Calendar

Dissertation Defense

Candidate: Alan Baer
Title: Protein Phosphatase 1 Alpha Modulates L Polymerase Phosphorylation and Regulates Rift Valley Fever Virus Replication

Abstract:

Rift Valley fever virus (RVFV), genus Phlebovirus family Bunyaviridae, is an arthropod-borne virus endemic throughout sub-Saharan Africa. Recent outbreaks have resulted in cyclic epidemics with an increasing geographic footprint, devastating both livestock and human populations. Despite being recognized as an emerging threat, relatively little is known about the virulence mechanisms and host interactions of RVFV. The Ser/Thr Protein Phosphatase 1 (PP1) has previously been shown to play a significant role in the replication of several viruses. Here we demonstrate PP1 playing a prominent role in RVFV replication early on during infection through interaction with the viral L polymerase.

The viral RNA-dependent polymerase of RVFV, L polymerase, is involved in both cytoplasmic viral mRNA transcription and genomic viral RNA replication. In our studies, PP1α was redistributed to the cytoplasmic and perinuclear regions following infection and L polymerase was found to colocalize and interact with PP1, suggesting that it may be a substrate of PP1α. Treatment with a novel  PP1-targeting small molecule 1E7-03 resulted in decreased viral titers with no cytotoxicity in vitro. Treatment with 1E7-03 was found to reduce both viral RNA and protein levels, while not inhibiting cellular transcription or translation. Phosphorylation of the viral L polymerase was also detected, along with an increase in polymerase phosphorylation following 1E7-03 treatment.

These results indicate that PP1α activity is important for RVFV replication early on during the viral life cycle, potentially through direct dephosphorylation of the viral L polymerase or through a viral or host intermediary.

Director or Committee Chair:

Dr. Kylene Kehn-Hall

Committee:

>Dr. Aarthi Narayanan
Dr. Ramin Hakami
Dr. Barney Bishop
Notes: A copy of the dissertation is available in the Mercer Library.  All are invited to attend the defense.

Dissertation Defense

Candidate: Cathy King Madsen
Title: Dependence of Two Arboviruses on the Host MicroRNA Pathway

Abstract:

Rift Valley fever virus (RVFV) and Venezuelan equine encephalitis virus (VEEV) are two mosquito-borne, select agent viruses with severe effects on humans and livestock, and for which no FDA-approved vaccines or specific treatments exist.  To identify potential therapeutic targets, this research focuses on viral interactions with host microRNA (miRNA), a class of small, non-coding RNA which bind to messenger RNA (mRNA) to regulate its endpoint proteins.  This study demonstrates dependence of both RVFV and VEEV on the host miRNA pathway through different means.  RVFV infection induces upregulation of miR-630 and miR-99a, which downregulate the anti-apoptotic protein IGF1R.  Inhibition of these miRNA partially rescues IGF1R and decreases viral replication.  Conversely, RVFV NSs protein inhibits the anti-apoptotic miR-17-92 cluster, revealing interplay between NSs and miRNA for control of host functions during infection, while overexpression of this cluster reduces viral replication.  In contrast, VEEV replication depends heavily on miRNA processing enzymes including Drosha, Exportin 5, and Argonaute 2 (Ago2).  Knockdown or inhibition of these enzymes leads to decreased replication and production of viral proteins. The Ago2 inhibitor acriflavine (ACF) reduces VEEV replication in both vaccine and virulent strains by approximately 6-log10 in culture, and is similarly effective against Eastern and Western equine encephalitis viruses.  Taken together, these data show the importance of the miRNA pathway for several types of virus, suggesting a fine-tuning function for replication in RVFV and an active use of the pathway itself for VEEV and related Alphaviruses.Director or Committee Chair:

Dr. Kylene Kehn-Hall

Committee:

Dr. Fatah KashanchpDr. Barney Bishop
Dr. Norman Lee

Notes: The thesis is on reserve in the Johnson Center Library, Fairfax Campus. All members of the George Mason University community are invited to attend.

