Pathways to Immunity
In the search for better ways to fight disease, Jing Fan is pushing the boundaries of immunometabolism.
Jing Fan recalls the first science experiment she ever performed. She was a kindergartener in Beijing, China, and her class made glue out of flower petals. After soaking the petals in water for some time, their components broke down into a sticky solution.
“It’s about chemistry,” she says, reflecting on the process and what she observed. “The world is fascinating, and I just want to ask ‘Why?’ ”
As an assistant professor of nutritional sciences in CALS and an investigator at the Morgridge Institute for Research, Fan continues to pursue that question through the exploration and understanding of metabolism. Metabolism refers to the chemical reactions that create the energy and resources needed to sustain life. It is a fundamental process that occurs in every cell of every living organism. When the process is impaired, it can become the underlying problem in many health issues, from diabetes to cancer.
“Understanding metabolism in specific systems will give us insights into general metabolic regulation,” says Fan. “It’s a very fundamental process; but, in terms of how cells use metabolism and their metabolic resource, it’s very diverse. It takes an interdisciplinary approach to study it, so it’s very fun.”
A Public-Private Partnership
The Morgridge Institute for Research is a private, nonprofit organization dedicated to improving human health through interdisciplinary biomedical research. It’s housed in UW’s Discovery Building, along with the public Wisconsin Institute for Discovery and the first-floor community space called the Town Center, managed by the Wisconsin Alumni Research Foundation. The Morgridge Institute uses mechanisms unique to a private entity to help recruit top scientific talent and build powerful research collaborations. Many faculty from CALS and across the UW campus serve as Morgridge investigators and affiliates and leverage the institute’s resources to advance their research.
Living cells contain many metabolic pathways, which are connected series of biochemical reactions that serve important functions. Fan compares these intracellular pathways to the ways in which cities control roadways. Just as roads contain markings, traffic signs, and signals, cells have specific enzymes, signaling molecules, and other regulatory components. In both contexts, different situations will affect how a path is regulated. Fan’s interest lies in the traffic flow. Sometimes the roads are clear. At other times, construction or an accident might bring traffic to a halt.
“Metabolism is fundamentally a very dynamic process,” Fan says. “Whether you are a cell undergoing stem cell differentiation, immune cell activation, or cancer proliferation, you respond and keep sensing the environment. You figure it out.”
Fan discovered her fascination with metabolism while completing her undergraduate studies at Peking University. But after 22 years in China, she was ready for a big change. So, she moved across the globe to pursue a graduate degree in chemistry at Princeton University. After earning her Ph.D., and following a postdoc appointment, she took on her current role at the Morgridge Institute and in the Department of Nutritional Sciences in 2017. Fan began her research career with a focus on cancer metabolism. But, just as science is constantly changing and evolving, the focus in Fan’s lab also shifted.
“I consider myself a metabolism researcher — anything metabolism. I never saw myself as just a cancer metabolism researcher,” Fan says. “What made me start to think about immune cells is how metabolism and cell function are related.”
While cancer research is obviously important, Fan says immune cells are interesting because they are functionally flexible. Cancer cells proliferate because of improper regulation, but they do little else other than grow. Immune cells are far more active — they have different functions depending on the environment.
“Immune cells go through a dynamic change that is really fascinating,” she says. “From killing to healing, one cell type can be doing all of this — it’s a complex spectrum. It’s a perfect platform to figure out how dynamic metabolic regulation and functional changes are connected.”
Macrophages and neutrophils are cells within the innate immune system, the nonspecific first line of defense against infectious agents such as viruses and bacteria as well as injury and wounds. Innate immune cells are relatively understudied compared to T cells and other immune cells involved in adaptive immunity, which is a specific response to an infection from a repeat offender.
Fan and her team ventured into this new territory with studies published in the July 2019 issue of Nature Metabolism and the October 2022 issue of Nature Chemical Biology, which investigate how changing metabolism can regulate the different functional states in macrophages over the course of an immune response.
The immune system requires a delicate balance and must be very precisely controlled. Too little response and the pathogens won’t be defeated; too much of a response and the body attacks its own cells and can cause tissue damage. Immune cells are activated by different stimulants, and each stimulation spurs its own dynamic response. Immune cells also communicate with and are influenced by one another, which adds another layer of complexity.
Using the city roadway analogy, the team zoomed in to look at specific regulation points and stimulants that influence the pathways in activated macrophages. “We’re measuring the traffic, the flow of metabolism, and examining how these pathways are regulated and controlled,” Fan says.
Gretchen Seim MS’16, PhD’22, lead author of the studies, completed her Ph.D. in Fan’s lab and now works as a scientist at Genentech, a California- based biotechnology company. Seim says the biggest takeaway is that the metabolic response of these immune cells is dynamic, so studying the process over time is important.
“It’s more dynamic and complicated than previously thought, and if you study its change over time, you can find new insights into how metabolism is supporting function,” Seim says. “It’s not a binary, on-or-off state, and looking at only one time point is really insufficient to capture the complexity of what’s going on, not just in metabolism, but across the board.”
Future studies would include examining other regulation points of the pathway, as well as the many other metabolic pathways involved in the complex cellular system. “The more we know about where those particular regulation points are, the better we can find ways to alter them, to change the flow and ultimately the function of the cells in diseases where the immune system is not behaving in the way that we want it to,” Seim says.
Fan notes that the jump from cancer metabolism to immunometabolism isn’t that big of a leap. Macrophages happen to be some of the most abundant non-cancer cells within a tumor environment. The ultimate goal is to define and understand the regulation points of all metabolic pathways to inform the development of immunotherapies for diseases, including cancer.
“I feel very flexible in terms of what I’m going to do,” Fan says. “I’m always very attracted to interdisciplinary work that connects many pieces together.”
