The metabolism of the HIV-infected CD4+ T cell

Viruses are not considered life-forms because they lack one defining feature that all other organisms share: metabolism. Being in essence a mobile genetic element, a virus is entirely dependent on the metabolism provided by the host it infects for replication. It is well known that viral infections alter the properties of living cells in order to replicate, often leading to disease. While interactions of viruses with their hosts are well studied at the macro-molecular and cellular level, the demand on small molecule building blocks and energy resources, the metabolites, has seldom been investigated. These demands are potentially conflicting with regard to virus replication and cell survival. Pioneering work on herpes viruses has revealed preferences for the use of certain metabolites during infections, which can be exploited for the development of antiviral drugs by denying the virus a supply of its preferred metabolites. This request for support from the MRC proposes to apply this strategy to HIV-1. HIV-1 infections continue to pose a global health threat and in the absence of a cure or vaccine, patients require antiviral treatment for their entire lives. Current treatments rely heavily on the use of modified building blocks of DNA, which target the viral protein that executes the replication of its genome. This treatment is associated with considerable side effects and can eventually fail owing to the development of resistance by the virus, requiring a switch of medication. Therefore, the development of new and improved agents that target HIV is an ongoing effort. In recent years there has been a great interest in targeting the host components that the virus usurps for its replication, as these are less likely to allow the emergence of viral resistance. We propose to investigate the complex dynamics of metabolites in the HIV infected cell to determine the viral metabolic demand. Our preliminary investigations indicate that we can detect depletion of certain metabolites, notably the amino acids that are the building blocks for proteins, in cells infected with HIV-1. Furthermore, we have observed that HIV alters the activity of mitochondria, which are the metabolic factories of the cell. The funds requested to elaborate on these findings will be targeted towards three main aims, being: i) To provide a comprehensive description of the levels and rate of usage of metabolites in the HIV infected cell, ii) to determine the means by which the virus influences the cellular metabolism and iii) to investigate the feasibility of interfering with metabolic processes on which the virus depends as antiviral drug targets.

Both treated and untreated HIV-infections are frequently associated with metabolic complications and recent studies are increasingly implicating metabolic factors as predictive for progression to AIDS. However, little is known about the bioenergetic and biosynthetic demands imposed on host cells by HIV-1. As HIV-1 is entirely dependent on the host metabolism, this represents a novel and unexplored target with potential for the development of antiretrovirals. Here, we propose to investigate the metabolism of HIV-infected CD4+ T cells that are the primary target for its replication. In the first instance, differences in the metabolism compared with uninfected cells will be investigated by parallel metabolic and transcriptional profiling using chromatography coupled mass spectrometry, respirometry and microarray technologies. This is expected to reveal viral dependency on specific metabolites and metabolic pathways. Preliminary date included in the proposal support this projection. Following the hypothesis that HIV-1 directly modulates the metabolic state of the cell, an unbiased mutational analysis of all viral proteins will seek to reveal its mode of control. Jointly, these studies will inform experiments that will aim to inhibit HIV-1 replication by interfering with the host-cell metabolism using RNA interference and small molecule inhibitors. Ulitmately, these studies aim to identify targets for the development of antiretrovirals.

Metabolic processes have been commonly been associated with cancer and neurodegenerative diseases, among others, leading to the development of drugs that target the metabolism for these indications. Investigating the metabolism of the HIV-1 infected cell could reveal similarities between apparently disparate diseases at a metabolic level and may provide clues as to the application of existing treatments to the management of HIV-1. Ultimately, it is hoped that the investigations into metabolic inhibitors particular will translate to a tangible health benefit to the victims of HIV/AIDS. Thus, the proposed work clearly has the potential to impact on the life sciences community in its widest sense, the pharmaceutical industry and the clinical practices associated with the treatment of HIV. Thus, the non-academic beneficiaries of this work would be the clinicians that treat HIV-positive individuals, pharmaceutical companies and the HIV patients. In the first instance, clinicians could benefit from an understanding of viral perturbance metabolic processes as to inform adequate treatment of the metabolic syndrome in HIV patients. The research has the potential to highlight instances where the current treatment of HIV-associated metabolic syndrome may be incompatible with the aim to limit virus replication. This would represent a health benefit to those patients. However, it is expected that such applicable insights would be gained towards the end of the grant period, and will take considerably longer to be developed into clinical practice. Pharmaceutical companies stand to gain from this work by the expected outcome of demonstrating that therapeutic interference with the host metabolism can inhibit HIV-1 replication. This would open up a new class of targets for the development of antiviral drugs. Furthermore, it is conceivable that the work may demonstrate efficacy against HIV of existing drugs that were developed for other indications. Again, this would represent a health-benefit to the patients. Obviously, the time scales for trial and approval of such potential treatments are well beyond the funding period.