Interaction of amisulpride with GLUT1 at the blood-brain barrier. Relevance to Alzheimer's disease

Blood-brain barrier (BBB) dysfunction may be involved in the increased sensitivity of Alzheimer's disease (AD) patients to antipsychotics, including amisulpride. Studies indicate that antipsychotics interact with facilitated glucose transporters (GLUT), including GLUT1, and that GLUT1 BBB expression decreases in AD. We tested the hypotheses that amisulpride (charge: +1) interacts with GLUT1, and that BBB transport of amisulpride is compromised in AD. GLUT1 substrates, GLUT1 inhibitors and GLUT-interacting antipsychotics were identified by literature review and their physicochemical characteristics summarised. Interactions between amisulpride and GLUT1 were studied using in silico approaches and the human cerebral endothelial cell line, hCMEC/D3. Brain distribution of [3H]amisulpride was determined using in situ perfusion in wild type (WT) and 5xFamilial AD (5xFAD) mice. With transmission electron microscopy (TEM) we investigated brain capillary degeneration in WT mice, 5xFAD mice and human samples. Western blots determined BBB transporter expression in mouse and human. Literature review revealed that, although D-glucose has no charge, charged molecules can interact with GLUT1. GLUT1 substrates are smaller (184.95±6.45g/mol) than inhibitors (325.50±14.40g/mol) and GLUT-interacting antipsychotics (369.38±16.04). Molecular docking showed beta-D-glucose (free energy binding: -15.39kcal/mol) and amisulpride (-29.04kcal/mol) interact with GLUT1. Amisulpride did not affect [14C]D-glucose hCMEC/D3 accumulation. [3H]amisulpride uptake into the brain (except supernatant) of 5xFAD mice compared to WT remained unchanged. TEM revealed brain capillary degeneration in human AD. There was no difference in GLUT1 or P-glycoprotein BBB expression between WT and 5xFAD mice. In contrast, caudate P-glycoprotein, but not GLUT1, expression was decreased in human AD capillaries versus controls. This study provides new details about the BBB transport of amisulpride, evidence that amisulpride interacts with GLUT1 and that BBB transporter expression is altered in AD. This suggests that antipsychotics could potentially exacerbate the cerebral hypometabolism in AD. Further research into the mechanism of amisulpride transport by GLUT1 is important for improving antipsychotics safety.

Multi-synaptic boutons are a feature of CA1 hippocampal connections in the stratum oriens

Excitatory synapses are typically described as single synaptic boutons (SSBs), where one presynaptic bouton contacts a single postsynaptic spine. Using serial section block-face scanning electron microscopy, we found that this textbook definition of the synapse does not fully apply to the CA1 region of the hippocampus. Roughly half of all excitatory synapses in the stratum oriens involved multi-synaptic boutons (MSBs), where a single presynaptic bouton containing multiple active zones contacted many postsynaptic spines (from 2 to 7) on the basal dendrites of different cells. The fraction of MSBs increased during development (from postnatal day 22 [P22] to P100) and decreased with distance from the soma. Curiously, synaptic properties such as active zone (AZ) or postsynaptic density (PSD) size exhibited less within-MSB variation when compared with neighboring SSBs, features that were confirmed by super-resolution light microscopy. Computer simulations suggest that these properties favor synchronous activity in CA1 networks.

A novel class of sulphonamides potently block malaria transmission by targeting a Plasmodium vacuole membrane protein

Phenotypic cell-based screens are critical tools for discovering candidate drugs for development, yet identification of the cellular target and mode of action of a candidate drug is often lacking. Using an imaging-based screen, we recently discovered an N-[(4-hydroxychroman-4-yl)methyl]-sulphonamide (N-4HCS) compound, DDD01035881, that blocks male gamete formation in the malaria parasite life cycle and subsequent transmission of the parasite to the mosquito with nanomolar activity. To identify the target(s) of DDD01035881, and of the N-4HCS class of compounds more broadly, we synthesised a photoactivatable derivative, probe 2. Photoaffinity labelling of probe 2 coupled with mass spectrometry identified the 16 kDa Plasmodium falciparum parasitophorous vacuole membrane protein Pfs16 as a potential parasite target. Complementary methods including cellular thermal shift assays confirmed that the parent molecule DDD01035881 stabilised Pfs16 in lysates from activated mature gametocytes. Combined with high-resolution, fluorescence and electron microscopy data, which demonstrated that parasites inhibited with N-4HCS compounds phenocopy the targeted deletion of Pfs16 in gametocytes, these data implicate Pfs16 as a likely target of DDD01035881. This finding establishes N-4HCS compounds as being flexible and effective starting candidates from which transmission-blocking antimalarials can be developed in the future.

Structural investigations into colour-tuneable fluorescent InZnP-based quantum dots from zinc carboxylate and aminophosphine precursors

Fluorescent InP-based quantum dots have emerged as valuable nanomaterials for display technologies, biological imaging, and optoelectronic applications. The inclusion of zinc can enhance both their emissive and structural properties and reduce interfacial defects with ZnS or CdS shells. However, the sub-particle distribution of zinc and the role this element plays often remains unclear, and it has previously proved challenging to synthesise Zn-alloyed InP-based nanoparticles using aminophosphine precursors. In this report, we describe the synthesis of alloyed InZnP using zinc carboxylates, achieving colour-tuneable fluorescence from the unshelled core materials, followed by a one-pot ZnS or CdS deposition using diethyldithiocarbamate precursors. Structural analysis revealed that the "core/shell" particles synthesised here were more accurately described as homogeneous extended alloys with the constituent shell elements diffusing through the entire core, including full-depth inclusion of zinc.

Sporophytic control of pollen meiotic progression is mediated by tapetum expression of ABORTED MICROSPORES

Pollen development is dependent on the tapetum, a sporophytic anther cell layer surrounding the microspores that functions in pollen wall formation but is also essential for meiosis-associated development. There is clear evidence of crosstalk and co-regulation between the tapetum and microspores, but how this is achieved is currently not characterized. ABORTED MICROSPORES (AMS), a tapetum transcription factor, is important for pollen wall formation, but also has an undefined role in early pollen development. We conducted a detailed investigation of chromosome behaviour, cytokinesis, radial microtubule array (RMA) organization, and callose formation in the ams mutant. Early meiosis initiates normally in ams, shows delayed progression after the pachytene stage, and then fails during late meiosis, with disorganized RMA, defective cytokinesis, abnormal callose formation, and microspore degeneration, alongside abnormal tapetum development. Here, we show that selected meiosis-associated genes are directly repressed by AMS, and that AMS is essential for late meiosis progression. Our findings indicate that AMS has a dual function in tapetum-meiocyte crosstalk by playing an important regulatory role during late meiosis, in addition to its previously characterized role in pollen wall formation. AMS is critical for RMA organization, callose deposition, and therefore cytokinesis, and is involved in the crosstalk between the gametophyte and sporophytic tissues, which enables synchronous development of tapetum and microspores.

Mutations in EPHB4 cause human venous valve aplasia

Venous valve (VV) failure causes chronic venous insufficiency, but the molecular regulation of valve development is poorly understood. A primary lymphatic anomaly, caused by mutations in the receptor tyrosine kinase EPHB4, was recently described, with these patients also presenting with venous insufficiency. Whether the venous anomalies are the result of an effect on VVs is not known. VV formation requires complex "organization" of valve-forming endothelial cells, including their reorientation perpendicular to the direction of blood flow. Using quantitative ultrasound, we identified substantial VV aplasia and deep venous reflux in patients with mutations in EPHB4. We used a GFP reporter in mice to study expression of its ligand, ephrinB2, and analyzed developmental phenotypes after conditional deletion of floxed Ephb4 and Efnb2 alleles. EphB4 and ephrinB2 expression patterns were dynamically regulated around organizing valve-forming cells. Efnb2 deletion disrupted the normal endothelial expression patterns of the gap junction proteins connexin37 and connexin43 (both required for normal valve development) around reorientating valve-forming cells and produced deficient valve-forming cell elongation, reorientation, polarity, and proliferation. Ephb4 was also required for valve-forming cell organization and subsequent growth of the valve leaflets. These results uncover a potentially novel cause of primary human VV aplasia.

