Human subcutaneous fibroblasts (HSCF) challenged with inflammatory mediators release huge amounts of ATP, which rapidly generates adenosine. Given the nucleoside’s putative relevance in wound healing, dermal fibrosis, and myofascial pain, we investigated the role of its precursor, AMP, and of its metabolite, inosine, in HSCF cells growth and collagen production. AMP (30 µM) was rapidly (t½ 3 ± 1 min) dephosphorylated into adenosine by CD73/ecto-5′-nucleotidase. Adenosine accumulation (t½ 158 ± 17 min) in the extracellular fluid reflected very low cellular adenosine deaminase (ADA) activity. HSCF stained positively against A2A and A3 receptors but were A1 and A2B negative. AMP and the A2A receptor agonist, CGS21680C, increased collagen production without affecting cells growth. The A2A receptor antagonist, SCH442416, prevented the effects of AMP and CGS21680C. Inosine and the A3 receptor agonist, 2Cl-IB-MECA, decreased HSCF growth and collagen production in a MRS1191-sensitive manner, implicating the A3 receptor in the anti-proliferative action of inosine. Incubation with ADA reproduced the inosine effect. In conclusion, adenosine originated from extracellular ATP hydrolysis favors normal collagen production by HSCF via A2A receptors. Inhibition of unpredicted inosine formation by third party ADA cell providers (e.g., inflammatory cells) may be a novel therapeutic target to prevent inappropriate dermal remodeling via A3 receptors activation.

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Metabolic reprogramming is a central hub in tumor development and progression. Therefore, several efforts have been developed to find improved therapeutic approaches targeting cancer cell metabolism. Recently, we identified the 7α-acetoxy-6β-benzoyloxy-12-O-benzoylroyleanone (Roy-Bz) as a PKCδ-selective activator with potent anti-proliferative activity in colon cancer by stimulating a PKCδ-dependent mitochondrial apoptotic pathway. Herein, we investigated whether the antitumor activity of Roy-Bz, in colon cancer, could be related to glucose metabolism interference. The results showed that Roy-Bz decreased the mitochondrial respiration in human colon HCT116 cancer cells, by reducing electron transfer chain complexes I/III. Consistently, this effect was associated with downregulation of the mitochondrial markers cytochrome c oxidase subunit 4 (COX4), voltage-dependent anion channel (VDAC) and mitochondrial import receptor subunit TOM20 homolog (TOM20), and upregulation of synthesis of cytochrome c oxidase 2 (SCO2). Roy-Bz also dropped glycolysis, decreasing the expression of critical glycolytic markers directly implicated in glucose metabolism such as glucose transporter 1 (GLUT1), hexokinase 2 (HK2) and monocarboxylate transporter 4 (MCT4), and increasing TP53-induced glycolysis and apoptosis regulator (TIGAR) protein levels. These results were further corroborated in tumor xenografts of colon cancer. Altogether, using a PKCδ-selective activator, this work evidenced a potential dual role of PKCδ in tumor cell metabolism, resulting from the inhibition of both mitochondrial respiration and glycolysis. Additionally, it reinforces the antitumor therapeutic potential of Roy-Bz in colon cancer by targeting glucose metabolism.

Disorganization of the subcutaneous tissue due to inflammation and fibrosis is a common feature in patients with myofascial pain. Dermal accumulation of adenosine favours collagen production by human subcutaneous fibroblasts (HSCF) via A2A receptors (A2AR) activation. Adenosine mimics the fibrogenic effect of inflammatory mediators (e.g. histamine, bradykinin), which act by promoting ATP release from HSCF via pannexin-1 (Panx1) and/or connexin-43 (Cx43) hemichannels. However, this mechanism was never implicated in the A2AR-mediated actions. NECA and CGS21680C, two enzymatically-stable A2AR agonists, increased Panx-1, but reduced Cx43, immunoreactivity in cultured HSCF. This effect was accompanied by increases in ATP release and collagen production by HSCF. Involvement of A2AR was verified upon blockage of NECA and CGS21680 effects with the selective A2AR antagonist, SCH442416. Inhibition of Panx1 hemichannels with probenecid also decreased ATP release and collagen production by HSCF under similar conditions. Superfluous ATP release by HSCF exposed to A2AR agonists overexpressing Panx1 hemichannels contributes to keep high [Ca2+]i levels in the presence of inflammatory mediators, like histamine. Adenosine A2AR-induced Panx1 overexpression was shown here for the first time; this feature indirectly implicates ATP release in the fibrogenic vicious cycle putatively operated by the nucleoside in subcutaneous tissue fibrosis and myofascial inflammatory conditions.