Background/Purpose:

Upon adenosine formation in stress conditions, the adenosine A_2A Receptor (A_2AR) activation promotes wound healing, but it is also detrimental in fibrotic conditions such as scarring, scleroderma and liver fibrosis. Although we have previously shown that the A_2AR regulates scarring and fibrosis by fine-tuning the collagen1 to collagen3 balance in human dermal fibroblasts, the intracellular pathway leading to collagen production upon A_2AR activation remains unclear. β-catenin is a central mediator of pro-fibrotic Wnt signaling in systemic sclerosis (Beyer et al. 2012) and the pro-fibrotic growth factor TGF-β1 targets the β-catenin pathway (Caraci et al. 2008). We therefore sought to determine whether A_2AR stimulates Wnt / β-catenin signaling in human dermal fibroblasts.

Methods:

Cells were stimulated for 24h with the specific A_2AR agonist CGS21680, in the presence or absence of the A_2AR antagonist SCH58211. β-catenin was knock-down with siRNA and collagen1, collagen3 and β-catenin expression were analyzed by western-blotting. Subcellular distribution of β-catenin was studied by cellular fractionation and confocal microscopy. 

Results:

The A2A agonist CGS21680 stimulated, in a dose-dependent fashion, a significant increase in β-catenin expression (increase over non-stimulated control: CGS21680 0.1μM 139.6±10.3%, P<0.01 n=5; 1μM 163.7±18.8%, P<0.001 n=3; 10μM 151.6±7.1%, P<0.001 n=5) and preincubation with the A2AR antagonist SCH21680 1μM prevented this effect (two-way ANOVA P<0.01, n=5). Subcellular fractionation after incubation with CGS21680 (1μM) showed a preferential increase of β-catenin in the nucleus, as assessed by Western Blot Analysis and confocal images demonstrate colocalization of the nuclear marker DAPI and β-catenin after A2AR stimulation. As expected, CGS21680 1μM stimulated an increase of both collagen1 (1.4 and 2.5 fold increase over control) and collagen3 (2.8 and 2.2 fold increase over control) but, interestingly, β-catenin knock-down prevented the CGS21680-mediated increase in collagen3, but not collagen1. 

Conclusion:

These results strongly support the hypothesis that activation of the A2AR leads to cross-talk with the pro-fibrotic Wnt / β-catenin signaling system. These findings suggest a mechanism for changes in the collagen1:collagen3 ratio in animal models of hypertrophic scars and scleroderma in which A2AR blockade or deletion prevents fibrosis and in which adenosine concentrations are dramatically increased.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/adenosine-a2a-receptor-activates-the-pro-fibrotic-wnt-%ce%b2-catenin-signaling-in-human-dermal-fibroblasts/