Macrophage glycine transporter supports IL-1β production by modulating the AKT1/mTOR/NLRP3 pathway

Increasing investigations indicate that neurotransmitters shape immune cell function; however, current results about glycine (Gly) in inflammatory macrophage responses are conflicting. Here, we found that Gly transporters support interleukin-1β (IL-1β) production in inflammatory macrophages, while Gly receptors inhibit it. Inflammatory macrophages have higher expression of Gly transporter 1 (GlyT1; also known as SLC6A9). Notably, SLC6A9 inhibition leads to extracellular accumulation of Gly and limits IL-1β production in inflammatory macrophages. Mechanically, extracellular Gly suppresses phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT1)/mammalian target of rapamycin (mTOR) signaling through the Gly receptor alpha-4 (Glrα4), thereby inhibiting activation of the NOD-like receptor 3 (NLRP3) inflammasome and IL-1β production. Furthermore, Gly supplementation or myeloid-specific SLC6A9 depletion alleviates the lipopolysaccharide (LPS)-induced inflammatory response in vivo. Collectively, our findings reveal a previously uncharacterized mechanism for the Gly-ergic system in regulating inflammatory macrophage function, providing a potential alleviating target for macrophage-associated diseases.