Brain-Relevant Molecules in the Blood

Despite several findings in post-mortem brain samples, our understanding of the molecular mechanisms increasing risk for suicide is limited by the inaccessibility of the brain. In contrast, blood is easily accessible and contains brain-relevant particles, such as extracellular vesicles and cell-free DNA, that may be utilized to understand brain health. Extracellular RNA communication has recently been associated with a variety of biological processes and shows biomarker and therapeutic potential in the neuropsychiatric field. Importantly, extracellular vesicles can cross the blood-brain barrier and published data from our team provides evidence that blood-based RNA from extracellular vesicles can be traced back to its cellular origins in the brain. Similarly, cell-free DNA can also cross the blood-brain-barrier to travel from the brain to the blood. Notably, increased levels of cell-free DNA has been seen in individuals with a history of suicide attempt, highlighting its potential as a biomarker of suicidal behavior. Cell-free DNA contains DNA methylation marks similar to genomic DNA, which can be used to determine its cell population of origin. Although research into brain-relevant extracellular vesicles and cell-free DNA is flourishing, no study has investigated them concurrently in relation to suicide. We hypothesize that extracellular vesicles and cell-free DNA are released by specific cells in the brain and echo systemic changes related to suicide. In Aim 1, we hypothesize that transcriptional changes in the brain associated with suicidal behavior can be inferred using extracellular vesicles mRNA levels in blood. We will use RNA sequencing to characterize blood extracellular vesicle mRNA levels in two independent cohorts (separated in discovery and replication groups) of a combined number of non-psychiatric controls (N=112), subjects with bipolar disorder with a history of attempted suicide (N=129), and subjects with bipolar disorder and no history of suicide attempts (N=137). In Aim 2, we hypothesize that DNA methylation marks on cell-free DNA will have a distinct pattern reflecting specific disrupted cell populations in the brain and novel DNA methylation changes associated with attempted suicide. We will use Oxford Nanopore sequencing to characterize blood cell-free DNA methylation in the same cohort described in Aim 1. We will also explore the extent to which the transcriptomic and methylomic data overlaps. For further validation, we will use Q-PCR and pyrosequencing to validate our top 5-10 findings in an independent cohort of individuals with bipolar disorder or major depressive disorder. The novel combination of extracellular vesicle mRNA expression and cell-free DNA methylation gives us the opportunity to infer brain health and predict individuals at risk for suicidal behavior. By addressing the need for non-invasive ways to study the brain in suicide, our proposal has the potential to significantly advance efforts to develop early detection tools and enable interventions to prevent suicide.