20 results on '"Seymour AJ"'
Search Results
2. Gelation of Uniform Interfacial Diffusant in Embedded 3D Printing.
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Shin S, Brunel LG, Cai B, Kilian D, Roth JG, Seymour AJ, and Heilshorn SC
- Abstract
While the human body has many different examples of perfusable structures with complex geometries, biofabrication methods to replicate this complexity are still lacking. Specifically, the fabrication of self-supporting, branched networks with multiple channel diameters is particularly challenging. Here, we present the Gelation of Uniform Interfacial Diffusant in Embedded 3D Printing (GUIDE-3DP) approach for constructing perfusable networks of interconnected channels with precise control over branching geometries and vessel sizes. To achieve user-specified channel dimensions, this technique leverages the predictable diffusion of crosslinking reaction-initiators released from sacrificial inks printed within a hydrogel precursor. We demonstrate the versatility of GUIDE-3DP to be adapted for use with diverse physicochemical crosslinking mechanisms by designing seven printable material systems. Importantly, GUIDE-3DP allows for the independent tunability of both the inner and outer diameters of the printed channels and the ability to fabricate seamless junctions at branch points. This 3D bioprinting platform is uniquely suited for fabricating lumenized structures with complex shapes characteristic of multiple hollow vessels throughout the body. As an exemplary application, we demonstrate the fabrication of vasculature-like networks lined with endothelial cells. GUIDE-3DP represents an important advance toward the fabrication of self-supporting, physiologically relevant networks with intricate and perfusable geometries., Competing Interests: Conflict of Interest S.S., J.G.R., A.J.S., and S.C.H. are inventors on a non-provisional patent application (no. 18/142,931, filed 3 May 2023) related to this work, submitted by the Board of Trustees of Stanford University.
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- 2023
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3. 3D printing microporous scaffolds from modular bioinks containing sacrificial, cell-encapsulating microgels.
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Seymour AJ, Kilian D, Navarro RS, Hull SM, and Heilshorn SC
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- Humans, Hydrogels chemistry, Biocompatible Materials chemistry, Printing, Three-Dimensional, Human Umbilical Vein Endothelial Cells, Gelatin chemistry, Tissue Scaffolds chemistry, Tissue Engineering, Microgels, Bioprinting
- Abstract
Microgel-based biomaterials have inherent porosity and are often extrudable, making them well-suited for 3D bioprinting applications. Cells are commonly introduced into these granular inks post-printing using cell infiltration. However, due to slow cell migration speeds, this strategy struggles to achieve depth-independent cell distributions within thick 3D printed geometries. To address this, we leverage granular ink modularity by combining two microgels with distinct functions: (1) structural, UV-crosslinkable microgels made from gelatin methacryloyl (GelMA) and (2) sacrificial, cell-laden microgels made from oxidized alginate (AlgOx). We hypothesize that encapsulating cells within sacrificial AlgOx microgels would enable the simultaneous introduction of void space and release of cells at depths unachievable through cell infiltration alone. Blending the microgels in different ratios produces a family of highly printable GelMA : AlgOx microgel inks with void fractions ranging from 0.03 to 0.35. As expected, void fraction influences the morphology of human umbilical vein endothelial cells (HUVEC) within GelMA : AlgOx inks. Crucially, void fraction does not alter the ideal HUVEC distribution seen throughout the depth of 3D printed samples. This work presents a strategy for fabricating constructs with tunable porosity and depth-independent cell distribution, highlighting the promise of microgel-based inks for 3D bioprinting.
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- 2023
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4. Tuning pro-survival effects of human induced pluripotent stem cell-derived exosomes using elastin-like polypeptides.
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Lee CH, Hunt D, Roth JG, Chiu CC, Suhar RA, LeSavage BL, Seymour AJ, Lindsay C, Krajina BA, Chen YT, Chang KH, Hsieh IC, Chu PH, Wen MS, and Heilshorn SC
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- Humans, Animals, Dogs, Mice, Elastin metabolism, Endothelial Cells, Peptides pharmacology, Peptides metabolism, Oligopeptides pharmacology, Oligopeptides metabolism, Induced Pluripotent Stem Cells, Exosomes metabolism
- Abstract
Exosome-based regenerative therapies are potentially easier to manufacture and safer to apply compared to cell-based therapies. However, many questions remain about how to bio-manufacture reproducible and potent exosomes using animal-free reagents. Here we evaluate the hypothesis that designer biomaterial substrates can be used to alter the potency of exosomes secreted by human induced pluripotent stem cells (iPSCs). Two animal-free designer matrices were fabricated based on recombinant elastin-like polypeptides (ELPs): one including a cell-adhesive RGD ligand and a second with a non-adhesive RDG peptide. While iPSCs cultured on these two substrates and Matrigel-coated controls had similar levels of proliferation, the RDG-ELP substrate significantly increased protein expression of stemness markers OCT4 and SOX2 and suppressed spontaneous differentiation compared to those on RGD-ELP. The pro-survival potency of iPSC-derived exosomes was evaluated using three distinct stress tests: serum starvation in murine fibroblasts, hypoxia in human endothelial cells, and hyperosmolarity in canine kidney cells. In all three cases, exosomes produced by iPSCs grown on RDG-ELP substrates had similar pro-survival effects to those produced using iPSCs grown on Matrigel, while use of RGD-ELP substrates led to significantly reduced exosome potency. These data demonstrate that recombinant substrates can be designed for the robust bio-manufacturing of iPSC-derived, pro-survival exosomes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)
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- 2022
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5. Local kisspeptin excitation of rat oxytocin neurones in late pregnancy.
