Changes in the regulation of connective tissue ATP-mediated mechano-transduction and remodeling may be an important link to the pathogenesis of chronic pain. It has been demonstrated that mast cell-derived histamine plays an important role in painful fibrotic diseases. Here we analyzed the involvement of ATP in the response of human subcutaneous fibroblasts to histamine. Acute histamine application caused a rise in intracellular Ca(2+) ([Ca(2+)]i) and ATP release from human subcutaneous fibroblasts via H1 receptor activation. Histamine-induced [Ca(2+)]i rise was partially attenuated by apyrase, an enzyme that inactivates extracellular ATP, and by blocking P2 purinoceptors with pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid) tetrasodium salt and reactive blue 2. [Ca(2+)]i accumulation caused by histamine was also reduced upon blocking pannexin-1 hemichannels with (10)Panx, probenecid, or carbenoxolone but not when connexin hemichannels were inhibited with mefloquine or 2-octanol. Brefeldin A, an inhibitor of vesicular exocytosis, also did not block histamine-induced [Ca(2+)]i mobilization. Prolonged exposure of human subcutaneous fibroblast cultures to histamine favored cell growth and type I collagen synthesis via the activation of H1 receptor. This effect was mimicked by ATP and its metabolite, ADP, whereas the selective P2Y1 receptor antagonist, MRS2179, partially attenuated histamine-induced cell growth and type I collagen production. Expression of pannexin-1 and ADP-sensitive P2Y1 receptor on human subcutaneous fibroblasts was confirmed by immunofluorescence confocal microscopy and Western blot analysis. In conclusion, histamine induces ATP release from human subcutaneous fibroblasts, via pannexin-1 hemichannels, leading to [Ca(2+)]i mobilization and cell growth through the cooperation of H1 and P2 (probably P2Y1) receptors.

Chronic musculoskeletal pain involves connective tissue remodeling triggered by inflammatory mediators, such as bradykinin. Fibroblast cells signaling involve changes in intracellular Ca2+ ([Ca2+]i). ATP has been related to connective tissue mechanotransduction, remodeling and chronic inflammatory pain, via P2 purinoceptors activation. Here, we investigated the involvement of ATP in bradykinin-induced Ca2+ signals in human subcutaneous fibroblasts.

Polymorphisms of the P2X7 receptor have been associated with increased risk of fractures in postmenopausal women. Although both osteoblasts and osteoclasts express P2X7 receptors, their function in osteogenesis remains controversial. Here, we investigated the role of the P2X7 receptor on osteogenic differentiation and mineralization of bone marrow mesenchymal stem cell (BMSC) cultures from postmenopausal women (age 71 ± 3 yr, n =18). We focused on the mechanisms related to intracellular [Ca ²⁺ ] _i oscillations and plasma membrane‐dynamics. ATP, and the P2X7 agonist BzATP (100 μM), increased [Ca ²⁺ ] _i in parallel to the formation of membrane pores permeable to TO‐PRO‐3 dye uptake. ATP and BzATP elicited reversible membrane blebs (zeiosis) in 38 ± 1 and 70 ± 1% of the cells, respectively. P2X7‐induced zeiosis was Ca ²⁺ independent, but involved phospholipase C, protein kinase C, and Rho‐kinase activation. BzATP (100 μM) progressively increased the expression of Runx‐2 and Osterix transcription factors by 452 and 226% (at d 21), respectively, alkaline phosphatase activity by 88% (at d 28), and mineralization by 329% (at d 43) of BMSC cultures in a Rho‐kinase‐dependent manner. In summary, reversible plasma membrane zeiosis involving cytoskeleton rearrangements due to activation of the P2X7‐Rho‐kinase axis promotes osteogenic differentiation and mineralization of BMSCs, thus providing new therapeutic targets for postmenopausal bone loss.—Noronha‐Matos, J. B., Coimbra, J., Sá‐e‐Sousa, A., Rocha, R., Marinhas, J., Freitas, R., Guerra‐Gomes, S., Ferreirinha, F., Costa, M. A., Correia‐de‐Sá, P., P2X7‐induced zeiosis promotes osteogenic differentiation and mineralization of postmenopausal bone marrow‐derived mesenchymal stem cells FASEB J. 28, 5208–5222 (2014). www.fasebj.org