Myo-inositol-mediated Efferocytosis Promotes Lysosomal Function and ROS Clearance Related to the Pentose Phosphate Pathway in Fish Muscle

Skeletal muscle constitutes the main consumable part of fish, and its quality and physiological integrity are critical to the sustainable advancement of aquaculture. This investigation focused on the consequences of dietary myo-inositol (MI) deficiency on muscle homeostasis in grass carp (Ctenopharyngodon idella) using six experimental diets with varying amounts of MI: 35 (basal diet, deficient group), 98, 195, 292, 389, and 487 mg/kg. Fish were fed for 8 weeks. Transcriptome analysis of grass carp muscle tissue was first performed, revealing that efferocytosis and the pentose phosphate pathway (PPP) were among the primary metabolic pathways affected by MI intervention. Further investigation demonstrated that MI administration within the range of 195-487 mg/kg effectively activated the PPP, as indicated by significantly increased activities of two key enzymes in its oxidative branch-glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). This enzymatic activation led to enhanced NADPH production. The consequent rise in NADPH levels resulted in decreased intracellular ratios of NADP+/NADPH and GSH/GSSG, reflecting a strengthened reductive cellular environment and thereby improving the capacity to scavenge reactive oxygen species (ROS). Furthermore, MI reduces cell death in muscle tissue and enhance macrophage-mediated efferocytosis. Concurrently, MI inhibits the polarization of macrophages towards pro-inflammatory phenotypes by enhancing lysosomal function. Therefore, the inclusion of appropriate levels of MI (195-389 mg/kg) in the diet is beneficial for maintaining muscle tissue homeostasis in grass carp.