How does polyunsaturated fatty acid biosynthesis regulate T lymphocyte function?

Lead Research Organisation: University of Southampton
Department Name: Human Development and Health


Polyunsaturated fatty acids (PUFA), also known as Omega-3 and Omega-6 fats, are important for the normal function of immune cells. When immune cells are activated by viruses or bacteria, they use PUFA to make chemical signals that control the immune response. However, older individuals are less able to fight infection or respond to vaccines, and are more likely develop inflammatory disease than their younger counterparts. The processes responsible for this decline in immune function are not understood fully. Therefore, it is important to understand how immune cells obtain PUFA to make the chemical signals that control the immune response and how this is affected by increasing age.

Immune cells can obtain PUFA from blood. However, a small number of studies have suggested immune cells may be able to make PUFA from essential fatty acids (EFAs) that are derived from plants and have to be consumed in the diet. We have recently published the findings of a project funded by the BBSRC that investigated the ability of human immune cells to make PUFA from EFAs. We found that the biochemical processes that convert EPAs to PUFA are switched on when immune cells are simulated in culture, a process that mimics the immune response. Our results showed that this involves changes in the control of a group of genes that contain the information to make the enzymes that convert EFAs to PUFA. This change in gene activity involved adaptation of a major gene control process; DNA methylation. We also found that blocking an enzyme involved in PUFA synthesis stopped immune cells proliferating, a critical early stage in the immune response. These results are important because they show for the first time that PUFA synthesis regulates the immune response.

The aim of this project is to investigate the processes that link the activation of PUFA synthesis in immune cells to their ability to multiply. We will study T cells, a type of immune cell with a wide range of functions, from two groups of healthy human volunteers. First, we will use T cells from men and women aged 18 to 30 years to carry out detailed characterisation of PUFA synthesis by decreasing, in turn, the activity of each of the genes involved. We will relate this to the ability of T cells to become activated and to proliferate over the time course of the immune response. We will investigate whether PUFA from the environment of the T cells or their ability to convert EPAs to PUFA is the most important source of PUFA for making for chemical signals that regulate the immune response. Two possible processes that could link PUFA synthesis to T cell proliferation will be investigated. Activated T cells form structures on their surface that facilitate the action of chemical signs that drive the immune response. These microdomains contain a specific type of PUFA; very long chain PUFA (VLCPUFA) that control their formation which are derived from PUFA of the type synthesised by activated T cells. We will test whether EFAs are converted to VLCPUFA in activated T cells and, if so, how this is controlled. We will investigate whether PUFA synthesised from EFAs are used to synthesise chemical signals that drive the immune response. We will also determine how DNA methylation controls the activation of genes involved in PUFA synthesis. Finally, T cells from a second group of older men and women (aged 65 to 75 years) will be studied to determine whether the processes that link PUFA synthesis to T cell activation change with increasing age.

This area of research is very new, but it has potential to substantially change understanding of the way in which immune cells become activated to mount an immune response. Potential benefits of this knowledge are that it may allow the development of new ways to support optimal immune function, for example through nutrition, and to understand how the effectiveness of the immune response differs between individuals and with increasing age.

Technical Summary

Polyunsaturated fatty acids (PUFA) play a critical role in immune function by modulating membrane fluidity and as substrates for lipid mediator synthesis. We have shown recently that activation of human peripheral blood mononuclear cells induces PUFA synthesis from essential fatty acids (EFA) via a novel pathway that regulates lymphocyte proliferation. Activation of PUFA synthesis also induced increased transcription of genes involved this pathway which involves altered DNA methylation. This project will investigate how PUFA synthesis regulates T cell proliferation and the effect of age on this process.
The project is comprised of integrated experiments using T cells from healthy men and women aged 18 to 30 years and 65 to 75 years (n = 15/age/sex).
1. We will use siRNA knockdown and stable isotope-labelled EFA to detail the role of specific metabolic reactions in T cell proliferation and their relationship to the time course of T cell activation. We will determine the roles of sex, and exogenous and newly synthesised PUFA in T cell activation and how the novel initial reactions affect regulation of PUFA synthesis by EFA.
2. These methods will also be used to determine whether newly synthesised PUFA are used preferentially for very long chain PUFA (>C24) synthesis and microdomain assembly, and for lipid mediator synthesis.
3. We will use pyrosequencing, transcription factor binding assays and cloning techniques to determine how altered DNA methylation regulates transcription of genes involved in PUFA synthesis during T cell activation.
4. Comparison of findings from these experiments between T cells from young and older subjects will be used to understand the role of PUFA synthesis in ageing-related immune decline.
This project will provide important information about a novel mechanism in the immune response that will have important implications for the dietary supplement and pharmaceutical industries, clinicians, immunologists, nutritionists and biochemists

