The University of Osaka links ALS to intercellular network dysfunction and motor neuron overexcitation

A research group led by Invited Faculty Member Eriko Takeuchi, Doctoral Student Yoshiaki Yasumizu (at the time of the research and currently Associate Research Scientist at Yale School of Medicine), and Invited Professor Hideki Mochizuki (Director of National Hospital Organization Osaka Toneyama Medical Center) at the Graduate School of Medicine, the University of Osaka; and Specially Appointed Professors Shigeo Murayama and Seiichi Nagano at the United Graduate School of Child Development, the University of Osaka has discovered changes in gene expression which indicate a state of "excessive neural excitation" in spinal motor neurons. This world's first discovery was made by simultaneously analyzing the brains and spinal cords of ALS (amyotrophic lateral sclerosis) patients at the single-cell level. Their findings were published in Brain.

ALS is a disease which causes muscle weakness throughout the body due to paralysis of motor neurons in the brain and spinal cord. It remains difficult to treat, with no reliable method to stop disease progression. Previous research has shown that in many ALS patients, the protein TDP-43 forms abnormal aggregates within neurons. However, it was not well understood "why motor neurons are particularly vulnerable" or "how non-neuronal cells are involved."

Traditional gene analysis could only obtain average information from entire tissues and could not accurately examine differences between individual cells. Therefore, the research team analyzed every cell in the brain and spinal cord at the single-nucleus level to investigate in detail which cells change and how they change in ALS.

First, they performed single-nucleus multiome analysis on approximately 130,000 cells from the brains and spinal cords of ALS patients and individuals without motor neuron disease. This was followed by classifying diverse cell types such as neurons and glial cells, then creating a comprehensive map of all the cells in the brain and spinal cord. By analyzing this data, they were the first in the world to reveal that the gene GRM5 is strongly activated in spinal motor neurons. This suggests that the function of glutamate, which excites neurons, may be excessive. They also found that some oligodendrocytes, which support neuronal signal transmission and nutrient supply, were reduced; it indicates that coordination between neurons had broken down.

Furthermore, they discovered many genetic characteristics which increase susceptibility to ALS are concentrated in microglia, the immune cells of the brain. These results revealed that ALS is a disease of intercellular networks, in which motor neurons themselves undergo abnormalities and influence neurons and surrounding cells.

This research raises expectations for the development of drugs that suppress excessive excitation of motor neurons, as well as therapies which regulate microglial function. It also shifts how the disease is viewed, suggesting that not only neurons but also "cells that support neurons" may become important therapeutic targets.

Nagano commented: "ALS is a difficult motor neuron disease, the causes of and fundamental treatments for which remain unclear, but advances in technology have enabled us to separately examine changes in the state of many brain and spinal cord cells, including motor neurons that exist in very small numbers, and we have been able to obtain new insights. We hope that these research results will lead to the development of effective treatments. We are currently in discussions with multiple companies regarding joint research and development. With one company, we are exploring the possibility of nucleic acid therapeutics."

Journal Information
Publication: Brain
Title: Single-nucleus multiome shows motor neuron glutamate overactivation in amyotrophic lateral sclerosis
DOI: 10.1093/brain/awaf426