Prof. Emmanuel Hansky from the Hebrew University, heads a team of joint research conducted in Singapore and Israel. The team published a study in the prestigious journal Cell Reports: "This study provides a precise understanding of the interactions between the Streptococcus type A bacterium and the host, and improves the ability to design effective treatments against it, such as engineered peptides that the bacterium cannot cleave."
The bacterium group A streptococcus causes a variety of diseases in humans, from superficial infections of the throat and skin to life-threatening invasive diseases, such as necrotizing fasciitis (NF) for which the bacterium earned the nickname "the predatory bacterium". In recent decades, it has In the incidence of the infection, the mortality rates from this disease range from 25-45% even when the patient is treated immediately and comprehensively Administration of antibiotics through the vein, surgical removal of infected tissues and support in the intensive care unit. Around 18 million people worldwide are ill with severe diseases caused by the bacterium, with approximately 1.78 million new cases each year. In addition, hundreds of millions of people develop a severe infection as a result of exposure to the streptococcus bacterium A, every year, this great morbidity burdens the health system, despite extensive research over the years, there is no effective vaccine against the disease caused by bacteria and therefore there is an urgent need to find new approaches for effective and useful treatment.
Antimicrobial peptides are small proteins that are formed in response to infection by bacteria, viruses, and fungi. This response is an integral part of the innate immune system, and exists in simple creatures such as molluscs, flies, through plants and even man himself. LL-37 is an antimicrobial peptide produced in humans by various cells, including white blood cells in response to the invasion of the skin and soft tissues by the streptococcus. Its homologue in the mouse is called CRAMP. A seminal study published in the scientific journal Nature twenty years ago showed that when the streptococcus is injected into CRAMP-deficient transgenic mice, they develop a more severe disease compared to normal mice that express CRAMP. The conclusion of the study was that the difference in the severity of the disease is due to the ability of CRAMP and LL-37 to directly kill the bacteria.
Challenging the conventional wisdom
"Two reasons led us to try and challenge this accepted view," claims Prof. Emeritus Emanuel Hansky, who recently published a scientific article on the subject in the scientific journal Cell Reports, edited by Israeli and Singaporean researchers from Prof. Hansky's laboratory. "The first is that the killing activity requires relatively high concentrations of LL-37 or CRAMP which apparently do not exist in the body even during the infection with the streptococcus A bacteria. The second reason is that the bacteria is able to sense LL-37 in concentrations much lower than the lethal concentration and react with an increased expression of several virulence factors of the bacteria, which make it invasive and life-threatening."
The severity of the disease caused by Streptococcus A is determined by the level of expression and activity of the bacteria's virulence factors on the one hand, and on the other hand by the strength of the innate immune system's response that tries to neutralize the destructive effects of the violence factors. One of the most important factors of the bacterium's violence is protease - an enzyme that cleaves proteins and peptides. "In the past, we showed that the same protease is found on the surface of the bacteria and is very specific. It cleaves and neutralizes the activity of the interleukin 8 (IL-8) molecule only. IL-8 is created in humans during infection and its role is to recruit white blood cells to the site of infection and activate them. When these cells reach the infection They ingest and kill the bacteria in the infected tissue.Thus, the bacterial protease activity is actually a way for the bacteria to prevent its removal from the tissue by The white blood cells therefore have this ability to invade soft tissues and cause a serious, life-threatening disease. LL-37 also has a similar ability to recruit white blood cells of the immune system to the site of infection," explains Prof. Hansky.
Engineered peptides
In Prof. Hansky's article in Cell Reports, it appears for the first time that the bacterial protease also cleaves the LL-37 peptide into two parts of 8 and 29 amino acids. The cleaved peptide still maintains its killing activity and also increases the expression of the bacteria's virulence factors, including the protease itself. However, the cut inhibits the ability of LL-37 to recruit white blood cells to the site of infection and eliminates the ability of LL-37 to extend the lifespan of these blood cells. In addition, the cleavage eliminates the ability of low concentrations of LL-37 to activate two receptors that are expressed on different cells and whose main function is to regulate the intensity of the immune response and the rate of repair of the damaged tissue: purinoceptor 7 (P2X7R) and EGFR epidermal growth factor receptor).
To "work" on the bacterium, the researchers changed amino acids at the LL-37 cleavage site, creating two LL-37 analogs that are not cleaved by the protease, but still retain all the other functions of LL-37. "When we injected bacteria under the skin of CRAMP-deficient transgenic mice and normal CRAMP-expressing mice and treated them with a low concentration of the non-cleavable LL-37 analogs, we found that the bacteria were cleared by the mouse's immune system and the mice recovered from the disease. The healing effect of the analogs was reversed when we injected antagonistic mice of the P2X7R or EGFR receptors this experiment proves first that contrary to the common notion that LL-37 kills the bacteria that penetrate soft tissues and thus helps the immune system to overcome the disease, in fact the activation of P2X7R and EGFR by low concentrations of LL-37 is the critical mechanism for protection against Streptococcus A infections in soft tissues. This research provides a precise understanding of the interactions between the bacterium and the host and improves the ability to design effective treatments against the bacterium, such as engineered peptides that the bacterium cannot cleave. Innovative treatments are especially important against life-threatening diseases that do not have a good therapeutic response," concludes the researcher.
More of the topic in Hayadan:
