Analysis of Iron and Iron-Interacting Protein Dynamics During T-Cell Activation

Abstract

Recent findings have shown that iron is a powerful regulator of immune responses, which is of broad importance because iron deficiency is highly prevalent worldwide. However, the underlying reasons of why iron is needed by lymphocytes remain unclear. Using a combination of mathematical modelling, bioinformatic analysis and experimental work, we studied how iron influences T-cells. We identified iron-interacting proteins in CD4+ and CD8+ T-cell proteomes that were differentially expressed during activation, suggesting that pathways enriched with such proteins, including histone demethylation, may be impaired by iron deficiency. Consistent with this, iron-starved Th17 cells showed elevated expression of the repressive histone mark H3K27me3 and displayed reduced RORγt and IL-17a, highlighting a previously unappreciated role for iron in T-cell differentiation. Quantitatively, we estimated T-cell iron content and calculated that T-cell iron demand rapidly and substantially increases after activation. We modelled that these increased requirements will not be met during clinically defined iron deficiency, indicating that normalizing serum iron may benefit adaptive immunity. Conversely, modelling predicted that excess serum iron would not enhance CD8+ T-cell responses, which we confirmed by immunising inducible hepcidin knock-out mice that have very high serum iron concentrations. Therefore, iron deficiency impairs multiple aspects of T-cell responses, while iron overload likely has milder effects.

Iron Regulatory Protein (Irp)-Mediated Iron Homeostasis Is Critical for Neutrophil Development and Differentiation in the Bone Marrow

“…This may reflect the fact that the flow of multipotent progenitors to the lymphoid lineage is low compared to the erythro-myeloid lineage, as shown by in vivo fate mapping (Höfer et al, 2016). This does not imply, however, that iron is not important for lymphoid compartment expansion at later stages of differentiation and, indeed, iron availability has been shown to be critical during lymphocyte activation (Frost et al, 2021, Teh et al, 2021. Both RBCs and platelets are derived from MEPs.…”

Plasma iron controls neutrophil production and function

“…Hemoglobin proteins (HBA1, HBB, HBD, HBG1, HBG2, HBM, HBQ1, and HBZ) were removed as these proteins should not be expressed in immune cells and their presence is likely indicative of red cell contamination. Protein copy number values for each iron interacting protein species was multiplied against the protein:iron atom stoichiometry values previously curated in Teh et al (Teh et al, 2021) to give the number of iron atoms per protein species. Total cellular iron counts were calculated as the sum of iron atoms attributed across all detected iron interacting protein species.…”

“…Protein copy number values for each iron interacting protein species was multiplied against the protein:iron atom stoichiometry values previously curated in Teh et al (Teh et al, 2021) to give the number of iron atoms per protein species. Total cellular iron counts were calculated as the sum of iron atoms attributed across all detected iron interacting protein species.…”

“…Iron counts per cell were calculated using the method described in Teh et al (Teh et al, 2021). Human iron interacting proteins were identified in human immune cell proteomes (Derived from (Rieckmann et al, 2017)) by cross-referencing against the list of human iron interacting proteins identified by Andreini et al (Andreini et al, 2018)).…”

“…Iron is required for cellular biochemistry, supporting processes such as oxidative metabolism, DNA synthesis and epigenetic remodelling (Andreini et al, 2018; Teh et al, 2021). Sequestration of iron from plasma, termed hypoferremia, commonly occurs during the acute phase of infection, driven by inflammatory induction of the iron regulatory hormone, hepcidin (Drakesmith and Prentice, 2012).…”