Scientist grow diseased brain cells in bulk to study Alzheimer’s and Parkinson’s disease

Daily trips to the local grocery store have become a thing of the past for many with the rise of wholesale stores like Costco and online giants like Amazon. Buying in bulk is attractive for people who lead busy lives, have large families, or just love having endless pairs of clean socks.

Scientists who study neurodegenerative diseases like Alzheimer’s and Parkinson’s use disease-in-a-dish models that are much like the daily visits to the nearby Safeway. They can make diseased brain cells, or neurons, from human pluripotent stem cells and study them in the lab. But often, they can’t generate large enough quantities of cells to do important experiments like test new drugs or develop diagnostic platforms to identify disease at an earlier age.

What scientists need is a Costco for brain cells, a source that can make diseased brain cells in bulk. Such a method would open a new avenue of research into what causes neurodegeneration and how the aging process affects its progression.

This week, this need was answered. A team of researchers from Lund University in Sweden developed a method that can efficiently generate neurons from patients with a range of neurodegenerative diseases including Parkinson’s, Huntington’s and Alzheimer’s disease. The study was published in EMBO Molecular Medicine and was led by senior author Dr. Malin Parmar.

Diseased neurons made by the Lund University team. (Photo, Kennet Ruona)

Parmar and her team took an alternative approach to making their neurons. Their technology involves converting human skin cells into neurons without reprogramming the skin cells back to a pluripotent stem cell state first. This process is called “direct conversion” and is considered an effective shortcut for generating mature cells like neurons in a dish. Direct conversion of skin cells into neurons was first published by Dr. Marius Wernig, a CIRM-grantee and professor at Stanford University.

There is also scientific evidence suggesting that reprogramming patient cells back to a pluripotent state wipes out the effects of aging in those cells and has a Benjamin Button-like effect on the resulting neurons. By directly converting patient skin cells into neurons, many of these aging “signatures” are retained and the resulting neurons are more representative of the aging brain.

So how did they make brain cells in bulk? Parmar explained their method in a Lund University news release,

Malin Parmar

“Primarily, we inhibited a protein, REST, involved in establishing identity in cells that are not nerve cells. After limiting this protein’s impact in the cells during the conversion process, we’ve seen completely different results.”

 

Besides blocking REST, the team also turned on the production of two proteins, Ascl1 and Brn2, that are important for the development of neurons. This combination of activating pro-neural genes and silencing anti-neural genes was successful at converting skin cells into neurons on a large scale. Parmar further explained,

“We’ve been playing around with changing the dosage of the other components in the previous method, which also proved effective. Overall, the efficiency is remarkable. We can now generate almost unlimited amounts of neurons from one skin biopsy.”

As mentioned previously, this technology is valuable because it provides better brain disease models for scientists to study and to screen for new drugs that could treat or delay disease onset. Additionally, scientists can study the effects of the aging in the brain at different stages of neurodegeneration. Aging is a well-known risk factor for many neurodegenerative diseases, especially Alzheimer’s, so the ability to make large quantities of brain cells from elderly Alzheimer’s patients will unlock new clues into how age influences disease.

Co-author Dr. Johan Jakobsson concluded,

Johan Jakobsson

“This takes us one step closer to reality, as we can now look inside the human neurons and see what goes on inside the cell in these diseases. If all goes well, this could fundamentally change the field of research, as it helps us better understand the real mechanisms of the disease. We believe that many laboratories around the world would like to start testing on these cells to get closer to the diseases.”

For more on this study, check out this short video provided by Lund University.

Telomere length matters: scientists find shorter telomeres may cause aging-related disease

Aging is inevitable no matter how much you exercise, sleep or eat healthy. There is no magic pill or supplement that can thwart growing older. However, preventing certain age-related diseases is a different story. Genetic mutations can raise the risk of acquiring age-related diseases like heart disease, diabetes, cancer and dementia. And scientists are on the hunt for treatments that target these mutations in hopes of preventing these diseases from happening.

Telomeres shown in white act as protective caps at the ends of chromosomes.

Another genetic component that can accelerate diseases of aging are telomeres. These are caps made up of repeat sequences of DNA that sit at the ends of chromosomes and prevent the loss of important genetic material housed within chromosomes. Healthy cells have long telomeres, and ascells divide these telomeres begin to shorten. If telomere shortening is left unchecked, cells become unhealthy and either stop growing or self-destruct.

