Scientists discover a new molecular pathway shared by two neurodegenerative disorders

Journal References:

  1. Anna-Leigh Brown, Oscar G. Wilkins, Matthew J. Keuss, Sarah E. Hill, Matteo Zanovello, Weaverly Colleen Lee, Alexander Bampton, Flora C. Y. Lee, Laura Masino, Yue A. Qi, Sam Bryce-Smith, Ariana Gatt, Martina Hallegger, Delphine Fagegaltier, Hemali Phatnani, Hemali Phatnani, Justin Kwan, Dhruv Sareen, James R. Broach, Zachary Simmons, Ximena Arcila-Londono, Edward B. Lee, Vivianna M. Van Deerlin, Neil A. Shneider, Ernest Fraenkel, Lyle W. Ostrow, Frank Baas, Noah Zaitlen, James D. Berry, Andrea Malaspina, Pietro Fratta, Gregory A. Cox, Leslie M. Thompson, Steve Finkbeiner, Efthimios Dardiotis, Timothy M. Miller, Siddharthan Chandran, Suvankar Pal, Eran Hornstein, Daniel J. MacGowan, Terry Heiman-Patterson, Molly G. Hammell, Nikolaos. A. Patsopoulos, Oleg Butovsky, Joshua Dubnau, Avindra Nath, Robert Bowser, Matthew Harms, Eleonora Aronica, Mary Poss, Jennifer Phillips-Cremins, John Crary, Nazem Atassi, Dale J. Lange, Darius J. Adams, Leonidas Stefanis, Marc Gotkine, Robert H. Baloh, Suma Babu, Towfique Raj, Sabrina Paganoni, Ophir Shalem, Colin Smith, Bin Zhang, Brent Harris, Iris Broce, Vivian Drory, John Ravits, Corey McMillan, Vilas Menon, Lani Wu, Steven Altschuler, Yossef Lerner, Rita Sattler, Kendall Van Keuren-Jensen, Orit Rozenblatt-Rosen, Kerstin Lindblad-Toh, Katharine Nicholson, Peter Gregersen, Jeong-Ho Lee, Sulev Kokos, Stephen Muljo, Jia Newcombe, Emil K. Gustavsson, Sahba Seddighi, Joel F. Reyes, Steven L. Coon, Daniel Ramos, Giampietro Schiavo, Elizabeth M. C. Fisher, Towfique Raj, Maria Secrier, Tammaryn Lashley, Jernej Ule, Emanuele Buratti, Jack Humphrey, Michael E. Ward, Pietro Fratta. TDP-43 loss and ALS-risk SNPs drive mis-splicing and depletion of UNC13A. Nature, 2022; DOI: 10.1038/s41586-022-04436-3
  2. X. Rosa Ma, Mercedes Prudencio, Yuka Koike, Sarat C. Vatsavayai, Garam Kim, Fred Harbinski, Adam Briner, Caitlin M. Rodriguez, Caiwei Guo, Tetsuya Akiyama, H. Broder Schmidt, Beryl B. Cummings, David W. Wyatt, Katherine Kurylo, Georgiana Miller, Shila Mekhoubad, Nathan Sallee, Gemechu Mekonnen, Laura Ganser, Jack D. Rubien, Karen Jansen-West, Casey N. Cook, Sarah Pickles, Björn Oskarsson, Neill R. Graff-Radford, Bradley F. Boeve, David S. Knopman, Ronald C. Petersen, Dennis W. Dickson, James Shorter, Sua Myong, Eric M. Green, William W. Seeley, Leonard Petrucelli, Aaron D. Gitler. TDP-43 represses cryptic exon inclusion in the FTD–ALS gene UNC13A. Nature, 2022; DOI: 10.1038/s41586-022-04424-7

“ALS and FTD patients have long participated in genetic studies looking for changes in genes that might contribute to risk for disease,” said Thomas Cheever, Ph.D., program director at the National Institute of Neurological Disorders and Stroke (NINDS). “Here, we see two independent research teams converging to explain how one of these changes can be a critical factor contributing to an entire class of neurodegenerative diseases, as well as a potential therapeutic target.”

One study, which is a collaboration between the labs of Michael Ward, M.D., Ph.D., scientist at the National Institutes of Health’s NINDS, and Pietro Fratta, Ph.D., professor at the University College London Queen Square Motor Neuron Disease Centre in the United Kingdom, initially looked at lab-grown neurons derived from human induced pluripotent stem cells (iPSCs) — stem cells created from a patient’s tissue sample, often skin or blood. Using powerful genetic tools, the researchers created neurons that made much less TDP-43 protein than normal, and this resulted in the appearance of abnormal mRNA sequences inserted into the instructions used to make several other proteins. These abnormally inserted sequences, called cryptic exons, can result in a defective protein or can even prevent the protein from being made at all.

The UNC13A gene is important for maintaining the connections between neurons and has been shown to be a risk factor for both ALS and FTD. UNC13A is also one of the mRNA sequences that contained cryptic exons when TDP-43 was reduced, and cryptic exons were also seen in neurons taken from postmortem tissue of ALS and FTD patients. These findings directly link a well-established risk factor for ALS and FTD with the loss of TDP-43.

“We have built on years of genetic research that identified that UNC13A was implicated in motor neuron disease and FTD and supported it with a new molecular biology finding that confirms that the gene is absolutely fundamental to the disease process,” said Dr. Ward.

At the same time, Aaron Gitler, Ph.D., professor at Stanford University in Stanford, California, and his lab, along with a team led by Len Petrucelli, Ph.D., professor at Mayo Clinic in Jacksonville, Florida, were also looking at the effects caused by a loss of TDP-43 as they pertained to FTD and ALS. They first analyzed existing datasets in which postmortem neurons from patients with FTD or ALS were sorted based on whether their nucleus contained TDP-43. When genes were compared between neurons with and without TDP-43, UNC13A again emerged as one that was significantly affected by TDP-43 loss. Knocking down TDP-43 in otherwise healthy cells also introduced cryptic exons into the UNC13A gene, suggesting that this is a direct effect on the gene itself. They also show that the genetic code differences in the variants of UNC13A that are associated with FTD and ALS occur where the cryptic exon is located. It is known that mislocalization of TDP-43 similarly causes cryptic exon splicing into another gene that encodes the protein stathmin 2, which is depleted in the motor neuron and implicated in neurodegeneration. Both studies suggest that developing means to increase the levels of UNC13A or stathmin 2 may be effective in preventing the death of neurons in these tragic disorders.

TDP-43 mislocalization is seen in other degenerative diseases, including Alzheimer’s disease, chronic traumatic encephalopathy (CTE), limbic predominant, age-related TDP-43 encephalopathy (LATE), and inclusion body myopathy, suggesting that these findings could be extended to those conditions as well.

The studies were supported in part by the Intramural Research Program at NINDS, and grants from NINDS (NS097263, NS097273, NS123743, NS084974, NS104437, NS120992, and NS113636) and the National Institute on Aging (AG071326, AG06267, and AG006786).

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Scientists discover a new molecular pathway shared by two neurodegenerative disorders