Name: optimized scratch assay for in vitro testing of cell migration with an automated optical camera
Uploaded: 2018-08-08T13:00:00
Description: Watch this Scientific Journal Video about Optimized Scratch Assay for In Vitro Testing of Cell Migration with an Automated Optical Camera at JoVE.com

Danish Council for Independent Research, Technology and Production, grant #4005-00029

The experimental setup has no ethical and legal restriction and was conducted in agreement with Roskilde University. An overview of the experimental set-up can be seen in Figure 1 and the mechanisms of the optical camera in Figure 2.
1. Preparation
<ol>
	<li>Perform all steps in a sterile laminar flow-bench by cleaning the bench and all equipments with 70% ethanol prior to the start of the experiment.</li>
	<li>Place the optical cam...

<ol>
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The importance of migration in studies of development, wound healing, immunology, and cancer has led to several different methods to study migration. Migration can either be an expression of the expansion or the closure of the gap by the cells. Most often closure of the scratch is tested, as it is easier to grow cells in a monolayer and then make a scratch than growing the cells in a specific form8. Our study demonstrates an optimized method for manual scratching, as the technique is easy to maste...

Migration is an important process that influences several physiological aspects. In wound healing, migration facilitates re-epithelization of the skin. In non-healing wounds, such as chronic wounds, opportunistic bacteria cause infection of the wound, and open wounds are ideal for bacteria growth and formation of biofilm1,2. Biofilm is one of the causes of the development of resistant bacteria, which is one of the biggest threats to our modern society3. In wound healing, the immune cells cannot penetrate the biofilm. In cancer, migration of the cancer cells is a pivotal step of metastasis, which is the primary cause of death for patients with solid tumors4,5. Therefore, it is crucial to be able to study migration.
The scratch assay is often used to test cell migration because it is cheap and easy to perform on adherent cell lines, such as fibroblast, endothelial, and epithelial cell lines6,7. Today, several methods exist for performing scratches8, and different materials have been reported to be used, including toothpicks9, cell scrapers10, lasers11, and electric currents12. All of the methods have different pros and cons, and the method should be decided upon according to the cell type, budget, and analysis tool. As an example, if the used cell type requires coating, manual pressure removal, e.g. with a toothpick or pipette tip, will influence migration within the area, a different method should be used. In this study, we will focus on manual scraping.
A downside for manual scraping is the variation of the size, shapes of the scratches, and accumulation of cell on the edges of the scratch. Many protocols exist, and a highly cited paper advises increased speed and/or thorough washing after scratching13. Additionally, several methods have been used to minimize proliferation, since the proliferation of the cells cannot be distinguished from migration and therefore may give false-positive results of migration. Some reported methods are serum starvation preceding the scratch14 and decreasing the amount of serum15. However, neither of these methods can ensure that there is no proliferation. Therefore, we report a pre-treatment of the cells with mitomycin C to ensure true results of migration. Mitomycin C is an antibiotic that inhibits DNA synthesis by forming a covalent bond with the DNA, which prevents the DNA from separating16. By pre-treating with mitomycin C and washing with PBS before scratching, the detected closure of the gap demonstrates the true migration of the cells (Figure 1).
A characteristic of all the methods is the need for a system to analyze the process of migration17. A common and an inexpensive method to analyze the progress is to use a light-field microscope to take images of the scratch at pre-determined time points, followed by an analysis of the closure of the gap in an image software18,19. This method is time-consuming, unreliable with regards to taking pictures at the same spot and focus, and the movement from incubator to camera forces cycles of temperature changes while pictures are taken. Other methods have been developed to detect migration by measuring the current flow. The current changes, as cells cover more space on the plate, which is read as an increase in the impedance20. By measuring impedance, the environment of the cells is not affected, and the method is therefore considered non-invasive. This method relies on specialized plates with gold electrodes, which are expensive, but they enable detection of many processes, such as cellular adherence, proliferation, migration, and cell death. A big disadvantage of this method is that the impedance measurement does not directly indicate migration, as factors such as temperature have a great impact on the impedance. Changes in the impedance can be caused by several factors that are not reviewed by the software, making the analysis of the data more difficult. Therefore, the lack of visualization requires a conventional light microscope to verify migration.
To overcome many of the downsides of the available techniques, we use a real-time automated optical camera. The optical camera is a detection system with a high-throughput microscope in a small platform with a lens, illumination unit, and a digital camera. It has a built-in software, which can test migration and proliferation among other things. To detect migration, two algorithms are used to analyze the growth and the migration kinetics of cells, which are called the proliferation and the wound healing analysis, respectively. The proliferation analysis is based on a two-step image segmentation algorithm that applies texture analysis to detect the difference between cell-covered areas (shown in yellow) and empty background areas by advanced histogram analysis. The wound healing analysis is based on a three-step algorithm that detects the cell monolayer, locates the wound gap, and determines the gap width. These steps are conducted at user-determined time-points, and the data is presented as covered area, gap width, and gap area. One of the great advantages of this machine is that it enables imaging of adherent cells through liquid because of the angle of the camera21. The camera lenstakes tilted images that are projected to a z-stack of a single z-plane generate to ensure that the pictures are in-focus (Figure 2). z-stacks are generated by merging the series of pictures (e.g. 40) taken perpendicular to the wound edge, and across the entire wound. The z-stacks enables capturing of the depth of the cell layer as well as an in-focus plane across the wound. Furthermore, the series of images can be put together to a video collection of the images, with the click of a button.
We demonstrate an optimized protocol for detection of migration in the keratinocyte cell line HaCaT. We tested Lactoferrin and its N-terminal peptide, Lactoferricin, from humans and cows, to analyze their effect on migration as these molecules have been demonstrated to have numerous applications as antimicrobial and immune modulating molecules22,23. The four compounds were compared to untreated HaCaT cells and epidermal growth factor (EGF) was used as a positive control.