Cells have machinery to regrow their telomeres, but in most cases, the machinery isn’t activated and over time, the resulting shortened telomeres can lead to problems like an impaired immune system and organ degeneration. Shortened telomeres are associated with age-related diseases, but the reasons why have remained elusive until recently.

Scientists from the Gladstone Institutes have found a clue to this telomere puzzle that they shared in a study published yesterday in the Journal of Clinical Investigation. This research was funded in part by a CIRM Discovery stage award.

In their study, the team found that mice with a mutation that causes a heart condition known as calcific aortic valve disease (CAVD) were more likely to get the disease if they had short telomeres. CAVD causes the heart valves and vessels to turn hard as rock due to a buildup of calcium. It’s the third leading cause of heart disease and the only effective treatment requires surgery to replace the calcified parts of the heart.

Old age and mutations in one of the copies of the NOTCH1 gene can cause CAVD in humans. However, attempts to model CAVD in mice using the same NOTCH1 mutation have failed to produce symptoms of the disease. The team at Gladstone knew that mice inherently have longer telomeres than humans and hypothesized that these longer telomeres could protect mice with the NOTCH1 mutation from getting CAVD.

They decided to study NOTCH1 mutant mice that had short telomeres and found that these mice had symptoms of CAVD including hardened arteries. Furthermore, mice that had the shortest telomeres had the most severe heart-related symptoms.

First author on the study Christina Theodoris, explained in a Gladstone news release how telomere length matters in animal models of age-related diseases:

“Our findings reveal a critical role for telomere length in a mouse model of age-dependent human disease. This model provides a unique opportunity to dissect the mechanisms by which telomeres affect age-dependent disease and also a system to test novel therapeutics for aortic valve disease.”

Deepak Srivastava and Christina Theodoris created mouse models of CAVD that may be used to test drug therapies for the disease. (Photo: Chris Goodfellow, Gladstone Institutes)

The team believes that there is a direct relationship between short telomeres and CAVD, likely through alterations in the activity of gene networks related to CAVD. They also propose that telomere length could influence how severe the symptoms of this disease manifest in humans.

This study is important to the field because it offers a new strategy to study age-related diseases in animal models. Senior author on the study, Dr. Deepak Srivastava, elaborated on this concept:

Deepak Srivastava, Gladstone Institutes

“Historically, we have had trouble modeling human diseases caused by mutation of just one copy of a gene in mice, which impedes research on complex conditions and limits our discovery of therapeutics. Progressive shortening of longer telomeres that are protective in mice not only reproduced the clinical disease caused by NOTCH1 mutation, it also recapitulated the spectrum of disease severity we see in humans.”

Going forward, the Gladstone team will use their new mouse model of CAVD to test drug candidates that have the potential to treat CAVD in humans. If you want to learn more about this study, watch this Gladstone video featuring an interview of Dr. Srivastava about this publication.

Keeping elderly cells old to understand the aging process

Aging is a key risk factor for many diseases, particularly disorders of the brain like Alzheimer’s or Parkinson’s, which primarily occur in the elderly. So a better understanding of the aging process should provide a better understanding of these neurodegenerative diseases.

The induced pluripotent stem cell (iPSC) technique makes it possible to grow human brain cells, or neurons, in the lab from elderly patient skin samples. Unfortunately, this method has a major pitfall when it comes to aging research: reprogramming skin cells back into the embryonic stem cell-like state of iPSCs strips away many of their old age-related characteristics.

Based on data published last week in Cell Stem Cell, Salk Institute researchers used a different technique called direct reprogramming as a means to keep old cells old. This alternative method sidesteps the need to make iPSCs (which brings cells all the way back to the pluripotent state) and instead converts a skin cell directly into the desired cell type.

First author Jerome Mertens and senior author Rusty Gage (Courtesy of the Salk Institute for Biological Studies).

First author Jerome Mertens and senior author Rusty Gage (Courtesy of the Salk Institute for Biological Studies).

iPSC and direct reprogramming go head-to-head

The study, funded in part by CIRM, relied on skin samples from people ranging in age from newly born to 89 years. The team generated iPSC and iPSC-derived neurons from these samples. They also made so-called induced neurons (iNs) from the skin cells using the direct reprogramming method. Other CIRM grantees have pioneered direct reprogramming of skin into nerve cells (see link below).

