Environmental risk factors and blood-brain barrier dysfunction in a dual-hit model of schizophrenia

Schizophrenia (SZ) is a chronic neurodevelopmental psychiatric disorder that arises from a complex interaction between genetic vulnerability and environmental risk factors occurring throughout different stages of life and across neurodevelopmental periods. Although substantial progress has been made in understanding the clinical manifestations of SZ, the biological mechanisms underlying the disorder remain poorly understood, limiting the identification of effective personalized therapeutic strategies. Increasing evidence suggests that neuroinflammatory processes and alterations in neurovascular function may contribute to SZ pathophysiology. In this context, the blood–brain barrier (BBB) has emerged as a critical dynamic interface between the peripheral circulation and the central nervous system. BBB dysfunction and increased permeability may facilitate the entry of toxins, inflammatory mediators, and immune cells into the brain, thereby promoting pathological processes associated with schizophrenia-related phenotypes.

Maternal immune activation (MIA) during pregnancy and cannabis exposure during adolescence are recognized as relevant environmental risk factors associated with increased susceptibility to SZ. Prenatal immune challenges may interfere with early neurodevelopmental processes, whereas adolescent exposure to cannabinoids may further affect brain maturation during vulnerable developmental periods. However, the mechanisms through which these factors interact with BBB dysfunction and glial alterations remain unclear.

The aim of the present study was to investigate the contribution of BBB dysfunction to SZ-related phenotypes using a dual-hit mouse model combining prenatal immune challenge and adolescent cannabinoid exposure. In addition, we aimed to evaluate whether targeted disruption of BBB integrity through Claudin-5 downregulation exacerbates molecular and cellular alterations associated with schizophrenia.

To address these objectives, we employed a previously established dual-hit mouse model consisting of prenatal MIA induced by polyinosinic-polycytidylic acid (Poly(I:C)) administration at gestational day 9 and adolescent exposure to delta-9-tetrahydrocannabinol (THC) during postnatal days 55–60. In a second experimental approach, BBB integrity was further challenged by inducing a targeted reduction of Claudin-5 expression using adeno-associated virus (AAV)-mediated gene modulation delivered stereotaxically into the prefrontal cortex at postnatal day 30. Molecular alterations were assessed by quantitative PCR (qPCR), and immunofluorescence analyses were performed to evaluate microglial (Iba1) and astrocytic (GFAP) immunoreactivity in the prefrontal cortex and hippocampus. Ongoing experiments in the AAV-modified model additionally include behavioral phenotyping and the assessment of BBB-related markers. Statistical analyses were performed using two-way or three-way ANOVA depending on the number of experimental groups, followed by Tukey’s post hoc test.

Preliminary results obtained from the unmodified dual-hit model revealed alterations in glial and astrocytic markers measured by qPCR, together with changes in Iba1 and GFAP immunoreactivity in the prefrontal cortex and hippocampus compared with control animals. Experiments involving the AAV-modified model are currently ongoing.

In conclusion, these studies aim to clarify the contribution of BBB dysfunction to schizophrenia-related phenotypes and to identify biological mechanisms associated with differential susceptibility or resilience to environmental risk factors linked to SZ.

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