Autocrine Purinergic Receptor Signaling Is Essential for Macrophage Chemotaxis

Chemotaxis, the movement of cells along chemical gradients, is critical for the recruitment of immune cells to sites of inflammation; however, how cells navigate in chemotactic gradients is poorly understood. Here, we show that macrophages navigate in a gradient of the chemoattractant C5a through the release of adenosine triphosphate (ATP) and autocrine "purinergic feedback loops" that involve receptors for ATP (P2Y(2)), adenosine diphosphate (ADP) (P2Y(12)), and adenosine (A2a, A2b, and A3). Whereas macrophages from mice deficient in pannexin-1 (which is part of a putative ATP release pathway), P2Y(2), or P2Y(12) exhibited efficient chemotactic navigation, chemotaxis was blocked by apyrase, which degrades ATP and ADP, and by the inhibition of multiple purinergic receptors. Furthermore, apyrase impaired the recruitment of monocytes in a mouse model of C5a-induced peritonitis. In addition, we found that stimulation of P2Y(2), P2Y(12), or adenosine receptors induced the formation of lamellipodial membrane protrusions, causing cell spreading. We propose a model in which autocrine purinergic receptor signaling amplifies and translates chemotactic cues into directional motility.