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Rosenzweig R.,University of Toronto | Kay L.E.,University of Toronto | Kay L.E.,Hospital for Sick Children
Annual Review of Biochemistry | Year: 2014

Large macromolecular assemblies, so-called molecular machines, are critical to ensuring proper cellular function. Understanding how proper function is achieved at the atomic level is crucial to advancing multiple avenues of biomedical research. Biophysical studies often include X-ray diffraction and cryo-electron microscopy, providing detailed structural descriptions of these machines. However, their inherent flexibility has complicated an understanding of the relation between structure and function. Solution NMR spectroscopy is well suited to the study of such dynamic complexes, and continued developments have increased size boundaries; insights into function have been obtained for complexes with masses as large as 1 MDa. We highlight methyl-TROSY (transverse relaxation optimized spectroscopy) NMR, which enables the study of such large systems, and include examples of applications to several cellular machines. We show how this emerging technique contributes to an understanding of cellular function and the role of molecular plasticity in regulating an array of biochemical activities. Copyright © 2014 by Annual Reviews. All rights reserved.


Back S.A.,Oregon Health And Science University | Miller S.P.,Hospital for Sick Children | Miller S.P.,University of Toronto
Annals of Neurology | Year: 2014

With advances in neonatal care, preterm neonates are surviving with an evolving constellation of motor and cognitive disabilities that appear to be related to widespread cellular maturational disturbances that target cerebral gray and white matter. Whereas preterm infants were previously at high risk for destructive brain lesions that resulted in cystic white matter injury and secondary cortical and subcortical gray matter degeneration, contemporary cohorts of preterm survivors commonly display less severe injury that does not appear to involve pronounced glial or neuronal loss. Nevertheless, these milder forms of injury are also associated with reduced cerebral growth. Recent human and experimental studies support that impaired cerebral growth is related to disparate responses in gray and white matter. Myelination disturbances in cerebral white matter are related to aberrant regeneration and repair responses to acute death of premyelinating late oligodendrocyte progenitors (preOLs). In response to preOL death, early oligodendrocyte progenitors rapidly proliferate and differentiate, but the regenerated preOLs fail to normally mature to myelinating cells required for white matter growth. Although immature neurons appear to be more resistant to cell death from hypoxia-ischemia than glia, they display widespread disturbances in maturation of their dendritic arbors, which further contribute to impaired cerebral growth. These complex and disparate responses of neurons and preOLs thus result in large numbers of cells that fail to fully mature during a critical window in development of neural circuitry. These recently recognized forms of cerebral gray and white matter dysmaturation raise new diagnostic challenges and suggest new therapeutic directions centered on reversal of the processes that promote dysmaturation. Ann Neurol 2014;75:469-486 © 2014 American Neurological Association.


Weinstein S.L.,University of Iowa | Dolan L.A.,University of Iowa | Wright J.G.,Hospital for Sick Children | Dobbs M.B.,University of Washington
New England Journal of Medicine | Year: 2013

BACKGROUND: The role of bracing in patients with adolescent idiopathic scoliosis who are at risk for curve progression and eventual surgery is controversial. METHODS: We conducted a multicenter study that included patients with typical indications for bracing due to their age, skeletal immaturity, and degree of scoliosis. Both a randomized cohort and a preference cohort were enrolled. Of 242 patients included in the analysis, 116 were randomly assigned to bracing or observation, and 126 chose between bracing and observation. Patients in the bracing group were instructed to wear the brace at least 18 hours per day. The primary outcomes were curve progression to 50 degrees or more (treatment failure) and skeletal maturity without this degree of curve progression (treatment success). RESULTS: The trial was stopped early owing to the efficacy of bracing. In an analysis that included both the randomized and preference cohorts, the rate of treatment success was 72% after bracing, as compared with 48% after observation (propensity-score-adjusted odds ratio for treatment success, 1.93; 95% confidence interval [CI], 1.08 to 3.46). In the intention-to-treat analysis, the rate of treatment success was 75% among patients randomly assigned to bracing, as compared with 42% among those randomly assigned to observation (odds ratio, 4.11; 95% CI, 1.85 to 9.16). There was a significant positive association between hours of brace wear and rate of treatment success (P<0.001). CONCLUSIONS: Bracing significantly decreased the progression of high-risk curves to the threshold for surgery in patients with adolescent idiopathic scoliosis. The benefit increased with longer hours of brace wear. Copyright © 2013 Massachusetts Medical Society.


