Stem Cell Model Creates 'ALS in a Dish'

by Amy Madsen on Thu, 2011-06-23 10:46

Cells from people with ALS and their unaffected siblings have been reprogrammed and developed into motor neurons, creating a new tool for studying ALS   

Human nerve cells derived from induced pluripotent stem cells can be used to model neurological diseases in the laboratory. Here, two compact masses of immature neuron "precursor" cells, derived from human iPSCs, are imaged with a fluorescent microscope. (Photo credit: M. Marchetto and A. Muotri)
Article Highlights:
  • A human cellular model of ALS generated from induced pluripotent stem cells (iPSCs) has been created by an MDA-supported research team. The iPSCs come from people with an ALS subtype known as ALS8, a familial (inherited) form of ALS caused by mutations in the VAPB gene.
  • The research model is enabling researchers to study the underlying mechanisms of ALS, including the role of the VAPB protein in the ALS disease process.
  • Information gained from the ALS8 model may be applicable to other forms of ALS, including some sporadic (noninherited) forms.

A human cellular model of ALS (amyotrophic lateral sclerosis, or Lou Gehrig's disease) has been created using cells taken from people with a subtype of the disease called ALS8.

This so-called “disease in a dish” research model already is enabling researchers to learn more about the role of a protein called VAPB in the ALS disease process.

The model was made possible by recent advances in stem cell technology, including the ability to generate induced pluripotent stem cells, or iPSCs. (An iPSC is an adult cell that has been "reprogrammed" back to an immature stem-cell-like state, after which it can be prompted to develop into any type of cell in the body.)

Although the model is based on one inherited subtype of ALS, its value likely will extend to other familial (inherited) forms of the disease, as well as to the noninherited, or sporadic, forms that make up the majority of ALS cases.

Scientists have begun using the model to study the mechanisms underlying ALS, and hope future studies will pinpoint biomarkers that enable ALS diagnosis at an earlier stage; provide an accurate evaluation of an individual's current disease status; predict how well an individual may respond to a proposed therapy; and uncover potential targets for therapeutic strategies.

About the study

ALS8 is an inherited form of the disease caused by mutations in the gene for a "vesicle-trafficking" protein called VAPB (vesicle-associated membrane protein-associated protein B/C). The subtype originally was found in several Brazilian families, but also has been identified in individuals with ALS from Germany and the United Kingdom, and in one individual of Japanese ancestry.

After collecting skin biopsies from people with ALS8 and their unaffected siblings (to serve as controls) in two families, the researchers reprogrammed the cells, turning them into iPSCs in 10 to 15 days.

Investigators chose to produce their model using iPSCs derived from people with ALS8 for several reasons, including:

  • In previous studies, iPSC models based on cells from people with sporadic ALS failed to manifest any motor neuron characteristics or traits that could be tracked and studied.
  • Cells cultured from a genetic form of ALS allowed the team to focus on the behavior of a gene previously associated with ALS.
  • The ALS8-associated neurodegeneration pathway appears to share common traits with other forms of the disease.
  • It's been observed that VAPB protein levels are decreased in patients with sporadic ALS.
  • It's thought that VAPB may play an important role in numerous forms of the disease.
Muotri says a "critical need" exists for new human cellular models of ALS. Advances in stem-cell biology, including the availability of iPSCs, may help unravel the molecular mechanisms underpinning ALS.

The process was described in an online report published June 17, 2011, in Human Molecular Genetics. The research team was led by MDA grantee Alysson Muotri, assistant professor at the University of California, San Diego in La Jolla.

Model yields new information about ALS8 and VAPB

In studies conducted using the ALS8-iPSCs, the investigators found that:

  • VAPB is present in cells at pluripotent stages, and that the characteristics of the protein in ALS8 iPSCs are similar to those of the protein in iPSCs derived from normal (control) cells.
  • Mutated VAPB does not inhibit differentiation (maturation) of the iPSCs into motor neurons.
  • The levels of VAPB protein in ALS8 iPSCs are lower than those in control iPSCs.
  • At all stages of differentiation, VAPB is significantly reduced in cells derived from ALS8 iPSCs when compared to controls.
  • In the control iPSCs, levels of VAPB protein gradually increase during the differentiation process, but such upregulation of the protein does not occur during differentiation in ALS8 iPSCs.

Reduced levels of VAPB might be an initial defect leading to the development of ALS8, the study authors wrote, and ALS8 iPSCs could be used to develop early diagnostic tools and to identify possible drugs and targets for future therapies.

VAPB regulation may play key role in ALS

Reduced levels of VAPB protein have been shown to correlate with disease progression in SOD1 ALS mice; they also have been observed in postmortem tissue taken from people with sporadic ALS. These earlier findings, coupled with the new findings concerning ALS8, appear to suggest that proper VAPB protein regulation may play a key role in the ALS disease process.

The VAPB protein has been associated with numerous cellular processes, but its role in ALS remains undefined.

Wide variability in the clinical course of ALS8 may help provide an answer. The course of the disease can vary drastically from one patient to the next — rapid and severe in some and slowly progressive in others. Determining blockers or modulators of the effects of VAPB mutations may open up a number of strategies for therapy development.

Stem-cell model avoids shortcomings of animal models

Animal models play a crucial role in disease research and a number of ALS animal research models have been developed. Many of these, including zebrafish, fruit flies, worms, rats and mice, have been created around the SOD1 gene.

Still, the study team noted, the underpinnings of ALS remain unclear, and drugs tested in ALS mice and other animal models have produced benefits that scientists are unable to duplicate in humans.

A human stem cell research model is expected to eliminate some of the difficulties associated with using mice and other animal models to recapitulate a human disease.

Precisely because the new model features DNA (akin to a "genetic blueprint") from people affected with ALS, scientists will be able to study ALS-causing flaws and mechanisms in human cells that reflect the genetic background in which the disease naturally occurs.

The new iPSC model, the investigators wrote, can recapitulate some aspects of ALS8 and be used to extract new biological information relevant to human motor neuron development.

"We believe this cellular model has the potential to complement other human and animal models and to accelerate the discovery of new compounds for treating ALS and other forms of motor neuron neurodegeneration."

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