Conference Agenda

Background: The brain undergoes important growth and plasticity during prenatal development, and altered activation of the glucocorticoid receptor (GR) system is one of the factors mediating stress effects during this time, likely through transcriptional dysregulation. To investigate these processes in a human-specific in vitro system, we used induced pluripotent stem cell-derived 3-dimensional brain organoids.

Methods: To determine cell-type specific GR activation response, we profiled the transcriptomes of thousands of individual cells using single-cell transcriptomic analyses following glucocorticoids exposure acutely, chronically, and using a two-hit model. We used immunofluorescence to better understand protein, and cell morphology-level long-term effects on cell-type population dynamics.

Results: Prolonged glucocorticoids exposure in cerebral organoids activated a robust cell-type-specific differential response of key transcription factors involved in neuronal cell fate regulation, including SOX2, PAX6, TBR1 and GAD1. Lineage analyses identified an over-commitment toward inhibitory neurons, whereby glucocorticoids acted directly on lineage driver genes and directed the likelihood of individual cells’ commitment to this neuronal lineage. in vitro findings were consistent across diverse genetic backgrounds, and were supported by in vivo human fetal brain data.

Conclusions: Cerebral organoids show responsiveness to GR activation consistent with in vivo data, including a cell-type specific transcriptional regulatory response through key lineage drivers capable of shifting lineage commitment. The likely outcome of aberrant overexposure is a lasting shift in neuronal type distribution and developing brain architecture. This work sheds light on the mechanisms by which environmental stimuli like maternal stress-mediated elevated glucocorticoids could lead to subtle changes in brain development and ultimately vulnerability to mental illness.

Background: Abnormal auditory processing of deviant stimuli, as reflected by mismatch negativity (MMN), is often reported in schizophrenia (SCZ). At present, it is still under debate whether this dysfunctional response is specific to the full-blown SCZ diagnosis or rather a marker of risk for psychosis. The present study tested MMN in patients with SCZ, bipolar disorder (BD), first episode of psychosis (FEP), and in people at clinical high risk for psychosis (CHR).

Methods: Source-based MEG activity evoked during a passive auditory oddball task was recorded from 135 patients grouped according to diagnosis (SCZ, BD, FEP, and CHR) and 135 healthy controls also divided into four subgroups, age- and gender-matched with diagnostic subgroups. The magnetic MMN (mMMN) was analyzed as event-related field (ERF), Theta power, and Theta inter-trial phase coherence (ITPC).

Results: The clinical group as a whole showed reduced mMMN ERF amplitude, Theta power, and Theta ITPC, without any statistically significant interaction between diagnosis and mMMN reductions. The mMMN subgroup contrasts showed lower ERF amplitude in all the diagnostic subgroups. In the analysis of Theta frequency, SCZ showed significant power and ITPC reductions, while only indications of diminished ITPC were observed in CHR, but no significant decreases characterized BD and FEP.

Conclusions: Significant mMMN alterations in people experiencing psychosis, also for diagnoses other than SCZ, suggest that this neurophysiological response may be a feature shared across psychotic disorders. Additionally, reduced Theta ITPC may be associated with risk for psychosis.

Patients with psychiatric disorders such as bipolar disorder (BD), schizophrenia (SZ) or major depressive disorder (MDD) show high rates of metabolic risk factors, which contribute to cardiovascular comorbidities and decreased life expectancy. To this regard, lifestyle factors and adverse effects of psychotropic drugs play a relevant role. However, psychiatric and metabolic traits are highly heritable, suggesting a potential contribution of shared genetic determinants in this comorbidity. This aspect, as well as the potential effect of gender, have been scarcely investigated. Analytical approaches based on pleiotropy leverage existing genome-wide association data to increase our understanding of genetic determinants underlying complex traits, while the integration of genomic with transcriptomic data can shed light on the potential functional effect of identified variants. We will present an overview of these methods and results from the largest analysis of genetic factors shared between psychiatric disorders and metabolic traits such as body mass index (BMI) and waist-to-hip ratio (WHR), taking gender into account. Using state-of-the art methods, such as bivariate causal mixture models and conditional false discovery rate, we quantified the genetic overlap between psychiatric and metabolic traits and identified novel shared genetic determinants. Annotation of identified variants, evaluation of functional relevance and druggability of the identified targets was assessed with a battery of tools. We observed a significant cross-trait enrichment in variants associated with psychiatric disorders when conditioning on metabolic traits in either women or men. However, there was heterogeneity in the direction of effect and only for MDD the majority of alleles associated with increased MDD risk was also associated with increased BMI or WHR. Substantial gender differences in terms of genetic correlation patterns, identified loci and druggable targets were observed, with a higher number of loci shared with psychiatric disorders found to be associated with higher BMI or WHR exclusively in women.

Cell cycle-associated protein 1 (CAPRIN1; OMIM* 601178) is a ubiquitous protein involved in cell proliferation and migration. In neurons, it likely regulates the transport and translation of mRNAs involved in synaptic plasticity. We have recently associated CAPRIN1 loss-of-function variants with an autosomal dominant neurodevelopmental disorder characterized by language impairment/speech delay (n:12; 100%), Intellectual Disability (83%), ADHD (82%), and ASD (67%). In this study, we have generated CRISPR/Cas9-engineered CAPRIN1^+/- hiPSCs-lines and differentiated them into neuronal cells, observing several defects including decreased processes length, overall disruption of the neuronal structure, enhanced neuronal death, impaired calcium signalling, increase protein translation and oxidative stress (PMID:35979925).

To further define the mechanisms behind those neuronal defects, we performed transcriptomics analysis in early and late differentiated neurons. The sequencing data explained the physiological defects we previously observed, highlighting impaired oxidative phosphorylation, neuronal outgrowth, and translation. We also found a significant increase in genes involved in cell cycle control, DNA replication, proliferation, and dopaminergic neurogenesis and a decrease in GABA pathway-related genes. Preliminary data on CAPRIN1^+/- neuronal progenitor cells, showed an increased proliferative rate and expression of PAX6, NESTIN and SOX2, further suggesting a possible loss of balance in neuronal proliferation/differentiation. To explore these features, we are currently generating forebrain cortical organoids from CAPRIN1 patient-derived hiPSCs lines. Patient-derived brain organoids will be analysed for their cellular architecture, neuronal activity and the cellular composition using a multicolor immunophenotyping panel (NeurOMIP assay, PMID:33852833). As CAPRIN1 is suggested to be a mRNA translation inhibitor and we observed defective translation in CAPRIN1^+/- neurons, we will combine our experiments with the SUnSET assay to assess protein translation. This will highlight which specific neuronal population is specifically affected by the translational defect.

In conclusion, our study will unravel the impact of CAPRIN1 loss in neurodevelopment, shedding light on its role in neuronal differentiation, neurogenesis and proliferation.