2009/11/28
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Researchers have identified the genes in gum-disease bacteria that allow them to invade and infect human arterial cells, offering one possible explanation for a perceived connection between gum disease and heart disease. Scientists from the University of Florida, Gainesville, present their findings today at the 106th General Meeting of the American Society for Microbiology in Orlando, Florida.
"Aside from lifestyle and genetic factors, there is increasing evidence that bacterial infections may play a role in heart disease. Porphyromas gingivalis, an important bacterium that causes gum disease, is also linked to cardiovascular disease. In this study we have identified and studied four genes of P. gingivalis that allow it to infect and survive inside artery cells," says Paulo Rodrigues, a researcher on the study.
Rodrigues and his colleagues had previously discovered that P. gingivalis had the ability to invade and survive inside human artery cells. In this study they examined the role four different genes play in this ability. They created four strains of the bacterium, each with a different gene mutated to disable it, and tested their ability to invade and survived in artery cells compared to a fully functioning strain of P. gingivalis.
"Our study showed that all four mutated strains were defective in invasion of the artery cells and that their ability to survive inside of the cells was diminished. These results show that these four genes play a role in the invasion and survival of P. gingivalis inside artery cells," says Rodrigues. "The knowledge of how this pathogenic bacterium interacts with artery cells is important and may lead to the development of therapeutics and diagnostic tools for the detection and possibly prevention of heart diseases caused by this association
"Aside from lifestyle and genetic factors, there is increasing evidence that bacterial infections may play a role in heart disease. Porphyromas gingivalis, an important bacterium that causes gum disease, is also linked to cardiovascular disease. In this study we have identified and studied four genes of P. gingivalis that allow it to infect and survive inside artery cells," says Paulo Rodrigues, a researcher on the study.
Rodrigues and his colleagues had previously discovered that P. gingivalis had the ability to invade and survive inside human artery cells. In this study they examined the role four different genes play in this ability. They created four strains of the bacterium, each with a different gene mutated to disable it, and tested their ability to invade and survived in artery cells compared to a fully functioning strain of P. gingivalis.
"Our study showed that all four mutated strains were defective in invasion of the artery cells and that their ability to survive inside of the cells was diminished. These results show that these four genes play a role in the invasion and survival of P. gingivalis inside artery cells," says Rodrigues. "The knowledge of how this pathogenic bacterium interacts with artery cells is important and may lead to the development of therapeutics and diagnostic tools for the detection and possibly prevention of heart diseases caused by this association
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Knockouts in Human Cells Point to Pathogenic Targets
researchers have developed a new type of genetic screen for human cells to pinpoint specific genes and proteins used by pathogens, according to their paper in Science.
In most human cell cultures genes are present in two copies: one inherited from the father and one from the mother. Gene inactivation by mutation is therefore inefficient because when one copy is inactivated, the second copy usually remains active and takes over.
In yeast, researchers have it easier: they use yeast cells in which all genes are present in only one copy (haploid yeast). Now Carette and co-workers have used a similar approach and used a human cell line, in which nearly all human chromosomes are present in a single copy.
In this rare cell line, Carette and co-workers generated mutations in almost all human genes and used this collection to screen for the host genes used by pathogens. By exposing those cells to influenza or to various bacterial toxins, the authors isolated mutants that were resistant to them. Carette then identified the mutated genes in the surviving cells, which code for a transporter molecule and an enzyme that the influenza virus hijacks to take over cells.
Working with Carla Guimaraes from Whitehead Member Hidde Ploegh's lab, Carette subjected knockout cells to several bacterial toxins to identify resistant cells and therefore the genes responsible.
The experiments identified a previously uncharacterized gene as essential for intoxication by diphtheria toxin and exotoxin A toxicity, and a cell surface protein needed for cytolethal distending toxin toxicity.
"We were surprised by the clarity of the results," says Jan Carette, a postdoctoral researcher in the Brummelkamp lab and first author on the Science article. "They allowed us to identify new genes and proteins involved in infectious processes that have been studied for decades, like diphtheria and the flu. In addition we found the first human genes essential for host-pathogen interactions where few details are known, as is the case for cytolethal distending toxin secreted by certain strains of E. coli. This could be important for rapidly responding to newly emerging pathogens or to study pathogen biology that has been difficult to study experimentally."
Brummelkamp sees the work as only the beginning.
"Having knockout cells for almost all human genes in our freezer opens up a wealth of biological questions that we can look at," he says. "In addition to many aspects of cell biology that can be studied, knockout screens could also be used to unravel molecular networks that are exploited by a battery of different viruses and bacteria."
This research was funded by Fundação para a Ciência ea Tecnologia (FCT) Portugal and the Kimmel Foundation.
Thijn Brummelkamp is a Fellow at Whitehead Institute for Biomedical Research, where his laboratory is located and all his research is conducted.
In most human cell cultures genes are present in two copies: one inherited from the father and one from the mother. Gene inactivation by mutation is therefore inefficient because when one copy is inactivated, the second copy usually remains active and takes over.
In yeast, researchers have it easier: they use yeast cells in which all genes are present in only one copy (haploid yeast). Now Carette and co-workers have used a similar approach and used a human cell line, in which nearly all human chromosomes are present in a single copy.
In this rare cell line, Carette and co-workers generated mutations in almost all human genes and used this collection to screen for the host genes used by pathogens. By exposing those cells to influenza or to various bacterial toxins, the authors isolated mutants that were resistant to them. Carette then identified the mutated genes in the surviving cells, which code for a transporter molecule and an enzyme that the influenza virus hijacks to take over cells.
Working with Carla Guimaraes from Whitehead Member Hidde Ploegh's lab, Carette subjected knockout cells to several bacterial toxins to identify resistant cells and therefore the genes responsible.
The experiments identified a previously uncharacterized gene as essential for intoxication by diphtheria toxin and exotoxin A toxicity, and a cell surface protein needed for cytolethal distending toxin toxicity.
"We were surprised by the clarity of the results," says Jan Carette, a postdoctoral researcher in the Brummelkamp lab and first author on the Science article. "They allowed us to identify new genes and proteins involved in infectious processes that have been studied for decades, like diphtheria and the flu. In addition we found the first human genes essential for host-pathogen interactions where few details are known, as is the case for cytolethal distending toxin secreted by certain strains of E. coli. This could be important for rapidly responding to newly emerging pathogens or to study pathogen biology that has been difficult to study experimentally."
Brummelkamp sees the work as only the beginning.
"Having knockout cells for almost all human genes in our freezer opens up a wealth of biological questions that we can look at," he says. "In addition to many aspects of cell biology that can be studied, knockout screens could also be used to unravel molecular networks that are exploited by a battery of different viruses and bacteria."
This research was funded by Fundação para a Ciência ea Tecnologia (FCT) Portugal and the Kimmel Foundation.
Thijn Brummelkamp is a Fellow at Whitehead Institute for Biomedical Research, where his laboratory is located and all his research is conducted.
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