Biology subjects

Phillips, A. T.

Publications and source records attributed to Phillips, A. T..

5 recordsLinked to original sources

bioRxiv2024

NeuroMechanics: Electrophysiological and Computational Methods to Accurately Estimate the Neural Drive to Muscles in Humans In Vivo

The ultimate neural signal for muscle control is the neural drive sent from the spinal cord to muscles. This neural signal comprises the ensemble of action potentials discharged by the active spinal motoneurons, which is transmitted to the innervated muscle fibres to generate forces. Accurately estimating the neural drive to muscles in humans in vivo is challenging since it requires the identification of the activity of a sample of motor units (MUs) that is representative of the active MU population. Current electrophysiological recordings usually fail in this task by identifying small MU samples with over-representation of higher-threshold with respect to lower-threshold MUs. Here, we describe recent advances in electrophysiological methods that allow the identification of more representative samples of greater numbers of MUs than previously possible. This is obtained with large and very dense arrays of electromyographic electrodes. Moreover, recently developed computational methods of data augmentation further extend experimental MU samples to infer the activity of the full MU pool. In conclusion, the combination of new electrode technologies and computational modelling allows for an accurate estimate of the neural drive to muscles and opens new perspectives in the study of the neural control of movement and in neural interfacing.

neuroscience↗

bioRxiv2023

A novel motoneuron-driven computational muscle model with motor unit resolution for subject-specific simulations of human voluntary muscle contraction

The computational simulation of human voluntary muscle contraction is possible with EMG-driven Hill-type models of whole muscles. Despite impactful applications in numerous fields, the neuromechanical information and the physiological accuracy such models provide remain limited because of multiscale simplifications that limit comprehensive description of muscle internal dynamics during contraction. We addressed this limitation by developing a novel motoneuron-driven neuromuscular model, that describes the force-generating dynamics of a population of individual motor units, each of which was described with a Hill-type actuator and controlled by a dedicated experimentally derived motoneuronal control. In forward simulation of human voluntary muscle contraction, the model transforms a vector of motoneuron spike trains decoded from high-density EMG signals into a vector of motor unit forces that sum into the predicted whole muscle force. The control of motoneurons provides comprehensive and separate descriptions of the dynamics of motor unit recruitment and discharge and decode the subjects intention. The neuromuscular model is subject-specific, muscle-specific, includes an advanced and physiological description of motor unit activation dynamics, and is validated against an experimental muscle force. Accurate force predictions were obtained when the vector of experimental neural controls was representative of the discharge activity of the complete motor unit pool. This was achieved with large and dense grids of EMG electrodes during medium-force contractions or with computational methods that physiologically estimate the discharge activity of the motor units that were not identified experimentally. This neuromuscular model advances the state-of-the-art of neuromuscular modelling, bringing together the fields of motor control and musculoskeletal modelling, and finding applications in neuromuscular control and human-machine interfacing research. Author SummaryNeuromuscular computational simulations of human muscle contractions are typically obtained with a mathematical model that transforms an electromyographic signal recorded from the muscle into force. This single-input single-output approach, however, limits the comprehensive description of muscle internal dynamics during contraction because of necessary multiscale simplifications. Here, we advance the state-of-the-art in neuromuscular modelling by proposing a novel mathematical model that describes the force-generating dynamics of the individual motor units that constitute the muscle. For the first time, the control to the population of modelled motor units was inferred from decomposed high-density electromyographic signals. The model was experimentally validated, and the sensitivity of its predictions to different experimental neural controls was assessed. The neuromuscular model, coupled with an image-based musculoskeletal model, includes a novel and advanced neuromechanical model of the motor unit excitation-contraction properties, and is suited for subject-specific simulations of human voluntary contraction, with applications in neurorehabilitation and the control of neuroprosthetics.

bioengineering↗

bioRxiv2022

Hill-type computational models of muscle-tendon actuators: a systematic review

Backed by a century of research and development, Hill-type models of skeletal muscle, often including a muscle-tendon complex and neuromechanical interface, are widely used for countless applications. Lacking recent comprehensive reviews, the field of Hill-type modelling is, however, dense and hard-to-explore, with detrimental consequences on innovation. Here we present the first systematic review of Hill-type muscle modelling. It aims to clarify the literature by detailing its contents and critically discussing the state-of-the-art by identifying the latest advances, current gaps, and potential future directions in Hill-type modelling. For this purpose, fifty-seven criteria-abiding Hill-type models were assessed according to a completeness evaluation, which identified the modelled muscle properties, and a modelling evaluation, which considered the level of validation and reusability of the models, as well as their modelling strategy and calibration. It is concluded that most models (1) do not significantly advance beyond historical gold standards, (2) neglect the importance of parameter identification, (3) lack robust validation, and (4) are not reusable in other studies. Besides providing a convenient tool supported by extensive supplementary material for navigating the literature, the results of this review highlight the need for global recommendations in Hill-type modelling to optimize inter-study consistency, knowledge transfer, and model reusability.

bioinformatics↗

bioRxiv2022

Daam1 negatively regulates USP10 activity

The differentiation of fibroblasts into pathological myofibroblasts during wound healing is in part characterized by increased cell surface expression of v-integrins. Our previous studies found that the deubiquitinase (DUB) USP10 removes ubiquitin from v-integrins, leading to cell surface integrin accumulation, subsequent TGF{beta}1 activation, and myofibroblast differentiation. In this study, a yeast-two hybrid screen elucidated a novel binding partner for USP10, the formin, Daam1. The USP10/Daam1 interaction was also supported by proximity ligation assay (PLA) activity. Treatment with TGF{beta}1 significantly increased USP10 and Daam1 protein expression, PLA signal, and co-localization to actin stress fibers. Furthermore, Daam1 siRNA knockdown significantly reduced a) co-precipitation of USP10 and Daam1 on purified actin stress fibers, and b) {beta}1- and {beta}5-integrin ubiquitination resulting in increased v-, {beta}1-, and {beta}5-integrin total protein levels, v integrin recycling to the cell surface, and extracellular fibronectin (FN) organization. Together, our data suggest that Daam1 negatively regulates USP10s DUB activity and subsequently maintains integrin protein homeostasis.

cell biology↗

bioRxiv2022

Identification of Salivary Gland Escape Barriers to Western Equine Encephalitis Virus in the Natural Vector, Culex tarsalis

Herein we describe a previously uninvestigated salivary gland escape barrier (SEB) in Culex tarsalis mosquitoes infected with two different strains of Western equine encephalitis virus (WEEV). The WEEV strains were originally isolated either from mosquitoes (IMP181) or a human patient (McMillan). Both IMP181 and McMillan viruses were fully able to infect the salivary glands of Culex tarsalis after intrathoracic injection as determined by expression of mCherry fluorescent protein. IMP181, however, was better adapted to transmission as measured by virus titer in saliva as well as transmission rates in infected mosquitoes. We used chimeric recombinant WEEV strains to show that inclusion of IMP181-derived structural genes partially circumvents the SEB. Author StatementDuring the first half of the previous century, WEEV was responsible for large outbreaks throughout the northern United States and Canada that caused severe disease in horses and people. Over the past 60 years, cases of WEEV have mysteriously faded and the pathogen is rarely encountered in the clinic today. Salivary gland escape barriers (SEB) are a relatively neglected field of study in arbovirology, and this study provides a valuable contribution to the field by describing a SEB found in otherwise vector competent Culex tarsalis mosquitoes. Although midgut barriers are well studied, less is known about barriers to transmission in the salivary glands. Although salivary gland infection occurs at a high rate following direct injection of virus into the hemocoel, we noticed that only [~]20-30% of infected mosquitoes transmit detectable infectious virus in their saliva. Additionally, although the more pathogenic patient-derived McMillan strain of WEEV infected salivary glands at a similar rate, its transmission was more severely restricted than the mosquito-derived but less pathogenic Imperial 181 strain. We were able to trace determinants of viral transmission to the 6K/E1 region of the gene encoding the viral structural polyprotein. WEEV is a valuable research model for the closely related Eastern equine encephalitis virus and Venezuelan equine encephalitis virus we believe that our findings are applicable to other members of Togaviridae.

microbiology↗