Reduction of synapsin in the hippocampus of patients with bipolar disorder and schizophrenia.

Several studies suggest that decreased expression of presynaptic proteins may be characteristic of schizophrenia. We examined one such protein, synapsin, in schizophrenia and bipolar disorder. Samples of hippocampal tissue from controls (n = 13), patients with schizophrenia (n = 16), or bipolar disorder (n = 6), and suicide victims (n = 7) were used. The membrane and cytosolic fractions were analyzed by Western immunoblotting for synapsin using an antibody that detects synapsin Ia, IIa, and IIIa proteins. Synaptophysin was also measured for comparison. Total synapsin was decreased significantly in patients with schizophrenia (P = 0.034) and in bipolar disorder (P = 0.00008) as compared to controls. The synapsin/synaptophysin ratios were decreased in schizophrenia and bipolar disorder, and additionally in suicide victims (P = 0.014). Age, postmortem interval, percentage of protein extracted, and pH of brain were not different between groups. No changes in total synapsin or synaptophysin in the hippocampus were produced by injecting rats with either lithium or haloperidol for 30 days. Reductions in synapsin in both patients with schizophrenia (synapsin IIa and IIIa) and bipolar disorder (synapsin Ia, IIa and IIIa) imply that altered or reduced synaptic function in the hippocampus may be involved in these disorders.

Characterization of human cleaved N-CAM and association with schizophrenia.

The neural cell adhesion molecule (N-CAM) is a cell recognition molecule involved in cellular migration, synaptic plasticity, and CNS development. A 105- to 115-kDa isoform of N-CAM (cleaved N-CAM or cN-CAM) is increased in schizophrenia in hippocampus, prefrontal cortex, and CSF. We purified and partially characterized cN-CAM, a putative novel isoform, and confirmed that the first 9 amino acids were identical to exon 1 of N-CAM, without the signal sequence. Analysis of trypsin-digested cN-CAM fragments by matrix-assisted laser desorption ionization on a time-of-flight mass spectrometer (MALDI-TOF) yielded peptides that could be identified as being derived from the first 548 amino acid residues of the expected N-CAM amino acid sequence. Immunological identification with four specific N-CAM antisera directed toward cytoplasmic, secreted, variable alternative spliced exon, or GPI epitopes failed to indicate other known splice variants. Neuraminidase treatment of cN-CAM produced a minor alteration resulting in a faster migrating immunoreactive band, indicating partial glycosylation of cN-CAM. Membranous particles from cytosolic brain extract containing cN-CAM were obtained by ultracentrifugation; however, CSF contained few such particles. cN-CAM and synaptophysin were colocalized on these particles. Both cN-CAM and N-CAM 180 were present in synaptosomal preparations of human brain. Following incubation of synaptosomes or brain tissue without protease inhibitors, N-CAM 180 was degraded and cN-CAM was increased. A cN-CAM-like band was present in human fetal neuronal cultures, but not in fetal astrocyte cultures. Thus, cN-CAM represents a protease- and neuraminidase-susceptible fragment possibly derived by proteolytic cleavage of N-CAM 180. An enlargement in ventricular volume in a group of adult patients with schizophrenia over a 2-year interval was found to be correlated with CSF cN-CAM levels as measured at the time of the initial MRI scan (r = 0.53, P = 0.01). cN-CAM is associated with ventricular enlargement; thus, the release of N-CAM fragments may be part of the pathogenic mechanism of schizophrenia in vulnerable brain regions such as the hippocampus and prefrontal cortex. Alternatively, the increases in cN-CAM in schizophrenia may be a reflection of a more general abnormality in the regulation of proteolysis or of extracellular matrix stability.

Elevated concentration of N-CAM VASE isoforms in schizophrenia.

Neural cell adhesion molecule (N-CAM) is a cell recognition molecule, four major isoforms (180, 140, 120, and 105-115 kDa) of which are present in brain. N-CAM has several roles in cellular organization and CNS development. Previously we have found an elevation in CSF N-CAM 120 kDa in the CSF of patients with schizophrenia, bipolar disorder, and depression. We now report an increase in the variable alternative spliced exon (VASE), a 10 amino acid sequence inserted into the fourth N-CAM domain, in the CSF of patients with schizophrenia, but not in bipolar disorder or depression. VASE-immunoreactive (VASE-ir) bands were measured in CSF from patients with schizophrenia (n = 14), bipolar disorder I (n = 7), bipolar disorder II (n = 9), unipolar depression (n = 17) and matched controls (n = 37) by Western immunoblotting. Three VASE-ir bands were distinguished in lumbar CSF corresponding to heavy (165 kDa), medium (155 kDa) and low (140 kDa) MW. A logarithmic transformation was applied to the VASE protein units and analyzed with a MANOVA. There was a 51% and 45% increase in VASE heavy (p = 0.0008) and medium (p = 0.04) MW protein, respectively, in patients with schizophrenia as compared with normal controls. Current neuroleptic treatment in patients with schizophrenia had no effect on CSF VASE concentrations. VASE concentration correlated significantly with behavioral ratings in patients with schizophrenia but not affective disorders. Thus, VASE immunoreactivity is increased in schizophrenia but not in affective disorders. These results provide further evidence of an abnormality of N-CAM protein in chronic schizophrenia and suggest differences between schizophrenia and affective disorders in regulation of N-CAM.