Overexpression of calbindinD28K increases hippocampal neurogenesis,a form of structural plasticity,via a CaMKII-and neuroD-involved pathway.

Abstract

The effects of calbindin, a calcium binding protein, on adult hippocampal neurogenesis were investigated. We overexpressed calbindin in primary hippocampal progenitor cell cultures using a plasmid transfection and a retroviral vector system. Overexpression of calbindin in hippocampal neural progenitor cells resulted in significant increases in the length of primary neurites and the total extent of neurites. The average neurite length of calbindin-transfected cells was 62% longer than that of control vector-transfected cells. We also found that calbindin overexpression increased neuronal differentiation over astrocytic differentiation and this was accompanied by a dramatic increase in NeuroD mRNA expression. Analysis of immunoblots revealed that this morphological differentiation was accompanied by the increased expressions of markers for neuronal maturation and activity such as MAP2 and p-CaMKII. Treatment of calbindin-overexpressed cells with KN62, a CaMKII inhibitor, completely blocked the increase in the expression of NeuroD mRNA. These results suggest that calbindin increases not only neurite outgrowth but also neuronal differentiation via CaMKII- and NeuroD-mediated pathway in hippocampal neurogenesis. To confirm the role of calbindin as a neurogenic factor, we attempted to block the synthesis of calbindin by RNA interference in the calbindin-overexpressing cells and the results will be discussed.