Human motor units in microfluidic devices are impaired by FUS mutations and improved by HDAC6 inhibition

Summary Neuromuscular junctions (NMJs) ensure communication between motor neurons (MNs) and muscle; however, in MN disorders, such as amyotrophic lateral sclerosis (ALS), NMJs degenerate resulting in muscle atrophy. The aim of this study was to establish a versatile and reproducible in vitro model of a human motor unit to investigate the effects of ALS-causing mutations. Therefore, we generated a co-culture of human induced pluripotent stem cell (iPSC)-derived MNs and human primary mesoangioblast-derived myotubes in microfluidic devices. A chemotactic and volumetric gradient facilitated the growth of MN neurites through microgrooves resulting in the interaction with myotubes and the formation of NMJs. We observed that ALS-causing FUS mutations resulted in reduced neurite outgrowth as well as an impaired neurite regrowth upon axotomy. NMJ numbers were likewise reduced in the FUS-ALS model. Interestingly, the selective HDAC6 inhibitor, Tubastatin A, improved the neurite outgrowth, regrowth, and NMJ morphology, prompting HDAC6 inhibition as a potential therapeutic strategy for ALS.
Highlights • Human motor units with functional NMJs can be generated using microfluidic devices • FUS-ALS motor units display impaired neurite regrowth, outgrowth and NMJ numbers • HDAC6 inhibition alleviate FUS-ALS motor unit pathology in vitro
This study provides a novel model of a motor unit in microfluidic devices. Van Den Bosch and colleagues report how mutations in FUS causing amyotrophic lateral sclerosis (ALS) compromise the motor neuron neurite outgrowth, regrowth, and number of neuromuscular junctions. These findings were alleviated by selective HDAC6 inhibition prompting this approach as a therapeutic strategy for ALS.