E-conferencing: Corpus and Discourse Insights

A selection of recent work by experts in academic written discourse illustrates how corpus linguistics and discourse analysis can work as complementary approaches

One-pot synthesis and aqueous solution properties of pH-responsive schizophrenic diblock copolymer nanoparticles prepared via RAFT aqueous dispersion polymerization

Schizophrenic diblock copolymers can form two types of nanoparticles in aqueous solution, with such self-assembly typically being driven by a change in solution temperature, solution pH or salt concentration. In the present study, we report the first wholly aqueous one-pot synthesis of a doubly pH-responsive schizophrenic diblock copolymer. This is achieved using RAFT aqueous dispersion polymerization, which is an example of polymerization-induced self-assembly (PISA). First, 2-(diethylamino)ethyl methacrylate (DEA) is homopolymerized in its protonated form at pH 2 to produce a cationic polyelectrolytic precursor. Subsequently, the RAFT aqueous dispersion polymerization of 2-carboxyethyl acrylate (CEA) is conducted to produce sterically-stabilized diblock copolymer nanoparticles in which the cationic PDEA block acts as the hydrophilic stabilizer block and the neutral PCEA block forms the hydrophobic core. On addition of sufficient NaOH, the PCEA becomes highly anionic at pH 10 and hence acts as a stabilizer block while the deprotonated PDEA block forms the hydrophobic core. Characterizing such polyampholytes via aqueous gel permeation chromatography is challenging. Thus a selective methylation protocol was developed to esterify the anionic carboxylate groups in the PCEA block to enable GPC analysis using THF as an eluent. However, optimization of the reaction conditions was required because using too large an excess of the trimethylsilyldiazomethane reagent led to unwanted quaternization of the tertiary amine groups on the PDEA block, which prevented meaningful GPC analysis. The aqueous self-assembly behaviour of a series of PDEA–PCEA diblock copolymers was examined using transmission electron microscopy, dynamic light scattering, 1H NMR spectroscopy and aqueous electrophoresis

Aqueous solution behavior of stimulus-responsive poly(methacrylic acid)-poly(2-hydroxypropyl methacrylate) diblock copolymer nanoparticles

Poly(methacrylic acid)-poly(2-hydroxypropyl methacrylate) (PMAA50-PHPMA237) diblock copolymer nanoparticles are synthesized via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization, which is an example of polymerization-induced self-assembly (PISA). These nanoparticles exhibit complex stimulus-responsive behavior in dilute aqueous solution. They undergo macroscopic precipitation at low pH owing to protonation of the PMAA steric stabilizer. However, adjusting the solution pH above the pKa of 6.3 for the PMAA block ensures colloidal stability and confers thermoresponsive behavior. The degree of ionization of these anionic stabilizer chains increases at high pH, which leads to increasingly negative zeta potentials as judged by aqueous electrophoresis. Variable temperature dynamic light scattering (DLS) studies indicate the formation of progressively larger nanoparticles at higher temperatures, with TEM images providing evidence for weakly anisotropic nanoparticles at 50 °C. These observations are consistent with variable temperature 1H NMR spectroscopy studies, which indicate gradual dehydration of the structure-directing PHPMA block. Rheology measurements on a 20% w/w copolymer dispersion indicate a critical gelation temperature of around 10 °C and a gel modulus (G′) of approximately 1000 Pa at 25 °C. Shear-induced polarized light imaging (SIPLI) studies confirm the presence of weakly anisotropic worm-like particles under such conditions

Aqueous one-pot synthesis of well-defined zwitterionic diblock copolymers by RAFT polymerization : an efficient and environmentally-friendly route to a useful dispersant for aqueous pigments

Various examples of well-defined zwitterionic diblock copolymers have been reported in the literature. However, synthetic routes to such copolymers have almost invariably involved protecting group chemistry and/or multi-step syntheses. Herein we use reversible addition–fragmentation chain transfer (RAFT) polymerization to develop an atom-efficient, wholly aqueous one-pot synthesis of zwitterionic diblock copolymers comprising anionic methacrylic acid (MAA) and cationic 2-(dimethylamino)ethyl methacrylate (DMA) repeat units. Empirically, we find that polymerizing DMA first leads to a more well-defined block architecture and a narrower molecular weight distribution as judged by 1H NMR spectroscopy and gel permeation chromatography, respectively. Aqueous electrophoresis studies indicate that the isoelectric point (IEP) exhibited by such zwitterionic diblock copolymers in aqueous solution can be tuned by varying the relative proportions of the anionic and cationic comonomers. The convenient removal of trithiocarbonate-based RAFT end-groups can be achieved using aqueous hydrazine, with subsequent macroscopic precipitation of the crude zwitterionic diblock copolymer at its IEP facilitating a highly convenient wholly aqueous work-up. This augurs well for potential applications of these fascinating materials. In this context, we show that such zwitterionic diblock copolymers serve as highly effective dispersants for nano-sized transparent yellow iron oxide nanoparticles, a notoriously problematic aqueous pigment