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Abbasi M, Perkinson MR, Seymour AJ, Piet R, Campbell RE, Iremonger KJ, and Brown CH
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- Action Potentials physiology, Animals, Female, Neurons physiology, Pregnancy, Rats, Supraoptic Nucleus physiology, Vasopressins metabolism, Kisspeptins metabolism, Kisspeptins pharmacology, Oxytocin metabolism
- Abstract
The hormone, oxytocin, is synthesised by magnocellular neurones of the supraoptic and paraventricular nuclei and is released from the posterior pituitary gland into the circulation to trigger uterine contractions during parturition. Kisspeptin fibre density increases around the supraoptic nucleus over pregnancy and intracerebroventricular kisspeptin excites oxytocin neurones only in late pregnancy. However, the mechanism of this excitation is unknown. Here, we found that microdialysis administration of kisspeptin into the supraoptic nucleus consistently increased the action potential (spike) firing rate of oxytocin neurones in urethane-anaesthetised late-pregnant rats (gestation day 18-21) but not in non-pregnant rats. Hazard analysis of action potential firing showed that kisspeptin specifically increased the probability of another action potential firing immediately after each action potential (post-spike excitability) in late-pregnant rats. Patch-clamp electrophysiology in hypothalamic slices showed that bath application of kisspeptin did not affect action potential frequency or baseline membrane potential in supraoptic nucleus neurones. Moreover, kisspeptin superfusion did not affect the frequency or amplitude of excitatory postsynaptic currents or inhibitory postsynaptic currents in supraoptic nucleus neurones. Taken together, these studies suggest that kisspeptin directly activates oxytocin neurones in late pregnancy, at least in part, via increased post-spike excitability. KEY POINTS: Oxytocin secretion is triggered by action potential firing in magnocellular neurones of the hypothalamic supraoptic and paraventricular nuclei to induce uterine contractions during birth. In late pregnancy, kisspeptin expression increases in rat periventricular nucleus neurones that project to the oxytocin system. Here, we show that intra-supraoptic nucleus administration of kisspeptin increases the action potential firing rate of oxytocin neurones in anaesthetised late-pregnant rats, and that the increased firing rate is associated with increased oxytocin neurone excitability immediately after each action potential. By contrast, kisspeptin superfusion of hypothalamic slices did not affect the activity of supraoptic nucleus neurones or the strength of local synaptic inputs to supraoptic nucleus neurones. Hence, kisspeptin might activate oxytocin neurons in late pregnancy by transiently increasing oxytocin neuron excitability after each action potential., (© 2022 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)
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- 2022
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6. Bioprinted microvasculature: progressing from structure to function.
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Seymour AJ, Westerfield AD, Cornelius VC, Skylar-Scott MA, and Heilshorn SC
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- Microvessels, Printing, Three-Dimensional, Tissue Engineering methods, Bioprinting methods, Tissue Scaffolds chemistry
- Abstract
Three-dimensional (3D) bioprinting seeks to unlock the rapid generation of complex tissue constructs, but long-standing challenges with efficient in vitro microvascularization must be solved before this can become a reality. Microvasculature is particularly challenging to biofabricate due to the presence of a hollow lumen, a hierarchically branched network topology, and a complex signaling milieu. All of these characteristics are required for proper microvascular-and, thus, tissue-function. While several techniques have been developed to address distinct portions of this microvascularization challenge, no single approach is capable of simultaneously recreating all three microvascular characteristics. In this review, we present a three-part framework that proposes integration of existing techniques to generate mature microvascular constructs. First, extrusion-based 3D bioprinting creates a mesoscale foundation of hollow, endothelialized channels. Second, biochemical and biophysical cues induce endothelial sprouting to create a capillary-mimetic network. Third, the construct is conditioned to enhance network maturity. Across all three of these stages, we highlight the potential for extrusion-based bioprinting to become a central technique for engineering hierarchical microvasculature. We envision that the successful biofabrication of functionally engineered microvasculature will address a critical need in tissue engineering, and propel further advances in regenerative medicine and ex vivo human tissue modeling., (© 2022 IOP Publishing Ltd.)
