Silencing NTPDase3 activity rehabilitates the osteogenic commitment of post-menopausal stem cell bone progenitors.

BACKGROUND: Endogenously released adenine and uracil nucleotides favour the osteogenic commitment of bone marrow-derived mesenchymal stromal cells (BM-MSCs) through the activation of ATP-sensitive P2X7 and UDP-sensitive P2Y6 receptors. Yet, these nucleotides have their osteogenic potential compromised in post-menopausal (Pm) women due to overexpression of nucleotide metabolizing enzymes, namely NTPDase3. This prompted us to investigate whether NTPDase3 gene silencing or inhibition of its enzymatic activity could rehabilitate the osteogenic potential of Pm BM-MSCs. METHODS: MSCs were harvested from the bone marrow of Pm women (69 ± 2 years old) and younger female controls (22 ± 4 years old). The cells were allowed to grow for 35 days in an osteogenic-inducing medium in either the absence or the presence of NTPDase3 inhibitors (PSB 06126 and hN3-B3s antibody); pre-treatment with a lentiviral short hairpin RNA (Lenti-shRNA) was used to silence the NTPDase3 gene expression. Immunofluorescence confocal microscopy was used to monitor protein cell densities. The osteogenic commitment of BM-MSCs was assessed by increases in the alkaline phosphatase (ALP) activity. The amount of the osteogenic transcription factor Osterix and the alizarin red-stained bone nodule formation. ATP was measured with the luciferin-luciferase bioluminescence assay. The kinetics of the extracellular ATP (100 µM) and UDP (100 µM) catabolism was assessed by HPLC RESULTS: The extracellular catabolism of ATP and UDP was faster in BM-MSCs from Pm women compared to younger females. The immunoreactivity against NTPDase3 increased 5.6-fold in BM-MSCs from Pm women vs. younger females. Selective inhibition or transient NTPDase3 gene silencing increased the extracellular accumulation of adenine and uracil nucleotides in cultured Pm BM-MSCs. Downregulation of NTPDase3 expression or activity rehabilitated the osteogenic commitment of Pm BM-MSCs measured as increases in ALP activity, Osterix protein cellular content and bone nodule formation; blockage of P2X7 and P2Y6 purinoceptors prevented this effect. CONCLUSIONS: Data suggest that NTPDase3 overexpression in BM-MSCs may be a clinical surrogate of the osteogenic differentiation impairment in Pm women. Thus, besides P2X7 and P2Y6 receptors activation, targeting NTPDase3 may represent a novel therapeutic strategy to increase bone mass and reduce the osteoporotic risk of fractures in Pm women.

Inhibition of cholinergic neurotransmission by ß3-adrenoceptors depends on adenosine release and A1-receptor activation in human and rat urinary bladders.

The direct detrusor relaxant effect of ß3-adrenoceptor agonists as a primary mechanism to improve overactive bladder symptoms has been questioned. Among other targets, activation of ß3-adrenoceptors downmodulate nerve-evoked acetylcholine (ACh) release, but there is insufficient evidence for the presence of these receptors on bladder cholinergic nerve terminals. Our hypothesis is that adenosine formed from the catabolism of cyclic AMP in the detrusor may act as a retrograde messenger via prejunctional A1 receptors to explain inhibition of cholinergic activity by ß3-adrenoceptors. Isoprenaline (1 µM) decreased [3H]ACh release from stimulated (10 Hz, 200 pulses) human (-47 ± 5%) and rat (-38 ± 1%) detrusor strips. Mirabegron (0.1 µM, -53 ± 8%) and CL316,243 (1 µM, -37 ± 7%) mimicked isoprenaline (1 µM) inhibition, and their effects were prevented by blocking ß3-adrenoceptors with L748,337 (30 nM) and SR59230A (100 nM), respectively, in human and rat detrusor. Mirabegron and isoprenaline increased extracellular adenosine in the detrusor. Blockage of A1 receptors with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 100 nM) or the equilibrative nucleoside transporters (ENT) with dipyridamole (0.5 µM) prevented mirabegron and isoprenaline inhibitory effects. Dipyridamole prevented isoprenaline-induced adenosine outflow from the rat detrusor, and this effect was mimicked by the ENT1 inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI, 30 µM). Cystometry recordings in anesthetized rats demonstrated that SR59230A, DPCPX, dipyridamole, and NBTI reversed the decrease in the voiding frequency caused by isoprenaline (0.1-1,000 nM). Data suggest that inhibition of cholinergic neurotransmission by ß3-adrenoceptors results from adenosine release via equilibrative nucleoside transporters and prejunctional A1-receptor stimulation in human and rat urinary bladder.

