Human Cytomegalovirus pUL37x1 is Important to Remodeling of Host Lipid Metabolism [Virus-Cell Interactions]

Human cytomegalovirus (HCMV) replication requires host metabolism. Infection alters the activity in multiple metabolic pathways, including increasing fatty acid elongation and lipid synthesis. The virus-host interactions regulating the metabolic changes associated with replication are essential to infection. While multiple host factors, including kinases and transcription factors, important to metabolic changes that occur following HCMV infection have been identified, little is known about the viral factors required to alter metabolism. In this study, we tested the hypothesis that pUL37x1 is important to the metabolic remodeling that is necessary for HCMV replication using a combination of metabolomics, lipidomics, and metabolic tracers to measure fatty acid elongation. We observed that fibroblast cells infected with wild-type (WT) HCMV had similar levels of metabolites as those infected with a mutant virus lacking the UL37x1 gene, subUL37x1. However, we found that relative to WT-infected cells subUL37x1-infected cells had reduced levels of two host proteins that were previously demonstrated to be important for lipid metabolism during HCMV infection—fatty acid elongase 7 (ELOVL7) and ER-stress related kinase PERK. Moreover, we observed that HCMV infection results in an increase in phospholipids with very long-chain fatty acid tails (PL-VLCFAs) that contain 26 or more carbons in one of their two tails. The levels of many PL-VLCFAs were lower in subUL37x1-infected cells compared to WT-infected cells. Overall, we conclude that although pUL37x1 is not necessary for network-wide metabolic changes associated with HCMV-infection, it is important to the remodeling of a subset of metabolic changes that occur during infection.

Importance

Human cytomegalovirus (HCMV) is a common pathogen that asymptomatically infects most people and establishes a lifelong infection. However, HCMV can cause end-organ disease that results in death in the immunosuppressed and is a leading cause of birth defects. HCMV infection depends on host metabolism, including lipid metabolism. However, the viral mechanisms for remodeling metabolism are poorly understood. In this study, we demonstrate that the viral UL37x1 protein (pUL37x1) is important for infection-associated increases in lipid metabolism, including fatty acid elongation to produce very long-chain fatty acids (VLCFAs). Further, we found that HCMV infection results in a significant increase in phospholipids, particularly those with VLCFA tails (PL-VLCFAs). We found that pUL37x1 was important for the high levels of fatty acid elongation and PL-VLCFAs accumulation that occurs in HCMV-infected cells. Our findings identify a viral protein that is important for changes to lipid metabolism that occurs following HCMV infection.

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