Day EA, Ford RJ, Smith BK, Mohammadi-Shemirani P, Morrow MR, Gutgesell RM, Lu R, Raphenya AR, Kabiri M, McArthur AG, McInnes N, Hess S, Paré G, Gerstein HC, Steinberg GR

Nature Metabolism 2019 Dec. 9 [Epub ahead of print]

Metformin is the most commonly prescribed medication for type 2 diabetes, owing to its glucose-lowering effects, which are mediated through the suppression of hepatic glucose production. However, in addition to its effects on the liver, metformin reduces appetite and in preclinical models exerts beneficial effects on ageing and a number of diverse diseases (for example, cognitive disorders, cancer, cardiovascular disease) through mechanisms that are not fully understood. Given the high concentration of metformin in the liver and its many beneficial effects beyond glycemic control, we reasoned that metformin may increase the secretion of a hepatocyte-derived endocrine factor that communicates with the central nervous system4. Here we show, using unbiased transcriptomics of mouse hepatocytes and analysis of proteins in human serum, that metformin induces expression and secretion of growth differentiating factor 15 (GDF15). In primary mouse hepatocytes, metformin stimulates the secretion of GDF15 by increasing the expression of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP; also known as DDIT3). In wild-type mice fed a high-fat diet, oral administration of metformin increases serum GDF15 and reduces food intake, body mass, fasting insulin and glucose intolerance; these effects are eliminated in GDF15 null mice. An increase in serum GDF15 is also associated with weight loss in patients with type 2 diabetes who take metformin. Although further studies will be required to determine the tissue source(s) of GDF15 produced in response to metformin in vivo, our data indicate that the therapeutic benefits of metformin on appetite, body mass and serum insulin depend on GDF15.

See the Commentary in SciTechDaily.

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Ahmad S, Wang B, Walker MD, Tran H-KR, Stogios PJ, Savchenko A, Grant RA, McArthur AG, Laub MT, Whitney JC

Nature 2019 Nov 6. [Epub ahead of print]

Bacteria have evolved sophisticated mechanisms to inhibit the growth of competitors. One such mechanism involves type VI secretion systems, which bacteria can use to inject antibacterial toxins directly into neighbouring cells. Many of these toxins target the integrity of the cell envelope, but the full range of growth inhibitory mechanisms remains unknown. Here we identify a type VI secretion effector, Tas1, in the opportunistic pathogen Pseudomonas aeruginosa. The crystal structure of Tas1 shows that it is similar to enzymes that synthesize (p)ppGpp, a broadly conserved signalling molecule in bacteria that modulates cell growth rate, particularly in response to nutritional stress. However, Tas1 does not synthesize (p)ppGpp; instead, it pyrophosphorylates adenosine nucleotides to produce (p)ppApp at rates of nearly 180,000 molecules per minute. Consequently, the delivery of Tas1 into competitor cells drives rapid accumulation of (p)ppApp, depletion of ATP, and widespread dysregulation of essential metabolic pathways, thereby resulting in target cell death. Our findings reveal a previously undescribed mechanism for interbacterial antagonism and demonstrate a physiological role for the metabolite (p)ppApp in bacteria.

See the Commentary at Nature.

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Alcock BP, Raphenya AR, Lau TTY, Tsang KK, Bouchard M, Edalatmand A, Huynh W, Nguyen A-LV, Cheng AA, Liu S, Min SY, Miroshnichenko A, Tran H-K, Werfalli RE, Nasir JA, Oloni M, Speicher DJ, Florescu A, Singh B, Faltyn M, Hernandez-Koutoucheva A, Sharma AN, Bordeleau E, Pawlowski AC, Zubyk HL, Dooley D, Griffiths E, Maguire F, Winsor GL, Beiko RG, Brinkman FSL, Hsiao WWL, Van Domselaar G, McArthur AG.

Nucleic Acids Research 2019 Oct 29. [Epub ahead of print]

The Comprehensive Antibiotic Resistance Database (CARD; https://card.mcmaster.ca) is a curated resource providing reference DNA and protein sequences, detection models and bioinformatics tools on the molecular basis of bacterial antimicrobial resistance (AMR). CARD focuses on providing high-quality reference data and molecular sequences within a controlled vocabulary, the Antibiotic Resistance Ontology (ARO), designed by the CARD biocuration team to integrate with software development efforts for resistome analysis and prediction, such as CARD’s Resistance Gene Identifier (RGI) software. Since 2017, CARD has expanded through extensive curation of reference sequences, revision of the ontological structure, curation of over 500 new AMR detection models, development of a new classification paradigm and expansion of analytical tools. Most notably, a new Resistomes & Variants module provides analysis and statistical summary of in silico predicted resistance variants from 82 pathogens and over 100 000 genomes. By adding these resistance variants to CARD, we are able to summarize predicted resistance using the information included in CARD, identify trends in AMR mobility and determine previously undescribed and novel resistance variants. Here, we describe updates and recent expansions to CARD and its biocuration process, including new resources for community biocuration of AMR molecular reference data.

