Name: a label-free segmentation approach for intravital imaging of mammary tumor microenvironment
Uploaded: 2022-05-24T13:00:00
Description: Watch this Scientific Journal Video about A Label-Free Segmentation Approach for Intravital Imaging of Mammary Tumor Microenvironment at JoVE.com

The authors would like to acknowledge NCI R01 CA216248, CA206458, and CA179556 grants for funding this work. We would also like to acknowledge Dr. Kevin Eliceiri and his imaging group for their technical expertise in the early development of our intravital program. We also thank Dr. Ben Cox and other members of the Eliceiri Fabrication Group at the Morgridge Institute for Research for their essential technical design during the early phases of the MIW. Dr. Ellen Dobson assisted with useful conversations about the ImageJ trainable WEKA segmentation tool. In addition, we would like to thank Dr. Melissa Skala and Dr. Alexa Barres-Heaton for the timely use of their microscope. Lastly, we would like to thank Dr. Brigitte Raabe, D.V.M, for all the thoughtful discussions and advice on our mouse handling and care.

All experiments described were approved by the University of Wisconsin-Madison&#39;s Institutional Animal Care and Use Committee. The well-being and pain management in all animal experiments is paramount. Thus, every effort is made to make sure the animal is comfortable and well-cared for at each step of the procedure.
1. Generation of the mammary imaging window (MIW)
<ol>
	<li>To construct the mammary imaging window, fabricate a 14 mm ring from surgical grade stainless stee...

4D intravital imaging is a powerful tool to investigate dynamic physiological interactions within the spatial and temporal context of the native tumor microenvironment. This manuscript provides a very basic and adaptable operational framework to compartmentalize dynamic cell interactions within the tumor mass, the adjacent stroma, or within proximity to the vascular network using only endogenous signals from second harmonic generation or NAD(P)H autofluorescence. This protocol provides a comprehensive, step-by-step metho...