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- 2022
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7. Inverse neurovascular coupling contributes to positive feedback excitation of vasopressin neurons during a systemic homeostatic challenge.
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Roy RK, Althammer F, Seymour AJ, Du W, Biancardi VC, Hamm JP, Filosa JA, Brown CH, and Stern JE
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- Action Potentials, Animals, Blood Flow Velocity, Cell Hypoxia, Cellular Microenvironment, Female, Homeostasis, Infusions, Intravenous, Male, Microscopy, Fluorescence, Multiphoton, Rats, Transgenic, Rats, Wistar, Saline Solution, Hypertonic administration & dosage, Time Factors, Vasopressins genetics, Rats, Cerebrovascular Circulation, Dendrites metabolism, Neurovascular Coupling, Supraoptic Nucleus blood supply, Vasoconstriction, Vasopressins metabolism
- Abstract
Neurovascular coupling (NVC), the process that links neuronal activity to cerebral blood flow changes, has been mainly studied in superficial brain areas, namely the neocortex. Whether the conventional, rapid, and spatially restricted NVC response can be generalized to deeper and functionally diverse brain regions remains unknown. Implementing an approach for in vivo two-photon imaging from the ventral surface of the brain, we show that a systemic homeostatic challenge, acute salt loading, progressively increases hypothalamic vasopressin (VP) neuronal firing and evokes a vasoconstriction that reduces local blood flow. Vasoconstrictions are blocked by topical application of a VP receptor antagonist or tetrodotoxin, supporting mediation by activity-dependent, dendritically released VP. Salt-induced inverse NVC results in a local hypoxic microenvironment, which evokes positive feedback excitation of VP neurons. Our results reveal a physiological mechanism by which inverse NVC responses regulate systemic homeostasis, further supporting the notion of brain heterogeneity in NVC responses., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)
- Published
- 2021
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8. 3D Printing of Microgel Scaffolds with Tunable Void Fraction to Promote Cell Infiltration.
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Seymour AJ, Shin S, and Heilshorn SC
- Subjects
- Gelatin, Human Umbilical Vein Endothelial Cells, Humans, Methacrylates, Printing, Three-Dimensional, Tissue Engineering, Tissue Scaffolds, Bioprinting, Microgels
- Abstract
Granular, microgel-based materials have garnered interest as promising tissue engineering scaffolds due to their inherent porosity, which can promote cell infiltration. Adapting these materials for 3D bioprinting, while maintaining sufficient void space to enable cell migration, can be challenging, since the rheological properties that determine printability are strongly influenced by microgel packing and void fraction. In this work, a strategy is proposed to decouple printability and void fraction by blending UV-crosslinkable gelatin methacryloyl (GelMA) microgels with sacrificial gelatin microgels to form composite inks. It is observed that inks with an apparent viscosity greater than ≈100 Pa s (corresponding to microgel concentrations ≥5 wt%) have rheological properties that enable extrusion-based printing of multilayered structures in air. By altering the ratio of GelMA to sacrificial gelatin microgels, while holding total concentration constant at 6 wt%, a family of GelMA:gelatin microgel inks is created that allows for tuning of void fraction from 0.20 to 0.57. Furthermore, human umbilical vein endothelial cells (HUVEC) seeded onto printed constructs are observed to migrate into granular inks in a void fraction-dependent manner. Thus, the family of microgel inks holds promise for use in 3D printing and tissue engineering applications that rely upon cell infiltration., (© 2021 Wiley-VCH GmbH.)
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- 2021
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9. Plasticity in Intrinsic Excitability of Hypothalamic Magnocellular Neurosecretory Neurons in Late-Pregnant and Lactating Rats.