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Guitor AK, Raphenya AR, Klunk J, Kuch M, Alcock B, Surette MG, McArthur AG, Poinar HN, Wright GD.

Editor’s Pick! Antimicrobial Agents and Chemotherapy 2019 Oct 14. [Epub ahead of print]

The identification and association of the nucleotide sequences encoding antibiotic resistance elements is critical to improve surveillance and monitor trends in antibiotic resistance. Current methods to study antibiotic resistance in various environments rely on extensive deep sequencing or laborious culturing of fastidious organisms, which are both heavily time-consuming operations. An accurate and sensitive method to identify both rare and common resistance elements in complex metagenomic samples is needed. Referencing the Comprehensive Antibiotic Resistance Database, we designed a set of 37,826 probes to specifically target over 2000 nucleotide sequences associated with antibiotic resistance in clinically relevant bacteria. Testing of this probeset on DNA libraries generated from multi-drug resistant bacteria to selectively capture resistance genes reproducibly produced higher reads on-target at greater length of coverage when compared to shotgun sequencing. We also identified additional resistance gene sequences from human gut microbiome samples that sequencing alone was not able to detect. Our method to capture the resistome enables sensitive gene detection in diverse environments where antibiotic resistance represents less than 0.1% of the metagenome.

Download the Baits & Protocol at the Comprehensive Antibiotic Resistance Database!

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Waglechner N, McArthur AG, Wright GD.

Nat Microbiol. 2019 Aug 12. [Epub ahead of print]

Glycopeptide antibiotics are produced by Actinobacteria through biosynthetic gene clusters that include genes supporting their regulation, synthesis, export and resistance. The chemical and biosynthetic diversities of glycopeptides are the product of an intricate evolutionary history. Extracting this history from genome sequences is difficult as conservation of the individual components of these gene clusters is variable and each component can have a different trajectory. We show that glycopeptide biosynthesis and resistance in Actinobacteria maps to approximately 150-400 million years ago. Phylogenetic reconciliation reveals that the precursors of glycopeptide biosynthesis are far older than other components, implying that these clusters arose from a pre-existing pool of genes. We find that resistance appeared contemporaneously with biosynthetic genes, raising the possibility that the mechanism of action of glycopeptides was a driver of diversification in these gene clusters. Our results put antibiotic biosynthesis and resistance into an evolutionary context and can guide the future discovery of compounds possessing new mechanisms of action, which are especially needed as the usefulness of the antibiotics available at present is imperilled by human activity.

More details at McMaster’s Brighter World.

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Kariuki MW, Githui E, McArthur AG, Aman RA, Njagi NM, Mwangemi AC, Kamau LW

Annual Research & Review in Biology, 32, 1-12.

Novel gene targets are needed in accurate diagnosis of malaria. Previous studies show that the dynein light chains (dlc) in Plasmodium are uniquely conserved within the species, possibly due to their role as the cargo adptor moiety. This study aimed at the development of PCR assay for the detection of Plasmodium based on the (dlc-Tctex) as a genus and species-specific tool in malaria diagnosis. Multiple primers were designed based on Plasmodium spp dlc(Tctex) genes. The primers were applied on PCR to detect malaria on clinical samples and on laboratory maintained isolates of P. falciparum and P. vivax for human infecting species and P. knowlesi and P. cynomolgi for zoonoses infection involving primates. The amplified PCR fragments were gene cleaned and sequenced. BLASTn e-values output from the raw nucleotide queries supports that the genes are uniquely conserved. Species-specific primers amplified P. falciparum infections with no cross-reactivity to P. vivax, P. knowlesi or P. cynomolgi species. In this assay only 11 out of the 30 microscope positive malaria positive clinical blood samples were positive for PCR detection of P. falciparum infection. Primers designed for Plasmodium genus amplified the target band in all clinical malaria samples but also had another specific band amplification. This preliminary data demonstrate that a species-specific dlc(Tctex) PCR assay can be used for detection of P. falciparum and optimized genus primers can be applied to differentiate mixed malaria infections.

