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.

Stem cell stories that caught our eye: insights into stem cell biology through telomeres, reprogramming and lung disease

Here are some stem cell stories that caught our eye this past week. Some are groundbreaking science, others are of personal interest to us, and still others are just fun.

Telomeres and stem cell stability: too much of a good thing

Just like those plastic tips at the end of shoelaces (fun fact: they’re called aglets), telomeres form a protective cap on the end of chromosomes. Because of the way DNA replication works, the telomeres shorten each time a cell divides. Trim away enough of the telomere over time and, like a frayed shoelace, the chromosomes become unstable and an easy target for damage which eventually leads to cell death.

telomere_caps

Telomeres (white dots) form a protective cap on chromsomes (gray). (Wikimedia) 

Stem cells are unique in that they contain an enzyme called telomerase that lengthens telomeres. Telomerase activity and telomere lengthening are critical for a stem cell’s ability to maintain virtually limitless cell divisions. So you’d assume the longer the telomere, the more stable the cell. But Salk Institute scientists reported this week that too much telomere can be just as bad, if not worse, than too little.

The CIRM-funded work, which was published in Nature Structural & Molecular Biology, used genetic engineering to artificially vary telomerase activity in human embryonic stem cells. Cells with low telomerase activity had shorter telomeres and died. This result wasn’t a surprise since the short telomeres-cell death observation has been well documented. Based on those results, the team was expecting cells with boosted telomerase activity and, in turn, extended telomeres would be especially stable. But that’s not what happened as senior author Jan Karlseder mentioned in a Salk press release:

“We were surprised to find that forcing cells to generate really long telomeres caused telomeric fragility, which can lead to initiation of cancer. These experiments question the generally accepted notion that artificially increasing telomeres could lengthen life or improve the health of an organism.”

The researchers also examined induced pluripotent stem (iPS) cells in the study and found that the cells contain “footprints” of telomere trimming. So the team is in a position to study how a cell’s telomere history relates to how well it can be reprogrammed into iPS cells. First author Teresa Rivera pointed out the big picture significance of this finding:

“Stem cell reprogramming is a major scientific breakthrough, but the methods are still being perfected. Understanding how telomere length is regulated is an important step toward realizing the promise of stem cell therapies and regenerative medicine.”

jan-karlseder_teresa-rivera-garcia0x8c7144w

Jan Karlseder and Teresa Rivera

Lego set of gene activators takes trial and error out of cellular reprogramming

To convert one cell type into another, stem cell researchers rely on educated guesses and a lot of trial and error. In fact, that’s how Shinya Yamanaka identified the four Yamanaka Factors which, when inserted into a skin cell, reprogram it into the embryonic stem cell-like state of an iPS cell. That ground-breaking discovery ten years ago has opened the way for researchers worldwide to specialize iPS cells into all sorts of cell types from nerve cells to liver cells. While some cell types are easy to generate this way, others are much more difficult.

Reporting this week in PNAS, a University of Wisconsin–Madison research team has developed a nifty systematic, high-throughput method for identifying the factors necessary to convert a cell from one type to another. Their strategy promises to free researchers from the costly and time consuming trial and error approach still in use today.

The centerpiece of their method is artificial transcription factors (ATFs). Now, natural transcription factors – Yamanaka’s Factors are examples – are proteins that bind DNA and activate or silence genes. Their impact on gene activity, in turn, can have a cascading effects on other genes and proteins ultimately causing, say a stem cell, to start making muscle proteins and turn into a muscle cell.

Transcription factors are very modular proteins – one part is responsible for binding DNA, another part for affecting gene activity and other parts that bind to other proteins. The ATFs generated in this study are like lego versions of natural transcription factors – each are constructed from combinations of different transcription factor parts. The team made nearly 3 million different ATFs.

