The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Nigel S. Atkinson - One of the best experts on this subject based on the ideXlab platform.
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A DNA element regulates Drug Tolerance and withdrawal in Drosophila.
PloS one, 2013Co-Authors: Alfredo Ghezzi, Jascha B. Pohl, Arun Y. Bohm, Nigel S. AtkinsonAbstract:Drug Tolerance and withdrawal are insidious responses to Drugs of abuse; the first increases Drug consumption while the second punishes abstention. Drosophila generate functional Tolerance to benzyl alcohol sedation by increasing neural expression of the slo BK-type Ca2+ activated K+ channel gene. After Drug clearance this change produces a withdrawal phenotype—increased seizure susceptibility. The Drug-induced histone modification profile identified the 6b element (60 nt) as a Drug responsive element. Genomic deletion of 6b produces the allele, sloΔ6b, that reacts more strongly to the Drug with increased induction, a massive increase in the duration of Tolerance, and an increase in the withdrawal phenotype yet does not alter other slo-dependent behaviors. The 6b element is a homeostatic regulator of BK channel gene expression and is the first cis-acting DNA element shown to specifically affect the duration of a Drug action.
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Functional mapping of the neuronal substrates for Drug Tolerance in drosophila
Behavior genetics, 2013Co-Authors: Alfredo Ghezzi, Yan Wang, Yazan M. Al-hasan, Harish R. Krishnan, Nigel S. AtkinsonAbstract:Physical dependence on alcohol and anesthetics stems from neuroadaptive changes that act to counter the effects of sedation in the brain. In Drosophila, exposure to either alcohol or solvent anesthetics have been shown to induce changes in expression of the BK-type Ca2+-activated K+ channel gene slo. An increase in slo expression produces an adaptive modulation of neural activity that generates resistance to sedation and promotes Drug Tolerance and dependence. Increased BK channel activity counteracts the sedative effects of these Drugs by reducing the neuronal refractory period and enhancing the capacity of neurons for repetitive firing. However, the brain regions or neuronal populations capable of producing inducible resistance or Tolerance remain unknown. Here we map the neuronal substrates relevant for the slo-dependent modulation of Drug sensitivity. Using spatially-controlled induction of slo expression we identify the mushroom bodies, the ellipsoid body and a subset of the circadian clock neurons as pivotal regions for the control of recovery from sedation.
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Homeostatic cont of neural activity: A drosophila model for Drug Tolerance and dependence
International review of neurobiology, 2011Co-Authors: Alfredo Ghezzi, Nigel S. AtkinsonAbstract:Drug addiction is a complex condition of compulsive Drug use that results in devastating physical and social consequences. Drosophila melanogaster has recently emerged as a valuable genetic model for investigating the mechanisms of addiction. Drug Tolerance is a measurable endophenotype of addiction that can be easily generated and detected in animal models. The counteradaptive theory for Drug dependence postulates that the homeostatic adaptations that produce Drug Tolerance become counteradaptive after Drug clearance, resulting in symptoms of dependence. In flies, a single sedation with ethanol or with an organic solvent anesthetic (benzyl alcohol) induces functional Tolerance, an adaptation of the nervous system that reduces the effect of these neural depressants. Here we review the role of the BK channel gene (slo) and genes that encode other synaptic proteins in the process of producing functional Tolerance. These proteins are predicted to be part of an orchestrated response that involves specific interactions across a highly complex synaptic protein network. The response of the slo gene to Drug exposure and the consequence of induced slo expression fit nicely the tenets of the counteradaptive theory for Drug Tolerance and dependence. Induction of slo expression represents an adaptive process that generates Tolerance because it enhances neuronal excitability, which counters the sedative effects of the Drugs. After Drug clearance, however, the increase in slo expression leads to an allostatic withdrawal state that is characterized by an increase in the susceptibility for seizure. Together, these results demonstrate a common origin for development of Drug Tolerance and withdrawal hyperexcitability in Drosophila.
