Autophagy Induction and Accumulation of Phosphorylated Tau in the Hippocampus and Prefrontal Cortex of Adult C57BL/6 Mice Subjected to Adolescent Fluoxetine Treatment

Background: Fluoxetine (FLX) represents the antidepressant of choice for the management of pediatric mood-related illnesses. Accumulating preclinical evidence suggests that ontogenic FLX exposure leads to deregulated affect-related phenotypes in adulthood. Mood-related symptomatology constitutes a risk-factor for various neurological disorders, including Alzheimer's disease (AD), making it possible for juvenile FLX history to exacerbate the development of neurodegenerative diseases.

Objective: Because AD is characterized by the pathological accumulation of hyperphosphorylated tau, which can result from impaired function of protein degradation pathways, such as autophagy and the ubiquitin-proteasome system (UPS), we evaluated the long-term effects of adolescent FLX exposure on these pathways, using mice as a model system.

Methods: We subjected C57BL/6 adolescent male mice to FLX (20 mg/kg/day) from postnatal day (PD) 35 to PD49. Twenty-one days after the last FLX injection (i.e., adulthood; PD70), mice were euthanized and, using immunoblotting analysis, we evaluated protein markers of autophagy (Beclin-1, LC3-II, p62) and the UPS (K48-pUb), as well as AD-associated forms of phosphorylated tau, within the hippocampus and prefrontal cortex.

Results: Juvenile FLX pre-exposure mediated long-term changes in the expression of protein markers (increased LC3-II and decreased p62) that is consistent with autophagy activation, particularly in the prefrontal cortex. Furthermore, FLX history induced persistent accumulation of AD-associated variants of tau in both the hippocampus and prefrontal cortexConclusion: Adolescent FLX treatment may have enduring effects in the neuronal protein degradation machinery, which could adversely influence clearance of abnormal proteins, potentially predisposing individuals to developing AD in later life.