Mitochondria form contact sites with the nucleus to couple prosurvival retrograde response

Mitochondria drive cellular adaptation to stress by retro-communicating with the nucleus. This process is known as mitochondrial retrograde response (MRR) and is induced by mitochondrial dysfunction. MRR results in the nuclear stabilization of prosurvival transcription factors such as the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Here, we demonstrate that MRR is facilitated by contact sites between mitochondria and the nucleus. The translocator protein (TSPO) by preventing the mitophagy-mediated segregation o mitochonria is required for this interaction. The complex formed by TSPO with the protein kinase A (PKA), via the A-kinase anchoring protein acyl-CoA binding domain containing 3 (ACBD3), established the tethering. The latter allows for cholesterol redistribution of cholesterol in the nucleus to sustain the prosurvival response by blocking NF-κB deacetylation. This work proposes a previously unidentified paradigm in MRR: the formation of contact sites between mitochondria and nucleus to aid communication.

De novo phosphatidylcholine synthesis is required for autophagosome membrane formation and maintenance during autophagy

Macroautophagy/autophagy can enable cancer cells to withstand cellular stress and maintain bioenergetic homeostasis by sequestering cellular components into newly formed double-membrane vesicles destined for lysosomal degradation, potentially affecting the efficacy of anti-cancer treatments. Using 13C-labeled choline and 13C-magnetic resonance spectroscopy and western blotting, we show increased de novo choline phospholipid (ChoPL) production and activation of PCYT1A (phosphate cytidylyltransferase 1, choline, alpha), the rate-limiting enzyme of phosphatidylcholine (PtdCho) synthesis, during autophagy. We also discovered that the loss of PCYT1A activity results in compromised autophagosome formation and maintenance in autophagic cells. Direct tracing of ChoPLs with fluorescence and immunogold labeling imaging revealed the incorporation of newly synthesized ChoPLs into autophagosomal membranes, endoplasmic reticulum (ER) and mitochondria during anticancer drug-induced autophagy. Significant increase in the colocalization of fluorescence signals from the newly synthesized ChoPLs and mCherry-MAP1LC3/LC3 (microtubule-associated protein 1 light chain 3) was also found on autophagosomes accumulating in cells treated with autophagy-modulating compounds. Interestingly, cells undergoing active autophagy had an altered ChoPL profile, with longer and more unsaturated fatty acid/alcohol chains detected. Our data suggest that de novo synthesis may be required to increase autophagosomal ChoPL content and alter its composition, together with replacing phospholipids consumed from other organelles during autophagosome formation and turnover. This addiction to de novo ChoPL synthesis and the critical role of PCYT1A may lead to development of agents targeting autophagy-induced drug resistance. In addition, fluorescence imaging of choline phospholipids could provide a useful way to visualize autophagosomes in cells and tissues.

ABBREVIATIONS

AKT: AKT serine/threonine kinase; BAX: BCL2 associated X, apoptosis regulator; BECN1: beclin 1; ChoPL: choline phospholipid; CHKA: choline kinase alpha; CHPT1: choline phosphotransferase 1; CTCF: corrected total cell fluorescence; CTP: cytidine-5'-triphosphate; DCA: dichloroacetate; DMEM: dulbeccos modified Eagles medium; DMSO: dimethyl sulfoxide; EDTA: ethylenediaminetetraacetic acid; ER: endoplasmic reticulum; GDPD5: glycerophosphodiester phosphodiesterase domain containing 5; GFP: green fluorescent protein; GPC: glycerophosphorylcholine; HBSS: hanks balances salt solution; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; LPCAT1: lysophosphatidylcholine acyltransferase 1; LysoPtdCho: lysophosphatidylcholine; MRS: magnetic resonance spectroscopy; MTORC1: mechanistic target of rapamycin kinase complex 1; PCho: phosphocholine; PCYT: choline phosphate cytidylyltransferase; PLA2: phospholipase A2; PLB: phospholipase B; PLC: phospholipase C; PLD: phospholipase D; PCYT1A: phosphate cytidylyltransferase 1, choline, alpha; PI3K: phosphoinositide-3-kinase; pMAFs: pancreatic mouse adult fibroblasts; PNPLA6: patatin like phospholipase domain containing 6; Pro-Cho: propargylcholine; Pro-ChoPLs: propargylcholine phospholipids; PtdCho: phosphatidylcholine; PtdEth: phosphatidylethanolamine; PtdIns3P: phosphatidylinositol-3-phosphate; RPS6: ribosomal protein S6; SCD: stearoyl-CoA desaturase; SEM: standard error of the mean; SM: sphingomyelin; SMPD1/SMase: sphingomyelin phosphodiesterase 1, acid lysosomal; SGMS: sphingomyelin synthase; WT: wild-type.

Regulatory T Cell Extracellular Vesicles Modify T-Effector Cell Cytokine Production and Protect Against Human Skin Allograft Damage

Regulatory T cells (Tregs) are a subpopulation of CD4⁺ T cells with a fundamental role in maintaining immune homeostasis and inhibiting unwanted immune responses using several different mechanisms. Recently, the intercellular transfer of molecules between Tregs and their target cells has been shown via trogocytosis and the release of small extracellular vesicles (sEVs). In this study, CD4⁺CD25⁺CD127^lo human Tregs were found to produce sEVs capable of inhibiting the proliferation of effector T cells (Teffs) in a dose dependent manner. These vesicles also modified the cytokine profile of Teffs leading to an increase in the production of IL-4 and IL-10 whilst simultaneously decreasing the levels of IL-6, IL-2, and IFNγ. MicroRNAs found enriched in the Treg EVs were indirectly linked to the changes in the cytokine profile observed. In a humanized mouse skin transplant model, human Treg derived EVs inhibited alloimmune-mediated skin tissue damage by limiting immune cell infiltration. Taken together, Treg sEVs may represent an exciting cell-free therapy to promote transplant survival.

Human venous valve disease caused by mutations in FOXC2 and GJC2

Venous valves (VVs) prevent venous hypertension and ulceration. We report that FOXC2 and GJC2 mutations are associated with reduced VV number and length. In mice, early VV formation is marked by elongation and reorientation ("organization") of Prox1hi endothelial cells by postnatal day 0. The expression of the transcription factors Foxc2 and Nfatc1 and the gap junction proteins Gjc2, Gja1, and Gja4 were temporospatially regulated during this process. Foxc2 and Nfatc1 were coexpressed at P0, and combined Foxc2 deletion with calcineurin-Nfat inhibition disrupted early Prox1hi endothelial organization, suggesting cooperative Foxc2-Nfatc1 patterning of these events. Genetic deletion of Gjc2, Gja4, or Gja1 also disrupted early VV Prox1hi endothelial organization at postnatal day 0, and this likely underlies the VV defects seen in patients with GJC2 mutations. Knockout of Gja4 or Gjc2 resulted in reduced proliferation of Prox1hi valve-forming cells. At later stages of blood flow, Foxc2 and calcineurin-Nfat signaling are each required for growth of the valve leaflets, whereas Foxc2 is not required for VV maintenance.

