Parkinson’s Disease and Stem Cells

Lila Collins, PhD

A few weeks ago we held a Facebook Live “Ask the Stem Cell Team About Parkinson’s Disease” event. As you can imagine we got lots of questions but, because of time constraints, only had time to answer a few. Thanks to my fabulous CIRM colleagues, Dr. Lila Collins and Dr. Kent Fitzgerald, for putting together answers to some of the other questions. Here they are.

Kent Fitzgerald, PhD

Q: It seems like we have been hearing for years that stem cells can help people with Parkinson’s, why is it taking so long?

A: Early experiments in Sweden using fetal tissue did provide a proof of concept for the strategy of replacing dopamine producing cells damaged or lost in Parkinson’s disease (PD) . At first, this seemed like we were on the cusp of a cell therapy cure for PD, however, we soon learned based on some side effects seen with this approach (in particular dyskinesias or uncontrollable muscle movements) that the solution was not as simple as once thought. 

While this didn’t produce the answer it did provide some valuable lessons.

The importance of dopaminergic (DA) producing cell type and the location in the brain of the transplant.  Simply placing the replacement cells in the brain is not enough. It was initially thought that the best site to place these DA cells is a region in the brain called the SN, because this area helps to regulate movement. However, this area also plays a role in learning, emotion and the brains reward system. This is effectively a complex wiring system that exists in a balance, “rewiring” it wrong can have unintended and significant side effects. 

Another factor impacting progress has been understanding the importance of disease stage. If the disease is too advanced when cells are given then the transplant may no longer be able to provide benefit.  This is because DA transplants replace the lost neurons we use to control movement, but other connected brain systems have atrophied in response to losing input from the lost neurons. There is a massive amount of work (involving large groups and including foundations like the Michael J Fox Foundation) seeking to identify PD early in the disease course where therapies have the best chance of showing an effect.   Clinical trials will ultimately help to determine the best timing for treatment intervention.

Ideally, in addition to the cell therapies that would replace lost or damaged cells we also want to find a therapy that slows or stops the underlying biology causing progression of the disease.

So, I think we’re going to see more gene therapy trials including those targeting the small minority of PD that is driven by known mutations.  In fact, Prevail Therapeutics will soon start a trial in patients with GBA1 mutations. Hopefully, replacing the enzyme in this type of genetic PD will prevent degeneration.

And, we are also seeing gene therapy approaches to address forms of PD that we don’t know the cause, including a trial to rescue sick neurons with GDNF which is a neurotrophic factor (which helps support the growth and survival of these brain cells) led by Dr Bankiewicz  and trials by Axovant and Voyager, partnered with Neurocrine aimed at restoring dopamine generation in the brain.

 A small news report came out earlier this year about a recently completed clinical trial by Roche Pharma and Prothena. This addressed the build up in the brain of what are called lewy bodies, a problem common to many forms of PD. While the official trial results aren’t published yet, a recent press release suggests reason for optimism.  Apparently, the treatment failed to statistically improve the main clinical measurement, but other measured endpoints saw improvement and it’s possible an updated form of this treatment will be tested again in the hopes of seeing an improved effect.

Finally, I’d like to call attention to the G force trials. Gforce is a global collaborative effort to drive the field forward combining lessons learned from previous studies with best practices for cell replacement in PD.  These first-in-human safety trials to replace the dopaminergic neurons (DANs) damaged by PD have shared design features including identifying what the best goals are and how to measure those.

The CIRA trial, Dr Jun Takahashi

The NYSTEM PD trial, Dr Lorenz Studer

The EUROSTEMPD trial, Dr Roger Barker.

And the Summit PD trial, Dr Jeanne Loring of Aspen Neuroscience.

Taken together these should tell us quite a lot about the best way to replace these critical neurons in PD.

As with any completely novel approach in medicine, much validation and safety work must be completed before becoming available to patients

The current approach (for cell replacement) has evolved significantly from those early studies to use cells engineered in the lab to be much more specialized and representing the types believed to have the best therapeutic effects with low probability of the side effects (dyskinesias) seen in earlier trials. 

If we don’t really know the cause of Parkinson’s disease, how can we cure it or develop treatments to slow it down?

PD can now be divided into major categories including 1. Sporadic, 2. Familial. 

For the sporadic cases, there are some hallmarks in the biology of the neurons affected in the disease that are common among patients.  These can be things like oxidative stress (which damages cells), or clumps of proteins (like a-synuclein) that serve to block normal cell function and become toxic, killing the DA neurons. 

