Significance of genotypes and resistance status of Mycobacterium tuberculosis strains in gene expression of apoptosis cell death and inflammatory pathways in A549 lung epithelial cell line.

Objectives: Tuberculosis (TB) has been a major health issue throughout history. As part of TB infection, host-Mycobacterium tuberculosis (Mtb) interactions are important. Through immune pathology and cell death control processes, Mtb infection facilitates intracellular growth. The relationship between apoptosis and inflammation in Mtb infection remains unclear. In this study, the levels of related apoptosis and inflammatory genes were assessed in A549 cells infected with a variety of Mtb strains.

Materials and methods: Mtb isolates with different phenotypes (sensitive, INH^R, Rif^R, MDR, and XDR) were collected from the Pasteur Institute of Iran, during this study. Whole genome sequencing was previously performed on all strains, and the Beijing genotype was selected as sensitive. Also, for other resistant strains, the New-1 genotype was available and isolated for genotype comparison. A549 lung carcinoma cells were also grown and infected with selected Mtb strains. Genes involved in inflammation and apoptosis were detected using reverse transcription-PCR (RT-PCR).

Results: All sensitive strains and resistant strains were found to significantly up-regulate anti-apoptotic (bcl2 and rb1), chemokine (IL-8 and MCP-1), and pro-inflammatory cytokine (TNF-α and IFN-γ) expression, while significant down-regulation was observed after 24 and 48 hr of infection in anti-inflammatory genes (IL-10) and pro-apoptotic genes (bad and bax). Besides resistance strains, Mtb genotypes also affected gene expression. The Beijing genotype (sensitive isolate) influences inflammatory and apoptotic genes more sharply than the New-1 genotype (INH^R, Rif^R, MDR, and XDR).

Conclusion: Gene expression differences related to apoptosis and inflammation examined in the current study may be attributed to genotypes rather than resistance status since the expression of most genes has been observed to be lower in resistant strains (INH^R, Rif^R, MDR, and XDR belonging to the New-1 genotype) compared to sensitive strains (Beijing genotype).