Dr. Patrick: Yeah, and, you know, the other interesting thing, this kind of brings me back to some of your work where I don't know if...I think you mentioned this very early in our discussion about the blood-brain barrier when it becomes "leaky," this allows molecules that usually don't pass into the brain to then pass. And you had a paper that you had published a couple of years ago with...I think it was with your postdoctoral mentor, Dr. Zlokovic, about a protein called fibrinogen. Which, interestingly enough, is also...like, when I go and get my inflammatory biomarkers measured, I like to look at fibrinogen as well as high-sensitivity C-reactive protein. It's an inflammatory marker. I mean, it's involved in blood coagulation but you found this in the brain. What is the significance of that?

Dr. Montagne: Yes, yes, and it's not only two years ago, I think there's...I think the first report, it's probably 10 years ago. But the first report was on, again, brain tissue samples, very valuable tissue samples from donors, where we see that if you compare a control brain, someone cognitively normal, no issues whatsoever, and another time an Alzheimer`s brain or a small vessel disease brain. You start seeing what we call this extravascular deposition, fibrinogen is one of them. It's one protein that is supposedly in the blood, it shouldn't be in the brain at all, but we start seeing this extravascular deposition of fibrinogen, which means that to cross, you have to have some degree of breakdown of the barrier.

So, it has been found in Alzheimer's disease. We also found that in animals that either do have Alzheimer's disease or have some sort of blood-brain barrier issues. And we know that this protein that is important for blood coagulation, as you said, and inflammation has nothing to do in the brain and it's toxic, it's just toxic. And we found that it's neurotoxic, so it's toxic to neurons. It's also toxic to oligodendrocytes, where we found that…the oligodendrocytes are basically cells that are making myelin and make sure that the white matter is intact and we can function properly. And those molecules are crucial in the brain.

And we show that when you have a leaky barrier and you have fibrinogen going in, the oligos are very sensitive to that fibrinogen. So, they take it up, so they internalize fibrinogen, and they die by what we call autophagy. So, it's almost like a suicide kind of death, which leads to white matter disease. And if we go back, white matter disease is a common feature of Alzheimer's and small vessel disease. And as I said earlier also, the source of white matter disease is likely a blood-brain barrier breakdown, fibrinogen might play a role in this formation of white matter disease. So, yes, it's a very important protein that we found.

Interestingly, in animals, we were able to reduce fibrinogen levels systemically in the blood, of course, at a level that you don't want to increase to have some coagulation problems or increases of bleedings and things like that. So, you have to reduce at a level that you don't start doing bleeding or clotting. But just by reducing the fibrinogen level in a mouse model that do have blood-brain barrier issues, we were able to demonstrate that there is less, obviously, it makes sense, less fibrinogen going into the brain, less white matter that is damaged. And also interestingly, by reducing fibrinogen, we were able to partially restore vascular function in terms of blood flow and also the integrity of the barrier.

So, fibrinogen has probably different roles, not only coagulation and inflammation but probably a bit more. But I think that's one other way, we can target toxic things in the blood to avoid doing damage to the brain but I think it's probably easier to fix...easier, I don't know, but fix the blood vessels rather than doing that. But at least it's another evidence that, okay, a leaky barrier is leading to damage to the brain and you don't want that obviously. And the last thing on fibrinogen is, I just remember now, fibrinogen can activate the brain resident immune cells that are microglial cells through CD11b, so that's a specific receptor.

So, when fibrinogen gets in, it can bind to microglia, so it will induce an overreaction or over-inflammation of the brain which will be detrimental for many things, for the functions of the cell surrounding. And that reminds me that there is a fantastic researcher, Katerina Akassoglou, at Gladstone University, UCSF area, where I think she developed an antibody that blocks the interaction between fibrinogen and microglia to avoid that overexpression of inflammation or overactivation of microglial cells because she's also a strong believer that vascular dysfunction is a very early and a major contributor to dementia. So, that's very interesting research.