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BK channels play a counter-adaptive role in Drug Tolerance and dependence
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Alfredo Ghezzi, Jascha B. Pohl, Yan Wang, Nigel S. AtkinsonAbstract:Disturbance of neural activity by sedative Drugs has been proposed to trigger a homeostatic response that resists unfavorable changes in net cellular excitability, leading to Tolerance and dependence. The Drosophila slo gene encodes a BK-type Ca2+-activated K+ channel implicated in functional Tolerance to alcohol and volatile anesthetics. We hypothesized that increased expression of BK channels induced by these Drugs constitutes the homeostatic adaptation conferring resistance to sedative Drugs. In contrast to the dogmatic view that BK channels act as neural depressants, we show that Drug-induced slo expression enhances excitability by reducing the neuronal refractory period. Although this neuroadaptation directly counters some effects of anesthetics, it also causes long-lasting enhancement of seizure susceptibility, a common symptom of Drug withdrawal. These data provide a possible mechanism for the long-standing counter-adaptive theory for Drug Tolerance in which homeostatic adaptations triggered by Drug exposure to produce Drug Tolerance become counter-adaptive after Drug clearance and result in symptoms of dependence.
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slo K+ channel gene regulation mediates rapid Drug Tolerance
Proceedings of the National Academy of Sciences of the United States of America, 2004Co-Authors: Alfredo Ghezzi, Yazan M. Al-hasan, Leo E. Larios, Rudolf A. Bohm, Nigel S. AtkinsonAbstract:Changes in neural activity caused by exposure to Drugs may trigger homeostatic mechanisms that attempt to restore normal neural excitability. In Drosophila, a single sedation with the anesthetic benzyl alcohol changes the expression of the slo K+ channel gene and induces rapid Drug Tolerance. We demonstrate linkage between these two phenomena by using a mutation and a transgene. A mutation that eliminates slo expression prevents Tolerance, whereas expression from an inducible slo transgene mimics Tolerance in naive animals. The behavioral response to benzyl alcohol can be separated into an initial phase of hyperkinesis and a subsequent phase of sedation. The hyperkinetic phase causes a drop in slo gene expression and makes animals more sensitive to benzyl alcohol. It is the sedative phase that stimulates slo gene expression and induces Tolerance. We demonstrate that the expression level of slo is a predictor of Drug sensitivity.
Alfredo Ghezzi - One of the best experts on this subject based on the ideXlab platform.
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A DNA element regulates Drug Tolerance and withdrawal in Drosophila.
PloS one, 2013Co-Authors: Alfredo Ghezzi, Jascha B. Pohl, Arun Y. Bohm, Nigel S. AtkinsonAbstract:Drug Tolerance and withdrawal are insidious responses to Drugs of abuse; the first increases Drug consumption while the second punishes abstention. Drosophila generate functional Tolerance to benzyl alcohol sedation by increasing neural expression of the slo BK-type Ca2+ activated K+ channel gene. After Drug clearance this change produces a withdrawal phenotype—increased seizure susceptibility. The Drug-induced histone modification profile identified the 6b element (60 nt) as a Drug responsive element. Genomic deletion of 6b produces the allele, sloΔ6b, that reacts more strongly to the Drug with increased induction, a massive increase in the duration of Tolerance, and an increase in the withdrawal phenotype yet does not alter other slo-dependent behaviors. The 6b element is a homeostatic regulator of BK channel gene expression and is the first cis-acting DNA element shown to specifically affect the duration of a Drug action.
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Functional mapping of the neuronal substrates for Drug Tolerance in drosophila
Behavior genetics, 2013Co-Authors: Alfredo Ghezzi, Yan Wang, Yazan M. Al-hasan, Harish R. Krishnan, Nigel S. AtkinsonAbstract:Physical dependence on alcohol and anesthetics stems from neuroadaptive changes that act to counter the effects of sedation in the brain. In Drosophila, exposure to either alcohol or solvent anesthetics have been shown to induce changes in expression of the BK-type Ca2+-activated K+ channel gene slo. An increase in slo expression produces an adaptive modulation of neural activity that generates resistance to sedation and promotes Drug Tolerance and dependence. Increased BK channel activity counteracts the sedative effects of these Drugs by reducing the neuronal refractory period and enhancing the capacity of neurons for repetitive firing. However, the brain regions or neuronal populations capable of producing inducible resistance or Tolerance remain unknown. Here we map the neuronal substrates relevant for the slo-dependent modulation of Drug sensitivity. Using spatially-controlled induction of slo expression we identify the mushroom bodies, the ellipsoid body and a subset of the circadian clock neurons as pivotal regions for the control of recovery from sedation.
