Na+, K+-ATPase α3 isoform in frontal cortex GABAergic neurons in psychiatric diseases.

Na+, K+-ATPase is an essential membrane transporter. In the brain, the α3 isoform of Na+, K+-ATPase is vital for neuronal function. The enzyme and its regulators, endogenous cardiac steroids (ECS), were implicated in neuropsychiatric disorders. GABAergic neurotransmission was also studied extensively in diseases such as schizophrenia and bipolar disorder (BD). Post mortem brain samples from subjects with depression, schizophrenia or BD and non-psychiatric controls were provided by the Stanley Medical Research Institute. ECS levels were determined by ELISA. Expression levels of the three Na+, K+-ATPase-α isoforms, α1, α2 and α3, were determined by Western blot analysis. The α3 levels in GABAergic neurons in different regions of the brain were quantified by fluorescence immunohistochemistry. The results show that Na+, K+ -ATPase α3 isoform levels were lower in GABAergic neurons in the frontal cortex in BD and schizophrenia as compared with the controls (n = 15 subjects per group). A study on a 'mini-cohort' (n = 3 subjects per group) showed that the α3 isoform levels were also lower in GABAergic neurons in the hippocampus, but not amygdala, of bipolar and schizophrenic subjects. In the temporal cortex, higher Na+, K+ -ATPase α3 protein levels were found in the three psychiatric groups. No significant differences in ECS levels were found in this brain area. This is the first report on the distribution of α3 in specific neurons in the human brain in association with mental illness. These results strengthen the hypothesis for the involvement of Na+, K+ -ATPase in neuropsychiatric diseases.