gms | German Medical Science

Objective: The small-conductance calcium activated K+ channel KCa2.3 has a fundamental role in regulating neuronal excitability. Its involvement in central nervous system disorders and cell migration of tumor has been reported. Increased channel activity, as modelled by KCa2.3 overexpression in mice, leads to deficits associated with cognitive performance and to a bilateral reduction of the hippocampal area. Microglia - the major components of the CNS immune system - are cellular mediators of neurodegenerative and neuroinflammatory processes. In an attempt to gain more insight in the cause of the hippocampal morphological changes, we performed microglia-neuron interaction studies.

Methods: Immunohistochemistry of brain sections was performed using differentiation and proliferation markers as NeuN and Ki67. Primary microglia cultures were prepared from the brain of KCa2.3 overexpressing mice and neuronal cultures from the hippocampus of wild type mice. The neurons cultured medium was replaced after day 5 with microglia conditioned medium in different concentrations (50 %, 25% or 10 %). Assessment of neuronal death is examined by evaluating changes in propidium iodide (PI) fluorescence. mRNA expression level of several genes in microglia was analyzed using qRT-PCR.

Results: Analysis of CA1 hippocampi region of KCa2.3 overexpressing mice revealed disperse neuronal organization. Co-localization analysis with NeuN and Ki67 showed a decrease in neuron proliferation. PI examination of wild type neuronal culture incubated with microglia-conditioned showed that there was no significant difference in neuronal death between the cultures of neurons incubated with the KCa2.3 overexpressing microglia conditioned or control medium. Nonetheless, expression analysis showed that microglia isolated from KCa2.3 overexpressing mice have an increased mRNA level of glutamate receptor Grm1 and chemokine receptor CXCR3.

Conclusion: Interruption of the neuronal layer continuity observed in CA1 region of hippocampus is probably not due to the changes in microglia. Considering the fact that microglia may also support neuronal survival, further examinations is needed. One step in this direction is the detected increase of Grm1 expression. It is possible that its increase could reduce a potentially neurotoxic export of glutamate. Detected increase in CXCR3 gives an important hint for changes in microglia recruitment, which is an essential element for neuronal reorganization.