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Microsomal triglyceride transfer protein (MTP) is essential for the assembly of triglyceride-rich apolipoprotein B-containing lipoproteins. Previous studies in our laboratory identified a novel splice variant of MTP in mice that we named MTP-B. MTP-B has a unique first exon (1B) located 2.7 kB upstream of the first exon (1A) for canonical MTP (MTP-A). The two mature isoforms, though nearly identical in sequence and function, have different tissue expression patterns. In this study we report the identification of a second MTP splice variant (MTP-C), which contains both exons 1B and 1A. MTP-C is expressed in all the tissues we tested. In cells transfected with MTP-C, protein expression was less than 15% of that found when the cells were transfected with MTP-A or MTP-B. In silico analysis of the 5'-UTR of MTP-C revealed seven ATGs upstream of the start site for MTP-A, which is the only viable start site in frame with the main coding sequence. One of those ATGs was located in the 5'-UTR for MTP-A. We generated reporter constructs in which the 5'-UTRs of MTP-A or MTP-C were inserted between an SV40 promoter and the coding sequence of the luciferase gene and transfected these constructs into HEK 293 cells. Luciferase activity was significantly reduced by the MTP-C 5'-UTR, but not by the MTP-A 5'-UTR. We conclude that alternative splicing plays a key role in regulating MTP expression by introducing unique 5'-UTRs, which contain elements that alter translation efficiency, enabling the cell to optimize MTP levels and activity.
Mammalian gestation and pregnancy are fast evolving processes that involve the interaction of the fetal, maternal and paternal genomes. Version 1.0 of the GEneSTATION database (http://genestation.org) integrates diverse types of omics data across mammals to advance understanding of the genetic basis of gestation and pregnancy-associated phenotypes and to accelerate the translation of discoveries from model organisms to humans. GEneSTATION is built using tools from the Generic Model Organism Database project, including the biology-aware database CHADO, new tools for rapid data integration, and algorithms that streamline synthesis and user access. GEneSTATION contains curated life history information on pregnancy and reproduction from 23 high-quality mammalian genomes. For every human gene, GEneSTATION contains diverse evolutionary (e.g. gene age, population genetic and molecular evolutionary statistics), organismal (e.g. tissue-specific gene and protein expression, differential gene expression, disease phenotype), and molecular data types (e.g. Gene Ontology Annotation, protein interactions), as well as links to many general (e.g. Entrez, PubMed) and pregnancy disease-specific (e.g. PTBgene, dbPTB) databases. By facilitating the synthesis of diverse functional and evolutionary data in pregnancy-associated tissues and phenotypes and enabling their quick, intuitive, accurate and customized meta-analysis, GEneSTATION provides a novel platform for comprehensive investigation of the function and evolution of mammalian pregnancy.
© The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.
Flecainide blocks ryanodine receptor type 2 (RyR2) channels in the open state, suppresses arrhythmogenic Ca2+ waves and prevents catecholaminergic polymorphic ventricular tachycardia (CPVT) in mice and humans. We hypothesized that differences in RyR2 activity induced by CPVT mutations determines the potency of open-state RyR2 blockers like flecainide (FLEC) and R-propafenone (RPROP) against Ca2+ waves in cardiomyocytes. Using confocal microscopy, we studied Ca2+ sparks and waves in isolated saponin-permeabilized ventricular myocytes from two CPVT mouse models (Casq2-/-, RyR2-R4496C+/-), wild-type (c57bl/6, WT) mice, and WT rabbits (New Zealand white rabbits). Consistent with increased RyR2 activity, Ca2+ spark and wave frequencies were significantly higher in CPVT compared to WT mouse myocytes. We next obtained concentration-response curves of Ca2+ wave inhibition for FLEC, RPROP (another open-state RyR2 blocker), and tetracaine (TET) (a state-independent RyR2 blocker). Both FLEC and RPROP inhibited Ca2+ waves with significantly higher potency (lower IC50) and efficacy in CPVT compared to WT. In contrast, TET had similar potency in all groups studied. Increasing RyR2 activity of permeabilized WT myocytes by exposure to caffeine (150 µM) increased the potency of FLEC and RPROP but not of TET. RPROP and FLEC were also significantly more potent in rabbit ventricular myocytes that intrinsically exhibit higher Ca2+ spark rates than WT mouse ventricular myocytes. In conclusion, RyR2 activity determines the potency of open-state blockers FLEC and RPROP for suppressing arrhythmogenic Ca2+ waves in cardiomyocytes, a mechanism likely relevant to antiarrhythmic drug efficacy in CPVT.