Prelamin A mediates myocardial inflammation in dilated and HIV-associated cardiomyopathies

Cardiomyopathies are complex heart muscle diseases that can be inherited or acquired. Dilated cardiomyopathy can result from mutations in LMNA, encoding the nuclear intermediate filament proteins lamin A/C. Some LMNA mutations lead to accumulation of the lamin A precursor, prelamin A, which is disease causing in a number of tissues, yet its impact upon the heart is unknown. Here, we discovered myocardial prelamin A accumulation occurred in a case of dilated cardiomyopathy, and we show that a potentially novel mouse model of cardiac-specific prelamin A accumulation exhibited a phenotype consistent with inflammatory cardiomyopathy, which we observed to be similar to HIV-associated cardiomyopathy, an acquired disease state. Numerous HIV protease therapies are known to inhibit ZMPSTE24, the enzyme responsible for prelamin A processing, and we confirmed that accumulation of prelamin A occurred in HIV+ patient cardiac biopsies. These findings (a) confirm a unifying pathological role for prelamin A common to genetic and acquired cardiomyopathies; (b) have implications for the management of HIV patients with cardiac disease, suggesting protease inhibitors should be replaced with alternative therapies (i.e., nonnucleoside reverse transcriptase inhibitors); and (c) suggest that targeting inflammation may be a useful treatment strategy for certain forms of inherited cardiomyopathy.

Small Extracellular Vesicles Are Key Regulators of Non-cell Autonomous Intercellular Communication in Senescence via the Interferon Protein IFITM3

Senescence is a cellular phenotype present in health and disease, characterized by a stable cell-cycle arrest and an inflammatory response called senescence-associated secretory phenotype (SASP). The SASP is important in influencing the behavior of neighboring cells and altering the microenvironment; yet, this role has been mainly attributed to soluble factors. Here, we show that both the soluble factors and small extracellular vesicles (sEVs) are capable of transmitting paracrine senescence to nearby cells. Analysis of individual cells internalizing sEVs, using a Cre-reporter system, show a positive correlation between sEV uptake and senescence activation. We find an increase in the number of multivesicular bodies during senescence in vivo. sEV protein characterization by mass spectrometry (MS) followed by a functional siRNA screen identify interferon-induced transmembrane protein 3 (IFITM3) as being partially responsible for transmitting senescence to normal cells. We find that sEVs contribute to paracrine senescence.

Mitochondrial abnormalities and disruption of the neuromuscular junction precede the clinical phenotype and motor neuron loss in hFUSWT transgenic mice

FUS (fused in sarcoma) mislocalization and cytoplasmic aggregation are hallmark pathologies in FUS-related amyotrophic lateral sclerosis and frontotemporal dementia. Many of the mechanistic hypotheses have focused on a loss of nuclear function in the FUS-opathies, implicating dysregulated RNA transcription and splicing in driving neurodegeneration. Recent studies describe an additional somato-dendritic localization for FUS in the cerebral cortex implying a regulatory role in mRNA transport and local translation at the synapse. Here, we report that FUS is also abundant at the pre-synaptic terminal of the neuromuscular junction (NMJ), suggesting an important function for this protein at peripheral synapses. We have previously reported dose and age-dependent motor neuron degeneration in transgenic mice overexpressing human wild-type FUS, resulting in a motor phenotype detected by ∼28 days and death by ∼100 days. Now, we report the earliest structural events using electron microscopy and quantitative immunohistochemistry. Mitochondrial abnormalities in the pre-synaptic motor nerve terminals are detected at postnatal day 6, which are more pronounced at P15 and accompanied by a loss of synaptic vesicles and synaptophysin protein coupled with NMJs of a smaller size at a time when there is no detectable motor neuron loss. These changes occur in the presence of abundant FUS and support a peripheral toxic gain of function. This appearance is typical of a ‘dying-back’ axonopathy, with the earliest manifestation being mitochondrial disruption. These findings support our hypothesis that FUS has an important function at the NMJ, and challenge the ‘loss of nuclear function’ hypothesis for disease pathogenesis in the FUS-opathies.

Tolerance of MRSA ST239-TW to chlorhexidine-based decolonization: Evidence for keratinocyte invasion as a mechanism of biocide evasion

OBJECTIVES

Information on genetic determinants of chlorhexidine tolerance (qacA carriage and MIC) in vitro is available, although evidence of the clinical impact and mechanisms remain poorly understood. We investigated why, following chlorhexidine intervention, prevalent epidemic MRSA ST22 and ST36 clones declined at an ICU, whilst an ST239-TW clone did not. The chlorhexidine tolerant ST239-TW phenotypes were assessed for their protein binding, cell adhesion and intracellular uptake potential.

METHODS

Six ST22, ST36 and ST239-TW bloodstream infection isolates with comparable chlorhexidine MICs were selected from a 2-year outbreak in an ICU at Guy's and St. Thomas' Hospital. Isolates were tested for fibrinogen and fibronectin binding, and adhesion/internalization into human keratinocytes with and without biocide.

RESULTS

Binding to fibrinogen and fibronectin, adhesion and intracellular uptake within keratinocytes (P < 0.001) and intracellular survival in keratinocytes under chlorhexidine pressure (ST22 3.18%, ST36 4.57% vs ST239-TW 12.79%; P < 0.0001) was consistently higher for ST239-TW.

CONCLUSIONS

We present evidence that MRSA clones with similarly low in vitro tolerance to chlorhexidine exhibit different in vivo susceptibilities. The phenomenon of S. aureus adhesion and intracellular uptake into keratinocytes could therefore be regarded as an additional mechanism of chlorhexidine tolerance, enabling MRSA to evade infection control measures.

Application of PLGA/FGF-2 coaxial microfibers in spinal cord tissue engineering: an in vitro and in vivo investigation

Aim: Scaffolds are a promising approach for spinal cord injury (SCI) treatment. FGF-2 is involved in tissue repair but is easily degradable and presents collateral effects in systemic administration. In order to address the stability issue and avoid the systemic effects, FGF-2 was encapsulated into core–shell microfibers by coaxial electrospinning and its in vitro and in vivo potential were studied. Materials & methods: The fibers were characterized by physicochemical and biological parameters. The scaffolds were implanted in a hemisection SCI rat model. Locomotor test was performed weekly for 6 weeks. After this time, histological analyses were performed and expression of nestin and GFAP was quantified by flow cytometry. Results: Electrospinning resulted in uniform microfibers with a core–shell structure, with a sustained liberation of FGF-2 from the fibers. The fibers supported PC12 cells adhesion and proliferation. Implanted scaffolds into SCI promoted locomotor recovery at 28 days after injury and reduced GFAP expression. Conclusion: These results indicate the potential of these microfibers in SCI tissue engineering.

[Formula: see text]

A Distance-Dependent Distribution of Presynaptic Boutons Tunes Frequency-Dependent Dendritic Integration

How presynaptic inputs and neurotransmitter release dynamics are distributed along a dendritic tree is not well established. Here, we show that presynaptic boutons that form onto basal dendrites of CA1 pyramidal neurons display a decrease in active zone (AZ) size with distance from the soma, resulting in a distance-dependent increase in short-term facilitation. Our findings suggest that the spatial distribution of short-term facilitation serves to compensate for the electrotonic attenuation of subthreshold distal inputs during repeated stimulation and fine-tunes the preferred input frequency of dendritic domains.

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Presynaptic inputs decrease in size with distance along CA1 basal dendrites

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Release probability decreases with distance along basal dendrites

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Short-term facilitation increases with distance along basal dendrites

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Increased synaptic facilitation offsets passive decay and boosts supralinear events

Cellular dissection of malaria parasite invasion of human erythrocytes using viable Plasmodium knowlesi merozoites

Plasmodium knowlesi, a zoonotic parasite causing severe-to-lethal malaria disease in humans, has only recently been adapted to continuous culture with human red blood cells (RBCs). In comparison with the most virulent human malaria, Plasmodium falciparum, there are, however, few cellular tools available to study its biology, in particular direct investigation of RBC invasion by blood-stage P. knowlesi merozoites. This leaves our current understanding of biological differences across pathogenic Plasmodium spp. incomplete. Here, we report a robust method for isolating viable and invasive P. knowlesi merozoites to high purity and yield. Using this approach, we present detailed comparative dissection of merozoite invasion (using a variety of microscopy platforms) and direct assessment of kinetic differences between knowlesi and falciparum merozoites. We go on to assess the inhibitory potential of molecules targeting discrete steps of invasion in either species via a quantitative invasion inhibition assay, identifying a class of polysulfonate polymer able to efficiently inhibit invasion in both, providing a foundation for pan-Plasmodium merozoite inhibitor development. Given the close evolutionary relationship between P. knowlesi and P. vivax, the second leading cause of malaria-related morbidity, this study paves the way for inter-specific dissection of invasion by all three major pathogenic malaria species.

