Proteomics Analysis in Japanese Medaka Oryzias latipes Exposed to Humic Acid Revealed Suppression of Innate Immunity and Coagulation Proteins

SIMPLE SUMMARY: Humic acids are one of the main components of the natural organic matter in surface waters that give them brown color. These compounds are known to have positive effects on aquatic animals such as increased growth and stress resistance. At the same time, there is experimental evidence that humic acids, being natural xenobiotics, act as follows: they cause stress responses at the molecular level. Our aim was to study humic acid-related effects on fish by performing the proteomic analysis of the blood plasma from Japanese medaka exposed to humic acid in concentrations that can be found in natural waters. Results of the study showed that most of the plasma proteins in the exposed fish had a lower abundance compared to that of the intact fish; humic acid caused a reduction in circulating levels of complement components, coagulation factors, and their regulators. ABSTRACT: Humic acids (HA), one of the major components of dissolved organic matter, can interfere with different metabolic pathways in aquatic animals, causing various biological effects. This study aimed to provide a molecular basis for HA-related responses in fish by analyzing changes in the blood plasma proteome following short-term exposure to environmentally relevant HA concentrations using the Japanese medaka Oryzias latipes Hd-rR strain as a model organism. Proteomics data were obtained by high-performance liquid chromatography with tandem mass spectrometry analysis employing a label-free quantification approach. HA caused dysregulation of proteins involved in various biological processes, including protein folding, signaling, transport, metabolism, regulation, immune response, and coagulation. The majority of the differentially abundant proteins were down-regulated, including those involved in humoral immunity and coagulation. HA caused the decrease of the complement cascade and membrane attack complex proteins abundance, as well as proteins participating in activation and regulation of secondary hemostasis. The most pronounced suppression was observed at the highest tested HA concentration.