Myo-inositol: A potential game-changer in preventing gill cell death and alleviating "gill rot" in grass carp (Ctenopharyngodon idellus)

Increasing evidence shows the potential threat of gill rot in freshwater fish culture. F. columnare is wide-spread in aquatic environments, which can cause fish gill rot and result in high mortality and losses of fish. This study investigated the effects of myo-inositol (MI) on the proliferation, structural integrity, and different death modes of grass carp (Ctenopharyngodon idella) gill epithelial cells, as well as its possible mechanism. 30 mg/L MI up-regulated CCK8 OD value and the protein level of solute carrier family 5A 3 (SLC5A3), and down-regulated the Reactive Oxygen Species (ROS) content in gill cells and Lactate Dehydrogenase (LDH) release in the culture medium (P < 0.05). MI up-regulated the protein level of Beclin1, the protein level and fluorescence expression of microtubule-associated protein light chain 3B (LC3B) and down-regulated the protein level of sequestosome-1 (SQSTM1, also called p62) (P < 0.05). MI down-regulated the protein levels of Cysteine aspartate protease-1 (Caspase-1), Gasdermin E (GSDME) and Cleaved interleukin 1 beta (IL-1β) (P < 0.05). MI up-regulated the protein level of Caspase-8 (P < 0.05), but had no effect on Apoptosis (P > 0.05). MI down-regulated the mRNA expressions and protein levels of tumor necrosis factor α (tnfα), TNF Receptor 1 (tnfr1), receptor interacting protein 1 (RIPK1), receptor interacting protein 3 (RIPK3) and Mixed Lineage Kinase domain-like protein (mlkl), and reduce the ratio of p-MLKL/MLKL (P < 0.05). The addition of MI or necrosulfonamide (NSA) alone, or the addition of MI after induction of Necroptosis, significantly up-regulated the cell activity and the protein level of SLC5A3 in gill cells, and significantly reduced the LDH release in the culture medium and the intracellular ROS content, the number of Necroptosis cells, the protein expression of TNFα, TNFR1 and RIPK1, and the ratio of p-RIPK3/RIPK3 and p-MLKL/MLKL (P < 0.05). It indicated MI induce Autophagy may relate to Beclin1/LC3/p62 signaling pathway, inhibits Pyroptosis may attribute to Caspase-1/GSDMD/IL-1β signaling pathway, and inhibits Necroptosis via MLKL signaling pathway. However, MI had no effect on Apoptosis.

Apoptosis; Autophagy; Gill cells; Myo-inositol; Necroptosis; Pyroptosis.