Director of national laboratory and program on host genetics and prion diseases
National Microbiology Laboratory, Health Canada and Public Health Agency of Canada
At A Glance
Name: Michael Coulthart
Position: Director of national laboratory and program on host genetics and prion diseases at the National Microbiology Laboratory, Health Canada and Public Health Agency of Canada, Winnepeg, Manitoba, since 1998.
Background: Research scientist in microbial genetics; chief of National Laboratory for Microbial Genetics, Laboratory Centre for Disease Control, Health Canada, Ottawa, Ontario, 1995-1998.
Postdoc, Gregory Dekaban's laboratory, John P. Robarts Research Institute, London, Ontario, 1993-1995.
Postdoc, Michael Gray's laboratory, Dalhousie University department of biochemistry, Halifax, Nova Scotia, 1987-1992.
PhD in genetics, Rama Singh's laboratory, McMaster University, Hamilton, Ontario, 1986.
Canadian prion researchers are in the process of setting up PrioNet Canada, a national network for prion research, focusing on Crutzfeldt-Jakob disease, Bovine Spongiform Encephalopathy, and Chronic Wasting Disease (see PrioNet Canada story). ProteoMonitor caught up with Michael Coulthart, one of the leaders of the network who has established a laboratory for national surveillance of human prion diseases, to find out about his background and his strategy for addressing prion diseases.
What is your educational background?
I did my PhD at McMaster University, and that was in the biochemical population genetics of fruit flies. It was about the fundamental questions of mechanisms that cause reproductive isolation in species. We were using 2D protein gels for that. It was essentially the old O'Farrell method, the classic method that was published in 1975. So it's really quite a venerable method, but that's still the basis for proteomic approaches using 2D gels today.
What kind of fruit fly populations were you comparing?
We were comparing populations of different species. What happens a lot of times with these little fruit flies is they look the same, but the different sibling species — when they attempt to interbreed — their offspring are sterile. So my objective was to look at the relationship between differences in the male reproductive organ proteins and the sterility between these species.
My core finding was that the male reproductive tract proteins appear to evolve more rapidly than other groups of proteins in fruit flies. That's actually held up over time, interesting enough, even with new technology applied to the question. It's possible that sexual selection is involved in the process, and possibly other kinds of factors like mutability of the proteins. For the people who still work in that area, that's a fairly hot topic of research — what actually drives this change, and it's not exactly understood yet. But the phenomenon has stood the test of time, that the male reproductive tract appears to evolve more rapidly on a molecular level in fruit flies, and in other species as well. It's part of a general phenomenon. This is very abstruse. You can see the very basic background I come from.
What did you do after the fly project?
Then I went into the molecular evolution of plant mitochondrial genomes. Basically, there was a need for anyone seriously studying molecular evolution to get down to the nucleic acid level. So, the most interesting postdoc opportunity I had was in the molecular evolution of plant mitochondrial genomes. That's when mitochondrial DNA in general was very hot in terms of molecular evolution.
Plants have an odd configuration to their mitochondrial DNA. It's maybe 50 times larger than animal mitochondrial genomes. Studying the evolutionary processes in those genomes occupied me for some time. It was a pretty technical project, and it had to do largely with genome mapping for these genomes that are around half a megabase in size. That's how I got involved with population genetics on the DNA level. And there's a bit of a human interest thing too, because we're coming back to proteins. Really, proteins, back in the days before it became the norm to use PCR and rapid sequencing techniques to study the DNA directly, proteins were the only game in town. And now we're coming back with a whole new set of tools, and we're asking much more sophisticated questions using proteomic tools and a whole armament of new information, like genome sequences.
What did you do after your postdoc?
Where I really started to cook was when I got into infectious diseases — that was in 1993. then shortly after that, I got a job in government and started to work in public health. From my own biased personal point of view, I think there was a real revolution in the way public health is undertaken for infectious diseases. In the mid-90's, things just went molecular. It was really quite amazing. And again, DNA and RNA were very much on top of the heap in terms of what you could do. But now I think we're coming around again on the level of application to practical problems to use a protein-oriented approach to try to understand infectious disease as it occurs in populations. So I honestly think that there's a whole frontier there that is barely explored in terms of application of proteomics to infectious disease questions. Not just how they work, but how they move through populations, and how you can prevent them and control them and do surveillance for them.
So when you got involved in infectious diseases, you were doing it at a molecular level?
Yes, it's what people still refer to as molecular epidemiology. It was with HTLV — human T-cell lymphotropic virus. It's a retrovirus. The types of questions I was most interested in at a population level were where strains are coming from, where they're going, how they're affecting the host, how they're responding to human intervention.
In 1998 was when I moved into prions, which I hope is the end of my long, wandering travels. And of course there, there's no known pathogen genome. There are a few people who still believe it's a virus with a conventional genome that you can study directly, but so far no one's pulled that one out of the woodwork. There may still be a surprising discovery, but I would consider it very surprising if somebody finds a virus. I think that when you've got a pathogen that has no known nucleic acid component, you're pretty much limited to either study the make-up of the host, or the physiological correlates of infection in the host.
What has been your strategy for studying prions?
We've actually got a large investment in microarray work. So there's a scientist in my lab named Stephanie Booth — we've co-authored a couple of papers in the last six months looking at host responses using c-DNA microarrays. So that work, I think, is going continue to be physiologically informative, and it may actually lead to the discovery of biomarkers. I consider that one portal through which you can look for changes in the host.
