Finding a Better Lithium: Mesencephalic Astrocyte-Derived Neurotrophic Factor as a Therapeutic for Bipolar Disorder

Abstract

Bipolar disorder (BD) is increasingly being recognized as a neuroprogressive illness characterized by progressively worsening cognitive function and structural brain changes. Although lithium remains the gold standard treatment for BD, its ability to halt neuroprogression is a crucial, yet not fully understood aspect of its therapeutic benefit. Accumulating evidence suggests that lithium may be neuroprotective through alleviating ER stress, a feature highly implicated in the pathogenesis of BD. Over the last 20 years, Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF), an ER resident protein, has gained significant attention due to its ability to alleviate ER stress, reduce inflammation, and enhance cellular survival. In this thesis, we investigated the relationship between lithium and MANF using in vitro cellular models and in vivo rodent models. We establish that lithium upregulates MANF expression via the AP-1 signalling pathway. Moreover, we show that MANF plays a crucial functional role in lithium’s neuroprotective effects, as inhibiting the AP-1 pathway negated lithium’s protection against ER stress-induced neurotoxicity and reduced MANF expression. Furthermore, we demonstrate that MANF deficiency increases striatal cell susceptibility to amphetamine-induced neurotoxicity, highlighting its protective function in preclinical models of mania. In vivo experiments further showed that overexpressing MANF in amphetamine-treated rats reduced hyperlocomotion, prevented the upregulation of ER stress markers, and prevented amphetamine-associated death. Collectively, these findings suggest that MANF may be a critical mediator of lithium’s ability to halt neuroprogression in BD and advance our understanding of BD pathophysiology. Importantly, we present MANF as a promising therapeutic candidate for future therapeutic interventions aimed at halting neuroprogression in BD and preventing fatality due to amphetamine overdose.