Casey J.R.,University of Alberta | Grinstein S.,Hospital for Sick Children | Orlowski J.,McGill University
Nature Reviews Molecular Cell Biology | Year: 2010

Protons dictate the charge and structure of macromolecules and are used as energy currency by eukaryotic cells. The unique function of individual organelles therefore depends on the establishment and stringent maintenance of a distinct pH. This, in turn, requires a means to sense the prevailing pH and to respond to deviations from the norm with effective mechanisms to transport, produce or consume proton equivalents. A dynamic, finely tuned balance between proton-extruding and proton-importing processes underlies pH homeostasis not only in the cytosol, but in other cellular compartments as well.


Canton J.,Hospital for Sick Children | Grinstein S.,Li Ka Shing Knowledge Institute
Trends in Immunology | Year: 2014

In mammals, engagement of Toll-like receptors by microbe-associated molecular patterns enhances the responsiveness of NADPH oxidases. Two recent papers report a similar 'priming' mechanism for the plant oxidase RbohD. Despite lacking structural homology, the functional parallels between plants and animals reveal that a common regulatory logic arose by convergent evolution. © 2014 Elsevier Ltd.


Cemma M.,Hospital for Sick Children
Current biology : CB | Year: 2012

Autophagy is a conserved cellular degradative pathway that is now established to be a vital part of the host immune response to microbial infection. Autophagy can directly eliminate intracellular pathogens by mediating their delivery to lysosomes. Canonical autophagy is characterized by the formation of a double-membrane autophagosome and the involvement of over 35 autophagy-related proteins (Atgs), including a commonly used autophagosome marker in mammalian cells, LC3. Recent studies have shown that a subset of autophagy components can lead to LC3 conjugation onto phagosomes. This process of LC3-associated phagocytosis (LAP) results in the degradation of the cargo by promoting phagosome fusion with lysosomes. Other components of the autophagy machinery also play roles in immunity that are distinct from the canonical autophagy and LAP pathways. This minireview highlights the complicated relationship between autophagy components and intracellular bacteria, including bacterial targeting mechanisms and the interaction between autophagy and effectors/toxins secreted by bacteria. Copyright © 2012 Elsevier Ltd. All rights reserved.


Offringa M.,Hospital for Sick Children
Cochrane database of systematic reviews (Online) | Year: 2012

Febrile seizures occurring in a child older than one month during an episode of fever affect 2% to 4% of children in Great Britain and the United States and recur in 30%. Rapid-acting antiepileptics and antipyretics given during subsequent fever episodes have been used to avoid the adverse effects of continuous antiepileptic drugs. To evaluate the effectiveness and safety of antiepileptic and antipyretic drugs used prophylactically to treat children with febrile seizures. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011. Issue 3); MEDLINE (1966 to May 2011); EMBASE (1966 to May 2011); Database of Abstracts of Reviews of Effectiveness (DARE) (May 2011). No language restrictions were imposed. We also contacted researchers in the field to identify continuing or unpublished studies. Trials using randomised or quasi-randomised patient allocation that compared the use of antiepileptic or antipyretic agents with each other, placebo or no treatment. Two review authors (RN and MO) independently applied pre-defined criteria to select trials for inclusion and extracted the pre-defined relevant data, recording methods for randomisation, blinding and exclusions. Outcomes assessed were seizure recurrence at 6, 12, 18, 24, 36 months and at age 5 to 6 years in the intervention and non-intervention groups, and adverse medication effects. The presence of publication bias was assessed using funnel plots. Thirty-six articles describing 26 randomised trials with 2740 randomised participants were included. Thirteen interventions of continuous or intermittent prophylaxis and their control treatments were analysed. Methodological quality was moderate to poor in most studies. We could not do a meta-analysis for eight of the 13 comparisons due to insufficient numbers of trials. No significant benefit for valproate, pyridoxine, intermittent phenobarbitone or ibuprofen versus placebo or no treatment was found; nor for diclofenac versus placebo followed by ibuprofen, acetominophen or placebo; nor for intermittent rectal diazepam versus intermittent valproate, nor phenobarbitone versus intermittent rectal diazepam.There was a significant reduction of recurrent febrile seizures with intermittent oral diazepam versus placebo with a relative risk (RR) of  0.67 (95% confidence interval (CI) 0.48 to 0.94) at 24 months), RR of 0.61 (95% CI 0.15 to 0.89) at 48 months, with no benefit at 6, 12 or 72 months. Phenobarbitone versus placebo or no treatment reduced seizures at 6, 12 and 24 months but not at 18 or 72 month follow up (RR 0.60, 95% CI 0.42 to 0.84 at 6 months; RR 0.59, 95% CI 0.46 to 0.75 at 12 months; and RR 0.65, 95% CI 0.49 to 0.88 at 24 months). Intermittent rectal diazepam versus no treatment or placebo also reduced seizures (RR 0.60, 95% CI 0.41 to 0.86 at 6 months; RR 0.65, 95% CI 0.49 to 0.87 at 12 months; RR 0.2, 95% CI 0.1 to 0.39 at 18 months; RR 0.36, 95% CI 0.18 to 0.71 at 36 months), with no benefit at 24 months. Intermittent clobazam compared to placebo at 6 months resulted in a RR of 0.09 (95% CI 0.02 to 0.30), an effect found against an extremely high (83.3%) recurrence rate in the controls and which is a result that needs replication.The recording of adverse effects was variable. Lower comprehension scores in phenobarbitone treated children were found in two studies. In general, adverse effects were recorded in up to some 30% of children in the phenobarbitone treated group and in up to 36% in benzodiazepine treated groups. Evidence of publication bias was found in the meta analyses of comparisons for phenobarbitone versus placebo (8 studies) at 12 months but not at 6 months (6 studies); and valproate versus placebo (4 studies) at 12 months; with too few studies to identify publication bias for the other comparisons. No clinically important benefits for children with febrile seizures were found for intermittent oral diazepam, phenytoin, phenobarbitone, intermittent rectal diazepam, valproate, pyridoxine, intermittent phenobarbitone or intermittent ibuprofen, nor for diclofenac versus placebo followed by ibuprofen, acetominophen or placebo. Adverse effects were reported in up to 30% of children. Apparent benefit for clobazam treatment in one recent trial needs to be replicated to be judged reliable. Given the benign nature of recurrent febrile seizures, and the high prevalence of adverse effects of these drugs, parents and families should be supported with adequate contact details of medical services and information on recurrence, first aid management and, most importantly, the benign nature of the phenomenon.


