Hydroxytyrosol confers resilience against the depressive, anxiogenic and cognition-disruptive effects of chronic stress

Our understanding of the causal mechanisms of disorders such as anxiety and depression remains rudimentary. There is a pressing need to develop disease-modifying and preventative therapies that can be administered early and reduce symptom emergence. Here, we used a novel chronic unpredictable restraint stress (CURS) model in female and male rats to investigate the protective potential of biotechnologically-produced hydroxytyrosol. The CURS model produced indicators of anxiety, depression, cognitive deficits and social dysfunction in the elevated plus maze, sucrose preference test, novel object recognition and social interaction, respectively. Oral dosing with hydroxytyrosol (50 mg/kg/day, oral jelly formulation) prior to and during the period of restraint stress successfully protected against the anxiety, mood, social and cognitive symptoms mediated by chronic stress. The effect of hydroxytyrosol on behaviour was accompanied by the prevention of stress-induced declines in dopamine and serotonin and increased serum levels of corticosterone. Using single-cell RNA sequencing (scRNA-seq) of the hippocampus, we identified transcriptional signatures associated with chronic stress and their normalisation by hydroxytyrosol. Chronic unpredictable restraint stress caused widespread transcriptional dysregulation across neurons, astrocytes, and microglia. Gene Ontology and KEGG analyses revealed stress-related dysregulation of glutamatergic, GABAergic, dopaminergic, and cholinergic transmission. Neurodegenerative disease-associated transcriptional modules were enriched in the genes dysregulated by chronic stress and pathways related to synaptic vesicle cycling, neurotransmitter release, oxidative phosphorylation, and protein translation were prominently disrupted. Hydroxytyrosol treatment markedly attenuated these transcriptional changes, preserving the expression of genes involved in synaptic signalling, mitochondrial integrity, and protein homeostasis, thereby protecting cognitive and mood/stress regulation functions. These findings demonstrate that hydroxytyrosol exerts broad neuroprotective and stress-resilience effects by preserving neuronal transcriptional homeostasis, identifying hydroxytyrosol as a potent dietary bioactive that can buffer the molecular and behavioural sequelae of chronic stress.