A reduced number of cortical neurons show increased Caldendrin protein levels in chronic schizophrenia

Caldendrin is a neuronal calcium sensor protein that is tightly associated with the postsynaptic density (PSD) of excitatory synapses. It has an established role in synapto-dendritic Ca2+-signaling as a multifunctional regulator of intracellular Ca2+ levels. Previous work has shown that expression levels of protein components involved in signaling processes at excitatory synapses are significantly altered in the brains of schizophrenic patients. Furthermore, it is widely accepted that synaptic pathology associated with the glutamatergic N-methyl-d-aspartate (NMDA) receptor is a feature of the disease. Here we report that in postmortem brains of chronic schizophrenics (N: 12) as compared to age-and sex-matched controls (N: 12) the number of Caldendrin-immunoreactive neurons are significantly reduced in the left dorsolateral prefrontal cortex, a brain region prominently associated with schizophrenia. Less dramatic changes were observed in other cortical regions. However, despite the reduced number of immunoreactive neurons, absolute Caldendrin protein levels were elevated and no change in Caldendrin PSD-levels were observed as compared to the left dorsolateral prefrontal cortex in the normal human brain. Thus, synapto-dendritic Ca2+-signaling via Caldendrin is altered in schizophrenic patients by a redistribution of the protein into a lower number of pyramidal neurons, which express higher Caldendrin levels. Since Caldendrin is a multivalent regulator of voltage dependent Ca2+-channels and Ca2+-release channels the loss of Caldendrin mediated synapto-dendritic Ca2+-signaling processes in some neurons together with its concurrent upregulation in others should profoundly change their synapto-dendritic Ca2+-signaling. These observations add to existing evidence for a de-regulation of neuronal Ca2+-signaling in schizophrenia.