Gamma-aminobutyric acid type A receptor alpha 4 coordinates autophagy, inflammation, and immunometabolism to promote innate immune activation.

Abstract

Gamma-aminobutyric acid type A receptor (GABA_AR), the ionotropic receptor of GABA, is expressed in macrophages and in the nervous system; however, its role in innate immunity is unknown. Herein, we identified myeloid GABA_AR subunit α4 (Gabra4) as a critical regulator of autophagy and a promoter of host innate defense during infection and inflammation. Myeloid Gabra4 deficiency led to defective mycobacterial clearance during infection and increased susceptibility to septic shock. Gabra4 deletion exaggerated inflammatory responses and suppressed the activation of autophagy in macrophages upon infectious and inflammatory stimuli. Mechanistically, Gabra4-mediated signaling led to upregulation of autophagy in macrophages via intracellular calcium release and AMP-activated protein kinase (AMPK) signaling activation, which was required for linking autophagy and antimicrobial responses. Additionally, Gabra4 was required to generate mitochondrial reactive oxygen species, thereby triggering autophagy and antimicrobial responses to mycobacteria. Metabolomics analysis showed that Gabra4 was critical for glucose metabolism and aerobic glycolysis in macrophages. Our findings demonstrate that myeloid Gabra4 coordinates autophagy, inflammation, and immunometabolism to promote innate host defense against pathogenic and dangerous stimuli. Abbreviation AM: Alveolar macrophage; AMPK: AMP-activated protein kinase; ASC: Apoptosis-associated speck-like protein containing a CARD; ATP: Adenosine 5'-triphosphate; BAL: Bronchoalveolar lavage; BCG: Mycobacterium bovis Bacillus Calmette-Guérin; BMDM: Bone marrow-derived macrophage; CCL: CC motif chemokine ligand; CFU: Colony forming unit; CKO: Conditional knock out; CXCL: C-X-C motif ligand; Dpi: Days post-infection; ECAR: Extracellular acidification rate; EGFP: Enhanced green fluorescent protein; FOXO3: Forkhead box O3; GABA: Gamma-aminobutyric acid; GABA_AR: GABA type A receptor; Gabarap: GABA type A receptor-associated protein; Gabarapl1: GABA type A receptor-associated protein like 1; GABRA4: Gamma-aminobutyric acid type A receptor subunit alpha4; HIF-1α: Hypoxia-inducible factor-1 alpha; IL: Interleukin; i.n.: Intranasal; i.p.: Intraperitoneal; LDHA: Lactate dehydrogenase A; LPS: Lipopolysaccharide; Mabc: Mycobacteroides abscessus subsp. abscessus; MOI: Multiplicities of infection; Mtb: Mycobacterium tuberculosis; mtROS: Mitochondrial reactive oxygen species; OCR: Oxygen consumption rate; OXPHOS: Oxidative phosphorylation; PM: Peritoneal macrophage; TNF: Tumor necrosis factor; WT: Wild type.