Publisher Correction: A protease cascade regulates release of the human malaria parasite Plasmodium falciparum from host red blood cells

In the version of this Letter originally published, Michele S. Y. Tan was incorrectly listed as Michele Y. S. Tan due to a technical error. This has now been amended in all online versions of the Letter.

3D microfluidic liver cultures as a physiological preclinical tool for hepatitis B virus infection

With more than 240 million people infected, hepatitis B virus (HBV) is a major health concern. The inability to mimic the complexity of the liver using cell lines and regular primary human hepatocyte (PHH) cultures pose significant limitations for studying host/pathogen interactions. Here, we describe a 3D microfluidic PHH system permissive to HBV infection, which can be maintained for at least 40 days. This system enables the recapitulation of all steps of the HBV life cycle, including the replication of patient-derived HBV and the maintenance of HBV cccDNA. We show that innate immune and cytokine responses following infection with HBV mimic those observed in HBV-infected patients, thus allowing the dissection of pathways important for immune evasion and validation of biomarkers. Additionally, we demonstrate that the co-culture of PHH with other non-parenchymal cells enables the identification of the cellular origin of immune effectors, thus providing a valuable preclinical platform for HBV research.

Stall in Canonical Autophagy-Lysosome Pathways Prompts Nucleophagy-Based Nuclear Breakdown in Neurodegeneration

The terminal stages of neuronal degeneration and death in neurodegenerative diseases remain elusive. Autophagy is an essential catabolic process frequently failing in neurodegeneration. Selective autophagy routes have recently emerged, including nucleophagy, defined as degradation of nuclear components by autophagy. Here, we show that, in a mouse model for the polyglutamine disease dentatorubral-pallidoluysian atrophy (DRPLA), progressive acquirement of an ataxic phenotype is linked to severe cerebellar cellular pathology, characterized by nuclear degeneration through nucleophagy-based LaminB1 degradation and excretion. We find that canonical autophagy is stalled in DRPLA mice and in human fibroblasts from patients of DRPLA. This is evidenced by accumulation of p62 and downregulation of LC3-I/II conversion as well as reduced Tfeb expression. Chronic autophagy blockage in several conditions, including DRPLA and Vici syndrome, an early-onset autolysosomal pathology, leads to the activation of alternative clearance pathways including Golgi membrane-associated and nucleophagy-based LaminB1 degradation and excretion. The combination of these alternative pathways and canonical autophagy blockade, results in dramatic nuclear pathology with disruption of the nuclear organization, bringing about terminal cell atrophy and degeneration. Thus, our findings identify a novel progressive mechanism for the terminal phases of neuronal cell degeneration and death in human neurodegenerative diseases and provide a link between autophagy block, activation of alternative pathways for degradation, and excretion of cellular components.

Organic cation transporter 1 (OCT1) is involved in pentamidine transport at the human and mouse blood-brain barrier (BBB)

Pentamidine is an effective trypanocidal drug used against stage 1 Human African Trypanosomiasis (HAT). At the blood-brain barrier (BBB), it accumulates inside the endothelial cells but has limited entry into the brain. This study examined transporters involved in pentamidine transport at the human and mouse BBB using hCMEC/D3 and bEnd.3 cell lines, respectively. Results revealed that both cell lines expressed the organic cation transporters (OCT1, OCT2 and OCT3), however, P-gp was only expressed in hCMEC/D3 cells. Polarised expression of OCT1 was also observed. Functional assays found that ATP depletion significantly increased [³H]pentamidine accumulation in hCMEC/D3 cells (***p<0.001) but not in bEnd.3 cells. Incubation with unlabelled pentamidine significantly decreased accumulation in hCMEC/D3 and bEnd.3 cells after 120 minutes (***p<0.001). Treating both cell lines with haloperidol and amantadine also decreased [³H]pentamidine accumulation significantly (***p<0.001 and **p<0.01 respectively). However, prazosin treatment decreased [³H]pentamidine accumulation only in hCMEC/D3 cells (*p<0.05), and not bEnd.3 cells. Furthermore, the presence of OCTN, MATE, PMAT, ENT or CNT inhibitors/substrates had no significant effect on the accumulation of [³H]pentamidine in both cell lines. From the data, we conclude that pentamidine interacts with multiple transporters, is taken into brain endothelial cells by OCT1 transporter and is extruded into the blood by ATP-dependent mechanisms. These interactions along with the predominant presence of OCT1 in the luminal membrane of the BBB contribute to the limited entry of pentamidine into the brain. This information is of key importance to the development of pentamidine based combination therapies which could be used to treat CNS stage HAT by improving CNS delivery, efficacy against trypanosomes and safety profile of pentamidine.

Parasitophorous vacuole poration precedes its rupture and rapid host erythrocyte cytoskeleton collapse in Plasmodium falciparum egress

In the asexual blood stages of malarial infection, merozoites invade erythrocytes and replicate within a parasitophorous vacuole to form daughter cells that eventually exit (egress) by sequential rupture of the vacuole and erythrocyte membranes. The current model is that PKG, a malarial cGMP-dependent protein kinase, triggers egress, activating malarial proteases and other effectors. Using selective inhibitors of either PKG or cysteine proteases to separately inhibit the sequential steps in membrane perforation, combined with video microscopy, electron tomography, electron energy loss spectroscopy, and soft X-ray tomography of mature intracellular Plasmodium falciparum parasites, we resolve intermediate steps in egress. We show that the parasitophorous vacuole membrane (PVM) is permeabilized 10-30 min before its PKG-triggered breakdown into multilayered vesicles. Just before PVM breakdown, the host red cell undergoes an abrupt, dramatic shape change due to the sudden breakdown of the erythrocyte cytoskeleton, before permeabilization and eventual rupture of the erythrocyte membrane to release the parasites. In contrast to the previous view of PKG-triggered initiation of egress and a gradual dismantling of the host erythrocyte cytoskeleton over the course of schizont development, our findings identify an initial step in egress and show that host cell cytoskeleton breakdown is restricted to a narrow time window within the final stages of egress.

Distance-dependent gradient in NMDAR-driven spine calcium signals along tapering dendrites

Neurons receive a multitude of synaptic inputs along their dendritic arbor, but how this highly heterogeneous population of synaptic compartments is spatially organized remains unclear. By measuring N-methyl-d-aspartic acid receptor (NMDAR)-driven calcium responses in single spines, we provide a spatial map of synaptic calcium signals along dendritic arbors of hippocampal neurons and relate this to measures of synapse structure. We find that quantal NMDAR calcium signals increase in amplitude as they approach a thinning dendritic tip end. Based on a compartmental model of spine calcium dynamics, we propose that this biased distribution in calcium signals is governed by a gradual, distance-dependent decline in spine size, which we visualized using serial block-face scanning electron microscopy. Our data describe a cell-autonomous feature of principal neurons, where tapering dendrites show an inverse distribution of spine size and NMDAR-driven calcium signals along dendritic trees, with important implications for synaptic plasticity rules and spine function.

