Biology subjects

Miehling, J.

Publications and source records attributed to Miehling, J..

6 recordsLinked to original sources

bioRxiv2025

GABAA receptor gating imaged on the millisecond timescale

Type-A {gamma}-aminobutyric receptors (GABAARs) are fast pentameric ligand gated ion channels (pLGICs)1-5. Within a millisecond, saturating agonist concentrations trigger activity bursts consisting of high-frequency fluctuations between conductive and non-conductive states6,7. These can last for tens to hundreds of milliseconds until, stochastically, receptors adopt stable, long-lived, desensitised conformations2,8,9. This highly dynamic process, known as gating, controls transient passages of chloride ions across plasma membranes to enable neurotransmission and other fundamental processes in animal physiology10-12. The conformational transitions inside activity bursts, inferred from electrophysiology, have remained inaccessible to structural biology investigation. Here we describe the gating motions of three GABAA receptor variants imaged within the first 10 milliseconds of agonist application by cryogenic electron microscopy (cryo-EM)13. We illustrate how activation and desensitisation proceed through multiple asymmetric states, supported by major secondary, tertiary and quaternary structural rearrangements, and demonstrate that the same gating principles apply to both homomeric and heteromeric GABAARs. Furthermore, we show that cholesterol and phospholipids stabilise newly formed inter-subunit interfaces and obstruct channel pores in short-lived desensitised states, while phosphatidylinositol 4,5-bisphosphate (PIP2) precludes the opening of both 1{beta}3 and 1{beta}3{gamma}2 GABAAR channels. Our results provide a novel framework to interpret decades of electrophysiology observations and suggest a broadly applicable approach to investigate mechanistically the vast arrays of physiological and pharmacological modulators of GABAARs5,14 and other fast neurotransmitter receptors15,16. Moreover, the subunit interfaces and lipid-binding pockets that form and disappear during GABAAR gating provide new opportunities to discover modulators with improved specificity and therapeutic properties. One sentence summarySingle-particle cryo-EM was used to explore the dynamic conformational landscape of three human GABAA receptor variants within the first 10 milliseconds of interaction with their neurotransmitter agonists.

neuroscience↗

bioRxiv2025

From Smartphone Images to Musculoskeletal Models: Personalized Inertial Parameter Estimation

Every human body is different, however, current movement analysis does not reflect that, as it heavily relies on generic musculoskeletal models. Usually, these models are scaled to match the participants body segment lengths and body weight, but not taking individual body shape into account. This can lead to errors in the estimation of joint forces and torques, which are important to accurately estimate musculoskeletal variables. Thus, we developed a method to estimate body segment inertial parameters based on body hulls acquired via smartphone pictures. From the body hull, we infer the skeletal shape and pose, and then estimate the distribution of bone, lean, and fatty tissues. We then segment the body hull and assign each tissue type a density, which is used to calculate the body segment inertial parameters. To allow for the use of our method with existing data, we also introduce two new generic musculoskeletal models, which are based on the average standing body shapes. Validation using MRI-derived ground-truth models shows that our method creates participant-specific musculoskeletal models that are closer to the MRI-derived ground truth than scaled generic models. Additionally, we performed lab-based gait experiments to evaluate the effect of our method on residual forces and joint moments, where we found that our method leads to a reduction of residual forces of up to 14.9 % and a reduction of metabolic cost of up to 12.8 % when compared to generic musculoskeletal models. Our new generic models show similar joint moment outcomes, but less reduction of residual forces than the personalized models.

bioengineering↗

bioRxiv2025

Does reduced reactivity explain altered postural control in Parkinson's disease? A predictive simulation study.

Postural instability represents one of the cardinal symptoms of Parkinsons disease (PD). Still, internal processes leading to this instability are not fully understood. Simulations using neuromusculoskeletal human models could help understand these internal processes leading to PD-associated postural deficits. In this paper, we investigated whether reduced reactivity amplitudes resulting from impairments due to PD can explain postural instability as well as increased muscle tone as often observed in individuals with PD. To simulate reduced reactivity, we gradually decreased previously optimized gain factors within the postural control circuitry of our model performing a quiet upright standing task. After each reduction step, the model was again optimized. Simulation results were compared to experimental data collected from 31 individuals with PD and 31 age- and sex-matched healthy control participants. Analyzing our simulation results, we showed that muscle activations increased with a models reduced reactivity, as well as joint angles ranges of motion (ROMs). However, sway parameters such as center of pressure (COP) path lengths and COP ranges did not increase as observed in our experimental data. These results suggest that a reduced reactivity does not directly lead to increased sway parameters, but could cause increased muscle tone leading to subsequent postural control alterations. To further investigate postural stability using neuromusculoskeletal models, analyzing additional internal model parameters and tasks such as perturbed upright standing requiring comparable reaction patterns could provide promising results. By enhancing such models and deepening the understanding of internal processes of postural control, these models may be used to assess and evaluate rehabilitation interventions in the future. Impact StatementAltered postural control in Parkinsons disease can be partly associated to reduced reactivity. Additional changes in the neural circuitry need to be further investigated to fully explain the observed differences.

bioengineering↗

bioRxiv2024

Investigating cerebellar control in slow gait adaptations: Insights from predictive simulations of split-belt walking

BackgroundDuring split-belt treadmill walking, neurotypical humans exhibit adaptations characterized by a gradual decrease in step length asymmetry (SLA) toward or beyond symmetry, whereas individuals with cerebellar damage do not show these motor adaptations. Neuromusculoskeletal simulations may help to better understand individual aspects of the underlying neural control, but are currently incapable of predicting adaptations to the continuous perturbations imposed by split-belt walking. MethodsWe extend a spinal reflex model with a biologically inspired model of the cerebellum, which enables error-based motor adaptation by modulating spinal control parameters in response to mismatches between a continuously updated internal prediction and actual motor outcomes. In this work, the cerebellum modulates only a single spinal control parameter, the timing of swing initiation in each leg, which allows examining its isolated contribution to gait adaptation as all other reflex pathways are held constant. We created 80 s predictive simulations of the model walking on a split-belt treadmill with a 2:1 belt-speed ratio, and compared predicted spatiotemporal parameters and kinematics to the reflex-only model and literature. ResultsThe reflex-only model could walk on the split-belt treadmill, but showed no step length adaptations. In contrast, the extended model adapted SLA from an initial asymmetric value toward symmetry or beyond, following an exponential time course similar to that observed in experiments. The model could adapt at varying rates and converge to different asymmetry levels. We found that, in simulation, SLA adaptation during split-belt walking is possible without changes in reflex gains, by adapting the timing of swing initiation. The modulation of timing alone also predicted the experimentally observed exponential adaptation in the temporal domain, but only a linear change in the spatial domain, indicating that additional control mechanisms are likely required to reproduce the full spatial adaptation observed in split-belt walking. ConclusionWe propose a computational model of the cerebellum which, when integrated into a spinal reflex model, autonomously drives feedforward gait adaptations during split-belt walking. This advances the current state of predictive simulations and may eventually help to better understand specific adaptation processes. The modular framework can be extended to test different hypotheses about motor control and adaptation during continuous perturbation tasks.

neuroscience↗

bioRxiv2024

A sensorimotor enhanced neuromusculoskeletal model for simulating postural control of upright standing

The humans upright standing is a complex control process that is not yet fully understood. Postural control models can provide insights into the bodys internal control processes of balance behaviour. Using physiologically plausible models can also help explaining pathophysiological motion behaviour. In this paper, we introduce a neuromusculoskeletal postural control model using sensor feedback consisting of somatosensory, vestibular and visual information. The sagittal plane model was restricted to effectively six degrees of freedom and consisted of nine muscles per leg. Physiological plausible neural delays were considered for balance control. We applied forward dynamic simulations and a single shooting approach to generate healthy reactive balance behaviour during quiet and perturbed upright standing. Control parameters were optimized to minimize muscle effort. We showed that our model is capable of fulfilling the applied tasks successfully. We observed joint angles and ranges of motion in physiological plausible ranges and comparable to experimental data. This model represents the starting point for subsequent simulation of pathophysiological postural control behaviour.

bioengineering↗

bioRxiv2020

Single-particle cryo-EM at atomic resolution

The three-dimensional positions of atoms in protein molecules define their structure and provide mechanistic insights into the roles they perform in complex biological processes. The more precisely atomic coordinates are determined, the more chemical information can be derived and the more knowledge about protein function may be inferred. With breakthroughs in electron detection and image processing technology, electron cryo-microscopy (cryo-EM) single-particle analysis has yielded protein structures with increasing levels of detail in recent years1,2. However, obtaining cryo-EM reconstructions with sufficient resolution to visualise individual atoms in proteins has thus far been elusive. Here, we show that using a new electron source, energy filter and camera, we obtained a 1.7 [A] resolution cryo-EM reconstruction for a prototypical human membrane protein, the {beta}3 GABAA receptor homopentamer3. Such maps allow a detailed understanding of small molecule coordination, visualisation of solvent molecules and alternative conformations for multiple amino acids, as well as unambiguous building of ordered acidic side chains and glycans. Applied to mouse apo-ferritin, our strategy led to a 1.2 [A] resolution reconstruction that, for the first time, offers a genuine atomic resolution view of a protein molecule using single particle cryo-EM. Moreover, the scattering potential from many hydrogen atoms can be visualised in difference maps, allowing a direct analysis of hydrogen bonding networks. Combination of the technological advances described here with further approaches to accelerate data acquisition and improve sample quality provide a route towards routine application of cryo-EM in high-throughput screening of small molecule modulators and structure-based drug discovery.

biophysics↗