Brain-derived neurotrophic factor (BDNF) promotes molecular polarization and differentiation of immature neuroblastoma cells into definitive neurons

Abstract Throughout development, neuronal progenitors undergo complex transformation into polarized nerve cells, warranting the directional flow of information in a neural grid. The majority of neuronal polarization studies have been carried out on rodent-derived precursor cells, programmed to develop into neurons. Unlike these rodent neuronal cells, SH-SY5Y cells derived from human bone marrow present a sub-clone of neuroblastoma line, with transformation into neuron-like cells showing a range of highly instructive neurobiological characteristics. We applied two-step retinoic acid (RA) and brain-derived neurotrophic factor (BDNF) protocol to monitor the conversion of undifferentiated SH-SY5Y cells into neuron-like cells with distinctly polarized axon-dendritic morphology and formation of bona fide synaptic connections. We show that BDNF is a key driver and regulator of the expression of axonal marker tau and dendritic microtubule-associated protein-2 (MAP2), with their sorting to distinct cellular compartments. Using selective kinase inhibitors downregulating BDNF-TrkB signaling, we show that constitutive activation of TrkB receptor is essential for the maintenance of established polarization of SH-SY5Y cells. Importantly, the proximity ligation assay applied in our preparation demonstrates that differentiating neuron-like cells develop elaborate synaptic connections enriched with hallmark pre- and postsynaptic proteins. Described herein observations highlight several fundamental processes related to neuronal polarization and synaptogenesis in human-derived cells, which are of major relevance to neuronal biology, neurodevelopment, and translational neuroscience.