Alzheimer's disease (AD) is the most common cause of dementia, which so far can not be effectively treated or prevented. It is believed that amyloid-β proteins are critical triggers of the disease. Under unknown pathological conditions, molecular structure of these proteins begin to form fibrillar aggregates that are believed to be neurotoxic. However, why neurons die is not well not understood yet. The failures of several clinical trials targeting amyloid-β proteins indicate that molecular mechanisms of AD are more complex and need to be further investigated; therefore, there is a need for a new method to address molecular mechanisms of AD.
In a new paper published in Light Science & Application , a team of scientists, led by Associate Professor Oxana Klementieva from the Faculty of Medicine at Lund University, and in collaboration with synchrotron facilities SOLEIL (France) and MAX IV (Sweden), reported a novel methodology of chemical imaging of protein states and metal ions directly in primary neurons at high spatial resolution. The paper assesses the suitability of the high-tech approach to study subcellular mechanisms related to Alzheimer’s disease. “Research community already knows that amyloid peptides can accumulate in neurons. However, it is not clear what happens in the neuron when amyloids accumulate there. In our study, we show that by using super-resolution infrared imaging combined with X-ray fluorescence nano-imaging, we are actually able to study molecular mechanisms of amyloid toxicity on a subcellular level”, says Oxana Klementieva.
“Scanning synchrotron-based hard X-ray Fluorescence (S-XRF) nano-imaging is a powerful, versatile, non-invasive technique to obtain spatially resolved semi-quantitative chemical information on most of the elements of the periodic table. A stable and high-intensity nano-beam can be easily tailored to the experimental needs in the 50-500 nm size range. Moreover, fast and continuous scanning with sensitive and high frame rate detectors helps to adapt straightforwardly the measured sample area, spatial resolution, and analytical sensitivity to the experimental needs. The unique characteristics make S-XRF nano-imaging well suited to complement the direct study of primary neurons by information about sub-cellular trace metal localization. Indeed, the high spatial resolution and high analytical sensitivity (ppm) of S-XRF permits to locate the target sites of trace elements/metals within an individual primary neuron and subcellular features,” says Andrea Somogyi, a scientist in charge at the Nanoscopium beamline at the Synchrotron SOLEIL.
“The O-PTIR technique is a new and upcoming measurement modality within photothermal methods. This technique provides a few-hundred-nanometre spatial resolution below the diffraction limit of mid-infrared wavelengths. As the infrared vibrational spectrum gives information on the molecular composition, hyperspectral maps contribute a very deep understanding of sample chemistry. For its capability of superresolution hyperspectral imaging, O-PTIR can be efficiently combined with other techniques, such as S-XRF, highlighted in this paper by complementing elemental mapping with molecular information. Using the gold standard of synchrotron-based infrared spectromicroscopy at the diffraction limit, we can validate the results obtained by O-PTIR and further push the technique towards a wider use and acceptance in laboratory studies and diagnostics.” – says Ferenc Borondics , the head of the SMIS infrared spectromicroscopy beamline at the SOLEIL synchrotron.
The most interesting finding is not only that we were able to see the specific protein structures, but we also observed the distribution of trace elements in the same neuron.
We demonstrated that the O-PTIR/S-XRF approach gives more complete information about the system than if the two techniques were to be used separately. The analysis of co-localization of amyloid structural features and elemental distribution can provide essential insights to the understanding of molecular mechanisms of Alzheimer’s disease. If we can find out what triggers the molecular changes of amyloid proteins in neurons, that would be a great step forward to understand how to prevent neuronal damage and subsequent memory deterioration.
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Light Science & Applications