Divergent miRNA-mRNA networks contribute to tissue-specific lipid homeostasis in triploid rainbow trout skeletal muscle during high-lipid diet challenge.

Rainbow trout (Oncorhynchus mykiss) is one of the most widely farmed salmonid species globally. To investigate the mechanisms regulating muscle fat content and enhancing tolerance to high-lipid diets, transcriptomic changes in muscle tissues (myotomes and myosepta) were analyzed after treatment with an elevated dietary lipid level (30 %). The results revealed that myotomes and myosepta employed distinct strategies to maintain lipid homeostasis under elevated dietary lipids. Myotomes suppressed lipid deposition by upregulating lipoic acid synthesis to enhance lipolysis and reducing lipoprotein sialylation, while myosepta inhibited lipid storage through AMP metabolism modulation in adipocytes and the decreased function of phosphatidylinositol-4-phosphate (PI4P) binding. Beyond these tissue-specific strategies, both myotomes and myosepta also adopted some common approaches against lipid surplus. The downregulation of GFRAL4 balanced energy acquisition, and MBLH2-mediated lipolysis prevented ectopic deposition. Crucially, miRNAs coordinated tissue-specific and systemic adaptations to dietary lipid fluctuations mainly by targeting key genes involved in lipid metabolism pathways. Overall, these findings identified potential protein targets and regulatory pathways for regulating myoseptal fat content to improve meat flavor attributes, and elucidated the metabolic adaptation mechanisms of triploid rainbow trout to high-lipid diets.