<table border="0" cellpadding="0" cellspacing="0" width="712">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">oCelloScope</td>
			<td style="width:156px;">BioSense Solution ApS</td>
			<td style="width:119px;"></td>
			<td style="width:221px;">Optical camera</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">UniExplorer software&#160;</td>
			<td style="width:156px;">BioSense Solution ApS</td>
			<td style="width:119px;"></td>
			<td>(8.0.0.7144 (RL3))</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">HaCaT cell</td>
			<td style="width:156px;"></td>
			<td style="width:119px;"></td>
			<td>Donated from Bispebjerg Hospital</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">DMEM (1x) + GlutaMAX</td>
			<td style="width:156px;">Gibco</td>
			<td style="width:119px;">31966-021</td>
			<td>Medium for HaCaT</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">FBS</td>
			<td style="width:156px;">Gibco</td>
			<td style="width:119px;">10270</td>
			<td>Fetal bovine serum</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">PBS</td>
			<td style="width:156px;">Gibco</td>
			<td style="width:119px;">D837</td>
			<td>Without Mg+ and Ca2+</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Pencillin-Streptomycin</td>
			<td style="width:156px;">Sigma</td>
			<td style="width:119px;">P0781</td>
			<td>Antibiotics</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Trypsin (10x)</td>
			<td style="width:156px;">Sigma</td>
			<td style="width:119px;">T3924</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Mitomycin C</td>
			<td style="width:156px;">Tocris</td>
			<td style="width:119px;">3258</td>
			<td>Inhibits proliferation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microtiter plate</td>
			<td style="width:156px;">Greiner Bio-one</td>
			<td style="width:119px;">677 180</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Incubator</td>
			<td style="width:156px;">Panasonic</td>
			<td style="width:119px;"></td>
			<td>37&#176;C, 5% CO2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hemocytometer</td>
			<td style="width:156px;">Assistent</td>
			<td style="width:119px;"></td>
			<td>T&#252;rk (0.1 mm)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Pipet boy</td>
			<td style="width:156px;">Accu-Jet pro</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

optimized scratch assay for in vitro testing of cell migration with an automated optical camera

Cell migration is an important process that influences many aspects of health, such as wound healing and cancer, and it is, therefore, crucial for developing methods to study the migration. The scratch assay has long been the most common in vitro method to test compounds with anti- and pro-migration properties because of its low cost and simple procedure. However, an often-reported problem of the assay is the accumulation of cells across the edge of the scratch. Furthermore, to obtain data from the assay, images of different exposures must be taken over a period of time at the exact same spot to compare the movements of the migration. Different analysis programs can be used to describe the scratch closure, but they are labor intensive, inaccurate, and forces cycles of temperature changes. In this study, we demonstrate an optimized method for testing the migration effect, e.g. with the naturally occurring proteins Human- and Bovine-Lactoferrin and their N-terminal peptide Lactoferricin on the epithelial cell line HaCaT. A crucial optimization is to wash and scratch in PBS, which eliminates the aforementioned accumulation of cells along the edge. This could be explained by the removal of cations, which have been shown to have an effect on keratinocyte cell-cell connection. To ensure true detection of migration, pre-treating with mitomycin C, a DNA synthesis inhibitor, was added to the protocol. Finally, we demonstrate the automated optical camera, which eliminates excessive temperature cycles, manual labor with scratch closure analysis, while improving on reproducibility and ensuring analysis of identical sections of the scratch over time.