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Homeostatic cont of neural activity: A drosophila model for Drug Tolerance and dependence
International review of neurobiology, 2011Co-Authors: Alfredo Ghezzi, Nigel S. AtkinsonAbstract:Drug addiction is a complex condition of compulsive Drug use that results in devastating physical and social consequences. Drosophila melanogaster has recently emerged as a valuable genetic model for investigating the mechanisms of addiction. Drug Tolerance is a measurable endophenotype of addiction that can be easily generated and detected in animal models. The counteradaptive theory for Drug dependence postulates that the homeostatic adaptations that produce Drug Tolerance become counteradaptive after Drug clearance, resulting in symptoms of dependence. In flies, a single sedation with ethanol or with an organic solvent anesthetic (benzyl alcohol) induces functional Tolerance, an adaptation of the nervous system that reduces the effect of these neural depressants. Here we review the role of the BK channel gene (slo) and genes that encode other synaptic proteins in the process of producing functional Tolerance. These proteins are predicted to be part of an orchestrated response that involves specific interactions across a highly complex synaptic protein network. The response of the slo gene to Drug exposure and the consequence of induced slo expression fit nicely the tenets of the counteradaptive theory for Drug Tolerance and dependence. Induction of slo expression represents an adaptive process that generates Tolerance because it enhances neuronal excitability, which counters the sedative effects of the Drugs. After Drug clearance, however, the increase in slo expression leads to an allostatic withdrawal state that is characterized by an increase in the susceptibility for seizure. Together, these results demonstrate a common origin for development of Drug Tolerance and withdrawal hyperexcitability in Drosophila.
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BK channels play a counter-adaptive role in Drug Tolerance and dependence
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Alfredo Ghezzi, Jascha B. Pohl, Yan Wang, Nigel S. AtkinsonAbstract:Disturbance of neural activity by sedative Drugs has been proposed to trigger a homeostatic response that resists unfavorable changes in net cellular excitability, leading to Tolerance and dependence. The Drosophila slo gene encodes a BK-type Ca2+-activated K+ channel implicated in functional Tolerance to alcohol and volatile anesthetics. We hypothesized that increased expression of BK channels induced by these Drugs constitutes the homeostatic adaptation conferring resistance to sedative Drugs. In contrast to the dogmatic view that BK channels act as neural depressants, we show that Drug-induced slo expression enhances excitability by reducing the neuronal refractory period. Although this neuroadaptation directly counters some effects of anesthetics, it also causes long-lasting enhancement of seizure susceptibility, a common symptom of Drug withdrawal. These data provide a possible mechanism for the long-standing counter-adaptive theory for Drug Tolerance in which homeostatic adaptations triggered by Drug exposure to produce Drug Tolerance become counter-adaptive after Drug clearance and result in symptoms of dependence.
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slo K+ channel gene regulation mediates rapid Drug Tolerance
Proceedings of the National Academy of Sciences of the United States of America, 2004Co-Authors: Alfredo Ghezzi, Yazan M. Al-hasan, Leo E. Larios, Rudolf A. Bohm, Nigel S. AtkinsonAbstract:Changes in neural activity caused by exposure to Drugs may trigger homeostatic mechanisms that attempt to restore normal neural excitability. In Drosophila, a single sedation with the anesthetic benzyl alcohol changes the expression of the slo K+ channel gene and induces rapid Drug Tolerance. We demonstrate linkage between these two phenomena by using a mutation and a transgene. A mutation that eliminates slo expression prevents Tolerance, whereas expression from an inducible slo transgene mimics Tolerance in naive animals. The behavioral response to benzyl alcohol can be separated into an initial phase of hyperkinesis and a subsequent phase of sedation. The hyperkinetic phase causes a drop in slo gene expression and makes animals more sensitive to benzyl alcohol. It is the sedative phase that stimulates slo gene expression and induces Tolerance. We demonstrate that the expression level of slo is a predictor of Drug sensitivity.
