Mitogen-activated protein kinases in schizophrenia

Background: Mitogen-activated protein kinases (MAPKs) are important mediators of signal transduction from the cell surface to the nucleus and have been implicated in the integration of a variety of physiologic processes in most cells, including neurons. To investigate the possible involvement of MAPKs in schizophrenia, we compared the levels of the MAPK intermediates in postmortem brain tissue obtained from schizophrenic and control subjects. Our focus was on the cerebellar vermis because of evidence suggesting that schizophrenia is associated with abnormalities of structure, function, and signal transduction in this brain region. Methods: Cytosolic proteins were fractionated by gel electrophoresis and subjected to Western blot analysis using polyclonal MAPK antibody, which detects total extracellular signal-regulated kinases (ERKs) 1 and 2 levels, and monoclonal MAP kinase phosphatase (MKP) 2 antibody. Results: Schizophrenic subjects had increased levels of ERK2 [2763 ± (SD) 203 vs. 2286 ± 607 arbitrary units, U = 17, p< .05] in cerebellar vermis. The levels of a dual specificity tyrosine phosphatase, MKP2, were significantly decreased in cerebellar vermis (1716 ± 465 versus 2372 ± 429 arbitrary units, U = 12, p< .02) from schizophrenic patients. ERK1/MKP2 and ERK2/MKP2 ratios in cerebellar vermis, but not in other brain regions, were significantly different in schizophrenic subjects as compared to control subjects (U = 15, p ≤ .027; U = 3, p< .001, respectively). Conclusions: MAPK levels are elevated in the cerebellar vermis of schizophrenic subjects. This could result from a protein dephosphorylation defect in vivo and might be involved in the pathology of the disease.