As a proof of principle, the researchers tried reproducing Yamanaka’s original, groundbreaking iPS cell experiment. They inserted the ATFs into skin cells that already had 3 of the 4 Yamanaka factors, they left out Oct4. They successfully generated iPS with this approach and then went back and studied the makeup of the ATFs that had caused cells to reprogram into iPS cells. Senior author Aseem Ansari gave a great analogy in a university press release:

“Imagine you have millions of keys and only a unique key or combination of keys can turn a motor on. We test all those keys in parallel and when we see the motor fire up, we go back to see exactly which key switched it on.”

atf_ips_cells

Micrograph of induced pluripotent stem cells generated from artificial transcription factors. The cells express green fluorescent protein after a key gene known as Oct4 is activated. (ASUKA EGUCHI/UW-MADISON)

The analysis showed that these ATFs had stimulated gene activity cascades which didn’t directly involve Oct4 but yet ultimately activated it. This finding is important because it suggests that future cell conversion experiments could uncover some not so obvious cell fate pathways. Ansari explains this point further:

“It’s a way to induce cell fate conversions without having to know what genes might be important because we are able to test so many by using an unbiased library of molecules that can search nearly every corner of the genome.”

This sort of brute force method to accelerate research discoveries is music to our ears at CIRM because it ultimately could lead to therapies faster.

Search for clues to treat deadly lung disease

When researchers don’t understand what causes a particular disease, a typical strategy is to compare gene activity in diseased vs healthy cells and identify important differences. Those differences may lead to potential paths to developing a therapy. That’s the approach a collaborative team from Cincinnati Children’s Hospital and Cedars-Sinai Medical took to tackle idiopathic pulmonary fibrosis (IPF).

IPF is a chronic lung disease which causes scarring, or fibrosis, in the air sacs of the lung. This is the spot where oxygen is taken up by tiny blood vessels that surround the air sacs. With fibrosis, the air sacs stiffen and thicken and as a result less oxygen gets diffused into the blood and starves the body of oxygen.  IPF can lead to death within 2 to 5 years after diagnosis. Unfortunately, no cures exist and the cause is unknown, or idiopathic.

(Wikimedia)

(Wikimedia)

The transfer of oxygen from air sacs to blood vessels is an intricate one with many cell types involved. So pinpointing what goes wrong in IPF at a cellular and molecular level has proved difficult. In the current study, the scientists, for the first time, collected gene sequencing data from single cells from healthy and diseased lungs. This way, a precise cell by cell analysis of gene activity was possible.

One set of gene activity patterns found in healthy sample were connected to proper formation of a particular type of air sac cell called the aveolar type 2 lung cell. Other gene patterns were linked to abnormal IPF cell types. With this data in hand, the researchers can further investigate the role of these genes in IPF which may open up new therapy approaches to this deadly disease.

The study funded in part by CIRM was published this week in Journal of Clinical Investigation Insight and a press release about the study was picked up by PR Newswire.

Science and Improv: Spotlight on CIRM Bridges Scholar Jill Tsai

As part of our CIRM scholar series, we’re featuring the research and career accomplishments of CIRM funded students.

What do science and improv have in common? The answer is not a whole lot. However, I recently met a talented student from our CIRM Bridges master’s program who one day is going to change this.

Jill Tsai

Jill Tsai, CIRM Bridges scholar

Meet Jill Tsai. She recently graduated from the CIRM Bridges program at the Scripps Research Institute in San Diego and is now starting a PhD program in cancer biology at the City of Hope in Duarte California.

Jill received her Bachelors from UC Merced general biology and went to Cal Poly Pomona for a Master’s program in cancer research. While at Cal Poly Pomona, she successfully applied for a CIRM Bridges internship that allowed her to finish her Master’s degree at Scripps in the lab of Dr. Lazzerini Denchi.

I met Jill at the 2016 Bridges Conference in July and was immediately impressed by her passion for science and communications. I was also intrigued by her interest in improv and how she balances her time between two very different passions. I’m thrilled that Jill agreed to an interview for the Stem Cellar as I think it’s valuable to read about scientists who are pursuing multiple passions not necessarily related to science.

Enjoy!

Q: What did you study during your Bridges internship?

JT: I was a research intern in the lab of Dr. Lazzerini Denchi. In his lab, we study telomeres, which are the pieces of DNA at the end of chromosomes that help protect them from being degraded. We’re specifically looking at proteins that help maintain telomere function in mouse stem cells. We do big protein pull downs to try to figure out what new and novel proteins are surrounding the mechanisms that maintain telomere function, and then we do functional assays to figure out what these proteins do.