Planned Impact

The primary objective of the proposed project is to generate data that can be translated to develop novel strategies which facilitate improved immunological health across the life course. This project will benefit stakeholders in the commercial and public sectors.
1. UK Government and the Healthcare Sector: The UK Government and the BBSRC recognise that immunological dysfunction related to ageing is a major barrier to maintaining the health and wellbeing of a population characterised by an increased number of older individuals. This represents a growing economic burden in the face of a limited financial resource. Consequently, identification of novel mechanisms that regulate immune cell function that are potential targets for strategies to support immune health, particularly through the diet, are likely to be of considerable benefit both in terms of sustained immune health and lower economic burden. Thus, the findings of this project are likely to be of marked interest to government organisations such as Public Health England and the NHS.
2. The Pharmaceutical Industry: Non-steroidal anti-inflammatory drugs are currently the primary treatment of chronic inflammatory disease. These medicines can produce significant side effects, particularly in older individuals, and hence there is an unmet need for novel anti-inflammatory therapeutics. Moreover, there is a lack of medicines that ameliorate ageing-related immune decline. This project will identify specific processes that mediate the role of PUFA synthesis in T cell activation which are potential targets for the development of novel anti-inflammatory therapeutic agents and of medicines to ameliorate ageing-related immune decline. Furthermore, drugs that inhibit PUFA synthesis may represent a novel means to reduce risk of tissue graft rejection.
3. The Nutraceutical, Dietary Supplement and Food Industries: These commercial organisations will benefit from findings that demonstrate targets for nutritional interventions, and for the formulation of novel functional foods and ingredients to enhance or ameliorate the immune response, particularly in preventing age-related immune decline.
4. Biotechnology/Biomarkers Industry: This project will develop our published findings which show the activation of PUFA synthesis involves changes in the epigenetic regulation of at least one key gene. Epigenetic biomarkers that predict treatment outcomes are being introduced into clinical practice, and new and established companies, such as Pfizer, have established precision medicine discovery programmes around epigenetic treatments outside cancer. Therefore, the findings of this project will generate commercial opportunities around the role of DNA methylation in regulating the immune response via PUFA synthesis.
5. Veterinary Medicines and Animal Nutrition Industries: Ageing domestic animals and larger species such as horses exhibit similar immune decline and inflammatory diseases to humans. Thus, the findings of this project will generate similar opportunities for companies producing veterinary therapeutics as those that produce medicines for humans. Functional foods for domestic animals are becoming increasingly popular and so the findings of this project are likely to be of marked interest to the animal food industry.
6. The UK economy. The findings of this project are likely to generate opportunities for several sectors of UK industry through identification and protection intellectual property arising from development of the findings of the project and the development of new products with associated benefits to the UK economy. Translation of the findings in terms of promoting health is also likely to reduce the burden of age-related immunological declne on the UK economy.
Description The project has been heavily negatively affected by the covid-19 pandemic because it relied on collecting white blood cells from healthy volunteers, including those in the most vulnerable age range, and consequently has not progressed at the anticipated rate. Nevertheless, all the objectives described in the application were achieved. The key findings are: (1) Essential fatty acid metabolism in T lymphocytes is distinct from that described in the liver and from other white blood cells. In particular, the primary products are members of a group of little-understood anti-inflammatory signalling molecules hydroxyoctadecatrienoic acids (HOTrEs) and pro-inflammatory hydroyoctadecadienoic acids (HODEs), instead of longer-chain polyunsaturated fatty acids (PUFA). The PUFA synthesis pathway appears to be adapted to facilitate HODE and HOTrE synthesis. (2) The production of both HODEs and HOTrEs is independent of cell activation which suggests involvement in immune homeostasis. However, relative HODE and HOTrE synthesis can be modified by the ratio of the psrent n-3 and n-6 essential fatty acids in the culture medium, which has implications for understanding how dietary fats influence immune function. (3) WE found that anti-inflammatory HOTrE synthesis declines across the life course which is consistent with an increased tendency towards an inflammatory phenotype in older individuals. We have identified an enzyme (elongase-5) that may regulate the metabolic branch point between HODE and HOTrE production and longer-chain PUFA synthesis. (4) We have also found that upregulation of mRNA expression of genes , including FADS2, that encode key enzymes involved in PUFA biosynthesis precedes the appearance of markers of T cell activation which suggests that this process may be involved in the early stages of Tcell activation. Our most recent findings extended this observation by showing that pharmacological inhibition of the enzyme encoded by the FADS2 gene or siRNA reduced T lymphocyte proliferation by more than 60%. This suggests the protein product of FADS2 is required for activation-induced T cell Proliferation. Further funding will be needed to determine the underlying mechanism.
Exploitation Route The constitutive production of hydroxyoctadecaenoic acids (HODEs and HOTREs) is a novel observation that when the precise function of this process has been identified could form the basis for developing new novel pharmaceuticals that modify T cell function. The effect of the ratio of n-3 and n-6 essential fatty acids in determining their partitioning between HODE and HOTrE biosynthesis is likely to be relevant to understanding the impact of dietary fats on immune function, and hence of interest nutritionists and food manufacturers.
Sectors Healthcare,Pharmaceuticals and Medical Biotechnology