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INTRODUCTION
The endometrium is a complex, multicellular tissue and is the site of embryo implantation. Dysregulations between embryo-endometrial interactions during implantation result in a variety of pregnancy disorders including recurrent pregnancy loss and implantation failure. Due to a lack of appropriate study models the mechanisms surrounding human embryo implantation are still largely unknown. Here, we describe how photocrosslinked GelMA hydrogels can be tailored to the culture of both endometrial stromal cells (ESCs) and endometrial organoids (EOs), which have been shown to recapitulate key features of in vivo endometrial glands.2,3 Our long-term goal is to engineer a platform to assess the processes that control implantation and address unanswered questions around reproductive failure.
METHODOLOGY
Two batches of GelMA with a degree of substitution (DS) of 70 & 100 % were prepared.1 5 and 10 % (w/v) GelMA hydrogels were fabricated, and their mechanical properties measured using rheology.
A simple protocol was developed whereby primary human endometrial cells were encapsulated in photocrosslinked GelMA hydrogels, employing a cytocompatible photoinitiator (LAP) and 3 minutes UV exposure (365 nm).
ESC viability in GelMA hydrogels was investigated using the XTT Cell Viability assay. The ability of ESCs to respond to steroid hormone treatment was examined using a prolactin ELISA. Collagen was used as a control.
Time-lapse imaging was used to observe the ability of epithelial cells encapsulated in GelMA hydrogels to form EOs. GelMA hydrogels were supplemented with the laminin protein at 2 different ratios. Geltrex was used as a control.
RESULTS
Rheological analysis demonstrates GelMA hydrogels can be produced with a range of stiffness degrees by altering the DS and concentration of GelMA.
ESCs in DS70 and DS100 GelMA hydrogels retained high levels of viability after a 7-day culture period, surpassing the commercially available collagen hydrogel. A clear differentiation response, monitored over 4-days of hormone treatment, was seen in both GelMA and collagen hydrogels.
Endometrial glandular organoids form in the presence of an appropriate 3D matrix. DS70 GelMA hydrogels resulted in a matrix too soft to support organoid formation. DS100 GelMA hydrogels provide a stiffer matrix, which enabled epithelial cells to form EOs. The efficiency of organoid formation could be enhanced through addition of the basement membrane protein, laminin to GelMA hydrogels.
Although optimal hydrogel compositions need to be determined for the co-culture of stromal and epithelial organoids, the results of this work suggest that GelMA hydrogels constitute versatile and tunable hydrogels for endometrial tissue modelling.
CONCLUSIONS
The mechanical properties of GelMA hydrogels can be tuned to suit the culture of different cell types.
Endometrial cells can quickly and simply be encapsulated in photocrosslinked GelMA hydrogels and maintain high cell viability.
Epithelial cells grown in DS100 GelMA supplemented with laminin form structures that resemble in vivo endometrial glands.
REFERENCES
1. Zhu, M. et al., Sci Rep, 9 (1), 6863 (2019)
2. Turco, M. Y. et al., Nat Cell Biol, 19 (5), 568-577 (2017)
3. Burton, G. et al., Protocol Exchange (2017)
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