Strontium Promotes Osteogenic Differentiation of Mesenchymal Stem Cells Through the Ras/MAPK Signaling Pathway

Abstract

Strontium ralenate is a new anti-osteoporosis agent. The cellular and molecular mechanism underlying the anabolic effect of strontium on bone remains to be elucidated. Osteoblasts, the main bone forming cells are known to be derived from bone marrow mesenchymal stem cells (MSCs). The present study therefore aimed to investigate the possible effects of strontium on MSCs and signaling pathways possibly involved. It was firstly demonstrated that strontium treatment significantly increased osteoblast-related gene expression and alkaline phosphatase (ALP) of osteogenic-differentiating MSCs. Accompanying the enhanced osteogenic differentiation, the increased phosphorylation of mitogen-activated protein kinase (MAPK) ERK1/2 and p38 was detected in strontium-treated MSCs. PD98059 and SB203580, selective inhibitors of ERK1/2 kinase and p38, attenuated the effect of strontium on osteogenesis. Furthermore, it was demonstrated that Rat Sarcoma viral oncogene homolog (RAS), an upstream regulator of ERK1/2 and p38, was activated by strontium treatment and siRNA-mediated Ras knockdown inhibited strontium-stimulated expression of osteogenic markers. Finally, the transcriptional activity and phosphorylation level of Runx2 was significantly increased in response to strontium treatment in MSCs. PD98059 and Ras siRNA inhibited the effect of strontium on Runx2 activation. Taken together, these results indicated that strontium can promote osteogenic differentiation of MSCs through activating the Ras/MAPK signaling pathway and the downstream transcription factor Runx2.

In vivo anabolic effect of strontium on trabecular bone was associated with increased osteoblastogenesis of bone marrow stromal cells

“…9,10,20 Our recent in vitro study demonstrated that Sr can promote osteogenic differentiation of C3H10T1/2 cells and primary murine BMSCs, suggesting that Sr can also promote the commitment of progenitor cells into osteoblastic lineage. 12 This study prompted us to investigate the in vivo response of BMSCs to Sr treatment. mRNA levels of Runx2 and osteocalcin were significantly up-regulated by Sr treatment in Sham or OVX rats, consistent with our previous study that demonstrated elevated Runx2 gene expression in long bones after Sr treatment in an OVX goat osteoporosis model.…”

“…Real-time PCR assay was performed according to a previous protocol. 12 The following genes were evaluated: Runt-related transcription factor-2 (Runx2, NM_053470), SP7 transcription factor (SP7 or Osterix, NM_001037632), osteocalcin (OC, NM_013414), peroxisome proliferator-activated receptor gamma 2 (PPARg-2, NM_013124), adipocyte protein 2 (aP2, NM_053365), receptor activator NF-kappa B (RANKL, NM_057149), osteoprotegerin (OPG, NM_012870), and the house-keeping gene glyceraldehyde 3-phosphate dehydrogenase (GAPDH, NM_017008). Each sample was run in duplicate in a 96-well plate, and data were analyzed by DDC T relative quantification methods, with each sample normalized for internal GAPDH.…”

“…9,10 Recent studies also demonstrated that Sr can increase in vitro osteogenic differentiation of BMSCs. 11,12 Based on the observation that Sr could increase osteoblastic differentiation of BMSCs in vitro, we hypothesized that the anabolic effect of Sr on bone was attributed, at least partially, to the modulation of in vivo differentiation of BMSCs towards osteoblastic lineage.…”

Orthopedic bioactive implants: Hydrogel enrichment of macroporous titanium for the delivery of mesenchymal stem cells and strontium

“…Our results demonstrated that a low concentration of SrCl 2 (5 lg/mL) improved BMSCs osteogenic differentiation, accordingly with data by Sila-Asna et al 24 Strontium has a positive effect on bone metabolism 21 and on MSCs osteogenic differentiation. 26,28 Furthermore, it has been demonstrated to improve osseointegration when delivered at the implant site by direct incorporation within titanium, 19 or inclusion in a hydroxyapatite coating 20 and in bone graft extenders. 46 As the in vivo effect of strontium on bone metabolism is associated with increased BMSCs osteogenesis, 27 we believe that the simultaneous inclusion of BMSCs and strontium in a hydrogel loaded into titanium may promote bone ingrowth by a dual action on host progenitor cells resident at the implant site and on cells encapsulated into the hydrogel.…”

“…19,20 Indeed, strontium ranelate is a drug used for the treatment of osteoporosis, thanks to its ability to increase bone neoformation and to reduce bone resorption. [21][22][23] Furthermore, strontium has a positive effect on osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), [24][25][26][27][28] which are resident at the implant site and are characterized by an intrinsic osteogenic potential. [29][30][31] It has been demonstrated that the use of autologous bone marrow concentrate, obtained by an intra-operative approach, improves bone healing.…”