Research in our laboratory focuses on host-pathogen interactions. In particular, we study the pathogenesis of Chlamydia trachomatis, which is the most frequently reported bacterial sexually transmitted disease, and the leading cause of infectious blindness worldwide. Chlamydia is particularly difficult to study, partly due to its intracellular lifestyle. While non-intracellular bacteria can be naturally destroyed by the immune system, intracellular bacteria hide inside human cells to escape immune defenses. To achieve this, Chlamydia manipulates host cells to create an intracellular niche, the so-called inclusion, in which it can multiply. Chlamydia constitutes an outstanding model to study host-pathogen interaction as it manipulates a large number of cellular pathways to support its intracellular development. Among these pathways, Chlamydia drastically reorganizes the cytoskeleton to provide scaffolds for its inclusion. Additionally, Chlamydia co-opts cellular vesicular trafficking to acquire lipids and nutrients. Finally, this bacterium is particularly attractive to study as it also induces novel membrane fusion events using bacterial proteins.
Our laboratory uses a multidisciplinary approach to understand mechanisms at the molecular level. We combine crystallographic analysis with a variety of sophisticated biochemical and cellular functional assays to understand how chlamydial proteins interfere with their host partners. Additionally, we have now the resources to mutagenize Chlamydia to create knock-outs, knock-ins, and mutants. Ultimately this strategy will open new avenues of research for other intracellular bacteria including Salmonella and Mycobacterium, which also manipulate their host cells to their advantage.
Determine how Chlamydia manipulates the host cytoskeleton during infection
Actin and microtubules are important cytoskeletal elements in eukaryotic cells. The cytoskeleton controls many cellular processes such as cell division and motility, as well as vesicle and organelle trafficking. Inside of its host cell, the human pathogen Chlamydia trachomatis rearranges the cytoskeleton to promote its survival and enhance its pathogenicity. In particular, Chlamydia induces the rearrangement of both actin and microtubules, which is vital for its entry, inclusion structure and development, and host cell exit. In this context, our laboratory seeks to understand the molecular machinery used by Chlamydia trachomatis to co-opt the host cytoskeleton and coordinate the reorganization of actin and microtubules. Furthermore, we study the impact of such reorganization on Chlamydia development and pathogenesis.
Identify the role of the host SNARE proteins during Chlamydia infection
SNAREs are ubiquitously expressed proteins, conserved from yeast to humans, that mediate intracellular membrane fusion events. In fact, they constitute the core machinery necessary to mediate specific membrane fusion. As such, they are key regulators of all intracellular vesicle trafficking events and cargo transport steps. Therefore, manipulation of individual SNARE proteins or SNARE complexes may help Chlamydia to subvert normal trafficking patterns, while the specific recruitment of host SNAREs to the chlamydial inclusion would afford the pathogen the ability to manipulate vesicular trafficking during infection. In this project, we seek to analyze the contribution of various SNARE proteins to Chlamydia infection, notably we are creating a library of CRIPR/Cas9 knockout cell lines for specific SNAREs, which will then be screened during Chlamydia infection.
Identify how Chlamydia escapes the cell degradative pathway: involvement of bacterial SNARE-like proteins
In vertebrates, innate immune cells such as macrophages engulf bacteria in phagosomes. Phagosomes, in turn, fuse with lysosomes to destroy the bacteria. While most bacteria are destroyed during the process, Chlamydia survives and replicates within these cells by blocking fusion between their inclusions and lysosomes. Some strategies that Chlamydia uses to block phagosomal maturation include modifying the lipid composition of the inclusion and interfering with small GTPases involved in vesicular trafficking. Another efficient way to block phagosomal maturation would be to interfere with the host membrane fusion machinery, the so-called SNARE proteins. Interestingly, Chlamydia uses SNARE-like proteins to mimic the host SNAREs and interfere with membrane fusion. This particular project seeks to further characterize this inhibitory system and understand the specificity of the chlamydial SNARE-like proteins during infection.
Characterize the machinery that controls homotypic fusion of the inclusion
As an obligate intracellular bacterium, Chlamydia trachomatis replicates in an intracellular inclusion. When several bacteria infect a cell, they each develop in their own inclusion, which undergo homotypic fusion ~10-12 hours post-infection. This homotypic fusion event is critical for C. trachomatis pathogenicity as natural non-fusing Chlamydia mutants have replication defects, grow slower than their wild-type counterparts, and cause significantly milder symptoms in human. Recent work in our laboratory has characterized the inclusion membrane protein IncA, which is essential for membrane fusion. IncA shares significant sequence similarities with eukaryotic SNARE proteins. In this project, we seek to establish the 3D structure of IncA and establish whether it uses an α-helical structure to promote membrane fusion, similar to the eukaryotic SNARE fusion system. We also seek to identify the entire fusion machinery responsible for this unique bacterial event.