Synthesis of polyampholytic diblock copolymers via RAFT aqueous solution polymerization

We report the synthesis of two new classes of polyampholytic diblock copolymers by RAFT aqueous solution polymerization. In each case, poly(methacrylic acid) (PMAA) is the anionic block while the cationic block comprises either poly(2-N-(morpholino)ethyl methacrylate) (PMEMA) or poly(2-(methacryloyloxy)ethyl trimethylammonium chloride) (PMETAC). Empirically, we found that polymerizing methacrylic acid as the second block afforded more well-defined diblock copolymers. Using this protocol, a series of copolymers of varying diblock composition is prepared for both classes. Robust derivatization protocols are developed to aid the characterization of such diblock copolymers via gel permeation chromatography (GPC). Thus the carboxylic acid groups within the PMAA block of the PMEMA–PMAA diblock copolymers are selectively methylated without quaternization of the tertiary amine groups on the PMEMA chains. In contrast, PMETAC–PMAA diblock copolymers are subjected to forced hydrolysis of the PMETAC ester groups to produce a PMAA homopolymer, which is then methylated to produce poly(methyl methacrylate) samples for GPC analysis. The aqueous solution properties of such polyampholytic diblock copolymers are explored using dynamic light scattering (DLS) and aqueous electrophoresis. These techniques enable identification of the isoelectric point. Unlike most other polyampholytic diblock copolymers reported in the literature, the PMEMA–PMAA diblock copolymers exhibit minimal variation in their isoelectric point when adjusting the diblock copolymer composition. This is because the pKa of the acidic PMAA block is close to the pKa of the conjugate acid form of the basic PMEMA block. For the PMETAC–PMAA system, no IEP is observed for PMETAC-rich copolymers because there is insufficient anionic charge to compensate for the cationic charge even if the PMAA chains are fully ionized

Chronic Periodontitis Genome-wide Association Studies: Gene-centric and Gene Set Enrichment Analyses

Recent genome-wide association studies (GWAS) of chronic periodontitis (CP) offer rich data sources for the investigation of candidate genes, functional elements, and pathways. We used GWAS data of CP (n = 4,504) and periodontal pathogen colonization (n = 1,020) from a cohort of adult Americans of European descent participating in the Atherosclerosis Risk in Communities study and employed a MAGENTA approach (i.e., meta-analysis gene set enrichment of variant associations) to obtain gene-centric and gene set association results corrected for gene size, number of single-nucleotide polymorphisms, and local linkage disequilibrium characteristics based on the human genome build 18 (National Center for Biotechnology Information build 36). We used the Gene Ontology, Ingenuity, KEGG, Panther, Reactome, and Biocarta databases for gene set enrichment analyses. Six genes showed evidence of statistically significant association: 4 with severe CP (NIN, p = 1.6 × 10−7; ABHD12B, p = 3.6 × 10−7; WHAMM, p = 1.7 × 10−6; AP3B2, p = 2.2 × 10−6) and 2 with high periodontal pathogen colonization (red complex–KCNK1, p = 3.4 × 10−7; Porphyromonas gingivalis–DAB2IP, p = 1.0 × 10−6). Top-ranked genes for moderate CP were HGD (p = 1.4 × 10−5), ZNF675 (p = 1.5 × 10−5), TNFRSF10C (p = 2.0 × 10−5), and EMR1 (p = 2.0 × 10−5). Loci containing NIN, EMR1, KCNK1, and DAB2IP had showed suggestive evidence of association in the earlier single-nucleotide polymorphism–based analyses, whereas WHAMM and AP2B2 emerged as novel candidates. The top gene sets included severe CP (“endoplasmic reticulum membrane,” “cytochrome P450,” “microsome,” and “oxidation reduction”) and moderate CP (“regulation of gene expression,” “zinc ion binding,” “BMP signaling pathway,” and “ruffle”). Gene-centric analyses offer a promising avenue for efficient interrogation of large-scale GWAS data. These results highlight genes in previously identified loci and new candidate genes and pathways possibly associated with CP, which will need to be validated via replication and mechanistic studies

P2X receptors: epithelial ion channels and regulators of salt and water transport.

