Osteogenic and Fluorescent Characterization of Pig-Derived Mesenchymal Stem Cells Between eGFP Transgenesis and Non-viral Plasmid Transfection

Abstract

BackgroundWidely used in recent years, mesenchymal stem cells (MSCs) expressing enhanced green fluorescent protein (eGFP) can be tracked during migration to injury sites, while also supporting tri-lineage differentiation. However, the relationship between the expression of green fluorescence and the magnitude of osteogenic differentiation is not clearly defined. Despite increasing use of eGFP-MSCs derived from the transgenic pigs and non-viral eGFP plasmid transfected MSCs in recent years, it remains unclear which cells are suitable for tracking during osteogenic differentiation, and whether the transfected plasmid alters osteogenic potential.MethodsWe compared the expression of green fluorescence and the magnitude of osteogenic differentiation between eGFP MSCs from a transgenic pig (group 1) and non-virally transfected eGFP-MSCs using transIT®-2020 (group 2). Non-transfected MSCs were used as control group (group 3). We also use a scaffold to compare the osteogenic induction environments created by 2-D monolayer cultures and 3-D cultures, respectivelyResultsIn the monolayer culture, flow cytometry from day 7 to day 28 showed that the percentage of green fluorescent cells in groups 1 and 2 were 99.6% and 59.7% of total cell counts, respectively. Quantification showed that eGFP expression peaked on day 7, decreased after day 14, and plateaued to day 28 in group 1 and group 2. Significant aggregation of eGFP over bone-like nodules was appreciated in group 1. In 3-D culture, eGFP expression increased from day 7 to day 28 in both groups, and was higher in group 1 than in group 2 at each time point. Osteogenic profiles and immunohistochemistry showed more significant osteogenic activity in group 1 and group 3 than in group 2. ConclusionsThe expression of eGFP in the test groups did not significantly change after osteogenic induction. However, quantification data was different in monolayer and 3-D cultures due to spatial limitations, differing extracellular environments, and heterogeneous cell morphology and methods of division. Osteogenic profiles and immunohistochemistry data confirmed that osteogenic potential did not change in transgenic pig-derived MSCs. However osteogenic potential decreased in pig MSCs (pig MSCs) treated with the transfection reagent, likely from related toxicity.