Discoidin domain receptor 2 activation of p38 mitogen-activated protein kinase as an important pathway for osteonectin-regulating osteoblast mineralization

Osteonectin bidirectionally regulates osteoblast mineralization

OBJECTIVE

The aim of this study was to investigate whether Osteonectin/Secreted protein acidic and rich in cysteine (ON/SPARC) had a two-way dose-dependent regulatory effect on osteoblast mineralization and its molecular mechanism.

METHODS

Initially, different concentrations of ON were added in osteoblasts, and the gene of bone sialoprotein (BSP), osteocalcin (OCN), osteopontin (OPN) and alkaline phosphatase (ALP) were detected using reverse-transcription quantitative polymerase chain reaction (RT-PCR). Secondly, based on the above results, the Optima and inhibitory concentration of ON for osteoblast mineralization were determined and regrouped, the Control group was also set up, and the gene detections of Collagen 1 (Col 1), Discoidin domain receptor 2 (DDR2) and p38 mitogen‑activated protein kinase were added using RT-PCR. In the third stage of the experiment, osteoblasts were pretreated with 0.4Mm ethyl-3,4-dihydroxybenzoate (DHB) (a specific inhibitor of collagen synthesis) for 3 h before adding the optima SPARC, the gene and protein expressions of OCN, OPN, BSP, ALP, DDR2, ALP, Col 1, DDR2 and P38 were detected by RT‑qPCR and western blot analysis, and the mineralized nodules were observed by alizarin red staining.

RESULTS

The results showed that the expression of OCN, OPN, BSP, ALP, DDR2, ALP, Col 1, DDR2 and P38 genes and proteins in osteoblasts were significantly enhanced by 1 ug/ml ON, 100 ug/ml ON or 1 ug/ml ON added with 3,4 DHB significantly inhibited the expressions of DDR2, P38 and the above-mentioned mineralization indexes, and significantly reduced the formation of mineralized nodules.

CONCLUSION

This study suggested that ON had a bidirectional dose-dependent regulatory effect on osteoblast mineralization, and the activation of P38 pathway by collagen binding to DDR2 was also an important molecular mechanism.

Extracellular matrix-induced signaling pathways in mesenchymal stem/stromal cells

The extracellular matrix (ECM) is a crucial component of the stem cell microenvironment, or stem-cell niches, and contributes to the regulation of cell behavior and fate. Accumulating evidence indicates that different types of stem cells possess a large variety of molecules responsible for interactions with the ECM, mediating specific epigenetic rearrangements and corresponding changes in transcriptome profile. Signals from the ECM are crucial at all stages of ontogenesis, including embryonic and postnatal development, as well as tissue renewal and repair. The ECM could regulate stem cell transition from a quiescent state to readiness to perceive the signals of differentiation induction (competence) and the transition between different stages of differentiation (commitment). Currently, to unveil the complex networks of cellular signaling from the ECM, multiple approaches including screening methods, the analysis of the cell matrixome, and the creation of predictive networks of protein-protein interactions based on experimental data are used. In this review, we consider the existing evidence regarded the contribution of ECM-induced intracellular signaling pathways into the regulation of stem cell differentiation focusing on mesenchymal stem/stromal cells (MSCs) as well-studied type of postnatal stem cells totally depended on signals from ECM. Furthermore, we propose a system biology-based approach for the prediction of ECM-mediated signal transduction pathways in target cells. Video Abstract.

The Role of Extracellular Matrix Proteins in Breast Cancer

The extracellular matrix is a structure composed of many molecules, including fibrillar (types I, II, III, V, XI, XXIV, XXVII) and non-fibrillar collagens (mainly basement membrane collagens: types IV, VIII, X), non-collagenous glycoproteins (elastin, laminin, fibronectin, thrombospondin, tenascin, osteopontin, osteonectin, entactin, periostin) embedded in a gel of negatively charged water-retaining glycosaminoglycans (GAGs) such as non-sulfated hyaluronic acid (HA) and sulfated GAGs which are linked to a core protein to form proteoglycans (PGs). This highly dynamic molecular network provides critical biochemical and biomechanical cues that mediate the cell–cell and cell–matrix interactions, influence cell growth, migration and differentiation and serve as a reservoir of cytokines and growth factors’ action. The breakdown of normal ECM and its replacement with tumor ECM modulate the tumor microenvironment (TME) composition and is an essential part of tumorigenesis and metastasis, acting as key driver for malignant progression. Abnormal ECM also deregulate behavior of stromal cells as well as facilitating tumor-associated angiogenesis and inflammation. Thus, the tumor matrix modulates each of the classically defined hallmarks of cancer promoting the growth, survival and invasion of the cancer. Moreover, various ECM-derived components modulate the immune response affecting T cells, tumor-associated macrophages (TAM), dendritic cells and cancer-associated fibroblasts (CAF). This review article considers the role that extracellular matrix play in breast cancer. Determining the detailed connections between the ECM and cellular processes has helped to identify novel disease markers and therapeutic targets.