Autologous vein grafts are commonly used for coronary and peripheral artery bypass but have a high incidence of intimal hyperplasia (IH) and failure. We present a nanopolyplex (NP) approach that efficiently delivers a mitogen-activated protein kinase (MAPK)-activated protein (MAPKAP) kinase 2 inhibitory peptide (MK2i) to graft tissue to improve long-term patency by inhibiting pathways that initiate IH. In vitro testing in human vascular smooth muscle cells revealed that formulation into MK2i-NPs increased cell internalization, endosomal escape, and intracellular half-life of MK2i. This efficient delivery mechanism enabled MK2i-NPs to sustain potent inhibition of inflammatory cytokine production and migration in vascular cells. In intact human saphenous vein, MK2i-NPs blocked inflammatory and migratory signaling, as confirmed by reduced phosphorylation of the posttranscriptional gene regulator heterogeneous nuclear ribonucleoprotein A0, the transcription factor cAMP (adenosine 3',5'-monophosphate) element-binding protein, and the chaperone heat shock protein 27. The molecular effects of MK2i-NPs caused functional inhibition of IH in human saphenous vein cultured ex vivo. In a rabbit vein transplant model, a 30-min intraoperative graft treatment with MK2i-NPs significantly reduced in vivo IH 28 days posttransplant compared with untreated or free MK2i-treated grafts. The decrease in IH in MK2i-NP-treated grafts in the rabbit model also corresponded with decreased cellular proliferation and maintenance of the vascular wall smooth muscle cells in a more contractile phenotype. These data indicate that nanoformulated MK2 inhibitors are a promising strategy for preventing graft failure.
Copyright © 2015, American Association for the Advancement of Science.
Cardiomyocytes (CMs) derived from human induced pluripotent stem cells (hiPSCs) are being increasingly used to model human heart diseases. hiPSC-CMs generated by earlier aggregation-based methods (i.e., embryoid body) often lack functional sarcoplasmic reticulum (SR) Ca stores characteristic of mature mammalian CMs. Newer monolayer-based cardiac differentiation methods (i.e., Matrigel sandwich or small molecule-based differentiation) produce hiPSC-CMs of high purity and yield, but their Ca handling has not been comprehensively investigated. Here, we studied Ca handling and cytosolic Ca buffering properties of hiPSC-CMs generated independently from multiple hiPSC lines at Stanford University, Vanderbilt University and University of Wisconsin-Madison. hiPSC-CMs were cryopreserved at each university. Frozen aliquots were shipped, recovered from cryopreservation, plated at low density and compared 3-5days after plating with acutely-isolated adult rabbit and mouse ventricular CMs. Although hiPSC-CM cell volume was significantly smaller, cell capacitance to cell volume ratio and cytoplasmic Ca buffering were not different from rabbit-CMs. hiPSC-CMs from all three laboratories exhibited robust L-type Ca currents, twitch Ca transients and caffeine-releasable SR Ca stores comparable to adult CMs. Ca transport by sarcoendoplasmic reticulum Ca ATPase (SERCA) and Na/Ca exchanger (NCX) was similar in all hiPSC-CM lines, but slower compared to rabbit-CMs. However, the relative contribution of SERCA and NCX to Ca transport of hiPSC-CMs was comparable to rabbit-CMs. Ca handling maturity of hiPSC-CMs increased from 15 to 21days post-induction. We conclude that hiPSC-CMs generated independently from multiple iPSC lines using monolayer-based methods can be reproducibly recovered from cryopreservation and exhibit comparable and functional SR Ca handling.
Copyright © 2015. Published by Elsevier Ltd.
