Inside Salk; Salk Insitute

Discovery Roundup

Combined Stem Cell-Gene Therapy Approach Cures Human Genetic Disease in Vitro

A Biochemical Pathway for Blocking Your Worst Fears?

Scientists Discover How Obesity Increases Risk for Diabetes

Stem Cells Provide Clues to Glial Cells Glut

Fruit Flies Soar as Lab Model

Missing Genomic "Fence Posts" Explain Inactivated Tumor Suppressor Genes in Breast Cancer


 

 

Combined Stem Cell-Gene Therapy Approach Cures Human Genetic Disease in Vitro

Colonies of Fanconi anemia-specific iPS cells stained in green.

A team of researchers led by Juan Carlos Izpisúa Belmonte, a professor in the Gene Expression Laboratory, has proved in principle that a human genetic disease can be cured using a combination of gene therapy and induced pluripotent stem (iPS) cell technology.

Belmonte's team, working with Salk colleague Inder Verma, a professor in the Laboratory of Genetics, and colleagues in Madrid, focused on Fanconi anemia (FA), a genetic disorder responsible for a series of hematological abnormalities that impair the body's ability to fight infection, deliver oxygen, and clot blood.

After taking hair or skin cells from patients with Fanconi anemia, the investigators corrected the defective gene in the patients' cells using gene therapy techniques pioneered in Verma's laboratory. They then successfully reprogrammed the repaired cells into induced pluripotent stem (iPS) cells using a combination of transcription factors. The resulting FA-iPS cells were indistinguishable from human embryonic stem cells and iPS cells generated from healthy donors.

Since bone marrow failure as a result of the progressive decline in the numbers of functional hematopoietic stem cells is the most prominent feature of Fanconi anemia, the researchers then tested whether patient-specific iPS cells could be used as a source for transplantable hematopoietic stem cells. They found that FA-iPS cells readily differentiated into hematopoietic progenitor cells primed to differentiate into healthy blood cells.

"We haven't cured a human being, but we have cured a cell," Belmonte explains. "In theory we could transplant it into a human and cure the disease."

A Biochemical Pathway for Blocking Your Worst Fears?

Scientists have found that glutamate, the most prominent neurotransmitter in the brain, plays a key role in the process of "unlearning." The team's study, led by Stephen F. Heinemann, a professor in the Molecular Neurobiology Laboratory, could eventually help scientists develop new drug therapies to treat a variety of disorders, including phobias and anxiety disorders, particularly post-traumatic stress disorder.

"Most studies focus on 'learning,' but the 'unlearning' process is probably just as important and much less understood," says Heinemann. "Most people agree that failure to unlearn is a hallmark of post-traumatic stress disorders and if we had a drug that affects this gene it could help soldiers coming back from the war to unlearn their fear memories."

Post-traumatic stress disorder or PTSD is an anxiety disorder that can develop after exposure to a terrifying event or ordeal in which grave physical harm occurred or was threatened. PTSD affects about 5.2 million Americans, according to the National Institute of Health. As many as one in eight returning soldiers suffer from PTSD.

Scientists Discover How Obesity Increases Risk for Diabetes

Obesity is probably the most important factor in the development of insulin resistance, but science's understanding of the chain of events is still spotty. Now, researchers at the Salk Institute have filled in the gap and identified the missing link between the two. Their findings explain how obesity sets the stage for diabetes and why thin people can become insulin-resistant.

The Salk team, led by Marc Montminy, a professor in the Clayton Foundation Laboratories for Peptide Biology, discovered how a condition known as ER (endoplasmic reticulum) stress, which is induced by a high-fat diet and is overly activated in obese people, triggers aberrant glucose production in the liver, an important step on the path to insulin resistance.

In healthy people, a "fasting switch" only flips on glucose production when blood glucose levels run low during fasting. "The existence of a second cellular signaling cascade-like an alternate route from A to B–that can modulate glucose production, presents the potential to identify new classes of drugs that might help to lower blood sugar by disrupting this alternative pathway," says Montminy.