Hassan Safi - One of the best experts on this subject based on the ideXlab platform.
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Phase variation in Mycobacterium tuberculosis glpK produces transiently heritable Drug Tolerance.
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Hassan Safi, Landry Blanc, Véronique Dartois, Pooja Gopal, Subramanya Lingaraju, Carly Levine, Michelle Yee, Hsin Pin Ho LiangAbstract:The length and complexity of tuberculosis (TB) therapy, as well as the propensity of Mycobacterium tuberculosis to develop Drug resistance, are major barriers to global TB control efforts. M. tuberculosis is known to have the ability to enter into a Drug-tolerant state, which may explain many of these impediments to TB treatment. We have identified a mechanism of genetically encoded but rapidly reversible Drug Tolerance in M. tuberculosis caused by transient frameshift mutations in a homopolymeric tract (HT) of 7 cytosines (7C) in the glpK gene. Inactivating frameshift mutations associated with the 7C HT in glpK produce small colonies that exhibit heritable multiDrug increases in minimal inhibitory concentrations and decreases in Drug-dependent killing; however, reversion back to a fully Drug-susceptible large-colony phenotype occurs rapidly through the introduction of additional insertions or deletions in the same glpK HT region. These reversible frameshift mutations in the 7C HT of M. tuberculosis glpK occur in clinical isolates, accumulate in M. tuberculosis-infected mice with further accumulation during Drug treatment, and exhibit a reversible transcriptional profile including induction of dosR and sigH and repression of kstR regulons, similar to that observed in other in vitro models of M. tuberculosis Tolerance. These results suggest that GlpK phase variation may contribute to Drug Tolerance, treatment failure, and relapse in human TB. Drugs effective against phase-variant M. tuberculosis may hasten TB treatment and improve cure rates.
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Phase variation in Mycobacterium tuberculosis glpK produces transiently heritable Drug Tolerance
2019Co-Authors: Hassan Safi, Landry Blanc, Véronique Dartois, Pooja Gopal, Subramanya Lingaraju, Carly Levine, Michelle Yee, Hsin Pin Ho LiangAbstract:The length and complexity of tuberculosis (TB) therapy, as well as the propensity of Mycobacterium tuberculosis to develop Drug resistance, are major barriers to global TB control efforts. M. tuberculosis is known to have the ability to enter into a Drug-tolerant state, which may explain many of these impediments to TB treatment. We have identified a novel mechanism of genetically encoded but rapidly reversible Drug-Tolerance in M. tuberculosis caused by transient frameshift mutations in a homopolymeric tract (HT) of seven cytosines (7C) in the glpK gene. Inactivating frameshift mutations associated with the 7C HT in glpK produce small colonies that exhibit heritable multi-Drug increases in minimal inhibitory concentrations and decreases in Drug-dependent killing; however, reversion back to a fully Drug-susceptible large-colony phenotype occurs rapidly through the introduction of additional insertions or deletions in the same glpK HT region. These reversible frameshift mutations in the 7C HT of M. tuberculosis glpK occur in clinical isolates, accumulate in M. tuberculosis infected mice with further accumulation during Drug treatment, and exhibit a reversible transcriptional profile including induction of dosR and sigH and repression of kstR regulons, similar to that observed in other in vitro models of M. tuberculosis Tolerance. These results suggest that GlpK phase variation may contribute to Drug-Tolerance, treatment failure and relapse in human TB. Drugs effective against phase-variant M. tuberculosis may hasten TB treatment and improve cure rates.
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Transcriptional Regulation of Multi-Drug Tolerance and Antibiotic-Induced Responses by the Histone-Like Protein Lsr2 in M. tuberculosis
PLoS pathogens, 2007Co-Authors: Roberto Colangeli, Hassan Safi, Danica Helb, Catherine Vilchèze, Manzour Hernando Hazbón, Chee Gun Lee, Brendan Sayers, Irene Sardone, Marcus B. Jones, Robert D. FleischmannAbstract:Multi-Drug Tolerance is a key phenotypic property that complicates the sterilization of mammals infected with Mycobacterium tuberculosis. Previous studies have established that iniBAC, an operon that confers multi-Drug Tolerance to M. bovis BCG through an associated pump-like activity, is induced by the antibiotics isoniazid (INH) and ethambutol (EMB). An improved understanding of the functional role of antibiotic-induced genes and the regulation of Drug Tolerance may be gained by studying the factors that regulate antibiotic-mediated gene expression. An M. smegmatis strain containing a lacZ gene fused to the promoter of M. tuberculosis iniBAC (PiniBAC) was subjected to transposon mutagenesis. Mutants with constitutive expression and increased EMB-mediated induction of PiniBAC::lacZ mapped to the lsr2 gene (MSMEG6065), a small basic protein of unknown function that is highly conserved among mycobacteria. These mutants had a marked change in colony morphology and generated a new polar lipid. Complementation with multi-copy M. tuberculosis lsr2 (Rv3597c) returned PiniBAC expression to baseline, reversed the observed morphological and lipid changes, and repressed PiniBAC induction by EMB to below that of the control M. smegmatis strain. Microarray analysis of an lsr2 knockout confirmed upregulation of M. smegmatis iniA and demonstrated upregulation of genes involved in cell wall and metabolic functions. Fully 121 of 584 genes induced by EMB treatment in wild-type M. smegmatis were upregulated (“hyperinduced”) to even higher levels by EMB in the M. smegmatis lsr2 knockout. The most highly upregulated genes and gene clusters had adenine-thymine (AT)–rich 5-prime untranslated regions. In M. tuberculosis, overexpression of lsr2 repressed INH-mediated induction of all three iniBAC genes, as well as another annotated pump, efpA. The low molecular weight and basic properties of Lsr2 (pI 10.69) suggested that it was a histone-like protein, although it did not exhibit sequence homology with other proteins in this class. Consistent with other histone-like proteins, Lsr2 bound DNA with a preference for circular DNA, forming large oligomers, inhibited DNase I activity, and introduced a modest degree of supercoiling into relaxed plasmids. Lsr2 also inhibited in vitro transcription and topoisomerase I activity. Lsr2 represents a novel class of histone-like proteins that inhibit a wide variety of DNA-interacting enzymes. Lsr2 appears to regulate several important pathways in mycobacteria by preferentially binding to AT-rich sequences, including genes induced by antibiotics and those associated with inducible multi-Drug Tolerance. An improved understanding of the role of lsr2 may provide important insights into the mechanisms of action of antibiotics and the way that mycobacteria adapt to stresses such as antibiotic treatment.
Hsin Pin Ho Liang - One of the best experts on this subject based on the ideXlab platform.
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Phase variation in Mycobacterium tuberculosis glpK produces transiently heritable Drug Tolerance.
