Neuromuscular organoids - faster, please!

Researchers can use neuromuscular organoids to investigate the mechanisms of serious neuromuscular diseases and to test drugs. Dr. Mina Gouti's team at the Max Delbrück Center has developed these three-dimensional tissue models from human stem cells. The scientists now want to find out how they can accelerate the maturation of the organoids.

How does a ballerina's big toe effectively support her entire body on its tip? Or what causes the esophagus to make the wave-like movements with which it transports food from the mouth to the stomach? The impulses for these processes originate in the brain. The fact that they reach the muscles and are translated into movements is facilitated by motor neurons, which constantly transmit signals from the brain to all regions of the body.

However, in neuromuscular diseases such as amyotrophic lateral sclerosis (ALS) or spinal muscular atrophy (SMA), the motor neurons die and the flow of signals comes to a standstill. The consequences can be seen in muscle weakness or atrophy, movement disorders and difficulties with speaking, swallowing or breathing. There is currently no cure for either disease. Current therapies aim to alleviate the symptoms and slow down the progression of the disease.

The neuromuscular junction in the Petri dish

Researchers around the world are looking for new treatment approaches. To investigate the disease mechanisms of ALS and SMA, they often use genetically modified mice. The animals carry a mutation that can cause the same or similar disease characteristics as in the human forms of ALS or SMA. The researchers also develop and test potential treatments using animal models. It is important to note, however, that findings from animal experiments cannot be directly extrapolated to humans. After all, a human is not a mouse.

“In order to gain new insights into the complex mechanisms of these serious diseases, we need complex human models," says Dr. Mina Gouti. She is the head of the “Stem Cell Modeling of Development and Disease” working group at the Max Delbrück Center. Together with her team, she has developed neuromuscular organoids, tiny three-dimensional tissue cultures that make the interaction of nerve and muscle cells in the Petri dish comprehensible. To achieve this, she used a mix of nutrients and growth factors to induce human stem cells to differentiate into the various motor neurons and skeletal muscle cells of the neuromuscular system. Her organoids are the first in the world in which two tissue types - nerve and muscle fibers - arise from the same precursor cells. As it is the case in the human body, the motor neurons and muscle cells are connected via synapses, and the motor neurons cause the muscle cells to contract and relax. These contractions are even visible under the microscope: the bean-shaped organoid pulsates like a small jellyfish. “We can use this model to understand which cell type is damaged first in the course of a disease,” says Mina Gouti. “It also helps us to understand why certain types of motor neurons are affected and others are not.”

On the path towards personalized medicine

Gouti's team not only wants to use the neuromuscular organoids to determine the cause of death of motor neurons. The researchers also want to use the models for drug testing. The advantage over animal testing is obvious: as organoids consist of human tissue, they are thus much more similar to patients than laboratory animals. Organoids can also reduce the number of laboratory animals because they already show how substances work in the Petri dish. Another advantage is that organoids can be produced from the patient’s own cells. This paves the way for personalized medicine, in which a patient receives exactly the medication that has previously produced the desired effect in a patient-specific model.

The group still has a few hurdles to overcome before it is ready. “We need to enhance the complexity of our organoid models in order to be able to capture more adult-like tissue maturation status,” says Dr Chrysanthi-Maria Moysidou, a postdoctoral researcher in Mina Gouti's laboratory. The group uses human pluripotent stem cells in order to generate their organoid models. This process mimics the pathways we see in embryonic development. The neuromuscular organoids generated this way grow and mature over time, showing the desired functionality, including contractile muscle movements. In fact, these organoids can be maintained without issues for several months, but, similar to other organoid models, they do not reach the maturation stage of adult tissues. “My goal is to engineer organoids that are more relevant and specific to human adult tissues to better model disorders that occur during adulthood, such as ALS,” says Chrysanthi-Maria Moysidou.

Organoids meet bioelectronics

This is one of the major challenges organoid researchers are concerned with. They are trying to enhance and accelerate the complexity and maturation status of organoids, for example with the help of optogenetics – with this technology, genes are modified, so that cells can respond to light – or pharmacological substances. Bioengineer Moysidou is working on a different approach that utilizes organic bioelectronics. In collaboration with experts from the University of Cambridge, she is interfacing complex neuromuscular organoids with tailor-made, flexible multi-electrode arrays based on organic polymers. This device has many tiny electrodes, that conform with the shape and size of the organoid. This way, she is able to record over time the neuronal activity of the neuromuscular organoids, but can also use the device electrodes to deliver electrical stimuli to the tissue. “This will provide crucial insights into the maturation status of neuromuscular organoids. I will be able to understand how patterns of neuronal activity develop as the neuronal and muscular parts of the organoids self-organise, and most importantly, how the tissue changes and matures over time, giving rise to contractile activity,” says Chrysanthi-Maria Moysidou. Next, she would like to intervene in these processes, aiming to accelerate and enhance the maturation status of the neuromuscular organoids. If successful, this will mark a significant stride forward in organoid research.

Text: Jana Ehrhardt-Joswig, December 2023