Monthly Archives: February 2012

Teeth ‘transform into liver cells’

 The compound that causes bad breath could help fuel the development of stem cells from dental pulp, according to a study.

Hydrogen sulphide (H2S) – which has the characteristic smell of rotten eggs – appears to help teeth stem cells transform into liver cells, which could prove a valuable treatment for patients, researchers found.

H2S is a major cause of halitosis or bad breath, which is of concern to millions of people worldwide.

A team of experts took stem cells from dental pulp – the central part of the tooth made up of connective tissue and cells – obtained from the teeth of dental patients undergoing routine tooth extractions.

The cells were separated into two groups, with one group incubated in a H2S chamber and the other group acting as a control. The cells were analysed after three, six and nine days to see if they had transformed into liver cells. Their ability to function as liver cells was also tested, including the ability to store glycogen and collect urea.

The study, published in the Journal of Breath Research, from the Institute of Physics, suggested liver cells could be produced in high numbers of high purity.

Lead author of the study, Dr Ken Yaegaki, from Nippon Dental University in Japan, said: “High purity means there are less ‘wrong cells’ that are being differentiated to other tissues, or remaining as stem cells. Moreover, these facts suggest that patients undergoing transplantation with the hepatic (liver) cells may have almost no possibility of developing teratomas (tumours) or cancers.

“Until now, nobody has produced the protocol to regenerate such a huge number of hepatic cells for human transplantation. Compared to the traditional method of using fetal bovine serum to produce the cells, our method is productive and, most importantly, safe.”

Professor Anthony Hollander, head of cellular and molecular medicine at Bristol University, said much more research was needed.

He said: “This is interesting work in a new direction but there’s a long way to go to see if it is usable therapeutically. This is potential evidence but the real test of the liver cell is whether it metabolises specific toxins,” he said, adding that that requires enzyme function tests.”

 

Source: The Press Association


Ovary Stem Cells Can Produce New Human Eggs, Scientists Say

 Although it has long been assumed that women are born with all the eggs they will ever have in a lifetime, recent research has hinted that that might not be the case. Now researchers report the strongest evidence yet that women may be able to replenish their supply of eggs after they are born — and perhaps after age or disease might have normally hindered their fertility.

The findings could help trigger new treatments for infertility and rejigger current views about how eggs develop in the ovary and whether aging should affect women’s ability to reproduce.

In the new study, a milestone in an eight-year research journey led by Jonathan Tilly, director of the Vincent Center for Reproductive Biology at Massachusetts General Hospital, scientists successfully isolated a population of egg stem cells from human ovarian tissue and showed that these cells could go on to produce what appear to be human eggs.

Tilly had previously isolated a similar population of egg stem cells from mouse ovaries, but critics raised questions about whether the cells were truly stem cells — cells that were truly the precursors of eggs, or oocytes — or whether they were actually very early, immature eggs themselves. Two groups, including Tilly’s, have since verified the results, showing that the cells are stem cells that were capable of going on to form viable oocytes that could be fertilized to produce healthy mouse pups.

That led Tilly to investigate whether a similar egg stem cell existed in humans. But obtaining healthy ovarian tissue was a problem, since most ovarian samples currently available for research are obtained from cancer patients hoping to spare their tissue from treatment. Coincidentally, Tilly learned that a former research fellow from his lab, now working at Saitama Medical University in Japan, had been perfecting a technique for removing and freezing intact ovaries from patients undergoing sex change operations because of a gender identity disorder.

By the time Tilly approached his colleague about his egg stem cell work, Yasushi Takai had already preserved 30 sets of intact ovaries. “When he told me this, I was jumping for joy. I couldn’t believe we’d have unique access to that amount of tissue,” says Tilly.

Through his work with the mouse egg stem cells, Tilly had developed a key system for identifying and isolating stem cells from ovarian tissue. Drawing on previous work in the field that identified certain proteins on the surface of cells that distinguished stem cells from other cells, he was able to separate out the appropriate marked cells.

