The role of adenosine receptors A2A and A2B signaling in renal fibrosis

Renal fibrosis, the key histopathological lesion in the development and progression of chronic kidney disease (CKD), has been the focus of much research in recent decades. The growing burden of CKD in both developed and developing nations highlights a need for novel therapies to halt the progression of renal disease. Insights into the pathogenesis of renal fibrosis and the key cellular and molecular mediators have been critical in the process of identifying potential targets of therapy. Adenosine signaling is an innate biological autocrine and paracrine cellular signaling pathway involving several key mediators: ectonucleotidases, adenosine, and adenosine receptors. Short-term activation of the adenosine A(2A) and A(2B) receptors decreases inflammation, which precedes renal fibrosis. However, in conditions of persistent, excessive adenosine exposure, such as in patients born with adenosine deaminase (ADA) deficiency, adenosine signaling via A(2B) receptor promotes renal fibrosis, as seen in chronic inflammation. This review will describe the increasingly recognized complex role of adenosine signaling in the development of renal fibrosis. We will speculate how the knowledge gained may be employed in the search for more effective therapies based on these complex signaling pathways.