Objectively assessed long-term wearing patterns and predictors of wearing orthopaedic footwear in people with diabetes at moderate-to-high risk of foot ulceration: a 12 months observational study.

BACKGROUND: Orthopaedic footwear can only be effective in preventing diabetic foot ulcers if worn by the patient. Robust data on long-term wearing time of orthopaedic footwear are not available, and needed to gain more insights into wearing patterns and associated factors (i.e. participants' demographic, disease-related characteristics, and footwear usability). We aimed to objectively assess long-term wearing patterns and identify factors associated with wearing orthopaedic footwear in people with diabetes at moderate-to-high risk of ulceration. METHODS: People diagnosed with diabetes mellitus type 1 and 2 with loss of protective sensation and/or peripheral artery disease and prescribed with orthopaedic footwear were included and followed for 12 months. The primary outcome was mean daily wearing time, continuously measured using a temperature sensor inside the footwear (Orthotimer®). Adherence to wearing orthopaedic footwear was calculated as percentage of wearing time of a total assumed 16 h out-of-bed daytime, where adherence < 60% was a pre-determined non-adherent threshold. Wearing time patterns were assessed by calculating participants' wearing (in)consistency. One-way analyses of variance tested for wearing time differences between subgroups, weekdays, and weekend days. Factors potentially associated with wearing time were collected by questionnaires and medical files. Univariately associated factors were included in multivariate linear regression analysis. RESULTS: Sixty one participants were included (mean (SD) age: 68.0 (7.4) years; females: n = 17; type 2 diabetes mellitus: n = 54). Mean (SD) overall daily wearing time was 8.3 (6.1) hours/day. A total of 40 (66%) participants were non-adherent. Participants with a consistent wearing pattern showed higher daily wearing times than participants with an inconsistent pattern. Mean (SD) wearing times were 12.7 (4.3) vs 3.6 (4.8) hours/day, respectively (P < 0.001). Mean (SD) wearing time was significantly higher (P < 0.010) during weekdays (8.7 (6.0) hours/day) compared to Saturday (8.0 (6.1) hours/day) and Sunday (6.9 (6.2) hours/day). In the multivariate model (R2 = 0.28), "satisfaction with my wear of orthopaedic footwear" was positively associated (P < 0.001) with wearing time. The other seven multivariate model factors (four demographic variables and three footwear usability variables) were not associated with wearing time. CONCLUSIONS: Only one out of three people at moderate to high risk of foot ulceration were sufficiently adherent to wearing their orthopaedic footwear. Changing people's wearing behaviour to a more stable pattern seems a potential avenue to improve long-term adherence to wearing orthopaedic footwear. Investigated factors are not associated with daily wearing time. Based on these factors the daily wearing time cannot be estimated in daily practice. TRIAL REGISTRATION: Netherlands Trial Register NL7710. Registered: 6 May 2019.

mGluR5 is transiently confined in perisynaptic nanodomains to shape synaptic function.

The unique perisynaptic distribution of postsynaptic metabotropic glutamate receptors (mGluRs) at excitatory synapses is predicted to directly shape synaptic function, but mechanistic insight into how this distribution is regulated and impacts synaptic signaling is lacking. We used live-cell and super-resolution imaging approaches, and developed molecular tools to resolve and acutely manipulate the dynamic nanoscale distribution of mGluR5. Here we show that mGluR5 is dynamically organized in perisynaptic nanodomains that localize close to, but not in the synapse. The C-terminal domain of mGluR5 critically controlled perisynaptic confinement and prevented synaptic entry. We developed an inducible interaction system to overcome synaptic exclusion of mGluR5 and investigate the impact on synaptic function. We found that mGluR5 recruitment to the synapse acutely increased synaptic calcium responses. Altogether, we propose that transient confinement of mGluR5 in perisynaptic nanodomains allows flexible modulation of synaptic function.

Precise Detection and Visualization of Nanoscale Temporal Confinement in Single-Molecule Tracking Analysis.

The plasma membrane consists of a diverse mixture of molecules that dynamically assemble into a highly non-random organization. The formation of nanoscale domains in the membrane is of particular interest as these domains underlie critical cellular functions. Single-molecule tracking is a powerful method to detect and quantify molecular motion at high temporal and spatial resolution and has therefore been instrumental in understanding mechanisms that underlie membrane organization. In single-molecule trajectories, regions of temporal confinement can be determined that might reveal interesting biophysical interactions important for domain formation. However, analytical methods for the detection of temporal confinement in single-molecule trajectories depend on a variety of parameters that heavily depend on experimental factors and the influence of these factors on the performance of confinement detection are not well understood. Here, we present elaborate confinement analyses on simulated random walks and trajectories that display transient confined behavior to optimize the parameters for different experimental conditions. Furthermore, we demonstrate a heatmap visualization tool that allows spatial mapping of confinement hotspots relative to subcellular markers. Using these optimized tools, we reliably detected subdiffusive behavior of different membrane components and observed differences in the confinement behavior of two types of glutamate receptors in neurons. This study will help in further understanding the dynamic behavior of the complex membrane and its role in cellular functioning.

Single-Molecule Localization Microscopy of Subcellular Protein Distribution in Neurons.

Over the past years several forms of superresolution fluorescence microscopy have been developed that offer the possibility to study cellular structures and protein distribution at a resolution well below the diffraction limit of conventional fluorescence microscopy (<200 nm). A particularly powerful superresolution technique is single-molecule localization microscopy (SMLM). SMLM enables the quantitative investigation of subcellular protein distribution at a spatial resolution up to tenfold higher than conventional imaging, even in live cells. Not surprisingly, SMLM has therefore been used in many applications in biology, including neuroscience. This chapter provides a step-by-step SMLM protocol to visualize the nanoscale organization of endogenous proteins in dissociated neurons but can be extended to image other adherent cultured cells. We outline a number of methods to visualize endogenous proteins in neurons for live-cell and fixed application, including immunolabeling, the use of intrabodies for live-cell SMLM, and endogenous tagging using CRISPR/Cas9.

Dynamics and nanoscale organization of the postsynaptic endocytic zone at excitatory synapses.

At postsynaptic sites of neurons, a prominent clathrin-coated structure, the endocytic zone (EZ), controls the trafficking of glutamate receptors and is essential for synaptic plasticity. Despite its importance, little is known about how this clathrin structure is organized to mediate endocytosis. We used live-cell and super-resolution microscopy to reveal the dynamic organization of this poorly understood clathrin structure in rat hippocampal neurons. We found that a subset of endocytic proteins only transiently appeared at postsynaptic sites. In contrast, other proteins were persistently enriched and partitioned at the edge of the EZ. We found that uncoupling the EZ from the synapse led to the loss of most of these components, while disrupting interactions with the actin cytoskeleton or membrane did not alter EZ positioning. Finally, we found that plasticity-inducing stimuli promoted the reorganization of the EZ. We conclude that the EZ is a stable, highly organized molecular platform where components are differentially recruited and positioned to orchestrate the endocytosis of synaptic receptors.

Contribution of Membrane Lipids to Postsynaptic Protein Organization.

The precise subsynaptic organization of proteins at the postsynaptic membrane controls synaptic transmission. In particular, postsynaptic receptor complexes are concentrated in distinct membrane nanodomains to optimize synaptic signaling. However, despite the clear functional relevance of subsynaptic receptor organization to synaptic transmission and plasticity, the mechanisms that underlie the nanoscale organization of the postsynaptic membrane remain elusive. Over the last decades, the field has predominantly focused on the role of protein-protein interactions in receptor trafficking and positioning in the synaptic membrane. In contrast, the contribution of lipids, the principal constituents of the membrane, to receptor positioning at the synapse remains poorly understood. Nevertheless, there is compelling evidence that the synaptic membrane is enriched in specific lipid species and that deregulation of lipid homeostasis in neurons severely affects synaptic functioning. In this review we focus on how lipids are organized at the synaptic membrane, with special emphasis on how current models of membrane organization could contribute to protein distribution at the synapse and synaptic transmission. Finally, we will present an outlook on how novel technical developments could be applied to study the dynamic interplay between lipids and proteins at the postsynaptic membrane.

Effect of different casting design characteristics on offloading the diabetic foot.

BACKGROUND: Non-removable knee-high devices, such as a total contact cast (TCC), are recommended for offloading diabetic plantar forefoot ulcers. However, it is insufficiently known how each of the different design characteristics of these devices contribute to offloading the diabetic foot. RESEARCH QUESTION: What is the offloading effect of the different design characteristics that make up a non-removable knee-high cast for people with diabetes and active or previous plantar forefoot ulcers? METHODS: Sixteen persons with diabetes, peripheral neuropathy and a healed or active plantar forefoot ulcer had their plantar pressures measured during walking in a non-removable knee-high device (TCC), in that device made removable (BTCC), in that device made below-ankle (cast shoe), in that cast shoe worn with a different walking sole and in a newly made cast shoe without a custom-moulded foot-device interface. Peak pressures, force-time integral, and perceived walking comfort were assessed. RESULTS: Compared with the BTCC, peak pressures in the TCC were 47% (P = 0.028), 26% (P = 0.003) and 15% (P = 0.050) lower at the hallux, midfoot and (previous) ulcer location, respectively. Compared to the cast shoe, peak pressures in the BTCC were 39-43% and 47% (both P < 0.001) lower in the forefoot regions and (previous) ulcer location, respectively. The total force-time integral was 21% and 11% (P < 0.007) lower in the TCC and BTCC compared to the cast shoe. Perceived walking comfort was 5.6 in the TCC and 6.5 in the BTCC (P = 0.037). Effects of the other design characteristics (i.e. walking sole and plantar moulding) were non-significant. SIGNIFICANCE: The TCC gives superior offloading, mostly because of being a knee-high and non-removable device, providing an optimal 'shaft effect'. The TCC does, however, negatively affect walking comfort. These results aid decision-making in offloading diabetic plantar forefoot ulcers.