STUDYING THE EFFECT OF HUMAN ADENOVIRUS 5 AND 36 ON HOST CELL METABOLISM

Abstract

In 1998, the World Health Organization defined five risk factors for Metabolic Syndrome (MS), including obesity, high serum triglyceride levels, low serum high-density lipoprotein (HDL) cholesterol levels, hypertension, and increased fasting blood glucose levels. MS contributes tremendously to diabetes, stroke, cardiovascular disease, infertility, cancer, liver disease, and cerebrovascular disease. Aberrant central carbon and lipid/fatty acid metabolism underlies MS, and it has become evident that some viruses substantially alter metabolic homeostasis of their host cells, potentially deranging lipid metabolism and contributing to MS. However, the details of how viral infections alter the lipid metabolic network are poorly described. Recent studies showed that human cytomegalovirus (HCMV), a member of the a-herpes virus family, can up-regulate metabolic fluxes into glycolysis, pyrimidine and fatty acid biosynthesis. Our work will explore the potential link between adenovirus infection and MS. HAdV-5 has been shown to cause obesity in animal models and HAdV-36 has been associated with obesity in humans. In twins discordant for infection with HAdV-36, the infected twins were heavier and fatter than their cotwins. Thus, it is of great interest to study adenovirus infection as a link to changes in lipid and fatty acid metabolism.

There are currently 52 identified serotypes of human adenovirus, grouped into six categories (A through F). HAdV-5 is a group C virus and was first isolated and cultured from adenoid tissue in 1953. Adenoviruses are common causative agents of upper respiratory illnesses, while they are associated with more serious clinical syndromes in the gastrointestinal tract. It is a non-enveloped virus with an icosahedral structure and a fiber at each vertex. A double-stranded DNA of about 36 kilobases in size resides inside the capsid. HAdV-5 has been widely applied to human gene therapy as a vector for gene transfer, mainly because it can easily infect different human cells and can be produced in large quantities.

Following the precedent established by the comprehensive earlier metabolomic studies on HCMV, the potential role of adenovirus in metabolic diseases can be investigated and novel therapeutic targets in patients with clinical adenovirus infection can be tested. Although it is generally acknowledged that virion membrane construction results in the perturbation of lipid metabolism, the complete picture behind the changes has not been explained. Because there's no structural lipid component of the adenovirus virion, it doesn't require making new or modifying existing membrane to assemble the virus. This study seeks to better understand a potential role for adenovirus in infectious MS and discover novel therapeutic targets for the virus.

The first aim of this thesis work was to characterize the metabolic alterations in core metabolism during infection with HAdV-5. A comprehensive metabolomic map was derived by measuring the relative and absolute pool sizes of intracellular metabolites. The dynamics of locally altered pathways, e.g. glycolysis, TCA cycle, and pentose phosphate pathway, was quantified by isotopic labeling and fluxomic analysis. These metabolic pathways were significantly altered during infection. Especially, glycolysis was reprogrammed as a result of NAD+ depletion.

The second aim was to focus on the adenovirus-altered lipid metabolism, in two models, HAdV-5 and HAdV-36. Comparative metabolic profiling, followed by high-resolution lipidomic analysis was implemented to characterize the changes in metabolism during both viral infections. Cellular metabolic enzymes involved in the lipid biosynthesis pathway were also probed to shed lights on the mechanistic side. The infected cell's lipidome was markedly changed, caused at least in part by the virus driving cell cycle progression.