The extracellular matrix (ECM) in the tumor microenvironment is known to be dynamically deposited and remodeled by multiple cell types to further facilitate disease progression1,2,3. These matrix alterations provide both mechanical and biological cues that alter cell behavior and often result in a continuing cycle of matrix remodeling4. Investigation into the dynamic, reciprocal interplay between tumor cells and the extracellular matrix is often conducted using three-dimensional (3D) in vitro culture or microfluidic systems. While these bottom-up approaches have demonstrated mechanisms of ECM remodeling5,6,7, increased proliferation8, epithelial to mesenchymal transition9,10,11,12, and tumor cell migration and invasion7, 13,14,15,16, their focus has been primarily on a few cell types (e.g., tumor cells or fibroblasts) within a homogeneous 3D matrix compared to the diversity and heterogeneity of interactions present within a physiological tissue. In addition to in vitro systems, ex vivo tumor histology can also provide some insight into these cell-cell and cell-ECM interactions17. Immunohistochemistry has the advantage of being able to analyze multiple cell types with respect to the spatially heterogeneous composition and architecture of the ECM, but the static endpoints of fixed tissue do not capture the dynamic nature of interactions between cells and the microenvironment. Intravital imaging has opened the door to interrogate diverse and dynamic interactions within the physiological&#160;context of the native tumor microenvironment.
The capabilities of intravital tumor imaging are rapidly advancing. Improvements in the design of imaging windows and surgical techniques to implant the windows have enabled long-term longitudinal tumor imaging at a variety of anatomical locations (i.e., primary tumor, lymph nodes, metastatic sites18,19,20). Moreover, the capacity of optical instrumentation to visualize and collect data in multiple dimensions (i.e., spectral, spatial fluorescence intensity, and lifetime), and at high resolution and speed (video rate) is becoming widely accessible. The improved technology provides an opportunity to explore rapid changes in cell signaling and phenotypic dynamics within a physiological environment. Lastly, the expansion of optogenetic tools and the wide array of genetic fluorescent constructs allow for the tagging of specific cell types to capture cell migration in the tumor microenvironment or cell lineage tracing during development or disease progression21,22. The use of these tools in combination with CRISPR/Cas9 technology provides researchers the opportunity to generate unique animal models in a timely manner.
While all these advances make intravital imaging an increasingly powerful method to explore dynamic and physiological cellular interactions, there is still an important need to develop strategies that provide spatial, temporal, and structural context at the tissue level to these biological interactions. Currently, many intravital imaging studies compensate for the lack of visual landmarks such as blood vessels by injecting fluorescent dyes into the vasculature or employing mouse models that exogenously express fluorescent proteins to delineate physical features. Injectable dyes and substrates like fluorescent dextrans are broadly utilized to successfully label the vasculature in intravital collections19, 23, 24. However, this approach is not without limitations. For one, it requires additional mouse manipulations and its utility is limited to short-term experiments. For longitudinal studies, fluorescent dextran can be problematic as we observe the accumulation of dextran in phagocytic cells or diffusion into the surrounding tissue over time25. Exogenous fluorescent protein incorporation into the mouse model has been presented as an alternative to fluorescent dextrans but presents limitations of its own. The availability and diversity of exogenous fluorophores within mouse models are still limited and expensive to create. Additionally, in specific models, such as PDX models, genetic manipulations are not desirable or possible. It has also been shown that the presence of fluorescent or bioluminescent proteins within cells are recognized as foreign within the mouse, and within immunocompetent mouse models, this reduces the amount of metastasis due to the response of the host immune system26,27. Lastly, exogenous fluorescent proteins or fluorescent dyes used for spatial context or to segment subsequent data often occupy prime ranges of the light spectrum that could otherwise be used to investigate the physiological interactions of interest.
The use of the intrinsic signal from the ECM or endogenous fluorescence from cells within the tissue represents a potential universal label-free means to segment intravital data for more in-depth cellular and spatial analysis. Second harmonic generation (SHG) has long been used to visualize the ECM28. With the subsequent development of important tools to aid in the characterization of fiber organization29,30,31, it is possible to characterize cell behavior relative to local ECM structure. In addition, autofluorescence from the endogenous metabolite, NAD(P)H, provides another label-free tool to compartmentalize the tumor microenvironment in vivo. NAD(P)H fluoresces brightly in tumor cells and can be used to discriminate the boundaries of the growing tumor nest from its surrounding stroma21,32. Lastly, the vasculature is an important physiological structure in the tumor microenvironment and the site of key cell-type-specific interactions33,34,35. The excitation of red blood cells (RBC) or blood plasma has been used to visualize the tumor vasculature, and using two- or three-photon excitation (2P; 3P) the measurement of blood flow rates has been shown to be possible36. However, while larger blood vessels are easily identifiable by their endogenous fluorescence signatures, the identification of subtle, variable, and less fluorescent small blood vessels requires more expertise. These inherent difficulties hinder optimal image segmentation. Fortunately, these sources of endogenous fluorescence (i.e., red blood cells and blood plasma) can also be measured by fluorescence lifetime imaging37, which capitalizes on the unique photophysical properties of the vasculature and represents a useful addition to the growing intravital toolbox.
In this protocol, a workflow for the segmentation of four-dimensional (4D) intravital imaging explicitly using intrinsic signals like endogenous fluorescence and SHG is described from acquisition to analysis. This protocol is particularly pertinent for longitudinal studies through a mammary imaging window where exogenous fluorescence may not be practical or possible, as is the case with PDX models. The segmentation principles outlined here, however, are broadly applicable to intravital users investigating tumor biology, tissue development, or even normal tissue physiology. The reported suite of analysis approaches will allow the users to differentiate cellular behavior between regions of aligned or random collagen fiber configurations, compare numbers or behaviors of cells residing in specific regions of the tumor microenvironment, and map the vasculature to the tumor microenvironment using only label-free or intrinsic signal. Together, these methods create an operational framework for maximizing the depth of information gained from 4D intravital imaging of the mammary gland while minimizing the need for additional exogenous labels.

