Name: imaging amyloid tissues stained with luminescent conjugated oligothiophenes by hyperspectral confocal microscopy and fluorescence lifetime imaging
Uploaded: 2017-10-20T15:00:00.000+00:00
Duration: 10 min 4 s
Description: Watch this Scientific Journal Video about Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy and Fluorescence Lifetime Imaging at JoVE.com

The authors wish to thank Mikael Lindgren and Chanan Sluzny for advice on fluorescence microscopy, and Adriano Aguzzi, Johan Bijzet, Bouke Hazenberg, Frank Heppner, Mathias Jucker, Therese Klingstedt, Karin Magnusson, Christina Sigurdson, Daniel Sj&#246;lander, Christoph R&#246;cken, Gunilla Westermark, Per Westermark, and Kurt Zatloukal for contributing tissue sections or micrographs displayed in this publication. The collection of presented data herein has been financed by contributions from Swedish Brain Foundation (Hj&#228;rnfonden), the Swedish Alzheimer association (Alzheimerfonden), the Swedish research council (VR), the G&#246;ran Gustafsson association, Georg &#38; Astrid Olsson, EU FP7 Health project LUPAS, and Link&#246;ping University.

NOTE: LCO synthesis has been performed in our labs for more than a decade. By essentially applying protocols for electrophilic aromatic substitution, palladium catalyzed cross-coupling, amide coupling, and ester hydrolysis, we synthetically customize probes for different purposes5,12. After synthesis, characterization, and purification, the LCO product is lyophilized and stored at room temperature. Some of the probes (among them hFTAA) are now commercially available (see Table of Materials).
1. LCO Staining Solution
NOTE: If hFTAA is purchased from a commercial vendor, please follow the vendor&#39;s instructions instead of section 1.
<ol>
	<li>Resuspend the lyophilized hFTAA in 2 mM NaOH to prepare a stock solution of 1 mg/mL. Keep the stock in a glass vial at 4 &#176;C. The stock can be stored for one year.</li>
	<li>On the day of staining, prepare a working solution by diluting the stock 1:10,000 in Phosphate-buffered saline (PBS).</li>
</ol>
2. Preparation of Tissue Samples
NOTE: Many tissue types can be imaged using hFTAA as an amyloid marker. See Figure 1 for examples. hFTAA is sensitive to aggregate conformation. The staining should hence preferably be performed on undisrupted aggregates with no epitope exposure. Optimal spectral quality is achieved if the tissue fixation is kept to a minimum. Hence fresh frozen material, gently fixed in ethanol at the time of staining, is preferred. However, it is possible to detect amyloid deposits also in tissue that has been fixed with e.g., formalin. hFTAA generally penetrates the tissue well. Select a specimen thickness that is compatible with the intended imaging technique.
<ol>
	<li>If formalin fixed, parafinembedded sections are used, deparafinize in xylene over night. Dip the sections in consecutive baths of 99% ethanol, 70% ethanol, dH2O, and PBS, 10 min in each. Allow the tissue sections to dry under ambient conditions. 
	Caution: Xylene is always handled in a chemical fume hood. Xylene and other organic solvents are harmful.
	<ol>
		<li>Thaw cryosections in room temperature. Fix the tissue sections in 10% formalin overnight and rehydrate by dipping them in consecutive baths of 99% ethanol, 70% ethanol, dH2O, and PBS, 10 min in each. Allow the tissue sections to dry under ambient conditions.</li>
	</ol>
	</li>
	<li>Add droplets of the hFTAA working solution (approximately 200 &#181;L) to the tissue sections to cover it. The droplet should stay in place by surface tension. Incubate for 30 min at room temperature for staining.</li>
	<li>Rinse off the staining solution with 500 &#181;L PBS using a pipette and then immerse the slide in the PBS bath for 10 min. Allow the section to dry under ambient conditions.</li>
	<li>Mount using the fluorescence mounting medium. Allow mounting medium to settle overnight. 
	NOTE: hFTAA staining can be performed in combination with other staining methods such as immunofluorescence, cell- or organelle specific markers, etc. To perform co-staining, run your complete staining protocol of choice and add hFTAA staining at the end, starting from step 2.2. See Figure 2 for examples. For immunofluorescence, preferably select a secondary antibody that is excited at 640 nm or higher. In this wavelength range, hFTAA does not absorb and hence cannot be excited and will not fluoresce. This ensures that no bleed-through is seen between hFTAA and antibody.</li>
</ol>
3. Microscopy
NOTE: Use a fluorescence microscope equipped with long pass filters. All settings below were used to generate the images in Figure 4. Adjustments may need to be made depending on the amyloid type and tissue sample. Although hFTAA bound to amyloid is stable towards bleaching, it is advisable to turn off the light source when the specimen is not examined or imaged.
<ol>
	<li>HIS 
	NOTE: The experiment was performed using an epifluorescence microscope with long pass emission filters and a camera head for HIS (see Table of Materials).
	<ol>
		<li>Use a standard fluorescence microscope equipped with long pass filters and a hyperspectral camera. Make sure that the spectral camera is calibrated.</li>
		<li>In the software, name the project, select &#34;spectral image&#34; and start acquisition.</li>
		<li>Select the object of interest through the ocular using the 436-nm excitation filter and shift the light path to the camera.</li>
		<li>In the Case Data Manager (CDM), select the sample type Spectral, label the sample, and press acquire. The acquisition window will open.</li>
		<li>In the acquisition window &#34;Spectral imaging&#34;, open the settings menu, select acquisition properties, and set the spectral range to 460 - 700, the speed quality at maximum speed, and the measurement type at gas/laser/narrow filters. Close the dialog box.</li>
		<li>In the image menu, select live full. In the icons bar, turn fringes off. Select or size a region to image that has the peak memory value below 800 MB. Set the exposure time to a value that gives a total image brightness between 1,000 and 3,000. In the icons bar, press the colored camera. Acquisition will start. When image acquisition is complete, press Save in the &#34;Acquire spectral image&#34; dialog box and &#34;New cell&#34; in the case data manager dialog box.</li>
		<li>From the CDM, open the collected image using the start analysis button. The data analysis window will open.</li>
		<li>Spectral information can be collected from each pixel of the image by selecting ROIs using the Spectral display dialog box. Choose &#34;define&#34; and select ROIs from the relevant areas of the image.</li>
		<li>Save the spectral data as a text file using the Lib button. The saved .txt file can be imported to any analysis software of choice. The .slb file can be used for analysis within the data analysis software. The hyperspectral cube data from the entire image can also be exported as a raw file, as &#34;layers as tif&#34;, or as &#34;layers in text format&#34; for data and image analysis applications using external software.</li>
	</ol>
	</li>
	<li>Confocal microscopy 
	NOTE: The confocal microscope is equipped with a tunable laser as the excitation source. For all fluorescence emission experiments, set the laser intensity to 0.2% (corresponding to an average power of 3 &#181;W), the pinhole to 1 airy unit, the frame size to 1,024 px x 1,024 px, the scan speed as 7 and averaging over 16 scans, and the bit depth as 8 bit (see Table of Materials). These settings need to be adjusted for each individual confocal system, laser source, and sample type.
	<ol>
		<li>For the emission spectrum, collect the data using lambda mode and the excitation using argon laser set to 488 nm. Collect emission between 503 and 687 nm using 22 channels in the 32 channel GASP detector. Set the gain to 755.</li>
		<li>To achieve single channel images, use the smart set up option. For FITC (green filter), set the gain to 750 and for Alexa 535 (red filter) set the gain to 845.</li>
		<li>To collect the excitation spectrum with the tunable laser, use excitation with 1 nm steps between 490 and 545 nm while collecting emission between 551 and 586 nm. Set the laser intensity to 2% (corresponding to an average power of 30 &#181;W) and the gain to 774.</li>
		<li>To collect Z-stack in the spectral mode, scan through the depth of the section in steps of 0.96 &#181;m. The same excitation and emission settings as in step 3.2.1 can be used but set the gain to 730.</li>
	</ol>
	</li>
	<li>FLIM 
	NOTE: The confocal microscope is equipped with a FLIM unit (see Table of Materials).
	<ol>
		<li>Set up the following parameters for the confocal microscope: Pinhole, 20; excitation wavelength, 490 nm; laser intensity, 0.5% (corresponding to an average power of 7.5 &#181;W). Use pulsed lasers at 40 MHz.</li>
		<li>In the FLIM software, set up photon counting over 550 nm. In the Display parameters window, follow the photon counting until the Max count is around 4,000 photon counts.</li>
		<li>Save the file and export it as SPC image.</li>
		<li>Fit the data to a 2-component exponential decay in the FLIM software. A fit that gives a &#967;2 &#60; 2 is good. The value on the y-axis is the number of counts for the given lifetime.</li>
		<li>Select a threshold for counts to include, e.g., 100. Color code by T1 and select lifetime range. The decay is dependent on the amyloid structure where the hFTAA is bound. Fluorescence lifetimes between 300 and 1,000 ps have been observed. Save the file.</li>
		<li>Export the raw data by using the export options and save the desired data in a new folder.</li>
	</ol>
	</li>
</ol>