Lazzerini Denchi’s lab focuses on basic research and how certain proteins affect telomere length and also the telomere deprotection response. One function of telomeres is that they suppress the double and single stranded DNA repair mechanism. If you don’t suppress those mechanisms, then the ends of those linear chromosomes look exactly like double stranded DNA breaks and repair proteins try to fix them by fusing those chromosomes together.

There are great pictures from Lazzerini Denchi’s first author publication showing chromosomes hooked end to end to end like long strings of spaghetti as a result of telomere deprotection. We are studying novel proteins that assist telomeres with the deprotection response and determining whether these proteins have some other kind of function as well.

Telomere deprotection results in chromosomes that are linked together (right) instead of separate (left). (Source Denchi et al. Nature)

Telomere deprotection results in chromosomes that are linked together (right) instead of separate (left). (Source Nature: Denchi et al., 2007)

Our larger focus in the lab is being able to understand cancer and specific telomere related genetic disorders that are associated with cancer.

Q: What was your CIRM Bridges experience like?

JT: CIRM was really amazing, and I credit it a lot for being able to start a PhD this fall. I’d been working in my lab at Cal Poly Pomona for five years, and my research unfortunately wasn’t working out. I was probably going to have to quit the program or take an out with an easier project. When I applied to CIRM, I was hoping to get the internship because if I didn’t get it, I was going to go down a completely different career path.

The CIRM internship was very valuable to me. It provided training through stem cell classes and lectures and allowed me to immerse myself in a real lab that had real equipment and personnel. The experience took my research knowledge to the next level and then some. And I knew for sure it had when I was at the poster session during the Bridges conference. I was walking around and asking students about their research, and I understood clearly the path of their research. I knew what questions were good to ask and what the graphs meant without having to take them home and dissect them. It was extremely satisfying to be able to understand other’s scientific research by just listening to them.

I am so excited to start my PhD in the fall. For the first time, I feel confident about my foundational biology and research skills. I also have a better understanding of myself and where I need to improve in comprehension and technique. I am ready to jump into grad school and improve as a scientist.

Q: What are your future career steps?

JT: I want to do something that involves teaching or being able to educate people. I’ve worked as a TA in my master’s program for a few years, and I really enjoy that experience of clarifying complex subjects for people. But to be honest, I also don’t know what I want to do right now so I’m keeping my options open.

Q: What’s your favorite thing about being scientist?

JT: Being a scientist forces you to never be complacent in what you understand. If I had never gotten my master’s, there would be this whole level of critical thinking that I wouldn’t have right now. Learning more is one of the biggest reasons why I want to get my PhD even if I don’t know exactly what I want to do yet.

I want to be able to think at a higher level because I think it’s valuable. And I see my Professor at Scripps: he has all these publications under his belt, but he’s always tinkering with things and he’s always learning new software and he’s always reading new papers. As a scientist, you can’t be stagnant in your learning, and I think because of that you’re always pushing yourself to your best potential.
Q: Do you have advice for future Bridges students?

JT: For anyone who is interested in doing a PhD, this is the world’s best preparatory program. After you start a PhD, you hit the ground running. If I were to give advice, I’d say to not be too hard on yourself. There’s going to be expectations put on you that you might not be ready for and you might not do the best job. But you should try your best and know it’s going to help you grow.

Usually people who go into PhD programs are people that have always done well in school. But it’s important to know that learning in grad school is very different than how we are taught to learn elsewhere. Every other time it’s just like show up, listen, take the test you’re done. A PhD relies on a little bit of luck, getting the right project, and doing everything meticulously.

Q: What are your hobbies?

JT: My favorite hobby is improv comedy. What I really like about improv is that it is so different from science and it helps me to relax after work.

Improv is performing comedic scenes on stage with a bunch of people without a script. Skills that it requires are not being stuck in your own head and really paying attention to what’s going on around you. You also need to take big risks and not worry so much about what the end result is going to be, which is very different from research. It’s a nice break to be able to make big giant mistakes and know that after that day it doesn’t matter.

As a researcher, it’s hard to make friends, and even if you have friends, it’s hard to find the time to hang out with them. I love improv because it’s a built in activity. All of my friends outside of work are in improv. We show up and we play make believe together on stage – it’s just a really nice atmosphere. In improv we teach a philosophy that everything you have is enough. Everything you come in with is enough. It’s really nice, because being an adult is hard and life is hard. So it’s a nice thing to hear.

