NEUROBIOLOGIA DEL SUICIDIO NEL DISTURBO DEPRESSIVO MAGGIORE: STUDIO MORFOLOGICO POST-MORTEM PER L¿INDAGINE DEL NETWORK GLIALE E VASCOLARE, CON ANALISI TOSSICOLOGICHE PER LA VALUTAZIONE DELL¿ADERENZA ALLA TERAPIA PSICHIATRICA

Suicide is one of the leading causes of death worldwide, with over 700,000 deaths each year. In recent years, numerous studies have focused on analyzing its epidemiology and predisposing factors. Among the biological factors involved, cerebral glial cells have attracted growing attention due to postmortem evidence linking their pathological alterations to major depressive disorder (MDD) and suicidal behavior. The research project underlying this thesis focused on the postmortem analysis of human brain tissue from individuals diagnosed with MDD who died by suicide, with the aim of investigating alterations in the glial network—astrocytes and microglia—as well as in cerebral vascularization, in brain regions involved in mood regulation and suicide vulnerability. The experimental approach combined morphological, immunohistochemical, and immunofluorescence techniques with tissue clearing and 3D reconstruction using the X CLARITY™ system. Additionally, a toxicological analysis was carried out to assess adherence to psychiatric pharmacological therapy in individuals with mood disorders undergoing treatment at the time of death. The analysis of astrocytic markers (GFAP – Glial Fibrillary Acidic Protein – , S100β – calcium binding protein S100β –, AQP4 – Aquaporin-4 –, ALDH1L1 – Aldehyde Dehydrogenase 1 Family Member L1) showed a trend toward increased cell number and marker expression in suicide cases, particularly in the dorsolateral prefrontal cortex (dlPFC) and white matter. GFAP/S100β colocalization patterns varied by sex and brain region, with higher expression and overlap in male suicide cases. Conversely, densitometric analysis revealed higher expression levels in females, with significant regional differences. No significant changes were observed in AQP4 expression, while pilot testing with ALDH1L1 validated the experimental staining protocol. Regarding microglia, the analysis of IBA1 (Ionized calcium-binding adapter molecule 1) and LEA (Lycopersicon esculentum Agglutinin) markers revealed reduced LEA/IBA1 colocalization in male suicide cases compared 11 to controls in the cortical areas examined. In contrast, increased colocalization was observed in the dlPFC of female suicide cases. Although these differences were not statistically significant, densitometric analysis indicated a trend toward reduced microglial activity in males and increased activity in females. The use of the X-CLARITY™ technique enabled high-resolution 3D reconstruction of glial and vascular architecture. Three-dimensional analysis revealed a statistically significant reduction in cerebral vascularization in suicide cases compared to controls, with a 52.8% decrease, suggesting a potential role of vascular network dysfunction in the pathophysiology of suicide. Finally, the toxicological investigation highlighted poor adherence to psychiatric therapy in individuals with mood disorders who died by suicide: in 70% of the cases analyzed, pharmacological levels were either absent or only partially consistent with prescribed therapy. Overall, the neuromorphological findings suggest the presence of complex and interconnected alterations in the glial and vascular networks in individuals with mood disorders who died by suicide, with notable differences based on sex and brain region. These findings contribute to a deeper understanding of the neurobiological mechanisms underlying suicidal behavior and open new avenues for research in neuropathological, clinical, and forensic contexts. Given that treatment adherence is a key factor in suicide prevention, prospective monitoring of postmortem drug levels, along with synergistic collaboration between clinicians and forensic pathologists, could improve the effectiveness of therapeutic interventions and support the development of more targeted suicide prevention strategies.