Role of IGF1 and IGF1/VEGF on Human Mesenchymal Stromal Cells in Bone Healing: Two Sources and Two Fates

Abstract

In the repair of skeletal defects one of the major obstacles still remains an efficient vascularization of engineered scaffolds. We have examined the ability of insulin growth factor-1, alone or in association with vascular endothelial growth factor, to modulate the osteoblastic or endothelial commitment of periosteum-derived progenitor cells (PDPCs) and skin-derived multipotent stromal cells (S-MSCs). A selected gene panel for endothelial and osteoblastic differentiation as well as genes that can affect MAPK and PI3K/AKT signaling pathways were investigated. Moreover, gene expression profile of Sox2, Oct4, and Nanog transcription factors was assessed. Our results showed that under growth factor stimulation PDPCs are induced toward an osteoblastic differentiation, while S-MSCs seem to move along an endothelial phenotype. This different commitment seems to be linked to a diverse MAPK or PI3K/AKT signaling pathway activation. The analysis of genes for stemness evidenced that at least in PDPCs multipotency and differentiation could coexist. These results open interesting perspective for the development of innovative bone tissue engineering approaches based on a good network of angiogenesis and osteogenesis processes.

Evidence Supporting a Paracrine Effect of IGF-1/VEGF on Human Mesenchymal Stromal Cell Commitment

“…To this aim and similarly to the previous investigation [Ferretti et al, 2014], we analyzed the expression of a defined panel of genes involved in endothelial and osteoblastic differentiation and in the signaling pathways activated by IGF-1-and VEGF-specific receptor binding [mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3 ′ -kinase (PI3K)/AKT]. For the endothelial phenotype, we took CD31 and CD34 mRNA expression into account, whilst we investigated gene expression profiles of runt-related transcription factor 2 (runx2), bone morphogenetic protein 2 (bmp2), matrix metalloproteinase 13 (mmp13), and osteocalcin (bglap) for osteoblastic differentiation.…”

“…S-MSCs and PDPCs) in a previous work [Ferretti et al, 2014]. VEGF is the most engaging and well-known factor for the development of new blood vessels, since it is a pivotal regulator of vascular growth both in normal and pathological conditions [Helmrich et al, 2013].…”

“…The results of the study by Ferretti et al [2014] suggested a diverse commitment of cells within the bone microenvironment: PDPCs move toward an osteoblastic differentiation, whilst S-MSCs seem to be driven to an endothelial phenotype. Moreover, the changes in cell commitment are at least in part associated with a main activation of the PI3K/AKT pathway in S-MSCs and of the MAPK pathway in PDPCs [Ferretti et al, 2014].…”

“…In this case, the high upregulation of mapk3 occurred concomitantly with a significant reduction in pi3k5 mRNA levels, confirming the mainly osteoblastic commitment of this stem cell population. Growth factor treatment also determines modifications in foxO1 expression, a transcriptional factor that acts in the PI3K/AKT pathway in response to IGF-1, strengthening its role in the generation of osteoblasts as well as in the control of bone homeostasis [Fowlkes et al, 2011;Ferretti et al, 2014].…”

“…On the basis of our previous experience on the ability of IGF-1, either alone or in combination with VEGF, to regulate the commitment of PDPCs and S-MSCs toward the osteoblastic or endothelial phenotype [Ferretti et al, 2014], we tried to deepen our knowledge on a possible paracrine effect of these two factors by means of a Transwell coculture approach in the present study.…”