The second class of “familial” cases all share one or more genetic changes that are believed to cause the disease.  Mutations in genes (like GBA, LRRK2, PRKN, SNCA) make up around fifteen percent of the population affected, but the similarity in these gene mutations make them attractive targets for drug development.

CIRM has funded projects to generate “disease in a dish” models using neurons made from adults with Parkinson’s disease.   Stem cell-derived models like this have enabled not only a deep probing of the underlying biology in Parkinson’s, which has helped to identify new targets for investigation, but have also allowed for the testing of possible therapies in these cell-based systems. 

iPSC-derived neurons are believed to be an excellent model for this type of work as they can possess known familial mutations but also show the rest of the patients genetic background which may also be a contributing factor to the development of PD. They therefore contain both known and unknown factors that can be tested for effective therapy development.

I have heard of scientists creating things called brain organoids, clumps of brain cells that can act a little bit like a brain. Can we use these to figure out what’s happening in the brain of people with Parkinson’s and to develop treatments?

There is considerable excitement about the use of brain organoids as a way of creating a model for the complex cell-to-cell interactions in the brain.  Using these 3D organoid models may allow us to gain a better understanding of what happens inside the brain, and develop ways to treat issues like PD.

The organoids can contain multiple cell types including microglia which have been a hot topic of research in PD as they are responsible for cleaning up and maintaining the health of cells in the brain.  CIRM has funded the Salk Institute’s Dr. Fred Gage’s to do work in this area.

If you go online you can find lots of stem cells clinics, all over the US, that claim they can use stem cells to help people with Parkinson’s. Should I go to them?

In a word, no! These clinics offer a wide variety of therapies using different kinds of cells or tissues (including the patient’s own blood or fat cells) but they have one thing in common; none of these therapies have been tested in a clinical trial to show they are even safe, let alone effective. These clinics also charge thousands, sometimes tens of thousands of dollars these therapies, and because it’s not covered by insurance this all comes out of the patient’s pocket.

These predatory clinics are peddling hope, but are unable to back it up with any proof it will work. They frequently have slick, well-designed websites, and “testimonials” from satisfied customers. But if they really had a treatment for Parkinson’s they wouldn’t be running clinics out of shopping malls they’d be operating huge medical centers because the worldwide need for an effective therapy is so great.

Here’s a link to the page on our website that can help you decide if a clinical trial or “therapy” is right for you.

Is it better to use your own cells turned into brain cells, or cells from a healthy donor?

This is the BIG question that nobody has evidence to provide an answer to. At least not yet.

Let’s start with the basics. Why would you want to use your own cells? The main answer is the immune system.  Transplanted cells can really be viewed as similar to an organ (kidney, liver etc) transplant. As you likely know, when a patient receives an organ transplant the patient’s immune system will often recognize the tissue/organ as foreign and attack it. This can result in the body rejecting what is supposed to be a life-saving organ. This is why people receiving organ transplants are typically placed on immunosuppressive “anti-rejection “drugs to help stop this reaction. 

In the case of transplanted dopamine producing neurons from a donor other than the patient, it’s likely that the immune system would eliminate these cells after a short while and this would stop any therapeutic benefit from the cells.  A caveat to this is that the brain is a “somewhat” immune privileged organ which means that normal immune surveillance and rejection doesn’t always work the same way with the brain.  In fact analysis of the brains collected from the first Swedish patients to receive fetal transplants showed (among other things) that several patients still had viable transplanted cells (persistence) in their brains.

Transplanting DA neurons made from the patient themselves (the iPSC method) would effectively remove this risk of the immune system attack as the cells would not be recognized as foreign.

CIRM previously funded a discovery project with Jeanne Loring from Scripps Research Institute that sought to generate DA neurons from Parkinson’s patients for use as a potential transplant therapy in these same patients.   This project has since been taken on by a company formed, by Dr Loring, called Aspen Neuroscience.  They hope to bring this potential therapy into clinical trials in the near future.    

A commonly cited potential downside to this approach is that patients with genetic (familial) Parkinson’s would be receiving neurons generated with cells that may have the same mutations that caused the problem in the first place. However, as it can typically take decades to develop PD, these cells could likely function for a long time. and prove to be better than any current therapies.

Creating cells from each individual patient (called autologous) is likely to be very expensive and possibly even cost-prohibitive. That is why many researchers are working on developing an “off the shelf” therapy, one that uses cells from a donor (called allogeneic)would be available as and when it’s needed.

