May 23, 2018
New cell lines will allow researchers to probe the basic biology of Alzheimer’s. Currently, however, there are no treatments that can prevent or slow the progression of this memory-robbing disease, which affects more than 5 million Americans.
One reason for this is that we really don’t know the cause of Alzheimer’s: It is known that brain cells that are crucial to forming new memories die. But we don’t know why.
One way to answer this question is to study brain cells of people with Alzheimer’s in the laboratory. For many diseases, cells can be obtained from a tissue sample—a biopsy—of the affected organ. But the brain is so delicate that it is typically only biopsied when something serious, like a brain cancer, is suspected.
One solution to this problem is to grow brain cells in the laboratory. This makes it possible to study their basic cellular processes and easily test their responses to different drugs.
But creating neuronal cell lines has proved challenging for scientists, because neurons, unlike cells from many other tissues, cannot be easily induced to grow in the laboratory.
Researchers, however, have been able to create neuronal cell lines from skin cells. But skin cells, too, have a drawback as a source for neuronal cell lines. Skin cells are exposed to many environmental factors from which the brain is protected, sunlight, for example, and chemicals we might touch. Brain cells, on the other hand, are largely isolated from the environment, hidden within the skull and a filtering system that protects the brain from toxins in the bloodstream, called the blood brain barrier.
As a result, skin cells are likely to have acquired very different genetic changes caused by environmental exposures—mutations that may have altered the genes themselves or caused changes in molecules that regulate genes, alterations called epigenetic modifications.
To get around this problem, researchers led by scientists from the UW Medicine’s Institute for Stem Cell & Regenerative Medicine and the UW Alzheimer’s Disease Research Center have for the first time created neurons from the tissue that tightly covers the brain, the leptomeninges.
Because the leptomeninges are found so close to the brain, the neurons generated from this tissue are expected to be much more similar to the brain cells of these patients than would neurons generated from their skin cells.
“Leptomeningeal-derived neurons are ideal for the study of neurodegenerative disease”, said Jessica Young, Ph.D., an assistant professor in the UW Department of Pathology and a researcher at the Institute for Stem Cell and Regenerative Medicine. “They lie within the skull, immediately next to the brain, and are immersed in the same fluid that bathes the brain—the cerebral spinal fluid—and so are likely to share many of the same environmental exposures during life as have the nearby brain cells.”
Young led the study with C. Dirk Keene, M.D., Ph.D., Nancy and Buster Alford Endowed Chair in Neuropathology and associate professor, Department of Pathology, who is Leader of the UW Alzheimer’s Disease Research Center’s Neuropathology and Targeted Molecular Testing Core. The results of their study were published online in the Journal of Neuropathology & Experimental Neurology.
Genetic and epigenetic changes
Alzheimer’s disease—and other neurodegenerative diseases—are thought to be caused by a combination of the genes we inherit, mutations that alter our genes during life, and changes, called epigenetic modifications, that influence how genes are expressed. These changes can either increase or decrease our risk of developing a brain disorder.
Neurons created by altering skin cells have provided insights into how these factors may lead to disease but, in addition, to having different epigenetics, they are typically collected while the patient is alive. This means, because Alzheimer’s can only be definitively diagnosed at autopsy, cause of patients’ dementia are uncertain .
To overcome these limitations, Young, Keene and their colleagues obtained tissue from the leptomeninges from patients with dementia shortly after death. All were volunteers in three studies in which patients are followed for many years, the Kaiser-Permanente Washington/ UW Adult Changes in Thought study, the Seattle Longitudinal Study, and the UW Alzheimer’s Disease Research Center study. Autopsies confirmed their brains had the classic changes seen with Alzheimer’s disease.
By using brains donated from subjects in these studies, researchers have not only information from the exhaustive neuropathological exams on each brain at autopsy, but also detailed information about the volunteers’ life exposures, medical history and neurocognitive status.
The researchers used the leptomeningeal tissue to create two types of cell lines. One line was created by returning the leptomeningeal cells to a stage seen early in fetal development, a stage when cells still retain the ability to become any cell type. These cells are called pluripotent stem cells because they have the potential to become many—pluri—different types of cells.
The researchers then induced these pluripotent stem cells to develop into neurons. Such neurons are valuable to researchers because they share the same genetic inheritance of the patient’s brain cells.
But such induced-pluripotent stem cells have one important shortcoming, says Keene: because they have been “reset” to a stem-cell state, they lose many of the epigenetic modifications that might have occurred in the patients’ cells during life. “The pluripotent cells allow you to study the background genetics of the cell but all the epigenetic changes are gone,” said Keene.
To get around this problem, the researchers created a second set of cells by converting the leptomeningeal cells into neurons directly without reverting them to the stem-cell state. Because these cells have not been reset, they are expected to have retained many of the epigenetic changes that are found in the adjacent brain cells that contributed to the patient’s neurodegenerative disease. “The epigenetic modifications will help tell us how certain epigenetic changes drive cells one way or the other,” Keene said.
Thousands of individuals with and without dementia have enrolled in the community studies being conducted by UW and its partners. In some cases, volunteers have been followed for more than 30 years. The long-term goal of the UW researchers is to create a bank of leptomeningeal-derived cell lines from every research brain autopsy collected as part of these studies. The bank will provide researchers from around the world access to the cell lines, the detailed neuropathological information gathered at autopsy, and the volunteers’ medical history, including the results of neuro-cognitive exams they may have undergone.
“This bank of cell lines will help us to understand the basic cellular mechanics that contribute to the pathological changes seen in neurodegenerative disease and to test new compounds that might treat or prevent these disorders,” said Young.
This study was supported by University of Washington (UW) Alzheimer’s Disease Research Center (NIH AG005136), Kaiser Permanente Adult Changes in Thought Study (NIH AG006781), Morris K. Udall Center of Excellence for Parkinson’s Disease Research (NIH NS062684), the Nancy and Buster Alvord Endowment, the Tietze Foundation, and the Ellison Foundation.
Reference: Rose SE, Frankowski H, Knupp A, Berry BJ, Martinez R, Dinh SQ, Bruner LT, Willis SL, Crane PK, Larson EB, Grabowski T, Darvas M, Keene CD, Young JE. Leptomeninges-Derived Induced Pluripotent Stem Cells and Directly Converted Neurons From Autopsy Cases With Varying Neuropathologic Backgrounds. J Neuropathol Exp Neurol. 2018 Feb 21. doi: 10.1093/jnen/nly013. [Epub ahead of print]