Name: methods for studying uterine contributions to pregnancy establishment in an ovariectomized mouse model
Uploaded: 2023-04-07T12:50:00
Description: Watch this Scientific Journal Video about Methods for Studying Uterine Contributions to Pregnancy Establishment in an Ovariectomized Mouse Model at JoVE.com

This work was made possible through the Victorian State Government Operational Infrastructure Support and Australian Government National Health and Medical Research Council (NHMRC) IRIISS. This work was supported by the Monash University Faculty of Medicine, Nursing and Health Science Platform Access Grant to A.L.W. (Winship-PAG18-0343) to access the Monash Reproductive Services Platform. A.L.W. is supported by DECRA funding DE21010037 from the Australian Research Council (ARC). J.N.H. and L.R.A. are supported by an Australian Government Research Training Program Scholarship. L.R.A. is supported by a Monash Graduate Excellence Scholarship. K.J.H. is supported by an ARC Future Fellowship FT190100265.

All animals were housed in temperature-controlled, high-barrier facilities (Monash University Animal Research Laboratory) with free food and water access and a 12 h light-dark cycle. All the procedures were performed in accordance with approval from the Monash Animal Research Platform Ethics committee (#21908, 17971) and performed in accordance with the National Health and Medical Research Council Code of Practice for the care and use of animals.
1. Surgical preparation
<ol>...

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N., 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=Biological+differences+between+functionalis+and+basalis+endometria+in+women+with+and+without+adenomyosis.">Biological differences between functionalis and basalis endometria in women with and without adenomyosis.</a> European Journal of Obstetrics, Gynecology, and Reproductive Biology. 203, 49-55 (2016).</li><li>Richards, J. S., Ren, Y. A., Candelaria, N., Adams, J. 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This article provides step-by-step instructions on how to perform OVX and provide exogenous hormones for studies focused on understanding the uterine contributions to pregnancy and fertility. Two detailed protocols are provided on two experimental applications of these methods, including performing embryo transfer and inducing decidualization artificially.
Whilst performing OVX can be challenging initially - especially for researchers new to rodent models - it is a relatively simple procedure ...

