Deepak Srivastava

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

/ Karen Ring / Leave a comment

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.

Understanding two heart problems by studying the domino effect of one gene network

/ Todd Dubnicoff / Leave a comment

Although heart muscle cells, or cardiomyocytes, are specialized to help pump blood to the organs, they nonetheless carry all the genetic instructions for becoming a nerve cell, an intestinal cell, a liver or any cell type in the body. But at the moment in time that the fetal heart begins to develop, master switch proteins, called transcription factors, act like the first tile in an extremely complex pattern of dominos and set off a chain of events which lead to the activation of heart muscle specific genes in cardiomyocytes as well as the silencing of genes important for the development other cells types.

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cardiomyocytes

It’s truly amazing that this process comes together to create functioning hearts in the about 355,000 babies that are born in the world each day. But it isn’t always flawless as heart defects occur in about 1% of all live births. By studying a family with a history of heart defects, scientists at the Gladstone Institutes have gained a deeper understanding of how gene networks go awry,  causing heart defects as well as heart disease later in life. This CIRM-funded work was published today in Cell.

Half the children in the family studied by the Gladstone team were born with a hole in the wall between the two chambers of the heart. Back in 2003, the family approached Deepak Srivastava, head of the cardiovascular institute at Gladstone, for help. A genetic analysis by Srivastava’s team found that all of the affected children carried a mutation in the GATA4 gene, which encodes a heart specific transcription factor protein. Seven years later the children developed heart disease that led to weaker heart pumping. Although the two heart problems were not related, they suspected both were caused by the GATA4 mutation and sought to understand how that could be the case.

Srivastava’s team sought to understand how the GATA4 mutation could be causing both health problems. They collected skin samples from the affected children and generated cardiomyocytes using the induced pluripotent stem cell technique. Cells were also collected from the children’s healthy siblings. In the laboratory, the cells were analyzed for how well they functioned, such as their ability to contract. All of these tests showed that the cells carrying the GATA4 mutation had impaired function compared to the healthy cells. These findings provide a basis for the heart disease found in the children during their teens.

In terms of the heart wall defect, the team examined the GATA4 protein’s interaction with the protein TBX5, another transcription factor that is also mutated in cases of this defect. Both proteins regulate genes by directly binding to DNA as well as interacting with each other. In cells with the defective GATA4, the research discovered TBX5 did not bind well to the DNA. The lack of TBX5 led to a disruption in the activation of genes that play a role in the development of the heart wall.

TBX5 and GATA4 also work together in cardiomyocytes to silence genes that play a role in other cell types. But the scientists found that the because the GATA4 mutation hindered its interaction with TBX5, those non-heart specific genes we’re no longer repressed causing further disruption to proper cardiomyocyte development. Srivastava summed up these results in an institute press release:

srivastava-profile

Deepak Srivastava

“By studying the patients’ heart cells in a dish, we were able to figure out why their hearts were not pumping properly. Investigating their genetic mutation revealed a whole network of genes that went awry, first causing septal [heart wall] defects and then the heart muscle dysfunction.”

Now, because GATA4 and TBX5 are those first domino tiles in very intricate networks of genes, targeting those proteins for future therapy development wouldn’t be wise. Their effects are so widespread that blocking their actions would do more harm than good. But finding drugs that might affect only a branch of GATA4/TBX5 actions could result in new therapy approaches to heart defects and disease.

deepak-yen-sin-22 Deepak Srivastava and Yen-Sin Ang [Photo: Chris Goodfellow, Gladstone Institutes]

Yen-Sin Ang, the first author on the report, thinks these finding could prove fruitful for other diseases as well:

“It’s amazing that by studying genes in a two-dimensional cluster of heart cells, we were able to discover insights into a disease that affects a complicated three-dimensional organ. We think this conceptual framework could be used to study other diseases caused by mutations in proteins that serve as master regulators of whole gene networks.”

The New World That iPS Cells Will Bring

/ Karen Ring / Leave a comment

A stem cell champion was crowned last month. Dr. Takahashi from the RIKEN center in Japan received the prestigious Ogawa-Yamanaka Prize for developing a human iPS cell therapy to treat a debilitating eye disease called macular degeneration. We wrote about the event held at the Gladstone Institutes in a previous blog and saved the juicy insights from Dr. Takahashi’s scientific presentation and her CIRM-exclusive interview for today.  We also put together a two minute video (see below) based on the interview with her as well as with Dr. Deepak Srivastava, Director of the Gladstone Institute of Cardiovascular Disease and Mr. Hiro Ogawa, a co-founder of the Ogawa-Yamanaka Prize.

Dawn of iPS Cells

As part of the ceremony, Dr. Takahashi gave a scientific talk on the “new world that iPS cells will bring”. She began with a historical overview of stem cell research, starting with embryonic stem cells and the immune rejection and ethical issues associated with their use. She then discussed Dr. Yamanaka’s game-changing discovery of iPS cells, which offered new strategies for disease modeling and potential treatments that avoid some of the issues can complicate embryonic stem cells.