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Faltyn, M., B. Alcock, & A.G. McArthur. 2019. Evolution and nomenclature of the trimethoprim resistant dihydrofolate (dfr) reductases. Preprints 2019, 2019050137. [Preprint]

Tsang, K.K., D.J. Speicher, & A.G. McArthur. 2019. Pathogen taxonomy updates at the Comprehensive Antibiotic Resistance Database: Implications for molecular epidemiology. Preprints 2019, 2019070222. [Preprint]

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Srinivasan, K.A., S.K. Virdee, & A.G. McArthur. 2019. Strandedness during cDNA synthesis, the stranded parameter in htseq-count, and analysis of RNA-Seq data. Preprints 2019, 2019030124. [Preprint]

Matthews, T., F. Bristow, E. Griffiths, A. Petkau, J. Adam, D. Dooley, P. Kruczkiewicz, J. Curatcha, J. Cabral, D. Fornika, G. Winsor, M. Courtot, C. Bertelli, A. Roudgar, P. Fejaio, P. Mabon, E. Enns, J. Thiessen, A.W.S. Keddy, J. Isaac-Renton, J. Gardy, P. Tang, The IRIDA consortium, J. Carriço, L. Chindelevitch, C. Chauve, M. Graham, A.G. McArthur, E. Taboada, R. Beiko, F.S.L. Brinkman, W.W.L. Hsiao, & G. Van Domselaar. 2018. The Integrated Rapid Infectious Disease Analysis (IRIDA) Platform. BioRxiv 381830 [Preprint].

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McGlory C, von Allmen MT, Stokes T, Morton RW, Hector AJ, Lago BA, Raphenya AR, Smith BK, McArthur AG, Steinberg GR, Baker SK, Phillips SM

J Gerontol A Biol Sci Med Sci. 2018 Jul 9;73(8):1070-1077.

(Press release: Putting your feet up for as little as two weeks can trigger diabetic symptoms in vulnerable patients)

BACKGROUND: Physical inactivity impairs insulin sensitivity, which is exacerbated with aging. We examined the impact of 2 wk of acute inactivity and recovery on glycemic control, and integrated rates of muscle protein synthesis in older men and women.

METHODS: Twenty-two overweight, prediabetic older adults (12 men, 10 women, 69 ± 4 y) undertook 7 d of habitual activity (baseline; BL), step reduction (SR; <1,000 steps.d-1 for 14 d), followed by 14 d of recovery (RC). An oral glucose tolerance test was used to assess glycemic control and deuterated water ingestion to measure integrated rates of muscle protein synthesis.

RESULTS: Daily step count was reduced (all p < .05) from BL at SR (7362 ± 3294 to 991 ± 97) and returned to BL levels at RC (7117 ± 3819). Homeostasis model assessment-insulin resistance increased from BL to SR and Matsuda insulin sensitivity index decreased and did not return to BL in RC. Glucose and insulin area under the curve were elevated from BL to SR and did not recover in RC. Integrated muscle protein synthesis was reduced during SR and did not return to BL in RC.

CONCLUSIONS: Our findings demonstrate that 2 wk of SR leads to lowered rates of muscle protein synthesis and a worsening of glycemic control that unlike younger adults is not recovered during return to normal activity in overweight, prediabetic elderly humans.

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Morgan TD, Graham CF, McArthur AG, Raphenya AR, Boreham DR, Manzon RG, Wilson JY, Lance SL, Howland KL, Patrick PH, Somers CM

Canadian Journal of Fisheries and Aquatic Sciences 2018 75(6):836-849.

Round whitefish (Prosopium cylindraceum) have a broad, disjunct range across northern North America and Eurasia, and little is known about their genetic population structure. We performed genetic analyses of round whitefish from 17 sites across its range using nine microsatellites, two mitochondrial DNA (mtDNA) loci, and 4918 to 8835 single-nucleotide polymorphism (SNP) loci. Our analyses identified deep phylogenetic division between eastern and western portions of the range, likely indicative of origins from at least two separate Pleistocene glacial refugia. Regionally, microsatellites and SNPs identified congruent patterns in subdivision, and population structure was consistent with expectations based on hydrologic connectivity. Within the Laurentian Great Lakes, Lake Huron and Lake Ontario were identified as key areas of interest. Lake Huron appears to be a contemporary source population for several other Great Lakes, and Lake Ontario contains a genetically discrete group of round whitefish. In all cases, multiple genetic markers yielded similar patterns, but SNPs offered substantially enhanced resolution. We conclude that round whitefish have population subdivision on several scales important for understanding their evolutionary history and conservation planning.

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