Susceptibility of Ovine Bone Marrow-Derived Mesenchymal Stem Cell Spheroids to Scrapie Prion Infection

SIMPLE SUMMARY: Prion diseases are fatal and incurable neurodegenerative disorders affecting both humans and animals. The development of in vitro cellular models from naturally susceptible species such as ruminants can be very useful for the study of prion disease mechanisms and the discovery of potential therapies. Our study shows for the first time how the culture, in the form of three-dimensional spheroids of ovine mesenchymal stem cells derived from bone marrow in growth and neurogenic conditions, makes these cells more permissive to prion infection, mimicking the prion toxicity occurring in these diseases. This three-dimensional system appears as a potential in vitro model for studying prion diseases in a microenvironment approaching in vivo conditions. ABSTRACT: In neurodegenerative diseases, including prion diseases, cellular in vitro models appear as fundamental tools for the study of pathogenic mechanisms and potential therapeutic compounds. Two-dimensional (2D) monolayer cell culture systems are the most used cell-based assays, but these platforms are not able to reproduce the microenvironment of in vivo cells. This limitation can be surpassed using three-dimensional (3D) culture systems such as spheroids that more effectively mimic in vivo cell interactions. Herein, we evaluated the effect of scrapie prion infection in monolayer-cultured ovine bone marrow-derived mesenchymal stem cells (oBM-MSCs) and oBM-MSC-derived spheroids in growth and neurogenic conditions, analyzing their cell viability and their ability to maintain prion infection. An MTT assay was performed in oBM-MSCs and spheroids subjected to three conditions: inoculated with brain homogenate from scrapie-infected sheep, inoculated with brain homogenate from healthy sheep, and non-inoculated controls. The 3D conditions improved the cell viability in most cases, although in scrapie-infected spheroids in growth conditions, a decrease in cell viability was observed. The levels of pathological prion protein (PrP(Sc)) in scrapie-infected oBM-MSCs and spheroids were measured by ELISA. In neurogenic conditions, monolayer cells and spheroids maintained the levels of PrP(Sc) over time. In growth conditions, however, oBM-MSCs showed decreasing levels of PrP(Sc) throughout time, whereas spheroids were able to maintain stable PrP(Sc) levels. The presence of PrP(Sc) in spheroids was also confirmed by immunocytochemistry. Altogether, these results show that a 3D culture microenvironment improves the permissiveness of oBM-MSCs to scrapie infection in growth conditions and maintains the infection ability in neurogenic conditions, making this model of potential use for prion studies.