Inflammation-induced behavioral changes is driven by alterations in Nrf2-dependent apoptosis and autophagy in mouse hippocampus: Role of fluoxetine

Abstract

Inflammation has been associated with the progression of many neurological diseases. Peripheral inflammation has also been vaguely linked to depression-like symptoms in animal models, but the underlying pathways that orchestrate inflammation-induced behavioral or molecular changes in the brain are still elusive. We have recently shown that intraperitoneal injections of lipopolysaccharide (LPS) to Swiss albino mice triggers systemic inflammation, leading to an activated immune response along with changes in monoamine levels in the brain. Herein we pinpoint the fundamental pathways linking peripheral inflammation and depression-like behavior in a mouse model, thereby identifying suitable targets of intervention to combat the situation. We show that LPS-induced peripheral inflammation provoked a depression-like behavior in mice and a distinct pro-inflammatory bias in the hippocampus, as evident from increased microglial activation and elevated levels of pro-inflammatory cytokines IL-6 and TNF-α, and activation of NFκB-p65 pathway. Significant alterations in Nrf2-dependent cellular redox status, coupled with altered autophagy and increased apoptosis were noticed in the hippocampus of LPS-exposed mice. We and others have previously shown that, fluoxetine (an anti-depressant) has effective anti-inflammatory and antioxidant properties by virtue of its abilities to regulate NFκB and Nrf2 signaling. We observed that treatment with fluoxetine or the Nrf2 activator tBHQ (tert-butyl hydroquinone), could reverse depression-like-symptoms and mitigate alterations in autophagy and cell death pathways in the hippocampus by activating Nrf2-dependent gene expressions. Taken together, the data suggests that systemic inflammation potentiates Nrf2-dependent changes in cell death and autophagy pathway in the hippocampus, eventually leading to major pathologic sequelae associated with depression. Therefore, targeting Nrf2 could be a novel approach in combatting depression and ameliorating its associated pathogenesis.