Recruitment of host factors and organelles to the Chlamydia trachomatis inclusion

Chlamydia trachomatis is the leading cause of non-congenital blindness and the causative agent of the most common sexually transmitted infection of bacterial origin. Upon entering a host cell, C. trachomatis resides within a membrane bound vacuole, the inclusion. Inclusion membrane proteins (Incs) are embedded within the inclusion membrane and possess cytosolic tails that can mediate interactions between the inclusion with host molecules and organelles. These interactions include the formation of membrane contact sites (MCS) between the inclusion and the host cell endoplasmic reticulum (ER), referred to as ER-Inclusion MCS. These contact sites are proposed to play an important role in C. trachomatis development through the non-vesicular trafficking of host cell lipids to the inclusion.
Overall, my thesis work has focused on how the C. trachomatis inclusion interacts with the host cell environment to establish and maintain a replicative niche. I first sought to better understand the formation and function of ER-inclusion MCS during C. trachomatis infection by determining their molecular composition. I used a proximity labeling approach to isolate and identify bacterial and host cell components of ER-inclusion MCS and identified six host glycolytic enzymes (Chapter 2). I demonstrated that host glycolytic enzymes, while not specific to ER-inclusion MCS, localize to the inclusion membrane. Additionally, I showed that the host glycolytic enzyme Aldolase A plays a role in C. trachomatis intracellular development (Chapter 3). These findings indicate that, in addition to interactions with host organelles, C. trachomatis relies on host cell metabolism for proper intracellular development.
Our lab had previously shown that the interaction of the C. trachomatis Inc protein IncV with the ER-resident protein VAP acts as a tether to support the formation/maintenance of ER-inclusion MCS. I next sough to identify cellular determinants that promote the assembly of this bacterial tether. In chapter 4, we demonstrated that the host kinase CK2 is recruited to the inclusion and that multiple layers of host cell kinase-mediated phosphorylation events govern the assembly of the IncV-VAP tethering complex and the formation of ER-inclusion MCS.
Finally, in chapter 5, I discuss how my findings shed light on the interplay between host and bacterial metabolism during C. trachomatis pathogenesis and provide insights into the general biology of MCS. Overall, my work could contribute to the identification of novel therapeutic targets and combat the blindness and infertility that can arise from chlamydial infections.