focused our discussion on studies related to the molecular mechanisms of the disease pathogenesis and the development of animal models for GD. It has become apparent that multiple factors contribute to the etiology of GD, including host genetic as well as environmental factors. Studies in experimental animals indicate that GD is a slowly progressing disease that involves activation and recruitment of thyrotropin receptor-specific T and B cells. This activation eventually results in the production of stimulatory antibodies that can cause hyperthyroidism. Similarly, significant new insights have been gained in our understanding of GO that occurs in a subset of patients with GD. As in GD, both environmental and genetic factors play important roles in the development of GO. Although a number of putative ocular autoantigens have been identified, their role in the pathogenesis of GO awaits confirmation. Extensive analyses of orbital tissues obtained from patients with GO have provided a clearer understanding of the roles of T and B cells, cytokines and chemokines, and various ocular tissues including ocular muscles and fibroblasts. Equally impressive is the progress made in understanding why connective tissues of the orbit and the skin in GO are singled out for activation and undergo extensive remodeling. Results to date indicate that fibroblasts can act as sentinel cells and initiate lymphocyte recruitment and tissue remodeling. Moreover, these fibroblasts can be readily activated by Ig in the sera of patients with GD, suggesting a central role for them in the pathogenesis. Collectively, recent studies have led to a better understanding of the pathogenesis of GD and GO and have opened up potential new avenues for developing novel treatments for GD and GO.

Antagonistic control of oxidative stress-induced cell death in Arabidopsis by two related, plant-specific zinc finger proteins

The most familiar form of plant programmed cell death is the hypersensitive response (HR) associated with successful plant immune responses. HR is preceded by an oxidative burst and the generation of both reactive oxygen intermediates (ROI) and NO. The Arabidopsis LSD1 gene encodes a negative regulator of plant programmed cell death that meets several criteria for a regulator of processes relevant to ROI management during pathogen responses. Here we demonstrate that a highly conserved LSD1 paralogue, LOL1, acts as a positive regulator of cell death. Manipulation of LOL1 expression alters both the superoxide-dependent, runaway cell death phenotype of lsd1 plants and the normal HR. We also show that LSD1 and LOL1 have antagonistic effects on copper-zinc superoxide dismutase accumulation, consistent with functions in cell death control via maintenance of ROI homeostasis.

Inflammation in neurodegenerative disease--a double-edged sword

Inflammation is a defense reaction against diverse insults, designed to remove noxious agents and to inhibit their detrimental effects. It consists of a dazzling array of molecular and cellular mechanisms and an intricate network of controls to keep them in check. In neurodegenerative diseases, inflammation may be triggered by the accumulation of proteins with abnormal conformations or by signals emanating from injured neurons. Given the multiple functions of many inflammatory factors, it has been difficult to pinpoint their roles in specific (patho)physiological situations. Studies of genetically modified mice and of molecular pathways in activated glia are beginning to shed light on this issue. Altered expression of different inflammatory factors can either promote or counteract neurodegenerative processes. Since many inflammatory responses are beneficial, directing and instructing the inflammatory machinery may be a better therapeutic objective than suppressing it.

The oligodendrocyte precursor mitogen PDGF stimulates proliferation by activation of alpha(v)beta3 integrins

Central nervous system development requires precise and localized regulation of neural precursor behaviour. Here we show how the interaction between growth factor and integrin signalling pathways provides a mechanism for such precision in oligodendrocyte progenitor (OP) proliferation. While physiological concentrations of platelet-derived growth factor (PDGF) were not in themselves sufficient to promote OP proliferation, they did so on extracellular matrix (ECM) substrates that bind alpha(v)beta3 integrin. Upon PDGF-AA exposure and alpha(v)beta3 engagement, a physical co-association between both receptors was demonstrated, confirming the interaction between these signalling pathways. Furthermore, we found that PDGFalphaR stimulated a protein kinase C-dependent activation of integrin alpha(v)beta3, which in turn induced OP proliferation via a phosphatidylinositol 3-kinase-dependent signalling pathway. These studies establish a mechanism by which OP proliferation is dependent on the availability of both an ECM ligand and a mitogenic growth factor. Growth factor- mediated integrin activation is the critical integrative step in proliferation signalling, and ensures that the response of neural precursor cells to long-range cues can be regulated by their cellular neighbours, allowing precise control of cell behaviour during development.

Lipid microdomains are involved in neurospecific binding and internalisation of clostridial neurotoxins

The neuroparalytic syndromes of tetanus and botulism are caused by tetanus and botulinum neurotoxins, which are produced by bacteria of the genus Clostridia. These neurotoxins are structurally organised in three-domains endowed with different functions: specific interaction with the neuronal surface, membrane translocation and specific cleavage of three key components of the neurotransmitter release apparatus. Despite an identical intracellular activity, tetanus and botulinum neurotoxins are characterised by a differential intraneuronal trafficking, which is likely to be responsible for the different symptoms observed in clinical tetanus and botulism. This review aims to highlight recent discoveries on the recruitment of clostridial neurotoxins (CNTs) to the surface of neurons and neuronally-differentiated cell lines and to discuss their relevance for the internalisation and sorting of these neurotoxins.