Ghrelin modulates differential expression of genes relevant to immune pathways and antimicrobial peptides in primary head kidney cells of rainbow trout (Oncorhynchus mykiss)

Authors: HAN, YUEH-CHIAN - Oak Ridge Institute For Science And Education (ORISE); LEAMAN, DOUGLAS - Auburn University; Shepherd, Brian

Submitted to: Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2023
Publication Date: 5/18/2023
Citation: Han, Y., Leaman, D.W., Shepherd, B.S. 2023. Ghrelin modulates differential expression of genes relevant to immune activities and antimicrobial peptides in primary head kidney cells of rainbow trout (Oncorhynchus mykiss). Animals. 13(10). https://doi.org/10.3390/ani13101683.
DOI: https://doi.org/10.3390/ani13101683

Interpretive Summary: We examined the effects of the multifunctional hormone, ghrelin, on the immune response of rainbow trout. Rainbow trout produce two unique forms of ghrelin, one that is acylated (rt-Ghrl) and another that is truncated (desVRQ-ghrl), with poorly characterized immune actions. We adapted and validated an in vitro model comprised of primary cells isolated from rainbow trout head kidney including lymphocytes and macrophages. We treated the cells with either form of trout ghrelin over a 24 h time-course and measured gene expression of messenger ribonucleic acids (mRNAs) using real-time quantitative polymerase chain reaction. We observed that ghrelin treatment generally exerted an elevating trend, whereas desVRQ-ghrelin exerted a decreasing effect on genes relevant to the immune processes of phagocytosis, pro-inflammation, chemotaxis, leukocyte adhesion, antigen presenting process, and antimicrobial peptides (AMPs). The actions of the ghrelin analogs were different on various immune processes, suggesting they may have divergent roles in fish immunity. These results show the differing immunomodulatory effects of ghrelin peptides in a commercially-important finfish. This information will provide a better understanding of how this hormone/cytokine influences the rainbow trout immune system, to potentially improve disease resistance in salmonid aquaculture.

Technical Abstract: Ghrelin is a peptide hormone/cytokine that is well known to regulate metabolic processes including food intake, appetite, growth and energy balance, but it also plays an essential role in immune system. To evaluate the immunomodulatory actions of ghrelin isoforms in rainbow trout, an in vitro model was utilized with primary cells isolated from rainbow trout head kidney. Under cell culture condition, differentiated myeloid and lymphoid cells were treated with synthetic acylated rainbow trout ghrelin and its truncated isoform desVRQ-ghrelin over a time-course (0, 2, 4 and 24 h) at a dose of 500 nM. The differential expression patterns of genes relevant to various immune processes including phagocytosis, inflammation, chemotaxis, leukocyte adhesion, antigen presenting process, and interferon-JAK/STAT signaling were measured by real-time quantitative PCR. Treatment of primary cells, with these ghrelin analogs, resulted in functional perturbations that displayed overlapping and divergent actions. In addition, the expression pattern of five selected genes of antimicrobial peptides (AMPs) were profiled after treating with ghrelin isoforms, and the differential expression profiles suggest ghrelin modulates the production of various types of AMPs. The differing actions between the two ghrelin analogs, on various immune processes, and at differing time points, suggest the two analogs may have divergent roles in fish immunity. These results further confirm the immunomodulatory effects of ghrelin peptides and provide a better understanding of this hormone/cytokine in fish immune system.