Stem Cells Provide Clues to Glial Cells Glut

An abundance of glial cells (shown in green) is caused by the synaptojanin-1 protein

A newly identified molecular pathway that direct stem cells to produce glial cells is yielding insights into the neurobiology of Down's syndrome and several other disorders of the central nervous system that are characterized by an overabundance of glia.

The findings, made by a team of scientists led by David Schubert, a professor and head of the Cellular Neurobiology Laboratory, indicate that synaptojanin-1, a central component of the pathway, is essential to production of glia, brain cells that act as neurons' personal assistants. Down's syndrome, spinal cord injury, Alzheimer's disease, and stroke all are linked by an overproduction of glia. Understanding this molecular pathway may also have implications for the onset of glioblastoma, the most common and malignant type of brain tumor.

"The discovery of this molecular signaling pathway promises to completely change the way we think about central nervous system maladies, allowing the development of drugs that inhibit glial proliferation and improve the prognosis of patients with a host of devastating conditions," Schubert says.

Fruit Flies Soar as Lab Model

Top: Normal fly brain for comparison. Glial cells are shown in red.
Bottom: Tumor cells (shown in green) have overtaken almost the entire brain of an adult fly.
Photo courtesy of Dr. Renee Read, Salk Institute

Researchers led by Salk's John B. Thomas, a professor in the Molecular Neurobiology Laboratory, have transformed the fruit fly into a laboratory model for an innovative study of gliomas, the most common malignant brain tumors. The investigators looked to the fruit fly as a useful model since most of its genes are conserved in humans, including 70 percent of all known human disease genes.

"Gliomas are a devastating disease but we still know very little about the underlying disease process," said Thomas. "We can now use the power of Drosophila genetics to uncover genes that drive these tumors and identify novel therapeutic targets, which will speed up the development of effective drugs."

Better models for research into human gliomas are urgently needed. Last year alone, about 21,000 people in the U.S. were diagnosed with brain and nervous system cancers, Senator Edward M. Kennedy the most famous among them.

About 77 percent of malignant brain tumors are gliomas and their prognosis is usually bleak. While they rarely spread to elsewhere in the body, cancerous glial cells quickly infiltrate the brain and grow rapidly, which renders them largely incurable even with current therapies.

Missing Genomic "Fence Posts" Explain Inactivated Tumor Suppressor Genes in Breast Cancer

Scientists led by Beverly Emerson, a professor in the Regulatory Biology Laboratory, have found that a breakdown in molecular fences blurs the lines between genomic neighborhoods and leads to the inactivation of at least two tumor suppressor genes. Their findings explain how a single event can put a cell on the road to becoming a tumor cell.

Tumors result when changes in the genome activate cancer-causing genes or inactivate tumor suppressor genes that tip this delicate balance in favor of uncontrolled cell growth. In many different types of cancers, the tumor suppressor gene p16 gets buried deep inside heterochromatin, a tightly condensed structure that protects DNA. As a result, it cannot be read by the transcription machinery and is unable keep watch over cell growth.

Most people looked for clues within the immediate vicinity of the gene but came up empty-handed. When postdoctoral researcher Michael Witcher extended his search further upstream, however, he discovered a binding site for CTCF, short for CCCTC-binding factor, which forms the centerpiece of the molecular fence posts that separate heterochromatin from the rest of the genome.

"We found that the binding of this protein is lost from several binding sites in numerous types of cancer cells, leading to the collapse of the molecular boundary," he says. "Once the boundary was gone, the adjacent heterochromatin encroached and silenced the nearest gene."

Further experiments revealed that CTCF was missing because it lacked a chemical modification known as "PARlation," lab lingo for poly(ADP-ribosyl)ation, which allows the protein to bind to select sites in the genome.

"Without PARlation, CTCF fails to form the complex necessary to regulate p16 and the tumor suppressor RASSF1A and possibly others, explaining why breast cancer cells always contain both silenced p16 and silenced RASSF1A," says Witcher.