February 19, 2013
Innovative Infectious Disease Research To Be Conducted Onboard The Space Station
April Flowers for redOrbit.com - Your Universe Online
All biologists know performing sensitive biological experiments is a delicate affair, akin to baking a soufflÃ© in a busy house. Few of those biologists, however, have to deal with the daily and unique challenges faced by Cheryl Nickerson, a microbiologist at Arizona State University's Biodesign Institute. Nickerson's working lab is aboard the International Space Station (ISS) hundreds of miles above Earth, traveling at approximately 17,000 miles per hour.
Nickerson is currently using her lab aboard the ISS to pursue new research into the effects of microgravity on disease-causing pathogens. She presented her research findings recently, and laid out future research goals for the ISS, at the annual meeting for the American Association for the Advancement of Science (AAAS).
"One important focus of my research is to use the microgravity environment of spaceflight as an innovative biomedical research platform. We seek to unveil novel cellular and molecular mechanisms related to infectious disease progression that cannot be observed here on Earth, and to translate our findings to novel strategies for treatment and prevention."
Nickerson and her team made a startling discovery during an earlier series of NASA space shuttle and ground-based experiments: spaceflight culture increased the disease-causing potential, or virulence, of the foodborne pathogen, Salmonella. Many of the genes known to be important for its virulence, however, were not turned on and off as expected when Salmonella is grown on Earth. Understanding the regulation of this switching mechanism may be useful for designing targeted strategies to prevent infection.
Given their implications for the health of astronauts on extended spaceflight missions, Nickerson's findings were revelatory for NASA. Astronauts are already faced with the potential for compromised immunity induced by the rigors of space travel. Nickerson's findings show they may also have to contend with the threat of disease-causing microbes with amped-up infectious abilities. It becomes vital, therefore, to have a more thorough understanding of infectious processes and host responses under these conditions in order to design therapeutics and other methods of limiting vulnerability for those on space missions.
Nickerson's team, which included NASA scientists, performed further research that pointed to important implications for the understanding of health and disease on Earth. One of the central factors affecting the behavior of pathogenic cells is the physical force produced by the movement of fluid over a bacterial cell's sensitive surface, called fluid shear. Fluid shear helps modulate a broad range of cell behaviors, including provoking changes in cell morphology, virulence, and global alterations in gene expression in pathogens like Salmonella.
"There are conditions that are encountered by pathogens during the infection process in the human body that are relevant to conditions that these same organisms experience when cultured in spaceflight. By studying the effect of spaceflight on the disease-causing potential of major pathogens like Salmonella, we may be able to provide insight into infectious disease mechanisms that cannot be attained using traditional experimental approaches on Earth, where gravity can mask key cellular responses," says Nickerson.
An evolutionarily conserved protein — called Hfq — was pinpointed by the study. Hfq appears to act as a global regulator of gene responses to spaceflight conditions. The research team also established Hfq is a central mediator in the responses of other bacterial pathogens induced by spaceflight, including Pseudomonas aeruginosa. This represents the first spaceflight- induced regulator acting across bacterial species.
To examine post-spaceflight alteration in bacterial behavior, Nickerson's team used microarray technology, which allows analysis of gene expression for the entire 4.8 million base pairs found in Salmonella's circular chromosome. The study showed 167 distinct genes and 73 proteins had been altered during growth under microgravity conditions, including (but not limited to) virulence-associated genes. One third of the 167 genes undergoing up- or down-regulation in response to spaceflight were under the control of the Hfq master regulator protein.
Salmonella is an aggressive pathogen responsible for infecting an estimated 94 million people globally and causing 155,000 deaths annually. More than 40,000 cases of Salmonellosis are reported annually in the United States alone. These result in at least 500 deaths, and health care costs in excess of $50 million. Only a small percentage of Salmonella infections are reported each year, with an estimated two to four million cases of Salmonella-induced gastroenteritis in the U.S. causing a reported $2 billion in lost productive work time annually.
