IPSC Technology Lead To Improved Modeling Of Alzheimer's Disease

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Working with a group from Nagasaki University, a research group at the Center for iPS Cell Research and Application (CiRA) at Japan's Kyoto University has announced in the online publication of Cell Stem Cell that it has successfully modeled Alzheimer's disease (AD) using both familial and sporadic patient-derived induced pluripotent stem cells (iPSCs), and revealed stress phenotypes and differential drug responsiveness associated with intracellular amyloid beta oligomers in AD neurons and astrocytes.

In a study published online in Cell Stem Cell, Associate Professor Haruhisa Inoue and his team at CiRA and a research group led by Professor Nobuhisa Iwata of Nagasaki University generated cortical neurons and astrocytes from iPSCs derived from two familial AD patients with mutations in amyloid precursor protein (APP), and two sporadic AD patients. The neural cells from one of the familial and one of the sporadic patients showed endoplasmic reticulum (ER)-stress and oxidative-stress phenotypes associated with intracellular amyloid beta oligomers. The team also found that these stress phenotypes were attenuated with docosahexaenoic acid (DHA) treatment. These findings may help explain the variable clinical results obtained using DHA treatment, and suggest that DHA may in fact be effective only for a subset of patients.

Using both familial and sporadic AD iPSCs, the researchers discovered that pathogenesis differed between individual AD patients. For example, secreted amyloid beta 42 levels were depressed in familial AD with APP E693 delta mutation, elevated in familial AD with APP V717L mutation, but normal in sporadic AD.

"This shows that patient classification by iPSC technology may contribute to a preemptive therapeutic approach toward AD,'' said Inoue, a principal investigator at CiRA who is also a research director for the CREST research program funded by the Japan Science and Technology Agency. "Further advances in iPSC technology will be required before large-scale analysis of AD patient-specific iPSCs is possible.''

Converting a Person's Own Cells into Functional Neurons with PTB

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UC San Diego

Repression of a single protein in ordinary fibroblasts is sufficient to directly convert the cells – abundantly found in connective tissues – into functional neurons. The findings, which could have far-reaching implications for the development of new treatments for neurodegenerative diseases like Huntington’s, Parkinson’s and Alzheimer’s, will be published online in advance of the January 17 issue of the journal Cell.

In recent years, scientists have dramatically advanced the ability to induce pluripotent stem cells to become almost any type of cell, a major step in many diverse therapeutic efforts.  The new study focuses upon the surprising and singular role of PTB, an RNA-binding protein long known for its role in the regulation of alternative RNA splicing.

Confocal micrograph of a primary human fibroblast cell grown in  culture stained blue for actin, a highly abundant protein that makes up the cytoskeleton of cells. Energy-producing mitochondria are shown in green. Image courtesy of Matthew Daniels, University of Oxford and Wellcome Images.

In in vitro experiments, scientists at University of California, San Diego School of Medicine and Wuhan University in China describe the protein’s notable regulatory role in a feedback loop that also involves microRNA – a class of small molecules that modulate the expression of up to 60 percent of genes in humans. Approximately 800 miRNAs have been identified and characterized to various degrees.

One of these miRNAs, known as miR-124, specifically modulates levels of PTB during brain development. The researchers found that when diverse cell types were depleted of PTB, they became neuronal-like cells or even functional neurons – an unexpected effect. The protein, they determined, functions in a complicated loop that involves a group of transcription factors dubbed REST that silences the expression of neuronal genes in non-neuronal cells.

According to principal investigator Xiang-Dong Fu, PhD, professor of cellular and molecular medicine at UC San Diego, it’s not known which neuronal signal or signals turn on the loop, which in principle can happen at any point in the circle. But the ability to artificially manipulate PTB levels in cells, inducing them to become neurons, offers tantalizing possibilities for scientists seeking new treatments for an array of neurodegenerative diseases.

It is estimated that over a lifetime, one in four Americans will suffer from a neurodegenerative disease, from Alzheimer’s and Parkinson’s to multiple sclerosis and amyotrophic lateral sclerosis (Lou Gehrig’s disease).

“All of these diseases are currently incurable. Existing therapies focus on simply trying to preserve neurons or slow the rate of degeneration,” said Fu. “People are working with the idea of replacing lost neurons using embryonic stem cells, but there are a lot of challenges, including issues like the use of foreign DNA and the fact that it’s a very complex process with low efficiency.”

Fu explained that REST is expressed in cells everywhere except in neurons. PTB is itself a target of miR-124, but also acts as a break for this microRNA to attack other cellular targets that include REST, which is responsible for repressing miR-124. 

In non-neuronal cells, REST keeps miR-124 down and PTB enforces this negative feedback loop, but during neural induction, miR-124 is induced, which diminishes PTB, and without PTB as a break, REST is dismantled, and without REST, additional miR-124 is produced.  This loop therefore becomes a positive feed forward, which turns non-neuronal cells into neurons.

“If we learn how to manipulate PTB, which appears to be a kind of master regulator, we might eventually be able to avoid some of these problems by creating new neurons in patients using their own cells adjacent deteriorating neurons,” said Fu.

Co-authors are Yuanchao Xue and Yu Zhou, Wuhan University, China and UCSD Department of Cellular and Molecular Medicine; Kunfu Ouyang, Gang Wang and Ju Cheng, UCSD Department of Medicine; Jie Huang, Qijia Wu, Yanzhen Bi, Li Jiang, Zhiqiang Cai, Hui Sun, UCSD Department of Cellular and Molecular Medicine; Hong Ouyang and Kang Zhang, UCSD Institute of Genomic Medicine; Hairi Li and Chaoliang Wei, UCSD Department of Cellular and Molecular Medicine; and Yi Zhang, Wuhan University, China and Center for Genome Analysis, Wuhan, China.

Funding for this research came, in part, from National Institutes of Health grants (GM049369, GM052872 and HG004659) and the China 973 programs.

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Media Contact: Scott LaFee, 619-543-6163, slafee@ucsd.edu