Lipoxygenases (LOX) play critical roles in mammalian biology in the generation of potent lipid mediators of the inflammatory response; consequently, they are targets for the development of isoform-specific inhibitors. The regio- and stereo-specificity of the oxygenation of polyunsaturated fatty acids by the enzymes is understood in terms of the chemistry, but structural observation of the enzyme-substrate interactions is lacking. Although several LOX crystal structures are available, heretofore the rapid oxygenation of bound substrate has precluded capture of the enzyme-substrate complex, leaving a gap between chemical and structural insights. In this report, we describe the 2.0 Å resolution structure of 8R-LOX in complex with arachidonic acid obtained under anaerobic conditions. Subtle rearrangements, primarily in the side chains of three amino acids, allow binding of arachidonic acid in a catalytically competent conformation. Accompanying experimental work supports a model in which both substrate tethering and cavity depth contribute to positioning the appropriate carbon at the catalytic machinery.
© 2014 by The American Society for Biochemistry and Molecular Biology, Inc.
UNLABELLED - Identifying characteristics of the human immunodeficiency virus type 1 (HIV-1) envelope that are effective in generating broad, protective antibodies remains a hurdle to HIV vaccine design. Emerging evidence of the development of broad and potent neutralizing antibodies in HIV-infected subjects suggests that founder and subsequent progeny viruses may express unique antigenic motifs that contribute to this developmental pathway. We hypothesize that over the course of natural infection, B cells are programmed to develop broad antibodies by exposure to select populations of emerging envelope quasispecies variants. To test this hypothesis, we identified two unrelated subjects whose antibodies demonstrated increasing neutralization breadth against a panel of HIV-1 isolates over time. Full-length functional env genes were cloned longitudinally from these subjects from months after infection through 2.6 to 5.8 years of infection. Motifs associated with the development of breadth in published, cross-sectional studies were found in both subjects. We compared the immunogenicity of envelope vaccines derived from time points obtained during and after broadening of neutralization activity within these subjects. Rabbits were coimmunized four times with selected multiple gp160 DNAs and gp140-trimeric envelope proteins. The affinity of the polyclonal response increased as a function of boosting. The most rapid and persistent neutralization of multiclade tier 1 viruses was elicited by envelopes that were circulating in plasma at time points prior to the development of 50% neutralization breadth in both human subjects. The breadth elicited in rabbits was not improved by exposure to later envelope variants. These data have implications for vaccine development in describing a target time point to identify optimal envelope immunogens.
IMPORTANCE - Vaccine protection against viral infections correlates with the presence of neutralizing antibodies; thus, vaccine components capable of generating potent neutralization are likely to be critical constituents in an effective HIV vaccine. However, vaccines tested thus far have elicited only weak antibody responses and very modest, waning protection. We hypothesized that B cells develop broad antibodies by exposure to the evolving viral envelope population and tested this concept using multiple envelopes from two subjects who developed neutralization breadth within a few years of infection. We compared different combinations of envelopes from each subject to identify the most effective immunogens and regimens. In each subject, use of HIV envelopes circulating during the early development and maturation of breadth generated more-potent antibodies that were modestly cross neutralizing. These data suggest a new approach to identifying envelope immunogens that may be more effective in generating protective antibodies in humans.
Copyright © 2014, American Society for Microbiology. All Rights Reserved.
OBJECTIVES/HYPOTHESIS - To investigate the effects of increasing time and magnitude doses of vibration exposure on transcription of the vocal fold's junctional proteins, structural alterations, and functional tissue outcomes.
STUDY DESIGN - Animal study.
METHODS - 100 New Zealand White breeder rabbits were studied. Dependent variables were measured in response to increasing time doses (30, 60, or 120 minutes) and magnitude doses (control, modal intensity, and raised intensity) of vibration exposure. Messenger RNA expression of occludin, zonula occluden-1 (ZO-1), E-cadherin, β-catenin, interleukin 1β, cyclooxygenase-2, transforming growth factor β-1, and fibronectin were measured. Tissue structural alterations were assessed using transmission electron microscopy (TEM). Transepithelial resistance was used to measure functional tissue outcomes.
