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.
Vawter
M P
MP
Development and Plasticity Section, Cellular Neurobiology Research Branch, National Institute on Drug Abuse, 5500 Nathan Shock Drive, Baltimore, Maryland 21224, USA.
Usen
N
N
Thatcher
L
L
Ladenheim
B
B
Zhang
P
P
VanderPutten
D M
DM
Conant
K
K
Herman
M M
MM
van Kammen
D P
DP
Sedvall
G
G
Garver
D L
DL
Freed
W J
WJ
D000328:Adult; D017398:Alternative Splicing; D001921:Brain / Q000378:metabolism; D002478:Cells, Cultured; D002555:Cerebrospinal Fluid / Q000737:chemistry; D000939:Epitopes / Q000378:metabolism; D005260:Female; D006031:Glycosylation; D006801:Humans; D007106:Immune Sera / Q000378:metabolism; D008297:Male; D019006:Neural Cell Adhesion Molecules / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009439:Neuraminidase / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012559:Schizophrenia / Q000378:metabolism*; D020539:Sequence Analysis, Protein; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013347:Subcellular Fractions / Q000737:chemistry; D013574:Synaptosomes / Q000737:chemistry / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
D000939:Epitopes; D007106:Immune Sera; D019006:Neural Cell Adhesion Molecules; D010446:Peptide Fragments; D020033:Protein Isoforms; D009439:Neuraminidase; D014357:Trypsin