ALS/FTD-associated FUS activates GSK-3β to disrupt the VAPB-PTPIP51 interaction and ER-mitochondria associations

Defective FUS metabolism is strongly associated with amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD), but the mechanisms linking FUS to disease are not properly understood. However, many of the functions disrupted in ALS/FTD are regulated by signalling between the endoplasmic reticulum (ER) and mitochondria. This signalling is facilitated by close physical associations between the two organelles that are mediated by binding of the integral ER protein VAPB to the outer mitochondrial membrane protein PTPIP51, which act as molecular scaffolds to tether the two organelles. Here, we show that FUS disrupts the VAPB–PTPIP51 interaction and ER–mitochondria associations. These disruptions are accompanied by perturbation of Ca²⁺ uptake by mitochondria following its release from ER stores, which is a physiological read‐out of ER–mitochondria contacts. We also demonstrate that mitochondrial ATP production is impaired in FUS‐expressing cells; mitochondrial ATP production is linked to Ca²⁺ levels. Finally, we demonstrate that the FUS‐induced reductions to ER–mitochondria associations and are linked to activation of glycogen synthase kinase‐3β (GSK‐3β), a kinase already strongly associated with ALS/FTD.

Alkaline ceramidase 1 is essential for mammalian skin homeostasis and regulating whole-body energy expenditure

The epidermis is the outermost layer of skin that acts as a barrier to protect the body from the external environment and to control water and heat loss. This barrier function is established through the multistage differentiation of keratinocytes and the presence of bioactive sphingolipids such as ceramides, the levels of which are tightly regulated by a balance of ceramide synthase and ceramidase activities. Here we reveal the essential role of alkaline ceramidase 1 (Acer1) in the skin. Acer1‐deficient (Acer1^−/−) mice showed elevated levels of ceramide in the skin, aberrant hair shaft cuticle formation and cyclic alopecia. We demonstrate that Acer1 is specifically expressed in differentiated interfollicular epidermis, infundibulum and sebaceous glands and consequently Acer1^−/− mice have significant alterations in infundibulum and sebaceous gland architecture. Acer1^−/− skin also shows perturbed hair follicle stem cell compartments. These alterations result in Acer1^−/− mice showing increased transepidermal water loss and a hypermetabolism phenotype with associated reduction of fat content with age. We conclude that Acer1 is indispensable for mammalian skin homeostasis and whole‐body energy homeostasis. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Bach1 differentially regulates distinct Nrf2-dependent genes in human venous and coronary artery endothelial cells adapted to physiological oxygen levels

The effects of physiological oxygen tension on Nuclear Factor-E2-Related Factor 2 (Nrf2)-regulated redox signaling remain poorly understood. We report the first study of Nrf2-regulated signaling in human primary endothelial cells (EC) adapted long-term to physiological O2 (5%). Adaptation of EC to 5% O2 had minimal effects on cell ultrastructure, viability, basal redox status or HIF1-α expression. Affymetrix array profiling and subsequent qPCR/protein validation revealed that induction of select Nrf2 target genes, HO-1 and NQO1, was significantly attenuated in cells adapted to 5% O2, despite nuclear accumulation and DNA binding of Nrf2. Diminished HO-1 induction under 5% O2 was stimulus independent and reversible upon re-adaptation to air or silencing of the Nrf2 repressor Bach1, notably elevated under 5% O2. Induction of GSH-related genes xCT and GCLM were oxygen and Bach1-insensitive during long-term culture under 5% O2, providing the first evidence that genes related to GSH synthesis mediate protection afforded by Nrf2-Keap1 defense pathway in cells adapted to physiological O2 levels encountered in vivo.

Wbp2 is required for normal glutamatergic synapses in the cochlea and is crucial for hearing

WBP2 encodes the WW domain-binding protein 2 that acts as a transcriptional coactivator for estrogen receptor α (ESR1) and progesterone receptor (PGR). We reported that the loss of Wbp2 expression leads to progressive high-frequency hearing loss in mouse, as well as in two deaf children, each carrying two different variants in the WBP2 gene. The earliest abnormality we detect in Wbp2-deficient mice is a primary defect at inner hair cell afferent synapses. This study defines a new gene involved in the molecular pathway linking hearing impairment to hormonal signalling and provides new therapeutic targets.

Tunable Ultra-high Aspect Ratio Nanorod Architectures grown on Porous Substrate via Electromigration

The interplay between porosity and electromigration can be used to manipulate atoms resulting in mass fabrication of nanoscale structures. Electromigration usually results in the accumulation of atoms accompanied by protrusions at the anode and atomic depletion causing voids at the cathode. Here we show that in porous media the pattern of atomic deposition and depletion is altered such that atomic accumulation occurs over the whole surface and not just at the anode. The effect is explained by the interaction between atomic drift due to electric current and local temperature gradients resulting from intense Joule heating at constrictions between grains. Utilizing this effect, a porous silver substrate is used to mass produce free-standing silver nanorods with very high aspect ratios of more than 200 using current densities of the order of 10⁸ A/m². This simple method results in reproducible formation of shaped nanorods, with independent control over their density and length. Consequently, complex patterns of high quality single crystal nanorods can be formed in-situ with significant advantages over competing methods of nanorod formation for plasmonics, energy storage and sensing applications.

The Biosynthesis of Infrared-Emitting Quantum Dots in Allium Fistulosum

The development of simple routes to emissive solid-state materials is of paramount interest, and in this report we describe the biosynthesis of infrared emitting quantum dots in a living plant via a mutual antagonistic reaction. Exposure of common Allium fistulosum to mercury and tellurium salts under ambient conditions resulted in the expulsion of crystalline, non-passivated HgTe quantum dots that exhibited emissive characteristics in the near-infrared spectral region, a wavelength range that is important in telecommunications and solar energy conversion.

Abstract 2897: Phosphatidylcholine synthesis is required for autophagosome membrane formation and maintenance during autophagy

Autophagy is a cellular stress survival mechanism in which newly formed double-membrane vesicles target parts of the cytosol and organelles for lysosomal degradation to maintain cellular energy production. The source of the autophagosome membrane in starvation has been subject to much debate, but has not been investigated in the more clinically relevant setting of drug-induced autophagy where nutrients are available.

By 1H-magnetic resonance spectroscopy (MRS) we show that autophagy, induced in human colorectal carcinoma cells HCT116 wt, HCT116 Bax-ko and HT29 by dichloroacetate, a pyruvate dehydrogenase kinase inhibitor, by PI-103, a dual PI3K/mTOR inhibitor, or by starvation in medium lacking amino acids and growth factors, is associated with significant increases in membrane phospholipid phosphatidylcholine (PtdCho) (p≤0.02). 13-C labeled choline 13C-MRS revealed that these increases are due to de novo synthesis of PtdCho (p≤0.02) and are linked with increased expression of the rate-limiting enzyme, CDP:phosphocholine cytidylyltransferase (CCTα) in its active, membrane-bound form. Autophagic cells labeled with propargylcholine, a choline analog, had significant increase in propargylcholine phospholipid synthesis (p≤0.02) and vesicular structures consistent with autophagosomes when imaged by fluorescence confocal microscopy. Electron microscopy with immunogold labeling reveals the incorporation of newly synthesized propargylcholine phospholipids into the membranes of autophagic vacuoles and the digested material in autophagolysosomes, as well as endoplasmic reticulum, mitochondrial membranes and nuclear envelope as in control cells.

To assess the role of PtdCho synthesis and CCTα in autophagy, we used Chinese hamster ovarian cells CHO-K1 MT58, with a temperature-sensitive mutation in the CCTα gene, resulting in reduced PtdCho synthesis at 40°C. PI-103 induced autophagy in wild-type CHO-K1 cells at both 33°C and 40°C. MT58 cells had normal autophagy induction with PI-103 at 33°C, but the autophagy marker LC3B-II was lower at 40°C than in the CHO-K1 cells. Loss of CCTα activity prevented PI-103-induced increase in PtdCho levels (p≤0.0003) and resulted in a reduced volume of autophagosomes in MT58 cells at 40°C (p≤0.01).