When the coronavirus happened, it seemed as if overnight the FDA was approving clinical trials for treatments for the virus. Why can’t it work that fast for Parkinson’s disease?

While we don’t know what will ultimately work for COVID-19, we know what the enemy looks like.  We also have lots of experience treating viral infections and creating vaccines.  The coronavirus has already been sequenced, so we are building upon our understanding of other viruses to select a course to interrupt it.  In contrast, the field is still trying to understand the drivers of PD that would respond to therapeutic targeting and therefore, it’s not precisely clear how best to modify the course of neurodegenerative disease.  So, in one sense, while it’s not as fast as we’d like it to be, the work on COVID-19 has a bit of a head start.

Much of the early work on COVID-19 therapies is also centered on re-purposing therapies that were previously in development.  As a result, these potential treatments have a much easier time entering clinical trials as there is a lot known about them (such as how safe they are etc.).  That said, there are many additional therapeutic strategies (some of which CIRM is funding) which are still far off from being tested in the clinic. 

The concern of the Food and Drug Administration (FDA) is often centered on the safety of a proposed therapy.  The less known, the more cautious they tend to be. 

As you can imagine, transplanting cells into the brain of a PD patient creates a significant potential for problems and so the FDA needs to be cautious when approving clinical trials to ensure patient safety.

Salk scientists explain why brain cells are genetically diverse


I’ve always wondered why some sets of genetically identical twins become not so identical later in life. Sometimes they differ in appearance. Other times, one twin is healthy while the other is plagued with a serious disease. These differences can be explained by exposure to different environmental factors over time, but there could also be a genetic explanation involving our brains.

The brain is composed of approximately 100 billion cells called neurons, each with a DNA blueprint that contains instructions that determine the function of these neurons in the brain. Originally it was thought that all cells, including neurons, have the same DNA. But more recently, scientists discovered that the brain is genetically diverse and that neurons within the same brain can have slightly different DNA blueprints, which could give them slightly different functions.

Jumping genes and genetic diversity


Fred “Rusty” Gage: Photo courtesy Salk Institute

Why and how neurons have differences in their DNA are questions that Salk Institute professor Fred Gage has pursued for more than a decade. In 2005, his lab discovered a mechanism during neural development that causes differences in the DNA of neurons. As a brain stem cell develops into a neuron, long interspersed nuclear elements (L1s), which are small pieces of DNA, copy and paste themselves, seemingly at random, throughout a neuron’s genome.

These elements were originally dubbed “jumping genes” because of their ability to hop around and insert themselves into DNA. It turns out that L1s do more than copy and paste themselves to create changes in DNA, they also can delete chunks of DNA. In a CIRM-funded study published this week in the journal Nature Neuroscience, Gage and colleagues at the Salk Institute reported new insights into L1 activity and how it creates genetic diversity in the brain.

Copy, paste, delete

Gage and his team had clues that L1s can cause DNA deletions in neurons back in 2013. They used a technique called single-cell sequencing to record the sequence of individual neuronal genomes and saw that some of their genomes had large sections of DNA added or missing.

They thought that L1s could be the reason for these insertions and deletions, but didn’t have proof until their current study, which used an improved method to identify areas of the neuronal genome modified by L1s. This method, combined with a computer algorithm that can easily tell the difference between various types of L1 modifications, revealed that areas of the genome with L1s were susceptible to DNA cutting caused by enzymes that home in on the L1 sequences. These breaks in the DNA then cause the observed deletions.

Gage explained their findings in a news release:

“In 2013, we discovered that different neurons within the same brain have various complements of DNA, suggesting that they function slightly differently from each other even within the same person. This recent study reveals a new and surprising form of variation that will help us understand the role of L1s, not only in healthy brains but in those affected by schizophrenia and autism.”

Jennifer Erwin, first author on the study, further elaborated:

“The surprising part was that we thought all L1s could do was insert into new places. But the fact that they’re causing deletions means that they’re affecting the genome in a more significant way,” says Erwin, a staff scientist in Gage’s group.”

Insights into brain disorders

It’s now known that L1s are important for the brain’s genetic diversity, but Gage also believes that L1s could play a role in causing brain disorders like schizophrenia and autism where there is heightened L1 activity in the neurons of these patients. In future work, Gage and his team will study how L1s can cause changes in genes associated with schizophrenia and autism and how these changes can effect brain function and cause disease.

