Directed neural lineage differentiation of adult hippocampal progenitor cells via modulation of hippocampal cholinergic neurostimulating peptide precursor expression

Hippocampal cholinergic neurostimulating peptide (HCNP), originally purified from young rat hippocampus, has been known to promote the differentiation of septo-hippocampal cholinergic neurons. Recently, the precursor protein of HCNP (HCNP-pp) has also received attention as a multifunctional protein with roles, in addition to serving as the HCNP precursor, such as acting as an ATP-binding protein, a Raf kinase inhibitor protein (RKIP), and phosphatidylethanolamine-binding protein (PEBP). In particular, the function of RKIP has attracted attention over several years for its role in controlling cellular proliferation and metastasis in cancer cells. HCNP-pp is also thought to be important in regulating the proliferation and differentiation of neuronal cells in vitro and in vivo by modification of the MAPK cascade. In the present study, we used cultured adult rat hippocampal progenitor cells (AHPs), which are thought to be important for memory formation, and focused on the role of HCNP-pp in adult neurogenesis, namely, the production of new neurons from neural stem/progenitor cells. We found that HCNP-pp expression in AHPs was closely associated with differentiation into MAP2ab-positive neurons and RIP-positive oligodendrocytes, but not into GFAP-positive astrocytes. By contrast, a down-regulated HCNP-pp expression in AHPs accompanied differentiation into GFAP-positive astrocytes. Direct manipulations of HCNP-pp via viral over-expression or siRNA downregulation further confirmed the HCNP-pp contribution to specific neural lineage commitment of AHPs. Our results show that the expression level of HCNP-pp acts as a key regulator for differentiation of cultured AHPs into specific neural lineages, indicating that the control of neural stem cell fate can be achieved via the HCNP-pp pathway.