INFORMATION TECHNOLOGY

Photothermal 3D imaging reveals tau aggregates


Obtaining three-dimensional spatial morphology and chemical information of intracellular amyloid aggregates without destroying cells has been a challenge in biological imaging. In order to overcome this problem, Professor Cheng Jixin of Boston University and Dr. Jian Zhao of the Massachusetts Institute of Technology and their collaborators recently developed a multimodal computational mid-infrared photothermal microscope. The imaging system combines three-dimensional quantitative chemical phase imaging with two-dimensional fluorescence imaging, and successfully extracts the three-dimensional morphological information, site-specific spectral information and three-dimensional spatial distribution information of protein secondary structure of amyloid aggregates in cells while maintaining cell integrity.

Research background

The study of tau protein aggregates, a type of amyloid, has become a frontier hotspot in the field of neurodegenerative diseases. Various types of tau protein aggregates, including tau fibers and oligomers, are thought to be closely associated with a variety of neurodegenerative diseases. However, the formation of tau aggregates and the associated pathogenic mechanisms are still poorly understood. Studying tau protein aggregates requires the ability to characterize their morphological distribution and chemical information in three-dimensional space in their native environment within cells. Several different types of solutions have been tried for this purpose, such as X-ray diffraction, cryo-EM, nuclear magnetic resonance spectroscopy, circular dichroic spectroscopy, and infrared spectroscopy based on atomic force microscopy. These methods have made important advances in characterizing various types of amyloid, including tau aggregates. However, existing solutions have limitations, such as the inability to provide site-specific spectroscopy and three-dimensional morphological distribution of intracellular protein aggregates. Therefore, obtaining three-dimensional chemical information of protein aggregates in a liquid environment within cells remains a great challenge.

Innovative research

Recently, Professor Cheng Jixin of Boston University’s Center for Photonics, Dr. Jian Zhao of MIT’s Pikaul Institute for Learning and Memory, and its main collaborators, including Professor Benjamin Wolozin of Boston University School of Medicine, Professor Tian Lei of the Department of Electrical and Computer Engineering of Boston University, and related team members, developed a new multimodal computational mid-infrared photothermal microscope called fluorescence-guided intensity diffraction tomography with chemical bond selectivity (FBS-IDT). FBS-IDT combines single-photon 2D fluorescence imaging with chemical 3D intensity diffraction tomography. This innovative technique enables molecular-specific 3D chemical imaging and site-specific mid-infrared spectroscopy of tau fibers in the cell’s liquid environment. Specifically, FBS-IDT is able to efficiently extract chemical information of target protein aggregates from complex background protein signals within cells. The 3D chemical imaging of FBS-IDT has the advantages of high speed (approx. 0.05 Hz, up to 6 Hz) and high resolution (approx. 350 nm laterally, approx. 1.1 μm axially). Using this hyperspectral 3D chemical imaging capability, FBS-IDT demonstrates a potential correlation between tau fibers and lipid accumulation within cells. More importantly, this technique is able to extract depth-resolved mid-infrared fingerprint spectra and visualize the protein secondary structure of intracellular tau fibers in three-dimensional space.

Notably, FBS-IDT performs 3D chemical imaging of intracellular amyloid aggregates and protein secondary structures in a liquid environment based on a scan-free, modular design. It takes advantage of a simple additional light source to retrofit low-cost brightfield microscopes. FBS-IDT systems cost at least 30 times less than state-of-the-art imaging techniques such as cryo-electron microscopy, and are small in size with negligible operating costs. This affordable benchtop format is accepted for everyday scientific applications in most laboratories.

Figure 1 FBS-IDT principle and workflow diagram.

prospect

The low cost, modular design of FBS-IDT technology, and the absence of additional pretreatment of biological samples themselves open up a new avenue for 3D imaging and chemical analysis of protein aggregates in the native environment of cells. The technology is expected to make new contributions to neurodegenerative disease research and other types of biomedical applications.

The article was published in the top international academic journal Light: Science & Applications under the title “Mid-infrared Chemical Imaging of Intracellular Tau Fibrils using Fluorescence-guided Computational Photothermal Microscopy”. Dr. Jian Zhao is the first author and corresponding author of this paper, and Professor Cheng Jixin is the co-corresponding author of this paper. (Source: LightScience Applications WeChat public account)

Related paper information:https://www.nature.com/articles/s41377‍-023-0‍1191-6

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