Her excitement over this discovery was palpable as she explained how she immediately jumped into the iPS cell field and got her hands dirty. Knowing that this technology could have huge implications for regenerative medicine and the development of stem cell therapies, she made herself a seemingly unattainable promise. “I said to myself, I will apply iPS cells to humans within five years. And I became a woman of her words.”

An iPS cell world

Dr. Takahashi went on to tell her success story, and why she chose to develop an iPS cell therapy to treat a disease of blindess, age-related macular degeneration (AMD). She explained how AMD is a serious unmet medical need. The current treatment involves injections of an antibody that blocks the activity of a growth factor called VEGF. This factor causes an overgrowth of blood vessels in the eye, which does major damage to the cells in the retina and can cause blindness. This therapy however, is only useful for some forms of AMD not all.

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Dr. Masayo Takahashi describing her team’s iPS-based therapy for macular degeneration during the inaugural ceremony for the Ogawa-Yamanaka Prize at The Gladstone Institutes.

She believed she could fix this problem by developing an iPS cell technology that would replace lost cells in the eye in AMD patients. To a captivated crowd, she described how she was able to generate a sheet of human iPS derived cells called retinal pigment epithelial (RPE) cells from a patient with AMD. This sheet was transplanted into the eye of the patient in the first ever iPS cell clinical trial. The transplant was successful and the patient had no adverse effects to the treatment.

While the clinical trial is currently on hold, Dr. Takahashi explained that she and her team learned a lot from this experience. They are currently pursuing additional safety measures for their iPS cell technology to make sure that the stem cell transplants will not cause cancer or other bad outcomes in humans.

Autologous vs. Allogeneic?

Another main topic in her speech, was the choice between using autologous (iPS cells made from a patient and transplanted back into the same patient) and allogeneic (iPS cells made from a donor and then transplanted into a patient) iPS cells for transplantation in humans. Dr. Tahakashi’s opinion was that autologous would be ideal, but not scaleable due to high costs and the amount of time it would take to make iPS cell lines for individual patients.

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iPS cells reprogrammed from a woman’s skin. Blue shows nuclei. Green and red indicate proteins found in reprogrammed cells but not in skin cells (credit: Kathrin Plath / UCLA).

Her solution is to use an arsenal of allogeneic iPS cells that can be transplanted into patients without rejection by the immune system. This may be possible if both the donor and the patient share the same combination (called a “haplotype”) of cell surface proteins on their immune cells called human leukocyte antigens (HLA). She highlighted the work ongoing in Japan to generate a stock of HLA haplotype matched iPS cell lines that could be used for most of the Japanese population.

 Changing the regulatory landscape in Japan

It was clear from her talk that her prize winning accomplishments didn’t happen without a lot of blood, sweat, and tears both at the bench and in the regulatory arena. In a CIRM exclusive interview, Dr. Takahashi further explained how her pioneering efforts to bring iPS cells to patients helped revolutionize the regulatory landscape in Japan to make it faster and easier to test iPS cells in the clinic.

“The power of iPS cells changed the Japanese [regulatory] law dramatically. We made a new chapter for regenerative medicine in pharmaceutical law. With that law, the steps are very quick for cell therapy. In the new chapter [of the law] … conditional approval will be given if you prove the safety of the cell [therapy]. It’s very difficult to show the efficacy completely in a statistical manner for regenerative medicine. So the law says we don’t have to prove the efficacy [of the therapy] thoroughly with thousands of patients. Only a small number of patients are needed for the conditional approval. That’s the big difference.”

We were curious about Dr. Takahashi’s involvement in getting these regulatory changes to pass, and learned that she played a significant role on the academic side to convince the Japanese ministry to change the laws.

“This law was made in the cooperation with the ministry and academia. That was one thing that had never happened before. Academia means mainly the Japanese society for the regenerative medicine, and I’m a committee member of that. So we talked about the ideal law for regenerative medicine, and our society suggested various points to the ministry. And to our surprise, the ministry accepted almost all of the points and included them into the law. That was wonderful. Usually we are very conservative and slow in changing, but this time, I was amazed how quickly the law has been changed. It’s the power of iPS cells.”

The iPS cell future is now

As a champion stem cell scientist and a leader in regenerative medicine, Dr. Takahashi took the opportunity at the end of the event to emphasize that all scientists and clinicians in the iPS cell therapy field need to consider three things: develop safe protocols for generating iPS cells that become standard practice, understand the patient’s needs by focusing on how to benefit patients the most, and think of iPS cells as a treatment and consider the risk when developing these therapies.

The new world of iPS cells is opening doors onto uncharted territory, but Dr. Takahashi’s wise words provide a solid roadmap for the future success of iPS cell therapies.