High resolution immunoelectron microscopic localization of functional domains of laminin, nidogen, and heparan sulfate proteoglycan in epithelial basement membrane of mouse cornea reveals different topological orientations

Thin and ultrathin cryosections of mouse cornea were labeled with affinity-purified antibodies directed against either laminin, its central segments (domain 1), the end of its long arm (domain 3), the end of one of its short arms (domain 4), nidogen, or low density heparan sulfate proteoglycan. All basement membrane proteins are detected by indirect immunofluorescence exclusively in the epithelial basement membrane, in Descemet's membrane, and in small amorphous plaques located in the stroma. Immunoelectron microscopy using the protein A-gold technique demonstrated laminin domain 1 and nidogen in a narrow segment of the lamina densa at the junction to the lamina lucida within the epithelial basement membrane. Domain 3 shows three preferred locations at both the cellular and stromal boundaries of the epithelial basement membrane and in its center. Domain 4 is located predominantly in the lamina lucida and the adjacent half of the lamina densa. The low density heparan sulfate proteoglycan is found all across the basement membrane showing a similar uniform distribution as with antibodies against the whole laminin molecule. In Descemet's membrane an even distribution was found with all these antibodies. It is concluded that within the epithelial basement membrane the center of the laminin molecule is located near the lamina densa/lamina lucida junction and that its long arm favors three major orientations. One is close to the cell surface indicating binding to a cell receptor, while the other two are directed to internal matrix structures. The apparent codistribution of laminin domain 1 and nidogen agrees with biochemical evidence that nidogen binds to this domain.

Intestinal Microbial Diversity during Early-Life Colonization Shapes Long-Term IgE Levels

Microbial exposure following birth profoundly impacts mammalian immune system development. Microbiota alterations are associated with increased incidence of allergic and autoimmune disorders with elevated serum IgE as a hallmark. The previously reported abnormally high serum IgE levels in germ-free mice suggests that immunoregulatory signals from microbiota are required to control basal IgE levels. We report that germ-free mice and those with low-diversity microbiota develop elevated serum IgE levels in early life. B cells in neonatal germ-free mice undergo isotype switching to IgE at mucosal sites in a CD4 T-cell- and IL-4-dependent manner. A critical level of microbial diversity following birth is required in order to inhibit IgE induction. Elevated IgE levels in germ-free mice lead to increased mast-cell-surface-bound IgE and exaggerated oral-induced systemic anaphylaxis. Thus, appropriate intestinal microbial stimuli during early life are critical for inducing an immunoregulatory network that protects from induction of IgE at mucosal sites.

Preeclampsia enhances neuroglial marker expression in umbilical cord Wharton's jelly-derived mesenchymal stem cells.

Objective: The aim of the study was to compare the neuroglial phenotype of Wharton's jelly-derived mesenchymal stem cells (WJ-MSC) from pregnancies complicated with preeclampsia and gestational age (GA)-matched controls. Methods: WJ-MSC were isolated from umbilical cords from both groups and analyzed for the cell surface expression of MSC markers and the gene and protein expression of neuroglial markers. Results: All WJ cells were highly positive for the MSC markers CD105, CD90 and CD73, but negative for markers specific for hematopoietic (CD34) and immunological cells (CD45, CD14, CD19 and HLA-DR). WJ-MSC from both groups expressed neuroglial markers (MAP-2, GFAP, MBP, Musashi-1 and Nestin) at the mRNA and protein level. The protein expressions of neuronal (MAP-2) and oligodendrocytic (MBP) markers were significantly increased in WJ-MSC from preeclampsia versus GA-matched controls. Conclusions: WJ-MSC from preeclamptic patients are possibly more committed to neuroglial differentiation through the activation of pathways involved both in the pathophysiology of the disease and in neurogenesis.

Ubiquitylation of voltage-gated sodium channels.

Ion channel proteins are regulated by different types of posttranslational modifications. The focus of this review is the regulation of voltage-gated sodium channels (Navs) upon their ubiquitylation. The amiloride-sensitive epithelial sodium channel (ENaC) was the first ion channel shown to be regulated upon ubiquitylation. This modification results from the binding of ubiquitin ligase from the Nedd4 family to a protein-protein interaction domain, known as the PY motif, in the ENaC subunits. Many of the Navs have similar PY motifs, which have been demonstrated to be targets of Nedd4-dependent ubiquitylation, tagging them for internalization from the cell surface. The role of Nedd4-dependent regulation of the Nav membrane density in physiology and disease remains poorly understood. Two recent studies have provided evidence that Nedd4-2 is downregulated in dorsal root ganglion (DRG) neurons in both rat and mouse models of nerve injury-induced neuropathic pain. Using two different mouse models, one with a specific knockout of Nedd4-2 in sensory neurons and another where Nedd4-2 was overexpressed with the use of viral vectors, it was demonstrated that the neuropathy-linked neuronal hyperexcitability was the result of Nav1.7 and Nav1.8 overexpression due to Nedd4-2 downregulation. These studies provided the first in vivo evidence of the role of Nedd4-2-dependent regulation of Nav channels in a disease state. This ubiquitylation pathway may be involved in the development of symptoms and diseases linked to Nav-dependent hyperexcitability, such as pain, cardiac arrhythmias, epilepsy, migraine, and myotonias.

Memory regulatory T cells reside in human skin.

Regulatory T cells (Tregs), which are characterized by expression of the transcription factor Foxp3, are a dynamic and heterogeneous population of cells that control immune responses and prevent autoimmunity. We recently identified a subset of Tregs in murine skin with properties typical of memory cells and defined this population as memory Tregs (mTregs). Due to the importance of these cells in regulating tissue inflammation in mice, we analyzed this cell population in humans and found that almost all Tregs in normal skin had an activated memory phenotype. Compared with mTregs in peripheral blood, cutaneous mTregs had unique cell surface marker expression and cytokine production. In normal human skin, mTregs preferentially localized to hair follicles and were more abundant in skin with high hair density. Sequence comparison of TCRs from conventional memory T helper cells and mTregs isolated from skin revealed little homology between the two cell populations, suggesting that they recognize different antigens. Under steady-state conditions, mTregs were nonmigratory and relatively unresponsive; however, in inflamed skin from psoriasis patients, mTregs expanded, were highly proliferative, and produced low levels of IL-17. Taken together, these results identify a subset of Tregs that stably resides in human skin and suggest that these cells are qualitatively defective in inflammatory skin disease.

Ubiquitin-specific protease USP2-45 acts as a molecular switch to promote α2δ-1-induced downregulation of Ca v1.2 channels

Availability of voltage-gated calcium channels (Cav) at the plasma membrane is paramount to maintaining the calcium homeostasis of the cell. It is proposed that the ubiquitylation/de-ubiquitylation balance regulates the density of ion channels at the cell surface. Voltage-gated calcium channels Cav1.2 have been found to be ubiquitylated under basal conditions both in vitro and in vivo. In a previous study, we have shown that Cav1.2 channels are ubiquitylated by neuronal precursor cell-expressed developmentally downregulated 4 (Nedd4-1) ubiquitin ligases, but the identity of the counterpart de-ubiquitylating enzyme remained to be elucidated. Regarding sodium and potassium channels, it has been reported that the action of the related isoform Nedd4-2 is counteracted by the ubiquitin-specific protease (USP) 2-45. In this study, we show that USP 2-45 also de-ubiquitylates Cav channels. We co-expressed USPs and Cav1.2 channels together with the accessory subunits β2 and α2δ-1, in tsA-201 and HEK-293 mammalian cell lines. Using whole-cell current recordings and surface biotinylation assays, we show that USP2-45 specifically decreases both the amplitude of Cav currents and the amount of Cav1.2 subunits inserted at the plasma membrane. Importantly, co-expression of the α2δ-1 accessory subunit is necessary to support the effect of USP2-45. We further show that USP2-45 promotes the de-ubiquitylation of both Cav1.2 and α2δ-1 subunits. Remarkably, α2δ-1, but not Cav1.2 nor β2, co-precipitated with USP2-45. These results suggest that USP2-45 binding to α2δ-1 promotes the de-ubiquitylation of both Cav1.2 and α2δ-1 subunits, in order to regulate the expression of Cav1.2 channels at the plasma membrane.

PDZ domain-binding motif regulates cardiomyocyte compartment-specific NaV1.5 channel expression and function

BACKGROUND Sodium channel NaV1.5 underlies cardiac excitability and conduction. The last 3 residues of NaV1.5 (Ser-Ile-Val) constitute a PDZ domain-binding motif that interacts with PDZ proteins such as syntrophins and SAP97 at different locations within the cardiomyocyte, thus defining distinct pools of NaV1.5 multiprotein complexes. Here, we explored the in vivo and clinical impact of this motif through characterization of mutant mice and genetic screening of patients. METHODS AND RESULTS To investigate in vivo the regulatory role of this motif, we generated knock-in mice lacking the SIV domain (ΔSIV). ΔSIV mice displayed reduced NaV1.5 expression and sodium current (INa), specifically at the lateral myocyte membrane, whereas NaV1.5 expression and INa at the intercalated disks were unaffected. Optical mapping of ΔSIV hearts revealed that ventricular conduction velocity was preferentially decreased in the transversal direction to myocardial fiber orientation, leading to increased anisotropy of ventricular conduction. Internalization of wild-type and ΔSIV channels was unchanged in HEK293 cells. However, the proteasome inhibitor MG132 rescued ΔSIV INa, suggesting that the SIV motif is important for regulation of NaV1.5 degradation. A missense mutation within the SIV motif (p.V2016M) was identified in a patient with Brugada syndrome. The mutation decreased NaV1.5 cell surface expression and INa when expressed in HEK293 cells. CONCLUSIONS Our results demonstrate the in vivo significance of the PDZ domain-binding motif in the correct expression of NaV1.5 at the lateral cardiomyocyte membrane and underline the functional role of lateral NaV1.5 in ventricular conduction. Furthermore, we reveal a clinical relevance of the SIV motif in cardiac disease.

Ribosomal and Immune Transcripts Associate with Relapse in Acquired ADAMTS13-Deficient Thrombotic Thrombocytopenic Purpura.

Approximately 40% of patients who survive acute episodes of thrombotic thrombocytopenic purpura (TTP) associated with severe acquired ADAMTS13 deficiency experience one or more relapses. Risk factors for relapse other than severe ADAMTS13 deficiency and ADAMTS13 autoantibodies are unknown. ADAMTS13 autoantibodies, TTP episodes following infection or type I interferon treatment and reported ensuing systemic lupus erythematosus in some patients suggest immune dysregulation. This cross-sectional study asked whether autoantibodies against RNA-binding proteins or peripheral blood gene expression profiles measured during remission are associated with history of prior relapse in acquired ADAMTS13-deficient TTP. Peripheral blood from 38 well-characterized patients with autoimmune ADAMTS13-deficient TTP in remission was examined for autoantibodies and global gene expression. A subset of TTP patients (9 patients, 24%) exhibited a peripheral blood gene signature composed of elevated ribosomal transcripts that associated with prior relapse. A non-overlapping subset of TTP patients (9 patients, 24%) displayed a peripheral blood type I interferon gene signature that associated with autoantibodies to RNA-binding proteins but not with history of relapse. Patients who had relapsed bimodally expressed higher HLA transcript levels independently of ribosomal transcripts. Presence of any one potential risk factor (ribosomal gene signature, elevated HLA-DRB1, elevated HLA-DRB5) associated with relapse (OR = 38.4; p = 0.0002) more closely than any factor alone or all factors together. Levels of immune transcripts typical of natural killer (NK) and T lymphocytes positively correlated with ribosomal gene expression and number of prior episodes but not with time since the most recent episode. Flow cytometry confirmed elevated expression of cell surface markers encoded by these transcripts on T and/or NK cell subsets of patients who had relapsed. These data associate elevated ribosomal and immune transcripts with relapse history in acquired, ADAMTS13-deficient TTP.

Synergism of peptide receptor-targeted Auger electron radiation therapy with anti-angiogenic compounds in a mouse model of neuroendocrine tumors.

BACKGROUND Neuroendocrine tumors are well vascularized and express specific cell surface markers, such as somatostatin receptors and the glucagon-like peptide-1 receptor (GLP-1R). Using the Rip1Tag2 transgenic mouse model of pancreatic neuroendocrine tumors (pNET), we have investigated the potential benefit of a combination of anti-angiogenic treatment with targeted internal radiotherapy. METHODS [Lys40(Ahx-DTPA-111In)NH2]-exendin-4, a radiopeptide that selectively binds to GLP-1R expressed on insulinoma and other neuroendocrine tumor cells, was co-administered with oral vatalanib (an inhibitor of vascular endothelial growth factor receptors (VEGFR)) or imatinib (a c-kit/PDGFR inhibitor). The control groups included single-agent kinase inhibitor treatments and [Lys40(Ahx-DTPA-natIn)NH2]-exendin-4 monotherapy. For biodistribution, Rip1Tag2 mice were pre-treated with oral vatalanib or imatinib for 0, 3, 5, or 7 days at a dose of 100 mg/kg. Subsequently, [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 was administered i.v., and the biodistribution was assessed after 4 h. For therapy, the mice were injected with 1.1 MBq [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 and treated with vatalanib or imatinib 100 mg/kg orally for another 7 days. Tumor volume, tumor cell apoptosis and proliferation, and microvessel density were quantified. RESULTS Combination of [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 and vatalanib was significantly more effective than single treatments (p < 0.05) and reduced the tumor volume by 97% in the absence of organ damage. The pre-treatment of mice with vatalanib led to a reduction in the tumor uptake of [Lys40(Ahx-DTPA-111In)NH2]-exendin-4, indicating that concomitant administration of vatalanib and the radiopeptide was the best approach. Imatinib did not show a synergistic effect with [Lys40(Ahx-DTPA-111In)NH2]-exendin-4. CONCLUSION The combination of 1.1 MBq of [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 with 100 mg/kg vatalanib had the same effect on a neuroendocrine tumor as the injection of 28 MBq of the radiopeptide alone but without any apparent side effects, such as radiation damage of the kidneys.

Prolonged activity of the pestiviral RNase Erns as an interferon antagonist after uptake by clathrin-mediated endocytosis

The RNase activity of the envelope glycoprotein E(rns) of the pestivirus bovine viral diarrhea virus (BVDV) is required to block type I interferon (IFN) synthesis induced by single-stranded RNA (ssRNA) and double-stranded RNA (dsRNA) in bovine cells. Due to the presence of an unusual membrane anchor at its C terminus, a significant portion of E(rns) is also secreted. In addition, a binding site for cell surface glycosaminoglycans is located within the C-terminal region of E(rns). Here, we show that the activity of soluble E(rns) as an IFN antagonist is not restricted to bovine cells. Extracellularly applied E(rns) protein bound to cell surface glycosaminoglycans and was internalized into the cells within 1 h of incubation by an energy-dependent mechanism that could be blocked by inhibitors of clathrin-dependent endocytosis. E(rns) mutants that lacked the C-terminal membrane anchor retained RNase activity but lost most of their intracellular activity as an IFN antagonist. Surprisingly, once taken up into the cells, E(rns) remained active and blocked dsRNA-induced IFN synthesis for several days. Thus, we propose that E(rns) acts as an enzymatically active decoy receptor that degrades extracellularly added viral RNA mainly in endolysosomal compartments that might otherwise activate intracellular pattern recognition receptors (PRRs) in order to maintain a state of innate immunotolerance. IMPORTANCE The pestiviral RNase E(rns) was previously shown to inhibit viral ssRNA- and dsRNA-induced interferon (IFN) synthesis. However, the localization of E(rns) at or inside the cells, its species specificity, and its mechanism of interaction with cell membranes in order to block the host's innate immune response are still largely unknown. Here, we provide strong evidence that the pestiviral RNase E(rns) is taken up within minutes by clathrin-mediated endocytosis and that this uptake is mostly dependent on the glycosaminoglycan binding site located within the C-terminal end of the protein. Remarkably, the inhibitory activity of E(rns) remains for several days, indicating the very potent and prolonged effect of a viral IFN antagonist. This novel mechanism of an enzymatically active decoy receptor that degrades a major viral pathogen-associated molecular pattern (PAMP) might be required to efficiently maintain innate and, thus, also adaptive immunotolerance, and it might well be relevant beyond the bovine species.

Stimulation of monocytes by placental microparticles involves toll-like receptors and nuclear factor kappa-light-chain-enhancer of activated B cells.

Human pregnancy is accompanied by a mild systemic inflammatory response, which includes the activation of monocytes circulating in maternal blood. This response is exaggerated in preeclampsia, a placental-dependent disorder specific to human pregnancies. We and others showed that placental syncytiotrophoblast membrane microparticles (STBM) generated in vitro from normal placentas stimulated peripheral blood monocytes, which suggest a contribution of STBM to the systemic maternal inflammation. Here, we analyzed the inflammatory potential of STBM prepared from preeclamptic placentas on primary monocytes and investigated the mode of action in vitro. STBM generated in vitro by placental villous explants of normal or preeclamptic placentas were co-incubated with human peripheral blood monocytes. In some cases, inhibitors of specific cellular functions or signaling pathways were used. The analysis of the monocytic response was performed by flow cytometry, enzyme-linked immunoassays, real-time PCR, and fluorescence microscopy. STBM derived from preeclamptic placentas up-regulated the cell surface expression of CD54, and stimulated the secretion of the pro-inflammatory interleukin (IL)-6 and IL-8 in a similar, dose-dependent manner as did STBM prepared from normal placentas. STBM bound to the cell surface of monocytes, but phagocytosis was not necessary for activation. STBM-induced cytokine secretion was impaired in the presence of inhibitors of toll-like receptor (TLR) signaling or when nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation was blocked. Our results suggest that the inflammatory reaction in monocytes may be initiated by the interaction of STBM with TLRs, which in turn signal through NF-κB to mediate the transcription of genes coding for pro-inflammatory factors.

Development of small molecular tools for the cellular study of adenosine receptors

The adenosine receptors are members of the G-protein coupled receptor (GPCR) family which represents the largest class of cell-surface proteins mediating cellular communication. As a result, GPCRs are formidable drug targets and it is estimated that approximately 30% of the marketed drugs act through members of this receptor class. There are four known subtypes of adenosine receptors: A1, A2A, A2B and A3. The adenosine A1 receptor, which is the subject of this presentation, mediates the physiological effects of adenosine in various tissues including the brain, heart, kidney and adipocytes. In the brain for instance, its role in epilepsy and ischemia has been the focus of many studies. Previous attempts to study the biosynthesis, trafficking and agonist-induced internalisation of the adenosine A1 receptor in neurons using fluorescent protein-receptor fusion constructs have been hampered by the sheer size of the fluorescent protein (GFP) that ultimately affected the function of the receptor. We have therefore initiated a research programme to develop small molecule fluorescent agonists that selectively activate the adenosine A1 receptor. Our probe design is based on the endogenous ligand adenosine and the known unselective adenosine receptor agonist NECA. We have synthesised a small library of non-fluorescent adenosine derivatives that have different cyclic and bicyclic moieties at the 6 position of the purine ring and have evaluated the pharmacology of these compounds using a yeast-based assay. This analysis revealed compounds with interesting behaviour, i.e. exhibiting subtype-selectivity and biased signalling, that can be potentially used as tool compounds in their own right for cellular studies of the adenosine A1 receptor. Furthermore, we have also linked fluorescent dyes to the purine ring and discovered fluorescent compounds that can activate the adenosine A1 receptor.

Proteomic analysis of Plasmodium in the mosquito: progress and pitfalls

Here we discuss proteomic analyses of whole cell preparations of the mosquito stages of malaria parasite development (i.e. gametocytes, microgamete, ookinete, oocyst and sporozoite) of Plasmodium berghei. We also include critiques of the proteomes of two cell fractions from the purified ookinete, namely the micronemes and cell surface. Whereas we summarise key biological interpretations of the data, we also try to identify key methodological constraints we have met, only some of which we were able to resolve. Recognising the need to translate the potential of current genome sequencing into functional understanding, we report our efforts to develop more powerful combinations of methods for the in silico prediction of protein function and location. We have applied this analysis to the proteome of the male gamete, a cell whose very simple structural organisation facilitated interpretation of data. Some of the in silico predictions made have now been supported by ongoing protein tagging and genetic knockout studies. We hope this discussion may assist future studies.

Discovery and characterization of a novel non-competitive inhibitor of the divalent metal transporter DMT1/SLC11A2

Divalent metal transporter-1 (SLC11A2/DMT1) uses the H+ electrochemical gradient as the driving force to transport divalent metal ions such as Fe2+, Mn2+ and others metals into mammalian cells. DMT1 is ubiquitously expressed, most notably in proximal duodenum, immature erythroid cells, brain and kidney. This transporter mediates H+-coupled transport of ferrous iron across the apical membrane of enterocytes. In addition, in cells such as to erythroid precursors, following transferrin receptor (TfR) mediated endocytosis; it mediates H+-coupled exit of ferrous iron from endocytic vesicles into the cytosol. Dysfunction of human DMT1 is associated with several pathologies such as iron deficiency anemia hemochromatosis, Parkinson's disease and Alzheimer's disease, as well as colorectal cancer and esophageal adenocarcinoma, making DMT1 an attractive target for drug discovery. In the present study, we performed a ligand-based virtual screening of the Princeton database (700,000 commercially available compounds) to search for pharmacophore shape analogs of recently reported DMT1 inhibitors. We discovered a new compound, named pyrimidinone 8, which mediates a reversible linear non-competitive inhibition of human DMT1 (hDMT1) transport activity with a Ki of ∼20 μM. This compound does not affect hDMT1 cell surface expression and shows no dependence on extracellular pH. To our knowledge, this is the first experimental evidence that hDMT1 can be allosterically modulated by pharmacological agents. Pyrimidinone 8 represents a novel versatile tool compound and it may serve as a lead structure for the development of therapeutic compounds for pre-clinical assessment.

The fusion protein of wild-type canine distemper virus is a major determinant of persistent infection.

The wild-type A75/17 canine distemper virus (CDV) strain induces a persistent infection in the central nervous system but infects cell lines very inefficiently. In contrast, the genetically more distant Onderstepoort CDV vaccine strain (OP-CDV) induces extensive syncytia formation. Here, we investigated the roles of wild-type fusion (F(WT)) and attachment (H(WT)) proteins in Vero cells expressing, or not, the canine SLAM receptor by transfection experiments and by studying recombinants viruses expressing different combinations of wild-type and OP-CDV glycoproteins. We show that low fusogenicity is not due to a defect of the envelope proteins to reach the cell surface and that H(WT) determines persistent infection in a receptor-dependent manner, emphasizing the role of SLAM as a potent enhancer of fusogenicity. However, importantly, F(WT) reduced cell-to-cell fusion independently of the cell surface receptor, thus demonstrating that the fusion protein of the neurovirulent A75/17-CDV strain plays a key role in determining persistent infection.