Evidence of the Autophagic Process during the Fish Immune Response of Skeletal Muscle Cells against Piscirickettsia salmonis

Autophagy is a fundamental cellular process implicated in the health of the cell, acting as a cytoplasmatic quality control machinery by self-eating unfunctional organelles and protein aggregates. In mammals, autophagy can participate in the clearance of intracellular pathogens from the cell, and the activity of the toll-like receptors mediates its activation. However, in fish, the modulation of autophagy by these receptors in the muscle is unknown. This study describes and characterizes autophagic modulation during the immune response of fish muscle cells after a challenge with intracellular pathogen Piscirickettsia salmonis. For this, primary cultures of muscle cells were challenged with P. salmonis, and the expressions of immune markers il-1β, tnfα, il-8, hepcidin, tlr3, tlr9, mhc-I and mhc-II were analyzed through RT-qPCR. The expressions of several genes involved in autophagy (becn1, atg9, atg5, atg12, lc3, gabarap and atg4) were also evaluated with RT-qPCR to understand the autophagic modulation during an immune response. In addition, LC3-II protein content was measured via Western blot. The challenge of trout muscle cells with P. salmonis triggered a concomitant immune response to the activation of the autophagic process, suggesting a close relationship between these two processes.