Metabolic abnormalities in fronto-striatal-thalamic white matter tracts in schizophrenia

Abstract

The anterior limb of the internal capsule (ALIC) is the major white matter tract providing reciprocal connections between the frontal cortex, striatum and thalamus. Mounting evidence suggests that this tract may be affected in schizophrenia, with brain imaging studies reporting reductions in white matter volume and density, changes in fractional anisotropy and reduced asymmetry. However, the molecular correlates of these deficits are currently unknown. The aim of this study was to identify alterations in protein and metabolite levels in the ALIC in schizophrenia. Samples were obtained post-mortem from individuals with schizophrenia (n=15) and non-psychiatric controls (n=13). Immunoreactivity for the myelin-associated protein myelin basic protein (MBP), and the axonal-associated proteins phosphorylated neurofilament and SNAP-25 was measured by enzyme-linked immunoadsorbent assay (ELISA). Metabolite concentrations were quantified by proton nuclear magnetic resonance ((1)H NMR) spectroscopy. Levels of myelin- or axonal-associated proteins did not differ between groups. Overall differences in metabolite concentrations were observed between the two groups (MANOVA F=2.685, p=0.036), with post-hoc tests revealing lower lactate (19%) and alanine (24%) levels in the schizophrenia group relative to controls. Observed changes in lactate and alanine levels indicate metabolic abnormalities within the ALIC in schizophrenia.

Figure 1

Immunoblotting studies indicate bands at the expected molecular weights for PNF (SMI-34), GFAP (SMI-22), SNAP-25 (SP12) and MBP (SMI94) in representative samples of human brain homogenate, PC12 and HTB-17 cell lysates.

Figure 2

Metabolites in ventral internal capsule. (A) 1H NMR spectrum of ventral internal capsule. M-Ins: myo-inositol, GPC: glycerophosphorylcholine, PC: phosphorylcholine, Cho: choline, Cr/PCr: creatine/phosphocreatine, NAAG: N-acetylaspartylglutamate, NAA: N-acetylaspartate, TSP: 3-trimethylsilyl propionic acid. (B) PLS-DA model showing separation of samples using scores on latent variables LV1 and LV2. The dashed blue circle represents the 99% confidence interval. (C) Scores for prediction of class (Y predicted score) for each sample. In plots B and C control samples are represented as blue circles and schizophrenia samples as red triangles. (D) Receiver operating characteristic (ROC) plots for the original (blue) and the cross-validated (green) PLS-DA models. The red circles represent the values for specificity and sensitivity based on optimum Bayesian-determined threshold derived by the software (red dashed line on plot C).

Figure 3

Plots of the relationship between alanine and lactate in the ventral internal capsule in control (blue) and schizophrenia (red) samples. A statistically significant relationship was seen only in the schizophrenia samples. Concentrations are mmol per kg wet weight of tissue.