Our evidence suggests that increased PtdCho synthesis in drug-induced autophagy provides membrane phospholipids for the growing autophagosomes and replaces phospholipids consumed from other organelles during autophagosome formation and degradation. Expression of CCTα, the rate-limiting enzyme of PtdCho synthesis, is increased in autophagy and its loss results in the inability of cells to maintain autophagosome formation. PtdCho synthesis might provide a new target for autophagy inhibition. Also, fluorescence imaging of propargylcholine labeling may offer a novel way to visualize newly formed autophagosome membranes in vitro.

Citation Format: Gabriela Andrejeva, Gigin Lin, Harry G. Parkes, James Mui, Anne-Christine LF Wong Te Fong, Gema Vizcay-Barrena, Roland Fleck, Martin O. Leach, Yuen-Li Chung. Phosphatidylcholine synthesis is required for autophagosome membrane formation and maintenance during autophagy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2897. doi:10.1158/1538-7445.AM2015-2897

ER-mitochondria associations are regulated by the VAPB-PTPIP51 interaction and are disrupted by ALS/FTD-associated TDP-43

Mitochondria and the endoplasmic reticulum (ER) form tight structural associations and these facilitate a number of cellular functions. However, the mechanisms by which regions of the ER become tethered to mitochondria are not properly known. Understanding these mechanisms is not just important for comprehending fundamental physiological processes but also for understanding pathogenic processes in some disease states. In particular, disruption to ER-mitochondria associations is linked to some neurodegenerative diseases. Here we show that the ER-resident protein VAPB interacts with the mitochondrial protein tyrosine phosphatase-interacting protein-51 (PTPIP51) to regulate ER-mitochondria associations. Moreover, we demonstrate that TDP-43, a protein pathologically linked to amyotrophic lateral sclerosis and fronto-temporal dementia perturbs ER-mitochondria interactions and that this is associated with disruption to the VAPB-PTPIP51 interaction and cellular Ca(2+) homeostasis. Finally, we show that overexpression of TDP-43 leads to activation of glycogen synthase kinase-3β (GSK-3β) and that GSK-3β regulates the VAPB-PTPIP51 interaction. Our results describe a new pathogenic mechanism for TDP-43.

Mechanical modelling quantifies the functional importance of outer tissue layers during root elongation and bending

Root elongation and bending require the coordinated expansion of multiple cells of different types. These processes are regulated by the action of hormones that can target distinct cell layers. We use a mathematical model to characterise the influence of the biomechanical properties of individual cell walls on the properties of the whole tissue. Taking a simple constitutive model at the cell scale which characterises cell walls via yield and extensibility parameters, we derive the analogous tissue-level model to describe elongation and bending. To accurately parameterise the model, we take detailed measurements of cell turgor, cell geometries and wall thicknesses. The model demonstrates how cell properties and shapes contribute to tissue-level extensibility and yield. Exploiting the highly organised structure of the elongation zone (EZ) of the Arabidopsis root, we quantify the contributions of different cell layers, using the measured parameters. We show how distributions of material and geometric properties across the root cross-section contribute to the generation of curvature, and relate the angle of a gravitropic bend to the magnitude and duration of asymmetric wall softening. We quantify the geometric factors which lead to the predominant contribution of the outer cell files in driving root elongation and bending.

Female and male gamete mitochondria are distinct and complementary in transcription, structure, and genome function

Respiratory electron transport in mitochondria is coupled to ATP synthesis while generating mutagenic oxygen free radicals. Mitochondrial DNA mutation then accumulates with age, and may set a limit to the lifespan of individual, multicellular organisms. Why is this mutation not inherited? Here we demonstrate that female gametes—oocytes—have unusually small and simple mitochondria that are suppressed for DNA transcription, electron transport, and free radical production. By contrast, male gametes—sperm—and somatic cells of both sexes transcribe mitochondrial genes for respiratory electron carriers and produce oxygen free radicals. This germ-line division between mitochondria of sperm and egg is observed in both the vinegar fruitfly and the zebrafish—species spanning a major evolutionary divide within the animal kingdom. We interpret these findings as an evidence that oocyte mitochondria serve primarily as genetic templates, giving rise, irreversibly and in each new generation, to the familiar energy-transducing mitochondria of somatic cells and male gametes. Suppressed mitochondrial metabolism in the female germ line may therefore constitute a mechanism for increasing the fidelity of mitochondrial DNA inheritance.

ABORTED MICROSPORES Acts as a Master Regulator of Pollen Wall Formation in Arabidopsis

Mature pollen is covered by durable cell walls, principally composed of sporopollenin, an evolutionary conserved, highly resilient, but not fully characterized, biopolymer of aliphatic and aromatic components. Here, we report that ABORTED MICROSPORES (AMS) acts as a master regulator coordinating pollen wall development and sporopollenin biosynthesis in Arabidopsis thaliana. Genome-wide coexpression analysis revealed 98 candidate genes with specific expression in the anther and 70 that showed reduced expression in ams. Among these 70 members, we showed that AMS can directly regulate 23 genes implicated in callose dissociation, fatty acids elongation, formation of phenolic compounds, and lipidic transport putatively involved in sporopollenin precursor synthesis. Consistently, ams mutants showed defective microspore release, a lack of sporopollenin deposition, and a dramatic reduction in total phenolic compounds and cutin monomers. The functional importance of the AMS pathway was further demonstrated by the observation of impaired pollen wall architecture in plant lines with reduced expression of several AMS targets: the abundant pollen coat protein extracellular lipases (EXL5 and EXL6), and CYP98A8 and CYP98A9, which are enzymes required for the production of phenolic precursors. These findings demonstrate the central role of AMS in coordinating sporopollenin biosynthesis and the secretion of materials for pollen wall patterning.

Systematic investigation of the physicochemical factors that contribute to the toxicity of ZnO nanoparticles

ZnO nanoparticles (NPs) are prone to dissolution, and uncertainty remains whether biological/cellular responses to ZnO NPs are solely due to the release of Zn(2+) or whether the NPs themselves have additional toxic effects. We address this by establishing ZnO NP solubility in dispersion media (Dulbecco's modified Eagle's medium, DMEM) held under conditions identical to those employed for cell culture (37 °C, 5% CO2, and pH 7.68) and by systematic comparison of cell-NP interaction for three different ZnO NP preparations. For NPs at concentrations up to 5.5 μg ZnO/mL, dissolution is complete (with the majority of the soluble zinc complexed to dissolved ligands in the medium), taking ca. 1 h for uncoated and ca. 6 h for polymer coated ones. Above 5.5 μg/mL, the results are consistent with the formation of zinc carbonate, keeping the solubilized zinc fixed to 67 μM of which only 0.45 μM is as free Zn(2+), i.e., not complexed to dissolved ligands. At these relatively high concentrations, NPs with an aliphatic polyether-coating show slower dissolution (i.e., slower free Zn(2+) release) and reprecipitation kinetics compared to those of uncoated NPs, requiring more than 48 h to reach thermodynamic equilibrium. Cytotoxicity (MTT) and DNA damage (Comet) assay dose-response curves for three epithelial cell lines suggest that dissolution and reprecipitation dominate for uncoated ZnO NPs. Transmission electron microscopy combined with the monitoring of intracellular Zn(2+) concentrations and ZnO-NP interactions with model lipid membranes indicate that an aliphatic polyether coat on ZnO NPs increases cellular uptake, enhancing toxicity by enabling intracellular dissolution and release of Zn(2+). Similarly, we demonstrate that needle-like NP morphologies enhance toxicity by apparently frustrating cellular uptake. To limit toxicity, ZnO NPs with nonacicular morphologies and coatings that only weakly interact with cellular membranes are recommended.

