220 Strontium enhances in vitro osteogenic differentiation of porcine adipocyte–derived stem cells
J. R. Glassey A , R. A. C. Rabel A , D. J. Milner A and M. B. Wheeler AA
The use of autologous bone grafts remains the gold standard for treatment and repair of bone defects. However, given the challenges of using autologous bone, osteogenic potential of mesenchymal stem cells (MSCs) such as adipose-derived stem cells (ASCs) has been thoroughly investigated over the last decade in various animal species including humans. Further, effects of various growth factors, small molecules, minerals, vitamins, and trace elements on osteogenic differentiation potential of MSCs have been studied to further understand and/or enhance bone tissue engineering (BTE). Strontium (Sr) is a trace element that has been researched by many BTE researchers. It is found naturally in bone tissue and it has a dual action on bone metabolism, simultaneously reducing bone resorption and increasing bone tissue formation. Research has shown that Sr enhances osteogenic differentiation of MSCs in humans and rodents. However, to date, effects of Sr on osteogenic differentiation of MSCs of porcine origin have not been studied to our knowledge. Considering the advantages of using the pig as an animal model in BTE-related research, we conducted this study to test the effects of different Sr concentrations on osteogenic potential of porcine ASCs (pASCs). Passage-3 pASCs were seeded in 24-well cell culture plates at 10 000 cells/cm2 (three technical replicates each from two breed, age, and sex-matched biological replicates) and treated with (1) standard osteogenic media (OM; 50 µg mL−1 L-ascorbic acid-2-phosphate, 0.1 µM dexamethasone, and 10 mM β-glycerophosphate in standard culture media), OM containing (2) 0.01 mM Sr, (3) 0.1 mM Sr, (4) 1 mM Sr, (5) 10 mM Sr, or (6) standard culture media as negative control. At the end of the experiment (Day-14 of osteogenic differentiation), cultures were stained with Alizarin Red S and numbers of osteogenic nodules (ON) formed in each replicate counted using photomicrographs. The effect of Sr on osteogenic differentiation was determined using a mixed effects model (PROC MIXED procedure of SAS). The number of ON formed in the two pASC cell lines was different (P < 0.0001; Pig 1: N = 112 ± 14.5 and Pig 2: N = 66 ± 6.6 in Sr-free OM), suggesting that the osteogenic potential of the two cell lines was different. There was variation in how the two cell lines responded to Sr as well. For example, ASCs from Pig 1 gave rise to higher numbers of ON in OM containing 0.1 mM (N = 145.7 ± 12.7, P < 0.01) and 1 mM (N = 153.7 ± 22.9, P < 0.001) Sr, compared with Sr-free OM (N = 112 ± 14.5). However, ASCs from Pig 2 gave rise to a higher number of ON in OM with 0.1 mM Sr only (N = 85.3 ± 7.8, 0.05 < P < 0.1), compared with Sr-free OM (N = 66 ± 6.6). An amounf of 10 mM Sr inhibited ON formation in both cell lines (Pig 1: N = 6.7 ± 6.1 and Pig 2: N = 8.3 ± 2.1). In conclusion, findings from our study suggest that 0.1–1 mM Sr enhances in vitro osteogenic differentiation of pASCs. Future studies are warranted to determine effects of Sr on in vivo osteogenic differentiation of pASCs.