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K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+amyloid-Congo+red+interface+at+atomic+resolution.">The amyloid-Congo red interface at atomic resolution.</a> Angewandte Chemie (International ed). 50 (26), 5956-5960 (2011).</li><li>Hammarstrom, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+fluorescent+pentameric+thiophene+derivative+detects+in+vitro-formed+prefibrillar+protein+aggregates.">A fluorescent pentameric thiophene derivative detects in vitro-formed prefibrillar protein aggregates.</a> Biochemistry. 49, 6838-6845 (2010).</li><li>CORDIS. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Final Report Summary - LUPAS (Luminescent polymers for in vivo imaging of amyloid signatures). , (2013).</li><li>Hahn, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Establishing+and+validating+the+fluorescent+amyloid+ligand+h-FTAA+(heptamer+formyl+thiophene+acetic+acid)+to+identify+transthyretin+amyloid+deposits+in+carpal+tunnel+syndrome.">Establishing and validating the fluorescent amyloid ligand h-FTAA (heptamer formyl thiophene acetic acid) to identify transthyretin amyloid deposits in carpal tunnel syndrome.</a> Amyloid. , 1-9 (2017).</li><li>Johansson, L. 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PH PN MB SN are minor shareholders in Ebba Biotech that commercializes hFTAA under the brand name Amytracker545.