With the rising use of assisted reproductive technologies in recent decades, many barriers to conception have been overcome, allowing many couples to start families despite fertility problems1. Oocyte or sperm deficits can often be bypassed using in vitro fertilization or intracytoplasmic sperm injection; however, issues related to the uterus and endometrial receptivity remain an elusive &#34;black box&#34; of reproductive potential2.
Pregnancy is established when a high-quality embryo successfully interacts with a receptive endometrium (uterine lining). The chances of successful pregnancy in any given menstrual cycle are low, at around 30%3,4. Of those that are successful, only 50%-60% advance past 20 weeks of gestation, with implantation failure being responsible for 75% of pregnancies that do not reach 20 weeks3. Despite these figures dating back to the late 1990s, the field is yet to overcome the limitations caused by an inadequately receptive endometrium. This has resulted in stagnating - and sometimes declining - IVF success rates in recent years5,6.
Women with unexplained infertility often have a displaced window of receptivity or are unable to achieve receptivity for unknown reasons. Recently, the endometrial receptivity array was developed, which assesses the expression of hundreds of genes with the purpose of tailoring the timing of embryo transfer to an individual&#39;s window of receptivity7,8,9. However, the field still lacks an understanding of the pathogenesis of pregnancy complications that manifest after the implantation process is complete.
The female reproductive system is highly dynamic and under tight hormonal control. The hypothalamic-pituitary-gonadal (HPG) axis controls the release of luteinizing hormone and follicle-stimulating hormone, which regulate aspects of the ovarian cycle, including follicle maturation and estrogen and progesterone activity. In turn, the uterine menstrual cycle is regulated by estrogens and progesterone10,11. Thus, studying uterine biological mechanisms is complicated by ovarian influence. For example, when studying how cancer therapies may impact the uterus, it can be difficult to distinguish if any uterine phenotype observed (such as pregnancy loss or menstrual acyclicity) is the result of a direct insult to the uterus or a consequential effect from damage to the ovaries.
To comprehensively understand fertility, the uterine contributions to pregnancy must be characterized. Importantly, this understanding must extend beyond uterine function under ovarian control. This cannot be studied in humans; therefore, animal models are often employed. As such, ovariectomy (OVX) is commonly used to enable researchers to regulate rodent estrous cycles (analogous to the menstrual cycle) by supplying hormones exogenously. Additionally, OVX allows uterine responses to be studied independently of ovarian influence12. However, if hormones are not immediately supplied post-OVX, a menopause phenotype will eventuate, which needs to be carefully considered by the researchers.
OVX is frequently utilized in rodent models13,14,15,16,17 and is relatively easy to perform after adequate training. Methods vary depending on whether the ovary alone or the ovary and oviduct are removed, as well as depending on the age of the animal (adult, cycling animals have larger ovaries with a visible corpus luteum on their surface, meaning their ovaries are easier to visualize). Similarly, many methods of hormone supplementation exist, including subcutaneous injections14, slow-release pellets15, osmotic mini pumps18, and ovarian grafting.
In this article, detailed instructions are provided on how to perform ovariectomy and prepare three types of hormone supplementation, including subcutaneous injections, slow-release pellets, and osmotic mini pumps. Two detailed protocols are provided for experimental endpoints that benefit from OVX followed by exogenous hormone supplementation (embryo transfer and artificial decidualization). This article discusses the strengths and weaknesses of each approach with the goal of guiding researchers regarding how to perform studies to isolate the impacts on the uterus, specifically in the pregnancy and fertility fields of research.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>ALZET 1002 mini osmotic pumps</td>
			<td>BioScientifica</td>
			<td>1002</td>
			<td>Delivers 0.25 &#181;L/h for 14 days. Use for section 7 (Experimental procedure - Embryo transfer).</td>
		</tr>
		<tr>
			<td>ALZET 1003D mini osmotic pumps</td>
			<td>BioScientifica</td>
			<td>1003D</td>
			<td>Delivers 1 &#181;L/h for 14 days. Use for section 8 (Experimental procedure - Artificial decidualization).</td>
		</tr>
		<tr>
			<td>ALZET Reflex 7 mm clips</td>
			<td>BioScientifica</td>
			<td>0009971</td>
			<td>Either Reflex clips or Michel clips can be used for wound closure, depending on preference</td>
		</tr>
		<tr>
			<td>ALZET Reflex clip applicator</td>
			<td>BioScientifica</td>
			<td>0009974</td>
			<td>Either Reflex clips or Michel clips can be used for wound closure, depending on preference</td>
		</tr>
		<tr>
			<td>ALZET Reflex clip remover</td>
			<td>BioScientifica</td>
			<td>0009976</td>
			<td>Either Reflex clips or Michel clips can be used for wound closure, depending on preference</td>
		</tr>
		<tr>
			<td>Bupivicaine injection</td>
			<td>Pfizer</td>
			<td>NA</td>
			<td>Stock 0.5%. Use at 0.05% in saline</td>
		</tr>
		<tr>
			<td>Estradiol</td>
			<td>Sigma</td>
			<td>E8875</td>
			<td></td>
		</tr>
		<tr>
			<td>Meloxicam</td>
			<td>Ilium</td>
			<td>NA</td>
			<td>Active constituent 0.5 mg/mL. Use 3.5 mL per 200 mL cage bottle, or as your institutions vet prescribes.</td>
		</tr>
		<tr>
			<td>Michel clips</td>
			<td>Daniels</td>
			<td>NS-000242</td>
			<td></td>
		</tr>
		<tr>
			<td>Multi purpose sealant</td>
			<td>Dow Corning</td>
			<td>732</td>
			<td></td>
		</tr>
		<tr>
			<td>Non-surgical embryo transfer (NSET) device</td>
			<td>ParaTechs</td>
			<td>60010</td>
			<td>Contains 6 mm speculum. Single use only.</td>
		</tr>
		<tr>
			<td>Progesterone</td>
			<td>Sigma</td>
			<td>P0130</td>
			<td>Soluble in ethanol. Use for&#160; section 3 (Hormone preparation - subcutaneous injection) and&#160; section 4 (Hormone preparation - slow-release pellets)</td>
		</tr>
		<tr>
			<td>Progesterone</td>
			<td>Sigma</td>
			<td>P7556</td>
			<td>Soluble in water. Use for section 5 (Hormone preparation - osmotic mini pumps)</td>
		</tr>
		<tr>
			<td>Refresh eye ointment</td>
			<td>Allergan</td>
			<td>NA</td>
			<td>42.5% w/v liquid paraffin, 57.3% w/v soft white paraffin</td>
		</tr>
		<tr>
			<td>Rimadyl Carprofen</td>
			<td>Zoetis</td>
			<td>NA</td>
			<td>Stock 50 mg/mL. Use at 5 mg/kg</td>
		</tr>
		<tr>
			<td>Rubber tubing</td>
			<td>Dow Corning</td>
			<td>508-008</td>
			<td>Washed in 100% ethanol and cut into 1 cm pieces. Inside diameter 1.57 mm &#177;&#160; 0.23 mm; outside diamater 3.18 mm &#177; 0.23 mm; wall 0.81 mm.</td>
		</tr>
		<tr>
			<td>Sesame oil</td>
			<td>Sigma</td>
			<td>S3547</td>
			<td></td>
		</tr>
		<tr>
			<td>Sofsilk Silk sutures size 3-0</td>
			<td>Covidien</td>
			<td>GS-832</td>
			<td></td>
		</tr>
	</tbody>
</table>

