Dopamine D1 receptor-mediated activation of the ERK signaling pathway is involved in the osteogenic differentiation of bone mesenchymal stem cells

Chen-Xi Wang,Xi-Yuan Ge,Ye Lin,Ting Ma,Ming-Yue Wang,Yu Zhang

doi:10.1186/s13287-019-1529-x

Abstract

BackgroundOsteogenic differentiation of bone mesenchymal stem cells (BMSCs) is regulated by numerous signaling pathways. Dopamine (DA), a neurotransmitter, has previously been demonstrated to induce new bone formation by stimulating the receptors on BMSCs, but the essential mediators of DA-induced osteogenic signaling remain unclear.MethodsIn this work, we evaluated the influence of both dopamine D1 and D2 receptor activation on BMSC osteogenic differentiation. Gene and protein expression of osteogenic-related markers were tested. The direct binding of transcriptional factor, Runx2, to those markers was also investigated. Additionally, cellular differentiation-associated signaling pathways were evaluated.ResultsWe showed that the expression level of the D1 receptor on BMSCs increased during osteogenic differentiation. A D1 receptor agonist, similar to DA, induced the osteogenic differentiation of BMSCs, and this phenomenon was effectively inhibited by a D1 receptor antagonist or by D1 receptor knockdown. Furthermore, the suppression of protein kinase A (PKA), an important kinase downstream of the D1 receptor, successfully inhibited DA-induced BMSC osteogenic differentiation and decreased the phosphorylation of ERK1/2. Compared with P38, MAPK, and JNK, DA mainly induced the phosphorylation of ERK1/2 and led to the upregulation of Runx2 transcriptional activity, thus facilitating BMSC osteogenic differentiation. On the other hand, an ERK1/2 inhibitor could reverse these effects.ConclusionsTaken together, these results suggest that ERK signaling may play an essential role in coordinating the DA-induced osteogenic differentiation of BMSCs by D1 receptor activation.

Highlights

Osteogenic differentiation of bone mesenchymal stem cells (BMSCs) is regulated by numerous signaling pathways
D1 and D2 receptors are expressed on BMSCs We investigated the expression of the first two DA receptors, D1 and D2 receptors, on Human bone mesenchymal stem cells (hBMSCs) using quantitative RT-PCR
These changes tended to stabilize after day 7, but the cells cultured in osteogenic media maintained higher expression levels than hBMSCs cultured in growth media (Fig. 1a)

Summary

Introduction

Osteogenic differentiation of bone mesenchymal stem cells (BMSCs) is regulated by numerous signaling pathways. Dopamine (DA), a neurotransmitter, has previously been demonstrated to induce new bone formation by stimulating the receptors on BMSCs, but the essential mediators of DA-induced osteogenic signaling remain unclear. Bone is constantly remodeled through the synchronized and balanced activities of osteoclasts and osteoblasts. This process is highly controlled by autocrine, paracrine, and endocrine factors from the external environment to ensure the systemic balance of calcium–phosphate metabolism while maintaining bone homeostasis. G protein-coupled receptors (GPCRs), such as dopamine receptor (DAR), parathyroid hormone receptor (PTHR), β2AR, calcium-sensing receptor (CaSR), and 5-hydroxytryptamine receptor (5-HTR), are cell membrane proteins with a seven-transmembrane structure that triggers signals within the cells, activates or inhibits specific effectors to induce cellular responses, and regulates many functions. GPCRs are expressed within osteoblasts and osteoclasts, which are thought to be two opposite sides of a coin, and play a crucial role in modulating bone turnover, highlighting the potential for these receptors in the treatment of bone-related diseases, namely, osteoporosis, through a long-lasting enhancement of bone formation with the relative inhibition of bone resorption [10]

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