Nickerson stresses although Salmonella has been a pathogen of choice for a broad range of spaceflight investigations, her findings have both spaceflight and Earth-based implications. She is confident her team's work will show microgravity culture also uniquely alters gene expression and pathogenesis-related responses in other microorganisms as well.
The ISS provides an unprecedented opportunity to study the infection process under microgravity conditions, Nickerson emphasizes, enabling advances in our understanding of microbial gene expression and accompanying host responses during infection in fine-grained detail. The team's unique approach has the potential to identify new classes of genes and proteins associated with infection and disease not possible using Earth conditions where gravity can mask certain cellular responses. ISS based experiments have an advantage over shuttle-based experiments as well, namely the ability to study microbial transitions and cellular responses to infection over a prolonged time frame.
Research aboard the ISS may also provide an opportunity to identify novel targets for vaccine development. Nickerson's team, along with Roy Curtiss, director of the Biodesign Institute's Center for Infectious Diseases and Vaccinology, has been working toward this goal. The results may be used to facilitate vaccine development on Earth.
The team flew a genetically modified Salmonella-based anti-pneumoccal vaccine developed in the Curtiss lab on a recent space shuttle mission, STS-135. The team's goal is the genetic modification of the strain back on Earth, which they hope to achieve by understanding the effect of microgravity culture on the gene expression and immunogenicity of the vaccine strain. This will allow them to enhance the ability of the gene to confer a protective immune response against pneumococcal pneumonia.
"Recognizing that the spaceflight environment imparts a unique signal capable of modifying Salmonella virulence, we will use this same principle in an effort to enhance the protective immune response of the recombinant attenuated Salmonella vaccine strain," Nickerson says.
To compare the behavior of bacterial cells under normal Earth gravity, the team's ISS experiments are carried out in conjunction with simultaneous Earth-based controls housed in the same hardware as those in orbit. Earth-based cell cultures provide additional information. These cultures are subjected to a kind of simulated microgravity, produced by culturing cells in a rotating wall vessel bioreactor (RWV). The RWV is a device designed by NASA engineers to replicate aspects of cell culture in the spaceflight environment.
The team conducted RWV reactor experiments back at ASU to help confirm Hfq plays a central regulatory role in the Salmonella response to spaceflight conditions. This RWV technology was used by the team to grow three dimensional (3-D) cell culture models that mimic key aspects of the structure and function of tissues in the body. These are used as human surrogates to provide insight into the infectious disease process not obtainable by conventional approaches and for drug/therapeutic testing and development for treatment and prevention.
Nickerson and her team also focus research efforts on determining the entire repertoire of environmental factors that may influence bacterial response to spaceflight culture. They found the ion concentration in the cell culture media played a key role in the resulting effect of spaceflight on Salmonella virulence, and using RWV they were able to identify specific salts that may be responsible for this effect.
Nickerson has a long list of firsts in the field of spaceflight research. She and her team were the first researchers to examine the effect of spaceflight on the virulence of a pathogen, first to obtain the entire gene expression response of a bacterium to spaceflight, first to profile the infection process in human cells in spaceflight, and first to identify a spaceflight-responsive global gene regulator acting across bacterial species.
These achievements will soon be augmented with a new experiment that will be flown on SpaceX Dragon slated for the ISS later this year. The project, nicknamed PHOENIX, will mark the first time a whole, living organism — in this case, a nematode - will be infected with a pathogen and simultaneously monitored in real time during the infection process under microgravity conditions.
Science's understanding of the molecular and cellular cues underlying pathogenic virulence will be deepened by this and future studies aboard the ISS. The team's work will open a new chapter in the understanding of health and disease to benefit the general public.
"It is exciting to me that our work to discover how to keep astronauts healthy during spaceflight may translate into novel ways to prevent infectious diseases here on Earth," Nickerson says.