Trancriptional Profile of Mycobacterium tuberculosis Replicating at in Artificial Intraocular Fluid

Intraocular tuberculosis (IOTB) is a significant cause of visual morbidity in TB-endemic countries. However, pathogenesis of Mycobacterium tuberculosis (M. tb) in the ocular compartment is poorly defined. IOTB is paucibacillary in a vast majority of patients although M. tb has been detected in both the retinal pigment epithelial (RPE) cells (Rao et al. 2006) and in the intraocular fluid (IOF) (Aggarwal et al., 2016; Bajgai et al., 2017) in some cases. In this study, we have examined the replication and whole genome transcriptome of M. tb in an IOF model (artificial IOF; AIOF) (Macri et al., 2015). Results show that, as reported for transcriptional profiles of M. tb in sputum (Sharma et al., 2017) and in a starvation model (PBS) (Betts et al., 2002), genes involved in active replication and aerobic respiration are either downregulated or not differentially expressed in the AIOF. In ARPE-19 cells (human RPE cell line), M. tb replicates poorly and exhibits a quiescent phenotype (Abhishek et al., 2018). As in sputum, PBS, and ARPE-19 cells, M. tb in AIOF downregulates genes of the DosR regulon indicating the suppression of dormancy. Importantly, genes encoding ESAT-6 and ESAT-6-like proteins are also downregulated or not differentially expressed in sputum, AIOF and ARPE-19 cells. This is stark contrast to the transcriptome of M. tb in alveolar epithelial cells (Ryndak et al., 2015) and in blood (Ryndak et al. 2014). These results paint a scenario wherein M. tb acquires a replicative and invasive phenotype when it infects a new host and disseminates systemically. However, M. tb acquires a quiescent phenotype upon reaching its final niche in an extrapulmonary site, the ocular environment. The global gene expression of M. tb H37Rv replicating in artificial intraocular fluid at Day 6 was compared to that of M. tb grown to log phase in Middlebrook 7H9 media.