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Hassan Safi, Landry Blanc, Véronique Dartois, Pooja Gopal, Subramanya Lingaraju, Carly Levine, Michelle Yee, Hsin Pin Ho LiangAbstract:The length and complexity of tuberculosis (TB) therapy, as well as the propensity of Mycobacterium tuberculosis to develop Drug resistance, are major barriers to global TB control efforts. M. tuberculosis is known to have the ability to enter into a Drug-tolerant state, which may explain many of these impediments to TB treatment. We have identified a mechanism of genetically encoded but rapidly reversible Drug Tolerance in M. tuberculosis caused by transient frameshift mutations in a homopolymeric tract (HT) of 7 cytosines (7C) in the glpK gene. Inactivating frameshift mutations associated with the 7C HT in glpK produce small colonies that exhibit heritable multiDrug increases in minimal inhibitory concentrations and decreases in Drug-dependent killing; however, reversion back to a fully Drug-susceptible large-colony phenotype occurs rapidly through the introduction of additional insertions or deletions in the same glpK HT region. These reversible frameshift mutations in the 7C HT of M. tuberculosis glpK occur in clinical isolates, accumulate in M. tuberculosis-infected mice with further accumulation during Drug treatment, and exhibit a reversible transcriptional profile including induction of dosR and sigH and repression of kstR regulons, similar to that observed in other in vitro models of M. tuberculosis Tolerance. These results suggest that GlpK phase variation may contribute to Drug Tolerance, treatment failure, and relapse in human TB. Drugs effective against phase-variant M. tuberculosis may hasten TB treatment and improve cure rates.
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Phase variation in Mycobacterium tuberculosis glpK produces transiently heritable Drug Tolerance
2019Co-Authors: Hassan Safi, Landry Blanc, Véronique Dartois, Pooja Gopal, Subramanya Lingaraju, Carly Levine, Michelle Yee, Hsin Pin Ho LiangAbstract:The length and complexity of tuberculosis (TB) therapy, as well as the propensity of Mycobacterium tuberculosis to develop Drug resistance, are major barriers to global TB control efforts. M. tuberculosis is known to have the ability to enter into a Drug-tolerant state, which may explain many of these impediments to TB treatment. We have identified a novel mechanism of genetically encoded but rapidly reversible Drug-Tolerance in M. tuberculosis caused by transient frameshift mutations in a homopolymeric tract (HT) of seven cytosines (7C) in the glpK gene. Inactivating frameshift mutations associated with the 7C HT in glpK produce small colonies that exhibit heritable multi-Drug increases in minimal inhibitory concentrations and decreases in Drug-dependent killing; however, reversion back to a fully Drug-susceptible large-colony phenotype occurs rapidly through the introduction of additional insertions or deletions in the same glpK HT region. These reversible frameshift mutations in the 7C HT of M. tuberculosis glpK occur in clinical isolates, accumulate in M. tuberculosis infected mice with further accumulation during Drug treatment, and exhibit a reversible transcriptional profile including induction of dosR and sigH and repression of kstR regulons, similar to that observed in other in vitro models of M. tuberculosis Tolerance. These results suggest that GlpK phase variation may contribute to Drug-Tolerance, treatment failure and relapse in human TB. Drugs effective against phase-variant M. tuberculosis may hasten TB treatment and improve cure rates.
Véronique Dartois - One of the best experts on this subject based on the ideXlab platform.
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Phase variation in Mycobacterium tuberculosis glpK produces transiently heritable Drug Tolerance.
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Hassan Safi, Landry Blanc, Véronique Dartois, Pooja Gopal, Subramanya Lingaraju, Carly Levine, Michelle Yee, Hsin Pin Ho LiangAbstract:The length and complexity of tuberculosis (TB) therapy, as well as the propensity of Mycobacterium tuberculosis to develop Drug resistance, are major barriers to global TB control efforts. M. tuberculosis is known to have the ability to enter into a Drug-tolerant state, which may explain many of these impediments to TB treatment. We have identified a mechanism of genetically encoded but rapidly reversible Drug Tolerance in M. tuberculosis caused by transient frameshift mutations in a homopolymeric tract (HT) of 7 cytosines (7C) in the glpK gene. Inactivating frameshift mutations associated with the 7C HT in glpK produce small colonies that exhibit heritable multiDrug increases in minimal inhibitory concentrations and decreases in Drug-dependent killing; however, reversion back to a fully Drug-susceptible large-colony phenotype occurs rapidly through the introduction of additional insertions or deletions in the same glpK HT region. These reversible frameshift mutations in the 7C HT of M. tuberculosis glpK occur in clinical isolates, accumulate in M. tuberculosis-infected mice with further accumulation during Drug treatment, and exhibit a reversible transcriptional profile including induction of dosR and sigH and repression of kstR regulons, similar to that observed in other in vitro models of M. tuberculosis Tolerance. These results suggest that GlpK phase variation may contribute to Drug Tolerance, treatment failure, and relapse in human TB. Drugs effective against phase-variant M. tuberculosis may hasten TB treatment and improve cure rates.