Skin cell samples from elderly human donors are directly converted into induced neurons (iNs), shown. (image: Courtesy of the Salk Institute for Biological Studies)

Skin cells from elderly human donors are directly converted into induced neurons (iNs), shown. (Image courtesy of the Salk Institute for Biological Studies).

When comparing skin cells from donors younger than 40 years old versus cells from the over 40 group, the team found several genes had age-dependent activity patterns. Those differences virtually disappeared in the iPSCs and iPSC-derived neurons from the same individuals. However, unlike iPSCs, direct reprogramming of the skin cells to neurons (iNs) hung on to age-dependent differences in gene activity.

Loss of RanBP17 protein a fountain of youth in reverse

A deeper analysis identified one gene called RanBP17 whose activity levels declined with increased age of the donor in both the original skin cells and those directly converted into iNs. But when those same donor skin cells were turned into iPSCs or even iPSC-derived neurons, RanBP17 levels in the older cells were no longer reduced and were on par with RanBP17 levels in the younger cells. In follow up experiments, a reduction in RanBP17 protein led to glitches in the transport of proteins into the cell’s nucleus, which other studies have linked to neurodegenerative diseases as well as the aging process.

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Gene expression patterns of age-related factors like RanBP17 are maintained in induced neurons but not iPSCs. (Mertens et al., 2015)

Altogether, these results encourage researchers to select iNs over iPSC-derived neurons when it comes to faithfully representing the aging process of brain cells. Based on a Salk Institute press release, you can tell that professor Martin Hezter, a contributing author, is excited about future studies with iNs:

By using this powerful approach, we can begin to answer many questions about the physiology and molecular machinery of human nerve cells–not just around healthy aging but pathological aging as well.

 


Related links:

Extending the Lease: Stanford Scientists Turn Back Clock on Aging Cells

In the end, all living things—even the cells in our bodies—must die. But what if we could delay the inevitable, even just for a bit? What new scientific advances could come as a result?

Stanford scientists have found a way to temporarily extend the life of an aging cell.

Stanford scientists have found a way to temporarily extend the life of an aging cell.

In research published this week in the FASEB Journal, scientists at the Stanford University School of Medicine have devised a new method that gives aging DNA a molecular facelift.

The procedure, developed by Stanford Stem Cell Scientist Helen Blau and her team at the Baxter Laboratory for Stem Cell Biology, physically lengthens the telomeres—the caps on the ends of chromosomes that protect the cell from the effects of aging.

When born, all cells contain chromosomes capped with telomeres. But during each round of cell division, those telomeres shrink. Eventually, the telomeres shorten to such an extent that the chromosomes can no longer replicate at the rate they once could. For the cell, this is the beginning of the end.

The link between telomeres and cellular aging has been an intense focus in recent years, including the subject of the 2009 Nobel Prize in Physiology or Medicine. Extending the lifespan of cells by preventing—or reversing— the shortening of telomeres can not only boost cell division during laboratory studies, but can also lead to new therapeutic strategies to treat age-related diseases.

“Now we have found a way to lengthen human telomeres… turning back the internal clock in these cells by the equivalent of many years of human life,” explained Blau in a press release. “This greatly increases the number of cells available for studies such as drug testing or disease modeling.”

The method Blau and her team describe involves the use of a modified bit of RNA that boosts the production of the protein telomerase. Telomerase is normally present in high levels in stem cells, but drops off once the cells mature. Blau’s modified RNA gives the aging cells a shot of telomerase, after which they begin behaving like cells half their age. But only for about 48 hours, after which they begin to degrade again.

The temporary nature of this change, say the researchers, offers significant advantages. On the biological level, it means that the treated cells won’t begin dividing out of control indefinitely, minimizing the risk of tumor formation. The study’s first author John Ramunas offers up some additional pluses to their method:

“Existing methods of extending telomeres act slowly, whereas our method acts over just a few days to reverse telomere shortening that occurs over more than a decade of normal aging. This suggests that a treatment using our method could be brief and infrequent.”

Indeed, the genetic disease Duchenne muscular dystrophy is in part characterized by abnormally short telomeres. Blau reasons that their discovery could lead to better treatments for this disease. Their immediate future steps involve testing their method in a variety of cell types. Said Blau:

“We’re working to understand more about the differences among cell types, and how we can overcome those differences to allow this approach to be more universally successful.”

Hear more about stem cells and muscular dystrophy in our recent Spotlight on Disease featuring Helen Blau: