Acetylation of human mitochondrial citrate carrier modulates mitochondrial citrate/malate exchange activity to sustain NADPH production during macrophage activation.

The mitochondrial citrate-malate exchanger (CIC), a known target of acetylation, is up-regulated in activated immune cells and plays a key role in the production of inflammatory mediators. However, the role of acetylation in CIC activity is elusive. We show that CIC is acetylated in activated primary human macrophages and U937 cells and the level of acetylation is higher in glucose-deprived compared to normal glucose medium. Acetylation enhances CIC transport activity, leading to a higher citrate efflux from mitochondria in exchange with malate. Cytosolic citrate levels do not increase upon activation of cells grown in deprived compared to normal glucose media, indicating that citrate, transported from mitochondria at higher rates from acetylated CIC, is consumed at higher rates. Malate levels in the cytosol are lower in activated cells grown in glucose-deprived compared to normal glucose medium, indicating that this TCA intermediate is rapidly recycled back into the cytosol where it is used by the malic enzyme. Additionally, in activated cells CIC inhibition increases the NADP+/NADPH ratio in glucose-deprived cells; this ratio is unchanged in glucose-rich grown cells due to the activity of the pentose phosphate pathway. Consistently, the NADPH-producing isocitrate dehydrogenase level is higher in activated glucose-deprived as compared to glucose rich cells. These results demonstrate that, in the absence of glucose, activated macrophages increase CIC acetylation to enhance citrate efflux from mitochondria not only to produce inflammatory mediators but also to meet the NADPH demand through the actions of isocitrate dehydrogenase and malic enzyme.

Palmieri EM ，Spera I ，Menga A ，Infantino V ，Porcelli V ，Iacobazzi V ，Pierri CL ，Hooper DC ，Palmieri F ，Castegna A ... -  《-》

The dicarboxylate carrier plays a role in mitochondrial malate transport and in the regulation of glucose-stimulated insulin secretion from rat pancreatic beta cells.

Huypens P ，Pillai R ，Sheinin T ，Schaefer S ，Huang M ，Odegaard ML ，Ronnebaum SM ，Wettig SD ，Joseph JW ... -  《-》

The mitochondrial citrate carrier: a new player in inflammation.

Infantino V ，Convertini P ，Cucci L ，Panaro MA ，Di Noia MA ，Calvello R ，Palmieri F ，Iacobazzi V ... -  《-》

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-1α (HIF-1α) binding sites in promoters of glycolytic genes to restrain glycolysis. HIF-1α 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.

Li Y ，Li YC ，Liu XT ，Zhang L ，Chen YH ，Zhao Q ，Gao W ，Liu B ，Yang H ，Li P ... -  《Cell Reports》

The mitochondrial citrate carrier: metabolic role and regulation of its activity and expression.

Gnoni GV ，Priore P ，Geelen MJ ，Siculella L ... -  《-》