Abstract
Bone loss is caused by inflammation and is mediated by pro-inflammatory cytokines that control bone formation and bone resorption. The study aimed to determine the effect of secreted factors from human bone marrow-derived stromal cells (hBMSC) of no-heterotopic bone-forming capacity (hBMSC(-Bone)) cells on the differentiation potential of hBMSC which capable of creating bone in-vivo (hBMSC(+Bone)) and dissect the molecular signature of these cells for understanding the complicated relationship of stem cells and microenvironment. hBMSC cultures are heterogenous with respect to differentiation and function. However, the nature of interaction between different cell populations within hBMSC cultures is poorly investigated. We employed two clonal hBMSC lines which exhibit different functional phenotypes based on the presence of either high or low osteoblastic differentiation capacity, bone forming (hBMSC(+Bone)) and non-bone forming (hBMSC(-Bone)), and examined their biological interaction. Adding conditioned media (CM) of hBMSC(-Bone) cultures resulted in suppression of cell proliferation and osteoblasts differentiation of hBMSC(+Bone). Microarray analysis of CM-treated hBMSC(+Bone) revealed significant enrichment of several pathways, including TGF beta signaling. Follow-up experiments corroborated the inhibitory effects on TGF beta signaling as evidenced by decreased SMAD2 phosphorylation and TGF beta-responsive genes (TAGLN, ACTA2 and TPM1). Interestingly, IL1 beta is highly expressed in hBMSC(-Bone) and is present in its CM. Incubating hBMSC(-Bone) with rhIL-1RI rescued the functional phenotype of hBMSC(-Bone) with respect to cell proliferation and differentiation into osteoblasts, and upregulated TGF beta-responsive genes. These data demonstrated that IL1 beta-TGF beta signaling is part of the intercellular communication within the heterogenous population of hBMSCs and regulates their commitment to osteoblastic fate.