Stem cells are unique from other cells in that they don’t divide to create two identical daughter cells. Their hallmark feature is the ability to continue generating new stem cells; to do this, they produce one daughter cell that goes on to divide and develop and eventually die, and another stem cell that doesn’t divide or develop into other cells, but instead retains its “stemness” in a type of anticipatory animation, ready to develop into whatever type of cell might be needed.

It was these egg stem cells in the ovary that Tilly pulled out from human tissue, using the same protocol he used to extract the egg stem cells from mice. “The cell sorting worked perfectly the first time. The cells popped right out. They were the right size, the right shape, the right morphology and in the right numbers,” he says.

Then came the verification, which included rigorous tests to ensure that they were indeed stem cells. One easy technique involved simply letting the cells grow. When Tilly and his team transferred the egg stem cells into a dish, they started to expand rapidly, blanketing the surface and dividing over and over again. That was a sign, he says, that they weren’t immature egg cells, but stem cells that had not yet embarked on the path to becoming oocytes.

Because eggs and sperm are germ line cells, they must go through a process in which they lose half their genetic material; in humans, eggs and sperm each contain only 23 pairs of chromosomes, so that after fertilization (when sperm meets egg), all of the cells in the resulting embryo contain a total of 46 pairs of chromosomes. In order to shed their extra DNA, eggs and sperm undergo a special cell division called meiosis; once they enter meiosis, they can’t divide again, which is how Tilly knew the cells in the dish were not eggs. 

But that still didn’t say anything about how the cells might work in the body. So he then embedded the egg stem cells back into the ovarian tissue samples from Japan and transplanted the entire system under the skin on the backs of mice, in order to give the tissue a nourishing supply of blood. (Transplanting the tissue into women would have posed ethical difficulties.) Within a week, the stem cells starting making immature egg cells in the makeshift human ovary that Tilly’s team had created in the mouse.

“We placed the cells in an environment that was the closest match to the natural in vivo [human] setting,” he says. “And we saw the new oocytes, made from the oocyte stem cells, embedded in the ovary tissue along with the host oocytes, indistinguishable from the host oocytes.”

How could they be sure the new eggs had originated from the transplanted stem cells? Because the researchers had tagged the egg stem cells with the gene that gives jellyfish their green glow — so any eggs arising from green-glowing stem cells would fluoresce green too.

Tilly is already pushing the work forward, collaborating with a group in England that has focused on documenting the earliest stages of oocyte development, just after it emerges from stem cells. By joining forces, he says it will be possible to take the next step and see whether the human version of oocytes generated from egg stem cells can be fertilized and generate viable embryos, just as the mouse versions have. (In the U.K., unlike in the U.S., it’s ethically acceptable to fertilize eggs and conduct research on early embryos.)

If women are constantly producing new eggs, says Tilly, that means it may be possible to intervene with the appropriate hormones or growth factors to help ovaries produce more eggs or to improve egg quality in order to reverse infertility.

It may also mean that current ideas about aging and waning fertility may be overturned as well. Recent mouse studies showed that when oocyte stem cells were removed from menopausal female mice and transferred into younger mice, the stem cells were able to make viable eggs. “When they transferred the tissue into a young ovarian environment, the stem cells woke back up and, lo and behold, a new population of oocytes formed,” says Tilly. “That tells us that perhaps ovarian failure at menopause isn’t incompatible with the idea of these cells existing. Maybe we need to rethink how menopause is happening and if these cells are still there, but it’s the organs that are failing with age, what does that mean down the road in terms of clinical interventions?”

In other words, if it’s aging equipment — the ovary — that’s the problem, understanding what it is about the ovarian environment that eventually makes it difficult for egg stem cells to continue generating new oocytes may be key to addressing problems behind infertility. And while we aren’t quite there yet, it certainly makes the possibility of being able to use egg stem cells to create new supplies of eggs and improve procedures like IVF that much more real.

Source: Alice Park, Time


Researchers Develop Method of Directing Stem Cells to Increase Bone Formation and Bone Strength

A research team led by UC Davis Health System scientists has developed a novel technique to enhance bone growth by using a molecule which, when injected into the bloodstream, directs the body’s stem cells to travel to the surface of bones. Once these cells are guided to the bone surface by this molecule, the stem cells differentiate into bone-forming cells and synthesize proteins to enhance bone growth. The study, which was published online today in Nature Medicine, used a mouse model of osteoporosis to demonstrate a unique treatment approach that increases bone density and prevents bone loss associated with aging and estrogen deficiency. 

