Dr. Johnson is a molecular biologist who studies the effects of diet and nutrition on the microbiome. She is particularly interested in the role that breast milk may play in the establishment of the infant microbiome.

Dr. Johnson attended Spelman College as an undergraduate, and received her Ph.D. in Molecular Biology from Princeton University. Dr. Johnson joined the faculty at Cornell in 2018 after completing a postdoc with Ruth Ley, a powerhouse in the microbiome field. Since beginning her postdoc at Cornell, she has focused on sphingolipids, a type of molecule important as signals for metabolism and cell proliferation.

Our bodies are not only composed of trillions of cells. They are also the ecosystem for diverse microbes that live on our skin, in our noses, our eyes, and our guts. Collectively, these organisms comprise our microbiome. Many of these bacteria likely have no impact on us at all, but there’s a lot of interest in trying to figure out how they might be related to all different aspects of our health. This includes diseases related to digestion like Crohn’s disease, celiac disease, and diabetes, but also things with less obvious connections like autism, depression, and Parkinson’s. It is important to note that the jury is still out on a lot of this research: people have found intriguing connections but not a lot that’s definitive yet.

Recently, Dr. Johnson and colleagues have looked at a potential connection between the gut microbiome and type 2 diabetes. In type 2 diabetes, cells are less responsive to insulin, the signal to take up more sugar from the blood to stabilize blood sugar. This loss of insulin response is associated with higher levels of a type of sphingolipids called ceramides. Previous research had shown that Bacteroidetes, a phylum of bacteria that are very abundant in the gut, can produce ceramides and that in a group of ~300 people in Denmark, those with lower levels of Bacteroidetes in their guts were less likely to have insulin insensitivity.

Thus, in a recent paper, Dr. Johnson wanted to know if the ceramides made by Bacteroidetes in the gut could impact the normal production of ceramides by the body.

First, she took human colon cells grown in a dish and exposed them to bacterial ceramides. She found that the human cells took up the bacterial ceramides, used those ceramides interchangeably with their own ceramides, and made more of the machinery they use to process ceramides.

Next, she wanted to show that this happened in a living mammal and wasn’t some side effect of growing in a dish. So she transferred bacteria making ceramides into the guts of mice, and found the same response in the mouse gut and liver. She also found that if mice ate a super low-fat diet that didn’t provide them with enough ceramides, the bacterial ceramides could help compensate. In contrast, mice fed a high-fat diet were more likely to have low responsiveness to insulin if they had the bacteria producing ceramides than if they didn’t.

Dr. Johnson’s research suggests that we need to think about the bacteria in the gut in order to understand and treat diabetes more effectively.