Neuron-specific deficits of bioenergetic processes in the dorsolateral prefrontal cortex in schizophrenia

Abstract

Schizophrenia is a devastating illness that affects over 2 million people in the United States and costs society billions of dollars annually. New insights into the pathophysiology of schizophrenia are needed to provide the conceptual framework to facilitate development of new treatment strategies. We examined bioenergetic pathways in the dorsolateral prefrontal cortex (DLPFC) of subjects with schizophrenia and control subjects using western blot analysis, quantitative real-time polymerase chain reaction, and enzyme/substrate assays. Laser-capture microdissection-quantitative polymerase chain reaction was used to examine these pathways at the cellular level. We found decreases in hexokinase (HXK) and phosphofructokinase (PFK) activity in the DLPFC, as well as decreased PFK1 mRNA expression. In pyramidal neurons, we found an increase in monocarboxylate transporter 1 mRNA expression, and decreases in HXK1, PFK1, glucose transporter 1 (GLUT1), and GLUT3 mRNA expression. These results suggest abnormal bioenergetic function, as well as a neuron-specific defect in glucose utilization, in the DLPFC in schizophrenia.

Figure 1

Region-level protein expression. Expression of lactate dehydrogenase (LDH), lactate dehydrogenase A (LDHA), lactate dehydrogenase B (LDHB), LDHA:LDHB, hexokinase 1 (HXK1), monocarboxylate transporter 1 (MCT1), and glucose transporter 3 (GLUT3) in the dorsolateral prefrontal cortex (DLPFC) of schizophrenia patients (SCZ) normalized to valosin-containing protein (VCP) and expressed as percent control (CTL) (A). Western blot representation of LDH, LDHA, LDHB, HXK1, MCT1 and VCP expression at predicted band weights in SCZ and CTL subjects (B) (n=16 per group). Data are expressed as mean ± SEM.

Figure 2

Enzyme activity. Lactate dehydrogenase (LDH), hexokinase (HXK), and phosphofructokinase (PFK) activity in the dorsolateral prefrontal cortex (DLPFC) in control subjects (CTL) and subjects with schizophrenia (SCZ) measured in nmoles nicotinamide adenine dinucleotide hydrate (NADH) over time (A, F, K). LDH, HXK, and PFK activity in rat prefrontal cortex (n=10 per group) treated with haloperidol-decanoate (28.5 mg kg−1) (HAL) or vehicle (CTL) for 9 months (B, G, L), and LDH, HXK, and PFK activity in rats simulating varying postmortem intervals (PMIs) expressed as percent of 0 hour PMI (E, J, O). Correlation of LDH, HXK, and PFK activity and pH (C, H, M) or PMI (D, I, N) in CTL subjects and subjects with SCZ. Data are expressed as mean ± SEM (n=16 per group).*P<0.05.

Figure 3

Substrate concentrations. Lactate (A) and G6P (E) concentration measured in the dorsolateral prefrontal cortex (DLPFC) of control subjects (CTL) and subjects with schizophrenia (SCZ) expressed as nmoles/μg protein. Lactate (B) and G6P (F) concentration in rat prefrontal cortex treated with haloperidol (HAL) or vehicle (CTL) for 9 months. Correlation of lactate (C) and G6P (G) concentration and pH in CTL subjects and subjects with SCZ. Correlation of lactate (D) and G6P (H) concentration and PMI in CTL subjects and subjects with SCZ. Data (A-F) are expressed as mean ± SEM (n=10 per group).

Figure 4

Relative expression levels of lactate dehydrogenase A (LDHA), LDHB, hexokinase 1 (HXK1), HXK2, phosphofructokinase (PFK), monocarboxylate transporter 1 (MCT1), MCT4, glucose transporter 1 (GLUT1), and GLUT3 transcripts in enriched pyramidal neuron populations from schizophrenia (SCZ) and control (CTL) subjects (A). Relative expression levels of HXK1, PFK1, MCT1, GLUT1, and GLUT3 transcripts in enriched pyramidal neuron populations from haloperidol and control treated rats (B). Data from pyramidal neuron enriched samples were normalized to the geometric mean of three housekeeping genes. Data are expressed as percent control ± SEM. *P<0.05.