67 research outputs found
A-Subclass ATP-Binding Cassette Proteins in Brain Lipid Homeostasis and Neurodegeneration
The A-subclass of ATP-binding cassette (ABC) transporters comprises 12 structurally related members of the evolutionarily highly conserved superfamily of ABC transporters. ABCA transporters represent a subgroup of âfull-sizeâ multispan transporters of which several members have been shown to mediate the transport of a variety of physiologic lipid compounds across membrane barriers. The importance of ABCA transporters in human disease is documented by the observations that so far four members of this protein family (ABCA1, ABCA3, ABCA4, ABCA12) have been causatively linked to monogenetic disorders including familial high-density lipoprotein deficiency, neonatal surfactant deficiency, degenerative retinopathies, and congenital keratinization disorders. Recent research also point to a significant contribution of several A-subfamily ABC transporters to neurodegenerative diseases, in particular Alzheimerâs disease (AD). This review will give a summary of our current knowledge of the A-subclass of ABC transporters with a special focus on brain lipid homeostasis and their involvement in AD
The human ABC transporter pseudogene family: Evidence for transcription and gene-pseudogene interference
<p>Abstract</p> <p>Background</p> <p>Pseudogenes are an integral component of the human genome. Little attention, however, has so far been paid to the phenomenon that some pseudogenes are transcriptionally active. Recently, we demonstrated that the human ortholog of the rodent testis-specific ATP-binding cassette (ABC) transporter Abca17 is a ubiquitously transcribed pseudogene (<it>ABCA17P</it>). The aim of the present study was to establish a complete inventory of all ABC transporter pseudogenes in the human genome and to identify transcriptionally active ABC transporter pseudogenes. Moreover, we tested the hypothesis that a regulatory interdependency exists between ABC transporter pseudogenes and their parental protein coding equivalents.</p> <p>Results</p> <p>Systematic bioinformatic analysis revealed the existence of 22 ABC transporter pseudogenes within the human genome. We identified two clusters on chromosomes 15 and 16, respectively, which harbor almost half of all pseudogenes (n = 10). Available information from EST and mRNA databases and RT-PCR expression profiling indicate that a large portion of the ABC transporter pseudogenes (45%, n = 10) are transcriptionally active and some of them are expressed as alternative splice variants. We demonstrate that both pseudogenes of the pseudoxanthoma elasticum gene <it>ABCC6</it>, <it>ABCC6P1 </it>and <it>ABCC6P2</it>, are transcribed. <it>ABCC6P1 </it>and <it>ABCC6 </it>possess near-identical promoter sequences and their tissue-specific expression profiles are strikingly similar raising the possibility that they form a gene-pseudogene dual transcription unit. Intriguingly, targeted knockdown of the transcribed pseudogene <it>ABCC6P1 </it>resulted in a significant reduction of <it>ABCC6 </it>mRNA expression levels.</p> <p>Conclusion</p> <p>The human genome contains a surprisingly small number of ABC transporter pseudogenes relative to other known gene families. They are unevenly distributed across the chromosomes. Importantly, a significant portion of the ABC transporter pseudogenes is transcriptionally active. The downregulation of <it>ABCC6 </it>mRNA levels by targeted suppression of the expression of its pseudogene <it>ABCC6P1 </it>provides evidence, for the first time, for a regulatory interdependence of a transcribed pseudogene and its protein coding counterpart in the human genome.</p
Molecular structure of a novel cholesterol-responsive A subclass ABC transporter, ABCA9
We recently identified a novel ABC A subclass transporter, ABCA6, in human macrophages. Here, we report the molecular cloning of an additional ABC A subfamily transporter from macrophages denoted ABCA9. The identified coding sequence is 4.9 kb in size and codes for a 1624 amino acid protein product. In accordance with the proposed nomenclature, the novel transporter was designated ABCA9. The putative full-length ABC transporter polypeptide consists of two transmembrane domains and two nucleotide binding folds and thus conforms to the group of full-size ABC transporters. We identified alternative ABCA9 mRNA variants in human macrophages that predict the existence of three truncated forms of the novel transporter. Among the human ABC A subfamily transporters, ABCA9 exhibits the highest amino acid sequence homology with ABCA8 (72%) and ABCA6 (60%), respectively. The striking amino acid sequence similarity between these transporter molecules supports the notion that they represent an evolutionary more recently emerged subgroup within the family of ABC A transporters, which we refer to as âABCA6-like transporters.â ABCA9 mRNA is ubiquitously expressed with the highest mRNA levels in heart, brain, and fetal tissues. Analysis of the genomic structure revealed that the ABCA9 gene consists of 39 exons that are located within a genomic region of âŒ85 kb size on chromosome 17q24.2. In human macrophages, ABCA9 mRNA is induced during monocyte differentiation into macrophages and suppressed by cholesterol import indicating that ABCA9, like other known ABC A subfamily transporters, is a cholesterol-responsive gene. Based on this information, ABCA9 is likely involved in monocyte differentiation and macrophage lipid homeostasis