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Phase variation in Mycobacterium tuberculosis glpK produces transiently heritable Drug Tolerance
2019Co-Authors: Hassan Safi, Landry Blanc, Véronique Dartois, Pooja Gopal, Subramanya Lingaraju, Carly Levine, Michelle Yee, Hsin Pin Ho LiangAbstract:The length and complexity of tuberculosis (TB) therapy, as well as the propensity of Mycobacterium tuberculosis to develop Drug resistance, are major barriers to global TB control efforts. M. tuberculosis is known to have the ability to enter into a Drug-tolerant state, which may explain many of these impediments to TB treatment. We have identified a novel mechanism of genetically encoded but rapidly reversible Drug-Tolerance in M. tuberculosis caused by transient frameshift mutations in a homopolymeric tract (HT) of seven cytosines (7C) in the glpK gene. Inactivating frameshift mutations associated with the 7C HT in glpK produce small colonies that exhibit heritable multi-Drug increases in minimal inhibitory concentrations and decreases in Drug-dependent killing; however, reversion back to a fully Drug-susceptible large-colony phenotype occurs rapidly through the introduction of additional insertions or deletions in the same glpK HT region. These reversible frameshift mutations in the 7C HT of M. tuberculosis glpK occur in clinical isolates, accumulate in M. tuberculosis infected mice with further accumulation during Drug treatment, and exhibit a reversible transcriptional profile including induction of dosR and sigH and repression of kstR regulons, similar to that observed in other in vitro models of M. tuberculosis Tolerance. These results suggest that GlpK phase variation may contribute to Drug-Tolerance, treatment failure and relapse in human TB. Drugs effective against phase-variant M. tuberculosis may hasten TB treatment and improve cure rates.
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Extreme Drug Tolerance of Mycobacterium tuberculosis in Caseum.
Antimicrobial agents and chemotherapy, 2017Co-Authors: Jansy Sarathy, Laura E. Via, Danielle M. Weiner, Landry Blanc, Helena I. Boshoff, Eliseo A. Eugenin, Clifton E. Barry, Véronique DartoisAbstract:Tuberculosis (TB) recently became the leading infectious cause of death in adults, while attempts to shorten therapy have largely failed. Dormancy, persistence, and Drug Tolerance are among the factors driving the long therapy duration. Assays to measure in situ Drug susceptibility of Mycobacterium tuberculosis bacteria in pulmonary lesions are needed if we are to discover new fast-acting regimens and address the global TB threat. Here we take a first step toward this goal and describe an ex vivo assay developed to measure the cidal activity of anti-TB Drugs against M. tuberculosis bacilli present in cavity caseum obtained from rabbits with active TB. We show that caseum M. tuberculosis bacilli are largely nonreplicating, maintain viability over the course of the assay, and exhibit extreme Tolerance to many first- and second-line TB Drugs. Among the Drugs tested, only the rifamycins fully sterilized caseum. A similar trend of phenotypic Drug resistance was observed in the hypoxia- and starvation-induced nonreplicating models, but with notable qualitative and quantitative differences: (i) caseum M. tuberculosis exhibits higher Drug Tolerance than nonreplicating M. tuberculosis in the Wayne and Loebel models, and (ii) pyrazinamide is cidal in caseum but has no detectable activity in these classic nonreplicating assays. Thus, ex vivo caseum constitutes a unique tool to evaluate Drug potency against slowly replicating or nonreplicating bacilli in their native caseous environment. Intracaseum cidal concentrations can now be related to the concentrations achieved in the necrotic foci of granulomas and cavities to establish correlations between clinical outcome and lesion-centered pharmacokinetics-pharmacodynamics (PK-PD) parameters.
