The Unsung Lung
Scientists at the Will Rogers Institute Pulmonary Research Center study the lungs' most basic inner workings for ways to manage pulmonary diseases.
The lung is an evolutionary marvel that invites open-mouthed awe. Its two lobes inflate and deflate some 25,000 times a day, drawing in more than 2,600 gallons of air. The tubes, or bronchi, through which that air is sucked in and blown out branch some 30 times before they finish, ending in 300 million blind sacs called alveoli. It is across each alveolus's single layer of tightly joined cells-called the alveolar epithelium-that the oxygen in the air is exchanged for the carbon dioxide in the blood. If spread out, this intricate cell layer, which is 50 times thinner than tissue paper, would cover a surface the size of a tennis court. And yet, only about 10 percent of the lung is tissue. Most of the space the lungs take up in the chest is filled with air and blood.
The body's other major organs-the liver, heart and brain-are protected from the outside world and all its germs and toxins by layers of skin and muscle and bone. But the lungs are afforded no such protection. They are constantly exposed to the dangers of the external environment with every breath. And unlike, for instance, the heart, which is little more than a simple-albeit extraordinarily powerful-blood pump, the lungs must juggle a variety of critical jobs. In addition to taking in oxygen, they are our first line of defense against a huge range of toxins-from viruses to pollutants to allergens.
Still, for all their life-giving and life-saving qualities, there is much about the lungs that remains shrouded in mystery-not the least of which is understanding how a healthy lung manages to keep air and blood separate, all the while bringing them close enough together so that they can exchange gasses and wastes.
Edward D. Crandall, Ph.D., M.D., the Hastings Professor and Kenneth T. Norris Jr. Chair in Medicine and chair of the Department of Medicine, is one of the nation's foremost pulmonary
scientists. He observes that it was only recently that scientists figured out how to isolate and grow in laboratory dishes the cells that make up 95 percent of the alveolar epithelium-the so-called Type 1 cells. That particular breakthrough-a step critical to the study of the lungs' inner workings-happened at the Keck School of Medicine of USC, in Crandall's laboratory at the Will Rogers Institute Pulmonary Research Center. And it is neither the first nor, if the past is any indication, the last such critical finding to come out of that center.
It would be fair to say that the work being done at the Pulmonary Research Center would take your breath away-or, more accurately, give it back to you.
Movie money
The Will Rogers Institute Pulmonary Research Center is a direct-though somewhat distant-descendent of a tuberculosis sanitarium for vaudevillians that was founded in Saranac Lake, N.Y., back in the 1920s. That sanitarium was handed over to a movie-industry-based commission that was looking to memorialize actor/writer/cowboy/philanthropist Will Rogers after his death in a plane crash in 1935. The commission raised money for the institution by creating the Will Rogers Memorial Fund, which produced a movie trailer that was shown in theaters and encouraged donations. That tradition continues to this day-the 2002 summer movie trailer starred Crocodile Hunter Steve Irwin, and was shown on more than 20,000 screens nationwide.
When effective tuberculosis treatments ended the need for TB sanitariums, the Fund decided to use the money it was collecting to support pulmonary research-and the Will Rogers Institute was born. Since that time, it has funded three laboratories: at New York's Cornell University, at the University of California, Los Angeles, and the Pulmonary Research Center at USC. Heading up each of these labs, in turn, was Crandall, who is also the Will Rogers Institute's medical advisor.
"There are 25 million people in the United States who are known to suffer from a lung disorder," Crandall says. "The institute allows our research scientists to study how the lung works at its most basic levels. What we learn results in new treatments for serious lung diseases and ultimately provides better health care for everybody."
The USC laboratory-the Pulmonary Research Center-was dedicated in 1991 with a celebration hosted by then-Disney executive Jeffrey Katzenberg. Today, it is a thriving enterprise, supported not only by the Will Rogers Institute, but also by grants from the Hastings Foundation, the Baxter Foundation, the American Heart Association, the American Lung Association and the National Institutes of Health (NIH). Crandall co-directs the center along with Zea Borok, M.D., associate professor of medicine and director of the Keck School's Pulmonary and Critical Care Medicine Fellowship Program.
Ones and twos
The Will Rogers Institute Pulmonary Research Center is focused on basic pulmonary biology-on understanding how the lung's epithelial cells transport molecules back and forth, how they defend against invaders and, especially, how they keep the air spaces dry and clean.
The latter role is especially critical, Crandall says. "Separating the air from the liquid space allows the air to get very close to the blood in the deep lung," he explains. "But if there is a malfunction of the alveolar epithelium, as in any lung injury, there is a likelihood that the air space will become filled with liquid-that is called pulmonary edema. Even when the epithelium is not breached, as in heart failure, you can still get pulmonary edema.
"Normally, the epithelium keeps the air spaces dry by actively pumping salt out of the air spaces-which then pulls any water along with it via osmosis. This pumping is important in keeping the air spaces dry, and in the recovery of an injured lung."
Crandall and Borok are focusing on the role of the Type 1 alveolar epithelial cells (or AT1 cells) in pumping salt and other ions from the airspaces into the blood. The other major cell types in the alveolar epithelium are the Type 2, which are equal in number to the Type 1, but smaller. A recent NIH grant renewal-which will bring the researchers $1.3 million over the next four years-will allow them to exploit their new-found ability to isolate relatively pure populations of the AT1 cells, and to thus manipulate and observe those cells.