Jill's Improv team.

Flyspace Improv team.

Q: Do you see yourself combining your passions for science and improve in the future?

JT: I do. I don’t know what I want to do yet as a career, but improv is such a big part of my identity that it will always play a role in my life. Improv is so important in communication and interpersonal connections. I believe everyone in science could benefit from it. Ideally, I will find a career that allows me to use both of these passions to help people.

Outsmarting cancer’s deadly tricks

Cancer cells are devious monsters that kill people by sabotaging normal cell functions toward a path of uncontrolled cell growth. Without an effective treatment, aggressive cancers can crowd out healthy tissue and ultimately cause organ failure and death. This devastation by design makes it seem as though a cancer cell has a mind of its own but in reality it’s all due to mindless mutations in DNA. Gaining a deep understanding of those mutations provides scientists with insights into the molecular mechanisms of cancer which can help pinpoint targets for potential cancer treatments.

A team at The Scripps Research Institute (TSRI) followed the trail of such a mutation in a gene called POT1. Today in Cell Reports the researchers, funded in part by CIRM, describe their identification of a novel mechanism for cancer progression in cells carrying the POT1 mutation and they also speculate on the development on a unique therapeutic strategy.

Chromosomes go to pot without POT1
The POT1 protein is one component of shelterin, a multi-protein structure that binds to and protects telomeres, a region of DNA found at the ends of chromosomes. The team found that when POT1’s function is disrupted by mutation, the telomeres become vulnerable to damage which leads to chromosome instability. As a result, many regions of DNA on the chromosomes get rearranged leading to further gene mutations that in turn can accelerate the process of cancerous growth.

Telomere_caps

Human chromosomes (grey) capped by telomeres (white) Wikipedia

However, in the case of POT1 mutations, the DNA damage in the unstable chromosomes stimulates an enzyme called ATR that’s known to shut down cell division and initiate apoptosis, or programmed cell death. Now, unless I’m missing something, cells that have either stopped dividing or even died would seem to be the opposite of cancer progression. So why then are POT1 mutations found in a number of cancers such as leukemia, melanoma (skin cancer) and glioma (brain cancer)? As TSRI Associate Professor Eros Lazzerini Denchi, a co-leader on the publication, mentions in a press release, this conundrum presented an opportunity to better understand POT1 related cancers:

lazzerini_denchi

Eros Lazzerini Denchi

“Somehow those cells found a way to survive—and thrive. We thought that if we could understand how that happens, maybe we could find a way to kill those cells.”

 

Mutant POT1 and p53: diabolical partners in cancer progression
The team looked for answers by studying the POT1 mutation in the presence of a mutated form of the p53 tumor suppressor gene, found in over 50% of all human cancers. Mice bred with the POT1 mutation alone formed no cancers while those animals with the p53 mutation alone developed T cell lymphomas, a type of immune system cancer, by 20 weeks and survived 24 weeks. Mice with both mutations fared much worse with median survival times of just 17 weeks. So somehow the p53 mutation was bringing out the potential of the POT1 mutation to cause aggressive cancer growth.

Further experiments revealed that the p53 mutation quashed the ATR enyzme’s programmed cell death signal which the team had shown was stimulated by the POT1 mutation. As a result, the cells avoided programmed cell death. Because the cells had no mechanism to die, more cancer-causing mutations had the opportunity to develop from the chromosome instability caused by the POT1 mutation.

The bright side to this diabolical cooperation between mutant POT1 and p53 is that it presents a possible opening for new treatment strategies. It turns out that no cell, not even a cancerous one, can survive in the complete absence of ATF. Since cells with the POT1 mutations already have a reduced level of ATF, the authors suggest that delivery of low doses of ATF inhibitors, which have already been developed for the clinic, could kill cancer cells without affecting healthy cells. No doubt the team is eager to follow up on this hypothesis.

It’s comforting to know that there are crafty scientists out there who are closing in on ways to outsmart the sneaky tactics of cancer cells. And it wouldn’t be possible without this fundamental research, as Lazzerini Denchi points out:

“This study shows that by looking at basic biological questions, we can potentially find new ways to treat cancer.”

 

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: