U of U Researchers Discover A Genetic Cause for Severe, Inflammatory ArthritisDec 16, 2013
University of Utah researchers have discovered a genetic variation in mice that predisposes them toward developing severe, inflammatory arthritis. The finding implicates a new class of genes in arthritis progression, potentially opening doors to new treatment options for sufferers of rheumatoid arthritis and Lyme arthritis. Dr. Janis Weis, professor of pathology, and Dr. Kenneth Bramwell, postdoctoral fellow in pathology, discuss what they found and where their work might lead.
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Interviewer: My guests are Dr. Janis Weis, a Professor of Pathology at the University of Utah and Postdoctoral Fellow Dr. Kenneth Bramwell, have identified a gene deficiency that makes individuals susceptible to developing severe inflammatory arthritis. Their work provides new insights into how the condition develops, and could one day lead to new treatments. When you started this study what were you hoping to understand?
Dr. Weis: We were hoping to understand, two things really. The mechanism by which infection with this bacteria, borrelia burgdorferi that is responsible for Lyme Disease, the mechanism by which it can cause severe arthritis in mice, and therefore, using that as a model for understanding severe arthritis in patients as well. And we were also hoping to identify genes that were responsible for the differences in disease severity.
Interviewer: And you've been working on this for some time, Dr. Bramwell you've started on these studies, I think just a few years ago, what was the state of the research when you came on board?
Dr. Bramwell: When I came into the lab the size of the interval contained about 350 different genes. My project was to find the needle in the haystack, to find the one or multiple genes in this interval that were regulating this disease severity. So we generated an animal that had 24 genes, so we'd excluded more than 90 percent of the genes. From those 24 genes our next step was to try to identify if there were any mutations or polymorphisms, and it turns out that 23 of these genes were 100 percent identical, at a DNA level. There was a gene that did have a polymorphism in the DNA sequence and it's called beta glucuronidase or GUSb, and so when we first found this and identified that this was a potential candidate, it was actually a disappointment because this is not the type of gene you go looking for in a study like this. It turns out, this is what's called a housekeeping gene, it carries out the normal boring processes of the cell, and if you look in the scientific literature, which I did, you back several years and almost every paper that's been published on this is not studying this gene at all, it's using this as a reference to study something else more interesting. So, I wasn't very pleased with that at the beginning, but I didn't let that get me down and I thought, OK, well, this looks to be what's causing the effect so let's follow it.
Interviewer: So Dr. Weis, how about you? Were you disappointed?
Dr. Weis: No, I wasn't disappointed. I think when you undertake an unbiased genetic mapping project, you go where the genetics takes you. I think you just say, well, we've got our work cut out for us, we have to do the correct experiments to really establish that there is plausibility for this gene to be associated with Lyme Arthritis severity.
Interviewer: So Dr. Bramwell, how do you follow up on that finding? And can you explain that experimental model?
Dr. Bramwell: Turns out that this is an enzyme, so we can measure the enzymatic activity, to see if it is fully functional or not. So we did that and it turns out that the C3H inbred strain of mice, which is the susceptible strain in our model, has a polymorphism. This polymorphism makes it so the beta glucuronidase function is reduced by about 90 percent below the activity of the wild type or the black 6 mouse, which is the resistant strain.
Interviewer: So what does GUSb do?
Dr. Bramwell: It's normal function is to breakdown what are called glycosaminoglycans. So these are always being produced, and because it's constantly being produced it also has to be degraded, it has to be removed. GUSb, and a variety of other enzymes that are of a similar type of enzyme, will nibble down these GAG chains to dispose of theme. And so, if you have a severe deficiency in any one of those genes, what happens is you end up with these GAG chains not being degraded properly, you get an accumulation of partially degraded compounds that then build up in the cell. So that's why it's called a lysosomal storage disease, you're storing these GAGs in the lysosome. That was kind of something interesting to think about because we really wanted to try and understand, we had very strong genetic evidence that GUSb was doing something, and this was the most plausible explanation, that it was related to its natural function.
Interviewer: And so you found this GAG accumulation in your mice with arthritis?
Dr. Bramwell: Right. So the next step that we wanted to do was to see if we could asses that. It turns out that there's a histochemical stain called Alcian blue, that will bind to these negatively charged glycosaminoglycans, you can see it visually, and so we did that and we saw a very striking difference. It turns out that in a variety of strains that have normal wild type GUSb activity, we always saw that if there was any arthritis severity, it would be minimal. And there was very little GAG alcian blue staining in these joints. And yet when we looked in a variety of different deficient strains, were they had either a partial or a more severe deficiency, and we stained for alcian blue, we saw that there was an extreme amount of the deposition of these GAGs that seemed to be in those areas that we were seeing the most inflammation.
Interviewer: So what is your model for how GAG accumulation is involved with arthritis?
Dr. Bramwell: Well, we're still studying this. There's a variety of different possibilities. It seems like these may be directly activating the innate immune response, that's one possibility. It could be that you actually have a modification of the GAGs that are being produced in these different cells, that's something that we're pursuing to understand. Right now we're really at the point where we've observed that this seems to be directly related and we're trying to understand it better.
Interviewer: You also found a connection between GUSb deficiency and rheumatoid arthritis.
Dr. Weis: He found that an increase in arthritis severity was also regulated by GUSb. So this was a very exciting finding, and I think that it tells us something about rheumatoid arthritis, something that was not predicted at all, so a novel new finding.
Interviewer: Is there any evidence that GUSb is involved in human arthritis?
Dr. Bramwell: Not at this point, and that's something that we have established with some new collaborations either with doctors at the University of Utah Hospital and Primary Children's Hospital, to begin to address some of these questions because a lot of the doctors we've spoken to who have familiarity with rheumatoid arthritis or juvenile rheumatoid arthritis or lysosomal storage disease, are quite excited about these findings and it seems obvious once you have identified it then, it seems like, oh we should have known this, we should have expected this or predicted this, so we've had a very positive response from a lot of clinicians that see patients. And we're just on the beginning stages of trying to transition into studying the effects, perhaps, in human populations
Interesting. Informative. And all in the name of better health. This is the Scope Health Sciences Radio.