Hypoxia Sensing and Persistence Genes Are Expressed during the Intragranulomatous Survival of Mycobacterium tuberculosis

Abstract

Although it is accepted that the environment within the granuloma profoundly affects Mycobacterium tuberculosis (Mtb) and infection outcome, our ability to understand Mtb gene expression in these niches has been limited. We determined intragranulomatous gene expression in human-like lung lesions derived from nonhuman primates with both active tuberculosis (ATB) and latent TB infection (LTBI). We employed a non-laser-based approach to microdissect individual lung lesions and interrogate the global transcriptome of Mtb within granulomas. Mtb genes expressed in classical granulomas with central, caseous necrosis, as well as within the caseum itself, were identified and compared with other Mtb lesions in animals with ATB (n = 7) or LTBI (n = 7). Results were validated using both an oligonucleotide approach and RT-PCR on macaque samples and by using human TB samples. We detected approximately 2,900 and 1,850 statistically significant genes in ATB and LTBI lesions, respectively (linear models for microarray analysis, Bonferroni corrected, P < 0.05). Of these genes, the expression of approximately 1,300 (ATB) and 900 (LTBI) was positively induced. We identified the induction of key regulons and compared our results to genes previously determined to be required for Mtb growth. Our results indicate pathways that Mtb uses to ensure its survival in a highly stressful environment in vivo. A large number of genes is commonly expressed in granulomas with ATB and LTBI. In addition, the enhanced expression of the dormancy survival regulon was a key feature of lesions in animals with LTBI, stressing its importance in the persistence of Mtb during the chronic phase of infection.

Lysine acetylation of DosR regulates the hypoxia response of Mycobacterium tuberculosis

“…Adaptations to hypoxia have been implicated to play a prominent role in the dormancy of Mtb 4 . Accumulating evidence has demonstrated that oxygen tension correlates tightly with Mtb growth, the formation of hard, fibrous, hypoxic granulomas, and, eventually, the development of infection 5 . Wayne et al 6 , 7 have pioneered the development of culture conditions that gradually deprive bacteria of oxygen to generate nonreplicating persistent bacilli in vitro as a model for latency.…”

Small Animal Model of Post-chemotherapy Tuberculosis Relapse in the Setting of HIV Co-infection

“…These paradigms are generally well-supported by observations in NHP models of TB latency and latent TB reactivation due to immune suppression such as following TNF blockade therapy or SIV infection (Diedrich et al, 2010;Mehra et al, 2011;Foreman et al, 2016). In NHPs that have developed LTBI, necropsy reveals well-organized lesions persisting in the lung despite the absence of detectable bacilli (Hudock et al, 2017). In an elegant study of latent TB reactivation in the NHP due to TNF-α blockade, fluorescence labeling of metabolic hotspots along with PET CT imaging of granulomas demonstrated activity in previously affected areas of the lung (Lin et al, 2016).…”

Host-pathogen redox dynamics modulate Mycobacterium tuberculosis pathogenesis

“…The relationship between hypoxia and the expression of the dormancy regulon was further validated in the second study from this group, which found that the dormancy regulon was induced in Mtb in association with lesion hypoxia and latency in infected NHPs (Hudock et al. 2017 ). It is interesting to note that the most hypoxic lesions also contained central necrosis and the subsequent accumulation of a lipid-rich caseum within the granuloma.…”

“…( 2015 ) and Hudock et al. ( 2017 ) established the Dos system as an essential part of Mtb virulence in vivo and that the expression of genes within the Dos dormancy regulon is associated with local hypoxia. A link between induction of the dormancy regulon and dormant Mtb , however, has yet to be conclusively established in vivo .…”