# Novel TRIM Proteins Modulating the Innate Immune Response of Rainbow Trout (Oncorhynchus mykiss)

## TL;DR

This study identifies OmTRIM25 as a novel TRIM protein in rainbow trout that modulates the innate immune response by promoting inflammation.

## Contribution

The study characterizes OmTRIM25 as a new immunomodulatory TRIM protein in rainbow trout gill cells.

## Key findings

- OmTRIM25 promotes the expression of pro-inflammatory cytokines TNF-α2 and IL-1β in vitro.
- OmTRIM25 and finTRIM2 are up-regulated in gills of rainbow trout after bacterial infection.
- RNAi confirmed the immunomodulatory role of OmTRIM25 in trout gill cells.

## Abstract

This study investigates the role of Tripartite Motif (TRIM) proteins at in vitro and in vivo levels in gills from rainbow trout (Oncorhynchus mykiss). In mammals, TRIM proteins are known for coordinating immune processes like antiviral defence, autophagy and inflammasome activation. However, TRIM function is still under investigation in fish. Contributing to the knowledge of these proteins, our data showed that OmTRIM25 (identified as a novel TRIM protein) had an immunomodulatory role by promoting the expression of key pro-inflammatory cytokines (i.e., TNF-α2 and IL-1β) linked to the innate immune response after challenges.

In higher vertebrates, Tripartite Motif (TRIM) proteins modulate the immune response by coordinating processes related to inflammation such as antiviral restriction, autophagy and inflammasome activation. In fish, TRIM proteins have been reported mainly in cyprinids (e.g., carp—Cyprinus carpio and zebrafish—Danio rerio) and salmonids (i.e., rainbow trout—Oncorhynchus mykiss). However, their molecular mechanisms and functions are still being described in aquatic animals. Thus, our study focused on characterizing novel TRIM proteins involved in the innate immunity of gill cells from rainbow trout (RTgill-W1 and primary cultures) stimulated with lipopolysaccharide (LPS) or polyinosinic–polycytidylic acid (poly I:C). Furthermore, an in vivo experiment with rainbow trout was performed to detect TRIM proteins after the challenge with Flavobacterium psychrophilum (a major bacterial pathogen affecting Chilean salmonid industry). In vitro results showed that OmTRIM25 triggered an LPS-induced expression of pro-inflammatory cytokines such as TNF-α2 and IL-1β. Moreover, in the fish experiment, OmTRIM25 and finTRIM2 were up-regulated in the gills two days post-infection (dpi), whereas IL-1β and TNF-α2 had a higher gene expression at four and six dpi, respectively. To investigate the immunological role of OmTRIM25, a gene silencing strategy using RNA interference (RNAi) was used, confirming the immunomodulatory function of OmTRIM25.