title: Osteogenesis Is Improved by Low Tumor Necrosis Factor Alpha Concentration through the Modulation of Gs-Coupled Receptor Signals.
abstract: 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 A2Badenosine receptor (A2BAR), 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 A2BAR 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 A2BAR 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.
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Daniele
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, Italy.
authors.forename: Letizia
authors.initials: L
authors.lastname: Natali
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Giacomelli
authors.affiliation: Department of Pharmacy, University of Naples Federico II, Naples, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Campiglia
authors.affiliation: Department of Pharmacy, University of Naples Federico II, Naples, Italy.
authors.forename: Ettore
authors.initials: E
authors.lastname: Novellino
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, Italy claudia.martini@unipi.it.
authors.forename: Claudia
authors.identifier: http://orcid.org/0000-0001-9379-3027
authors.initials: C
authors.lastname: Martini
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, Italy.
authors.forename: Maria Letizia
authors.initials: ML
authors.lastname: Trincavelli
mesh_terms: D058908:Adenosine A2 Receptor Agonists / Q000494:pharmacology; D002113:Calcification, Physiologic / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000378:metabolism; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects; D043704:Receptor, Adenosine A2B / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000494:pharmacology
chemical_list: D058908:Adenosine A2 Receptor Agonists; D043704:Receptor, Adenosine A2B; D043562:Receptors, G-Protein-Coupled; D014409:Tumor Necrosis Factor-alpha; C496567:GRK2 protein, human; D054769:G-Protein-Coupled Receptor Kinase 2; D019205:GTP-Binding Protein alpha Subunits, Gs
keywords: A2B adenosine receptor; G protein-coupled receptor kinases; mesenchymal stem cells; osteoblasts; proteasome; tumor necrosis factor alpha