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LIVER AND BILIARY TRACT

Adenosine inhibits cytosolic calcium signals and chemotaxis in hepatic stellate cells

¹Section of Digestive Diseases, Yale University, New Haven, Connecticut; and ²Gilead Sciences Incorporated, Foster City, California

Submitted 12 May 2006 ; accepted in final form 6 September 2006

Adenosine is produced during cellular hypoxia and apoptosis, resulting in elevated tissue levels at sites of injury. Adenosine is also known to regulate a number of cellular responses to injury, but its role in hepatic stellate cell (HSC) biology and liver fibrosis is poorly understood. We tested the effect of adenosine on the cytosolic Ca²⁺ concentration, chemotaxis, and upregulation of activation markers in HSCs. We showed that adenosine did not induce an increase in the cytosolic Ca²⁺ concentration in LX-2 cells and, in addition, inhibited increases in the cytosolic Ca²⁺ concentration in response to ATP and PDGF. Using a Transwell system, we showed that adenosine strongly inhibited PDGF-induced HSC chemotaxis in a dose-dependent manner. This inhibition was mediated via the A_2a receptor, was reversible, was reproduced by forskolin, and was blocked by the adenylate cyclase inhibitor 2,5-dideoxyadenosine. Adenosine also upregulated the production of TGF- and collagen I mRNA. In conclusion, adenosine reversibly inhibits Ca²⁺ fluxes and chemotaxis of HSCs and upregulates TGF- and collagen I mRNA. We propose that adenosine provides 1) a "stop" signal to HSCs when they reach sites of tissue injury with high adenosine concentrations and 2) stimulates transdifferentiation of HSCs by upregulating collagen and TGF- production.

platelet-derived growth factor; Ca²⁺; fibrosis

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