SNAP-25a/b Isoform Levels in Human Brain Dorsolateral Prefrontal Cortex and Anterior Cingulate Cortex

Abstract

SNAP-25 is a neurotransmitter vesicular docking protein which has been associated with brain disorders such as attention deficit hyperactivity disorder, bipolar disorder and schizophrenia. In this project, we were interested if clinical factors are associated with differential SNAP-25 expression. We examined the SNAP-25 isoform mRNA and protein levels in postmortem cortex Brodmann's area 9 (BA9) and BA24 (n = 29). Subjects were divided by psychiatric diagnosis, clinical variables including mood state in the last week of life and lifetime impulsiveness. We found affected subjects with a diagnosis of alcohol use disorder (AUD) had a lower level of SNAP-25b BA24 protein compared to those without AUD. Hispanic subjects had lower levels of SNAP-25a, b and BA9 mRNA than Anglo-American subjects. Subjects who smoked had a total pan (total) SNAP-25 BA9/BA24 ratio. Subjects in the group with a low level of anxious-psychotic symptoms had higher SNAP-25a BA24 mRNA compared to normal controls, and both the high and low symptoms groups had higher pan (total) SNAP-25 BA9/BA24 ratios than normal controls. These data expand our understanding of clinical factors associated with SNAP-25. They suggest that SNAP-25 total and isoform levels may be useful biomarkers beyond limited neurological and psychiatric diagnostic categories.

Keywords: Alcohol dependence; Bipolar disorder; Ethnicity; Exocytosis; Molecular psychiatry; Prefrontal cortex; SNAP-25; Schizophrenia; Smoking; Synaptic neurobiology.

Fig. 1

Western blot of SNAP-25a and b protein isoforms BA9 and BA24. The two panels on the left are representative fluorescent scans of SNAP-25a protein blots, and the two panels on the right are representative scans of SNAP-25b blots. The top band is actin and the bottom band is SNAP-25. The upper two panels are samples from BA9, while the lower two panels are samples from BA24. Samples were run in duplicate, and their respective diagnosis is listed below each lane: BP, schizophrenia, control. Molecular weight markers (not shown) are labeled in the center, the 38-kDa band of the ladder appearing near the green sample bands (β-actin, molecular weight 42 kDa), and the 28-kDa band of the ladder appearing near the red sample bands (SNAP-25, molecular weight 25 kDa). Colors refer to the online version only.

Fig. 2

SNAP-25 pan (total) BA9/BA24 mRNA ratio and SNAP-25a BA9 protein level with smoking. a SNAP-25a BA9 protein relative immunointensity. b SNAP-25a BA9 protein relative immunointensity grouped by sex. c Pan (total) SNAP-25 BA9/BA24 mRNA ratio. d Pan (total) SNAP-25 BA9/BA24 mRNA ratio grouped by the affected (combined BP and schizophrenia) subjects and normal controls. Error bars = ±1 SD.

Fig. 3

SNAP-25b BA24 protein-relative immunointensity and symptom level in AUD. a SNAP-25b BA24 protein relative immunointensity. b Psychiatric symptom level at the end of life: Barratt (Barratt Impulsiveness Scale), BPRS (Brief Psychiatric Rating Scale), total BISS (total BISS score), depression (BISS depression factor score), mania (BISS factor score), irritability (BISS irritability factor score), anxiety (BISS anxiety factor score) and psychosis (BISS psychosis factor score). 1 = Significant difference (p < 0.05) between the normal control and AUD and between normal control and no AUD; 2 = significant difference (p < 0.05) between normal control and no AUD; 3 = significant difference (p < 0.05) between normal control and AUD. There were no significant differences in symptoms between the AUD and no AUD groups. Error bars = ±1 SD.

Fig. 4

Psychiatric symptoms, SNAP-25 mRNA and protein level in BP, schizophrenia and normal controls. a Psychiatric symptom level at the end of life: Barratt (Barratt Impulsiveness Scale), BPRS (Brief Psychiatric Rating Scale), total BISS (total BISS score), depression (BISS depression factor score), mania (BISS factor score), irritability (BISS irritability factor score), anxiety (BISS anxiety factor score) and psychosis (BISS psychosis factor score). 1 = Significant (p < 0.05) difference between normal control and BP, and between normal control and schizophrenia groups; 2 = significant difference (p < 0.05) between normal control and schizophrenia, and nonsignificant (p = 0.07) difference between normal control and BP; 3 = significant difference between normal control and BP, and nonsignificant difference (p = 0.06) between normal control and schizophrenia groups. Error bars = ±1 SD. b SNAP-25 mRNA levels. c SNAP-25 protein levels. d SNAP-25b/a BA24 protein and mRNA levels; SNAP-25b/a BA24 ratio, and pan (total) SNAP-25 mRNA BA9/BA24 ratio.

Fig. 5

SNAP-25 mRNA levels in subjects of Hispanic and Anglo-American origin. a SNAP-25a BA9. b SNAP-25b BA9. c SNAP-25a BA24. Error bars = ±1 SD.

Fig. 6

SNAP-25 mRNA pan (total) BA9/BA24 ratio and SNAP-25a BA24 mRNA in the combined BISS factor anxiety and psychosis groups. a SNAP-25 mRNA pan (total) BA9/BA24 ratio with subjects grouped by level of combined BISS factors anxiety and psychosis and normal control. b Same as in a, with subjects subgrouped by smoking status. c SNAP-25a BA24 mRNA with subjects grouped by level of combined BISS factors anxiety and psychosis and normal control. Error bars = ±1 SD.