92 research outputs found

    Investigating novel regulators of mTORC1 activation in human skeletal muscle

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    The mechanistic target of rapamycin (mTOR), specifically mTOR complex 1 (mTORC1) is believed to be a central regulator of muscle size, however, the upstream mechanisms which activate this kinase in response to anabolic stimuli remain to be fully elucidated. This thesis therefore aimed to investigate the role of several novel regulators of mTORC1 activity in human skeletal muscle. Chapter 3 displays that mTOR translocation to the cell periphery is mTORC1-specific and is greater following resistance exercise (RE) and protein-carbohydrate (PRO-CHO) feeding compared to feeding alone. In chapter 4 we validate and optimise a immunofluorescent staining protocol to visualise L-Type amino acid transporter 1 (LAT1) in human skeletal muscle, where it was more greatly expressed in fast twitch fibres and localised close to sarcolemma and microvasculature. Chapter 5 investigated the role of vacuolar protein sorting 34 (Vps34), a potential nutrient ‘sensor’, in mTORC1 activation in skeletal muscle. Here, both in vitro and in vivo experimental designs were utilised to display that changes in Vps34 cellular location, rather than kinase activity, may be important for nutrient sensing in skeletal muscle. Finally, chapter 6 reports how mTORC1 activation can occur without alterations in Vps34 protein content, kinase activity or LAT1 fibre type distribution in response to RE and/or PRO-CHO feeding. Overall, this thesis enhanced our understanding of the intricate regulation of mTORC1 activity in human skeletal muscle, identifying new potential mechanisms by which anabolic stimuli may regulate this kinase

    The skeletal muscle fiber periphery: a nexus of mTOR-related anabolism

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    Skeletal muscle anabolism is driven by numerous stimuli such as growth factors, nutrients (i.e., amino acids, glucose), and mechanical stress. These stimuli are integrated by the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) signal transduction cascade. In recent years, work from our laboratory and elsewhere has sought to unravel the molecular mechanisms underpinning the mTOR-related activation of muscle protein synthesis (MPS), as well as the spatial regulation of these mechanisms within the skeletal muscle cell. These studies have suggested that the skeletal muscle fiber periphery is a region of central importance in anabolism (i.e., growth/MPS). Indeed, the fiber periphery is replete with the substrates, molecular machinery, and translational apparatus necessary to facilitate MPS. This review provides a summary of the mechanisms underpinning the mTOR-associated activation of MPS from cell, rodent, and human studies. It also presents an overview of the spatial regulation of mTORC1 in response to anabolic stimuli and outlines the factors that distinguish the periphery of the cell as a highly notable region of skeletal muscle for the induction of MPS. Future research should seek to further explore the nutrient-induced activation of mTORC1 at the periphery of skeletal muscle fibers

    Adherence to guidelines on documentation required for registration to London GP practice websites: a mixed-methods cross-sectional study

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    Background The most common obstacle to registration with a GP practice in the UK is difficulty presenting proof of address. NHS guidelines stipulate that inability to provide ID or proof of address is not reasonable grounds to refuse registration. Practices may ask patients to present ID/proof of address, but need a policy in case patients cannot. Aim To find out how many London GP practice websites ask for documentation without a policy for where this cannot be provided and compare how GP practice websites describe the registration process in patient-facing material. Design and setting Cross-sectional study of practices from 10 London boroughs (n = 100). Method A proforma was piloted and then implemented, recording whether practices ‘demanded’, ‘requested’, or ‘mentioned’ photo ID or proof of address and whether there was a plan for patients without documentation. Text relating to documentation from all 100 practices for registration was subjected to thematic analysis. Results Out of 100 practices 75% asked for documentation. The majority of these were ‘demanded’. A plan was included for people without documentation in 12% of practice websites. Five themes emerged from analysis of website content: reassuring people without documentation; diverse requirements between practices; conflating administration and treatment; withholding treatment; and immigration and ethnicity. Conclusion Many practice websites breached NHS Standard Operating Principles and possibly the Equalities Act 2010. All practices should create a clear policy for patients who do not have photo ID/proof of address (for example, including a named receptionist), and update their websites accordingly

    How should institutions help clinicians to practise greener anaesthesia : first-order and second-order responsibilities to practice sustainably