RESULTS - Occludin gene expression was downregulated in vocal folds exposed to 120-minute time doses of raised-intensity phonation, relative to control, and modal-intensity phonation. ZO-1 gene expression was upregulated following a 120-minute time dose of modal-intensity phonation, compared to control, and downregulated after a 120-minute time dose of raised-intensity phonation, compared to modal-intensity phonation. E-cadherin gene expression was downregulated after a 120-minute time dose of raised-intensity phonation, compared to control and modal-intensity phonation. TEM revealed extensive desquamation of the stratified squamous epithelial cells with increasing time and magnitude doses of vibration exposure. A general observation of lower transepithelial resistance measures was made in tissues exposed to raised-intensity phonation compared to all other groups.
CONCLUSIONS - This study provides evidence of vocal fold tissue responses to varying time and magnitude doses of vibration exposure.
LEVEL OF EVIDENCE - NA.
© 2014 The American Laryngological, Rhinological and Otological Society, Inc.
OBJECTIVES/HYPOTHESIS - The purpose of this study was to use nonlinear dynamic analysis methods such as phase space portraits and correlation dimension (D2) as well as descriptive spectrographic analyses to characterize acoustic signals produced during evoked rabbit phonation.
METHODS - Seventeen New Zealand white breeder rabbits were used to perform the study. A Grass S-88 stimulator (SA Instrumentation, Encinitas, CA) and constant current isolation unit (Grass Telefactor, model PSIU6; West Warwick, RI) were used to provide electrical stimulation to laryngeal musculature, and transglottal airflow rate and stimulation current (mA) were manipulated to elicit modal, raised intensity, and pressed phonations. Central 1 second portions of the most stable portion of the acoustic waveform for modal, raised intensity, and pressed phonations were edited and then analyzed via phase space portraits, Poincaré sections, and the estimation of the D2. In an attempt to limit the effects of the highly variable and nonstationary characteristics of some of the signals being analyzed, D2 analysis was also performed on the most stable central 200-millisecond portion of the acoustic waveform. Descriptive analysis of each phonation was also conducted using sound spectrograms.
RESULTS - Results showed that the complexity of phonation and the subsequent acoustic waveform is increased as transglottal airflow rate and degree of glottal adduction are manipulated in the evoked rabbit phonation model. In particular, phonatory complexity, as quantified via D2 analyses and demonstrated via spectrographic characteristics, increases from "modal" (ie, phonation elicited at just above the phonation threshold pressure) to raised intensity (phonation elicited by increasing transglottal airflow rate) to pressed (phonation elicited by increasing the stimulation current delivered to the larynx). Variations in a single dynamic dimension (airflow rate or adductory force) resulted in significantly increased productions of nonlinear phenomenon, including bifurcations from periodicity to regions of subharmonic content, fundamental frequency, and harmonic jumps, and evidence of periodicity within aperiodic regions ("chaos").
CONCLUSIONS - The evoked rabbit phonation model described in this study allows for the elicitation of various types of phonations under controlled conditions and, therefore, has the potential to provide insight regarding important variables that may elicit examples of nonlinear phenomena such as subharmonics and deterministic chaos.
Copyright © 2014 The Voice Foundation. Published by Elsevier Inc. All rights reserved.
Because the vocal folds undergo repeated trauma during continuous cycles of vibration, the epithelium is routinely susceptible to damage during phonation. Excessive and prolonged vibration exposure is considered a significant predisposing factor in the development of vocal fold pathology. The purpose of the present study was to quantify the extent of epithelial surface damage following increased time and magnitude doses of vibration exposure using an in vivo rabbit phonation model. Forty-five New Zealand white breeder rabbits were randomized to nine groups and received varying phonation time-doses (30, 60, or 120 minutes) and magnitude-doses (control, modal intensity phonation, or raised intensity phonation) of vibration exposure. Scanning electron microscopy and transmission electron microscopy was used to quantify the degree of epithelial surface damage. Results revealed a significant reduction in microprojection density, microprojection height, and depth of the epithelial surface with increasing time and phonation magnitudes doses, signifying increased epithelial surface damage risk with excessive and prolonged vibration exposure. Destruction to the epithelial cell surface may provide significant insight into the disruption of cell function following prolonged vibration exposure. One important goal achieved in the present study was the quantification of epithelial surface damage using objective imaging criteria. These data provide an important foundation for future studies of long-term tissue recovery from excessive and prolonged vibration exposure.