 Okay, so thank you. So now we are welcoming our next speaker, which is Karin Wurst from ETH Zurich. And so if you've seen the program of the summer school, we've tried to cover modeling aspects over different disciplines, cardiac, vascular, musculoskeletal modeling, and so over different scales. And so in this sense, Karin is an illustration of cross-disciplinary professional. So she's pharmacist, and then she did a PhD in biology. And so now she's working as ETH as a professor in immunoengineering and regenerative medicine. But she's indeed working in a biomechanics group. So she's indeed confronted in assessing the relevance of what she does in molecular and cellular biology and to all the physical cues that an organ has to support, as Bart already mentioned, for the heart. So thank you, Karin. Thank you. Well, hello, everyone. Can I just quickly ask who of you is actually working in discs, spine, anyone? Yes? Perfect. So, most of you I guess are cardiovascular area, but I think there are two things that are important about what I'm going to tell you today. And that is a lot of these basic cellular biological principles you can actually apply to a lot of other areas. So that's one positive aspect, I hope. And the other one is if you look at the discs, this plays a very important role in back pain development. So if I ask you now who of you has or had back pain or knows someone that has back pain, if you could raise your hand there, take it. Perfect. So you see that this is a really high prevalence. And if you go home and you talk to your parents or your grandparents and they have back pain issues, spine issues, you can probably be quite impressive about telling them some stories and understanding what is actually going on. And this is a conversation that comes up a lot in your normal life. And you can always look smart by knowing what you're going to learn now. So I hope that's going to be an advantage for you to be here today. For the ones that don't really know anything about the intervertebral disc, this is the spine. And you have different levels of the spine. You have the sacral area, the lumbar area, which is actually very prone to degeneration and spinal problems. We will talk about that a lot. Then you have the psoracic area and the cervical area. And if you look at the intervertebral disc, what you actually have is that it lies between the vertebra. So it lies in between here, which is why it is actually called intervertebral disc. And you have two distinct zones. And this is quite important. If you think about modeling, you need to understand these different zones and the different composition and their function. You have an inner area, which is called nucleus proposes. And that is a very cell-like area. Lots of product ligands. These have negative charge-fixed density, so they can absorb a lot of water. And this is where the spine actually has its cushion function from. And then you have the outer area, the annulus fibrosis. That's a very highly structured area. And this schematic you don't really see. It just looks like a blob thingy. But if you look at this schematic, you actually see this high structure. You have lamellas. They are orientated at certain degree angles, turned left and right. And this high structure is possible because the main component in the annulus fibrosis collagen type 1, which you might know is very hierarchically built. And this annulus fibrosis not only encircles the nucleus proposes and therefore gives its properties, but it also allows flexion and extension, for example. And therefore also has a very important function in stability of the spine, but in movement of the spine also. Now, if you look at the composition in a bit more detail, we're not going to talk about every single detail. But just in general, an important aspect to understand is that these two zones, they look very different. They have very different functionality, but they're made up from the same stuff. And it's just the type that is different and also the composition, like the ratio of the one matrix component to the other. In all of these areas, the annulus fibrosis, the nucleus proposes also the end plate. You have proteoglycans, but you have much more in the inner area compared to the outer area, which is why you also have more water content in the inner area than the outer area. And you have collagen, but you have different types of collagen in the inner area. You have mostly collagen type 2, which is kind of a not so highly structured collagen. And these fibres, they're just intermingled in this proteoglycan-rich matrix. And then you have these highly structured collagen type 1 fibres in the outer area, the annulus fibrosis. So this is what I just told you now. And this is where you can actually see it. So this would be a human disc, very, very young, because only in very young human discs you can actually see nicely these two different structures. And you can distinguish the nice gel-like nucleus proposes and also the annulus fibrosis that is collagen-rich and fibrotic. Now, here is the problem. On the left side you have a young spine. Not as young as the other one, because you cannot distinguish the nucleus proposes so nicely anymore, but still very, very young. And then on the right side you have something that we would call a severely deteriorated spine. And you can see that the structure is kind of completely gone. The disc height also decreases a lot. And you also have structural deficits in the bone happening. All of that can happen during your aging. And it is, in fact, a typically aging process. So yours might not end up being so bad when you're old, but it will look relatively bad at some point of time. And, in fact, if you are older than 30 years or something like that, it's probably kind of your age range, maybe a little bit younger. You can almost for sure know that you have some level of degeneration in your discs happening already, but you might not have any problems. And this is important to understand. This degeneration is an aging process and everyone of us will get it at some point