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			<td>#1.5 12mm round cover glass</td>
			<td>Warner Instruments</td>
			<td># 64-0712</td>
			<td>MIW construction</td>
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			<td>1.0 mL syringe for SQ injection</td>
			<td>BD</td>
			<td>309659</td>
			<td>Syringe</td>
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			<td>20x objective</td>
			<td>Zeiss</td>
			<td>421452-988</td>
			<td>Water immersion</td>
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			<td>27G needle for SQ injection</td>
			<td>Covidien</td>
			<td>1188827012</td>
			<td>Needle</td>
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			<td>40x objective</td>
			<td>Nikon</td>
			<td>MRD77410</td>
			<td>Water immersion</td>
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			<td>5-0 silk braided suture</td>
			<td>Ethicon</td>
			<td>K870</td>
			<td>Suture for MIW implantation</td>
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			<td>Artificial tears gel</td>
			<td>Akorn</td>
			<td>NDC 59399-162-35</td>
			<td>Eye gel</td>
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			<td>Betadine solution, 5%</td>
			<td>Fisher Scientific</td>
			<td>NC1558063</td>
			<td>Surgery antiseptic</td>
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			<td>cotton-tipped applicator</td>
			<td>Fisher Scientific</td>
			<td>23-400-101</td>
			<td></td>
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			<td>Cyanoacrylate adhesive</td>
			<td>Loctite</td>
			<td>1365882</td>
			<td>MIW construction</td>
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		<tr>
			<td>fluorescent dextran</td>
			<td>Sigma</td>
			<td>T1287-50mg</td>
			<td>intravenous labelling of vasculature</td>
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			<td>forceps</td>
			<td>Mckesson.com</td>
			<td>Miltex&#160;#18-782</td>
			<td>stainless, 4 inch, curved</td>
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			<td>GaAsP photomultiplier tube</td>
			<td>Hamamatsu&#160;</td>
			<td></td>
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			<td>heating blanket</td>
			<td>CARA 72 heating pad</td>
			<td>&#160;038056000729</td>
			<td>Temperature selectable</td>
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			<td>heating chamber</td>
			<td>home built</td>
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			<td></td>
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			<td>Fluorescent lifetime handbook</td>
			<td>Becker and Hickl</td>
			<td></td>
			<td>https://www.becker-hickl.com/literature/handbooks</td>
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			<td>inverted microscope base</td>
			<td>Nikon</td>
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			<td>Isoflurane</td>
			<td>Akorn</td>
			<td>NDC 59399-106-01</td>
			<td>Anesthesia</td>
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			<td>Liqui-Nox</td>
			<td>Fisher Scientific</td>
			<td>16-000-125</td>
			<td>MIW cleaning</td>
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			<td>Meloxicam</td>
			<td>Norbrook</td>
			<td>NDC 55529-040-10</td>
			<td>Analgesic</td>
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			<td>Micro Hose</td>
			<td>Scientific Commodities INC.</td>
			<td>&#160;BB31695-PE/1</td>
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			<td>multiphoton scan head</td>
			<td>Bruker Ultima II</td>
			<td></td>
			<td>Multiphoton scanhead and imaging platform</td>
		</tr>
		<tr>
			<td>NADH FLIM filter</td>
			<td>Chroma</td>
			<td>284994</td>
			<td>ET 440/80 m-2P</td>
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		<tr>
			<td>Nair</td>
			<td>CVS</td>
			<td>339826</td>
			<td>Depilatory cream</td>
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			<td>objective heater</td>
			<td>Tokai Hit</td>
			<td>STRG-WELSX-SET</td>
			<td></td>
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			<td>SHG/FAD filter</td>
			<td>Chroma</td>
			<td>320740</td>
			<td>ET450/40m-2P</td>
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		<tr>
			<td>Sparkle glass cleaner</td>
			<td>Amazon.com</td>
			<td>B00814ME24</td>
			<td>Glass Cleaner for implanted MIW</td>
		</tr>
		<tr>
			<td>SPC-150 photon counting board</td>
			<td>Becker and Hickl</td>
			<td></td>
			<td></td>
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		<tr>
			<td>surgical light</td>
			<td>FAJ</td>
			<td>B06XV1VQVZ</td>
			<td>Magnetic LED gooseneck light</td>
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			<td>surgical micro-scissors</td>
			<td>Excelta</td>
			<td>366</td>
			<td>stainless, 3 inch</td>
		</tr>
		<tr>
			<td>Triple antibiotic ointment</td>
			<td>Actavis Pharma</td>
			<td>NDC 0472-0179-34</td>
			<td>Antibiotic</td>
		</tr>
		<tr>
			<td>TV catheter</td>
			<td>Custom</td>
			<td>BD 30G needle: 305106</td>
			<td>Catheter for TV injection</td>
		</tr>
		<tr>
			<td>Two photon filter</td>
			<td>Chroma</td>
			<td>320282</td>
			<td>ET585/65m-2P</td>
		</tr>
		<tr>
			<td>two-photon laser</td>
			<td>Coherent charmeleon</td>
			<td></td>
			<td>Tunable multiphoton laser</td>
		</tr>
		<tr>
			<td>ultrasound gel</td>
			<td>Parker</td>
			<td>PKR-03-02</td>
			<td>Water immersion gel</td>
		</tr>
		<tr>
			<td>Urea crystals</td>
			<td>Sigma</td>
			<td>U5128-5G</td>
			<td>Optional: FLIM IRF</td>
		</tr>
	</tbody>
</table>

