Investigating the Mechanism and Function of Peroxisome Remodeling During HCMV Infection

Abstract

Upon infection, viruses orchestrate extensive changes in organelle shape, abundance, and function to reprogram the cellular landscape into a pro-viral state. One virus that induces remarkable remodeling of all major organelles is human cytomegalovirus (HCMV), which causes significant morbidity and mortality in infants and immunocompromised individuals. As an organelle that plays diverse roles in metabolic and immune signaling pathways, peroxisomes undergo various alterations during HCMV infection. Notably, two polarized populations of peroxisomes are observed during late stages of infection: one that exhibits irregular, enlarged morphology as well as increased association with the ER and one that is significantly smaller in size. Concomitantly, plasmalogen synthesis, a process that involves collaboration between peroxisomes and the ER and is required for the formation of viral envelopes, is enhanced. While peroxisome enlargement is thought to promote plasmalogen synthesis due to the shared dependence of both processes on ER-contact, the mechanisms and functions of peroxisome remodeling during HCMV infection otherwise remain largely unclear. Additionally, the role of peroxisome contact sites with other organelles during infection has thus far been underexplored. Here, we combine super-resolution microscopy and genetic perturbations with proteomic and lipidomic approaches to investigate the contribution of ER-Peroxisome contact, mediated by the tethering proteins ACBD5 and VAPB, to peroxisome enlargement and its functional consequence for virus replication. We find that increasing ACBD5-VAPB-mediated ER-Peroxisome contacts is sufficient to induce peroxisome enlargement, however, it adversely impacts viral titers and viral gene expression as well as alters the infection-induced increase in plasmalogen synthesis, contrary to previous hypotheses. Additionally, we identify and characterize a new contact site between peroxisomes and virion-containing MVB-like structures that appear during late stages of infection and provide evidence that peroxisome-mitochondria contacts may also be altered by HCMV. Lastly, we examine the potential involvement of peroxisome enlargement in mediating dynamics of the virus microenvironment, demonstrating that modulating peroxisome size can impact antiviral immune signaling. Our findings provide insight into the mechanisms and consequences of alterations to peroxisome size, function, and membrane contact sites during infection and have implications for expanding understanding of infection-induced organelle remodeling and peroxisome biology more broadly.