Blockage of citrate export prevents TCA cycle fragmentation via Irg1 inactivation

The metabolism of activated macrophages relies on aerobic glycolysis, while mitochondrial oxidation is disrupted. In lipopolysaccharide-activated macrophages, the citrate carrier (CIC) exports citrate from mitochondria to enhance glycolytic genes through histone acetylation. CIC inhibition or Slc25a1 knockdown reduces the occupancy of H3K9ac to hypoxia-inducible factor-1a (HIF-1a) binding sites in promoters of glycolytic genes to restrain glycolysis. HIF-1a also transcriptionally upregulates immune-responsive gene 1 for itaconate production, which is inhibited by CIC blocking. Isotopic tracing of [U -13C6] glucose shows that CIC blockage prevents citrate accumulation and itaconate production by reducing glycolytic flux and facilitating metabolic flux in the TCA cycle. Isotopic tracing of [U -13C5] glutamine reveals that CIC inhibition reduces succinate accumulation from glutaminolysis and the gamma-aminobutyric acid shunt by enhancing mitochondrial oxidation. By restraining glycolysis, CIC inhibition increases NAD+ content to ensure mitochondrial biogenesis for oxidative phosphorylation. Furthermore, blockage of citrate export reduces cerebral thrombosis by inactivation of peripheral macrophages.

Automated summary

The metabolism of activated macrophages relies on aerobic glycolysis, and the export of citrate enhances glycolytic gene expression. Blocking the export of citrate inhibits glycolysis and reduces succinate accumulation, while increasing NAD+ content and mitochondrial biogenesis.