# 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

## TL;DR

This study shows how Mycobacterium tuberculosis curli pili influence gene expression related to lipid and lactate metabolism in different environments.

## Contribution

The study reveals the regulatory role of MTP in modulating metabolic gene expression in broth and intracellular settings.

## Key findings

- MTP increases expression of genes like Rv2799 and lldD2 in broth cultures.
- Intracellular MTP bacteria show altered expression of genes like Rv0966c and fadA5.
- Δmtp bacteria display increased expression of omamB and mceG during early infection.

## Abstract

Introduction. The adhesin, Mycobacterium tuberculosis 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.

Gap statement.MTP has not been investigated in relation to genes involved in import/transport/breakdown of substrates.

Aim. This study aimed to investigate the possible regulatory role of MTP in modulating metabolic changes of the pathogen in different microenvironments.

Methods. Ribonucleic acid was harvested from bacterial broth cultures of adhesin-proficient and adhesin-deficient M. tuberculosis. 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 (lucA, mce1D, mceG, Rv2799, Rv0966c and omamB), β-oxidation (fadA5 and fadB), lactate oxidation (lldD1 and lldD2) and gluconeogenic carbon flow (pckA) were analysed by absolute quantification.

Results. The gene expression levels of lucA, mce1D and pckA were significantly lower, and those of Rv2799, Rv0966c, mceG, fadA5 and lldD2 were significantly higher in the adhesin-proficient cultured bacterial strains relative to the Δmtp strain. The intracellular adhesin-proficient bacteria displayed significantly higher gene expression levels of Rv2799 and significantly lower gene expression levels of Rv0966c, fadA5, lldD1 and pckA relative to the Δmtp strain. Interestingly, during early infection, the intracellular Δmtp displayed significantly increased expression of omamB, mceG, fadB, lldD1 and lldD2 relative to the broth culture. This trend was inverted in the WT models.

Conclusion.MTP are significantly associated with the regulation of genes involved in lipid transport, β-oxidation and lactate oxidation.