Interpreting an apoptotic corpse as anti-inflammatory involves a chloride sensing pathway

Apoptotic cell clearance (efferocytosis) elicits an anti-inflammatory response by phagocytes, but the mechanisms that underlie this response are still being defined. Here, we uncover a chloride-sensing signalling pathway that controls both the phagocyte ‘appetite’ and its anti-inflammatory response. Efferocytosis transcriptionally altered the genes that encode the solute carrier (SLC) proteins SLC12A2 and SLC12A4. Interfering with SLC12A2 expression or function resulted in a significant increase in apoptotic corpse uptake per phagocyte, whereas the loss of SLC12A4 inhibited corpse uptake. In SLC12A2-deficient phagocytes, the canonical anti-inflammatory program was replaced by pro-inflammatory and oxidative-stress-associated gene programs. This ‘switch’ to pro-inflammatory sensing of apoptotic cells resulted from the disruption of the chloride-sensing pathway (and not due to corpse overload or poor degradation), including the chloride-sensing kinases WNK1, OSR1 and SPAK—which function upstream of SLC12A2—had a similar effect on efferocytosis. Collectively, the WNK1–OSR1–SPAK–SLC12A2/SLC12A4 chloride-sensing pathway and chloride flux in phagocytes are key modifiers of the manner in which phagocytes interpret the engulfed apoptotic corpse. Perry and Morioka et al. show that the chloride transporter SLC12A2 regulates apoptotic cell uptake by phagocytes and, together with SLC12 kinases WNK1, OSR1 and SPAK, this pathway maintains an anti-inflammatory gene signature.