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    There is a need for all industries, including healthcare, to reduce their greenhouse gas emissions. In anaesthetic practice, this not only requires a reduction in resource use and waste, but also a shift away from inhaled anaesthetic gases and towards alternatives with a lower carbon footprint. As inhalational anaesthesia produces greenhouse gas emissions at the point of use, achieving sustainable anaesthetic practice involves individual practitioner behaviour change. However, changing the practice of healthcare professionals raises potential ethical issues. The purpose of this paper is twofold. First, we discuss what moral duties anaesthetic practitioners have when it comes to practices that impact the environment. We argue that behaviour change among practitioners to align with certain moral responsibilities must be supplemented with an account of institutional duties to support this. In other words, we argue that institutions and those in power have second-order responsibilities to ensure that practitioners can fulfil their first-order responsibilities to practice more sustainably. The second goal of the paper is to consider not just the nature of second-order responsibilities but the content. We assess four different ways that second-order responsibilities might be fulfilled within healthcare systems: removing certain anaesthetic agents, seeking consensus, education and methods from behavioural economics. We argue that, while each of these are a necessary part of the picture, some interventions like nudges have considerable advantages

    Take patients seriously when they say financial incentives help with adherence

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    Small financial incentives have been proven effective at promoting healthy behaviours across medicine, including in psychiatry. There are a range of philosophical and practical objections to financial incentives. Drawing on the existing literature, specifically attempts to use financial incentives to promote antipsychotic adherence, we propose a ‘patient-centred’ view of evaluating financial incentive regimes. We argue that there is evidence that mental health patients like financial incentives, considering them fair and respectful. The enthusiasm of mental health patients for financial incentives lends support to their use, although it does not invalidate all objections against them

    Differential localization and anabolic responsiveness of mTOR complexes in human skeletal muscle in response to feeding and exercise

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    Mechanistic target of rapamycin (mTOR) resides as two complexes within skeletal muscle. mTOR complex 1 (mTORC1-Raptor positive) regulates skeletal muscle growth, whereas mTORC2 (Rictor positive) regulates insulin sensitivity. To examine the regulation of these complexes in human skeletal muscle, we utilised immunohistochemical analysis to study the localisation of mTOR complexes prior to and following protein-carbohydrate feeding (FED) and resistance exercise plus protein-carbohydrate feeding (EXFED) in unilateral exercise model. In basal samples, mTOR and the lysosomal marker LAMP2 were highly co-localized and remained so throughout. In the FED and EXFED states, mTOR/LAMP2 complexes were redistributed to the cell periphery (WGA positive staining) (time effect; p=.025), with 39\% (FED) and 26\% (EXFED) increases in mTOR/WGA association observed 1h post-feeding/exercise. mTOR/WGA colocalisation continued to increase in EXFED at 3h (48\% above baseline) whereas colocalisation decreased in FED (21\% above baseline). A significant effect of condition (p=.05) was noted suggesting mTOR/WGA co-localization was greater during EXFED. This pattern was replicated in Raptor/WGA association, where a significant difference between EXFED and FED was noted at 3h post-exercise/feeding (p=.014). Rictor/WGA colocalization remained unaltered throughout the trial. Alterations in mTORC1 cellular location coincided with elevated S6K1 kinase activity, which rose to a greater extent in EXFED compared to FED at 1h post-exercise/feeding (p<.001), and only remained elevated in EXFED at the 3h time point (p=.037). Collectively these data suggest that mTORC1 redistribution within the cell is a fundamental response to resistance exercise and feeding, whereas mTORC2 is predominantly situated at the sarcolemma and does not alter localisation

    Characterisation of L-Type Amino Acid Transporter 1 (LAT1) Expression in Human Skeletal Muscle by Immunofluorescent Microscopy

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    The branch chain amino acid leucine is a potent stimulator of protein synthesis in skeletal muscle. Leucine rapidly enters the cell via the L-Type Amino Acid Transporter 1 (LAT1); however, little is known regarding the localisation and distribution of this transporter in human skeletal muscle. Therefore, we applied immunofluorescence staining approaches to visualise LAT1 in wild type (WT) and LAT1 muscle-specific knockout (mKO) mice, in addition to basal human skeletal muscle samples. LAT1 positive staining was visually greater in WT muscles compared to mKO muscle. In human skeletal muscle, positive LAT1 staining was noted close to the sarcolemmal membrane (dystrophin positive staining), with a greater staining intensity for LAT1 observed in the sarcoplasmic regions of type II fibres (those not stained positively for myosin heavy-chain 1, Type II—25.07 ± 5.93, Type I—13.71 ± 1.98, p < 0.01), suggesting a greater abundance of this protein in these fibres. Finally, we observed association with LAT1 and endothelial nitric oxide synthase (eNOS), suggesting LAT1 association close to the microvasculature. This is the first study to visualise the distribution and localisation of LAT1 in human skeletal muscle. As such, this approach provides a validated experimental platform to study the role and regulation of LAT1 in human skeletal muscle in response to various physiological and pathophysiological models