Salk Scientists Unlock New Secrets of Autism Using Human Stem Cells

Autism is a complex neurodevelopmental disorder whose mental, physical, social and emotional symptoms are highly variable from person to person. Because individuals exhibit different combinations and severities of symptoms, the concept of autism spectrum disorder (ASD) is now used to define the range of conditions.

There are many hypotheses for why autism occurs in humans (which some estimates suggest now affects around 3.5 million people in the US). Some of the disorders are thought to be at the cellular level, where nerve cells do not develop normally and organize properly in the brain, and some are thought to be at the molecular level where the building blocks in cells don’t function properly. Scientists have found these clues by using tools such as studying human genetics and animal models, imaging the brains of ASD patients, and looking at the pathology of ASD brains to see what has gone wrong to cause the disease.

Unfortunately, these tools alone are not sufficient to recreate all aspects of ASD. This is where cellular models have stepped in to help. Scientists are now developing human stem cell derived models of ASD to create “autism in a dish” and are finding that the nerve cells in these models show characteristics of these disorders.

Stem cell models of autism and ASD

We’ve reported on some of these studies in previous blogs. A group from UCSD lead by CIRM grantee Alysson Muotri used induced pluripotent stem cells or iPS cells to model non-syndromic autism (where autism is the primary diagnosis). The work has been dubbed the “Tooth Fairy Project” – parents can send in their children’s recently lost baby teeth which contain cells that can be reprogrammed into iPS cells that can then be turned into brain cells that exhibit symptoms of autism. By studying iPS cells from individuals with non-syndromic autism, the team found a mutation in the TRPC6 gene that was linked to abnormal brain cell development and function and is also linked to Rett syndrome – a rare form of autism predominantly seen in females.

Another group from Yale generated “mini-brains” or organoids derived from the iPS cells of ASD patients. They specifically found that ASD mini-brains had an increased number of a type of nerve cell called inhibitory neurons and that blocking the production of a protein called FOXG1 returned these nerve cells back to their normal population count.

Last week, a group from the Salk Institute in collaboration with scientists at UC San Diego published findings about another stem cell model for ASD that offers new clues into the early neurodevelopmental defects seen in ASD patients.  This CIRM-funded study was led by senior author Rusty Gage and was published last week in the Nature journal Molecular Psychiatry.

Unlocking clues to autism using patient stem cells

Gage and his team were fascinated by the fact that as many as 30 percent of people with ASD experience excessive brain growth during early in development. The brains of these patients have more nerve cells than healthy individuals of the same age, and these extra nerve cells fail to organize properly and in some cases form too many nerve connections that impairs their overall function.

To understand what is going wrong in early stages of ASD, Gage generated iPS cells from ASD individuals who experienced abnormal brain growth at an early age (their brains had grown up to 23 percent faster when they were toddlers compared to normal toddlers). They closely studied how these ASD iPS cells developed into brain stem cells and then into nerve cells in a dish and compared their developmental progression to that of healthy iPS cells from normal individuals.

Neurons derived from people with ASD (bottom) form fewer inhibitory connections (red) compared to those derived from healthy individuals (top panel). (Salk Institute)

Neurons derived from people with ASD (bottom) form fewer inhibitory connections (red) compared to those derived from healthy individuals (top panel). (Salk Institute)

They quickly observed a problem with neurogenesis – a term used to describe how brain stem cells multiply and create new nerve cells in the brain. Brain stem cells derived from ASD iPS cells displayed more neurogenesis than normal brain stem cells, and thus were creating an excess amount of nerve cells. The scientists also found that the extra nerve cells failed to form as many synaptic connections with each other, an essential process that allows nerve cells to send signals and form a functional network of communication, and also behaved abnormally and overall had less activity compared to healthy neurons. Interestingly, they saw fewer inhibitory neuron connections in ASD neurons which is contrary to what the Yale study found.

The abnormal activity observed in ASD neurons was partially corrected when they treated the nerve cells with a drug called IGF-1, which is currently being tested in clinical trials as a possible treatment for autism. According to a Salk news release, “the group plans to use the patient cells to investigate the molecular mechanisms behind IGF-1’s effects, in particular probing for changes in gene expression with treatment.”

Will stem cells be the key to understanding autism?

It’s clear that human iPS cell models of ASD are valuable in helping tease apart some of the mechanisms behind this very complicated group of disorders. Gage’s opinion is that:

“This technology allows us to generate views of neuron development that have historically been intractable. We’re excited by the possibility of using stem cell methods to unravel the biology of autism and to possibly screen for new drug treatments for this debilitating disorder.”