Nanohydroxyapatite shape and its potential role in bone formation: an analytical study

Bone cells (osteoblasts) produce a collagen-rich matrix called osteoid, which is mineralized extracellularly by nanosized calcium phosphate (CaP). Synthetically produced CaP nanoparticles (NPs) have great potential for clinical application. However few studies have compared the effect of CaP NPs with different properties, such as shape and aspect ratio, on the survival and behaviour of active bone-producing cells, such as primary human osteoblasts (HOBs). This study aimed to investigate the biocompatibility and ultrastructural effects of two differently shaped hydroxyapatite [Ca10(PO4)6(OH)2] nanoparticles (HA NPs), round- (aspect ratio 2.12, AR2) and rice-shaped (aspect ratio 3.79, AR4). The ultrastructural response and initial extracellular matrix (ECM) formation of HOBs to HA NPs were observed, as well as matrix vesicle release. A transmission electron microscopy (TEM)-based X-ray microanalytical technique was used to measure cytoplasmic ion levels, including calcium (Ca), phosphorus (P), sodium (Na) and potassium (K). K/Na ratios were used as a measure of cell viability. Following HA NP stimulation, all measured cytoplasmic ion levels increased. AR2 NPs had a greater osteogenic effect on osteoblasts compared with AR4 NPs, including alkaline phosphatase activity and matrix vesicle release. However, they produced only a moderate increase in intracellular Ca and P levels compared with AR4. This suggests that particular Ca and P concentrations may be required for, or indicative of, optimal osteoblast activity. Cell viability, as measured by Na and K microanalysis, was best maintained in AR2. Initial formation of osteoblast ECM was altered in the presence of either HA NP, and immuno-TEM identified fibronectin and matrilin-3 as two ECM proteins affected. Matrilin-3 is here described for the first time as being expressed by cultured osteoblasts. In summary, this novel and in-depth study has demonstrated that HA NP shape can influence a range of different parameters related to osteoblast viability and activity.

Endophilin, Lamellipodin, and Mena cooperate to regulate F-actin-dependent EGF-receptor endocytosis

The epidermal growth factor receptor (EGFR) plays an essential role during development and diseases including cancer. Lamellipodin (Lpd) is known to control lamellipodia protrusion by regulating actin filament elongation via Ena/VASP proteins. However, it is unknown whether this mechanism supports endocytosis of the EGFR. Here, we have identified a novel role for Lpd and Mena in clathrin-mediated endocytosis (CME) of the EGFR. We have discovered that endogenous Lpd is in a complex with the EGFR and Lpd and Mena knockdown impairs EGFR endocytosis. Conversely, overexpressing Lpd substantially increases the EGFR uptake in an F-actin-dependent manner, suggesting that F-actin polymerization is limiting for EGFR uptake. Furthermore, we found that Lpd directly interacts with endophilin, a BAR domain containing protein implicated in vesicle fission. We identified a role for endophilin in EGFR endocytosis, which is mediated by Lpd. Consistently, Lpd localizes to clathrin-coated pits (CCPs) just before vesicle scission and regulates vesicle scission. Our findings suggest a novel mechanism in which Lpd mediates EGFR endocytosis via Mena downstream of endophilin.

Cooperation between a BAR domain protein and a regulator of actin filament elongation during lamellipodia protrusion reveals actin cytoskeleton roles in endocytic vesicle scission in mammalian cells.

Assessment of inflammation with a very small iron-oxide particle in a murine model of reperfused myocardial infarction

PURPOSE

To investigate a very small iron-oxide particle (VSOP) in a mouse model of acute ischemia-reperfusion to access the mechanism of such particles in areas of myocardial inflammation.

MATERIALS AND METHODS

Animals were injected with VSOP at several time points, in a mouse model of acute myocardial infarction (MI), before and after MI. MRI was used to localize areas of VSOP enhancement, evaluate VSOP areas extension, and determine the related T2* values. Histology, electron microscopy, macrophage counting, and Evan's Blue staining were also performed.

RESULTS

We found that areas of VSOP uptake decreased from 1 to 8 days post-MI while the related T2* values increased. T2* and VSOP areas, defined from MRI data, correlated well between 1 and 3 days post-MI but not at 7 days after injection. Histological analysis and electron microscopy showed colocalization of macrophages with areas of VSOP staining. However, there was no correlation between number of macrophages and the extension of the VSOP areas achieved by MR. We found that only areas of increased permeability (assessed by Evan's Blue staining) showed colocalization of macrophages and VSOP uptake.

CONCLUSION

This study demonstrates that VSOP allows the assessment of myocardial inflammation associated with increased permeability during infarct healing in a mouse model of ischemia-reperfusion.

Energy, ageing, fidelity and sex: oocyte mitochondrial DNA as a protected genetic template

Oxidative phosphorylation couples ATP synthesis to respiratory electron transport. In eukaryotes, this coupling occurs in mitochondria, which carry DNA. Respiratory electron transport in the presence of molecular oxygen generates free radicals, reactive oxygen species (ROS), which are mutagenic. In animals, mutational damage to mitochondrial DNA therefore accumulates within the lifespan of the individual. Fertilization generally requires motility of one gamete, and motility requires ATP. It has been proposed that oxidative phosphorylation is nevertheless absent in the special case of quiescent, template mitochondria, that these remain sequestered in oocytes and female germ lines and that oocyte mitochondrial DNA is thus protected from damage, but evidence to support that view has hitherto been lacking. Here we show that female gametes of Aurelia aurita, the common jellyfish, do not transcribe mitochondrial DNA, lack electron transport, and produce no free radicals. In contrast, male gametes actively transcribe mitochondrial genes for respiratory chain components and produce ROS. Electron microscopy shows that this functional division of labour between sperm and egg is accompanied by contrasting mitochondrial morphology. We suggest that mitochondrial anisogamy underlies division of any animal species into two sexes with complementary roles in sexual reproduction. We predict that quiescent oocyte mitochondria contain DNA as an unexpressed template that avoids mutational accumulation by being transmitted through the female germ line. The active descendants of oocyte mitochondria perform oxidative phosphorylation in somatic cells and in male gametes of each new generation, and the mutations that they accumulated are not inherited. We propose that the avoidance of ROS-dependent mutation is the evolutionary pressure underlying maternal mitochondrial inheritance and the developmental origin of the female germ line.

XBP1 mRNA splicing triggers an autophagic response in endothelial cells through BECLIN-1 transcriptional activation

Sustained activation of X-box-binding protein 1 (XBP1) results in endothelial cell (EC) apoptosis and atherosclerosis development. The present study provides evidence that XBP1 mRNA splicing triggered an autophagic response in ECs by inducing autophagic vesicle formation and markers of autophagy BECLIN-1 and microtubule-associated protein 1 light chain 3β (LC3-βII). Endostatin activated autophagic gene expression through XBP1 mRNA splicing in an inositol-requiring enzyme 1α (IRE1α)-dependent manner. Knockdown of XBP1 or IRE1α by shRNA in ECs ablated endostatin-induced autophagosome formation. Importantly, data from arterial vessels from XBP1 EC conditional knock-out (XBP1eko) mice demonstrated that XBP1 deficiency in ECs reduced the basal level of LC3β expression and ablated response to endostatin. Chromatin immunoprecipitation assays further revealed that the spliced XBP1 isoform bound directly to the BECLIN-1 promoter at the region from nt -537 to -755. BECLIN-1 deficiency in ECs abolished the XBP1-induced autophagy response, whereas spliced XBP1 did not induce transcriptional activation of a truncated BECLIN-1 promoter. These results suggest that XBP1 mRNA splicing triggers an autophagic signal pathway through transcriptional regulation of BECLIN-1.