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Perkinson MR, Augustine RA, Bouwer GT, Brown EF, Cheong I, Seymour AJ, Fronius M, and Brown CH
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- Action Potentials drug effects, Action Potentials physiology, Animals, Basal Nucleus of Meynert pathology, Female, Hypothalamus metabolism, Lactation metabolism, Lactation physiology, Milk Ejection drug effects, Neurons metabolism, Oxytocin pharmacology, Paraventricular Hypothalamic Nucleus metabolism, Pregnancy, Rats, Supraoptic Nucleus metabolism, Vasopressins pharmacology, Basal Nucleus of Meynert metabolism, Oxytocin metabolism, Vasopressins metabolism
- Abstract
Oxytocin and vasopressin secretion from the posterior pituitary gland are required for normal pregnancy and lactation. Oxytocin secretion is relatively low and constant under basal conditions but becomes pulsatile during birth and lactation to stimulate episodic contraction of the uterus for delivery of the fetus and milk ejection during suckling. Vasopressin secretion is maintained in pregnancy and lactation despite reduced osmolality (the principal stimulus for vasopressin secretion) to increase water retention to cope with the cardiovascular demands of pregnancy and lactation. Oxytocin and vasopressin secretion are determined by the action potential (spike) firing of magnocellular neurosecretory neurons of the hypothalamic supraoptic and paraventricular nuclei. In addition to synaptic input activity, spike firing depends on intrinsic excitability conferred by the suite of channels expressed by the neurons. Therefore, we analysed oxytocin and vasopressin neuron activity in anaesthetised non-pregnant, late-pregnant, and lactating rats to test the hypothesis that intrinsic excitability of oxytocin and vasopressin neurons is increased in late pregnancy and lactation to promote oxytocin and vasopressin secretion required for successful pregnancy and lactation. Hazard analysis of spike firing revealed a higher incidence of post-spike hyperexcitability immediately following each spike in oxytocin neurons, but not in vasopressin neurons, in late pregnancy and lactation, which is expected to facilitate high frequency firing during bursts. Despite lower osmolality in late-pregnant and lactating rats, vasopressin neuron activity was not different between non-pregnant, late-pregnant, and lactating rats, and blockade of osmosensitive ΔN-TRPV1 channels inhibited vasopressin neurons to a similar extent in non-pregnant, late-pregnant, and lactating rats. Furthermore, supraoptic nucleus ΔN-TRPV1 mRNA expression was not different between non-pregnant and late-pregnant rats, suggesting that sustained activity of ΔN-TRPV1 channels might maintain vasopressin neuron activity to increase water retention during pregnancy and lactation.
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- 2021
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10. Bioprinting Cell- and Spheroid-Laden Protein-Engineered Hydrogels as Tissue-on-Chip Platforms.
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Duarte Campos DF, Lindsay CD, Roth JG, LeSavage BL, Seymour AJ, Krajina BA, Ribeiro R, Costa PF, Blaeser A, and Heilshorn SC
- Abstract
Human tissues, both in health and disease, are exquisitely organized into complex three-dimensional architectures that inform tissue function. In biomedical research, specifically in drug discovery and personalized medicine, novel human-based three-dimensional (3D) models are needed to provide information with higher predictive value compared to state-of-the-art two-dimensional (2D) preclinical models. However, current in vitro models remain inadequate to recapitulate the complex and heterogenous architectures that underlie biology. Therefore, it would be beneficial to develop novel models that could capture both the 3D heterogeneity of tissue (e.g., through 3D bioprinting) and integrate vascularization that is necessary for tissue viability (e.g., through culture in tissue-on-chips). In this proof-of-concept study, we use elastin-like protein (ELP) engineered hydrogels as bioinks for constructing such tissue models, which can be directly dispensed onto endothelialized on-chip platforms. We show that this bioprinting process is compatible with both single cell suspensions of neural progenitor cells (NPCs) and spheroid aggregates of breast cancer cells. After bioprinting, both cell types remain viable in incubation for up to 14 days. These results demonstrate a first step toward combining ELP engineered hydrogels with 3D bioprinting technologies and on-chip platforms comprising vascular-like channels for establishing functional tissue models., (Copyright © 2020 Duarte Campos, Lindsay, Roth, LeSavage, Seymour, Krajina, Ribeiro, Costa, Blaeser and Heilshorn.)
- Published
- 2020
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11. Multi-phase catheter-injectable hydrogel enables dual-stage protein-engineered cytokine release to mitigate adverse left ventricular remodeling following myocardial infarction in a small animal model and a large animal model.
