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.
© 2026. The Author(s).

Objective Subgroups of mental illness patients have been seen to display disturbed proteostasis, with specific proteins aggregating in their brain, which is generally determined by assaying protein insolubility in the post mortem samples. Such studies typically only look at one region of the brain, and therefore we aimed to determine the distribution of protein across a single brain, using this insolubility-based approach. Methods We looked at 20 post mortem tissue samples from across the brain of a single patient, with schizophrenia and Alzheimer’s disease, determined which protein(s) aggregated in his brain relative to controls, based on purification of insoluble protein fractions. The individual samples were then similarly analysed. Results Disrupted in Schizophrenia 1 (DISC1) protein was seen to be insoluble in the patient’s brain, however in a very heterogenous picture, with differences in insoluble DISC1 even between samples of the same region, but opposite hemispheres. Conclusions While caution must be taken in extrapolating from a single individual, this raises the possibility that aggregates of DISC1 may spread throughout the brain, as is the case for proteins in neurodegenerative disorders, and suggests that current studies looking at single brain regions may be underestimating the prevalence of protein aggregates in schizophrenia.

Disrupted proteostasis is an emerging area of research into major depressive disorder. Several proteins have been implicated as forming aggregates specifically in the brains of subsets of patients with psychiatric illnesses. These proteins include CRMP1, DISC1, NPAS3 and TRIOBP-1. It is unclear, however, whether these proteins normally aggregate together in the same individuals and, if so, whether each protein aggregates independently of each other ("parallel aggregation") or if the proteins physically interact and aggregate together ("co-aggregation").
Post mortem insular cortex samples from major depressive disorder and Alzheimer's disease patients, suicide victims and control individuals had their insoluble fractions isolated and tested by Western blotting to determine which of these proteins are insoluble and, therefore, likely to be aggregating. The ability of the proteins to co-aggregate (directly interact and form common aggregate structures) was tested by systematic pairwise expression of the proteins in SH-SY5Y neuroblastoma cells, which were then examined by immunofluorescent microscopy.
Many individuals displayed multiple insoluble proteins in the brain, although not enough to imply interaction between the proteins. Cell culture analysis revealed that only a few of the proteins analyzed can consistently co-aggregate with each other: DISC1 with each of CRMP1 and TRIOBP-1. DISC1 was able to induce aggregation of full length TRIOBP-1, but not individual domains of TRIOBP-1 when they were expressed individually.
While specific proteins are capable of co-aggregating, and appear to do so in the brains of individuals with mental illness and potentially also with suicidal tendency, it is more common for such proteins to aggregate in a parallel manner, through independent mechanisms. This information aids in understanding the distribution of protein aggregates among mental illness patients and is therefore important for any future diagnostic or therapeutic approaches based on this aspect of mental illness pathology.

Schizophrenia is a chronic illness of heterogenous biological origin. We hypothesized that, similar to chronic progressive brain conditions, persistent functional disturbances of neurons would result in disturbed proteostasis in the brains of schizophrenia patients, leading to increased abundance of specific misfolded, insoluble proteins. Identification of such proteins would facilitate the elucidation of molecular processes underlying these devastating conditions. We therefore generated antibodies against pooled insoluble proteome of post-mortem brains from schizophrenia patients in order to identify unique, disease-specific epitopes. We successfully identified such an epitope to be present on collapsin-response mediator protein 1 (CRMP1) in biochemically purified, insoluble brain fractions. A genetic association analysis for the CRMP1 gene in a large Finnish population cohort (n = 4651) corroborated the association of physical and social anhedonia with the CRMP1 locus in a DISC1 (Disrupted-in-schizophrenia 1)-dependent manner. Physical and social anhedonia are heritable traits, present as chronic, negative symptoms of schizophrenia and severe major depression, thus constituting serious vulnerability factors for mental disease. Strikingly, lymphoblastoid cell lines derived from schizophrenia patients mirrored aberrant CRMP1 immunoreactivity by showing an increase of CRMP1 expression, suggesting its potential role as a blood-based diagnostic marker. CRMP1 is a novel candidate protein for schizophrenia traits at the intersection of the reelin and DISC1 pathways that directly and functionally interacts with DISC1. We demonstrate the impact of an interdisciplinary approach where the identification of a disease-associated epitope in post-mortem brains, powered by a genetic association study, is rapidly translated into a potential blood-based diagnostic marker.