An Interdisciplinary Approach
As an undergrad with many interests, Fan remembers the difficulty of settling on a research direction. Her initial interest was in physics and math, but those fields led her to engineering, then chemistry, and, naturally, biology. Through biology, she found metabolism, “the perfect playground,” she says, “where I can do a little bit of everything. Intellectual freedom is a huge draw for me.”
She explains that, at its most fundamental level, metabolism is simply chemical reactions, how atoms move around. Zoom out one level, and it’s a biochemical process: how proteins work and are regulated. Zoom out further, and it’s an engineering problem: how pathways within the network are controlled. And the lab work involved utilizes a variety of tools and methods, from cell culture and molecular biology techniques to quantitative analysis and network modeling. So, by its very nature, the study of metabolism requires interdisciplinarity in terms of both topics and approach, which suits Fan well.
“Jing is a perfect example of why people who are driven by curiosity make such stupendous scientists,” says Morgridge Institute CEO Brad Schwartz. “She is endlessly inquisitive, she loves what she’s doing, and she’s never afraid to follow the data to see where it leads. This is a great recipe for making exciting discoveries.”
When Fan began thinking about exploring the role of metabolism in immune cells, she started with the literature. But because little published research existed on topics such as neutrophil metabolism, she turned to experts on campus.
“When she approached me about collaborating, I was excited to interact with her,” says Anna Huttenlocher, a physician-scientist and professor of pediatrics and medical microbiology and immunology in UW’s School of Medicine and Public Health. “Jing is a thoughtful researcher who is pushing the boundaries in immunometabolism.”
Huttenlocher’s lab studies the mechanisms that regulate innate immunity, with a focus on tissue damage and wound healing, through a zebrafish animal model that mimics biological processes in humans. Her lab is also interested in the migration and invasion of cancer cells. Fan’s and Huttenlocher’s labs collaborated on a study, published in the March 2022 issue of Nature Metabolism, exploring the metabolic pathways that power neutrophils.
As the first line of immune defense, neutrophils need to activate quickly to recognize and react to infectious pathogens. Billions of these cells are produced in the bone marrow each day, so the cells are plentiful but also short-lived.
Fan’s graduate student, Emily Britt (Huttenlocher is a member of her thesis committee) was first author on the study. She mentions how the lab began to think about neutrophils in a different way: “Because they are so fast-acting, it probably means they change their metabolism really quickly, and we thought it would be worth pursuing.”
When neutrophils are activated, they undergo an “oxidative burst,” through which they convert oxygen into a reactive form that can damage pathogens. This is a metabolically demanding process.
They found that the oxidative burst was being powered by a dynamic shift from metabolizing glucose through glycolysis to using the pentose phosphate pathway, a unique metabolic mode that helps power the neutrophil to quickly turn on and attack pathogens at the immunological front line. And not only was glucose diverted to the pentose phosphate pathway, but some steps of glycolysis were reversed so that the glucose molecules could be recycled to pass through the pentose phosphate pathway again.
“As we saw those core changes, the next question was, if we mess up those changes, are the cells still able to perform their functions?” says Britt.
Indeed, when the team experimentally blocked the pathway, there was no longer an oxidative burst, and the neutrophils lost the ability to kill pathogens.
Fan emphasizes how brave it is to start something new, and it was Britt’s enthusiasm that played a huge role in getting the lab to begin work on neutrophil metabolism research. Britt’s perspective: “Jing has been a great mentor in building my confidence as a scientist.”
A major challenge for the researchers was the onset of the COVID-19 pandemic, which brought some of their initial work to a halt. But Fan motivated Britt to embrace the “mix of fun and challenges” to push forward as they learned how to connect remotely and work in a whole different way.
Fan adds that this work demonstrates the beauty of having an unbiased approach to discovery, especially in a relatively new field such as neutrophil metabolism. “And we’re seeing that anything is possible,” she says.
As a private research institute, the Morgridge Institute is structured to be interdisciplinary by nature, and Fan says this gives her and other researchers the flexibility to pursue potentially paradigm-shifting science. And the partnership between Morgridge and UW, she says, is critical for her career and her lab’s success. “We can have an expert on campus bring the immunology piece, and I bring the metabolism piece; then something interesting happens,” she says.
“This is what makes science fun,” Huttenlocher adds. “Where new discoveries happen because you are allowing collaborations across fields.”
Into Unexplored Territory
With her lab and continued collaborations, Fan hopes to continue expanding her knowledge in the immunometabolism field. As the development of immunotherapies to treat diseases continues to grow, so does the need to better understand the complexities of the immune system and its metabolic processes.
“Immune cells are a huge area with so many things to study,” she says.
Right now, the lab is focused on the metabolism of macrophages and neutrophils individually; but inside a living organism, there is a lot of interaction between different cell types.
“We’re very interested in expanding into cell-cell interactions, like how macrophages and neutrophils interact,” she says. “There’s also obviously the interaction between immune cells and microbes, the pathogens and harmless bacteria alike in the microbiome. Immune cells need to figure out how to deal with that.”
Fan’s lab has just started to gather metabolic data looking at myeloid progenitor cell differentiation, how precursor cells (derived from stem cells) mature into macrophages, neutrophils, and other innate immune cells. UW and the Morgridge Institute have strong regenerative biology and stem cell research expertise, which Fan is ready to tap into if the opportunity arises. She’d also like to explore the interaction between immune cells and cancer cells, the area of research where her lab got its start.
And she continues to look ahead with an interdisciplinary approach in mind. “There’s enough science to study. I can’t spread myself too thin, but I just can’t stop,” Fan laughs. “And I know the collaborations will be fun.”