Background. Early life adversity (ELA) is a major risk factor for development of suicidal behaviors, and early developmental periods have profound effects on the structure and functional organization of the brain. The extracellular matrix (ECM), particularly perineuronal nets (PNNs) ”a specialized form of ECM" regulates brain plasticity, and is sensitive to ELA. Therefore, understanding the role of PNNs is timely given the relationship between ELA and the development of psychiatric disorders and suicidal outcomes. Although much is known about the ECM, the processes underlying the formation and maintenance of PNNs have not been determined, and identifying the precise cellular origins of PNN components would provide important insight into brain plasticity and its relationship with the development of suicidal behaviors. Extracellular vesicles (EVs) are important signaling molecules which are associated with various forms of neural plasticity. EVs carry matrix-remodeling proteins, and are known to play an integral role in remodeling the ECM. Furthermore, our preliminary studies have identified components of the PNN within EVs isolated from the brain.
Research aims and hypotheses. The overall goal of this project is to identify the molecular basis by which the elevated levels of PNNs associated with ELA are related to the development of suicidal behaviors. To address this question, we have three specific aims: Aim 1. Study isolated brain cell types to assess their specific contributions to PNN formation. We hypothesize that PNN molecules are released by specific cell types. Our recent findings indicate that oligodendrocyte precursor cells (OPCs) are particularly relevant for PNN formation, given their enriched expression of PNN-related genes, and proximity to PNN-enwrapped parvalbumin positive neurons. Aim 2. Test whether EVs from cell culture systems containing PNNs are enriched for PNN cargo. We hypothesize that 1) EVs from PNN-expressing cultures will show an enrichment of PNN-component cargo compared to cultures in which PNN formation is blocked, and 2) OPCs will show a specific increase in PNN related transcripts in PNN-expressing cultures. Aim 3. Transplantation of EVs isolated from brains where increased prevalence of PNNs was previously identified, to induce the formation of PNNs in culture. We hypothesize that EV cargo from individuals with histories of severe ELA is sufficient for the formation of PNNs on hippocampal neurons.
Samples, measures, and procedures. Primary cells and dissociated hippocampal cells will be used to test the relationships between EVs and the development of PNNs, which will be assessed using proteomics and single cell transcriptomic profiling. EVs from the brains of individuals who died by suicide with a history of abuse will be transplanted onto cell culture to test for the induction of PNNs. PNN formation will be assess using cells staining techniques, sensitive to the presence and concentration (i.e. intensity) of the nets.
Potential impact and next steps. Understanding the processes which influence or control PNN development represents a key frontier for the development of interventions which are specific to suicidal behaviours in the context of ELA. This will be a further step towards a suicide prevention strategy and potential mitigation tactic for ELA.
