HtrA, fatty acids, and membrane protein interplay in Chlamydia trachomatis to impact stress response and trigger early cellular exit

UNLABELLED: Chlamydia trachomatis is an intracellular bacterial pathogen that undergoes a biphasic developmental cycle, consisting of intracellular reticulate bodies and extracellular infectious elementary bodies. A conserved bacterial protease, HtrA, was shown previously to be essential for Chlamydia during the reticulate body phase, using a novel inhibitor (JO146). In this study, isolates selected for the survival of JO146 treatment were found to have polymorphisms in the acyl-acyl carrier protein synthetase gene (aasC). AasC encodes the enzyme responsible for activating fatty acids from the host cell or synthesis to be incorporated into lipid bilayers. The isolates had distinct lipidomes with varied fatty acid compositions. A reduction in the lipid compositions that HtrA prefers to bind to was detected, yet HtrA and MOMP (a key outer membrane protein) were present at higher levels in the variants. Reduced progeny production and an earlier cellular exit were observed. Transcriptome analysis identified that multiple genes were downregulated in the variants especially stress and DNA processing factors. Here, we have shown that the fatty acid composition of chlamydial lipids, HtrA, and membrane proteins interplay and, when disrupted, impact chlamydial stress response that could trigger early cellular exit.IMPORTANCE: Chlamydia trachomatis is an important obligate intracellular pathogen that has a unique biphasic developmental cycle. HtrA is an essential stress or virulence protease in many bacteria, with many different functions. Previously, we demonstrated that HtrA is critical for Chlamydia using a novel inhibitor. In the present study, we characterized genetic variants of Chlamydia trachomatis with reduced susceptibility to the HtrA inhibitor. The variants were changed in membrane fatty acid composition, outer membrane proteins, and transcription of stress genes. Earlier and more synchronous cellular exit was observed. Combined, this links stress response to fatty acids, membrane proteins, and HtrA interplay with the outcome of disrupted timing of chlamydial cellular exit.</p

Determination of the effect of JO146, a CtHtrA inhibitor, on the chlamydial developmental cycle and persistence

The role of Chlamydia trachomatis HtrA (CtHtrA) for the growth and pathogenesis of this organism is presented. Inhibition of CtHtrA led to loss of infectious progeny in Chlamydia, particularly during heat stress or recovery from penicillin persistence. Isolation of CtHtrA inhibitor resistant mutants identified positive selection for mutants in fatty acid related pathways. Importantly, HtrA inhibition was effective against clinical isolates of C. trachomatis. Thus the findings combined indicate that CtHtrA is an important chlamydial growth factor that has the potential to be targeted for the development of anti-chlamydial drugs in the future

CtHtrA: the lynchpin of the chlamydial surface and a promising therapeutic target

Chlamydia trachomatis is the most prevalent sexually transmitted bacterial infection worldwide and the leading cause of preventable blindness. Reports have emerged of treatment failure, suggesting a need to develop new antibiotics to battle Chlamydia infection. One possible candidate for a new treatment is the protease inhibitor JO146, which is an effective anti-Chlamydia agent that targets the CtHtrA protein. CtHtrA is a lynchpin on the chlamydial cell surface due to its essential and multifunctional roles in the bacteria’s stress response, replicative phase of development, virulence and outer-membrane protein assembly. This review summarizes the current understanding of CtHtrA function and presents a mechanistic model that highlights CtHtrA as an effective target for anti-Chlamydia drug development

CtHtrA: The lynchpin of the chlamydial surface and a promising therapeutic target

Chlamydia trachomatis is the most prevalent sexually transmitted bacterial infection worldwide and the leading cause of preventable blindness. Reports have emerged of treatment failure, suggesting a need to develop new antibiotics to battle Chlamydia infection. One possible candidate for a new treatment is the protease inhibitor JO146, which is an effective anti-Chlamydia agent that targets the CtHtrA protein. CtHtrA is a lynchpin on the chlamydial cell surface due to its essential and multifunctional roles in the bacteria’s stress response, replicative phase of development, virulence and outer-membrane protein assembly. This review summarizes the current understanding of CtHtrA function and presents a mechanistic model that highlights CtHtrA as an effective target for anti-Chlamydia drug development

The protease inhibitor JO146 demonstrates a critical role for CtHtrA for Chlamydia trachomatis reversion from penicillin persistence

The Chlamydia trachomatis serine protease HtrA (CtHtrA) has recently been demonstrated to be essential during the replicative phase of the chlamydial developmental cycle. A chemical inhibition strategy (serine protease inhibitor JO146) was used to demonstrate this essential role and it was found that the chlamydial inclusions diminish in size and are lost from the cell after CtHtrA inhibition without formation of viable elementary bodies. The inhibitor (JO146) was used in this study to investigate the role of CtHtrA for penicillin persistence and heat stress model cultures for Chlamydia trachomatis. JO146 addition during penicillin persistence resulted in only minor reductions (~1 log) in the final viable infectious yield after persistent Chlamydia were reverted from persistence. However, JO146 treatment during the reversion and recovery from penicillin persistence was completely lethal for Chlamydia trachomatis. JO146 was completely lethal when added either during heat stress conditions, or during the recovery from heat stress conditions. These data together indicate that CtHtrA has essential roles during some stress environments (heat shock), recovery from stress environments (heat shock and penicillin persistence), as well as the previously characterised essential role during the replicative phase of the chlamydial developmental cycle. Thus, CtHtrA is an essential protease with both replicative phase and stress condition functions for Chlamydia trachomatis

Excitability changes that complement Hebbian learning

Experiments have shown that the intrinsic excitability of neurons is not constant, but varies with physiological stimulation and during various learning paradigms. We study a model of Hebbian synaptic plasticity which is supplemented with intrinsic excitability changes. The excitability changes transcend time delays and provide a memory trace. Periods of selective enhanced excitability can thus assist in forming associations between temporally separated events, such as occur in trace conditioning. We demonstrate that simple bidirectional networks with excitability changes can learn trace conditioning paradigms