Interaction induced collapse of a section of the Fermi sea in in the zig-zag Hubbard ladder
Using the next-nearest neighbor (zig-zag) Hubbard chain as an one
dimemensional model, we investigate the influence of interactions on the
position of the Fermi wavevectors with the density-matrix renormalization-group
technique (DMRG). For suitable choices of the hopping parameters we observe
that electron-electron correlations induce very different renormalizations for
the two different Fermi wavevectors, which ultimately lead to a complete
destruction of one section of the Fermi sea in a quantum critical point
Tuning the 3D microenvironment of reprogrammed tubule cells enhances biomimetic modeling of polycystic kidney disease
Renal tubular cells frequently lose differentiation markers and physiological properties when propagated in conventional cell culture conditions. Embedding cells in 3D microenvironments or controlling their 3D assembly by bioprinting can enhance their physiological properties, which is beneficial for modeling diseases in vitro. A potential cellular source for modeling renal tubular physiology and kidney diseases in vitro are directly reprogrammed induced renal tubular epithelial cells (iRECs). iRECs were cultured in various biomaterials and as bioprinted tubular structures. They showed high compatibility with the embedding substrates and dispensing methods. The morphology of multicellular aggregates was substantially influenced by the 3D microenvironment. Transcriptomic analyses revealed signatures of differentially expressed genes specific to each of the selected biomaterials. Using a new cellular model for autosomal-dominant polycystic kidney disease, Pkd1 iRECs showed disrupted morphology in bioprinted tubules and a marked upregulation of the Aldehyde dehydrogenase 1a1 (Aldh1a1). In conclusion, 3D microenvironments strongly influence the morphology and expression profiles of iRECs, help to unmask disease phenotypes, and can be adapted to experimental demands. Combining a direct reprogramming approach with appropriate biomaterials will facilitate construction of biomimetic kidney tubules and disease models at the microscale
A TNF-Regulated Recombinatorial Macrophage Immune Receptor Implicated in Granuloma Formation in Tuberculosis
Macrophages play a central role in host defense against mycobacterial infection and anti- TNF therapy is associated with granuloma disorganization and reactivation of tuberculosis in humans. Here, we provide evidence for the presence of a T cell receptor (TCR) αÎČ based recombinatorial immune receptor in subpopulations of human and mouse monocytes and macrophages. In vitro, we find that the macrophage-TCRαÎČ induces the release of CCL2 and modulates phagocytosis. TNF blockade suppresses macrophage-TCRαÎČ expression. Infection of macrophages from healthy individuals with mycobacteria triggers formation of clusters that express restricted TCR VÎČ repertoires. In vivo, TCRαÎČ bearing macrophages abundantly accumulate at the inner host-pathogen contact zone of caseous granulomas from patients with lung tuberculosis. In chimeric mouse models, deletion of the variable macrophage-TCRαÎČ or TNF is associated with structurally compromised granulomas of pulmonary tuberculosis even in the presence of intact T cells. These results uncover a TNF-regulated recombinatorial immune receptor in monocytes/macrophages and demonstrate its implication in granuloma formation in tuberculosis
Kondo effect in coupled quantum dots: a Non-crossing approximation study
The out-of-equilibrium transport properties of a double quantum dot system in
the Kondo regime are studied theoretically by means of a two-impurity Anderson
Hamiltonian with inter-impurity hopping. The Hamiltonian, formulated in
slave-boson language, is solved by means of a generalization of the
non-crossing approximation (NCA) to the present problem. We provide benchmark
calculations of the predictions of the NCA for the linear and nonlinear
transport properties of coupled quantum dots in the Kondo regime. We give a
series of predictions that can be observed experimentally in linear and
nonlinear transport measurements through coupled quantum dots. Importantly, it
is demonstrated that measurements of the differential conductance , for the appropriate values of voltages and inter-dot tunneling
couplings, can give a direct observation of the coherent superposition between
the many-body Kondo states of each dot. This coherence can be also detected in
the linear transport through the system: the curve linear conductance vs
temperature is non-monotonic, with a maximum at a temperature
characterizing quantum coherence between both Kondo states.Comment: 20 pages, 17 figure
Reception Test of Petals for the End Cap TEC+ of the CMS Silicon Strip Tracker
The silicon strip tracker of the CMS experiment has been completed and was inserted into the CMS detector in late 2007. The largest sub system of the tracker are its end caps, comprising two large end caps (TEC) each containing 3200 silicon strip modules. To ease construction, the end caps feature a modular design: groups of about 20 silicon modules are placed on sub-assemblies called petals and these self-contained elements are then mounted onto the TEC support structures. Each end cap consists of 144 such petals, which were built and fully qualified by several institutes across Europe. Fro
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