Levels of aggregation of proteins related to mental illness, assayed by insolubility, vary across the brains of individuals

An emerging area of research into major mental illnesses is to investigate the formation of insoluble aggregates of specific proteins in the brains of patients with these conditions. These studies are normally based on examining insoluble protein in post mortem brain samples, but, for practical reasons, typically consider only one region of the brain per subject. Here, we tested post mortem brain samples from multiple brain regions of various individuals, which included patients with major depressive disorder, schizophrenia and victims of suicide. Samples from patients with Alzheimer's disease and control individuals were used for comparison. Notably, 20 tissue samples were available from across the brain of one individual who had both schizophrenia and Alzheimer's disease. Consistently, while insolubility of DISC1 (Disrupted in Schizophrenia 1), CRMP1 (Collapsin Response Mediator Protein 1) and/or TRIOBP-1 (Trio and F-actin Binding Protein, isoform 1) were often present in multiple brain regions, this was not homogenous across the brain. While this study looks at a relatively small number of subjects, and caution must be taken in over-generalising, it is possible that aggregation of these proteins spreads throughout the brain, in a similar manner to the staging seen in neurodegenerative disease. Previous studies may therefore have underestimated the prevalence of protein aggregation in mental illness, due to this heterogeneity of insoluble protein across the brain.