Activation of P2Y6 Receptors Facilitates Nonneuronal Adenosine Triphosphate and Acetylcholine Release from Urothelium with the Lamina Propria of Men with Bladder Outlet Obstruction.

PURPOSE: Deregulation of purinergic bladder signaling may contribute to persistent detrusor overactivity in patients with bladder outlet obstruction. Activation of uridine diphosphate sensitive P2Y6 receptors increases voiding frequency in rats indirectly by releasing adenosine triphosphate from the urothelium. To our knowledge this mechanism has never been tested in the human bladder. MATERIALS AND METHODS: We examined the role of the uridine diphosphate sensitive P2Y6 receptor on tetrodotoxin insensitive nonneuronal adenosine triphosphate and [(3)H]acetylcholine release from the human urothelium with the lamina propria of control organ donors and patients with benign prostatic hyperplasia. RESULTS: The adenosine triphosphate-to-[(3)H]acetylcholine ratio was fivefold higher in mucosal urothelium/lamina propria strips from benign prostatic hyperplasia patients than control men. The selective P2Y6 receptor agonist PSB0474 (100 nM) augmented by a similar amount adenosine triphosphate and [(3)H]acetylcholine release from mucosal urothelium/lamina propria strips from both groups of individuals. The facilitatory effect of PSB0474 was prevented by MRS2578 (50 nM) and by carbenoxolone (10 µM), which block P2Y6 receptor and pannexin-1 hemichannels, respectively. Blockade of P2X3 (and/or P2X2/3) receptors with A317491 (100 nM) also attenuated release facilitation by PSB0474 in control men but not in patients with benign prostatic hyperplasia. Immunolocalization studies showed that P2Y6, P2X2 and P2X3 receptors were present in choline acetyltransferase positive urothelial cells. In contrast to P2Y6 staining, choline acetyltransferase, P2X2 and P2X3 immunoreactivity decreased in the urothelium of benign prostatic hyperplasia patients. CONCLUSIONS: Activation of P2Y6 receptor amplifies mucosal adenosine triphosphate release underlying bladder overactivity in patients with benign prostatic hyperplasia. Therefore, we propose selective P2Y6 receptor blockade as a novel therapeutic strategy to control persistent storage symptoms in obstructed patients.

Deficits in endogenous adenosine formation by ecto-5'-nucleotidase/CD73 impair neuromuscular transmission and immune competence in experimental autoimmune myasthenia gravis.

AMP dephosphorylation via ecto-5'-nucleotidase/CD73 is the rate limiting step to generate extracellular adenosine (ADO) from released adenine nucleotides. ADO, via A2A receptors (A2ARs), is a potent modulator of neuromuscular and immunological responses. The pivotal role of ecto-5'-nucleotidase/CD73, in controlling extracellular ADO formation, prompted us to investigate its role in a rat model of experimental autoimmune myasthenia gravis (EAMG). Results show that CD4(+)CD25(+)FoxP3(+) regulatory T cells express lower amounts of ecto-5'-nucleotidase/CD73 as compared to controls. Reduction of endogenous ADO formation might explain why proliferation of CD4(+) T cells failed upon blocking A2A receptors activation with ZM241385 or adenosine deaminase in EAMG animals. Deficits in ADO also contribute to neuromuscular transmission failure in EAMG rats. Rehabilitation of A2AR-mediated immune suppression and facilitation of transmitter release were observed by incubating the cells with the nucleoside precursor, AMP. These findings, together with the characteristic increase in serum adenosine deaminase activity of MG patients, strengthen our hypothesis that the adenosinergic pathway may be dysfunctional in EAMG. Given that endogenous ADO formation is balanced by ecto-5'-nucleotidase/CD73 activity and that A2ARs exert a dual role to restore use-dependent neurocompetence and immune suppression in myasthenics, we hypothesize that stimulation of the two mechanisms may have therapeutic potential in MG.