of time earlier, later, more severe, less severe, but you will have it for sure. But you certainly have older relatives that don't have any back pain issues, or they might have had it for a week or so, but then it was gone again. So the question is, where is actually the collaboration between degeneration on the one hand and pain development on the other hand? And we're going to look into that, because that's really important also when you do modeling and you want to model clinical cases, basically. You need to distinguish between age-related degeneration that is asymptomatic and something that happens and asymptomatic and causes pain. Now, so many of us will have degeneration, but then the ones that actually have to undergo surgery, the number is relatively low. You can see that in the lumbar spine, it's said to be around 7-10% plus-minus. In the cervical spine, the numbers are lower, only around 1%. A lot of these cases are actually trauma cases, because as you can imagine, in cervical spine, if you have a car accident or a skiing accident or whatever, you kind of jump with your snowboard and you make turns and then you fall badly, a lot of these will end up having cervical spine surgery. But for the lumbar spine surgery, it is, in fact, mostly degenerative cases. So it can either be this degeneration that is symptomatic or it can be disc herniation, which we will look at in a second. And one of the reasons why the lumbar spine is much more prone to surgical interventions and to problems than the cervical spine and also the other areas of the spine is that on the one hand, the loads are higher in the lumbar area. So you can imagine that the lumbar area is actually carrying your upper body heft. So that is where the most loads are. And these are also the biggest intervertebrate discs. And we're going to see in a second that the discs actually have a real problem, because they are very low in nutrient supply. And this is because the disc is avascular. So it's actually the largest avascular tissue in the body. Normally, in basically all tissues, you have blood vessels growing in and with the blood vessels, blood comes and with the blood nutrients come, glucose, for example. And these will keep the cells going. And in a disc you don't have that. You only have blood vessels in the vertebra. And then everything needs to be used into the disc, which means that basically your cells in the nucleus proposes especially are starving. And this is why the tissue degenerates earliest in your entire body. There is no other tissue that degenerates so early on. If you have a degenerated disc, so this is just an illustration and that would be a normal one, you have two different types of pathologies that might in the end cause you problems, because this one might not cause you any problems. And the two pathologies that we basically speak about is degenerative disc disease. So this is disc degeneration but painful compared to the other ones that have no problems. And then what is called disc herniation. Disc herniation is also called disc sequestration or extrusion. Does anyone know anyone who had it at some point of time? Can anyone of you tell me what the main symptoms are? There are two main symptoms. In the back. Did you have it yourself or someone else? Yep. So there's pain in the back with the general body and then what else is there? Does anyone know? Exactly. That is very, very typical. So depending on whether you have your disc herniation in the cervical area or the lumbar area, you will have loss of function either in the arm or in the leg. Loss of function is basically related to kind of a tingling sensation, numbness. People describe it differently. And the reason for that is that you can see it here. You have a structural defect in the annulus fibrosis and then the inner material is squeezed out and it presses on the spinal nerves here. And because of that, it irritates the nerves. It's not simply the compression but it is also what we're going to see later, the inflammation of the tissue. And then the spinal nerves, they're either in the lumbar area that are responsible for the feeling in the leg or in the arm if it's the cervical area. And that is why you have this very, very typical symptom. So if you have ever a friend or a relative that complains about having pain and a weird sensation in the leg or the arm, you should probably send them to the doctor and have them checked out. And you can see that very nicely on an MRI then. We will probably see a few MRI pictures later. I'm not quite sure. But it's something that is relatively easy to identify. This here is really difficult to identify for clinicians because you come. You say you have back pain. They take an MRI. They see a degenerative disc but then everyone has it. And you might even have a few of these. So how do they then know what of the discs are painful and which ones are not? Does anyone know how it's done? How they try to identify whether your problem is actually coming from a disc and which one it is? Ever heard anything? Provocative discography tells you something? It used to be done. I will say why it's not done so much more. So provocative discography is that you inject contrast medium. And it was contrast medium because it was about the visualization. And you would inject that into the disc that you were thinking is probably the pain source. So it would be this one here. And then, of course, you also need to somehow make a control. So you would pick a disc that you think looks really healthy that should for sure not be the problem. So you wouldn't inject it here. And typically the patients would, with the provocative discography, describe that they have a really severe moment of the pain that they have just more extreme. And then it should be the case that it's here but it shouldn't be here. And I will tell you later what the reason actually is for that. People didn't really know why it was. It was just a technique that worked but no one really knew why the pain was there then when they did it. The problem is that, of course, when you stick a needle