Long-term High-Resolution Intravital Microscopy in the Lung with a Vacuum Stabilized Imaging Window

Summary

This protocol describes the use of multiphoton microscopy to perform long-term high-resolution, single cell imaging of the intact lung in real time using a vacuum stabilized imaging window.

Abstract

Metastasis to secondary sites such as the lung, liver and bone is a traumatic event with a mortality rate of approximately 90% ¹. Of these sites, the lung is the most difficult to assess using intravital optical imaging due to its enclosed position within the body, delicate nature and vital role in sustaining proper physiology. While clinical modalities (positron emission tomography (PET), magnetic resonance imaging (MRI) and computed tomography (CT)) are capable of providing noninvasive images of this tissue, they lack the resolution necessary to visualize the earliest seeding events, with a single pixel consisting of nearly a thousand cells. Current models of metastatic lung seeding postulate that events just after a tumor cell's arrival are deterministic for survival and subsequent growth. This means that real-time intravital imaging tools with single cell resolution ² are required in order to define the phenotypes of the seeding cells and test these models. While high resolution optical imaging of the lung has been performed using various ex vivo preparations, these experiments are typically single time-point assays and are susceptible to artifacts and possible erroneous conclusions due to the dramatically altered environment (temperature, profusion, cytokines, etc.) resulting from removal from the chest cavity and circulatory system ³. Recent work has shown that time-lapse intravital optical imaging of the intact lung is possible using a vacuum stabilized imaging window ^2,4,5 however, typical imaging times have been limited to approximately 6 hr. Here we describe a protocol for performing long-term intravital time-lapse imaging of the lung utilizing such a window over a period of 12 hr. The time-lapse image sequences obtained using this method enable visualization and quantitation of cell-cell interactions, membrane dynamics and vascular perfusion in the lung. We further describe an image processing technique that gives an unprecedentedly clear view of the lung microvasculature.

Introduction

High resolution intravital optical imaging has proven to be crucial to understanding many biological processes, allowing single-cell and sub-cellular parameters to be measured and quantified. In cancer research, intravital imaging of tumor and stromal cells has led to the discovery of many microenvironmental interactions ^6-11 that are only present in the intact animal.

Discoveries about microenvironments associated with intravasation and dissemination of tumor cells in breast cancer using single cell resolution optical imaging in vivo has even led to novel markers for prognosis and response to treatment in breast cancer ....

Protocol

All procedures described in this protocol have been performed in accordance with guidelines and regulations for the use of vertebrate animals, including prior approval by the Albert Einstein College of Medicine Institutional Animal Care and Use Committee.

1. Generating Fluorescently Labeled Mouse Model and Tumor Cells

1. Prepare 100 ml of 0.1 % (w/v) bovine serum albumin/phosphate buffered saline (BSA/PBS) buffer by mixing 0.1 g of BSA with 100 ml of PBS.
2. Prepare fluorescently labeled tumor cells by stable transfection.
   NOTE: Here we use E0771-LG cells, a highly metastatic derivative of E0771 mouse mammary adenocar....

Results

To demonstrate the type of results that can be achieved with this method, we injected E0771-LG tumor cells labeled with the fluorescent protein Clover into the tail vein of MacBlue mice ⁴⁴ at varying time points before surgery. After surgery, 155 kD rhodamine labeled dextran was injected IV to mark the vasculature and time-lapse imaging was performed.

When imaging mice 24 hr post injection, single cells are visible in.......