Dissertation Defense

Candidate: Cathy King Madsen
Title: Dependence of Two Arboviruses on the Host MicroRNA Pathway

Abstract:

Rift Valley fever virus (RVFV) and Venezuelan equine encephalitis virus (VEEV) are two mosquito-borne, select agent viruses with severe effects on humans and livestock, and for which no FDA-approved vaccines or specific treatments exist.  To identify potential therapeutic targets, this research focuses on viral interactions with host microRNA (miRNA), a class of small, non-coding RNA which bind to messenger RNA (mRNA) to regulate its endpoint proteins.  This study demonstrates dependence of both RVFV and VEEV on the host miRNA pathway through different means.  RVFV infection induces upregulation of miR-630 and miR-99a, which downregulate the anti-apoptotic protein IGF1R.  Inhibition of these miRNA partially rescues IGF1R and decreases viral replication.  Conversely, RVFV NSs protein inhibits the anti-apoptotic miR-17-92 cluster, revealing interplay between NSs and miRNA for control of host functions during infection, while overexpression of this cluster reduces viral replication.  In contrast, VEEV replication depends heavily on miRNA processing enzymes including Drosha, Exportin 5, and Argonaute 2 (Ago2).  Knockdown or inhibition of these enzymes leads to decreased replication and production of viral proteins. The Ago2 inhibitor acriflavine (ACF) reduces VEEV replication in both vaccine and virulent strains by approximately 6-log10 in culture, and is similarly effective against Eastern and Western equine encephalitis viruses.  Taken together, these data show the importance of the miRNA pathway for several types of virus, suggesting a fine-tuning function for replication in RVFV and an active use of the pathway itself for VEEV and related Alphaviruses.

Director or Committee Chair:

Dr. Kylene Kehn-Hall

Committee:

Dr. Fatah Kashanchi
Dr. Barney Bishop
Dr. Norman Lee

Notes: The thesis is on reserve in the Mercer Library, Science & Tech Campus. All members of the George Mason University community are invited to attend.

Dissertation Defense

Candidate: Crystal Propst
Title: Lung-Directed Delivery of Therapeutics for the Treatment of Pulmonary Francisella Infection

Abstract:

According to the World Lung Foundation, acute respiratory infections result in 4.25 million deaths each year, are the third largest cause of mortality worldwide, and are the number one cause of death in low- and middle- income countries. These infections require few infectious particles and tend to be serious, difficult to treat, and spread quickly.  Despite existing treatments, many researchers work on additional therapy options including new drug development, more effective drug combinations, and developing ways to overcome antibacterial resistance.  However, delivery of existing treatments in a novel manner may lead to better therapeutic regimens without the high cost and length of time required for discovery and development of new drugs.

The Institute of Theoretical and Experimental Biophysics in Moscow recently developed a new nanoaerosol generator. This study evaluated this novel technology, which has the potential to enhance therapeutic delivery. First, the analysis of quantum dots distribution in cryosections of murine lungs demonstrated that nanoaerosols penetrate the alveoli, the site of lower respiratory infections and entry point to the circulatory system. Second, using a pulmonary Francisella tularensis subsp. novicida infection of BALB/c mice as a model, the generator was used to aerosolize the antibiotic, levofloxacin, and was able to rescue mice more efficiently than traditional delivery methods, including large particle aerosol. In addition, it was found that treatment with nanoaerosols consumes less total volume of therapeutic solutions and is gentler on sprayed material than the aerosolization by a conventional three-jet collision nebulizer.  Nanoaerosols can be produced using numerous types of drugs, not just antibiotics, and should be explored further as treatments for additional forms of respiratory disease.

Director or Committee Chair:

Dr. Monique van Hoek

Committee:

Dr. Kylene Kehn-Hall
Dr. Calvin Carpenter
Dr. Victor Morozov

Notes: A copy of the dissertation is available in the Mercer Library, Science & Tech Campus. All members of the George Mason University community are invited to attend.

Dissertation Defense

Candidate: Morgan Gostel
Title: Systematics and Evolution of Commiphora Jacq. (Burseraceae) in Madagascar

Abstract:

