UO researchers discover a gut bacterial protein that stimulates insulin-producing cells to expand in zebrafish

Zebrafish

Researchers at the University of Oregon have identified a novel bacterial protein that induces pancreatic beta cell proliferation during zebrafish development. Beta cells in the pancreas are the only cells that produce the hormone insulin, which regulates sugar metabolism in the body.

The research appeared online on Dec. 13 in the open access journal eLife.

The research demonstrates the important developmental role of the teeming community of bacteria and other microbes, known as the microbiota, that inhabit the bodies of animals. As researchers gain a better understanding of how those microbes affect beta cell expansion in other animals and humans, this could lead to new diagnostic, preventative, and therapeutic approaches for the nearly 1.5 million Americans with Type 1 diabetes who lack the ability to produce insulin.

“We're realizing what a rich source the microbiome is for discovering new biomolecules that have enormous potential for manipulating and promoting our health.” said co-author Karen Guillemin, a professor in the UO Department of Biology and the Institute of Molecular Biology who also serves as director of the UO’s META Center for Systems Biology.

Karen Guillemin

Using germ-free zebrafish as a model, the team showed that certain gut bacteria are necessary for the pancreas to populate itself with a robust number of beta cells during development. Researchers found that, during their development, microbe-free fish did not undergo the same proliferation of beta cells as conventionally reared fish. Exposing the germ-free fish to certain bacteria restored beta cell production to normal levels. The research team went on to identify a novel secreted protein produced by those bacteria, now known as BefA, that caused beta cells to multiply.

“The research really suggests that animals very much rely on the cues and signals of the microbial communities that inhabit their bodies and that they (bacteria) are important for very intricate parts of development,” said lead author Jennifer Hampton Hill, a senior graduate student pursuing a Ph.D. in biology. “It’s exciting to think that bacteria could play such an important role in a process that is so essential for homeostasis, for the ability to regulate sugar metabolism.”

“This is a new idea that the microbiome could be a source for signals for pancreas development,” Guillemin said. “And this is the first time that anyone has made a connection between the microbiome and the development of beta cells.”

Scientists have been increasing their understanding of the role of host-associated microbes in the development of the gut and the immune system but, the researchers said, the role of microbes in the development of other digestive organs such as the pancreas remains an underexplored area.

The UO has been a leader in zebrafish research since the 1960s when biologist George Streisinger pioneered a new method for the study of vertebrate development and genetics with the introduction of the zebrafish as a model organism. Over the past 15 years, Guillemin and co-workers have developed methods for growing germ-free zebrafish, allowing them to ask what happens when the animals develop in the absence of microbes.

In the current study, Hampton Hill used germ-free zebrafish to screen for specific gut bacteria that on their own could stimulate beta cell proliferation. Once she had identified such bacteria, she asked whether any of them secreted products that could cause beta cells to expand when added to the water of germ-free fish.

The positive outcome of this experiment started Hampton Hill’s hunt for the specific beta cell expanding factor in a large soup of secreted bacterial products. She narrowed down her list of suspects to 163 proteins made by one bacterium. Fortunately, she could turn back to the genome sequences of all the bacteria she had screened and ask which of these candidate proteins were shared by the beta cell expanding bacteria and absent from the inert bacteria.

Remarkably, this narrowed her list to a single protein that had never been studied before. When she made a pure version of this protein and added it to her germ-free fish, sure enough their beta cell numbers swelled, leading her to name this new protein Beta Cell Expansion Factor A, or BefA.

With this new knowledge of the molecular identity of BefA, the researchers could now search all other known bacterial genomes for genes encoding related proteins. They found such relatives in several common human gut bacteria, two of which they tested in their microbe-free fish and found to be equally potent at inducing beta cell expansion.

“We had spent many years collecting and characterizing zebrafish gut bacteria, and it was gratifying that we could harness all of this knowledge in the discovery of BefA,” Guillemin said.

The study sheds new light on associations between the microbiome and development of Type 1 diabetes, an autoimmune disease in which beta cells are destroyed by the body’s immune system. Previous studies have suggested that children who develop Type 1 diabetes tend to have fewer types of bacteria in their microbiomes. Guillemin and Hampton Hill suspect that these low diversity microbiomes could be less capable of stimulating beta cell expansion early in life, leaving these children with little buffer if their immune systems go on the attack. Immediate implications of the research from the Guillemin group would be to encourage best practices in promoting healthy microbiome development in children, for example by encouraging breast feeding and avoiding excessive use of antibiotics.

“Antibiotics are valuable for preventing infections, but they have been viewed as causing no real collateral damage, whereas now we appreciate that there’s actually a risk associated with antibiotic use. We should be questioning whether practices make sense such as impregnating our kids’ pajamas with antimicrobials,” Guillemin said.

Long term, the findings could someday lead to screening for the presence or absence of beta cell promoting bacteria in children and developing strategies to prevent or possibly treat Type 1 diabetes with bacterial products. But first, further research is needed to study the mechanism by which the BefA proteins affects beta cell development and to determine whether they have the same effect on other animals including humans.

Seeking to further our understanding of microbial diversity and its impacts on human development with the goal of developing future therapeutics for improving health and combatting diseases, such as diabetes, is the type of translational research that could eventually be conducted at the recently announced Phil and Penny Knight Campus for Accelerating Scientific Impact. The Knight Campus is designed to fast-track scientific discoveries and ensure that they are quickly tested, refined and developed into innovations that improve the human condition. The facility is expected to enhance and expand collaborations between scientists and faculty members at other premier research universities, and to recruit new types of scientists to the campus, such as those interested in clinical translation of new discoveries.                                                   

“Ultimately we’d like to team up with researchers studying Type 1 diabetes to look at developing BefA-related molecules as potential therapeutics,” Guillemin said.

The research was funded by the National Institute of General Medical Sciences of the National Institutes of Health under award numbers P50GM098911 and T32 GM007413-37. Grant P01HD22486 provided support for the Oregon Zebrafish Facility.


For the story behind the story of this UO research discovery, see "Pursuing a Hunch."