Differential expression of genes associated with lipid import, β-oxidation and lactate oxidation induced by Mycobacterium tuberculosis curli pili in broth culture compared to intracellular bacilli within THP-1 macrophages

<b>Introduction.</b> The adhesin, <i>Mycobacterium tuberculosis</i> curli pili (MTP), assists the pathogen in attachment, invasion and disease progression. Previously, this adhesin was demonstrated to contribute to the pathogen's cell wall functions and fatty acid metabolism and affects total metabolite abundance in central carbon metabolism and fatty acid metabolism of the host. The accumulation/depletion of metabolites is reliant on the gene expression of proteins involved in the import, transport and breakdown of substrates.<b>Gap statement.</b> MTP has not been investigated in relation to genes involved in import/transport/breakdown of substrates.<b>Aim.</b> This study aimed to investigate the possible regulatory role of MTP in modulating metabolic changes of the pathogen in different microenvironments.<b>Methods.</b> Ribonucleic acid was harvested from bacterial broth cultures of adhesin-proficient and adhesin-deficient <i>M. tuberculosis</i>. These strains were also used to infect differentiated THP-1 macrophages for 4 h prior to isolation of intracellular bacteria, RNA extraction and reverse transcription real-time quantitative PCR. The expression levels of selected genes involved in fatty acid transport (<i>lucA</i>, <i>mce1D</i>, <i>mceG</i>, <i>Rv2799</i>, <i>Rv0966c</i> and <i>omamB</i>), β-oxidation (<i>fadA5</i> and <i>fadB</i>), lactate oxidation (<i>lldD1</i> and <i>lldD2</i>) and gluconeogenic carbon flow (<i>pckA</i>) were analysed by absolute quantification.<b>Results.</b> The gene expression levels of <i>lucA</i>, <i>mce1D</i> and <i>pckA</i> were significantly lower, and those of <i>Rv2799</i>, <i>Rv0966c</i>, <i>mceG</i>, <i>fadA5</i> and <i>lldD2</i> were significantly higher in the adhesin-proficient cultured bacterial strains relative to the Δ<i>mtp</i> strain. The intracellular adhesin-proficient bacteria displayed significantly higher gene expression levels of <i>Rv2799</i> and significantly lower gene expression levels of <i>Rv0966c</i>, <i>fadA5</i>, <i>lldD1</i> and <i>pckA</i> relative to the Δ<i>mtp</i> strain. Interestingly, during early infection, the intracellular Δ<i>mtp</i> displayed significantly increased expression of <i>omamB</i>, <i>mceG</i>, <i>fadB</i>, <i>lldD1</i> and <i>lldD2</i> relative to the broth culture. This trend was inverted in the WT models.<b>Conclusion.</b> MTP are significantly associated with the regulation of genes involved in lipid transport, β-oxidation and lactate oxidation.