gms | German Medical Science

Objectives: Treating large bone defects is a major challenge in Orthopedics and Trauma Surgery. Recent tissue engineering (TE) approaches that combine stem cells, scaffolds, and growth factors to treat large bone defects have shown great potential in both preclinical and clinical studies. While the use of electrical stimulation (ES) for treating bone defects is not new, recent studies show that it stimulates stem cell proliferation, migration, osteogenic differentiation and adherence to scaffolds, all essential in the success of TE approaches. The aim of this study was to compare the osteogenic effect ES has on bone marrow-derived MSC (BM-MSC) vs. adipose tissue-derived MSC (AT-MSC), for application in bone TE treatments and to investigate the mechanisms by which ES promotes osteogenic differentiation of BM-MSC under 2D and 3D in-vitro conditions.

Methods: In a purpose-built ES-cell culture chamber BM-MSC and AT-MSC were cultured with (3D) and without (2D) scaffold material (ß-TCP) and exposed to low voltage (100mV/mm) direct current electrical stimulation (DC ES), for 1h/day, for 3, 7, 14 and 21 days. The same setup was used for Controls but without ES. MTT assay was used to assure that ES treatment was not cytotoxic. Cell proliferation and osteogenic differentiation were assessed using PicoGreen assay and gene expression analysis (RT-qPCR).

Results and Conclusion: At all time points and under all conditions tested ES treatment was not cytotoxic. In cells treated with ES increased expression of gene markers for osteogenesis (RunX2, Osteopontin, Bmp2, TGF-ß1, Calmodulin) as well as increased Ca2+ concentration were observed still 7 days after exposure. In addition, expression of osteogenic markers remained high in ES treated cells even after ES exposure was terminated. Osteogenic gene expression in ES treated BM-MSC and AT-MSC differed at different time points.

We showed that ES affects osteogenic gene expression patterns differently in BM- and AT-derived MSC at different time points. Our findings suggest that ES affects osteogenic differentiation through calcium ion pathways and activates a switch that causes sustained, long-lasting osteogenic effects in cells. These observed effects and differences should be taken into consideration when applying these two cell sources in tissue engineering applications. Studying ES-induced changes in cellular behavior could lead to the development of methods to control and optimize cell behavior in tissue engineering treatments.