17β-trenbolone increases circulating myeloid-derived MMP8 in CSDS-induced mice and drives depressive tendencies to social threat.

Chronic psychosocial stress is a major risk factor for major depressive disorder (MDD). The impact of 17β-trenbolone (17-TB), an anabolic steroid and potential environmental endocrine disruptor, on stress responses and mood states in mammals is unclear. In this study, we explored how 17-TB interacts with chronic social defeat stress (CSDS) to drive neuroinflammatory cascades and behavioral abnormalities in mice. Utilizing a multidisciplinary cross-cutting approach integrating behavioral analysis, molecular biology, neuroimmunology, and electrophysiology, we ascertained that 17-TB exacerbated CSDS-induced mice peripheral inflammation by increasing IL-6, IL-1β, TNF-α, and myeloid-derived Matrix metalloproteinase 8 (MMP8). Furthermore, the study identified a concomitant downregulation of blood-brain barrier (BBB) tight junction proteins (ZO-1, Occludin), accompanied by an increase in BBB permeability. This led to degradation of the extracellular matrix (ECM) and altered neuronal excitability, evidenced by elevated EPSC amplitude/frequency and abnormal action potential firing, which were linked to heightened anxiety and depressive-like behaviors. Interestingly, 17-TB enhanced social dominance in CSDS-induced mice, associated with increased c-Fos+ expression in the medial prefrontal cortex (mPFC), indicating a disconnect between social competitiveness and emotional vulnerability. In conclusion, our study identified 17-TB as a neurotoxin that exacerbates stress-induced depression-like behaviors through BBB leakage, neuroinflammation, and ECM-driven synaptic dysfunction. The paradoxical social dominance highlights the ability of endocrine-disrupting chemicals (EDCs) to dysregulate neural circuits controlling emotional and social behavior. These findings underscore the imperative for a re-evaluation of EDC regulatory policy and the formulation of a therapeutic strategy that targets MMP8, a pivotal mediator of neuro-immune crosstalk in mood disorders.