Background: Schizophrenia is a chronic disease characterized by the impairment of mental functions. Several studies have carried out the proteomic characterization of post-mortem brain tissue, but only a few of these, have deepened into the subcellular analysis. A subcellular characterization using iTRAQ labeling shotgun proteomics and SRM-based targeted proteomic approaches applied to the mitochondria (MIT), crude nuclear fraction (NUC) and cytoplasm (CYT), allowed the observation of dynamic cellular changes providing valuable insights about schizophrenia physiopathology.
Methodologies: Post-mortem brain tissues from the orbitofrontal cortex of 12 schizophrenia patients and eight healthy controls were prepared following Gray & Whittaker´s and Cox and Emili protocol. Extracted proteins were digested and labeled with iTRAQ 4-plex. Three reporter groups were used for patients and one for a pool of controls. The peptide mixture was injected in an EASY-1000 nanoLC coupled to LTQ Orbitrap Velos. Mass spectra were analyzed in Proteome Discoverer 2.1 against the Human Uniprot database and the statistical analysis was made in the InfernoRDN software. The SRM validation was performed in the TSQ Quantiva mass spectrometer and in the Skyline software.
Results: We identified 940 protein groups in MIT fraction, 2022 in NUC and 2433 in CYT. Among all enriched cellular fractions, 359 protein groups were dysregulated. Quantitative proteomic analysis reveals the dysregulation of biological pathways related to calcium and apoptosis in MIT. The cell signaling disruption of CREB activation and the increase of NF-kB signaling and complement proteins C3 were the main findings in the NUC fraction. Finally, axon guidance proteins were the most dysregulated pathway in CYT.
Conclusion: The dysregulation of CREB and NF-kB signaling together with the imbalance of glutamate, calcium, and apoptosis activation are related to synaptic damage associated with behavioral and cognitive dysfunction. These findings contribute to a better understanding of the pathophysiological process in schizophrenia