Some people are better protected against urinary tract infections than others because their bodies may produce higher levels of the protein uromodulin. An interdisciplinary research team has now discovered how the helper protein works in the emergency response and what can be deduced from this for the treatment and prevention of painful inflammations.
Most people that have gone through a bladder infection know: urinary tract infections (UTIs) can be both troublesome and painful. They can usually be treated with antibiotics, but if left untreated they can also be fatal. The infections are usually caused by uropathogenic Escherichia coli (UPEC) bacteria strains. A certain protein in the body, uromodulin, offers protection against this: around 70 percent of all people carry a uromodulin gene variant in their genome, which means that they produce this protective protein in, particularly large quantities. Accordingly, they have a lower risk of contracting UTIs.
However, it was not known how exactly the uromodulin prevents inflammations. This has now been discovered by an interdisciplinary team composed of three research groups at the ETH Zurich (in English: Swiss Federal Institute of Technology Zurich) who collaborated with researchers from Universität Zürich (in English: University of Zurich) and the Kinderspitals Zürich (in English: Zurich’s Children Hospital). The researchers investigated the means by which uromodulin neutralizes the uropathogenic E. coli. Their findings were published in the journal "Science" and should help to develop new strategies for thUTIs treatment in the future.
The researchers first analyzed how the protein binds to the bacterial pili at the molecular level. "Although it was known in advance that binding would take place and that this would probably contribute to the protein’s protective function, nothing more was known", says Gregor Weiss, a doctoral student at ETH Zurich. The biochemical research now showed that the bacterial pili recognizes certain sugar chains on the surface of the uromodulin and binds strongly to them in a very specific way.
The team then examined the uromodulin using electron cryotomography (CryoET). This enables the three-dimensional structures of proteins and cells to be visualized without having to chemically alter or dehydrate them. They discovered that the uromodulin forms long filaments. These consist of an average of around 400 individual protein molecules strung together. And each link of this protein chain contains the characteristic pattern of sugar chains to which bacterial pili like to bind.
The team again used CryoET to investigate the effect of these properties on a larger scale, but this time in the presence of the uropathogenic E. coli bacteria. It was shown that the uromodulin filaments literally envelop the pathogens’ pili. A single uromodulin filament can dock to several bacterium pili. "This neutralizes the pathogens," explains Gregor Weiss. "Shielded in this way, the bacteria can no longer bind to the cells in the urinary tract and therefore cannot cause infection." Under the microscopic light, the team also discovered that large clumps of hundreds of uromodulin filaments and E. coli cells form, which are then probably simply excreted with the urine.
Finally, the researchers checked whether all these processes observed in the laboratory also occur in patients. To this end, they analyzed urine samples from infected patients from the Zurich Children's Hospital and found exactly the same interactions between the uromodulin and the pathogens. "Without the interdisciplinary cooperation between different research groups and institutes, it would have been impossible to obtain the knowledge we gained," emphasizes ETH Professor Martin Pilhofer, who headed the CryoET investigations.
The research team’s work has resulted in indications of antibiotic-free treatment and UTIs prevention. "Through our analyses, we now know that the bacteria with their pili recognize not only mannose but also other sugars on the uromodulin," says Ph.D. student Jessica Stanisich. "This could indicate that treatment with combined sugar supplements would be more effective."
The new results also help in the development of new active substances, adds ETH-Professor Rudi Glockshuber. This is because uropathogenic E. coli adheres to the same sugar chains on the cell surfaces of the urinary tract during an infection as does uromodulin. That is why pharmaceutical companies are trying to prevent precisely these interactions with new active substances - but with the risk that the binding of the protective uromodulin to the bacteria is also disturbed. "This would of course be a highly undesired side effect if a drug were to simultaneously interfere with a natural protective function," says Glockshuber. However, the analyses carried out by the research team have now made it clear that the combinations of bacteria and uromodulin are extremely stable and can no longer be disrupted by active substances - an important finding in the search for remedies for the troublesome urinary tract infections.
Weiss GL, Stanisich JJ, Sauer MM, Lin C, Eras J, Zyla DS, Trück J, Devuyst O, Aebi M, Pilhofer M and Glockshuber R. Architecture and function of human uromodulin filaments in urinary tract infections. Science (2020). Online publiziert 2. Juli 2020. DOI: 10.1126/science.aaz9866