Direct and cell signaling-based, geometry-induced neuronal differentiation of neural stem cells

Neural Stem Cells (NSCs) are multipotent precursors inhabiting the subventricular and hippocampal subgranular regions of the adult mammalian brain, able to self-renew and differentiate into neurons, astrocytes, and oligodendrocytes, the three primary neural cell types of the adult brain. NSC fate is influenced by the physical and chemical microenvironment experienced by the cell, both in vitro and in vivo. Towards characterizing the influence of topographical, geometric cues on NSC fate, we fabricated highly aligned, single- and double-layer polystyrene nanofiber meshes. Seeding of NSCs on laminin-coated fibers induces polarized NSC morphology and cellular elongation in the directions of fiber alignment, with cells extending membranous processes over hundreds of microns along the fiber surfaces. Additionally, these aligned fiber substrates promote neuronal lineage specification of NSCs with an efficiency of 82.3 ± 11.1% within days of seeding. Moreover, not only do cells on fibers yield neurons, but also neighboring cells in close proximity to those differentiating on aligned fibers, with an efficiency of 72.8 ± 9.7%. This neighboring, cell-induced differentiation occurs without cell-cell contact over millimetres away from the fibers, suggesting a paracrine signaling effect not previously reported for NSCs undergoing neurogenesis. In contrast, NSCs farther away from these fiber substrates nearly uniformly yield glia.