A microfluidic culture platform for CNS axonal injury, regeneration and transport

Abstract

Investigation of axonal biology in the central nervous system (CNS) is hindered by a lack of an appropriate in vitro method to probe axons independently from cell bodies. Here we describe a microfluidic culture platform that polarizes the growth of CNS axons into a fluidically isolated environment without the use of targeting neurotrophins. In addition to its compatibility with live cell imaging, the platform can be used to (i) isolate CNS axons without somata or dendrites, facilitating biochemical analyses of pure axonal fractions and (ii) localize physical and chemical treatments to axons or somata. We report the first evidence that presynaptic (Syp) but not postsynaptic (Camk2a) mRNA is localized to developing rat cortical and hippocampal axons. The platform also serves as a straightforward, reproducible method to model CNS axonal injury and regeneration. The results presented here demonstrate several experimental paradigms using the microfluidic platform, which can greatly facilitate future studies in axonal biology.Neurons in the CNS extend axons over considerable distances and through varying extracellular microenvironments to form synapses, the basis of neuronal connectivity. Axonal damage is critical to the etiology of CNS injuries and neurodegenerative disease (for example, spinal cord injury and Alzheimer disease) 1-3 ; therefore, considerable effort focuses on the molecular and cellular mechanisms that influence axonal plasticity and response to injury. In vitro models facilitate the study of axonal biology in the peripheral nervous system (PNS), but no suitable method has been developed for the study of the CNS because of the challenges associated with culturing CNS neurons.In vitro studies using compartmentalized 'Campenot' chambers have greatly improved the understanding of axonal biology within the PNS 4-6 . Campenot chambers use a compartmented Teflon divider attached to a collagen-coated petri dish via a thinly applied silicone grease layer; typically nerve growth factor (NGF) promotes neuritic growth through the grease layer. Much of the work involving Campenot chambers focused on the influence and transport of NGF.

Microfluidic construction of minimalistic neuronal co-cultures

“…A great strength of compartmentalized neuronal co-culture systems is the ability to selectively treat cell or outgrowth compartments, 11,39 making fluidic isolation in the CNA systems a pre-requisite for general applicability. Although apparently trivial, this requires pressures and flow rates to be precisely balanced throughout the period of treatment.…”

“…Arrayed and disentangled neurite outgrowths provide a useful analytical display, [6][7][8] and the compartmentalized arrangement also brings the opportunity for selectively treating or isolating the soma or outgrowths for off-chip analysis. 11,12 These systems have been used to great effect to study axon degeneration and regeneration following chemical 12,13 or laser [13][14][15] axotomy, tauopathy 16 and viral 17,18 dissemination, and mRNA localization in axons. 11 The systems have also been adapted for engineering the polarity of the synaptic junction using geometric diodes 19 or for synaptogenesis screening using HEK293 cells disguised as post-synaptic structures by recombinant decoration with neurolignin-1.…”

Surface Coating as a Key Parameter in Engineering Neuronal Network Structures In Vitro

“…The development of polarized morphology follows cell adhesion, and continues for days and weeks before maturation, introducing additional challenges for engineering the neurites after the establishment of the patterns of adhesion. Microfluidics [33][34][35][36] has been used for positioning neuronal somata. However, culturing neurons within microfluidic chips over long terms is a challenge, possibly due to limited nutrient exchange.…”

Somatic and axonal LIGHT signaling elicit degenerative and regenerative responses in motoneurons, respectively

“…Microfluidic devices were prepared as described in [10]. Axonal length and branching were determined in 50-100 neurons per condition from triplicate wells per experiment and from at least three independent experiments.…”