into the disc and you inject something, you also create a defect. And then a few years back it was actually studied how much of a defect and how many problems you would create afterwards. And what they found is that when you do this, then you induce, because you use also the healthy control tissue, you actually induce deterioration in that and then people tended to have problems on that level later on, which is why now they don't really do it so much anymore. And there was also a lot of false positive results. So it was never if the provocative discography is positive, it for sure is the disc that you need to take out. So based on that combination, it's now not being done so much anymore. So we've seen this picture of the degenerated disc earlier and here you have two other examples here on this side as well, the healthy one and the degenerated one, not as severely degenerated as the one that you've seen before. And again you see this loss in this card and you see basically the loss of the nucleus proposals which becomes very fibrotic. You cannot really distinguish any more between this outer and inner area. Here you can nicely see inner outer area. Here you could not really be able to say specifically where the one zone ends and the other one starts. And the reason for that is that this inner area loses a lot of product liking content over time and therefore also water content. And the collagen type 2 that you originally had will be replaced by collagen type 1. So you make the tissue more fibrotic which is why it becomes more similar than the outer area. And one thing that is also interesting to know for your normal life is when you get up in the morning you're usually taller than in the evening and one of the reasons for that is because your disc has water in it and then when you move during your daily activities you press water out and therefore the tissue becomes compressed so you become a little bit smaller and then in the evening or in the night it absorbs the water again so you become your normal height again. This change is not very huge but what you probably know is that old people are often much smaller at age compared to when they were young and one of the reasons is that you have those collapsing discs and if several of the discs become smaller in height then obviously the overall body height will also become smaller and people will become more tiny. There is the additional effect that you might also have vertebral fractures so the vertebrae sink together or you might also have a change in posture. You sometimes see those old ladies especially that kind of bent over so it's a combination but the degeneration of the disc plays an important role in why you're smaller at higher age compared to young age. Now we have this loss of proteoglycan content we have the loss of water content in the inner area and the collagen composition that changes and we also have a change on the cellar level of course happening because ultimately the cells in the disc are the ones that are responsible for making the matrix. That's something that you should probably know like in each tissue it is that way you have the cells and the cells are responsible for remodeling your matrix and building up new matrix and keeping it young and healthy. In the disc you have one specific problem and that is that you have very few cells compared to the matrix. If you would need to guess how many... like percentage wise how many cells do you have in the disc? Yeah, that is right but you know it of course. In other tissues like the lung for example you have lots and lots of cells that have only cells and very little matrix. So for these cells it's much easier to really make this matrix whereas for the disc cells like you need to imagine like three of you need to build a bridge in the city and you don't have any more people and you still need to finish it so either you finish it or you don't finish it and in the disc it's basically not really getting done properly and then it breaks down again over time. And then the problem is you start with very few cells and then in addition you have increasing cell senescence occurring so you in the end have even less cells that are able to make the matrix and that is of course kind of a vicious circle because you will need to run into degeneration there is no way around it. This is an MRI picture of a spine and you can see here the healthy discs and here you see a degenerated disc which turns up black. Do you know why the disc is showing up as black and it's actually called black disc? It's the underlying principle. Exactly. So because of the protaglycans that go away and are not rebuilt the water content is lower and that's exactly what you see. The outer area is always black because there is a lower water content and then the inner area becomes black because the water content decreases. And in this case you also see a protrusion of the disc so the disc being squeezed out already not super super severe and that's also something that you can very easily see. And if you would need to describe what a disc herniation actually is like to someone that has no clinical understanding whatsoever the best comparison that you can probably bring up is a donor that is filled with jelly. So the jelly, the inner part, the water rich part would be the nucleus proposes and the dough of the donut would be your annulus fibrosis and if you have a structural defect as you can see here what happens is if you press on it now and there is jelly inside then it will be pressed out and this is what a disc herniation would be like. So it's a very easy picture to understand and keep in mind. Now if you want to know why a disc degenerates some of we've already touched on there are basically three different main reasons. There is on the one hand loading and I've already told you that the lumber discs are the highest loaded ones and they're also the ones that degenerate most and we're going to look into that in a bit more detail. However, loading alone is not really the reason why things progress faster in certain patients and generally