In the kitchen, a way to treat cystic fibrosis?

A spice may protect a mutant, but functional, protein from the cell’s quality control system.

A possible compound for the treatment of cystic fibrosis may be as close as the kitchen spice rack. Researchers at Yale and the University of Toronto reported recently in Science that curcumin, an element of the spice turmeric, helps correct a protein defect associated with this genetic disease.

Through a mechanism that is not completely understood, curcumin protects a mutant, yet functional, protein from the cell’s quality control machinery. Cystic fibrosis stems from a defect in this protein, the cystic fibrosis transmembrane conductance regulator (CFTR), which moves chloride across cellular membranes to maintain a balance of ions and water. When that balance is disrupted, mucous becomes a sludge that clogs respiratory and digestive pathways, ultimately causing infections. Most people with cystic fibrosis do not live past the age of 30.

The most common form of cystic fibrosis is called delta F508, and is due to the deletion of a single amino acid from the sequence of CFTR. Although the protein is still able to mitigate most cystic fibrosis symptoms, cellular quality control machinery tags it for degradation, because without the amino acid it cannot fold properly. “Even though [it] works, it gets thrown out,” said Michael J. Caplan, M.D. ’87, Ph.D. ’87, professor of cellular and molecular physiology and cell biology and the principal investigator of the study. Working with Marie E. Egan, M.D., associate professor of pediatrics and cellular and molecular physiology, and others, he may have found a way to subvert quality control.

As part of the quality control process, some chaperone proteins bind to calcium, commonly found in the endoplasmic reticulum (ER). To help CFTR evade quality control, Caplan and Egan sought compounds that would disable the chaperones by depleting calcium stores in the ER. Previously identified compounds blocked calcium pump action in the ER, but proved to be toxic. A search through the literature turned up curcumin, a weak inhibitor of ER calcium pumps.

Remarkably, it worked—and well, at least in tissue culture and mouse models. The researchers noted a restoration of ion transport in mice that received curcumin, and in cell lines bathed in curcumin, a fraction of the mutated protein migrated to the cell membrane and restored a significant level of ion transport function.

Given these findings, Egan and Caplan plan to collaborate with the Cystic Fibrosis Foundation and Seer Pharmaceuticals in a clinical trial to assess curcumin’s potency in patients with cystic fibrosis. However, Egan stresses that more research is needed: “What it does to people versus what it does in mice may be very different. We first need to get a better handle on the mechanism,” Egan said. To that end, Egan and Caplan are trying to determine whether curcumin blocks calcium pump action or whether it binds to CFTR to help stabilize it. They are also investigating whether the active compound is curcumin or a metabolite of curcumin. If the data from both the clinical and basic research investigations prove its efficacy, curcumin may be the first cystic fibrosis drug that treats the cause of the disease rather than just the symptoms.

—Kara Nyberg

Molecular players shown to affect nerve fibers in multiple sclerosis

Until recently, researchers knew very little about the neural molecules associated with secondary progressive multiple sclerosis (MS), a nerve-degenerating autoimmune disease that afflicts almost 3 million people worldwide. Scientists had typically studied the disease in mouse models, but Stephen G. Waxman, Ph.D., M.D., professor of neurology, pharmacology and neurobiology, and his colleagues looked for clues at the source—postmortem spinal cord tissue from MS patients. In a study published in May in the Proceedings of the National Academy of Sciences, Waxman’s team and researchers from the VA Connecticut Healthcare System in West Haven and University College London described the first observations in humans of key molecules that contribute to nerve fiber degeneration. These molecules, though produced to compensate for a short in the neural signaling circuit, ultimately—and ironically—initiate a series of events that cause nerve damage.

To relay signals to other neurons, healthy nerve cells are studded with sodium channels that open in succession along the nerve fiber to allow in surges of sodium when neurons become activated. To help propagate this signal, an outer coating of myelin insulates the nerve cells. But in those with MS, the myelin breaks down, causing a short in the signal circuit. Waxman and colleagues found that MS neurons compensate for this defect by overexpressing the sodium channel Nav1.6—normally present only at small regions called nodes of Ranvier—all along the nerve fiber to improve the signal relay. However, the atypical Nav1.6 expression appears to cause more harm than good, as it coincides with regions of axon injury.

There are at least 10 types of sodium channels in human nerve cells, each with a different task, Waxman explained. “It’s as if you have 10 different types of batteries. Only the right batteries will make a device work properly.” In this case, the cells are using the wrong batteries in the wrong place. The researchers observed that another protein called NCX, a sodium-calcium exchanger, is expressed near Nav1.6 sites. The aberrant placement and overabundance of Nav1.6 causes too much sodium to enter the cells. Overexpression of NCX adjacent to Nav1.6 channels presumably flushes out the excess sodium and replaces it with calcium. But too much calcium provokes molecular chain reactions, sending cells into activity overdrive that results in cellular damage and disease symptoms.

In a field long dominated by immunobiologists, Waxman is enthusiastic about the contributions to the understanding of MS that he and his neurobiologist colleagues are making. “We are chipping away at the disease molecule by molecule, and we are understanding more about the disease process,” he said. Based on his research, Waxman is eager to try targeting the neurons for treatment; all approved MS therapies currently target the immune system. Consistent with his research findings, he said, “Drugs that block sodium channels prevent axonal death.” Consequently, he is involved in an upcoming clinical trial that will test sodium channel blockers in MS patients.

—K.N.

Et Cetera

Picturing an enzymatic RNA

More than 20 years ago scientists discovered that RNA, and not just proteins, could act like an enzyme. Now Yale researchers have obtained the first X-ray crystal structure of this type of enzymatic RNA. The image caught an RNA molecule as it spliced together two exons, the parts of a gene that code for proteins. Also visible in the image were a full-length noncoding intron and metal ions bound in the molecule’s active site.

The RNA acts like an enzyme so it can overcome an inherent hindrance to protein synthesis—the intron that separates the exons. With the help of the metal ions, the RNA connects the exons and removes the intron sequence.

“This is the first RNA splicing complex to be visualized in molecular detail,” said Scott A. Strobel, Ph.D., professor of molecular biophysics and biochemistry and chemistry, and principal investigator of the study published in the journal Nature in June.

—K.N.

How Salmonella survives

Yale scientists have discovered how Salmonella, a bacterium that causes food poisoning and typhoid, escapes the innate immune system’s efforts to destroy it. Typically, bacteria are gobbled up by macrophages, which send bacteria to an execution chamber called a lysozome for degradation.

While they await degradation, Salmonella sit in a holding cell called a vacuole and begin to plan their escape. They secrete a protein, SopB, that changes the composition of the vacuole. This allows the bacterium to escape and find a friendlier compartment where they can replicate and avoid innate immune defenses.

“Salmonella have an elegant strategy for surviving and replicating and avoiding this cellular disposal system,” said Jorge E. Galán, D.V.M., Ph.D., chair of the Section of Microbial Pathogenesis, the Lucille P. Markey Professor of Microbiology and principal investigator of the study published in Science in June. “Our work is revealing a fundamental mechanism by which these bacteria cause disease—and may lead to new targets or strategies for controlling them.”

—John Curtis


			Originally published in Yale Medicine, Fall/Winter 2004. Copyright © 2004 Yale University School of Medicine. All rights reserved.