We demonstrate the ability to exploit in-plane resolution of ~ 15 nm and axial resolution of ~ 35 nm by combining X10 Expansion Microscopy with Airyscan 3D imaging.
Expansion Microscopy is the newest of super-resolution imaging methods which allows finer details of samples to be visualised with relatively conventional fluorescence imaging techniques by physically expanding the sample. This is achieved by embedding the samples in an acrylamide hydrogel matrix, crosslinking the fluorescent probes, enzymatically clearing the sample and then osmotically swelling the hydrogel (this paper demonstrates ~ 1000-fold volume expansion).
The enhanced three-dimensional resolution achieved by combining this with Airyscan microscopy (hence, the name Enhanced Expansion Microscopy, or EExM) is better suited than conventional implementations of localisation microscopies, particularly for imaging cell interiors and ultrastructures in cell types with 3D complexity, more so than some of the more popular super-resolution techniques. We demonstrate this by imaging cytoskeletal alpha-actinin lattices and RyR nanodomains in ventricular cardiomyocytes. We go a step further to show how this single-channel resolution can reveal dispersed RyR array structures and the altered single-channel phosphorylation patterns which coincide with the fatal heart pathology – right ventricular failure. To better-understand the functional implications, we have teamed up with Dr Michael Colman (http://physicsoftheheart.com/) to simulate the local calcium signalling events based on the experimentally-mapped RyRs.
This is the first research paper for Tom Sheard, and marks the first home-publication for the Nanoscale Microscopy Group together with a multi-lateral collaboration. Well done, everyone! This work was funded by the MRC DiMeN and Wellcome Trust Seed Award.
On the 12 October, Miriam ran an event funded by The Physiological Society to promote Physiology Friday at The University of Leeds. The aim of this outreach event was to raise awareness of how technological advancements in microscopy are improving our understanding of how human physiology can change within health and disease at the cellular level, specifically related to the heart.
Within research, the knowledge of our own physiology in health and disease has developed in part from the advancement in microscopy, which has enabled the visualisation of single proteins. This advancement can be likened to the difference between an individual who is legally blind compared to someone who has 20/20 vision. Our event utilised visual impairment glasses which distorted an individual’s vision. Participants were asked how well they could resolve the outline of a structure in the absence and presence of the glasses to convey the significance of the development which has occurred within microscopy. Supplementary posters led individuals through the physiological relevance of this technological advancement, with images detailing the single protein structure within the heart. With the use of an anatomical heart model, the function and structure of the heart within health and disease was explained. We communicated how current research is using a super-resolution version of microscopy to characterise how a change in function during heart failure can be due in part to a change in the protein structure within a heart cell. To help convey the scale at which the cellular remodelling within heart failure is occurring, real-life examples were used. For example, if a person was tall enough to reach a plane flying at 30,000 feet then the proteins that we are imaging would still be smaller than the width of that person’s hair. Smartphone microscopes were available to allow individuals to experience first-hand the ability that a microscope has to study an object at a more detailed scale compared to what can be seen by the human eye alone.
Over the course of the day a dialogue was created with students from all disciplines. This sparked a variety of questions on the topic of physiology; what is a heart attack? What happens to the proteins within your heart during heart failure? The event even led to one student exclaiming that “microscopes are so cool”, with another stating “I learned how much I need to take care of my body”.
Many thanks to The Physiological Society who funded and supported this event – now to start planning the next one!
In June 2018 Miriam attended a Public Engagement Training Day which was run by The Physiological Society. Building upon the skills learnt at this event Miriam gained funding from the Society to organise and run an event at The University of Leeds to promote Physiology Friday. Her reflections upon this training day can be read on Page 47 in the Winter 2018 Issue of Physiology News which can be accessed here.
In October 2018 I flew across the world to the laboratory of Dr David Crossman at the University of Auckland in New Zealand. The goal: to study pathological remodelling in human heart biopsies from patients with idiopathic dilated cardiomyopathy (IDCM), using the super-resolution imaging technique expansion microscopy (ExM).
Our interest lies in seeing whether nanodomain remodelling observed in a rat model of heart failure in Leeds, including reorganisation of the internal calcium compartments and functional modification to calcium-handling proteins, is also present in end-stage human heart failure. Understanding the mechanisms of remodelling is one of the first steps towards investigating whether they can be targeted for preventative therapies.
ExM is novel imaging technique, enabling super-resolution imaging by spatially separating fluorophores within a swellable hydrogel. The compatibility of ExM gels with standard microscopes enables greater imaging depth and improved axial resolution over competing super-resolution techniques. ExM therefore provides a practical tool to observe remodelling within dyadic calcium release clusters. I was responsible for starting ExM experiments from scratch in a new lab across the world, requiring efficient independent work to obtain meaningful data in the space of just 4 weeks.
It was fantastic to take this journey and work in a laboratory that is home to a strong consortium of leading cardiovascular researchers. In my final week I gave a 30-minute seminar, in which I presented work to the physiology department and the wider bio-imaging facility. This allowed me to reach an international audience and receive valuable feedback on the progression of my research.
Many thanks to the MRC and DiMeN flexible fund grant which made this trip possible, and special thanks to David Crossman for welcoming me into his lab.
Our new review article to mark 10 years since the first super-resolution imaging experiments on cardiac muscle: Abstract: Remodelling of the membranes and protein clustering patterns during the pathogenesis of cardiomyopathies has renewed the interest in spatial visualisation of these structures in cardiomyocytes. Coincidental emergence of single molecule (super-resolution) imaging and tomographic electron microscopy tools in the last decade have led to a number of new observations on the structural features of the couplons, the primary sites of excitation-contraction coupling in the heart. In particular, super-resolution and tomographic electron micrographs have revised and refined the classical views of the nanoscale geometries of couplons, t-tubules and the organisation of the principal calcium handling proteins in both healthy and failing hearts. These methods have also allowed the visualisation of some features which were too small to be detected with conventional microscopy tools. With new analytical capabilities such as single-protein mapping, in situ protein quantification, correlative and live cell imaging we are now observing an unprecedented interest in adapting these research tools across the cardiac biophysical research discipline. In this article, we review the depth of the new insights that have been enabled by these tools toward understanding the structure and function of the cardiac couplon. We outline the major challenges that remain in these experiments and emerging avenues of research which will be enabled by these technologies. Read the full text usingthis link
Nanodomains are naturally assembled signaling stations, which facilitate fast and highly regulated signaling within and between cells. Calcium (Ca2+) nanodomains known as junctional membrane complexes (JMCs) transduce fast and highly synchronized intracellular signals, which are required by a variety of cell types. Common to most such nanodomains are clustered assemblies of the principal intracellular Ca2+ release channels, ryanodine eceptors (RyRs). JMCs found in cardiac muscle cells have been studied extensively as self-assembled clusters of RyR. While known to form crystalline arrays in vitro, the organization of RyRs in situ within the JMCs has been less clear. The development of single-molecule localization microscopy (SMLM or super-resolution) optical methods have transformed our ability to visualize and accurately quantify the spatial geometries and sizes of RyR clusters. The recent application of the novel DNA-PAINT super-resolution technology has exploited an unprecedented optical resolution of 10–15 nm to visualize the natural arrays of RyRs within JMCs. In this chapter, we review the key insights into the in situ RyR assembly within cardiac nanodomains that have been gained over the last decade with the utility of super-resolution microscopy and the major considerations in interpreting and validating such image data.
To request a preprint version of the chapter, please contact the authors via Researchgate.
Full text of the chapter can be accessed via this direct link.
Miriam recently entered the ‘Three Minute Thesis’ competition held at The University of Leeds. A video of the presentation has since been uploaded to the conference YouTube channel which you can access here. A particular highlight of this competition for Miriam was hearing fellow researchers from a variety of disciplines communicate the wide-ranging impact of their research. The other presentations on the channel are a wonderful demonstration of this.