However, to me it’s also clear that different autism stem cell models yield different results, but these differences are likely due to which populations the iPS cells are derived from. Creating more cell lines from different ASD subpopulations will surely answer more questions about the developmental differences and differences in brain function seen in adults.

Lastly, one of the co-authors on the study, Carolina Marchetto, made a great point in the Salk news release by acknowledging that their findings are based on studying cells in a dish, not actual patient’s brains. However, Marchetto believes that these cells are useful tools for studying autism:

“It never fails to amaze me when we can see similarities between the characteristics of the cells in the dish and the human disease.”

Rusty Gage and Carolina Marchetto. (Salk Institute)

Rusty Gage and Carolina Marchetto. (Salk Institute)

Related Links

Bipolar Disorder-in-a-Dish: Game On for Finding New Drugs

Amy Winehouse: a tremendous talent lost to bipolar disorder. Credit: Wikimedia Commons

Amy Winehouse: a tremendous talent lost to bipolar disorder. Credit: Wikimedia Commons

The tragic path of biopolar disorder
Ernest Hemingway, Kurt Cobain, Amy Winehouse and Virginia Woolf – the world lost their creativity too soon. Each took their own life or succumbed to substance abuse, most likely due to their struggles with bipolar disorder. Also called manic depression, bipolar disorder is one of the most severe types of mental illness. It’s characterized by episodes of extreme manic behavior preceded or followed by bouts of devastating depression. Bipolar disorder is thought to affect 3-5% of the world’s population and, if left untreated, has a 15% risk of death by suicide.

Lithium is the most effective treatment for long term management of the disorder though the drug’s mechanism of action isn’t well understood. Sadly, many people who are bipolar don’t respond to lithium and instead must wade through a complex mix of drugs that attempts to tackle the varied symptoms.

Imaging studies suggest unique changes in the bipolar brain and studies of twins show a genetic component but scientists are far from unraveling the direct causes of bipolar disorder. Now, exciting research at the Salk Institute reported in Nature provides a powerful new tool for not only understanding the disease at a cellular level but also finding new drug treatments.

“The cells of these patients really are different”
Using induced pluripotent stem cell (iPSC) technology, the Salk team successfully grew nerve cells, or neurons, in the lab from skin samples of six people with bipolar disorder as well as from healthy individuals. When compared to the healthy neurons, the researchers saw a higher sensitivity of the bipolar neuron to stimuli. Jerome Mertens, a postdoctoral fellow and the lead author of the study, explained the result further in a Salk Institute press release:

“Neurons are normally activated by a stimuli and respond. The cells we have from all six patients are much more sensitive in that you don’t need to activate them very strongly to see a response.”

And Salk professor Rusty Gage, a CIRM grantee and the senior scientist of the study, points out that these cells represent a game-changer for the study of bipolar disorder:

“Researchers hadn’t all agreed that there was a cellular cause to bipolar disorder. So our study is important validation that the cells of these patients really are different.”

Lithium response in lab dish = lithium response in patients
And now comes the really exciting part. The team next studied the effects of lithium on these six bipolar patients’ cells. Three of the patients were responders to lithium treatment while the other three were not helped by the drug. When grown in lithium, the cells from the lithium responders became less sensitive, you might even say less “manic”, to stimuli while the cells from the lithium non-responders remained hyperactive.


Salk scientists discover cellular differences between brain cells from bipolar patients that respond to lithium and those that don’t. Neurons (white/red) from a subset of bipolar patients show changes in their electrical activity in response to lithium.Credit: Salk Institute

So the response of these “disease in a dish” cells to lithium corresponds perfectly with the lithium response in the patients. This result will undoubtedly propel the use of these iPSC-derived neurons to examine the causes of the diseases at a cellular and molecular level. Not only that but the cells should become a key resource for testing lithium alternatives that may help the portion of the bipolar population that doesn’t response to lithium.

In order words, this use of iPSC technology begins a new chapter in the effort to free sufferers from the life-long grip of bipolar disorder.

CIRM’s got skin in the game too
The incredible power of iPSCs to examine human disease like never before is not lost on the CIRM team. That’s why we’re so excited that our iPSC bank is now open for business. It’s a major effort by the agency to create a public stem cell bank developed from thousands of individuals. These cells will be available to scientists worldwide to better understand and to develop therapies for diseases of heart, lung and liver as well as neurodegenerative and childhood neurological disorders.

Related Links:
Seminar video: Carol Marchetto, Salk Institute staff scientist, discusses the study in greater detail