BACKGROUND 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. METHODS In 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. RESULTS We 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. CONCLUSIONS Taken 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.

中文翻译：

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多巴胺 D1 受体介导的 ERK 信号通路激活参与骨间充质干细胞的成骨分化。

背景技术骨间充质干细胞(BMSC)的成骨分化受到多种信号通路的调节。多巴胺 (DA) 是一种神经递质，此前已被证明可以通过刺激 BMSC 上的受体来诱导新骨形成，但 DA 诱导的成骨信号传导的重要介质仍不清楚。方法在这项工作中，我们评估了多巴胺 D1 和 D2 受体激活对 BMSC 成骨分化的影响。测试了成骨相关标志物的基因和蛋白表达。还研究了转录因子 Runx2 与这些标记的直接结合。此外，还评估了细胞分化相关的信号通路。结果我们发现 BMSC 上 D1 受体的表达水平在成骨分化过程中增加。与DA类似，D1受体激动剂诱导BMSCs成骨分化，并且这种现象可以被D1受体拮抗剂或D1受体敲除有效抑制。此外，抑制蛋白激酶A（PKA）（D1受体下游的一种重要激酶）可成功抑制DA诱导的BMSC成骨分化，并降低ERK1/2的磷酸化。与P38、MAPK和JNK相比，DA主要诱导ERK1/2磷酸化，导致Runx2转录活性上调，从而促进BMSC成骨分化。另一方面，ERK1/2 抑制剂可以逆转这些影响。结论 综上所述，这些结果表明 ERK 信号传导可能在通过 D1 受体激活协调 DA 诱导的 BMSC 成骨分化中发挥重要作用。