Fetal vs adult mesenchymal stem cells achieve greater gene expression, but less osteoinduction

To investigate adenoviral transduction in mesenchymal stem cells (MSCs) and effects on stemness in vitro and function as a cell therapy in vivo.

Bone marrow-derived adult and fetal MSC were isolated from an equine source and expanded in monolayer tissue culture. Polyethylenimine (PEI)-mediated transfection of pcDNA3-eGFP or adenoviral transduction of green fluorescent protein (GFP) was evaluated in fetal MSCs. Adenoviral-mediated transduction was chosen for subsequent experiments. All experiments were carried out at least in triplicate unless otherwise noted. Outcome assessment was obtained by flow cytometry or immunohystochemistry and included transduction efficiency, cell viability, stemness (i.e., cell proliferation, osteogenic and chondrogenic cell differentiation), and quantification of GFP expression. Fetal and adult MSCs were then transduced with an adenoviral vector containing the gene for the bone morphogenic protein 2 (BMP2). In vitro BMP2 expression was assessed by enzyme linked immunosorbent assay. In addition, MSC-mediated gene delivery of BMP2 was evaluated in vivo in an osteoinduction nude mouse quadriceps model. New bone formation was evaluated by microradiography and histology.

PEI provided greater transfection and viability in fetal MSCs than other commercial chemical reagents. Adenoviral transduction efficiency was superior to PEI-mediated transfection of GFP in fetal MSCs (81.3% ± 1.3% vs 35.0% ± 1.6%, P < 0.05) and was similar in adult MSCs (78.1% ± 1.9%). Adenoviral transduction provided significantly greater expression of GFP in fetal than adult MSCs (7.4 ± 0.1 vs 4.4 ± 0.3 millions of mean fluorescence intensity units, P < 0.01) as well as significantly greater in vitro BMP2 expression (0.16 pg/cell-day vs 0.10 pg/cell-day, P < 0.01). Fraction of fetal MSC GFP positive cells decreased significantly faster than adult MSCs (1.15% ± 0.05% vs 11.4% ± 2.1% GFP positive at 2 wk post-transduction, P < 0.05). Cell proliferation and osteogenic differentiation in vitro were not affected by Ad transduction in both fetal and adult MSCs, but fetal MSCs had reduced chondrogenic differentiation in vitro when compared to adult (P < 0.01). Chondrogenic differentiation was also significantly reduced in Ad-GFP transduced cells (P < 0.05). Ad-BMP2 transduced adult MSCs induced new bone formation in more thighs than Ad-BMP2 transduced fetal MSCs (83% vs 17% of the six treated thighs per group, P < 0.05) and resulted in increased femur midshaft diameter due to greater extent of periosteal new bone (1.57 ± 0.35 mm vs 1.27 ± 0.08 mm, P < 0.05).

Fetal MSCs may be genetically manipulated ex vivo with adenoviral vectors. Nonetheless, the abbreviated expression of the exogenous gene may limit their applications in vivo.