The myrrh genus, Commiphora, comprises a clade of nearly 200 species of shrubs and trees that grow in warm tropical regions in Africa, Madagascar, the Arabian Peninsula, the Indian sub-continent, and South America. Commiphora is the most species-rich genus in the frankincense and myrrh family, Burseraceae, and species belonging to it are ecologically important throughout their range in eastern, sub-Saharan Africa and western Madagascar. Aromatic oleoresins extracted from several species have been used extensively as an olfactory aesthetic and medicine with demonstrated pharmacological benefits throughout both antiquity and contemporary time. Despite its diversity and ecological and economical significance, evolutionary relationships in the genus are poorly understood and few studies have sought to reconstruct the phylogenetic history of Commiphora. As a result, relationships of this widespread group of plants are not well characterized. Species of Commiphora are morphologically diverse and the genus provides an opportunity to study the evolutionary significance of traits such as the presence of thorns, production of oleoresins, and diverse types of indumentum. This dissertation research seeks to reconstruct the evolutionary history of Commiphora, with an emphasis on species in Madagascar, all of which are endemic. Toward this objective, we have applied molecular phylogenetic methods to resolve infrageneric relationships in the genus using molecular markers developed from three approaches. The first approach samples molecular markers that have been designed from previously published and widely sampled genetic loci for phylogenetic reconstruction in angiosperm genera, including two nuclear ribosomal markers (ETS and ITS) and three chloroplast spacers (ndhF-rpl32, psbA-trnH, and trnD-trnT). Our second approach uses molecular markers designed from a bioinformatics pipeline specifically targeting conserved genetic loci predicted to be within close proximity to more informative, intronic regions of the genome. The third approach was transcriptome-enabled and utilizes microfluidic PCR techniques and Illumina MiSeq to sample a set of putative shared, single-copy nuclear genomic loci. We screened 192 primer pairs for their phylogenomic utility in Commiphora. 91 of these primer pairs amplified a single product and 49 sequenced loci were used for comparative phylogenetic analyses to reconstruct evolutionary relationships among species of Malagasy Commiphora. Our results suggest that previous attempts to circumscribe the diversity of Commiphora produce unnatural groups, Commiphora has experienced complex biogeographic radiations, diversity in the genus is characterized by strong geographic structure, and expanded taxonomic and genomic sampling improves our ability to discern infrageneric groups. We have also begun a partial and ongoing revision of the genus in Madagascar, including a revision of six species, five of which are new. We outline priorities for future studies in this group, including expanded taxonomic revision and molecular systematics research to improve species delimitation and better understand evolutionary trajectories. A key priority is to sample species from tropical east Africa.

Director:

Dr. Andrea Weeks

Committee:

Dr. James D. Lawrey
Dr. Cody W. Edwards
Dr. Don Seto,

Notes: The thesis is on reserve in the Johnson Center Library, Fairfax Campus. All members of the George Mason University community are invited to attend.

Dissertation Defense

Candidate: Golala Arya
Title: Endocrine Disrupting Chemicals in Water, Sediments, and Fish Observed in Urban Tributaries of the Freshwater Tidal Potomac River: Occurrence, Bioaccumulation and Tissue Distribution.

Abstract:

The goal of the present study was to assess the ecological impacts of legacy endocrine disruptor chemicals in the upper tidal Potomac River associated with WWTP discharge. The present study was able to quantify total-PCBs and dl-PCBs in bed sediments and biota from Hunting Creek and Gunston cove to evaluate the significance of dl-PCBs in the upper Potomac River, assessed geospatial differences between highly urbanized embayments, compared the fish and sediment profiles of dl-PCBs to identify differences in distributions between matrices, and determined sediment concentrations and profiles of dl-PCBs can be used to predict corresponding concentrations and profiles in fish species.

This study also assessed the ecological impacts of contemporary endocrine disruptor chemicals (EDCs) in Hunting Creek, Accotink Creek and Pohick Creek associated with WWTP discharge. Triclosan and dextromethorphan were the two analytes detected in water, sediments and fish samples. Triclosan (TCS) is a broad spectrum antibacterial mostly used in soap and dextromethorphan (DXM) is an antittusive agent readily available in over-the-counter (OTC) drugs. Tissue distribution analysis for DXM and TCS in fish revealed selective bioaccumulation of the two analytes in skin, stomach and gonads, without any correlation to the lipid content of the perspective tissues. Parental transfer of TCS and DXM to the offspring was also evaluated and warrants further research.

Director or Committee Chair:

Dr. Gregory D. Foster

Committee:

Dr. John Schreifels
Dr. Kim de Mutsert
Dr. Barney Bishop

Notes: The thesis is on reserve in the Johnson Center Library, Fairfax Campus. All members of the George Mason University community are invited to attend.

