Study of Spinal Muscular Atrophy in a Human Neuromuscular Junction Three-Dimensional Optogenetic Model

Topic Area: Spinal Muscular Atrophy.

Area of Encouragement: Research into phenotyping the spinal muscular atrophy disease state.

Spinal muscular atrophy (SMA) is degenerative genetic disease that causes progressive muscular weakness and movement impairment, and it's the most common genetic cause of infant deaths. It affects one in 6,000-10,000 newborns, and there is currently only one drug approved for its treatment. It is known that SMA is caused by a deficiency of the survival of motoneuron protein (SMN), but the exact mechanism of action of this protein remains undetermined.

There is evidence that the fist manifestations of SMA occur at the neuromuscular junctions (NMJ), the synapses between motoneurons and skeletal muscle fibers. Unfortunately, studying NMJs in human is very challenging, especially at early stages of the disease, not only due the difficulties to access and visualize the synapses but also because of the advanced state of the disease upon diagnosis.

Our proposal seeks to study SMA in a laboratory setting, by growing muscular tissue and motoneurons in a custom-made device that will allow for the formation of NMJs. In a first approach, the cells will be derived from SMA patient biopsies and then modified to express a light-sensitive protein, allowing us to activate the NMJ using blue light, which will cause contraction of the miniaturized muscle. We will use this strategy to compare the behavior of the neuromuscular synapses generated from SMA patients and healthy controls over time.

In the second approach, we will recreate the disease in healthy cells by manipulating the expression of the SMN protein. Using gene-editing tools, we will be able to reduce the amount of SMN in the cell at a specific time. We will use these cells in the same system explained above to repress the SMN proteins during different stages of NMJ development to identify the vulnerable window for patients with SMA.

The results of our study will allow us to gain a better understanding of the mechanism underlying the first stages of the SMA disease and the role of the SMN protein. Furthermore, this will be the first system that will allow us to generate functional data from human tissues afflicted by SMA as opposed to animal models, which will greatly accelerate the process of drug discovery and treatment.