    LAT1 and SNAT2 Protein Expression and Membrane Localization of LAT1 Are Not Acutely Altered by Dietary Amino Acids or Resistance Exercise Nor Positively Associated with Leucine or Phenylalanine Incorporation in Human Skeletal Muscle

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    The influx of essential amino acids into skeletal muscle is primarily mediated by the large neutral amino acid transporter 1 (LAT1), which is dependent on the glutamine gradient generated by the sodium-dependent neutral amino acid transporter 2 (SNAT2). The protein expression and membrane localization of LAT1 may be influenced by amino acid ingestion and/or resistance exercise, although its acute influence on dietary amino acid incorporation into skeletal muscle protein has not been investigated. In a group design, healthy males consumed a mixed carbohydrate (0.75 g·kg−1) crystalline amino acid (0.25 g·kg−1) beverage enriched to 25% and 30% with LAT1 substrates L-[1-13C]leucine (LEU) and L-[ring-2H5]phenylalanine (PHE), respectively, at rest (FED: n = 7, 23 ± 5 y, 77 ± 4 kg) or after a bout of resistance exercise (EXFED: n = 7, 22 ± 2 y, 78 ± 11 kg). Postprandial muscle biopsies were collected at 0, 120, and 300 min to measure transporter protein expression (immunoblot), LAT1 membrane localization (immunofluorescence), and dietary amino acid incorporation into myofibrillar protein (ΔLEU and ΔPHE). Basal LAT1 and SNAT2 protein contents were correlated with each other (r = 0.55, p = 0.04) but their expression did not change across time in FED or EXFED (all, p > 0.05). Membrane localization of LAT1 did not change across time in FED or EXFED whether measured as outer 1.5 ”m intensity or membrane-to-fiber ratio (all, p > 0.05). Basal SNAT2 protein expression was not correlated with ΔLEU or ΔPHE (all, p ≄ 0.05) whereas basal LAT1 expression was negatively correlated with ΔPHE in FED (r = −0.76, p = 0.04) and EXFED (r = −0.81, p = 0.03) but not ΔLEU (p > 0.05). Basal LAT1 membrane localization was not correlated with ΔLEU or ΔPHE (all, p > 0.05). Our results suggest that LAT1/SNAT2 protein expression and LAT1 membrane localization are not influenced by acute anabolic stimuli and do not positively influence the incorporation of dietary amino acids for de novo myofibrillar protein synthesis in healthy young males

    Resistance exercise initiates mechanistic target of rapamycin (mTOR) translocation and protein complex co-localisation in human skeletal muscle

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    The mechanistic target of rapamycin (mTOR) is a central mediator of protein synthesis in skeletal muscle. We utilized immunofluorescence approaches to study mTOR cellular distribution and protein-protein co-localisation in human skeletal muscle in the basal state as well as immediately, 1 and 3 h after an acute bout of resistance exercise in a fed (FED; 20 g Protein/40 g carbohydrate/1 g fat) or energy-free control (CON) state. mTOR and the lysosomal protein LAMP2 were highly co-localised in basal samples. Resistance exercise resulted in rapid translocation of mTOR/LAMP2 towards the cell membrane. Concurrently, resistance exercise led to the dissociation of TSC2 from Rheb and increased in the co-localisation of mTOR and Rheb post exercise in both FED and CON. In addition, mTOR co-localised with Eukaryotic translation initiation factor 3 subunit F (eIF3F) at the cell membrane post-exercise in both groups, with the response significantly greater at 1 h of recovery in the FED compared to CON. Collectively our data demonstrate that cellular trafficking of mTOR occurs in human muscle in response to an anabolic stimulus, events that appear to be primarily influenced by muscle contraction. The translocation and association of mTOR with positive regulators (i.e. Rheb and eIF3F) is consistent with an enhanced mRNA translational capacity after resistance exercise
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