Deposition of aberrantly folded proteins into amyloid is a key event of many disease processes. Extracellular amyloid plaques composed of A&#946; peptides and intracellular neurofibrillary tangles formed by hyperphosphorylated tau are found in the brain of Alzheimer&#39;s disease patients. A range of different proteins, e.g., transthyretin (TTR), Serum Amyloid A component (SAA), and IgG light chain misfold and manifest as amyloid deposits in tissues outside of the CNS. Although amyloid deposits have been known and studied for more than a century, we still lack detailed knowledge of how amyloid deposition is initiated at the molecular level and what can be done to prevent this process. For Alzheimer&#39;s disease, it is necessary to corroborate how the process of amyloidosis is associated with neurodegeneration. One key quest on the mission to treat amyloidosis is to develop novel fine-tuned tools for monitoring amyloid initiation, progression, and regression; hence targeted amyloid detection is key. In the long run, clinical diagnostics will benefit from increasing the sensitivity and selectivity of amyloid staining methods7,15. Current challenges in this respect are tremendous and is a very active research area. One main issue for clinical development and trials is prognostic diagnosis. These diseases likely start well before symptoms appear, but to start with treatment there needs to be identification of the disease. Herein, sensitivity is a key aspect for novel methodologies. Furthermore, this issue is even more complex because some protein aggregates are toxic, some are protective, and some are neutral. Hence the ability to monitor specific aggregated morphotypes is essential since the existence of distinct aggregated species has been suggested to explain the heterogeneous phenotype reported for a diversity of neurodegenerative protein aggregation diseases. For instance, the prion protein is a classic example of how an identical primary sequence of amino acids can misfold into distinct aggregate morphotypes, which give rise to specific prion strains. Similar polymorphism has also been reported for the A&#946; peptide, &#945;-synuclein, and tau. In this regard, LCOs have been shown to be outstanding tools for optical assignment of distinct aggregated morphotypes. Prion-strain-specific protein aggregates, protein deposits found in several types of systemic amyloidosis, as well as polymorphic A&#946; and tau aggregates have been distinguished due to the conformationally induced optical phenomenon observed from the LCOs.
Amyloid deposition is an event that takes place in tissues that are hard to penetrate with biochemical or biophysical methods of molecular precision. The possibility to probe events ex vivo, in vivo, and in vitro using the same LCO molecules sets the stage for unraveling events that occur in vivo using techniques that are only possible to apply on ex vivo or in vitro samples11,17. A recently reported high resolution structural model shows that the LCO pentameric FTAA (pFTAA) binds in a cavity formed by aligned side chains parallel with the fibril axis spanning 6 in-register parallel beta-strands18, demonstrating that it is possible to gain atomic resolution knowledge about the entities of the LCO target. In essence the binding cavity and binding mode of pFTAA is similar to Congo red19, dictated by a groove lined with repetitive positive charged Lys side-chains. The affinity of LCOs appear to be better compared to Congo red likely due to chain flexibility and strong van der Waals interactions of the sulfur atoms of the thiophene rings towards the hydrophobic cavity. The detection of prefibrillar species (before ThT responds)5,20 appears dependent on repetitive &#946; sheets, composed of in-register parallel-beta-strands, which for hFTAA being two thiophene units longer than pFTAA would span crossing of up to 8 beta-strands.
The staining protocol requires paying attention to trouble shooting at the following steps: (i) Fixation: Extensive fixation of tissue samples can disrupt the amyloid structure and limit the possibility to detect variation in fluorescence spectra induced by conformational distortion of the hFTAA molecule. Mild fixation of cryosections from fresh-frozen material is preferred to achieve optimal spectral resolution. However, hFTAA will stain and fluoresce amyloid in fixed tissue but with reduced efficacy and less spectral variation. (ii) Epitope exposure: Pre-treatment of tissue to achieve epitope exposure for antibody binding might occasionally reduce the ability for hFTAA to bind because of disrupted amyloid structure. If this is an issue, and epitope exposure is a crucial step in the antibody staining protocol, using consecutive sections for antibody and hFTAA, respectively can be considered. (iii) Overstaining: hFTAA is extremely sensitive. Working solutions should be kept at low nM concentration. Decrease the concentration of hFTAA if background staining is a problem. If elements that bind hFTAA are sparse in the tissue, an excess of hFTAA can aggregate and accumulate in the mounting medium. This is recognized as fluorescence that is not in the focus plane of the tissue itself. If this appears, immerse the mounted slide in PBS until the cover slip can be slid of the section, wash with PBS, and remount with fresh mounting medium and a new cover slip. (iv) Filter based imaging: This paper describes mostly spectrally resolved fluorescence imaging using long pass filters or multiple detection channels. hFTAA can also be monitored using short pass filters. Please be aware that this will reduce the contrast and abolish the possibilities to detect multiple colors.
Over the past years it has become evident that as research tools, fluorescent LCOs and in particular hFTAA show highly promising properties. Results have been demonstrated for a vast variety of proteins and disease states, ranging from hFTAA detection of aggregates inside cells (tau, inclusion body myositis), systemic amyloid of serum amyloid A, transthyretin, Immunoglobulin light chains (kappa and lambda) seminogelin 1, prion protein (including clinical samples)21, Islet amyloid polypeptide, and insulin7,15. A limiting factor for the implementation of hFTAA as a diagnostic tool is that fluorescence microscopy is not extensively used in routine amyloid pathology labs. Furthermore, HIS is not readily available in the clinic. However, hFTAA amyloid staining and fluorescence microscopy have been used in clinical labs in a filter based fluorescence microscope and should be considered as a complimentary diagnostic method. This was recently demonstrated on carpal tunnel biopsies with transthyretin amyloidosis using basic settings for fluorescence in an automated fashion22.
Furthermore, in addition to various proteins, hFTAA fluorescence recognizes a vast variety of fibril types and pre-fibrillar amyloid aggregates, e.g., pathway fibrillar species have been detected and characterized. In this publication, we have demonstrated one LCO on various sample types using three microscopy techniques. The use of controlled synthesis has also allowed for the development of LCOs for versatile detection of biomolecular targets, e.g., recording of interactions by surface plasmon resonance (SPR)23 and radiolabeling for positron emission tomography (PET)24.
To date, over 25 different LCOs with have been published. An increased use of LCOs for imaging of amyloid deposits will increase the knowledge and understanding of how these disease-associated aggregates assemble, disassemble, and interfere with the organs and individuals in which they reside.

Deposition of amyloid in tissue is a pathologic hallmark in a number diseases such as Alzheimer&#39;s disease, Parkinson&#39;s disease, systemic amyloidosis, and prion diseases. Despite the prevalence of amyloid-related diseases, and the fact that close to 40 different proteins to date have been classified as amyloid precursors in human1, little is known about the relation between amyloid deposition and disease phenotype. Histology of samples from human patients has been used both for diagnostic and scientific purposes. A large number of animal models have been established to investigate the correlation between amyloid burden and behavior, life span, and a number of other phenotypic read outs of disease progression2,3. Large efforts are also being made in drug discovery and design to battle some of our most feared widespread diseases. However, the evaluation of the connection between genotype, phenotype, amyloid plaque load, and drug administration is not straight forward. The tools for staining and imaging of amyloid in tissue are often blunt and provide low resolution information on amyloid formation and structure.
Congo red birefringence, ThT , and ThS fluorescence are examples of classical methods for detecting and analyzing amyloid burden in tissue samples from patient biopsies and post mortem samples, and animal models of disease4. These techniques have been used for several decades (Congo red since the 1920s and ThT and derivatives since the 1960s), and although instrumentation has been refined and allows for detailed analysis, the staining procedures and analysis are still being performed in the same manner as almost a century ago.
In this paper, we describe the utilization of a highly sensitive novel amyloid dye, hFTAA5, that allows the detection of small immature protein deposits with high accuracy, as well as detection of mature amyloid. Compared to conventional dyes, hFTAA has been proven to detect a wider range of disease associated protein aggregates5,6,7. In addition, hFTAA can also be applied for optical assignment of distinct aggregated morphotypes8. Herein, we describe hFTAA staining and analysis of tissue from established animal models of prion disease and Amyloid-&#946; Precursor Protein (APP) transgenic mice designed to mimic plaque development in Alzheimer&#39;s disease9,10. We also show analysis of diagnostic and post mortem samples from patients suffering from systemic amyloidosis. The LCOs have intrinsic properties that enables them to report on conformational differences within one plaque; and by combining two LCOs with different properties regarding binding and fluorescence, the difference is even more pronounced11. An epifluorescence microscope equipped with long pass filters and a hyperspectral camera head is used to enable objective classification of spectral properties and recording of micrographs for spectral analysis. Confocal fluorescence microscopy with a tunable laser as the excitation source is used to evaluate the three-dimensional properties of an amyloid plaque in greater detail. The tunable laser enables collection of excitation spectrum and a step less selection of emission wavelengths on the microscope enables co-imaging of LCO fluorescence and immunofluorescence to determine co-localization of target protein and amyloid. FLIM offers unprecedented sensitivity to conformational differences imposed on the LCOs and reveals differences that might not be detected on the fluorescence emission spectra.
The main goals with the described staining method are to facilitate sensitive detection of small amyloid deposits and to characterize conformational polymorphism within amyloid deposits. This knowledge is important for the basic understanding of protein aggregation diseases.

<table><tbody><tr><td>hFTAA/Amytracker545</td><td>Ebba Biotech</td><td></td><td></td></tr><tr><td>Dako fluorescene mounting medium</td><td>Agilent technologies</td><td>GM304</td><td></td></tr><tr><td>LeicaDM6000</td><td>Leica</td><td></td><td></td></tr><tr><td>Lumen 200</td><td>Prior</td><td></td><td></td></tr><tr><td>Spectraview system</td><td>ASI spectral imaging</td><td></td><td></td></tr><tr><td>Spectraview software</td><td>ASI spectral imaging</td><td></td><td></td></tr><tr><td>LSM780</td><td>Zeiss</td><td></td><td></td></tr><tr><td>Zen 2010b v6.0 software</td><td>Zeiss</td><td></td><td></td></tr><tr><td>FLIM system</td><td>Becker &amp;amp; Hickl</td><td></td><td></td></tr><tr><td>Ar/ML 458/488/514</td><td>Zeiss</td><td></td><td></td></tr><tr><td>Tunable Laser In Tune</td><td>Zeiss</td><td></td><td></td></tr></tbody></table>

imaging amyloid tissues stained with luminescent conjugated oligothiophenes by hyperspectral confocal microscopy and fluorescence lifetime imaging

Proteins that deposit as amyloid in tissues throughout the body can be the cause or consequence of a large number of diseases. Among these we find neurodegenerative diseases such as Alzheimer&#39;s and Parkinson&#39;s disease afflicting primarily the central nervous system, and systemic amyloidosis where serum amyloid A, transthyretin and IgG light chains deposit as amyloid in liver, carpal tunnel, spleen, kidney, heart, and other peripheral tissues. Amyloid has been known and studied for more than a century, often using amyloid specific dyes such as Congo red and Thioflavin T (ThT) or Thioflavin (ThS). In this paper, we present heptamer-formyl thiophene acetic acid (hFTAA) as an example of recently developed complements to these dyes called luminescent conjugated oligothiophenes (LCOs). hFTAA is easy to use and is compatible with co-staining in immunofluorescence or with other cellular markers. Extensive research has proven that hFTAA detects a wider range of disease associated protein aggregates than conventional amyloid dyes. In addition, hFTAA can also be applied for optical assignment of distinct aggregated morphotypes to allow studies of amyloid fibril polymorphism. While the imaging methodology applied is optional, we here demonstrate hyperspectral imaging (HIS), laser scanning confocal microscopy and fluorescence lifetime imaging (FLIM). These examples show some of the imaging techniques where LCOs can be used as tools to gain more detailed knowledge of the formation and structural properties of amyloids. An important limitation to the technique is, as for all conventional optical microscopy techniques, the requirement for microscopic size of aggregates to allow detection. Furthermore, the aggregate should comprise a repetitive &#946;-sheet structure to allow for hFTAA binding. Excessive fixation and/or epitope exposure that modify the aggregate structure or conformation can render poor hFTAA binding and hence pose limitations to accurate imaging.

Sensitive and selective staining of amyloid deposits from a large number of proteins in many different tissue types from both human patients and experimental animals is vital for clinical diagnostics as well as in scientific research. In this paper, we demonstrate how this can be achieved using LCOs, exemplified by hFTAA, for staining and multimodal imaging of amyloid from a selection of tissue types. Since the first publication of thiophene-based amyloid ligands over ten years ago13, amyloid deposits composed of a wide range of proteins in a variety of tissues have been imaged using LCOs6,7,11,14,15,16 (Figure 1). In combination with antibodies or other histological markers, the LCOs provide excellent tools for both diagnostic and scientific purposes (Figure 1a, Figure 2). With an appropriate selection of fluorescent markers, several fluorophores can be imaged on the same section (Figure 1a, hFTAA and DAPI, Figure 2a hFTAA in immunofluorescence setup). It is also possible to use consecutive sections for staining using brightfield and fluorescence (Figure 2b, hFTAA and DAB antibody staining). Recently, hFTAA has been proven to be a highly promising complement to Congo red staining in clinical diagnostics7,15 (Figure 3).
Development of imaging techniques over the last decades has increased the need of amyloid dyes that can discriminate between minute, but at the same time profound differences in amyloid deposits in a quantitative manner. The conjugated system within the LCO provides it with a unique ability to report on variation in its mode of binding. Twisting of the molecule can lead to distortion in the binding angles in the conjugated system and impede the transport of electrons (Figure 4a). This in turn reflects on the fluorescent properties of the LCO both in excitation and emission wavelength and in emission lifetime. We use HIS in an upright fluorescence microscope equipped with long pass filters for emission. For excitation and emission spectra in confocal microscopy and FLIM, we use an LSM780 with pulsed laser. To exemplify the different techniques, we imaged one object (the beta amyloid (A&#946;) plaque in an APP transgenic mouse) (Figure 4b-e). Hyperspectral fluorescence spectra (Figure 4b) allows for the evaluation of spectral shifts and intensity variation within different regions of the plaque. Excitation spectrum in confocal microscopy (Figure 4c) can be used to determine the optimal excitation wavelength for downstream experiments, e.g., combination staining with several fluorophores. This method can also prove useful for detection of conformational differences in the binding mode of the LCO. Emission spectrum in confocal mode can be used to determine the fluorescence emission properties from hFTAA or from a combination of several fluorophores to evaluate colocalization in combination experiments with several LCOs or LCO and immunofluorescence combinations. The fluorescence lifetime of hFTAA is highly influenced by small variations in the binding mode of hFTAA. Hence FLIM is a powerful tool in discriminating between the differences imposed on hFTAA by the binding target (Figure 4d). This can be used for example in the discrimination between different prion strains8. Confocal imaging and processing Z-stacks into three-dimensional images is a useful tool for exploring the overall shape of an amyloid aggregate (Figure 4e). Again, the use of additional fluorophores can aid in understanding the composition of a deposit.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56279/56279fig1.jpg" /> 
Figure 1: Various tissue types and proteins aggregates showing h-FTAA staining of: (a) Mallory-Denk bodies consisting of keratin aggregates in a liver (counterstained with DAPI), (b) p62-positive r inclusions in sporadic inclusion-body myositis (s-IBM) muscle tissue, (c) Amyloid of islet amyloid polypeptide in human pancreas, (d) Amyloid of Immunoglobulin light chain in human intestine, (e) Sheep scrapie (prions) in mouse brain, (f) Chronic wasting disease (prions) in mouse brain, (g) A&#946; plaques in APP23 mouse brain, (h) A&#946; pathology in APP/PS1 mouse brain, and (i) Fat biopsy smears from diagnostic samples of transthyretin amyloid in human patients graded 1 - 4 according to standard Congo red (CR) scoring. Yellow areas show hFTAA stained amyloid deposits and blue is autofluorescence from adipose tissue. The scale bar length is specified in each panel. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56279/56279fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56279/56279fig2.jpg" /> 
Figure 2: Examples of co-staining with antibodies. (a) Co-staining with anti-serum amyloid protein A (AA) immunofluorescence and hFTAA of human AA amyloid on the same section. Upper left: AA antibody emission 640 nm; upper right hFTAA at 488 nm; bottom panel overlay image showing colocalization in yellow. (b) Antibody staining and hFTAA fluorescence on consecutive sections. Top panel: AA antibody DAB staining, bottom panel: hFTAA imaged with a longpass emission filter. Scale bar: 100 &#181;m. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56279/56279fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56279/56279fig3.jpg" /> 
Figure 3: Comparing fluorescence with short pass filters on transthyretin amyloid in human heart stained with Mayer&#39;s hematoxylin/Congo red (a-d) and Mayer&#39;s hematoxylin/hFTAA (e). (a) Brightfield image, (b) Brightfield + fluorescence, (c) Brightfield + crossed polarizers, (d) Brightfield + fluorescence + crossed polarizers, (e) hFTAA fluorescence in 405 nm + 480 nm excitation (consecutive sections to a-d). Scale bar: 100 &#181;m. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56279/56279fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56279/56279fig4.jpg" /> 
Figure 4: The same object stained with hFTAA and imaged with several techniques is demonstrated using one A&#946; plaque in an aged APP23 mouse. (a) The fluorescence properties of hFTAA is dictated by its conformational state. Structure of hFTAA in planar and twisted state is shown. (b) Hyperspectral imaging for evaluation of continuous emission spectrum. Spectra in the lower panel are color coded according to boxed regions of interest in the image. (c) (i) Confocal imaging for excitation imaging and (ii and iii) spectrum and emission imaging in filter mode or (iv) spectral mode. (d) Fluorescence lifetime imaging for detection of conformational differences in the amyloid, where shorter lifetimes are found in the periphery of the A&#946; plaque and the life times are longer in the center of the plaque. Histogram in the lower panel shows distribution of life times for the entire plaque. The image is colored according to the scale below the histogram. (e) Confocal Z-stack collected in filter mode to display the three-dimensional structure of objects. The scale bar length is specified in each panel. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56279/56279fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy and Fluorescence Lifetime Imaging at JoVE.com

Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy and Fluorescence Lifetime Imaging

Amyloid deposition is a hallmark of different diseases and afflicts many different organs. This paper describes the application of luminescent conjugated oligothiophene fluorescence staining in combination with fluorescence microscopy techniques. This staining method represents a powerful tool for detection and exploration of protein aggregates in both clinical and scientific setups.