HaCaT is a keratinocyte cell line, one of the most abundant cell types in the skin. When a wound occurs, the skin cells start to proliferate and migrate over to the wound bed to close the wound (Figure 3). Both processes are, therefore, of utmost importance for proper healing.
The optical camera can follow both processes in real-time. For migration, the system gives three data sets: cell covered are...

Watch this Scientific Journal Video about Optimized Scratch Assay for In Vitro Testing of Cell Migration with an Automated Optical Camera at JoVE.com

Optimized Scratch Assay for In Vitro Testing of Cell Migration with an Automated Optical Camera

Here we describe a procedure to test the cell migration in vitro with an automated optical camera microscope. The scratch assay has been widely used where the closure of the scratch is followed for a set period. The optical microscope enables dependable and cheap detection of cell migration.

Optimized Scratch Assay for In Vitro Testing of Cell Migration with an Automated Optical Camera

Cell migration is an important process that influences many aspects of health, such as wound healing and cancer, and it is, therefore, crucial for ...

The main advantage of this technique is that you can look at the cells real time in the automatic optical microscope. The implications of this treatment extends to a therapy of chronic wounds or cancer where migration plays a crucial role in these diseases. Begin by washing a confluent culture of HaCaT cells two times with five milliliters of sterile magnesium and calcium free PBS per wash.Next, incubate the cells with one milliliter of trypsin in a 37 degree Celsius incubator for five to eight minutes. After confirming detachment under a light microscope stop the enzymatic reaction with nine milliliters of culture medium supplemented with FBS. And dilute the cells to a 7.5 times 10 to the fourth cells per 250 microliters of medium plus FBS concentration.Next, seed 250 microliters of cells to each well of a round-bottomed 48-well tissue culture plate, and gently slide the plate from side to side to ensure the cells are equally distributed across the well bottoms. Then transfer the plate to a cell culture incubator. When the cultures have reached a 90 to 95%confluency, replace the supernatant in each well with 250 microliters of freshly prepared medium supplemented with 10 micrograms per milliliter of mitomycin C, and return the plate to the incubator for another two hours.At the end of the incubation wash the cells with 250 microliters of PBS and add 250 microliters of fresh PBS to each well. Then use a 200 microliter micropipette tip to make one vertical scratch in each cell monolayer. When all of the monolayers have been scratched replace the PBS in each well with 250 microliters with the peptide stimulus of interest and mount the plate into an optical camera system with the lid intact.To set up the optical camera open the acquire window and select wound healing. Select the plate type and unselect the wells not in use. Next click enable and right click on one of the wells to adjust the focus to fit the position of the cells.Set the time period for the images under picture interval and set the number of repetitions to fit the desired period. Then select the appropriate analysis type. Then click start to begin imaging the cells.When a wound occurs the skin cells begin to proliferate and to migrate across the wound bed to close the wound, a process that can be observed through the optical camera. After a 48-hour incubation endothelial growth factor treatment induces a nearly 95%closure of the wound, compared to a 38%closure in the untreated control wells, and 33 and 62%closures in the lactoferrin and lactoferricin cultures respectively. The percentage of wound closure determined from changes in gap width from the initial scratch can also be plotted for each growth stimulus.This video describes a straightforward and efficient protocol for studying migration of keratinocytes across a scratch made in a monolayer of healthy cells. Though the cells used in this assay is HaCaT cells, the method can also be applied on other cell lines, fungi, or even bacteria, as long as they are adherent to the bottom of the microtiter plate.

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Endothelial Cell Tube Formation Assay for the In Vitro Study of Angiogenesis

Endothelial Cell Tube Formation Assay for the In Vitro Study of Angiogenesis

Angiogenesis is a vital process for normal tissue development and wound healing, but is also associated with a variety of pathological conditions. Using ...

An Assay for Lateral Line Regeneration in Adult Zebrafish

Due to the clinical importance of hearing and balance disorders in man, model organisms such as the zebrafish have been used to study lateral line ...

Imaging Intermediate Filaments and Microtubules with 2-dimensional Direct Stochastic Optical Reconstruction Microscopy

The cytoskeleton, composed of actin microfilaments, microtubules, and intermediate filaments (IF), plays a key role in the control of cell shape, ...

Preparation of Cell Extracts by Cryogrinding in an Automated Freezer Mill

The ease of genetic manipulation and the strong evolutionary conservation of eukaryotic cellular machinery in the budding yeast Saccharomyces cerevisiae ...