Discussion

High resolution in vivo optical imaging combined with fluorescently labelled functional tags such as proteins and antibodies has dramatically increased our understanding of the metastatic cascade. It has enabled direct visualization and quantification of single-cell and sub-cellular parameters in tumor cells, host cells and their microenvironment. This imaging within the primary tumor has led, for example, to the discovery of discrete microenvironments that are supportive of either growth invasion or disseminati.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Nickel-Plated Brass Vacuum Regulator 1/8 NPT Female, w/ Gauge, 0 - 20" Hg Vacuum	McMaster Carr	4172K12	Vacuum Regulator
Brass Barbed Hose Fitting Adapter for 1/4" Hose ID X 1/8" NPTF Male Pipe	McMaster Carr	5346K13	Vacuum Regulator Hose Adapter
Pyrex Brand Filtering Flasks with Tubulation; Neck tooled for rubber stopper No. 4; Capacity: 50 ml	Corning Life Sciences Glass	5360-50	Vacuum Flask
Round Glass Coverslips Thickness #1.5, 0.16 - 0.19 mm 10 mm dia.	Ted Pella, Inc.	260368	Cover slips
Exel International Disposable Safelet I.V. Catheters; 22 g x 1 in.	Exel International	26746	Tracheal Catheter
PERMA-HAND Black Braided Silk Sutures, ETHICON LIGAPAK Dispensing Reel Size 2-0	VWR	95056-992	String
Liquid Super Glue, Clear, 0.14 oz	Hendel Corp.	LOC1647358	Cyano-acrylate Glue
Tetramethylrhodamine isothiocyanate–Dextran	Sigma-Aldrich	T1287-500MG	155 kD Dextran
Laboratory Clear Tygon PVC Tubing, 1/16" ID, 1/8" OD, 1/32" Wall Thickness, 25 ft. Length	McMaster Carr	5155T12	Thin Tubing & Tubing for Luer
Crack-Resistant Polyethylene Tubing, 1/8" ID, 1/4" OD, 1/16" Wall Thickness, White, 50 ft. Length	McMaster Carr	5181K24	Thick Tubing
Depillatory Lotion	Nair	-
Micro Medical Tubing 95 Durometer LDPE	Scientific Commodities Inc.	BB31695-PE/1	Tubing for tail vein catheter
30 G x 1 in. BD PrecisionGlide Needle	BD	305128	Needles for tail vein catheter
Puritan Nonsterile Cotton-Tipped Swabs	Fisher Scientific	867WCNOGLUE
Clear Polycarbonate Barbed Tube Fitting, Reducing Straight for 3/32" x 1/16" Tube ID	McMaster Carr	5117k51	Connectors between tubes
One-Hole Rubber Stoppers	Fisher Scientific	14-135F	Stopper for Vacuum Flask
SHARP Precision Barrier Tips, For P-100, 100 µl	Denville Scientific Inc.	P1125	Pipette Tip
Laboratory tape	Fisher Scientific	159015R
Puralube	Henry Schein Animal Health	008897	Opthalmic Ointment
Gemini Cautery Kit	Harvard Apparatus	726067	Cautery Pen
Graefe Micro Dissecting Forceps; Serrated; Slight Curve; 0.8 mm Tip Width; 4" Length	Roboz Surgical	RS-5135	Forceps
Extra Fine Micro Dissecting Scissors 4" Straight Sharp/Sharp 24 mm	Roboz Surgical	RS-5912	Sharp Scissors
Micro Dissecting Scissors 4" Straight Blunt/Blunt	Roboz Surgical	RS-5980	Blunt Scissors
Wipes	Fisher Scientific	06-666-A	Harness
PhysioSuite System	Kent Scientific	PhysioSuite	Vitals Monitor
1 ml Syringe, Tuberculin Slip Tip	BD	309659	Syringe
Cyano acrylate	Staples	LOC1647358	Cover Slip Adhesive
Petroleum Jelly	Fisher Scientific	19-086291	Water Barrier
Adapter Luer Cannulla 1.5 - 2.2 mm	Harvard Apparatus	734118	Catheter Connector
PhysioSuite MouseSTAT pulse oximeter	Kent Scientific		Pulse Oximeter
Isoethesia (isoflurane)	Henry Schein Animal Health	50033	250 ml
Oxygen	TechAir	OX TM
1x PBS	Life Technologies	10010-023
PVC Ball Valve, Push to Connect, 1/4 In	Grainger	3CGJ7	Vacuum Valve
Small Animal Ventilator	Harvard Apparatus	683	Alternative is available from Kent Scientific: MouseVent
OptiMEM Reduced Serum Medium	ThermoFisher Scientific	31985062
Lipofectamine 2000 Transfection Reagent	ThermoFisher Scientific	11668019
MacBlue Tg(Csf1r*-GAL4/VP16,UAS-ECFP)1Hume/J Mice	Jackson Laboratory	026051
Multiphoton Microscope	Olympus	Fluoview FV1000	Alternative to custom built scope
Environmental Enclosure	Precision Plastics	Chamber for FV1000	Alternative to custom built enclosure
Phosphate Buffered Saline	ThermoFisher Scientific	14190136
Laser Power Meter	Coherent	FieldMaxIITOP
Laser Power Meter Head	Coherent	PM10
pcDNA3-Clover Fluorescent Protein Vector	Addgene	40259
G418 Sulfate Selective Antibiotic	ThermoFisher Scientific	10131027
MoFlo Fluorescent-Activate Cell Sorter	Beckman Coulter	XDP
Trypsin EDTA 1x	Corning	25-052-Cl
40 µm Mesh	Falcon	352235
96 Well Plate	Costar	3599
60 mm Culture Dish	Corning	430196
10 cm Culture Dish	Corning	353003
Bovine Serum Albumin	Sigma-Aldrich	A4503
Dulbecco's Phosphate Buffered Saline 1x	Corning	21-031-CV
C57BL/6J Mouse	Jackson Laboratory	000664
Kim Wipes	Fisher Scientific	06-666-A