Nearly 850,000 people die by suicide in the world each year, i.e., one death every 40 seconds. However, the neurobiological mechanisms underlying the pathogenesis of suicide are not well understood. Recent literature suggests a neuroinflammatory hypothesis for suicide and the commonest associated psychiatric disorder, namely, Major Depressive Disorder (MDD). MDD patients and depressed suicide attempters have elevated levels of inflammatory markers which are hypothesized to have neurotoxic effects on brain regions modulating mood, emotion regulation and decision-making, particularly the dorsolateral prefrontal cortex (dlPFC). This may result in functional deficits that increase suicide risk.
The blood brain barrier (BBB) is a selectively permeable membrane made by endothelial cells sealed by tight junction proteins, pericytes and astrocytes, that prevent potentially harmful molecules (e.g., inflammatory agents) in the blood from entering the brain. Stress exposure can compromise BBB integrity leading to high levels of brain inflammatory molecules associated with MDD and suicide, and depressive-like behavior in mice. In humans, we have preliminary data showing that suicide decedents exhibit higher stress scores, and display differential expression of genes involved in BBB maintenance, such as CLAUDIN-5 (CLDN5). CLDN5 DNA is also hypermethylated and CLDN5 protein is mislocalized (in brain parenchyma instead of microvessels) in the dlPFC of suicide decedents. In mice, we have preliminary data showing that recent life stress (RLS) increases BBB permeability and reduces CLDN5 expression in the medial prefrontal cortex (mPFC, homologous to human dlPFC), while inhibition of the inflammatory marker cyclooxygenase-2 (COX-2) can restore BBB integrity. However, critical gaps in knowledge remain. For example, the full transcriptomic and DNA methylation profiles of the BBB and related inflammatory genes in suicide is not known, and whether pharmacological inhibition of COX-2 can restore BBB permeability and normal function at both the molecular and behavioral level.
Here we propose to examine the transcriptomic and DNA methylation profiles of BBB gene ontology families and related inflammatory pathways in the dlPFC from MDD suicide decedents, MDD non-suicides and nonpsychiatric controls and use ELISA and immunohistochemistry to identify the cellular localization of CLDN5, and other BBB markers (e.g., ALBUMIN, IgG) in a subset of samples (Aim 1). We will then test whether pharmacological inhibition of Cox-2 expression in a mouse model of stress restores BBB integrity and rescues normal behavior (Aim 2). Numerous techniques will be utilized including bulk RNA-seq, ELISA, immunolabelin, and enabled imaging of solvent-cleared organs (iDISCO). We hypothesize that genes associated with BBB maintenance are downregulated, genes associated with BBB breakdown are upregulated, and CLDN5 is mislocalized in brain parenchyma in suicide decedents. Moreover, we hypothesize that COX-2 inhibition rescues stress-induced BBB breakdown and reduces maladaptive behaviors in mice.
In summary, by elucidating how stress impacts BBB integrity and identifying novel therapeutic targets, we aim to develop more effective treatments for suicide prevention. This proposal combines human postmortem brain analysis with murine models, offering a translational approach with the potential for real-world impact on suicide prevention and treatment.