When the results from electrophysiological studies of renal epithelial cells are combined with data from in vivo tubule microperfusion experiments and immunohistochemical surveys of the nephron, the accumulated evidence suggests that ATP-gated ion channels, P2X receptors, play a specialized role in the regulation of ion and water movement across the renal tubule and are integral to electrolyte and fluid homeostasis. In this short review, we discuss the concept of P2X receptors as regulators of salt and water salvage pathways, as well as acknowledging their accepted role as ATP-gated ion channels

Novel diabetes gene discovery through comprehensive characterization and integrative analysis of longitudinal gene expression changes

Type 2 diabetes is a complex, systemic disease affected by both genetic and environmental factors. Previous research has identified genetic variants associated with type 2 diabetes risk; however, gene regulatory changes underlying progression to metabolic dysfunction are still largely unknown. We investigated RNA expression changes that occur during diabetes progression using a two-stage approach. In our discovery stage, we compared changes in gene expression using two longitudinally collected blood samples from subjects whose fasting blood glucose transitioned to a level consistent with type 2 diabetes diagnosis between the time points against those who did not with a novel analytical network approach. Our network methodology identified 17 networks, one of which was significantly associated with transition status. This 822-gene network harbors many genes novel to the type 2 diabetes literature but is also significantly enriched for genes previously associated with type 2 diabetes. In the validation stage, we queried associations of genetically determined expression with diabetes-related traits in a large biobank with linked electronic health records. We observed a significant enrichment of genes in our identified network whose genetically determined expression is associated with type 2 diabetes and other metabolic traits and validated 31 genes that are not near previously reported type 2 diabetes loci. Finally, we provide additional functional support, which suggests that the genes in this network are regulated by enhancers that operate in human pancreatic islet cells. We present an innovative and systematic approach that identified and validated key gene expression changes associated with type 2 diabetes transition status and demonstrated their translational relevance in a large clinical resource

Genome-wide Association Study of Periodontal Pathogen Colonization

Pathological shifts of the human microbiome are characteristic of many diseases, including chronic periodontitis. To date, there is limited evidence on host genetic risk loci associated with periodontal pathogen colonization. We conducted a genome-wide association (GWA) study among 1,020 white participants of the Atherosclerosis Risk in Communities Study, whose periodontal diagnosis ranged from healthy to severe chronic periodontitis, and for whom “checkerboard” DNA-DNA hybridization quantification of 8 periodontal pathogens was performed. We examined 3 traits: “high red” and “high orange” bacterial complexes, and “high” Aggregatibacter actinomycetemcomitans (Aa) colonization. Genotyping was performed on the Affymetrix 6.0 platform. Imputation to 2.5 million markers was based on HapMap II-CEU, and a multiple-test correction was applied (genome-wide threshold of p < 5 × 10−8). We detected no genome-wide significant signals. However, 13 loci, including KCNK1, FBXO38, UHRF2, IL33, RUNX2, TRPS1, CAMTA1, and VAMP3, provided suggestive evidence (p < 5 × 10−6) of association. All associations reported for “red” and “orange” complex microbiota, but not for Aa, had the same effect direction in a second sample of 123 African-American participants. None of these polymorphisms was associated with periodontitis diagnosis. Investigations replicating these findings may lead to an improved understanding of the complex nature of host-microbiome interactions that characterizes states of health and disease

Enrichment analyses identify shared associations for 25 quantitative traits in over 600,000 individuals from seven diverse ancestries

Since 2005, genome-wide association (GWA) datasets have been largely biased toward sampling European ancestry individuals, and recent studies have shown that GWA results estimated from self-identified European individuals are not transferable to non-European individuals because of various confounding challenges. Here, we demonstrate that enrichment analyses that aggregate SNP-level association statistics at multiple genomic scales—from genes to genomic regions and pathways—have been underutilized in the GWA era and can generate biologically interpretable hypotheses regarding the genetic basis of complex trait architecture. We illustrate examples of the robust associations generated by enrichment analyses while studying 25 continuous traits assayed in 566,786 individuals from seven diverse self-identified human ancestries in the UK Biobank and the Biobank Japan as well as 44,348 admixed individuals from the PAGE consortium including cohorts of African American, Hispanic and Latin American, Native Hawaiian, and American Indian/Alaska Native individuals. We identify 1,000 gene-level associations that are genome-wide significant in at least two ancestry cohorts across these 25 traits as well as highly conserved pathway associations with triglyceride levels in European, East Asian, and Native Hawaiian cohorts