Dr. Patrick: It's very interesting, again, like you said, it really shows the importance of maintaining the blood-brain barrier so that it doesn't allow, you know, things like fibrinogen, which is involved in blood coagulation to cross into the brain. And, again, as you mentioned, the inflammation, it's activating microglial cells and it's causing them...I mean, that whole process you described earlier, the inflammaging and pericyte detachment perhaps and all that. Also, as I was reading and doing some background research on some of your work and because I knew of the inflammatory role of fibrinogen, you know, I'd already been familiar with that protein, you know, separate of what happens when it gets into the brain, I was looking up omega-3 because I had remembered coming across some studies with it.

And interestingly, people...air particulate matter, so when you have like air pollution and particulate matter, when people are exposed to high amounts of it, it causes their fibrinogen to go up, right? It's, again, an inflammatory marker as well. But people that were taking in high amounts of omega-3, it blunted the increase in fibrinogen and plasma. And so, it would be very interesting to see in some of the animal models you were discussing if omega-3 could blunt, you know, the white matter dysfunction caused by fibrinogen getting into the brain. So, again, it's another prevention, easier, low-hanging fruit thing that people can do now, right? I mean, making sure they're taking in enough omega-3.

Dr. Montagne: Yes, exactly. No, I cannot agree more. We don't need to repeat what we said but, yeah, there's this kind of vicious cycle where omega-3 may play a major role in vascular functions, of course. It's not even, "may play," I think it does play a role and it might play an even more important role in people at risk for Alzheimer's, it's possible the idea of APOE4 carriers that we've talked about. And you mentioned...interestingly, you mentioned airborne particles, like pollution, right? And I think it's linked to what we've said earlier. So, there's Alzheimer's, to keep it simple, if we think about Alzheimer's, it's a multifactorial disease, so you have a genetic risk possibly, you have lifestyle, exercise and everything.

There's also what we call environmental factors and pollution is one, and there is multiple studies, as you know, showing that if you live in the city, big city, you have more chance to develop some sort of dementia. And then part of two studies that we've published four to five years ago maybe where we exposed mice to airborne particles from Los Angeles. We were taking from the highway, the particles, and giving it to the mouse to see what's the impact of the pollution on vascular function. Because there's some evidence, also using scans, those people tend to have more white matter disease and things like that.

So, we started looking into that and we found...very interestingly, we found a high peak of vascular...it's a longitudinal disease, but very rapidly a few days after giving the particles to the mouse, we were seeing blood-brain barrier breakdown and pericyte degeneration very quickly, one of the first signs that we could see. Of course, now there is debate on the mechanisms, whether the particles can penetrate into the brain through the olfactory area, or whether it's directly the particles in the bloodstream that activate maybe, as we said, the endothelium a bit too much, which will indirectly cause some vascular issues.

That, I think, there's more studies going on, but definitely environmental factors and pollution is a big thing to take into consideration when it comes to dementia and especially vascular function because we breathe that every day, right? So, this has to do something with vascular. So, it's another factor but I guess it's not good...I guess if you have APOE4 and not doing exercise and living in a big city, you probably have much more chance to develop some sort of vascular problems, as we know, but we try to understand how this is happening.

Dr. Patrick: Yes, I remember reading a study where babies, you know, in Mexico City, postmortem they found, unfortunately, in babies, they had like all sorts of amyloid plaques in their brain and I don't think that's normal. And Mexico City is like...yeah.

Dr. Montagne: Yeah, yeah, it's highly polluted.

Dr. Patrick: Highly polluted, yeah. It makes me wonder about filtering out the air. I mean, if there's some HEPA filter or something that helps a little bit, as well as omega-3 has been shown...I know I keep going back to that, but it's been shown to help blunt some of the air pollution. I know, you know, the research shows it, you know?

Dr. Montagne: Yeah. I mean, I don't know. I mean, it'd be nice to...I'm pretty sure people are working on that, but there are some countries or cities that are wearing masks and things like that, in China, for example. So, I guess it will be a long study, but I guess we could compare highly polluted cities and people wearing some filtering and masks and things like that to see whether they can preserve better vascular functions and things like that. But, yeah, I guess there's probably ongoing studies on that. Yeah.