“There are many stem cells, even in elderly people, but they do not readily migrate to bone,” said Wei Yao, the principal investigator and lead author of the study. “Finding a molecule that attaches to stem cells and guides them to the targets we need is a real breakthrough.”

Researchers are exploring stem cells as possible treatments for a wide variety of conditions and injuries, ranging from peripheral artery disease and macular degeneration to blood disorders, skin wounds and diseased organs. Directing stem cells to travel and adhere to the surface of bone for bone formation has been among the elusive goals in regenerative medicine.

The researchers made use of a unique hybrid molecule, LLP2A-alendronate, developed by a research team led by Kit Lam, professor and chair of the UC Davis Department of Biochemistry and Molecular Medicine. The researchers’ hybrid molecule consists of two parts: the LLP2A part that attaches to mesenchymal stem cells in the bone marrow, and a second part that consists of the bone-homing drug alendronate. After the hybrid molecule was injected into the bloodstream, it picked up mesenchymal stem cells in the bone marrow and directed those cells to the surfaces of bone, where the stem cells carried out their natural bone-formation and repair functions.

“Our study confirms that stem-cell-binding molecules can be exploited to direct stem cells to therapeutic sites inside an animal,” said Lam, who also is an author of the article. “It represents a very important step in making this type of stem cell therapy a reality.”

Twelve weeks after the hybrid molecule was injected into mice, bone mass in the femur (thigh bone) and vertebrae (in the spine) increased and bone strength improved compared to control mice who did not receive the hybrid molecule. Treated mice that were normally of an age when bone loss would occur also had improved bone formation, as did those that were models for menopause.

Alendronate, also known by the brand name Fosamax, is commonly taken by women with osteoporosis to reduce the risk of fracture. The research team incorporated alendronate into the hybrid molecules because once in the bloodstream, it goes directly to the bone surface, where it slows the rate of bone breakdown. According to Nancy Lane, a co-investigator on the study and director of the UC Davis Musculoskeletal Diseases of Aging Research Group, the dose of alendronate in the hybrid compound was low and unlikely to have inhibited the compound’s therapeutic effect.

“For the first time, we may have potentially found a way to direct a person’s own stem cells to the bone surface where they can regenerate bone,” said Lane, who is an Endowed Professor of Medicine and Rheumatology and an expert on osteoporosis. “This technique could become a revolutionary new therapy for osteoporosis as well as for other conditions that require new bone formation.”

Osteoporosis is a major public health problem for 44 million Americans. One in two women will suffer a fracture due to osteoporosis in their lifetime. Although effective medications are available to help prevent fracture risk, including alendronate, their use is limited by potential harmful effects of long-term use.

The major causes for osteoporosis in women include estrogen deficiency, aging and steroid excess from treatment of chronic inflammatory conditions such as rheumatoid arthritis. Generally, the osteoporosis generated by these metabolic conditions results from change in the bone remodeling cycle that weakens the bone’s architecture and increases fracture risk.

Mesenchymal stem cells from bone marrow induce new bone remodeling, which thicken and strengthen bone.

The authors noted that the potential use of this stem cell therapy is not limited to treating osteoporosis. They said it may prove invaluable for other disorders and conditions that could benefit from enhanced bone rebuilding, such as bone fractures, bone infections or cancer treatments.

“These results are very promising for translating into human therapy,” said Jan Nolta, professor of internal medicine, an author of the study and director of the UC Davis Institute for Regenerative Cures. “We have shown this potential therapy is effective in rodents, and our goal now is to move it into clinical trials.”

Funding for the study came from the Endowment on Healthy Aging and the National Institutes of Health. The California Institute for Regenerative Medicine has given the team a planning grant to develop a proposal for human clinical trials.

