Hypercapnia alters mitochondrial gene expression and acylcarnitine production in monocytes.

CO 2 is produced during aerobic respiration. Normally, levels of CO 2 in the blood are tightly regulated but pCO 2 can rise (hypercapnia, pCO 2 > 45 mmHg) in patients with lung diseases e.g. Chronic Obstructive Pulmonary Disease (COPD). Hypercapnia is a risk factor in COPD but may be of benefit in the context of destructive inflammation. The effects of CO 2 per se, on transcription, independent of pH change are poorly understood and warrant further investigation. Here we elucidate the influence of hypercapnia on monocytes and macrophages through integration of state-of-the-art RNA-sequencing, metabolic and metabolomic approaches. THP-1 monocytes and IL4 polarised primary murine macrophages were exposed to 5% CO 2 Vs 10% CO 2 for up to 24 h in pH- buffered conditions. In hypercapnia, we identified ~370 differentially expressed genes (DEGs) under basal and ~1889 DEGs under LPS-stimulated conditions in monocytes. Transcripts relating to both mitochondrial and nuclear-encoded gene expression were enhanced in hypercapnia in basal and LPS-stimulated cells. Mitochondrial DNA content was not enhanced, but acylcarnitine species and genes associated with fatty acid metabolism were increased in hypercapnia. Primary macrophages exposed to hypercapnia also increased activation of genes associated with fatty acid metabolism and reduced activation of genes associated with glycolysis. Thus, hypercapnia elicits metabolic shifts in lipid metabolism in monocytes and macrophages under pH buffered conditions. These data indicate that CO 2 is an important modulator of monocyte transcription that can influence immunometabolic signalling in immune cells in hypercapnia. These immunometabolic insights may be of benefit in the treatment of patients experiencing hypercapnia.