Spatial aspects of GDNF functions revealed in a compartmentalized microfluidic neuromuscular co-culture system

Bidirectional molecular communication between the motoneuron and the muscle is vital for neuromuscular junction (NMJ) formation and maintenance. The molecular mechanisms underlying such communication are of keen interest and may provide new targets for intervention in motor neuron disease. Here we developed a microfluidic platform with motoneuron (MN) cell bodies on one side and muscle cells on the other, connected via motor axons extending through microgrooves to form functional NMJs. Using this system, we were able to differentiate between the proximal and distal effects of oxidative stress and Glial Derived Neurotrophic Factor (GDNF), demonstrating a dying-back degeneration and retrograde transmission of pro-survival signaling, respectively. Furthermore, we show that GDNF acts differently on MN axons versus soma, promoting axonal growth and innervation only when applied locally to axons. Finally, we track for the first time the retrograde transport of secreted GDNF from muscle to neuron. Thus, our data suggests spatially distinct effects of GDNF: facilitating growth and muscle innervation at axon terminals, and survival pathways in the soma.