Daniele Simona, Natali Letizia, Giacomelli Chiara, Campiglia Pietro, Novellino Ettore, Martini Claudia, Trincavelli Maria Letizia
Department of Pharmacy, University of Pisa, Pisa, Italy.
Department of Pharmacy, University of Naples Federico II, Naples, Italy.
Mol Cell Biol. 2017 Mar 31;37(8). doi: 10.1128/MCB.00442-16. Print 2017 Apr 15.
In the early phase of bone damage, low concentrations of the cytokine tumor necrosis factor alpha (TNF-α) favor osteoblast differentiation. In contrast, chronic high doses of the same cytokine contribute to bone loss, demonstrating opposite effects depending on its concentration and on the time of exposure. In the bone microenvironment, TNF-α modulates the expression/function of different G protein-coupled receptors (GPCRs) and of their regulatory proteins, GPCR-regulated kinases (GRKs), thus dictating their final biological outcome in controlling bone anabolic processes. Here, the effects of TNF-α were investigated on the expression/responsiveness of the A adenosine receptor (AAR), a Gs-coupled receptor that promotes mesenchymal stem cell (MSC) differentiation into osteoblasts. Low TNF-α concentrations exerted a prodifferentiating effect on MSCs, pushing them toward an osteoblast phenotype. By regulating GRK2 turnover and expression, the cytokine impaired AAR desensitization, accelerating receptor-mediated osteoblast differentiation. These data supported the anabolic effect of TNF-α submaximal concentration and demonstrated that the cytokine regulates GPCR responses by interfering with the receptor desensitization machinery, thereby enhancing the anabolic responses evoked by AAR ligands. Overall, these results indicated that GPCR desensitization plays a pivotal role in osteogenesis and that its manipulation is an effective strategy to favor bone remodeling.
在骨损伤的早期阶段,低浓度的细胞因子肿瘤坏死因子α(TNF-α)有利于成骨细胞分化。相反,相同细胞因子的慢性高剂量会导致骨质流失,这表明其作用取决于浓度和暴露时间,呈现出相反的效果。在骨微环境中,TNF-α调节不同G蛋白偶联受体(GPCRs)及其调节蛋白GPCR调节激酶(GRKs)的表达/功能,从而决定它们在控制骨合成代谢过程中的最终生物学结果。在此,研究了TNF-α对A1腺苷受体(A1AR)表达/反应性的影响,A1AR是一种Gs偶联受体,可促进间充质干细胞(MSC)分化为成骨细胞。低浓度的TNF-α对MSC具有促分化作用,促使它们向成骨细胞表型分化。通过调节GRK2的周转和表达,该细胞因子削弱了A1AR的脱敏作用,加速了受体介导的成骨细胞分化。这些数据支持了TNF-α亚最大浓度的合成代谢作用,并表明该细胞因子通过干扰受体脱敏机制来调节GPCR反应,从而增强A1AR配体引起的合成代谢反应。总体而言,这些结果表明GPCR脱敏在骨生成中起关键作用,并且对其进行调控是促进骨重塑的有效策略。