We're also just getting into proteomic work on prions now. So there is some work going on with 2D gels in my lab, but we haven't actually set up our SELDI unit yet. The next phase would be to compare the proteomes of infected versus non-infected mice. That's the next phase. We've already been working for a few years on the mRNA profiling.
That reflects a general approach that I had decided we would take when we established the prion lab back in 1998. I was the founder of the prion lab program back at Health Canada, which is now the Public Health Agency of Canada. I decided at that time that taking a genomic/proteomic approach would be very important for prion disease.
Was your lab always involved in diagnosing prion diseases?
Yes, that was the initial rationale for founding the lab actually — to assist in the surveillance of human prion diseases by providing lab diagnostic services.
We get a couple of hundred samples per year. It's a rare disease in Canada, on the order of one in a million population per year that develop Creutzfeldt-Jakob disease. So in Canada we get in the neighborhood of 30 confirmed cases of CJD per year. In the US they have more like 300. The vast bulk of that is not traceable to BSE at all, or any other risk factor. It's just termed sporadic CJD.
Do people know what causes sporadic CJD?
It's a bit mysterious. There are some theories. The predominant one is that the prion protein goes through a spontaneous post-translational misfolding event on the molecular level. You get a small subpopulation, and if the misfolded proteins are not cleared through cell death or some other kind of mechanism, they begin to form aggregates, and because the protein is able to template the conversion of the normal form of the protein into the abnormal form, you get a kind of propagation effect. It's analogous to cancer, only it's something that people propose happens only on the protein level, rather than the cellular level. You get a somatic accident of some sort that is able to propagate through the body.
When you diagnose a case of CJD, how do you go about trying to trace it back to a source?
That's part of the surveillance process. You can't exactly trace things easily to consumption of beef because the practice of eating beef is so widespread that there's really very little discriminatory power between those that may have been exposed to BSE by that route and those who haven't. So questions are asked about various risk factors, but we don't know a lot about what kinds of questions to ask for sporadic CJD. One of the main things is to essentially eliminate any reasonable suspicion of it actually being the human form of mad cow disease. So one of the questions on the questionnaire for people and their families who may have been affected by CJD is 'Have you lived in the UK, or in Europe?' And the single case of variant CJD that was confirmed in a Canadian resident in 2002 was actually linked to a three-year stay in the UK back in the late 80s and early 90s.
For the various cases of BSE that have popped up in Canada, have they caused human disease at all?
There's no evidence for that having happened. The cases that were detected actually — most of those animals did not go into the human food chain.
Do you think you might to study the humans that come down with CJD every year?
It's possible. We work with other countries that also are involved with surveillance with CJD, and the UK is the lead country in that international consortium. So in collaboration with them, our findings on the fundamental proteomics of prion diseases, even in other species, may prove to be applicable to the variant CJD question.
Do you think some people are more susceptible to CJD than others?
Almost certainly. There's something going on. The way you can see most clearly that people are not equally susceptible is in the prion coding gene in humans, there's a common polymorphism at codon 129. It can be either methionine or valine. In western European populations, the allele frequency is roughly 60 percent methionine, 40 percent valine. So the corresponding diploid phenotype are about 40 percent, 50 percent, 10 percent for methionine homozygotes to heterozygotes to valine homozygotes [respectively]. With every case of variant CJD that's been diagnosed so far, the genotype has been homozygous for methionine. So that's a very high risk ratio for being homozygous at that position for methionine. And nobody really knows what the basis for that is.
Are there cases in the normal population where people are infected with CJD, but they don't have the disease?
There are very likely people like that in various countries. It's not possible to say how many, and it's not possible to say if some of them may never come down with the disease in their lifetime. This is a large public health concern because you can't detect those people by any simple means, and yet they may be infectious if they gave blood for instance.
There's a lot of research going on to try to develop a blood test for vCJD, but we haven't actually seen any commercial product yet. Our lab is not working on that directly. We took a look around and saw how many people were pursuing the most obvious path — the ultrasensitive detection of this abnormal prion protein — and we thought we're better not compete with all the commercial interests that have much bigger labs than ours and megabucks at their disposal. So if we make a contribution, it'll be through a less obvious route, through this biomarker approach.
Are you working on any kind of a vaccine or therapeutic?
No. That's one area we don't get into.
What other projects will you be working on in the future?
One of the dominant thrusts for us will be to try to facilitate the application of useful biomarkers for CJD surveillance. That's our primary task here in the public health agency. The surveillance part of it really needs to be enhanced with the application of new technical approaches.
Right now, there are some candidate biomarkers, but we haven't heard much about them in terms of their actual application. There was one that was published back in 1999, but I haven't heard a thing about it since really.
I think in terms of discovery research, we're very interested in pursuing biomarkers on the protein level. We also have the advantage of being able to apply them to real world problems.
In Canada right now, there's a very important opportunity, because different sectors are converging on the same basic set of questions. You have the university-based research sector that has just been very nicely supported with the formation of PrioNet Canada. At the same time you have the formation of the Public Health Agency, which occurred last fall, in September of 2004. So we have this nice convergence between the federal government sector interested in public health applications, and the academically-based sector. And the private sector is contributing to PrioNet Canada as well. We're all coming together with this national network that I hope will bring Canada's research capacities and talent to a head.