Expression patterns of alpha-2 macroglobulin reveal potential immune functions in brood pouch of the lined seahorse Hippocampus erectus

Seahorses (family Syngnathidae) are ovoviviparous fish whose embryos can obtain paternal immunoprotection through the male's brood pouch, which is a specialized organ for pregnancy. Previous studies have revealed that seahorses have a unique immune system and alpha-2 macroglobulin (alpha 2M) may be involved in male pregnancy. To ascertain the significance of alpha 2M in the immune system of the brood pouch, the characteristics of the alpha 2M gene were first investigated in the lined seahorse (Hippocampus erectus). In this study, alpha 2M showed a broad expression pattern, with the highest expression in the liver and brood pouch. Interestingly, during the six-month seahorse culture, expression level of alpha 2M in the liver was particularly decreased during brood pouch formation (fourth and fifth months), but was restored the complete development of this brood pouch (sixth months), and a similar expression occurred in the brood pouch. This suggests that the seahorse might be able to regulate its immune response while a new organ develops. Further investigation also examined the immune regulation of alpha 2M in brood pouches by injecting lipopolysaccharide and polyinosinic-polycytidylic acid. The results showed that, after the challenge experiment, alpha 2M expression in the inner pseudoplacenta was upregulated, along with other important immune factors, such as Toll-like receptors (TLRs), tumor necrosis factor-alpha (TNF alpha), interleukin-6 (IL-6) and interferon-gamma (IFN gamma). Taken together, our results reveal that alpha 2M plays an important role in immunoprotection of the brood pouch, and may provide new insights into studies of male pregnancy regulation in seahorses.

Automated summary

Seahorses, being ovoviviparous fish, have a unique immune system where alpha-2 macroglobulin (alpha 2M) plays a significant role in paternal immunoprotection during male pregnancy. The study revealed that alpha 2M gene in seahorses has a broad expression pattern, with the highest expression in the liver and brood pouch. After challenge experiments, alpha 2M expression in the inner pseudoplacenta of the brood pouch was upregulated along with important immune factors, indicating its crucial role in immunoprotection and immune response regulation during male pregnancy in seahorses.