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Steele AN, Paulsen MJ, Wang H, Stapleton LM, Lucian HJ, Eskandari A, Hironaka CE, Farry JM, Baker SW, Thakore AD, Jaatinen KJ, Tada Y, Hollander MJ, Williams KM, Seymour AJ, Totherow KP, Yu AC, Cochran JR, Appel EA, and Woo YJ
- Subjects
- Animals, Catheters, Cells, Cultured, Disease Models, Animal, Hepatocyte Growth Factor metabolism, Humans, Hyaluronic Acid administration & dosage, Myocardial Ischemia drug therapy, Myocardial Ischemia metabolism, Myocardium pathology, Rats, Hydrogels administration & dosage, Myocardial Infarction drug therapy, Myocardial Infarction metabolism, Myocardium metabolism, Ventricular Function, Left drug effects, Ventricular Remodeling drug effects
- Abstract
Although ischemic heart disease is the leading cause of death worldwide, mainstay treatments ultimately fail because they do not adequately address disease pathophysiology. Restoring the microvascular perfusion deficit remains a significant unmet need and may be addressed via delivery of pro-angiogenic cytokines. The therapeutic effect of cytokines can be enhanced by encapsulation within hydrogels, but current hydrogels do not offer sufficient clinical translatability due to unfavorable viscoelastic mechanical behavior which directly impacts the ability for minimally-invasive catheter delivery. In this report, we examine the therapeutic implications of dual-stage cytokine release from a novel, highly shear-thinning biocompatible catheter-deliverable hydrogel. We chose to encapsulate two protein-engineered cytokines, namely dimeric fragment of hepatocyte growth factor (HGFdf) and engineered stromal cell-derived factor 1α (ESA), which target distinct disease pathways. The controlled release of HGFdf and ESA from separate phases of the hyaluronic acid-based hydrogel allows extended and pronounced beneficial effects due to the precise timing of release. We evaluated the therapeutic efficacy of this treatment strategy in a small animal model of myocardial ischemia and observed a significant benefit in biological and functional parameters. Given the encouraging results from the small animal experiment, we translated this treatment to a large animal preclinical model and observed a reduction in scar size, indicating this strategy could serve as a potential adjunct therapy for the millions of people suffering from ischemic heart disease., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)
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- 2020
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12. Engineered materials for organoid systems.
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Kratochvil MJ, Seymour AJ, Li TL, Paşca SP, Kuo CJ, and Heilshorn SC
- Abstract
Organoids are 3D cell culture systems that mimic some of the structural and functional characteristics of an organ. Organoid cultures provide the opportunity to study organ-level biology in models that mimic human physiology more closely than 2D cell culture systems or non-primate animal models. Many organoid cultures rely on decellularized extracellular matrices as scaffolds, which are often poorly chemically defined and allow only limited tunability and reproducibility. By contrast, the biochemical and biophysical properties of engineered matrices can be tuned and optimized to support the development and maturation of organoid cultures. In this Review, we highlight how key cell-matrix interactions guiding stem-cell decisions can inform the design of biomaterials for the reproducible generation and control of organoid cultures. We survey natural, synthetic and protein-engineered hydrogels for their applicability to different organoid systems and discuss biochemical and mechanical material properties relevant for organoid formation. Finally, dynamic and cell-responsive material systems are investigated for their future use in organoid research.
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- 2019
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13. Author Correction: Bi-directional cell-pericellular matrix interactions direct stem cell fate.
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Ferreira SA, Motwani MS, Faull PA, Seymour AJ, Yu TTL, Enayati M, Taheem DK, Salzlechner C, Haghighi T, Kania EM, Oommen OP, Ahmed T, Loaiza S, Parzych K, Dazzi F, Varghese OP, Festy F, Grigoriadis AE, Auner HW, Snijders AP, Bozec L, and Gentleman E
- Abstract
The original version of this Article contained an error in the author affiliations. The affiliation of Marjan Enayati with 'Ludwig Boltzmann Cluster for Cardiovascular Research at the Center for Biomedical Research, Medical University of Vienna, Austria' was inadvertently omitted. This has now been corrected in both the PDF and HTML versions of the Article.
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- 2018
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14. Bi-directional cell-pericellular matrix interactions direct stem cell fate.
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Ferreira SA, Motwani MS, Faull PA, Seymour AJ, Yu TTL, Enayati M, Taheem DK, Salzlechner C, Haghighi T, Kania EM, Oommen OP, Ahmed T, Loaiza S, Parzych K, Dazzi F, Varghese OP, Festy F, Grigoriadis AE, Auner HW, Snijders AP, Bozec L, and Gentleman E
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- Amides pharmacology, Cell-Matrix Junctions drug effects, Humans, Hydrogel, Polyethylene Glycol Dimethacrylate, Mesenchymal Stem Cells drug effects, Mesenchymal Stem Cells metabolism, Paclitaxel pharmacology, Pyridines pharmacology, Stem Cells drug effects, Cell Communication drug effects, Cell Lineage drug effects, Cell-Matrix Junctions metabolism, Stem Cells cytology, Stem Cells metabolism
- Abstract
Modifiable hydrogels have revealed tremendous insight into how physical characteristics of cells' 3D environment drive stem cell lineage specification. However, in native tissues, cells do not passively receive signals from their niche. Instead they actively probe and modify their pericellular space to suit their needs, yet the dynamics of cells' reciprocal interactions with their pericellular environment when encapsulated within hydrogels remains relatively unexplored. Here, we show that human bone marrow stromal cells (hMSC) encapsulated within hyaluronic acid-based hydrogels modify their surroundings by synthesizing, secreting and arranging proteins pericellularly or by degrading the hydrogel. hMSC's interactions with this local environment have a role in regulating hMSC fate, with a secreted proteinaceous pericellular matrix associated with adipogenesis, and degradation with osteogenesis. Our observations suggest that hMSC participate in a bi-directional interplay between the properties of their 3D milieu and their own secreted pericellular matrix, and that this combination of interactions drives fate.