Proteins that deposit as amyloid in tissues throughout the body can be the cause or consequence of a large number of diseases. Among these we find ...

imaging-amyloid-tissues-stained-with-luminescent-conjugated

Nanyang Technological University

Research

JoVE Journal

Biochemistry

13.3K Views.  Linköping University. Amyloïde afzetting is een kenmerk van verschillende ziekten en treft vele verschillende organen. Deze paper beschrijft de toepassing van de fluorescentie van de verlichte geconjugeerd oligothiophene in combinatie met fluorescentie microscopie technieken kleuring. Deze kleuringstechniek vertegenwoordigt een krachtige tool voor de detectie en verkenning van eiwit-aggregaten in zowel klinische en wetenschappelijke opstellingen.

Video: Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy and Fluorescence Lifetime Imaging

Simple Elimination of Background Fluorescence in Formalin-Fixed Human Brain Tissue for Immunofluorescence Microscopy

Immunofluorescence is a common method used to visualize subcellular compartments and to determine the localization of specific proteins within a tissue sample. A great hindrance to the acquisition of high quality immunofluorescence images is endogenous autofluorescence of the tissue caused by aging pigments such as lipofuscin or by common sample preparation processes such as aldehyde fixation. This protocol describes how background fluorescence can be greatly reduced through photobleaching using white phosphor light emitting diode (LED) arrays prior to treatment with fluorescent probes. The broad-spectrum emission of white phosphor LEDs allow for bleaching of fluorophores across a range of emission peaks. The photobleaching apparatus can be constructed from off-the-shelf components at very low cost and offers an accessible alternative to commercially available chemical quenchers. A photobleaching pre-treatment of the tissue followed by conventional immunofluorescence staining generates images free of background autofluorescence. Compared to established chemical quenchers which reduced probe as well as background signals, photobleaching treatment had no effect on probe fluorescence intensity while it effectively reduced background and lipofuscin fluorescence. Although photobleaching requires more time for pre-treatment, higher intensity LED arrays may be used to reduce photobleaching time. This simple method can potentially be applied to a variety of tissues, particularly postmitotic tissues that accumulate lipofuscin such as the brain and cardiac or skeletal muscles.

Background autofluorescence of biological samples often complicates fluorescence-based imaging techniques, especially in aged human postmitotic tissues. This protocol describes how autofluorescence from these samples can be effectively removed using a commercially available light emitting diode light source to photobleach the sample prior to immunostaining.

Immunofluorescence is a common method used to visualize subcellular compartments and to determine the localization of specific proteins within a tissue ...

Characterization of Amyloid Structures in Aging C. Elegans Using Fluorescence Lifetime Imaging

Amyloid fibrils are associated with a number of neurodegenerative diseases such as Huntington&#39;s, Parkinson&#39;s, or Alzheimer&#39;s disease. These amyloid fibrils can sequester endogenous metastable proteins as well as components of the proteostasis network (PN) and thereby exacerbate protein misfolding in the cell. There are a limited number of tools available to assess the aggregation process of amyloid proteins within an animal. We present a protocol for fluorescence lifetime microscopy (FLIM) that allows monitoring as well as quantification of the amyloid fibrilization in specific cells, such as neurons, in a noninvasive manner and with the progression of aging and upon perturbation of the PN. FLIM is independent of the expression levels of the fluorophore and enables an analysis of the aggregation process without any further staining or bleaching. Fluorophores are quenched when they are in close vicinity of amyloid structures, which results in a decrease of the fluorescence lifetime. The quenching directly correlates with the aggregation of the amyloid protein. FLIM is a versatile technique that can be applied to compare the fibrilization process of different amyloid proteins, environmental stimuli, or genetic backgrounds in vivo in a non-invasive manner.

Characterization of Amyloid Structures in Aging C. Elegans Using Fluorescence Lifetime Imaging

Fluorescence lifetime imaging monitors, quantifies and distinguishes the aggregation tendencies of proteins in living, aging, and stressed C. elegans disease models.

Amyloid fibrils are associated with a number of neurodegenerative diseases such as Huntington&#39;s, Parkinson&#39;s, or Alzheimer&#39;s disease. These ...

Characterizing Spherulites with Polarization-Sensitive Two-Photon Microscopy

Polarization-Sensitive Two-Photon Microscopy for a Label-Free Amyloid Structural Characterization

Compared to its one-photon counterpart, two-photon excitation is beneficial for bioimaging experiments because of its lower phototoxicity, deeper tissue penetration, efficient operation in densely packed systems, and reduced angular photoselection of fluorophores. Thus, the introduction of polarization analysis in two-photon fluorescence microscopy (2PFM) provides a more precise determination of molecular organization in a sample compared to standard imaging methods based on linear optical processes. In this work, we focus on polarization-sensitive 2PFM (ps-2PFM) and its application in the determination of molecular ordering within complex bio-structures-amyloid spherulites. Neurodegenerative diseases such as Alzheimer's or Parkinson's are often diagnosed through the detection of amyloids-protein aggregates formed due to an impaired protein misfolding process. Exploring their structure leads to a better understanding of their creation pathway and consequently, to developing more sensitive diagnostic methods. This paper presents the ps-2PFM adapted for the determination of local fibril ordering inside the bovine insulin spherulites and spherical amyloidogenic protein aggregates. Moreover, we prove that the proposed technique can resolve the three-dimensional organization of fibrils inside the spherulite.

Author Spotlight: Non-Invasive Imaging of Complex Bio-Structures Using Polarization-Sensitive Two-Photon Microscopy 

This paper describes how polarization-sensitive two-photon microscopy could be applied to characterize the local organization within label-free amyloid superstructures-spherulites. It also describes how to prepare and measure the sample, assemble the required setup, and analyze the data to obtain information about the local organization of amyloid fibrils.

