A team of British researchers has discovered that some bacteria are able to change the make-up of supporting cells within the nerve system, called Schwann cells, so that these cells take on the properties of stem cells. The team made the discovery studying Mycobacterium leprae, a bacterium that causes leprosy.
Mycobacterium leprae reprogram adult Schwann cells by altering host-gene expression. Bacterially reprogrammed cells resemble progenitor/stem-like cells of mesenchymal trait that promote bacterial spread to mesenchymal tissues by redifferentiation. Progenitor/stem-like cells then secrete immune factors, recruit macrophages, transfer bacteria, form granulomas, and disseminate infection (Toshihiro Masaki et al)
The study, carried out in mice, found that in the early stages of infection, M. leprae were able to protect themselves from the body’s immune system by hiding in the Schwann cells. Once the infection was fully established, the bacteria were able to convert the Schwann cells to become like stem cells.
Like typical stem cells, these cells were pluripotent, meaning they could then become other cell types, for instance muscle cells. This enabled M. leprae to spread to tissues in the body.
The study, published in the journal Cell, also shows that the bacteria-generated stem cells have unexpected characteristic. They can secrete specialized proteins – called chemokines – that attract immune cells, which in turn pick up the bacteria and spread the infection.
“We have found a new weapon in a bacteria’s armory that enables them to spread effectively in the body by converting infected cells to stem cells. Greater understanding of how this occurs could help research to diagnose bacterial infectious diseases, such as leprosy, much earlier,” said study lead author Prof Anura Rambukkana, Medical Research Council Center for Regenerative Medicine at the University of Edinburgh.
“This is very intriguing as it is the first time that we have seen that functional adult tissue cells can be reprogrammed into stem cells by natural bacterial infection, which also does not carry the risk of creating tumorous cells. Potentially you could use the bacteria to change the flexibility of cells, turning them into stem cells and then use the standard antibiotics to kill the bacteria completely so that the cells could then be transplanted safely to tissue that has been damaged by degenerative disease.”
Dr Rob Buckle, Head of Regenerative Medicine at the Medical Research Council Center for Regenerative Medicine at the University of Edinburgh, said: “this ground-breaking new research shows that bacteria are able to sneak under the radar of the immune system by hijacking a naturally occurring mechanism to ‘reprogramme’ cells to make them look and behave like stem cells. This discovery is important not just for our understanding and treatment of bacterial disease, but for the rapidly progressing field of regenerative medicine. In future, this knowledge may help scientists to improve the safety and utility of lab-produced pluripotent stem cells and help drive the development of new regenerative therapies for a range of human diseases, which are currently impossible to treat.”
The scientists believe mechanisms used by leprosy bacteria could exist in other infectious diseases. Knowledge of this newly discovered tactic used by bacteria to spread infection could help research to improve treatments and earlier diagnosis of infectious diseases.
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Bibliographic information: Toshihiro Masaki et al. 2013. Reprogramming Adult Schwann Cells to Stem Cell-like Cells by Leprosy Bacilli Promotes Dissemination of Infection. Cell, vol. 152, no. 1, 51-67; doi: 10.1016/j.cell.2012.12.014
