Adenosine Metabolism Pathway Alterations in Frontal Cortical Neurons in Schizophrenia

Abstract

Schizophrenia is a neuropsychiatric illness characterized by altered neurotransmission, in which adenosine, a modulator of glutamate and dopamine, plays a critical role that is relatively unexplored in the human brain. In the present study, postmortem human brain tissue from the anterior cingulate cortex (ACC) of individuals with schizophrenia (n = 20) and sex- and age-matched control subjects without psychiatric illness (n = 20) was obtained from the Bronx-Mount Sinai NIH Brain and Tissue Repository. Enriched populations of ACC pyramidal neurons were isolated using laser microdissection (LMD). The mRNA expression levels of six key adenosine pathway components-adenosine kinase (ADK), equilibrative nucleoside transporters 1 and 2 (ENT1 and ENT2), ectonucleoside triphosphate diphosphohydrolases 1 and 3 (ENTPD1 and ENTPD3), and ecto-5'-nucleotidase (NT5E)-were quantified using real-time PCR (qPCR) in neurons from these individuals. No significant mRNA expression differences were observed between the schizophrenia and control groups (p > 0.05). However, a significant sex difference was found in ADK mRNA expression, with higher levels in male compared with female subjects (Mann-Whitney U = 86; p < 0.05), a finding significantly driven by disease (t₍₁₇₎ = 3.289; p < 0.05). Correlation analyses also demonstrated significant associations (n = 12) between the expression of several adenosine pathway components (p < 0.05). In our dementia severity analysis, ENTPD1 mRNA expression was significantly higher in males in the "mild" clinical dementia rating (CDR) bin compared with males in the "none" CDR bin (F_{(2, 13)} = 5.212; p < 0.05). Lastly, antipsychotic analysis revealed no significant impact on the expression of adenosine pathway components between medicated and non-medicated schizophrenia subjects (p > 0.05). The observed sex-specific variations and inter-component correlations highlight the value of investigating sex differences in disease and contribute to the molecular basis of schizophrenia's pathology.

Keywords: adenosine kinase; anterior cingulate cortex; ecto-5′-nucleotidases; ectonucleoside triphosphate diphosphohydrolases; equilibrative nucleoside transporters; neuromodulation; pyramidal neurons; schizophrenia.

Figure 1

Expression of adenosine metabolism pathway components in an enriched population of anterior cingulate cortex (ACC) pyramidal neurons in control (CTL) vs. schizophrenia (SCZ) subjects. (A) ADK, (B) ENT1, (C) ENT2, (D) ENTPD1, (E) ENTPD3, and (F) NT5E mRNA expression levels were not significantly different between CTL and SCZ subjects. Open circles indicate females; closed circles indicate males. n = 11–19/group. Data are presented as means ± standard errors of the means (SEMs).

Figure 2

Expression of adenosine kinase (ADK) in an enriched population of anterior cingulate cortex (ACC) pyramidal neurons in female vs. male subjects. (A) ADK mRNA expression was significantly higher in male compared with female SCZ and CTL subjects combined. (B) ADK mRNA expression was significantly higher in male compared with female SCZ subjects only. (C) ADK mRNA expression was not significantly different between female and male CTL subjects only. Open circles indicate females; closed circles indicate males. n = 7–22/group. Data presented as means ± standard errors of the means (SEMs). * p < 0.05. ** p < 0.005.

Figure 3

Spearman’s correlation analyses between adenosine kinase (ADK) and equilibrative nucleoside transporters 1 (ENT1) and 2 (ENT2). Significant negative associations were observed between (A) ADK and ENT1 mRNA expression and between (B) ADK and ENT2 mRNA expression across all schizophrenia and control subjects. n = 38/group. * p < 0.05.

Figure 4

Spearman’s correlation analyses between ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1) and 3 (ENTPD3) and ecto-5′-nucleotidase (NT5E). Significant positive associations were observed between (A) ENTPD1 and ENTPD3 mRNA expression, between (B) ENTPD1 and NT5E mRNA expression, and between (C) ENTPD3 and NT5E across all schizophrenia and control subjects. n = 26–38/group. * p < 0.05.

Figure 5

Spearman’s correlation analyses between equilibrative nucleoside transporters 1 and 2 (ENT1 and ENT2) and ectonucleoside triphosphate diphosphohydrolases 1 and 3 (ENTPD1 and ENTPD3). Significant positive associations were observed between (A) ENT1 and ENTPD1 mRNA expression, between (B) ENT1 and ENTPD3 mRNA expression, between (C) ENT2 and ENTPD1 mRNA expression, and between (D) ENT2 and ENTPD3 mRNA expression across all schizophrenia and control subjects. n = 29–38/group. * p < 0.05.

Figure 6

Spearman’s correlation analyses between equilibrative nucleoside transporters 1 (ENT1) and 2 (ENT2) and 5′-nucleotidase ecto (NT5E). Significant positive associations were observed between (A) ENT1 and ENT2 mRNA expression, between (B) ENT1 and NT5E mRNA expression, and between (C) ENT2 and NT5E across all schizophrenia and control subjects. n = 26–38/group. * p < 0.05.

Figure 7

Expression of ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1) in an enriched population of anterior cingulate cortex (ACC) pyramidal neurons in control and schizophrenia subjects binned according to clinical dementia rating (CDR) scores. (A) ENTPD1 mRNA expression was not significantly different across CDR bins. (B) ENTPD1 mRNA expression was not significantly different across CDR bins in female subjects. (C) ENTPD1 mRNA expression was significantly higher in the “mild” CDR bin compared with the “none” CDR bin in male subjects (F_{(2, 13)} = 5.212; p = 0.022). Open circles indicate females; closed circles indicate males. n = 3–12/group. * p < 0.05.