Feed-forward inhibition of CD73 and upregulation of adenosine deaminase contribute to the loss of adenosine neuromodulation in postinflammatory ileitis.

Purinergic signalling is remarkably plastic during gastrointestinal inflammation. Thus, selective drugs targeting the "purinome" may be helpful for inflammatory gastrointestinal diseases. The myenteric neuromuscular transmission of healthy individuals is fine-tuned and controlled by adenosine acting on A(2A) excitatory receptors. Here, we investigated the neuromodulatory role of adenosine in TNBS-inflamed longitudinal muscle-myenteric plexus of the rat ileum. Seven-day postinflammation ileitis lacks adenosine neuromodulation, which may contribute to acceleration of gastrointestinal transit. The loss of adenosine neuromodulation results from deficient accumulation of the nucleoside at the myenteric synapse despite the fact that the increases in ATP release were observed. Disparity between ATP outflow and adenosine deficit in postinflammatory ileitis is ascribed to feed-forward inhibition of ecto-5'-nucleotidase/CD73 by high extracellular ATP and/or ADP. Redistribution of NTPDase2, but not of NTPDase3, from ganglion cell bodies to myenteric nerve terminals leads to preferential ADP accumulation from released ATP, thus contributing to the prolonged inhibition of muscle-bound ecto-5'-nucleotidase/CD73 and to the delay of adenosine formation at the inflamed neuromuscular synapse. On the other hand, depression of endogenous adenosine accumulation may also occur due to enhancement of adenosine deaminase activity. Both membrane-bound and soluble forms of ecto-5'-nucleotidase/CD73 and adenosine deaminase were detected in the inflamed myenteric plexus. These findings provide novel therapeutic targets for inflammatory gut motility disorders.

Bradykinin-induced Ca2+ signaling in human subcutaneous fibroblasts involves ATP release via hemichannels leading to P2Y12 receptors activation.

BACKGROUND: 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. RESULTS: Bradykinin, via B2 receptors, caused an abrupt rise in [Ca2+]i to a peak that declined to a plateau, which concentration remained constant until washout. The plateau phase was absent in Ca2+-free medium; [Ca2+]i signal was substantially reduced after depleting intracellular Ca2+ stores with thapsigargin. Extracellular ATP inactivation with apyrase decreased the [Ca2+]i plateau. Human subcutaneous fibroblasts respond to bradykinin by releasing ATP via connexin and pannexin hemichannels, since blockade of connexins, with 2-octanol or carbenoxolone, and pannexin-1, with 10Panx, attenuated bradykinin-induced [Ca2+]i plateau, whereas inhibitors of vesicular exocytosis, such as brefeldin A and bafilomycin A1, were inactive. The kinetics of extracellular ATP catabolism favors ADP accumulation in human fibroblast cultures. Inhibition of ectonucleotidase activity and, thus, ADP formation from released ATP with POM-1 or by Mg2+ removal from media reduced bradykinin-induced [Ca2+]i plateau. Selective blockade of the ADP-sensitive P2Y12 receptor with AR-C66096 attenuated bradykinin [Ca2+]i plateau, whereas the P2Y1 and P2Y13 receptor antagonists, respectively MRS 2179 and MRS 2211, were inactive. Human fibroblasts exhibited immunoreactivity against connexin-43, pannexin-1 and P2Y12 receptor. CONCLUSIONS: Bradykinin induces ATP release from human subcutaneous fibroblasts via connexin and pannexin-1-containing hemichannels leading to [Ca2+]i mobilization through the cooperation of B2 and P2Y12 receptors.

Histamine induces ATP release from human subcutaneous fibroblasts, via pannexin-1 hemichannels, leading to Ca2+ mobilization and cell proliferation.

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.