A2: PROJ 2: NEUROGENESIS IN THE ADULT BRAIN: ROLE OF BASAL LAMINA NETWORK

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The major goal of this project is to identify the mechanisms leading to neural stem cell proliferation and differentiation in the neurogenic niche of adult brain. We recently characterized by confocal and transmission electron microscopy specialized basal lamina labyrinths (fractones) that directly contact neural progenitor cells and neural stem cells in the neurogenic niche (Mercier et al., 2002; 2003). Our hypothesis is that fractones are sites of extracellular matrix/growth factor interactions that ultimately trigger proliferation and differentiation of abutting neural stem cells. Last year we reported that fractones contain ubiquitous extracellular matrix components of basal laminae such as collagen IV, laminin gamma-1 and beta-1, nidogen, and the heparan sulfate proteoglycan (HSPG) perlecan. Perlecan is a high affinity binder and activator of the heparin-binding growth factor fibroblast growth factor-2 (FGF-2). Our working hypothesis for this year was that fractones capture heparin-binding growth factors to trigger neurogenesis. We studied the binding activity of FGF-2, amphiregulin (AR), and heparin-binding epidermal growth factor (HB-EGF), three powerful neurogenic factors. After biotinylation, each growth factor was either incubated on frozen sections of the adult rat brain (in situ binding), or introduced in vivo by intracerebroventricular injection (in vivo binding). Using both methods, we demonstrated that FGF-2 and AR strongly and exclusively bind to fractones. In contrast, the diffuse binding sites of HB-EGF in the ventricle walls indicated that HB-EGF regulates stem cell fate by means that do not involve fractone binding. The binding of FGF-2 and AR to fractones is highly important for the neural stem cell field, revealing for the first time a mechanism by which growth factors trigger stem cell activation in the neurogenic niche. Future research will focus on identifying fractone HSPG and other molecules that bind to FGF-2, and the precise mechanisms by which these molecules interact to trigger neural stem cell activation. Understanding the mechanisms occurring in the neural stem cell niche will permit to accurately design stem cell therapies for neurotrauma and neurodegenerative diseases.