"We've been able to get Type 2 cells to grow in the lab for about 20 years," notes Crandall. "And one of our earlier major contributions in this laboratory was to show that we could get those Type 2 cells to differentiate into Type 1 cells in a dish. That discovery led us to the even bigger discovery that there is a pump in those cells that keeps the lungs dry. But nobody had been able to harvest Type 1 cells directly until the past two years when we developed the technology to do it.
"This was a major advance. The ability to study Type 1s is tremendously important to studying the biology of these cells and the ways in which the lungs recover from injury."
Crandall and Borok plan on perfecting their AT1 isolation and purification techniques and using them to study both the basic properties of these cells and how they respond to injury. In addition, Borok explains, "We are one of several major laboratories working on understanding the process that regulates the transdifferentiation between Type 1 and 2 cells. We can make 1s turn into 2s, and vice versa, in a laboratory dish."
This is more than just a scientific exercise, notes Borok. "Being able to manipulate the cell types has huge practical implications," she says. "It suggests that with the right combination of growth factors and scaffolding for the cells, we might be able to create actual organs-or, at the very least, help our lungs recover after injury."
In a similar vein, Crandall and Borok are looking at the uses for adult stem cells in regenerating or repairing lung tissue that has been injured or destroyed. They have already shown-in the laboratory-that given the right environment, stem cells can be coaxed to migrate to lung tissue and differentiate into viable, functional alveolar epithelial cells.
These findings tie into yet another of Crandall and Borok's research interests: gene therapy. They recently published a paper in the Journal of Virology, says Borok, "showing we could use a lentivirus [a type of retrovirus] to deliver genes to lung cells. In a laboratory dish, they got in quite easily, with high efficiency."
But lentiviruses are not the only way in which therapeutic genes might be delivered to the lungs, notes Borok-and that is where the connection between gene therapy and stem cell research comes into play. "If we can reliably get stem cells to travel to the alveolar epithelium, why not use them to deliver genes, or even large protein drugs, to the lungs?" she muses.
Borok is also targeting Type 1 cells specifically for gene therapy. She has identified and cloned a gene specific to the Type 1s-called aquaporin-5-and is now working on using that gene to help gene-carrying lentiviruses home in on only the Type 1s.
Borok is also focusing on ways to help people whose lungs are filled with fluid as a result of pulmonary edema. She and her Will Rogers colleagues have shown that a small protein called epidermal growth factor, or EGF, which normally plays a role in lung growth and development, also seems to prompt injured lung epithelial cells in the laboratory to step up their transport of sodium ions from the air side of the epithelium to the blood side. Where sodium goes, so does water, reducing the edema in the air spaces. In addition, says Borok, the growth factor also seems to help make the cells water-tight. "EGF appears to strengthen the junctions between individual cells," she explains, "thereby further preventing flooding of the alveolar space."
Crossing barriers
Kwang-Jin Kim, Ph.D., associate professor of medicine and physiology and biophysics and one of the center's group leaders, like Crandall and Borok, also is looking at the way in which the lung epithelium transports molecules from the air spaces to the bloodstream. But the molecules he is looking at are much larger than the minute ions that his colleagues are considering-molecules such as albumin and immunoglobulins.
"In small concentrations, these molecules are normal," Kim says . "But if albumin-like molecules keep building up, they can create problems by pulling water into the air spaces after them. That is why my interest is in understanding how these big serum proteins are removed from the air side of the alveolar epithelium back into the blood."
How they do this is the subject of Kim's recently renewed $1.1 million, four-year NIH grant.
"What we've discovered is that most of this large protein transport occurs across the epithelial cell, rather than between the cells," says Kim.
The group identified several albumin- and immunoglobulin-loving cell protein receptors, which grab the proteins, transport them across the cell and release them on the blood side.
"Having found the receptors," Kim says, "it is critical that we start to understand how key proteins move across the epithelial barrier in health and disease. By knowing all the basic features, we will be able to think about better therapeutics and ways to manage some of the most devastating lung diseases."
Just inhale
To that end, Crandall and Kim are also involved in a $3.2 million NIH-sponsored effort to explore ways to deliver drugs across the alveolar epithelium.
The human lung, notes Crandall, has a currently untapped potential to enhance and improve the delivery of certain drugs from insulin to human growth hormone-large pharmaceuticals that currently have to be delivered by injection because they would be chemically chewed up by the stomach's digestive juices if given in pill form.
"The idea of being able to inhale a drug such as insulin has recently become hotly pursued by industry," says Crandall. "We're studying at the molecular and cellular levels the mechanisms by which peptide and protein drugs can get across the lung."
Adds Kim: "We're really excited about using the lung as a portal for drug delivery. Now that we're beginning to understand the basic mechanisms for transporting large molecules across the epithelium, we can try to figure out how to tweak the system, to rev it up."
Joining Crandall and Kim in this drug delivery effort are Vincent Lee, Ph.D., the Gavin S. Herbert Professor and chair of the Department of Pharmaceutical Sciences in the USC School of Pharmacy, and Wei-Chiang Shen, Pharm.D., professor of pharmaceutical sciences.
All of these integrated efforts, says Crandall, are allowing the Will Rogers Institute Pulmonary Research Center to make enormous strides in understanding basic lung science-and to translate those strides into new ways to corral a variety of lung conditions.
"Having all of these state-of-the-art approaches available to us," says Borok, "places USC in a great position to make significant advances in the treatment of serious lung diseases."
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