Taxifolin Modulates Transcriptomic Response to Heat Stress in Rainbow Trout, Oncorhynchus mykiss

SIMPLE SUMMARY: Cultivated rainbow trout face with multiple stressors that impact their viability, growth, and welfare. Heat stress provoked by summer temperature rise leads to increased mortality and accelerated transmission of bacterial and parasite pathogens in fish population. Feed supplements of plant-origin could alleviate stress in fish presumably via stimulation of their defense systems. To understand the mechanism of beneficial effects of taxifolin, an antioxidant extracted from larix wood, we compared transcriptomic responses to both temperature rise and flatworm infection in rainbow trout individuals fed either a standard ration or supplemented with taxifolin. Dietary taxifolin has been shown to mitigate some heat-induced responses in fish, such as biosynthesis of sterols, heat-shock proteins, and cell death regulators, while it does not interfere with temperature-dependent antioxidant induction. Interestingly, no transcriptomic response was induced due to Gyrodactylus infestation in trout, whereas parasite load was diminished due to heat treatment. Thus, the plant-origin supplementation of fish diet could be an easy way to improve the health of fish and promote their ability to tolerate stresses under intensive production. ABSTRACT: Taxifolin is a natural flavonoid known for its antioxidant, anti-inflammatory, and antiproliferative effects on animals. In this work, we have studied the effect of this compound on rainbow trout, Oncorhynchus mykiss, a major object of aquaculture, under slowly increasing ambient temperature and Gyrodactylus flatworm infection. Transcriptomic profiling of liver samples performed by using the Illumina HiSeq 2500 sequencing platform shows that a combined taxifolin/heat treatment, unlike heat treatment alone, downregulates the production of isopentenyl diphosphate, likely affecting the production of cholesterol and other sterols. Taxifolin treatment also modulates multiple apoptosis regulators and affects the expression of HSPs in response to increasing temperature. On the other hand, the expression of antioxidant enzymes in response to heat is not significantly affected by taxifolin. As for the Gyrodactylus infection, the parasite load is not affected by taxifolin treatment, although it was lower in the high-temperature group. Parasite load also did not induce a statistically significant transcriptomic response within the no heat/no taxifolin group.