Subcellular and single-molecule imaging of plant fluorescent proteins using total internal reflection fluorescence microscopy (TIRFM)

Total internal reflection fluorescence microscopy (TIRFM) has been proven to be an extremely powerful technique in animal cell research for generating high contrast images and dynamic protein conformation information. However, there has long been a perception that TIRFM is not feasible in plant cells because the cell wall would restrict the penetration of the evanescent field and lead to scattering of illumination. By comparative analysis of epifluorescence and TIRF in root cells, it is demonstrated that TIRFM can generate high contrast images, superior to other approaches, from intact plant cells. It is also shown that TIRF imaging is possible not only at the plasma membrane level, but also in organelles, for example the nucleus, due to the presence of the central vacuole. Importantly, it is demonstrated for the first time that this is TIRF excitation, and not TIRF-like excitation described as variable-angle epifluorescence microscopy (VAEM), and it is shown how to distinguish the two techniques in practical microscopy. These TIRF images show the highest signal-to-background ratio, and it is demonstrated that they can be used for single-molecule microscopy. Rare protein events, which would otherwise be masked by the average molecular behaviour, can therefore be detected, including the conformations and oligomerization states of interacting proteins and signalling networks in vivo. The demonstration of the application of TIRFM and single-molecule analysis to plant cells therefore opens up a new range of possibilities for plant cell imaging.

PERSISTENT TAPETAL CELL1 encodes a PHD-finger protein that is required for tapetal cell death and pollen development in rice

In higher plants, timely degradation of tapetal cells, the innermost sporophytic cells of the anther wall layer, is a prerequisite for the development of viable pollen grains. However, relatively little is known about the mechanism underlying programmed tapetal cell development and degradation. Here, we report a key regulator in monocot rice (Oryza sativa), PERSISTANT TAPETAL CELL1 (PTC1), which controls programmed tapetal development and functional pollen formation. The evolutionary significance of PTC1 was revealed by partial genetic complementation of the homologous mutation MALE STERILITY1 (MS1) in the dicot Arabidopsis (Arabidopsis thaliana). PTC1 encodes a PHD-finger (for plant homeodomain) protein, which is expressed specifically in tapetal cells and microspores during anther development in stages 8 and 9, when the wild-type tapetal cells initiate a typical apoptosis-like cell death. Even though ptc1 mutants show phenotypic similarity to ms1 in a lack of tapetal DNA fragmentation, delayed tapetal degeneration, as well as abnormal pollen wall formation and aborted microspore development, the ptc1 mutant displays a previously unreported phenotype of uncontrolled tapetal proliferation and subsequent commencement of necrosis-like tapetal death. Microarray analysis indicated that 2,417 tapetum- and microspore-expressed genes, which are principally associated with tapetal development, degeneration, and pollen wall formation, had changed expression in ptc1 anthers. Moreover, the regulatory role of PTC1 in anther development was revealed by comparison with MS1 and other rice anther developmental regulators. These findings suggest a diversified and conserved switch of PTC1/MS1 in regulating programmed male reproductive development in both dicots and monocots, which provides new insights in plant anther development.

The ASH1 HOMOLOG 2 (ASHH2) histone H3 methyltransferase is required for ovule and anther development in Arabidopsis

Background

SET-domain proteins are histone lysine (K) methyltransferases (HMTase) implicated in defining transcriptionally permissive or repressive chromatin. The Arabidopsis ASH1 HOMOLOG 2 (ASHH2) protein (also called SDG8, EFS and CCR1) has been suggested to methylate H3K4 and/or H3K36 and is similar to Drosophila ASH1, a positive maintainer of gene expression, and yeast Set2, a H3K36 HMTase. Mutation of the ASHH2 gene has pleiotropic developmental effects. Here we focus on the role of ASHH2 in plant reproduction.

Methodology/Principal Findings

A slightly reduced transmission of the ashh2 allele in reciprocal crosses implied involvement in gametogenesis or gamete function. However, the main requirement of ASHH2 is sporophytic. On the female side, close to 80% of mature ovules lack embryo sac. On the male side, anthers frequently develop without pollen sacs or with specific defects in the tapetum layer, resulting in reduction in the number of functional pollen per anther by up to ∼90%. In consistence with the phenotypic findings, an ASHH2 promoter-reporter gene was expressed at the site of megaspore mother cell formation as well as tapetum layers and pollen. ashh2 mutations also result in homeotic changes in floral organ identity. Transcriptional profiling identified more than 300 up-regulated and 600 down-regulated genes in ashh2 mutant inflorescences, whereof the latter included genes involved in determination of floral organ identity, embryo sac and anther/pollen development. This was confirmed by real-time PCR. In the chromatin of such genes (AP1, AtDMC1 and MYB99) we observed a reduction of H3K36 trimethylation (me3), but not H3K4me3 or H3K36me2.

Conclusions/Significance

The severe distortion of reproductive organ development in ashh2 mutants, argues that ASHH2 is required for the correct expression of genes essential to reproductive development. The reduction in the ashh2 mutant of H3K36me3 on down-regulated genes relevant to the observed defects, implicates ASHH2 in regulation of gene expression via H3K36 trimethylation in chromatin of Arabidopsis inflorescences.

MALE STERILITY1 is required for tapetal development and pollen wall biosynthesis

The Arabidopsis thaliana MALE STERILITY1 (MS1) gene is critical for viable pollen formation and has homology to the PHD-finger class of transcription factors; however, its role in pollen development has not been fully defined. We show that MS1 transcription appears to be autoregulated by the wild-type MS1 transcript or protein. Using a functional green fluorescent protein (GFP) fusion to analyze the temporal and spatial expression of MS1, we demonstrate that the MS1:GFP protein is nuclear localized within the tapetum and is expressed in a developmentally regulated manner between late tetraspore and microspore release, then rapidly breaks down, probably by ubiquitin-dependent proteolysis. Absence of MS1 expression results in changes in tapetal secretion and exine structure. Microarray analysis has shown that 260 (228 downregulated and 32 upreglated) genes have altered expression in young ms1 buds. These genes are primarily associated with pollen wall and coat formation; however, a number of transcription factors and Cys proteases have also been identified as the putative primary regulatory targets of MS1. Ectopic expression of MS1 alters transcriptional regulation of vegetative gene expression, resulting in stunted plants with increased levels of branching, partially fertile flowers and an apparent increase in wall material on mature pollen. MS1 therefore plays a critical role in the induction of pollen wall and pollen coat materials in the tapetum and, ultimately, the production of viable pollen.

Altered tapetal PCD and pollen wall development in the Arabidopsis ms1 mutant

The Arabidopsis male sterility1 mutation results in mature anthers that are devoid of pollen. Meiosis and early development progress normally; however, after microspore release, the microspore cytoplasm and tapetum become abnormally granular and vacuolated, and degeneration occurs. Pollen wall development is seriously affected; primexine formation within the callose wall appears to occur normally, however, once the callose is degraded, abnormal deposits of electrodense material are detected which result in irregular spike-shaped structures, rather than the characteristic rod-like shape of the wild-type bacula. The internal intine wall is also reduced compared with wild type. TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling) staining and ultrastructural analysis have indicated that programmed cell death (PCD) occurs in the wild-type tapetum after microspore mitosis I. However, no signs of PCD are seen in the ms1 tapetum, where large autophagic vacuoles and mitochondrial swelling suggest that necrotic-based breakdown of the tapetum is occurring in the ms1 mutant rather than the normal, regulated PCD process. After the formation of the large, autophagic vacuole in the tapetum, TUNEL staining is detected in the mutant microspores, indicating that they may go through a PCD-based breakdown as a secondary consequence of the observed tapetal aberrations. Based on these observations, two possible roles for MS1 can be hypothesized; MS1 may function by modifying the transcription of tapetal-specific genes implicated in pollen wall development, which then regulate pollen wall material secretion and in turn wall development and tapetal PCD. Alternatively, the MS1 gene may control tapetal development by directly regulating tapetal PCD and breakdown.