Circadian iron metabolism, implications for health, and response to inflammatory disease.

Iron related disorders are a leading factor contributing to global diseases. According to the World Health Organisation (WHO) approximately 42% of children under the age of 6 years and 40% of pregnant women worldwide are anaemic, a condition in which the number of red blood cells and iron content within these cells are far lower than normal. Iron poor diets and infectious diseases, including malaria and tuberculosis, that are common in low to middle income countries, lead to anaemia. Changes to iron metabolism are also associated with common liver and metabolic diseases often observed in high income countries as well as being prominant in chronic inflammatory conditions such as arthritis.
From helping our cells produce energy to carrying oxygen within our blood, iron is essential for life on earth. However, the chemical properties that make iron so important for biological processes can also lead to toxicity and cell damage if levels of this nutrient are not strictly controlled. Complex living organisms, like humans and mice, have the ability to regulate iron levels through the production of hepcidin, a hormone produced within the liver that reduces both the uptake of dietary iron within the digestive system and the release of stored iron reserves within cells.
Hepcidin can also be stimulated by inflammatory signals produced by immune responses during an infectious disease, this is thought to occur to limit growth of invading micro-organisms as they also require iron to survive. Although the stimulation of hepcidin is beneficial in stopping a microbe infection it can enhance the severity of common diseases that are characterised by inflammation, such as arthritis, a common age-related illness. In these conditions hepcidin is stimulated by inflammatory signals causing reduced iron levels even though a pathogenic infection is not present. This often causes a long-term reduction in iron which can cause anaemia and other health problems.
Recently, our studies have shown that the production of hepcidin within the liver of mice changes dependent on time of day. This finding may explain why taking iron at different times of day affects its absorption. Moreover, in inflammation the rhythm of hepcidin changes, with a peak at a different time of the day.
We now have a good understanding of how cells can keep track of time. Interestingly, some proteins that are important in keeping a daily rhythm within cells can be controlled by iron and, in turn, control iron metabolism. This shows that iron and the circadian clock have an intimate relationship and it is likely that if one is changed during disease the other will also be affected. This study will determine to what extent this is true and would potentially open a new therapeutic avenue to treat iron imbalances by delivering treatments at specific times of the day. Mice are an excellent model to study this relationship as they regulate iron and keep time in a very similar manner to humans, and we will manipulate iron levels in mice to determine the effects this has on the circadian clock of the liver.
Disruption to either iron or the circadian clock often occurs during disease, and inflammation has been shown to alter both iron levels and circadian rhythms in living organisms. We will establish the effect of inflammation, a common characteristic of many diseases, with use of a mouse model of arthritis, a common inflammatory disease. This will help us determine how inflammation contributes to the disruption of iron regulation and the circadian clock and may identify potential drug targets specific to inflammatory conditions that may help ameliorate dual effects on circadian and iron pathways. This will have benefits for many inflammatory diseases, aside from arthritis, a number of common diseases that affect the liver, as well as obesity and metabolic disorders.

We recently discovered that the liver-derived hormone hepcidin, which controls iron absorption, and mobilisation, lies under strong circadian control. In inflammation it remains circadian, but with a phase shift resulting in an earlier peak. Indeed, this may explain why iron is absorbed from the diet more efficiently at specific times of day.
Iron metabolism in cells is closely linked to redox state, and an ancient function of the circadian clock is to regulate cellular redox state. Indeed, dietary iron manipulation results in changes in the circadian regulation of glucose metabolism in the liver. Heme abundance, and redox status may directly regulate the core clock factor REVERBa.
We now propose to investigate:-
1. How iron metabolism regulates the liver metabolic clock. Here, we will delete hepcidin from the liver, post-natally, and investigate the function of the liver circadian system, using primary cell culture, and whole animal recording. As hepcidin is produced by hepatocytes, and acts on myeloid cells we will use single cell RNA-Seq to determine the cell-type specific impacts of hepcidin loss. We will investigate the downstream consequences for glucose and lipid metabolism, using dynamic metabolic tests, and metabolomics screening.
2. How timing affects iron metabolism. Here we will make a new mouse which has hepcidin driven from a non-circadian promoter. In this way we can study iron metabolism by time of day in the presence of a circadian, and a non-circadian hepcidin driver. This will determine why hepcidin, and iron are so strongly circadian, and identify the role of chronotherapy for targeting disorders of iron metabolism.
3. How chronic inflammation regulates hepcidin and iron metabolism to drive liver function. Here we will use an inducible, liver-specific hepcidin knockout, and examine how chronic inflammatory arthritis impacts on liver circadian function. We will return to some of the analytical approaches developed above.