Systematic deletion of adenosine receptors reveals novel roles in inflammation and pyroptosis in THP-1 macrophages

Abstract

Macrophages perform the fundamental function of sensing cellular damage, initiating and mediating immune response and tissue repair. Adenine nucleotides are in relatively high abundance in cells and are released from cells during tissue damage that are converted to adenosine in the extracellular environment. The A₁, A_2A, A_2B and A₃ adenosine receptors serve to regulate immune function. Despite characterization of the adenosine receptors, a comprehensive examination of adenosine receptor signaling in THP-1 macrophage cells has not been done. Moreover, previous studies employed chemical agonists and antagonists that have the potential for off-target affects. Here we systematically knockdown each of the four known adenosine receptors in THP-1 macrophages using validated siRNA and investigated their function under LPS stimulation. We demonstrate that the A₁ receptor is required for adenosine-stimulated IL-10 and IL-1β secretion indicating an important role of this receptor during resolution of inflammation and tissue repair in these cells. The A₁ and A₃ receptor were required for IL-6 and IL-1β secretion showing a net pro-inflammatory role for these receptors. Finally, we present the novel finding that THP-1 macrophages lacking the A_2B receptor undergo pyroptosis when exposed to LPS, demonstrating a novel role of the A_2B receptor in regulation of programmed cell death during inflammation. This work underscores the fundamental importance of adenosine signaling and provides insight into the independent roles of the adenosine receptors in modulating cytokine signaling.

Keywords: Adenosine receptors; Inflammation; Pyroptosis; THP-1 macrophages.