Inhibition of microglial glutaminase alleviates chronic stress-induced neurobehavioral and cognitive deficits

Major depressive disorder (MDD) is a prevalent and debilitating psychiatric condition with significant societal and economic impacts. Many patients are resistant to current antidepressant therapies, underscoring the need for novel treatments targeting underlying mechanisms. We previously discovered that glutaminase (GLS1), an enzyme converting glutamine to glutamate, is upregulated specifically in activated microglia in mice exposed to Chronic Social Defeat Stress (CSDS). Importantly, GLS1 mRNA was also upregulated in microglia within postmortem brain tissue of MDD patients, highlighting a potential role for microglial GLS1 in MDD pathophysiology. However, existing GLS1 inhibitors lack brain penetrance and/or cause gastrointestinal toxicities, limiting their translational potential. To address this, we utilized a hydroxyl-terminated poly(amidoamine) dendrimer nanoparticle system to selectively target microglial GLS1. Using structurally distinct GLS1 inhibitors, we synthesized two hydroxyl-dendrimer-GLS1 inhibitor conjugates: dendrimer-TTM020 (D-TTM020) and dendrimer-JHU29 (D-JHU29). In the murine CSDS model, we evaluated their microglial target engagement, safety, and efficacy using immunofluorescence, GLS1 activity assays, gastrointestinal histopathology, and a battery of behavioral tests. Using a Cy5 fluorescently labeled hydroxyl-dendrimer (D-Cy5), we confirmed that systemically administered D-Cy5 crossed the blood-brain barrier and was selectively engulfed by activated microglia in mice after CSDS. D-TTM020 and D-JHU29 attenuated CSDS-induced microglial GLS1 activity elevation without affecting non-microglial cells. Furthermore, D-TTM020 and D-JHU29 both alleviated CSDS-induced social avoidance, and D-TTM020 additionally reduced anxiety-like behavior and improved recognition memory. Both conjugates were well tolerated, with no overt or gastrointestinal toxicities. Collectively, these findings suggest that microglia-targeted GLS1 inhibition is a promising therapeutic approach for chronic stress-associated depression.