Differential Cellular Interactome in Schizophrenia and Bipolar Disorder-Discriminatory Biomarker Role

Abstract

Schizophrenia (SCH) and bipolar disorder (BD) are two of the most important psychiatric pathologies due to their high population incidence and disabling power, but they also present, mainly in their debut, high clinical similarities that make their discrimination difficult. In this work, the differential oxidative stress, present in both disorders, is shown as a concatenator of the systemic alterations-both plasma and erythrocyte, and even at the level of peripheral blood mononuclear cells (PBMC)-in which, for the first time, the different affectations that both disorders cause at the level of the cellular interactome were observed. A marked erythrocyte antioxidant imbalance only present in SCH generalizes to oxidative damage at the plasma level and shows a clear impact on cellular involvement. From the alteration of protein synthesis to the induction of death by apoptosis, including proteasomal damage, mitochondrial imbalance, and autophagic alteration, all the data show a greater cellular affectation in SCH than in BD, which could be linked to increased oxidative stress. Thus, patients with SCH in our study show increased endoplasmic reticulum (ER)stress that induces increased proteasomal activity and a multifactorial response to misfolded proteins (UPR), which, together with altered mitochondrial activity, generating free radicals and leading to insufficient energy production, is associated with defective autophagy and ultimately leads the cell to a high apoptotic predisposition. In BD, however, oxidative damage is much milder and without significant activation of survival mechanisms or inhibition of apoptosis. These clear differences identified at the molecular and cellular level between the two disorders, resulting from progressive afflictions in which oxidative stress can be both a cause and a consequence, significantly improve the understanding of both disorders to date and are essential for the development of targeted and preventive treatments.

Keywords: cellular death; mitochondria; oxidative stress; proteasome; psychiatric disorder; reticulum stress.

Figure 1

Oxidative stress status of control individuals (CON) and patients with schizophrenia (SCH) and bipolar disorder (BD). (A) Lipid peroxidation (LPO) (expressed as nmol MDA + 4-HNE/g protein) and total antioxidant activity (TAA) (expressed as mg equivalents Trolox/mL). (B) Superoxide dismutase (SOD) activity (expressed as SOD units/mg of protein) and catalase (CAT) activity (expressed as µmol H₂O₂/min mg of protein). Data are represented as the mean ± SEM. * CON vs. SCH or BD; # SCH vs. BP. Number of symbols marks the level of significance: 1 for p < 0.05, 2 for p < 0.01, and 3 for p < 0.001.

Figure 2

Inflammatory response in plasma of CON and patients with SCH and BD. (A) IL-6 and (B) TNF-α levels (expressed as pg of protein/mL). Data are represented as the mean ± SEM. * CON vs. SCH or BD; # SCH vs. BP. Number of symbols marks the level of significance: 2 for p < 0.01, and 3 for p < 0.001.

Figure 3

Oxidative phosphorylation profile and mitochondrial dynamics in peripheral blood mononuclear cells (PBMC) of CON and patients with SCH and BD. (A) Levels of subunits from the protein complexes of the mitochondrial electron transport chain (NADH dehydrogenase (ubiquinone) 1b subcomplex 8 (NDUFB8) from complex I; iron–sulfur subunit (SDHB) from complex II; ubiquinol cytochrome c reductase core protein II (UQCRC2) from complex III; cytochrome c oxidase subunit I (MTCO1) from complex IV, and ATP synthase subunit α (ATP5A) from complex V) (expressed as optical densities (O.D.) arbitrary units). Representative images of western blots. Ponceau staining was used as loading control. (B) ATP content (expressed as µM ATP). (C) Quantification of TOM20 expression (expressed as O.D. arbitrary units). (D) Protein levels of MNF1 (expressed as O.D. arbitrary units). (E) Levels of DRP1 (expressed as O.D. arbitrary units). Representative images of western blots. Ponceau staining was used as loading control. Data are represented as the mean ± SEM. * CON vs. SCH or BD; # SCH vs. BP. Number of symbols marks the level of significance: 1 for p < 0.05, 2 for p < 0.01, and 3 for p < 0.001.

Figure 4

Unfolded protein response (UPR) signaling pathways in PBMCs of CON and patients with SCH and BD. (A) Protein levels of BiP (expressed as O.D. arbitrary units). (B) Quantification of ATF6α, IRE1α, phospho-eIF2α, and eIF2α expression and p-eIF2α/eIF2α ratio (expressed as O.D. arbitrary units). (C) Proteasome activity ratio (expressed as pmol AMCx min/mg of protein). Representative images of western blots. Ponceau staining was used as loading control. Data are represented as the mean ± SEM. * CON vs. SCH or BD; # SCH vs. BP. Number of symbols marks the level of significance: 1 for p < 0.05, 2 for p < 0.01, and 3 for p < 0.001.

Figure 5

Autophagic response in PBMCs of CON and patients with SCH and BD. (A) Protein levels of Beclin-1, LC3-I, and LC3-II proteins and the LC3-II/LC3-I ratio (expressed as O.D. arbitrary units). (B) p62 protein expression (expressed as O.D. arbitrary units). (C) LAMP2A protein expression (expressed as O.D. arbitrary units). Representative images of western blots. Ponceau staining was used as loading control. Data are represented as the mean ± SEM. * CON vs. SCH or BD; # SCH vs. BP. The number of symbols marks the level of significance: 1 for p < 0.05, 2 for p < 0.01, and 3 for p < 0.001.

Figure 6

Caspase-3/7 activity in PBMCs of CON and patients with SCH and BD (expressed as luminescence (URL)). Data are represented as the mean ± SEM. * CON vs. SCH or BD; # SCH vs. BP. Number of symbols marks the level of significance: 3 for p < 0.001.