Selenium is a vital trace element present as selenocysteine (Sec) in proteins that are, thus, known as selenoproteins. Humans have 25 selenoproteins, most of which are functionally characterized as oxidoreductases, where the Sec residue plays a catalytic role in redox regulation and antioxidant activity. Glutathione peroxidase plays a pivotal role in scavenging and inactivating hydrogen and lipid peroxides, whereas thioredoxin reductase reduces oxidized thioredoxins as well as non-disulfide substrates, such as lipid hydroperoxides and hydrogen peroxide. Selenoprotein R protects the cell against oxidative damage by reducing methionine-R-sulfoxide back to methionine. Selenoprotein O regulates redox homeostasis with catalytic activity of protein AMPylation. Moreover, endoplasmic reticulum (ER) membrane selenoproteins (SelI, K, N, S, and Sel15) are involved in ER membrane stress regulation. Selenoproteins containing the CXXU motif (SelH, M, T, V, and W) are putative oxidoreductases that participate in various cellular processes depending on redox regulation. Herein, we review the recent studies on the role of selenoproteins in redox regulation and their physiological functions in humans, as well as their role in various diseases.

Immune activation associates with the intracellular generation of reactive oxygen species (ROS). To elicit effective immune responses, ROS levels must be balanced. Emerging evidence shows that ROS-mediated signal transduction can be regulated by selenoproteins such as methionine sulfoxide reductase B1 (MsrB1). However, how the selenoprotein shapes immunity remains poorly understood. Here, we demonstrated that MsrB1 plays a crucial role in the ability of dendritic cells (DCs) to provide the antigen presentation and costimulation that are needed for cluster of differentiation antigen four (CD4) T-cell priming in mice. We found that MsrB1 regulated signal transducer and activator of transcription-6 (STAT6) phosphorylation in DCs. Moreover, both in vitro and in vivo, MsrB1 potentiated the lipopolysaccharide (LPS)-induced Interleukin-12 (IL-12) production by DCs and drove T-helper 1 (Th1) differentiation after immunization. We propose that MsrB1 activates the STAT6 pathway in DCs, thereby inducing the DC maturation and IL-12 production that promotes Th1 differentiation. Additionally, we showed that MsrB1 promoted follicular helper T-cell (Tfh) differentiation when mice were immunized with sheep red blood cells. This study unveils as yet unappreciated roles of the MsrB1 selenoprotein in the innate control of adaptive immunity. Targeting MsrB1 may have therapeutic potential in terms of controlling immune reactions.

Wheat leaf rust caused by Puccinia triticina is a destructive fungal disease causing considerable grain yield loss. In this study, we developed a novel assay to test the rust resistance of detached wheat leaves on defined media with retarded senescence. We observed that salicylic and jasmonic acid confer leaf rust resistance to a susceptible Keumkang wheat (Triticum aestivium L.). Transcription analysis revealed that atchi8 was highly expressed with an increased chitinase activity in the salicylic acid-treated leaves, while expression of PR-9, atpodL, and PR-5 increased in the jasmonic acid-treated leaves. Additionally, the metabolic profile suggested that the phenylalanine pathway might link flavonoid production to leaf rust resistance in the salicylic acid-treated leaves, while the alanine, aspartate, and glutamate metabolism might control the production of other amino acids to enhance pathogen stress response in the jasmonic acid-treated leaves. Finally, all identified genes and metabolites could be potential targets for screening chemical compounds for leaf rust resistance. Future studies on the underlying mechanisms of leaf rust resistance obtained by exogenous treatment of salicylic and jasmonic acids remain necessary.