Abstract
ABSTRACTBidirectional 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 could provide new targets for intervention in motoneuron disease. Here, we developed a microfluidic platform with motoneuron cell bodies on one side and muscle cells on the other, connected by 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 motoneuron 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.
Highlights
Motoneurons extend axons over long distances and through varying extracellular microenvironments to form synapses with muscles
Co-culture of muscle and motoneurons in a microfluidic chamber To study spatial and temporal processes occurring at the neuromuscular junction (NMJ) sites compared to the cell body site, and the bidirectional communication between neurons and muscle, we used the compartmental microfluidic system (Park et al, 2006) to create an optimized compartmental motoneuron–muscle platform
We examined the role of glial-derived neurotrophic factor (GDNF), a neurotrophic factor known to promote motoneuron survival, taking advantage of the microfluidic culture to assess the spatial aspects of GDNF pro-survival signaling
Summary
Motoneurons extend axons over long distances and through varying extracellular microenvironments to form synapses with muscles. Studies on NMJs have shed light on some central signaling pathways and principles of synapse assembly (Shi et al, 2012; Sanes and Lichtman, 1999). Much of the difficulty in deciphering these mechanisms is due to the technical challenges of studying these complex intra- and extracellular communications at the subcellular level.
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