A microfluidic platform to study the effects of GDNF on neuronal axon entrapment.

BACKGROUND: One potential treatment strategy to enhance axon regeneration is transplanting Schwann Cells (SCs) that overexpress glial cell line-derived neurotrophic factor (GDNF). Unfortunately, constitutive GDNF overexpression in vivo can result in failure of regenerating axons to extend beyond the GDNF source, a phenomenon termed the "candy-store" effect. Little is known about the mechanism of this axon entrapment in vivo. NEW METHOD: We present a reproducible in vitro culture platform using a microfluidic device to model axon entrapment and investigate mechanisms by which GDNF causes axon entrapment. The device is comprised of three culture chambers connected by two sets of microchannels, which prevent cell soma from moving between chambers but allow neurites to grow between chambers. Neurons from dorsal root ganglia were seeded in one end chamber while the effect of different conditions in the other two chambers was used to study neurite entrapment. RESULTS: The results showed that GDNF-overexpressing SCs (G-SCs) can induce axon entrapment in vitro. We also found that while physiological levels of GDNF (100 ng/mL) promoted neurite extension, supra-physiological levels of GDNF (700 ng/mL) induced axon entrapment. COMPARISON WITH EXISTING METHOD: All previous work related to the "candy-store" effect were done in vivo. Here, we report the first in vitro platform that can recapitulate the axonal entrapment and investigate the mechanism of the phenomenon. CONCLUSIONS: This platform facilitates investigation of the "candy-store" effect and shows the effects of high GDNF concentrations on neurite outgrowth.