Cell-specific expression of Epac2 in the subventricular and subgranular zones

Aim: cAMP signal transduction cascade activation is important in regulating neurogenesis in adult rodents by increasing the proliferation of newborn cells. Although the ventricular-subventricular zone (V-SVZ) and subgranular zone (SGZ) both contain large populations of neural stem/precursor cells; it remains unclear whether an alternative target of cAMP, the exchange protein directly activated by cAMP (Epac2), is involved in adult neurogenesis in the V-SVZ and SGZ. Here, we investigated the cell-specific expression of Epac2 protein in the V-SVZ and SGZ of the adult mouse brain. Methods: Immunohistochemical analyses were performed using antibodies against Epac2, glial fibrillary acidic protein (GFAP), doublecortin (DCX), and beta-catenin, to examine the co-localization of Epac2 protein and neural stem/precursor cells in the V-SVZ and SGZ in three 8-week-old male mice. Results: In the V-SVZ of the lateral ventricle, most GFAP-positive adult neural stem cells (NSC, defined as type B cells) and 75% of DCX-positive migrating neuroblasts (type A cells) expressed Epac2 proteins. Ninety-three percent of beta-catenin-positive ependymal cells (type E cells), which are in direct contact with NSCs and the ventricles, also expressed Epac2 protein. Similarly, in the SGZ of the hippocampus, Epac2-immunopositive signals were shown by 83% of GFAP-positive radial-glia-like NSCs (type 1 cells), 86% of DCX-positive transiently amplifying cells (type 2 and type 3 cells), and 71% of DCX-positive immature neurons. The present data suggest that a PKA-independent cAMP signaling pathway via Epac2 may be party to adult neurogenesis in the V-SVZ and the SGZ.