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- 2018
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15. Neighboring cells override 3D hydrogel matrix cues to drive human MSC quiescence.
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Ferreira SA, Faull PA, Seymour AJ, Yu TTL, Loaiza S, Auner HW, Snijders AP, and Gentleman E
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- Bone Marrow metabolism, Cell Communication, Cell Differentiation, Cell Survival, Cells, Cultured, Extracellular Matrix metabolism, Glycoproteins chemistry, Humans, Mesenchymal Stem Cells cytology, Tissue Engineering methods, Hyaluronic Acid chemistry, Hydrogels chemistry, Mesenchymal Stem Cells physiology
- Abstract
Physical properties of modifiable hydrogels can be tuned to direct stem cell differentiation in a role akin to that played by the extracellular matrix in native stem cell niches. However, stem cells do not respond to matrix cues in isolation, but rather integrate soluble and non-soluble signals to balance quiescence, self-renewal and differentiation. Here, we encapsulated single cell suspensions of human mesenchymal stem cells (hMSC) in hyaluronic acid-based hydrogels at high and low densities to unravel the contributions of matrix- and non-matrix-mediated cues in directing stem cell response. We show that in high-density (HD) cultures, hMSC do not rely on hydrogel cues to guide their fate. Instead, they take on characteristics of quiescent cells and secrete a glycoprotein-rich pericellular matrix (PCM) in response to signaling from neighboring cells. Preventing quiescence precluded the formation of a glycoprotein-rich PCM and forced HD cultures to differentiate in response to hydrogel composition. Our observations may have important implications for tissue engineering as neighboring cells may act counter to matrix cues provided by scaffolds. Moreover, as stem cells are most regenerative if activated from a quiescent state, our results suggest that ex vivo native-like niches that incorporate signaling from neighboring cells may enable the production of clinically relevant, highly regenerative cells., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)
- Published
- 2018
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16. Integrative neuro-humoral regulation of oxytocin neuron activity in pregnancy and lactation.
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Augustine RA, Seymour AJ, Campbell RE, Grattan DR, and Brown CH
- Abstract
Oxytocin is required for normal birth and lactation. Oxytocin is synthesised by hypothalamic supraoptic and paraventricular nuclei neurons and is released into the circulation from the posterior pituitary gland. Under basal conditions, circulating oxytocin levels are relatively constant but during birth and lactation, pulsatile oxytocin release triggers rhythmic contraction of the uterus during birth and milk ejection during suckling. Oxytocin levels are principally determined by the pattern of action potential firing that is, in turn, determined by the interplay between the intrinsic properties of the oxytocin neurons, regulation of their excitability by surrounding glia as well as by synaptic drive from their afferent inputs. During birth and suckling, oxytocin neurons fire high-frequency bursts of action potentials that are coordinated across the population of neurons and these bursts underpin the pulsatile secretion of oxytocin required for normal birth and lactation. Neuroglial regulation of oxytocin neurons changes during pregnancy to favour burst firing. However, these changes still require afferent input activity to drive activity. While it has long been known that noradrenergic inputs to oxytocin neurons are activated during birth and lactation, the involvement of other afferent inputs is less clear. Here, we provide a brief overview of the current understanding of the mechanisms that regulate oxytocin neuron activity during pregnancy and lactation, and focus on recent evidence from our laboratory identifying an input that increases kisspeptin production to excite oxytocin neurons in late pregnancy. This article is protected by copyright. All rights reserved., (This article is protected by copyright. All rights reserved.)
- Published
- 2018
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17. Development of an excitatory kisspeptin projection to the oxytocin system in late pregnancy.
