Molecular insights into schizophrenia

In vivo evidence for cerebral bioenergetic abnormalities in schizophrenia measured using 31P magnetization transfer spectroscopy

IMPORTANCE

Abnormalities in neural activity and cerebral bioenergetics have been observed in schizophrenia (SZ). Further defining energy metabolism anomalies would provide crucial information about molecular mechanisms underlying SZ and may be valuable for developing novel treatment strategies.

OBJECTIVE

To investigate cerebral bioenergetics in SZ via measurement of creatine kinase activity using in vivo 31P magnetization transfer spectroscopy.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional case-control study in the setting of clinical services and a brain imaging center of an academic psychiatric hospital. Twenty-six participants with chronic SZ (including a subgroup diagnosed as having schizoaffective disorder) and 26 age-matched and sex-matched healthy control subjects (25 usable magnetic resonance spectroscopy data sets from the latter).

INTERVENTION

31P magnetization transfer spectroscopy.

MAIN OUTCOMES AND MEASURES

The primary outcome measure was the forward rate constant (k(f)) of the creatine kinase enzyme in the frontal lobe. We also collected independent measures of brain intracellular pH and steady-state metabolite ratios of high-energy phosphate-containing compounds (phosphocreatine and adenosine triphosphate [ATP]), inorganic phosphate, and the 2 membrane phospholipids phosphodiester and phosphomonoester.

RESULTS

A substantial (22%) and statistically significant (P = .003) reduction in creatine kinase kf was observed in SZ. In addition, intracellular pH was significantly reduced (7.00 in the SZ group vs 7.03 in the control group, P = .007) in this condition. The phosphocreatine to ATP ratio, inorganic phosphate to ATP ratio, and phosphomonoester to ATP ratio were not substantially altered in SZ, but a significant (P = .02) reduction was found in the phosphodiester to ATP ratio. The abnormalities were similar between SZ and schizoaffective disorder.

CONCLUSIONS AND RELEVANCE

Using a novel 31P magnetization transfer magnetic resonance spectroscopy approach, we provide direct and compelling evidence for a specific bioenergetic abnormality in SZ. Reduced kf of the creatine kinase enzyme is consistent with an abnormality in storage and use of brain energy. The intracellular pH reduction suggests a relative increase in the contribution of glycolysis to ATP synthesis, providing convergent evidence for bioenergetic abnormalities in SZ. The similar phosphocreatine to ATP ratios in SZ and healthy controls suggest that the underlying bioenergetics abnormality is not associated with change in this metabolite ratio.

Abnormalities of the Duo/Ras-related C3 botulinum toxin substrate 1/p21-activated kinase 1 pathway drive myosin light chain phosphorylation in frontal cortex in schizophrenia

BACKGROUND

Recent studies on GTPases have suggested that reduced Duo and cell division cycle 42 (Cdc42) transcript expression is involved in dendritic spine loss in schizophrenia. In murine models, Duo and Cdc42 phosphorylate p21-activated kinase 1 (PAK1), which modifies the activity of regulatory myosin light chain (MLC) and cofilin by altering their phosphorylation. Therefore, we hypothesized that in schizophrenia abnormal Duo and Cdc42 expression result in changes in MLC and/or cofilin phosphorylation, which might alter actin cytoskeleton dynamics underlying dendritic spine maintenance.

METHODS

We performed Western blot protein expression analysis in postmortem brains from patients diagnosed with schizophrenia and a comparison group. We focused our studies in the anterior cingulate cortex (ACC; n = 33 comparison group; n = 36 schizophrenia) and dorsolateral prefrontal cortex (DLPFC; n = 29 comparison group; n = 35 schizophrenia).

RESULTS

In both ACC and DLPFC, we found a reduction of Duo expression and PAK1 phosphorylation in schizophrenia. Cdc42 protein expression was decreased in ACC but not in DLPFC. In ACC, we observed decreased PAK1 phosphorylation and increased MLC phosphorylation (pMLC), whereas in DLPFC pMLC remained unchanged.

CONCLUSIONS

These data suggest a novel mechanism that might underlie dendritic spine loss in schizophrenia. The increase in pMLC seen in ACC might be associated with dendritic spine shrinkage. The lack of an effect on pMLC in DLPFC suggests that in schizophrenia PAK1 downstream pathways are differentially affected in these cortical areas.

In vivo 31P MRS of human brain at high/ultrahigh fields: a quantitative comparison of NMR detection sensitivity and spectral resolution between 4 T and 7 T

The primary goal of this study was to establish a rigorous approach for determining and comparing the NMR detection sensitivity of in vivo 31P MRS at different field strengths (B0). This was done by calculating the signal-to-noise ratio (SNR) achieved within a unit sampling time at a given field strength. In vivo 31P spectra of human occipital lobe were acquired at 4 and 7 T under similar experimental conditions. They were used to measure the improvement of the human brain 31P MRS when the field strength increases from 4 to 7 T. The relaxation times and line widths of the phosphocreatine (PCr) resonance peak and the RF coil quality factors (Q) were also measured at these two field strengths. Their relative contributions to SNR at a given field strength were analyzed and discussed. The results show that in vivo 31P sensitivity was significantly improved at 7 T as compared with 4 T. Moreover, the line-width of the PCr resonance peak showed less than a linear increase with increased B0, which leads to a significant improvement in 31P spectral resolution. These findings indicate the advantage of high-field strength to improve in vivo 31P MRS quality in both sensitivity and spectral resolution. This advantage should improve the reliability and applicability of in vivo 31P MRS in studying high-energy phosphate metabolism, phospholipid metabolism and cerebral biogenetics in the human at both normal and diseased states noninvasively. Finally, the approach used in this study for calculating in vivo 31P MRS sensitivity provides a general tool in estimating the relative NMR detection sensitivity for any nuclear spin at a given field strength.