A new technique has been developed for generating dopamine-producing neurons from induced pluripotent stem cells (IPSCs). The technique could be used to generate patient-specific neurons that could help to accelerate research into new therapies for Parkinson’s disease.
Dopaminergic neurons in the midbrain are the main source of the neurotransmitter dopamine. Dopamine has many functions in cells and is involved in sleep and arousal, behavior and cognition, pleasure reward and motivation, memory, and helps to regulate body movements. There are three main types of dopaminergic nerve cells in the midbrain – A8, A9, and A10 – and each plays a different role in the function of the brain. It is the degeneration of A9 dopaminergic DA neurons in the substantia nigra region of the brain that is the main cause of motor symptoms in Parkinson’s disease patients.
“These neurons are pacemakers that continuously fire action potentials regardless of excitatory inputs from other neurons,” said Jian Feng, PhD, professor of physiology and biophysics at the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo and lead author of the study. “Their pacemaking property is very important to their function and underlies their vulnerability in Parkinson’s disease.”
Researchers have been working on techniques for generating dopaminergic nerve cells from IPSCs for research and to develop more effective therapies; however, differentiating IPSCs into the right types of neurons has proven to be a challenge. Feng and his team have now developed a new technique that allows them to make A9 dopamine neurons from IPSCs, which means patient-specific neurons can be generated for any Parkinson’s disease patient to study their disease and potentially provide personalized therapy.
A9 dopaminergic neurons are possibly the largest cells in the body and have around four times the volume of a human egg. “Over 99 percent of the volume is contributed by their extremely extensive axon branches. The total length of axon branches of a single A9 DA neuron is about 4.5 meters,” said Feng. “The cell is like the water supply system in a city, with a relatively small plant and hundreds of miles of water pipes going to each building”
In order to maintain their pacemaking functions, these cells depend on Ca2+ channels and need to deal with considerable stress from handling both Ca2+ ions and dopamine. The cells are particularly vulnerable, and the key to developing new treatments for diseases such as Parkinson’s disease involves learning about those vulnerabilities and finding ways to protect the neurons and prevent their loss.
Now that a reliable method has been developed for generating these neurons in the lab, it will be possible to conduct studies to identify compounds that can protect them and prevent their loss due to Parkinson’s disease. These cells could also potentially be candidates for transplantation therapies for Parkinson’s disease patients.
Feng said the differentiation process from human IPSCs occurs in three stages, with each stage of the differentiation process controlled by different chemicals that mimic natural differentiation processes. One of the main challenges has been determining the right combination and concentration of those chemicals, and the duration that each needs to be applied. That has been a painstaking process, which has been based on previous studies at the Jacobs School of Medicine and the work of other researchers. “There was previously no way to make human dopamine neurons from a PD patient so we could study these neurons to find out what goes wrong,” said Feng.
You can read more about the study in the paper – Generation of human A9 dopaminergic pacemakers from induced pluripotent stem cells – which was recently published in Molecular Psychiatry. DOI: 10.1038/s41380-022-01628-1