Compared to its one-photon counterpart, two-photon excitation is beneficial for bioimaging experiments because of its lower phototoxicity, deeper tissue ...

Chemistry

Quantitative 3D In Silico Modeling (q3DISM) of Cerebral Amyloid-beta Phagocytosis in Rodent Models of Alzheimer's Disease

Neuroinflammation is now recognized as a major etiological factor in neurodegenerative disease. Mononuclear phagocytes are innate immune cells responsible for phagocytosis and clearance of debris and detritus. These cells include CNS-resident macrophages known as microglia, and mononuclear phagocytes infiltrating from the periphery. Light microscopy has generally been used to visualize phagocytosis in rodent or human brain specimens. However, qualitative methods have not provided definitive evidence of in vivo phagocytosis. Here, we describe quantitative 3D in silico modeling (q3DISM), a robust method allowing for true 3D quantitation of amyloid-&#946; (A&#946;) phagocytosis by mononuclear phagocytes in rodent Alzheimer&#39;s Disease (AD) models. The method involves fluorescently visualizing A&#946; encapsulated within phagolysosomes in rodent brain sections. Large z-dimensional confocal datasets are then 3D reconstructed for quantitation of A&#946; spatially colocalized within the phagolysosome. We demonstrate the successful application of q3DISM to mouse and rat brains, but this methodology can be extended to virtually any phagocytic event in any tissue.

Quantitative 3D In Silico Modeling q3DISM of Cerebral Amyloid-beta Phagocytosis in Rodent Models of Alzheimer's Disease

We developed a methodology for quantitative 3D in silico modeling (q3DISM) of cerebral amyloid-&#946; (A&#946;) phagocytosis by mononuclear phagocytes in rodent models of Alzheimer&#39;s disease. This method can be generalized for the quantitation of virtually any phagocytic event in vivo.

Neuroinflammation is now recognized as a major etiological factor in neurodegenerative disease. Mononuclear phagocytes are innate immune cells responsible ...

Medicine

In vivo Imaging of Biological Tissues with Combined Two-Photon Fluorescence and Stimulated Raman Scattering Microscopy

Stimulated Raman scattering (SRS) microscopy enables label-free imaging of the biological tissues in its natural microenvironment based on intrinsic molecular vibration, thus providing a perfect tool for in vivo study of biological processes at subcellular resolution. By integrating two-photon excited fluorescence (TPEF) imaging into the SRS microscope, the dual-modal in vivo imaging of tissues can acquire critical biochemical and biophysical information from multiple perspectives which helps understand the dynamic processes involved in cellular metabolism, immune response and tissue remodeling, etc. In this video protocol, the setup of a TPEF-SRS microscope system as well as the in vivo imaging method of the animal spinal cord is introduced. The spinal cord, as part of the central nervous system, plays a critical role in the communication between the brain and peripheral nervous system. Myelin sheath, abundant in phospholipids, surrounds and insulates the axon to permit saltatory conduction of action potentials. In vivo imaging of myelin sheaths in the spinal cord is important to study the progression of neurodegenerative diseases and spinal cord injury. The protocol also describes animal preparation and in vivo TPEF-SRS imaging methods to acquire high-resolution biological images.

In vivo Imaging of Biological Tissues with Combined Two-Photon Fluorescence and Stimulated Raman Scattering Microscopy

Stimulated Raman scattering (SRS) microscopy allows label-free imaging of biomolecules based on their intrinsic vibration of specific chemical bonds. In this protocol, the instrumental setup of an integrated SRS and two-photon fluorescence microscope is described to visualize cellular structures in the spinal cord of live mice.

Stimulated Raman scattering (SRS) microscopy enables label-free imaging of the biological tissues in its natural microenvironment based on intrinsic ...

Bioengineering

Unveiling Mitochondrial Ultrastructure in Neurons Using STED Microscopy

Using Live Cell STED Imaging to Visualize Mitochondrial Inner Membrane Ultrastructure in Neuronal Cell Models

Mitochondria play many essential roles in the cell, including energy production, regulation of Ca2+ homeostasis, lipid biosynthesis, and production of reactive oxygen species (ROS). These mitochondria-mediated processes take on specialized roles in neurons, coordinating aerobic metabolism to meet the high energy demands of these cells, modulating Ca2+ signaling, providing lipids for axon growth and regeneration, and tuning ROS production for neuronal development and function. Mitochondrial dysfunction is therefore a central driver in neurodegenerative diseases. Mitochondrial structure and function are inextricably linked. The morphologically complex inner membrane with structural infolds called cristae harbors many molecular systems that perform the signature processes of the mitochondrion. The architectural features of the inner membrane are ultrastructural and therefore, too small to be visualized by traditional diffraction-limited resolved microscopy. Thus, most insights on mitochondrial ultrastructure have come from electron microscopy on fixed samples. However, emerging technologies in super-resolution fluorescence microscopy now provide resolution down to tens of nanometers, allowing visualization of ultrastructural features in live cells. Super-resolution imaging therefore offers an unprecedented ability to directly image fine details of mitochondrial structure, nanoscale protein distributions, and cristae dynamics, providing fundamental new insights that link mitochondria to human health and disease. This protocol presents the use of stimulated emission depletion (STED) super-resolution microscopy to visualize the mitochondrial ultrastructure of live human neuroblastoma cells and primary rat neurons. This procedure is organized into five sections: (1) growth and differentiation of the SH-SY5Y cell line, (2) isolation, plating, and growth of primary rat hippocampal neurons, (3) procedures for staining cells for live STED imaging, (4) procedures for live cell STED experiments using a STED microscope&#160;for reference, and (5) guidance for segmentation and image processing using examples to measure and quantify morphological features of the inner membrane.

