Narrowing the Field Continued:

Unlike Dr. Dean’s most recent study, just out in the Journal of Bacteriology, most of the earlier studies on C. pneumoniae have been linear, looking for a specific gene involved in the entry of the organism into the host cells, or an individual marker of inflammation. These kinds of studies can have limited scope however, when so little is yet known about a pathogen.

As Dr. Dean explains, “If you look at a single gene this early in the game, you can miss the forest for the trees. By identifying genes that are part of a network system, you get a much better idea of what is going on, of what is involved in each step of the infectious process – from entry into the host cell to replication and development. You can then go backwards and knock out genes in the network to determine key players.”

One aspect of the systems network approach, after identifying the diversity of genes that are up or down regulated based on whole human gene expression microarrays as Dr. Dean did in her study, is a technique called RNA interference, in which researchers disable the RNA of specific genes and then evaluate the effect that ‘knocking down’ any given gene has on the different pathways the bacteria triggers.
Chlamydiae Pneumoniae bacteria (green) inside host cell (red)
“When you have an infection with an organism, the entry of the organism into the cell is going to set in motion a whole cascade of events. That’s why we wanted to identify a systemic network, to discover the whole system that might be triggered when the organism first encounters the cell and enters it,” Dr. Dean says.

In this case, Dr. Dean and her colleagues evaluated what was going in different cell systems over a timed response: after the first 5 minutes of infection; at 25 minutes; and at 2 hours. During the course of this timed response, Dr. Dean and her colleagues were able to identify 6 different proteins that play a major role in entry, a significant finding in and of itself, and yet, only part of the picture.

“While identifying these key players is important, what is even more interesting is that we found that to really inhibit entry and disable the bacteria completely, you have to knock down at least three of the six genes before you see any results. That is huge,” says Dr. Dean.

“Everyone is looking for the one receptor that the bacteria needs to enter the cell, but the likelihood is – and our study suggests this – that it’s not just one receptor we need to find but many, as wells as other mechanisms for entry.”
"As always with organisms that have been around for millennia, the plot just continues to thicken," says Dr. Dean.

In the mean time, Dr. Dean’s research provides first-time evidence of which different players researchers should focus on, remarkably narrowing the research field to six key genes to target, rather than having to search through the vast forest of possibilities.

“It’s the beginning of a very huge story, we don’t know the rest yet, but it provides us a good direction of where to focus to make the next big discovery,” says Dr. Dean.

In fact, Dr. Dean is already working on that next discovery, planning a study to compare human microarrays – a map of all the genes – with microarrays from the C. pneumoniae bacteria. In the mean time, however, this latest publication offers landmark new clues into the mystery of C. pneumoniae and how it is able to infect host cells – a major step in the path toward finally finding a way to stop C. pneumoniae infections in their tracks.


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