Modern scientific discovery often relies on taking things down to their micro level. This allows researchers to explore the individual actions of various components in naturally occurring systems. But the complicated cellular interactions, characterizing both normal biological processes and diseases such as cancer and Alzheimer’s disease, need a holistic approach.
“For many diseases, we want to look at many different aspects of cell behaviors,” says Nozomi Nishimura, Biomedical Engineering. “Many types of cells interact all at once in the live system, especially in the case of an injury or disease. In addition to the cells native to an organ, members of the inflammatory and immune systems—the white blood cells such as macrophages, lymphocytes, and T cells—come into play.”
“If you’re studying a disease like cancer,” Nishimura continues, “there will be the tumor cells, as well as new and pre-existing structures like blood vessels. We are working on methods to visualize all these different cells as they move and interact with each other.”
Identifying and Tracking Cells, In Vivo, as They Interact
Nishimura and her lab have been developing sophisticated tools and methods to image these different cells interacting in vivo—that is, within a living animal. “We’re pushing the imaging, especially the use of multiphoton microscopy, to capture the dynamics of cells inside the living body,” Nishimura says. “We also innovate in the development of fluorescent techniques to label different cell types so that we can identify and track them as they interact in vivo.”
Multiphoton microscopy was originally invented at Cornell in 1990 by Watt W. Webb and his postdoctoral associate Winfred Denk, now director of the Max Planck Institute of Neurobiology in Martinsreid, Germany. It relies on lasers and fluorescent tags at the cellular level to register cellular activity. “The multiphoton microscope lets us look deep inside intact, living tissue,” Nishimura explains. “For example, we can image as deep as a half to one millimeter inside the brains of live mouse models. And we can do that with a resolution that allows us to see individual neurons and other cells, which has resulted in an explosion of new data on the brain and neurodegenerative diseases. We are working to extend this technology to different kinds of organ systems, such as the heart and the intestine. Now we are expanding to look at cancer. Developing new imaging tools for biology is very exciting because we are often the first to see previously unknown, interesting cell behaviors.”
Captivated—Watching How Stem Cells Work in the Gut
Using their imaging techniques, Nishimura and her lab turned their attention to the behavior of stem cells in the gut. Cells that make up the inner lining of the gut replace themselves about every week, and the stem cells are the ultimate source of all these new cells. To keep stem cells safe, the gut has little test-tube-shaped pockets known as crypts. At the bottom of the crypt, the stem cells and another type of cell, called a Paneth cell, alternate in a precise soccer ball-like pattern. “We wanted to see what would happen if that pattern were disrupted,” Nishimura says. “We thought there had to be a mechanism to repair the crypt and recover the alternating pattern.”
Nishimura and her colleagues used mouse models equipped with fluorescent tags expressed in their intestinal stem cells. With a finely focused laser, the researchers selectively damaged individual cells within the intestinal crypts. Then they imaged the crypts over several days using the multiphoton microscope. “We expected the stem cells would use cell division to make new cells that reform the crypt pattern,” Nishimura says. “But rather than dividing, the remaining cells migrated and simply rearranged themselves back into this precisely alternating pattern.”
“A portion of the common behavioral deficits in Alzheimer’s is probably due to blood flow changes…Going after blood flow changes might lead to some relief of symptoms and cognitive improvement in patients.”
The stem cells then coordinated a pumping motion to push the leftover debris from the damaged cells through the middle of the crypt and out. “We didn’t think stem cells could actuate like a mechanical pump, but that’s just what these cells were doing,” Nishimura says. “They pushed this debris out in a coordinated manner. This is an example of the types of unexpected things we observe for the first time looking in vivo. In this case, we had a hypothesis, and we thought we knew what to look for; but when we saw the behavior, it was much more complicated and richer than we thought.”
Seeing What Happens in an Alzheimer’s Diseased Brain
In another project, Nishimura, with colleague Chris Schaffer, Biomedical Engineering, had a significant breakthrough concerning a long-standing question surrounding Alzheimer’s disease. It is widely believed that the buildup of amyloid beta proteins in the brain is the ultimate cause of Alzheimer’s. At the same time, scientists are aware that the brains of patients with the disease have decreased blood flow. The mechanisms behind the blood flow change, however, were a mystery. Nishimura and Schaffer used multiphoton microscopy to peer at the blood flow in the brains of Alzheimer’s mouse models. They discovered that one to two percent of the smallest blood vessels in the brains were plugged due to a mild, but chronic, inflammatory reaction that caused white blood cells to stick to the inside of the capillaries.
“Even though it’s only a small percentage of the capillaries that are plugged at any one time, it turns out that if one capillary is plugged, the next two are slowed and the next two and so on,” Nishimura says. “It actually takes six to 10 branches before the level of blood flow recovers to normal. When we add that up across all the capillaries of the brain, we find Alzheimer’s mouse models have approximately 70 to 80 percent of normal blood flow to their brains.”
While this finding was intriguing, the researchers were even more excited by the outcomes of a further experiment where they removed the plugs from the brains of the mouse models, reestablishing normal blood flow. “Within a very short time, we found that the mouse recovered its performance on short-term memory tests to about the same level as a nondiseased mouse,” Nishimura says. “This indicates that a portion of the common behavioral deficits in Alzheimer’s is probably due to blood flow changes. Although it’s not a cure for the disease, going after blood flow changes might lead to some relief of symptoms and cognitive improvement in patients.”
Now, Nishimura and her lab will be collaborating with Claudia Fischbach-Teschl, Biomedical Engineering, to study breast cancer, and they anticipate the unexpected. “Using mouse models, we will be observing the same systems that people studied previously,” Nishimura says. “But with our new tools, we hope and expect to see different behaviors due to the interactions of many different cells that could not be seen before.”