Author Spotlight: Decoding Mitochondrial Aging 

This protocol presents a workflow for the propagation, differentiation, and staining of cultured SH-SY5Y cells and primary rat hippocampal neurons for mitochondrial ultrastructure visualization and analysis using stimulated emission depletion (STED) microscopy.

Mitochondria play many essential roles in the cell, including energy production, regulation of Ca2+ homeostasis, lipid biosynthesis, and production of ...

Neuroscience

Open Source High Content Analysis Utilizing Automated Fluorescence Lifetime Imaging Microscopy

We present an open source high content analysis instrument utilizing automated fluorescence lifetime imaging (FLIM) for assaying protein interactions using F&#246;rster resonance energy transfer (FRET) based readouts of fixed or live cells in multiwell plates. This provides a means to screen for cell signaling processes read out using intramolecular FRET biosensors or intermolecular FRET of protein interactions such as oligomerization or heterodimerization, which can be used to identify binding partners. We describe here the functionality of this automated multiwell plate FLIM instrumentation and present exemplar data from our studies of HIV Gag protein oligomerization and a time course of a FRET biosensor in live cells. A detailed description of the practical implementation is then provided with reference to a list of hardware components and a description of the open source data acquisition software written in &#181;Manager. The application of FLIMfit, an open source MATLAB-based client for the OMERO platform, to analyze arrays of multiwell plate FLIM data is also presented. The protocols for imaging fixed and live cells are outlined and a demonstration of an automated multiwell plate FLIM experiment using cells expressing fluorescent protein-based FRET constructs is presented. This is complemented by a walk-through of the data analysis for this specific FLIM FRET data set.

We present an open source high content analysis (HCA) instrument utilizing automated fluorescence lifetime imaging (FLIM) for assaying protein interactions using F&#246;rster resonance energy transfer (FRET) based readouts. Data acquisition for this openFLIM-HCA instrument is controlled by software written in &#181;Manager and data analysis is undertaken in FLIMfit.

We present an open source high content analysis instrument utilizing automated fluorescence lifetime imaging (FLIM) for assaying protein interactions ...

Biology

Fluorescence Lifetime Macro Imager for Biomedical Applications

This paper presents a new photoluminescence lifetime imager designed to map the molecular oxygen (O2) concentration in different phosphorescent samples ranging from solid-state, O2-sensitive coatings to live animal tissue samples stained with soluble O2-sensitive probes. In particular, the nanoparticle-based near-infrared probe NanO2-IR, which is excitable with a 625 nm light-emitting diode (LED) and emits at 760 nm, was used. The imaging system is based on the Timepix3 camera (Tpx3Cam) and the opto-mechanical adaptor, which also houses an image intensifier. O2 phosphorescence lifetime imaging microscopy (PLIM) is commonly required for various studies, but current platforms have limitations in their accuracy, general flexibility, and usability.
The system presented here is a fast and highly sensitive imager, which is built on an integrated optical sensor and readout chip module, Tpx3Cam. It is shown to produce high-intensity phosphorescence signals and stable lifetime values from surface-stained intestinal tissue samples or intraluminally stained fragments of the large intestine and allows the detailed mapping of tissue O2 levels in about 20 s or less. Initial experiments on the imaging of hypoxia in grafted tumors in unconscious animals are also presented. We also describe how the imager can be re-configured for use with O2-sensitive materials based on Pt-porphyrin dyes using a 390 nm LED for the excitation and a bandpass 650 nm filter for emission. Overall, the PLIM imager was found to produce accurate quantitative measurements of lifetime values for the probes used and respective two-dimensional maps of the O2 concentration. It is also useful for the metabolic imaging of ex vivo tissue models and live animals.

This paper describes the use of a new, fast optical imager for the macroscopic photoluminescence lifetime imaging of long decay emitting samples. The integration, image acquisition, and analysis procedures are described, along with the preparation and characterization of the sensor materials for the imaging and the application of the imager in studying biological samples.

This paper presents a new photoluminescence lifetime imager designed to map the molecular oxygen (O2) concentration in different phosphorescent samples ...

Analyzing Amyloid Structures in a Tissue Section Using Fluorescence Lifetime Imaging Microscopy

<a href='https://app-jove-com.remotexs.ntu.edu.sg/v/56279/imaging-amyloid-tissues-stained-with-luminescent-conjugated'>Source: Nystr&#246;m, S., et al.,&#160;Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy and Fluorescence Lifetime Imaging. J. Vis. Exp.&#160;(2017).</a>This video demonstrates analyzing amyloid structures with fluorescence lifetime imaging microscopy or FLIM, using hFTAA dye to reveal compact cores as blue/green and unstable peripheries as red/yellow in color-coded images, reflecting amyloid organization.

Source: Nystr&#246;m, S., et al.,&#160;Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy ...

JoVE Encyclopedia of Experiments

Neuroimaging

Neurodegeneration & Disease Monitoring

hFTAA Staining of Amyloid Deposits: A Technique to Visualize Amyloid Fibrils Using Oligothiophene-Based Dye for Fluorescence Imaging in Tissue Sections

Source: Nystr&#246;m, S. et al., <a href="https://www-jove-com.remotexs.ntu.edu.sg/v/56279">Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy and Fluorescence Lifetime Imaging.</a> J. Vis. Exp. (2017).
This video describes a technique to stain amyloids in tissue sections using a luminescent-conjugated oligothiophene dye - heptamer-formyl thiophene acetic acid, or hFTAA - for fluorescence imaging. Amyloids are &#946;-sheet-rich abnormal protein aggregates. Their detection in tissue samples is helpful in the diagnosis and treatment of amyloid-associated diseases or proteinopathies.

Source: Nystr&#246;m, S. et al., Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy and ...

Imaging Amyloid Tissues Stained with Luminescent Conjugated Oligothiophenes by Hyperspectral Confocal Microscopy and Fluorescence Lifetime Imaging

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