Correlative imaging of a single neuronal cell opens the door to profound multi-perspective sub-cellular examinations

Scientists combined two nano-imaging techniques that stand at opposite ends of the electromagnetic spectrum to demonstrate the benefits of correlative imaging to examine individual neurons from different perspectives. To showcase this, they studied the molecular structures of amyloid proteins and investigated the role metal ions may play in the development of Alzheimer’s Disease at a previously never achieved resolution. Their detailed observations at the sub-cellular level underscore the potential of using combined nanospectroscopic tools to deal with uncertainties due to the complex nature of a biological sample.

Alzheimer’s Disease is the most common cause of dementia. Many research groups are working to reveal molecular mechanisms to better understand the process by which the disease evolves. Due to the current lack of effective treatments that could stop or prevent Alzheimer’s Disease, new approaches are necessary to find out how people can age without memory loss.

High-resolution microscopy techniques such as electron microscopy and immunofluorescence microscopy are most often used to detect amyloidogenic protein molecules, often considered key factors in the disease’s evolution. However, these commonly used methods generally lack the sensitivity necessary to depict molecular structures. This is why scientists from Lund University in collaboration with SOLEIL and MAX IV carried out a proof of concept study which showcases that combining two imaging modalities can be used as effective tools to assess structural and chemical information directly within a single cell.

“Infrared spectroscopic imaging is rapidly evolving, providing new possibilities, and photothermal infrared spectroscopy is one such approach that allows looking at molecular structures at nanoscale,”  said Oxana Klementieva, Associated Senior Lecturer in Medical Microspectroscopy at the Department of Experimental Medical Science at Lund University, who led the study in collaboration with Gunnar Gouras, professor from the same department’s Experimental Dementia Research division, and Tomas Deierborg, professor at the department’s Experimental Neuroinflammation Laboratory. ”

a O-PTIR setup: a pulsed, tunable IR laser is guided onto the sample surface (1). b X-ray fluorescence nanoimaging of individual neuronal cells deposited on Si3N4 (1). c Conceptualization of the data analysis based on superimposed optical, O-PTIR, and S-XRF images.

However, because of the complexity of biological samples, a combination of different imaging techniques applied on the same samples is needed to help us understand phenomena and come up with new ideas and hypotheses.”

The research team combined super-resolution microspectroscopy for sub-cellular imaging based on novel optical photothermal infrared (O-PTIR) to image protein structures and synchrotron-based X-ray fluorescence (S-XRF) to analyze the composition of elements within the cell because detection of metal ions in primary neurons can only be performed using a nano-focused high energy beam. MAX IV’s NanoMAX hard X-ray nanoprobe beamline delivered X-ray fluorescence microscopy of the brain tissue samples and X-ray absorption near edge structure (XANES) spectra were collected at MAX IV’s Balder beamline.

“We believe that our proof of concept study could motivate other researchers to use synchrotron-based imaging tools available at MAX IV,” said Klementieva. “Currently, we are focused on the question of why beta-amyloid aggregation happens in neurons. To better understand the mechanisms of beta‐amyloid aggregation, our approach has to be further developed, for example, by combining it with immunofluorescent microscopy. Such multimodal imaging may provide a more thorough analysis of structural changes of specific proteins in different cellular compartments. This, in turn, could help us understand why the first Alzheimer’s Disease changes begin and could thus – hopefully – open the doors towards developing preventative therapies for the disease.”

Publication:

Gustavsson, N., Paulus, A., Martinsson, I. et al. Correlative optical photothermal infrared and X-ray fluorescence for chemical imaging of trace elements and relevant molecular structures directly in neurons. Light Sci Appl 10, 151 (2021). DOI: 10.1038/s41377-021-00590-x