Dissertation Defense

Candidate: Sangeeta Shukla
Title: Multiscale Modeling of the Regulation of Mitochondrial Function by Metabolites and Ultrastructure

Abstract:

Mitochondria are responsible for producing ATP, the energy currency in all cells.  To do this, the mitochondria has a complex microarchitecture upon which occur biomolecular processes that break down energy substrate to produce ATP.  In a heart which is constantly beating, mitochondrial energy metabolism is well regulated, allowing for increases during exercise. Energy metabolism is thought to be regulated both by changes in metabolite concentration as well as the microarchitecture of the cristae which are the folds in the mitochondrial inner membrane.  The two questions addressed here are 1) how is calcium in the mitochondria regulated and what effect does this have on energy metabolism and 2) how does the cristae structure contribute to the regulation of energy metabolism.  To this end, a multiscale computational modeling approach has been used to integrate experimental information across disparate scales and gain an understanding of the complex dynamics of this system.

Calcium activates three dehydrogenases in the mitochondria and the ATP synthase all of which are involved in energy metabolism.  In the experimental literature there is disagreement upon whether calcium dynamics in the mitochondrial is fast or slow.  Fast dynamics lead to large beat-to-beat changes in mitochondrial calcium.  Slow dynamics result in a time averaging of the calcium transients similar to a low pass filter. The computational studies suggest that slow calcium dynamics are more efficient at stimulating ATP production than fast dynamics.

The cristae structure in mitochondria varies in different cells, under different physiological conditions, and during disease.  We hypothesize that these changes might play role in the efficiency of energy metabolism.  The computational studies suggest that there are gradients in the intercristae spaces of metabolites such as calcium, ATP, and ADP.  These gradients change when mitochondria structure changes.  The computational models also suggest that the changes in gradient affect the efficiency of energy metabolism. With greater accumulation of calcium in mitochondrial matrix, activation of TCA cycle dehydrogenases and ATP synthase produces more ATP. Our model simulations suggest that  depending on the structure, gradients across the length of mitochondrial crista change as does the matrix volume. Such variation in the localized concentrations of metabolites may dictate the overall function of mitochondria.

Director or Committee Chair:

Dr. Saleet Jafri

Committee:

Dr. Iosif Vaisman
Dr. Kim Blackwell

Notes: The thesis is on reserve in the Johnson Center Library, Fairfax Campus. All members of the George Mason University community are invited to attend.

Dissertation Defense

Candidate: Christopher Lockhart
Title: All-Atom Explicit-Solvent Replica-Exchange Molecular Dynamics Simulations of the Alzheimer’s Disease Aβ Monomer

Abstract:

Using all-atom explicit-solvent replica-exchange molecular dynamics simulations, we have explored the changes in the conformational ensemble of the Aβ monomer in various environments. In the simplest case, the Aβ monomer in water forms mostly turn and random coil conformations. We show that the anti-aggregation agent ibuprofen, the zwitterionic DMPC lipid bilayer, and even the introduction of sequence truncation (to generate the Aβ29-40 monomer) are capable of dramatically altering Aβ conformations, resulting in stable helical structure present in the peptide’s C-terminal. For comparison, the FDDNP biomarker and other sequence truncations (e.g., Aβ23-40 and Aβ28-40 monomers) do not exhibit a strong influence on Aβ conformations. Thus, we conclude that there is an inherent helix propensity in the Aβ C-terminal that can be revealed by certain environments.

More specifically, our work has demonstrated that the small ligands ibuprofen and FDDNP bind to the Aβ monomer via the hydrophobic effect. Although ibuprofen promotes a change in Aβ helical content, its low binding affinity and stabilization of the Asp23-Lys28 salt-bridge may partially explain its modest efficiency as an anti-aggregation agent. At the same time, the biomarker FDDNP induces minor change in the Aβ conformational ensemble but binds with high affinity partially due to ligand clustering at hydrophobic binding sites. Although we argue that this benign effect on Aβ is advantageous for in vivo neuroimaging of Aβ fibrils, the high affinity binding of FDDNP to the Aβ monomer raises the question of selectivity of this biomarker.

