What is the project about?
Immunometabolic dysfunction is implicated in depression and other psychiatric disorders, which may moderate the effect of antidepressant treatment. Existing case-control studies show changes in various blood immunometabolic biomarkers in depression, psychosis and other psychiatric disorders compared with controls, but longitudinal studies needed to assess temporality of association is scarce. Existing studies have almost exclusively used circulating blood biomarker levels as exposure which is informative, but does not reflect activity of the biomarker at cellular level accurately. Therefore, there is a need for developing novel measures reflecting biomarker activity/signalling more accurately to better understand the role of inflammation in psychiatric conditions.

My project will address these key issues using: i) longitudinal analysis testing the relationship of blood immunometabolic and related biomarkers with depression and other psychiatric outcomes; ii) develop and implement novel measures of activity/signalling of specific biomarkers (namely, interleukin 6 or IL-6, renin-angiotensin system or RAS) in analyses testing their associations with blood biomarkers and psychiatric outcomes.

Why is the project important?
Depression is a global public health concern, with recent research suggesting that it affects around 1 in 6 people in the UK. About 1 in 3 people with depression do not respond to currently available medications suggesting other mechanisms are involved. Demonstrating prospective associations of blood immunometabolic biomarkers with depression will strengthen causal inference and identify specific biomarkers for future investigation. Demonstrating how the activity of specific depression related biomarkers (e.g., IL-6 signalling) relates to depression risk will highlight specific pathways for intervention.

What do we know already?
While it is known that abnormal functioning of neurotransmitters such as serotonin are associated with depression, there is emerging evidence to suggest that inflammation may play a key role in its development. Studies have shown that individuals with major depressive disorder (MDD) have increased levels of interleukin 6 (IL-6) in the blood than healthy controls. Mendelian randomisation studies suggest a potential causal effect of IL-6 on depression and schizophrenia. However, which particular IL-6 signalling pathway underlies these associations remain unclear.