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Seymour AJ, Scott V, Augustine RA, Bouwer GT, Campbell RE, and Brown CH
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- Animals, Female, Oxytocin physiology, Pregnancy, Rats, Sprague-Dawley, Receptors, G-Protein-Coupled genetics, Receptors, Kisspeptin-1, Kisspeptins physiology, Neurons physiology, Paraventricular Hypothalamic Nucleus physiology, Pregnancy, Animal physiology, Receptors, G-Protein-Coupled physiology, Supraoptic Nucleus physiology
- Abstract
Key Points: Oxytocin release from the posterior pituitary gland stimulates uterine contraction during birth but the central mechanisms that activate oxytocin neurones for birth are not well characterized. We found that that kisspeptin fibre density around oxytocin neurones increases in late-pregnant rats. These kisspeptin fibres originated from hypothalamic periventricular nucleus neurones that upregulated kisspeptin expression in late pregnancy. Oxytocin neurones were excited by central kisspeptin administration in late-pregnant rats but not in non-pregnant rats or early- to mid-pregnant rats. Our results reveal the emergence of a new excitatory kisspeptin projection to the oxytocin system in late pregnancy that might contribute to oxytocin neurone activation for birth., Abstract: The hormone oxytocin promotes uterine contraction during parturition. Oxytocin is synthesized by magnocellular neurones in the hypothalamic supraoptic and paraventricular nuclei and is released into the circulation from the posterior pituitary gland in response to action potential firing. Systemic kisspeptin administration increases oxytocin neurone activity to elevate plasma oxytocin levels. Here, immunohistochemistry revealed that rats on the expected day of parturition (day 21 of gestation) had a higher density of kisspeptin-positive fibres in the perinuclear zone surrounding the supraoptic nucleus (which provides dense glutamatergic and GABAergic innervation to the supraoptic nucleus) than was evident in non-pregnant rats. Retrograde tracing showed the kisspeptin projections to the perinuclear zone originated from the hypothalamic periventricular nucleus. Quantitative RT-PCR showed that kisspeptin receptor mRNA, Kiss1R mRNA, was expressed in the perinuclear zone-supraoptic nucleus and that the relative Kiss1R mRNA expression does not change over the course of pregnancy. Finally, intracerebroventricular administration of kisspeptin increased the firing rate of oxytocin neurones in anaesthetized late-pregnant rats (days 18-21 of gestation) but not in non-pregnant rats, or in early- or mid-pregnant rats. Taken together, these results suggest that kisspeptin expression is upregulated in the periventricular nucleus projection to the perinuclear zone of the supraoptic nucleus towards the end of pregnancy. Hence, this input might activate oxytocin neurones during parturition., (© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.)
- Published
- 2017
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18. Reproductive Regulation of Gene Expression in the Hypothalamic Supraoptic and Paraventricular Nuclei.
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Augustine RA, Bouwer GT, Seymour AJ, Grattan DR, and Brown CH
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- Animals, Female, Lactation metabolism, Neurons metabolism, Oxytocin genetics, Phosphorylation, Pregnancy, Rats, STAT5 Transcription Factor genetics, STAT5 Transcription Factor metabolism, Gene Expression Regulation, Paraventricular Hypothalamic Nucleus metabolism, Reproduction genetics, STAT5 Transcription Factor biosynthesis, Supraoptic Nucleus metabolism
- Abstract
Oxytocin secretion is required for successful reproduction. Oxytocin is synthesised by magnocellular neurones of the hypothalamic supraoptic and paraventricular nuclei and the physiological demand for oxytocin synthesis and secretion is increased for birth and lactation. Therefore, we used a polymerase chain reaction (PCR) array screen to determine whether genes that might be important for synthesis and/or secretion of oxytocin are up- or down-regulated in the supraoptic and paraventricular nuclei of late-pregnant and lactating rats, compared to virgin rats. We then validated the genes that were most highly regulated using real time-quantitative PCR. Among the most highly regulated genes were those that encode for suppressors of cytokine signalling, which are intracellular inhibitors of prolactin signalling. Prolactin receptor activation changes gene expression via phosphorylation of signal transducer and activator of transcription 5 (STAT5). Using double-label immunohistochemistry, we found that phosphorylated STAT5 was expressed in almost all oxytocin neurones of late-pregnant and lactating rats but was almost absent from oxytocin neurones of virgin rats. We conclude that increased prolactin activation of oxytocin neurones might contribute to the changes in gene expression by oxytocin neurones required for normal birth and lactation., (© 2015 British Society for Neuroendocrinology.)
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- 2016
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19. Induction of hypertension blunts baroreflex inhibition of vasopressin neurons in the rat.
