Cell spheroid fusion: beyond liquid drops model

Nastasia V Kosheleva,Yuri M Efremov,Boris S Shavkuta,Irina M Zurina,Deying Zhang,Shicheng Wei,Irina N Saburina,Peter S Timashev,Anastasia I Shpichka,Yuanyuan Zhang,Nikita V Minaev,Anastasiya A Gorkun

doi:10.1038/s41598-020-69540-8

Abstract

Biological self-assembly is crucial in the processes of development, tissue regeneration, and maturation of bioprinted tissue-engineered constructions. The cell aggregates—spheroids—have become widely used model objects in the study of this phenomenon. Existing approaches describe the fusion of cell aggregates by analogy with the coalescence of liquid droplets and ignore the complex structural properties of spheroids. Here, we analyzed the fusion process in connection with structure and mechanical properties of the spheroids from human somatic cells of different phenotypes: mesenchymal stem cells from the limbal eye stroma and epithelial cells from retinal pigment epithelium. A nanoindentation protocol was applied for the mechanical measurements. We found a discrepancy with the liquid drop fusion model: the fusion was faster for spheroids from epithelial cells with lower apparent surface tension than for mesenchymal spheroids with higher surface tension. This discrepancy might be caused by biophysical processes such as extracellular matrix remodeling in the case of mesenchymal spheroids and different modes of cell migration. The obtained results will contribute to the development of more realistic models for spheroid fusion that would further provide a helpful tool for constructing cell aggregates with required properties both for fundamental studies and tissue reparation.

Highlights

Biological self-assembly is crucial in the processes of development, tissue regeneration, and maturation of bioprinted tissue-engineered constructions
Cell-based therapies in ophthalmology are based on the combined use of epithelial cells [such as retinal pigment epithelium (RPE) cells] and mesenchymal stem cells (MSCs)[13]
Expression of the mesenchymal marker vimentin and synthesis of the extracellular matrix component fibronectin were found in MSC monolayers (Fig. 1B), while the epithelial basal membrane marker laminin was expressed only in cytoplasm, and the marker of undifferentiated cells, nestin, was present just in a few cells (Fig. 1C)

Summary

Introduction

Biological self-assembly is crucial in the processes of development, tissue regeneration, and maturation of bioprinted tissue-engineered constructions. We analyzed the fusion process in connection with structure and mechanical properties of the spheroids from human somatic cells of different phenotypes: mesenchymal stem cells from the limbal eye stroma and epithelial cells from retinal pigment epithelium. The obtained results will contribute to the development of more realistic models for spheroid fusion that would further provide a helpful tool for constructing cell aggregates with required properties both for fundamental studies and tissue reparation. As long as scaffold-free spheroids have prefabricated intercellular junctions and extracellular matrix, which promotes the preservation of cell viability and developmental plasticity, using them, not singlecell suspension, as building blocks in bioprinting will stimulate the formation and maturation of the obtained tissue-engineered constructions[19,20]

Methods

Results

Discussion

Conclusion