The Role And Mechanism Of Mitophagy Receptor NIX In Depressive-like Behaviors In Mice

Objective: Mitophagy is an important quality control mechanism for intracellular mitochondria.The latest animal studies suggest that the impairment of mitophagy mediated by the receptor protein,NIP3-like protein X(NIX),may be involved in the stress-related cognitive impairment induced by glucocorticoids.However,the role of NIX-mediated mitophagy in the psychiatric diseases is not well understood.Studies have shown that tumor necrosis factor-α(TNF-α)is involved in the pathogenesis of depression.This study aims to investigate the role of NIX-mediated mitophagy in the pathogenesis of depressive-like behaviors in mice induced by TNF-α and chronic social defeat stress,and explore its mechanisms.Methods: Intraperitoneal injection of lipopolysaccharide,injection of TNF-α into the media prefrontal cortex and chronic social defeated stress were used to induce depressive-like behaviors in mice.A series of behavioral tests,including tail suspension test and forced swimming test,were measured to evaluate depressive-like behaviors in mice.The effects of NIX knockout,overexpression or knockdown on depression-like behavior in mice were observed.The changes of autophagy related proteins and synaptic proteins were detected by western blotting.The number of mitophagosomes was determined by transmission electron microscopy.Quantitative polymerase chain reaction was utilized to quantify the levels of related genes.Primary neurons were transfected with lentivirus to overexpress NIX to explore the mechanisms.Results:(1)Intraperitoneal injection of lipopolysaccharide or injection of TNF-α into the media prefrontal cortex inhibited NIX-mediated mitophagy in the media prefrontal cortex and led to depressive-like behaviors in mice.(2)TNF-α inhibited the initiation of NIXmediated mitophagy in primary cortical neurons.(3)NIX knockdown in excitatory neurons in the medial prefrontal cortex resulted in depressive-like behaviors in mice.(4)Overexpression of NIX in the media prefrontal cortex or primary cortical neurons in vitro alleviated the inhibition of mitophagy caused by TNF-α and improved mitochondrial function.(5)Overexpression of NIX in the media prefrontal cortex mitigated the loss of dendritic spines and reduction of synaptic proteins caused by TNF-α and reversed the depressive-like behaviors induced by TNF-α.(6)Intraperitoneal injection of ketamine alleviated the loss of synaptic proteins and improved the TNF-α-induced depressive-like behaviors,which was dependent on the activation of NIX-mediated mitophagy in the media prefrontal cortex.(7)Infliximab improved lipopolysaccharide-induced depressive-like behaviors in mice,and its effect was closely related to the activation of NIX-mediated mitophagy in the medial prefrontal cortex.(8)Infliximab ameliorated depressive-like behaviors induced by chronic social defeat stress in mice,and the mechanism was closely related to reversing the damage of NIX-mediated mitophagy caused by stress.(9)NIX mRNA levels in the peripheral blood of depression models mice were negatively correlated with depressive-like behaviors,and NIX mRNA levels in the peripheral blood of depression patients were negatively correlated with depressive symptoms.Conclusion: TNF-α inhibits mitophagy by reducing NIX expression in the medial prefrontal cortex of mice,which leads to accumulation of damaged mitochondria,causes dendritic spine loss and induces depressive-like behaviors in mice.The inhibition of TNF-α on NIX-mediated mitophagy may be involved in the chronic social defeat stress-induced depressive-like behaviors in mice.Restoration of NIX-mediated mitophagy in the medial prefrontal cortex of mice reversed TNF-α-induced mitophagy dysfunction and dendritic spine loss,resulting in antidepressant-like effects.