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Han SY, Bouwer GT, Seymour AJ, Korpal AK, Schwenke DO, and Brown CH
- Subjects
- Adrenergic alpha-1 Receptor Agonists pharmacology, Angiotensin II Type 1 Receptor Blockers pharmacology, Animals, Blood Pressure drug effects, Losartan pharmacology, Male, Neurons drug effects, Phenylephrine pharmacology, Pituitary Gland drug effects, Rats, Rats, Inbred F344, Rats, Transgenic, Subfornical Organ drug effects, Subfornical Organ physiology, Baroreflex, Hypertension physiopathology, Neurons physiology, Pituitary Gland physiology, Vasopressins physiology
- Abstract
Vasopressin secretion from the posterior pituitary gland is determined by action potential discharge of hypothalamic magnocellular neurosecretory cells. Vasopressin is a potent vasoconstrictor, but vasopressin levels are paradoxically elevated in some patients with established hypertension. To determine whether vasopressin neurons are excited in hypertension, extracellular single-unit recordings of vasopressin neurons from urethane-anaesthetized Cyp1a1-Ren2 rats with inducible angiotensin-dependent hypertension were made. The basal firing rate of vasopressin neurons was higher in hypertensive Cyp1a1-Ren2 rats than in non-hypertensive Cyp1a1-Ren2 rats. The increase in firing rate was specific to vasopressin neurons because oxytocin neuron firing rate was unaffected by the induction of hypertension. Intravenous injection of the α1-adrenoreceptor agonist, phenylephrine (2.5 μg/kg), transiently increased mean arterial blood pressure to cause a baroreflex-induced inhibition of heart rate and vasopressin neuron firing rate (by 52 ± 9%) in non-hypertensive rats. By contrast, intravenous phenylephrine did not inhibit vasopressin neurons in hypertensive rats, despite a similar increase in mean arterial blood pressure and inhibition of heart rate. Circulating angiotensin II can excite vasopressin neurons via activation of afferent inputs from the subfornical organ. However, the increase in vasopressin neuron firing rate and the loss of inhibition by intravenous phenylephrine were not blocked by intra-subfornical organ infusion of the angiotensin AT1 receptor antagonist, losartan. It can be concluded that increased vasopressin neuron activity at the onset of hypertension is driven, at least in part, by reduced baroreflex inhibition of vasopressin neurons and that this might exacerbate the increase in blood pressure at the onset of hypertension., (© 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)
- Published
- 2015
- Full Text
- View/download PDF
20. Prevalence of human papillomavirus genotypes among African women with normal cervical cytology and neoplasia: a systematic review and meta-analysis.
- Author
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Ogembo RK, Gona PN, Seymour AJ, Park HS, Bain PA, Maranda L, and Ogembo JG
- Subjects
- Adult, Africa epidemiology, Carcinoma, Squamous Cell pathology, Carcinoma, Squamous Cell virology, Cervix Uteri pathology, Cervix Uteri virology, Female, Genotype, Humans, Middle Aged, Papillomaviridae classification, Papillomaviridae isolation & purification, Papillomaviridae pathogenicity, Papillomavirus Infections pathology, Papillomavirus Infections virology, Prevalence, Registries, Squamous Intraepithelial Lesions of the Cervix pathology, Squamous Intraepithelial Lesions of the Cervix virology, Uterine Cervical Neoplasms pathology, Uterine Cervical Neoplasms virology, Uterine Cervical Dysplasia pathology, Uterine Cervical Dysplasia virology, Carcinoma, Squamous Cell epidemiology, Papillomaviridae genetics, Papillomavirus Infections epidemiology, Squamous Intraepithelial Lesions of the Cervix epidemiology, Uterine Cervical Neoplasms epidemiology, Uterine Cervical Dysplasia epidemiology
- Abstract
Background: Several meta-analyses confirmed the five most prevalent human papillomavirus (HPV) strains in women with and without cervical neoplastic diseases are HPV16, 18, 31, 52, and 58. HPV16/18 are the predominant oncogenic genotypes, causing approximately 70% of global cervical cancer cases. The vast majority of the women studied in previous analyses were from Europe, North America, Asia, and most recently Latin America and the Caribbean. Despite the high burden of cervical cancer morbidity and mortality in Africa, a robust meta-analysis of HPV genotype prevalence and distribution in African women is lacking., Methods and Findings: We systematically searched 14 major databases from inception to August 2013 without language restriction, following the Meta-Analysis of Observational Studies in Epidemiology and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Seventy-one studies from 23 African countries were identified after screening 1162 citations and data abstracted and study quality appraised from 195 articles. HPV type-specific prevalence and distribution was estimated from 17,273 cases of women with normal cervical cytology; 1019 women with atypical squamous cells of undetermined significance (ASCUS); 1444 women with low-grade squamous intraepithelial lesion (LSIL); 1571 women with high-grade squamous intraepithelial lesion (HSIL); and 4,067 cases of invasive cervical carcinoma (ICC). Overall prevalence of HPV16/18 were 4.4% and 2.8% of women with normal cytology, 12.0% and 4.4% with ASCUS, 14.5% and 10.0% with LSIL, 31.2% and 13.9% with HSIL, and 49.7% and 18.0% with ICC, respectively. Study limitations include the lack of adequate data from Middle and Northern African regions, and variations in the HPV type-specific sensitivity of different genotyping protocols., Conclusions: To our knowledge, this study is the most comprehensive assessment of the overall prevalence and distribution of HPV genotypes in African women with and without different cervical neoplasias. We have established that HPV16/18 account for 67.7% of ICC cases among African women. Based on our findings, we highly recommend the administration of existing prophylactic vaccines to younger women not infected with HPV16/18 and an increase in HPV screening efforts for high-risk genotypes to prevent cervical cancer., Review Registration: International Prospective Register of Systematic Reviews CRD42013006558.
- Published
- 2015
- Full Text
- View/download PDF
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