methods for studying uterine contributions to pregnancy establishment in an ovariectomized mouse model

For pregnancy to be established, a viable blastocyst must successfully interact with a receptive uterine lining (endometrium) to facilitate implantation and placenta formation and enable ongoing pregnancy. The limitations to pregnancy success caused by embryonic defects are well known and have been largely overcome in recent decades with the rise of in vitro fertilization (IVF) and assisted reproductive technologies. As yet, however, the field has not overcome the limitations caused by an inadequately receptive endometrium, thus resulting in stagnating IVF success rates. Ovarian and endometrial functions are closely intertwined, as hormones produced by the ovary are responsible for the endometrium's menstrual cyclicity. As such, when using rodent models of pregnancy, it can be difficult to ascertain whether an observed result is due to an ovarian or uterine deficit. To overcome this, an ovariectomized mouse model was developed with embryo transfer or artificial decidualization to allow the study of uterine-specific contributions to pregnancy. This article will provide instructions on how to perform ovariectomy and offer insights into various techniques for supplying exogenous hormones to support successful artificial decidualization or pregnancy following embryo transfer from healthy donors. These techniques include subcutaneous injection, slow-release pellets, and osmotic mini pumps. The key advantages and disadvantages of each method will be discussed, enabling researchers to choose the best study design for their specific research question.

A well-characterized model of artificial decidualization is described in this protocol paper (Figure 1A). Here, young adult female mice (8 weeks old) underwent surgical ovariectomy as described in section 1 and section 2. The mice were then rested for 2 weeks to ensure that the endogenous ovarian hormones dissipated before being supported with exogenous hormones as described in sections 3-7 and section 9. Artificial decidualization was induced by an intravaginal injecti...

Watch this Scientific Journal Video about Methods for Studying Uterine Contributions to Pregnancy Establishment in an Ovariectomized Mouse Model at JoVE.com

Methods for Studying Uterine Contributions to Pregnancy Establishment in an Ovariectomized Mouse Model

Pregnancy establishment is a dynamic process involving complex embryo and uterine crosstalk. The precise contributions of the maternal uterine environment to these processes remain an active area of investigation. Here, detailed protocols are provided to aid in designing in vivo animal models to address these research questions.

For pregnancy to be established, a viable blastocyst must successfully interact with a receptive uterine lining (endometrium) to facilitate implantation ...

