A Method for Ovarian Follicle Encapsulation and Culture in a Proteolytically Degradable 3 Dimensional System

Summary

A new method for ovarian follicle encapsulation in a 3D fibrin-alginate interpenetrating network is described. This system combines structural support with proteolytic degradation to support the development of immature follicles to produce mature oocytes. This method may be applied to culture cell aggregates to maintain cell-cell contacts without limiting expansion.

Abstract

The ovarian follicle is the functional unit of the ovary that secretes sex hormones and supports oocyte maturation. In vitro follicle techniques provide a tool to model follicle development in order to investigate basic biology, and are further being developed as a technique to preserve fertility in the clinic^1-4. Our in vitro culture system employs hydrogels in order to mimic the native ovarian environment by maintaining the 3D follicular architecture, cell-cell interactions and paracrine signaling that direct follicle development ⁵. Previously, follicles were successfully cultured in alginate, an inert algae-derived polysaccharide that undergoes gelation with calcium ions^6-8. Alginate hydrogels formed at a concentration of 0.25% w/v were the most permissive for follicle culture, and retained the highest developmental competence ⁹. Alginate hydrogels are not degradable, thus an increase in the follicle diameter results in a compressive force on the follicle that can impact follicle growth¹⁰. We subsequently developed a culture system based on a fibrin-alginate interpenetrating network (FA-IPN), in which a mixture of fibrin and alginate are gelled simultaneously. This combination provides a dynamic mechanical environment because both components contribute to matrix rigidity initially; however, proteases secreted by the growing follicle degrade fibrin in the matrix leaving only alginate to provide support. With the IPN, the alginate content can be reduced below 0.25%, which is not possible with alginate alone ⁵. Thus, as the follicle expands, it will experience a reduced compressive force due to the reduced solids content. Herein, we describe an encapsulation method and an in vitro culture system for ovarian follicles within a FA-IPN. The dynamic mechanical environment mimics the natural ovarian environment in which small follicles reside in a rigid cortex and move to a more permissive medulla as they increase in size¹¹. The degradable component may be particularly critical for clinical translation in order to support the greater than 10⁶-fold increase in volume that human follicles normally undergo in vivo .

Protocol

1. Follicle Isolation

Experiments on animals were performed in accordance with the guidelines and regulations set forth by the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the established Institutional Animal Use and Care protocol at Northwestern University.

For optimal results, all dissections are carried out in L15 media for pH control at ambient levels of CO₂, on 37°C heated stages for temperature control, and on a clean bench to minimize bacterial contamination. The dissection media (DM) is prepared with L15 media supplemented with 50 IU/mL penicillin and 50 μL/....

Discussion

The presented ovarian follicle encapsulation method in a FA-IPN allows follicle culture in a 3D environment in vitro. A FA-IPN is a dynamic, cell-responsive matrix in which the initial mechanical properties are determined by the combination of both fibrin and alginate. During the culture, the encapsulated follicle activates proteases that degrade only one component of the IPN, the fibrin, which results in a gradually decreasing gel rigidity that is contributed solely by the remaining alginate at the end of the c.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Fetuin	Sigma-Aldrich	F3385
FBS	Invitrogen	10082-139
Aprotinin	Roche Group	10236624001
CaCl2	Wako Pure Chemical Industries, Ltd.	039-00475	40 mM
EGF	Sigma-Aldrich	A412
rFSH	National Institute of Diabetes and Digestive and Kidney Diseases
hCG	Sigma-Aldrich	CG-5
Hyaluronidase	Sigma-Aldrich	A1603
ITS	Sigma-Aldrich	I1884-1VL
L-15	GIBCO, by Life Technologies	11415
αMEM+Gluta MAX	GIBCO, by Life Technologies	32561
Pen-Strep	Cellgro	30-002-CI
TBS	Pierce, Thermo Scientific	28379
Tisseel Fibrin kit	Baxter Internationl Inc.	921030
Sodium Alginate	FMC BioPolymers	LF200DL	Mw 418kDa