a label-free segmentation approach for intravital imaging of mammary tumor microenvironment

The ability to visualize complex and dynamic physiological interactions between numerous cell types and the extracellular matrix (ECM) within a live tumor microenvironment is an important step toward understanding mechanisms that regulate tumor progression. While this can be accomplished through current intravital imaging techniques, it remains challenging due to the heterogeneous nature of tissues and the need for spatial context within the experimental observation. To this end, we have developed an intravital imaging workflow that pairs collagen second harmonic generation imaging, endogenous fluorescence from the metabolic co-factor NAD(P)H, and fluorescence lifetime imaging microscopy (FLIM) as a means to non-invasively compartmentalize the tumor microenvironment into basic domains of the tumor nest, the surrounding stroma or ECM, and the vasculature. This non-invasive protocol details the step-by-step process ranging from the acquisition of time-lapse images of mammary tumor models to post-processing analysis and image segmentation. The primary advantage of this workflow is that it exploits metabolic signatures to contextualize the dynamically changing live tumor microenvironment without the use of exogenous fluorescent labels, making it advantageous for human patient-derived xenograft (PDX) models and future clinical use where extrinsic fluorophores are not readily applicable.

The installation of the MIW and basic experimental planning are the first steps in this process. This particular MIW design and protocol are more amenable to longitudinal studies19 and has been successfully utilized with both upright and inverted microscopes. In this case, an inverted microscope was used as it has resulted in greater image stability of the mammary gland with fewer breathing artifacts. In Figure 1A, we provide the dimensions of the rigid MIW and a grap...

Watch this Scientific Journal Video about A Label-Free Segmentation Approach for Intravital Imaging of Mammary Tumor Microenvironment at JoVE.com

A Label-Free Segmentation Approach for Intravital Imaging of Mammary Tumor Microenvironment

The intravital imaging method described here utilizes collagen second harmonic generation and endogenous fluorescence from the metabolic co-factor NAD(P)H to non-invasively segment an unlabeled tumor microenvironment into tumor, stromal, and vascular compartments for in-depth analysis of 4D intravital images.

The ability to visualize complex and dynamic physiological interactions between numerous cell types and the extracellular matrix (ECM) within a live tumor ...

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