So it's difficult to separate the role of uterine and ovarian hormonal influences on pregnancy establishment as both are intimately linked. So this protocol allows us to directly examine the uterine contributions. While some of these techniques like ovariectomy are quite invasive, they are relatively simple to perform after practice and training, which makes them suitable for researchers that are new to mouse models.So this method can be utilized to understand the broader regulation of the HPG axis as both the ovaries and the uterus play an important role in regulation of this axis. If you've never performed these techniques before, consult with your institute's veterinarian team for training and support. To begin, apply eye lubricant generously to an anesthetized mouse by gently dabbing it on the eye after shaving a small area at dent below the spine hunch.Inject 0.1 milliliters of carprofen subcutaneously into the scruff of the neck. Test if the animal is anesthetized by pinching its back toe and checking for a reflex. Next, apply Betadine to the surgical site.Then cover it with a surgical drape. Using rat-toothed forceps, pull away the skin at the hunch upwards, and make a five millimeter longitudinal incision. Then, using blunt forceps, dissect the skin away from the underlying muscle layer down to one side toward the kidney.Identify the kidney, ovary, and ovarian fat pad through the muscle wall. Grab and lift the muscle layer with the forceps. Then, using scissors, make a 0.5 to one centimeter long incision, and pull the ovarian pad through the incision with a pair of blunt forceps.Next, using a curved needle holder, clamp underneath the ovary and oviduct at the distal end of the uterine horn and excise the ovary with scissors. After 30 seconds, remove the clamp and dab with sterile gauze. To close the muscle wall incision, lift the top of the incision using forceps.Then tie the incision with a surgeon's knot using silk sutures. Topically apply a few drops of bupivacaine using a one-milliliter syringe with no needle attachment, and dab the excess with sterile gauze. After similarly performing the ovariectomy on the other side, close the skin incision by pressing the two sides of the skin together and applying a couple of seven-millimeter surgical clips, leaving room for wound swelling.Place all required equipment on a foil inside a laminar flow or Class II biosafety hood and UV sterilize for 20 minutes. Wash the silastic tubing in 100%desinol and allow it to air dry inside the hood. Once dry, cut the tubing into one-centimeter long segments using a scalpel.Next, squeeze approximately 200 microliters of sealant into a syringe without a plunger. Replace the plunger and push out a small amount of sealant. Apply the sealant to one end of the tubing, smoothing it over with a gloved finger.And allow the sealant to dry overnight or under UV light for 30 minutes in the hood. Next, pour progesterone powder into a sterilized Petri dish. Scoop the powder into pellets with the help of forceps.Tap the sealed end of the pellet down the hood surface to condense the powder. Then seal the open end with the sealant. Wrap the Petri dish containing the pellets in foil to protect them from light.About 72 hours before subcutaneous insertion, activate the pellets by incubating them in charcoal-stripped FCS. Demonstrating this procedure will be Dr.Fiona Cousins, an early career research scientist from the Hudson Institute of Medical Research. After hormone priming the animals with subcutaneous estradiol injections, prime the animals with subcutaneous progesterone pellets two days before artificial decidualization.Before the surgery, anesthetize the mouse and test the depth of anesthesia by checking for the toe pinch reflex. Then place the mouse in a prone position, lift its tail and slowly insert a six millimeter speculum into its vagina. Place the lower body of the mouse between the first two fingers of the non-dominant hand.Then, using the index finger, gently push the tail upward to allow for better vaginal accessibility. Transfer 20 microliters of sesame oil into a non-surgical embryo transfer tip, and insert the tip through the vagina and cervix into the uterine horn. Slowly expel the oil.Once done, remove the speculum from the vagina. In this study, 80%of the the mice underwent successful decidualization, while 20%did not. So it's important to keep all your surgical equipment and working areas sterile and having patients when inserting the NSAID device through the cervix into the uterine horn of the mouse.After inducing artificial decidualization, the progesterone palate can be removed to mimic menstruation and study endometrial breakdown. Using this method, we can study uterine biology and regulation independent of the influence of the ovaries. This is really exciting in the area of fertility and women's health in general.

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