Immunometabolic involvement of hepcidin genes in iron homeostasis, storage, and regulation in gilthead seabream (Sparus aurata)

Abstract

Iron is essential for all living things, especially marine organisms, due to its low availability in the marine environment. Iron regulation is key in all vertebrates and is controlled by hepcidin–ferroportin. To improve the knowledge of iron homeostasis in fish, an iron overload was induced in gilthead seabream (Sparus aurata), which was chosen as a study species because of its high interest in Mediterranean aquaculture. The amount of iron in different tissues was measured to determine its biodistribution and/or bioaccumulation. Since the liver is directly involved in iron metabolism, the morphological changes induced in this organ as a consequence of the iron increase were studied. The bactericidal activity of fish skin mucus was also determined, observing that it decreased in fish with high iron levels compared to control fish. In addition, to better understand iron regulation, the gene expression of hepcidin, ferroportin, transferrin, and ferritin was evaluated in the head kidney (the main hematopoietic organ in this species) and in the liver. Special interest was taken in the study of the multiple copies of the hamp2 gene present in the gilthead seabream genome. Bioinformatic analysis of the protein sequences derived from these hepcidin genes allowed us to determine the presence of one type I hepcidin and 12 type II hepcidins, all of them with antimicrobial potential. This number of mature hepcidin sequences found in gilthead seabream is the highest within Eupercaria described to date. All the results obtained indicate that the modulation of iron in seabream seems to be much more complicated than in other vertebrates, probably due to the possible involvement of the different hepcidins as mediators between iron metabolism and host immune response.

Participation of Hepcidins in the Inflammatory Response Triggered by λ-Carrageenin in Gilthead Seabream (Sparus aurata)

“…However, as homeostatic mechanism seemed to be initiated in in vivo assays at 12 and 24 h after carrageenin injection in seabream, we focused on earlier sampling times (1.5, 3, and 6 h p.i.) (Campos-Sánchez et al 2021a , b , c , d , 2022a , b ). Therefore, different and consistent expression patterns of hepcidins were found in HK (particularly in leucocytes), liver, and skin during the inflammatory response caused by intramuscular injection of λ-carrageenin.…”

“…Following the iron overload, caused by infection or inflammation, hepcidin is induced to posttranslationally inhibit iron-exporting ferroportin, resulting in its internalization and degradation (Nemeth and Ganz 2006 ). This fact leads to a decrease in iron release to plasma from hepatocytes, macrophages, and enterocytes (Nemeth and Ganz 2006 ; Serna-Duque et al 2022a ). As a result, circulating iron is limited, being unavailable for bacterial growth.…”