Three-dimensional culture of rabbit nucleus pulposus cells in collagen microspheres

Background: Degenerative disc disease poses an increasing threat to our quality of life as we age. Existing treatments have limitations. New treatment modalities focusing on biologic rather than surgical approach would be appealing.

Purpose: Culturing intervertebral disc cells in a three-dimensional (3D) model that can retain cellular characteristics and phenotype is a critical step toward understanding how the disc cells respond to and interact with extrinsic signals before better therapeutics can be derived.

Study design: In this work, we studied the culture of rabbit nucleus pulposus (NP) cells in a collagen microsphere system and compared their cell morphology and expression of a few potential phenotypic markers with that in monolayer culture.

Methods: Specifically, rabbit NP cells isolated from both young and old animals were encapsulated and cultured in collagen microspheres with different monomeric concentrations and with different cell encapsulation density for different period of time. Evaluation on the growth kinetics, the viability, the cell morphology, the expression of Types I and II collagen, glycosaminoglycans (GAGs), and Keratin 19, and the ultrastructure of the fiber meshwork were conducted to compare the microsphere 3D culture system and the traditional monolayer cultures.

Results: Nucleus pulposus cells in two-dimensional culture lost the phenotypic expression of Type II collagen and keratin 19 and expressed Type I collagen. In contrast, the 3D collagen microsphere culture system consistently outperformed the traditional monolayer culture in maintaining a round morphology and preserving the phenotypes of NP cells with persistent expression of Type II collagen and Keratin 19. These cells also remodeled the template collagen matrix in the microspheres by depositing new matrices, including collagen Type II and GAGs in a cell seeding density and collagen concentration dependent manner.

Conclusions: This study demonstrates the appeal of the 3D collagen microsphere system for NP cell culture over traditional monolayer culture because it preserves the phenotypic characteristics of NP cells. This system also enables the NP cells to remodel the template collagen matrix by depositing new matrices, suggesting an innovative way to reconstitute cell-specific and native tissue-like environment in vitro for future studies on stem cell matrix niche and interactions of NP cell with extrinsic factors.