Finally, we have investigated the interactions of the Aβ monomer with the zwitterionic DMPC bilayer. The bilayer causes a dramatic structural transition in Aβ, resulting in stable C-terminal helix and formation of the Asp23-Lys28 salt-bridge. The central hydrophobic cluster and C-terminal of Aβ not only govern binding to the bilayer but also penetrate into the bilayer hydrophobic core. As a result, Aβ reduces the density of lipids in its binding footprint and indents the bilayer. Addition of calcium to these simulations results in a more profound effect, where lipid disorder and bilayer thinning by Aβ are enhanced. These effects can be explained by a strengthening of Aβ-bilayer interactions by calcium via enhanced electrostatic interactions between charged amino acids and lipid polar headgroups. Binding of Aβ does not affect either water or calcium permeation into the bilayer. We propose that the limited scope of structural perturbations in the zwitterionic bilayer caused by the Aβ monomer represents the molecular basis of its low cytotoxicity.

Director or Committee Chair:

Dr. Dmitri Klimov

Committee:

Dr. Iosif Vaisman
Dr. Saleet Jafri
Dr. Estela Blaisten-Barojas

Notes: A copy of the dissertation is available in the Mercer Library, Prince William Campus. All members of the George Mason University community are invited to attend.

Dissertation Defense

Candidate: Gideon Bass
Title: Ensemble Supervised and Unsupervised Learning with Kepler Variable Stars

Abstract:

Variable star analysis and classification is an important task in the understanding of stellar features and processes. While historically classifications have been done manually by highly skilled experts, the recent and rapid expansion in the quantity and quality of data has demanded new techniques, most notably automatic classification through supervised machine learning. I present a study on variable stars in the Kepler field using these techniques, and the novel work of unsupervised learning. I use new methods of characterization and multiple independent classifiers to produce an ensemble classifier that equals or matches existing classification abilities. I also explore the possibilities of  unsupervised learning in discovering novel feature of these stars.

Dissertation Director:

Dr. Joe Weingartner

Committee:

Dr. Kirk Borne
Dr. Michael Summers
Dr. Ruixin Yang

Notes: The thesis is on reserve in the Johnson Center Library, Fairfax Campus. All members of the George Mason University community are invited to attend.

Dissertation Defense

Candidate: Massih Abawi
Title: Imbalance of Selected Hormones in Non-Alcoholic Fatty Liver Disease (NAFLD) and Non-Alcoholic Steatohepatitis (NASH)

Abstract:

Non-alcoholic fatty liver disease (NAFLD) is an increasingly common condition affecting about 70% of obese individuals and is now considered a major cause of liver-related morbidity and mortality.  NAFLD encompasses a spectrum of hepatic pathologies with excessive accumulation of fat in the liver in patients consuming less than 20 grams of alcohol per day.  NAFLD related liver injury ranges from simple hepatic steatosis to more severe forms of the disease including NASH, which can progress to fibrosis, cirrhosis, and ultimately organ failure.  There is evidence that causally links NAFLD with imbalance of various hormones, especially these also involved in the development of insulin resistance and obesity.

The research presented herein involves quantitation of various soluble hormones in serum of morbidly obese bariatric patients with different confirmed stages of NAFLD. The first study explores the role of vitamin D deficiency in NAFLD/NASH patients. Serum samples of 210 morbidly obese bariatric patients were profiled for the following markers: 25(OH)D3; Vitamin D Binding protein (VDBP); Intact Parathyroid Hormone (1-84) and Cytokeratin 18 (M30) levels.  The second study herein profiles three small gastric peptides, acylated ghrelin (AG), non-acylated ghrelin (DAG), and Obestatin, and a number of proinflammatory cytokines in circulation of patients with obesity related NAFLD.  In both studies, correlation analysis was conducted to associate these biomarkers with clinical parameters routinely measured in NAFLD patients, including histological scores of inflammation and fibrosis of their liver biopsies, and predictive regression models were built. A third study reported herein investigates the interplay of circulatory melanogenesis-related hormones, α-Melanocyte Stimulating Hormone (α-MSH) and Melanin Concentrating Hormone (MCH), with NAFLD and obesity-induced low grade chronic.

Director or Committee Chair:

Dr. Ancha Baranova

Committee:

Dr. Kylene Kehn-Hall, Dr. Emanuel F. Petricoin III, Dr. Timothy Born

Notes: The thesis is on reserve in Gateway Library, Science and Technology Campus. All members of the George Mason University community are invited to attend.