Lingwood C.A.,Hospital for Sick Children
Cold Spring Harbor perspectives in biology | Year: 2011

The combination of carbohydrate and lipid generates unusual molecules in which the two distinctive halves of the glycoconjugate influence the function of each other. Membrane glycolipids can act as primary receptors for carbohydrate binding proteins to mediate transmembrane signaling despite restriction to the outer bilayer leaflet. The extensive heterogeneity of the lipid moiety plays a significant, but still largely unknown, role in glycosphingolipid function. Potential interplay between glycolipids and their fatty acid isoforms, together with their preferential interaction with cholesterol, generates a complex mechanism for the regulation of their function in cellular physiology.


Flannagan R.S.,Hospital for Sick Children | Jaumouille V.,Hospital for Sick Children | Grinstein S.,Hospital for Sick Children
Annual Review of Pathology: Mechanisms of Disease | Year: 2012

Engulfment and destruction of invading microorganisms by phagocytosis are critical components of the innate immune response. In addition, phagocytosis is also required for the clearance of apoptotic bodies, an essential aspect of tissue homeostasis and remodeling. Here, we summarize the current knowledge of the cellular and molecular basis of phagosome formation and maturation. We discuss the manner in which phagocytosis is subverted by certain pathogens and consider congenital disorders that affect phagocyte function. Copyright ©2012 by Annual Reviews. All rights reserved.


Hui C.-C.,Hospital for Sick Children | Hui C.-C.,University of Toronto | Angers S.,University of Toronto
Annual Review of Cell and Developmental Biology | Year: 2011

Gli zinc-finger proteins are transcription factors involved in the intracellular signal transduction controlled by the Hedgehog family of secreted molecules. They are frequently mutated in human congenital malformations, and their abnormal regulation leads to tumorigenesis. Genetic studies in several model systems indicate that their activity is tightly regulated by Hedgehog signaling through various posttranslational modifications, including phosphorylation, ubiquitin-mediated degradation, and proteolytic processing, as well as through nucleocytoplasmic shuttling. In vertebrate cells, primary cilia are required for the sensing of Hedgehog pathway activity and involved in the processing and activation of Gli proteins. Two evolutionarily conserved Hedgehog pathway components, Suppressor of fused and Kif7, are core intracellular regulators of mammalian Gli proteins. Recent studies revealed that Gli proteins are also regulated transcriptionally and posttranslationally through noncanonical mechanisms independent of Hedgehog signaling. In this review, we describe the regulation of Gli proteins during development and discuss possible mechanisms for their abnormal activation during tumorigenesis. © 2011 by Annual Reviews. All rights reserved.

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