“This research was a collaboration of stem cell biologists, biochemists, translational scientists, a bone biologist and clinicians,” said Lane. “It was a truly fruitful team effort with remarkable results.”

Source: Charles Casey, University of California – Davis Health System


Stem Cells Could Drive Hepatitis Research Forward

Hepatitis C, an infectious disease that can cause inflammation and organ failure, has different effects on different people. But no one is sure why some people are very susceptible to the infection, while others are resistant.

Scientists believe that if they could study liver cells from different people in the lab, they could determine how genetic differences produce these varying responses. However, liver cells are difficult to obtain and notoriously difficult to grow in a lab dish because they tend to lose their normal structure and function when removed from the body.

Now, researchers from MIT, Rockefeller University and the Medical College of Wisconsin have come up with a way to produce liver-like cells from induced pluripotent stem cells, or iPSCs, which are made from body tissues rather than embryos; the liver-like cells can then be infected with hepatitis C. Such cells could enable scientists to study why people respond differently to the infection.

This is the first time that scientists have been able to establish an infection in cells derived from iPSCs — a feat many research teams have been trying to achieve. The new technique, described this week in the Proceedings of the National Academy of Sciences, could also eventually enable “personalized medicine”: Doctors could test the effectiveness of different drugs on tissues derived from the patient being treated, and thereby customize therapy for that patient.

The new study is a collaboration between Sangeeta Bhatia, the John and Dorothy Wilson Professor of Health Sciences and Technology and Electrical Engineering and Computer Science at MIT; Charles Rice, a professor of virology at Rockefeller; and Stephen Duncan, a professor of human and molecular genetics at the Medical College of Wisconsin.

Stem cells to liver cells

Last year, Bhatia and Rice reported that they could induce liver cells to grow outside the body by growing them on special micropatterned plates that direct their organization. These liver cells can be infected with hepatitis C, but they cannot be used to proactively study the role of genetic variation in viral responses because they come from organs that have been donated for transplantation and represent only a small population.

To make cells with more genetic variation, Bhatia and Rice decided to team up with Duncan, who had shown that he could transform iPSCs into liver-like cells.

Such iPSCs are derived from normal body cells, often skin cells. By turning on certain genes in those cells, scientists can revert them to an immature state that is identical to embryonic stem cells, which can differentiate into any cell type. Once the cells become pluripotent, they can be directed to become liver-like cells by turning on genes that control liver development.

In the current paper, MIT postdoc Robert Schwartz and graduate student Kartik Trehan took those liver-like cells and infected them with hepatitis C. To confirm that infection had occurred, the researchers engineered the viruses to secrete a light-producing protein every time they went through their life cycle.

“This is a very valuable paper because it has never been shown that viral infection is possible” in cells derived from iPSCs, says Karl-Dimiter Bissig, an assistant professor of molecular and cellular biology at Baylor College of Medicine. Bissig, who was not involved in this study, adds that the next step is to show that the cells can become infected with hepatitis C strains other than the one used in this study, which is a rare strain found in Japan. Bhatia’s team is now working toward that goal.

Genetic differences

The researchers’ ultimate goal is to take cells from patients who had unusual reactions to hepatitis C infection, transform those cells into liver cells and study their genetics to see why they responded the way they did. “Hepatitis C virus causes an unusually robust infection in some people, while others are very good at clearing it. It’s not yet known why those differences exist,” Bhatia says.

One potential explanation is genetic differences in the expression of immune molecules such as interleukin-28, a protein that has been shown to play an important role in the response to hepatitis infection. Other possible factors include cells’ expression of surface proteins that enable the virus to enter the cells, and cells’ susceptibility to having viruses take over their replication machinery and other cellular structures.

The liver-like cells produced in this study are comparable to “late fetal” liver cells, Bhatia says; the researchers are now working on generating more mature liver cells.

As a long-term goal, the researchers are aiming for personalized treatments for hepatitis patients. Bhatia says one could imagine taking cells from a patient, making iPSCs, reprogramming them into liver cells and infecting them with the same strain of hepatitis that the patient has. Doctors could then test different drugs on the cells to see which ones are best able to clear the infection.

Source: Anne Trafton, MIT News Office