4D-Imaging / Cardiac NanoDynamics | Universitätsklinikum Freiburg

4D Imaging / Cardiac NanoDynamics

We use experimental approaches to investigate dynamic cardiac ultrastructure on a nano-to-micro scale. Through our research we attempt to understand how the various cells in the heart respond to their environment, for example to mechanical cues (such as contraction), or the signals generated by their neighbours.

Main research areas are:

Ultrastructure and function of sub-cellular domains in the beating heart

The external appearance of uniformity of cardiomyocyte contractions emerges from coordination of numerous, spatio-temporally heterogeneous processes, involving specialised sub-cellular nano-domains. We investigate the beat-by-beat auto-regulation of heart function at the nano-scale, and propose that the heartbeat is not merely the consequence of cardiomyocyte activity, but an intrinsic regulator that continually modifies nano-domain structure and function in preparation for the next beat. We use time-resolved 3D electron microscopy, sub-cellular functional imaging, ultrastructural proteomics, and artificial intelligence-assisted data analysis, to map out the ultrastructural dynamics of the heart in at the scale of nanometres and milliseconds.

Segmentation of cardiomyocyte organelles in a 3D electron tomography volume. Image: Dr. J. Greiner.

Cardiomyocyte-fibroblast cross talk in the heart

We study the nano-scale cross-talk between cardiomyocytes and fibroblasts in the context of fibrotic remodelling. Specifically, we investigate the role of dynamic fibroblast membrane nanotubes in the process of extracellular matrix deposition at the interface with cardiomyocytes and within cardiomyocyte nano-domains. We use time-resolved light and electron microscopy, human induced pluripotent stem cell (hiPSC) models, and proteomics, to gain insights into nano-scale mechanisms of fibrotic remodelling, and develop strategies to steer fibroblast-cardiomyocyte interactions.

A: Co-culture of primary human cardiac fibroblast (FB, right) and hiPSC-cardiomyocyte (left); fibroblast membrane nanotubes (FB-MNT) directly interact with hiPSC-cardiomyocyte membranes. B: Fibroblast membrane nanotubes can be visualised using 3D cryo-electron tomography. Numerous structures are detected within fibroblast membrane nanotubes, including actin, vesicles, and organelles such as mitochondria.

Cardiomyocyte-neuron cross talk in the heart

The intracardiac nervous system plays a fundamental role in the fine-tuned regulation of cardiac function. The efficiency and precision of neuro–cardiac communication are thought to be critically determined by the ultrastructural geometry of the interface between neurons and cardiomyocytes. Despite its functional importance, the nano-scale architecture and dynamic organisation of the neuro–cardiac junction remain poorly understood. We investigate the structural organisation and functional properties of the neuro–cardiac junction at the nano-scale, using hiPSC models, and advanced high-resolution imaging approaches.

A: Schematic of a proposed structure of the neuro–cardiac junction, showing a sympathetic neuron bouton forming a close synapse-like approximation with a cardio-myocyte, positioning vesicle release sites directly opposite post-synaptic receptors. B: 3D electron microscopy imaging and reconstruction of unmyelinated nerve fibers in murine sino-atrial node.