not the only reason for deterioration. An additional aspect is the nutrition aspect. So this aspect of there is no vasculature in the disc and therefore you don't really have a lot of nutrients which makes the cells starving which gives them really crappy conditions to produce the matrix considering that there are so few cells anyways. And then you have the aspect of genetics which is a really interesting one because it distinguishes why certain patients developed this degeneration earlier and why are some actually painful and others not. So traditionally these two were thought to be the two important ones, kind of the two only ones and then the genetic aspect only came maybe 10 years ago when people started to look more into that. And if you look at what has been published up to now you will see that there are lots of lots of papers and depending on where people actually come from so there is a difference between different races you will find that there are probably more than 20 genetic polymorphisms, so gene defects and changes that are associated with this degeneration and they cover areas such as matrix production so collagen, worn or aggregate and brode glycans these genes might be disrupted and that leads to degeneration early on but then there are also genes that are associated with pain development such as cytokines and we're going to look at that in a second. Then this aspect I've already touched on it a little bit before is the nutrition aspect so you can see here that in fact you really only have blood vessels the ones that are shown in red as always are only in the vertebra and the very, very outer area of the intervertebral disc but then in the disc there are no blood vessels so all the nutrients need to diffuse into the disc which means that in the outer area it's probably still quite good the more you come to the middle the more horrible it becomes which is why you often hear people saying that the disc is kind of like a desert where cells are starving, they don't really have a lot of nutrients and that is also important if you think about regeneration of the disc with stem cells for example huge topic in basically any area, tissue regeneration you do have a certain problem if you bring a lot of cells in there especially knowing that stem cells are kind of the cells in your body that kind of really handle a lot of things super well you bring them in there and they come into an area that is so hostile that they might not really survive or they survive and they need nutrients and they take nutrients away from the existing disc cells so the question is what does it actually bring you if you bring cells in how many should you bring in if you bring in too many that's great but they probably don't survive if you bring in a few they might survive but maybe they don't really do a lot of good because they're not a lot of cells then and this is something that maybe you've seen before very famous study looking at glucose and oxygen concentrations in the disc and also at pH levels and this is one of the underlying principles that explains a lot about degeneration of the disc and also if you want to go towards regeneration why it is so troublesome so you have the end plates here and you would have the annulus fibrosis and here this would be the nucleus proposes area so you go basically through the disc from one side to the other and of course because you have blood vessels in the vertebra and the outer annulus fibrosis in the outer areas you still have quite good oxygen and glucose and the more you come to the center the lower these levels will be which means your cells are more starving on the other hand you have something that is called lactic acid which you probably know is a metabolic byproduct and as the name tells you it will also decrease the pH level because it is an acid and if you've heard something about the disc before have you maybe heard about the pH in the disc or let's ask first what's the normal pH of blood for example that's something that you know for sure most other tissues probably quite similar what do you guess what has the intervertebrate disc when it's quite severely degenerated for a pH any guesses can't really go wrong at least if you pick the right 50% then everything is fine what do you say six other guesses yeah six is approximately right it can go down even down to like 5.8 and a really severely degenerated disc quite low I mean it doesn't really seem possibly too much for you like from 7.4 to 6 but it is a huge change in pH for the body and it does change so much because you have the lactic acid being produced by the cells but you don't have the blood vessels that bring the lactic acid out of the disc so it kind of just gets stuck in the disc and only with some kind of diffusion it can get out but you have therefore very high levels of lactic acid and low pH in the inner area of the disc and that's also something that might then potentially be negative if you bring cells in like stem cells not only do they have leonitrients but then they will also have an acidic pH so overall they might not really thrive in such an environment and it's of course also important if you want to bring drugs in and they have different pH optimus for example you need to keep in mind that the pH in the disc is quite low if it's degenerated now the one was genetics the other one was nutrition and then we have the last aspect that is loading and this is a little figure that shows you the situation in the spine where you have the nucleus proposes which in project like can kind of a question thingy that keeps the nucleus proposes keeps the disc as it is and functions as the shock absorber of the spine so you have high hydrostatic pressures in the inner area of the disc and then you also have of course normal movement during your daily activities such as flexing and extension so you bend forward or to the side or backwards and this is something that is enabled by the annulus fibrosis structure and this is how the situation looks like in a schematic way and it's important to understand you have really quite complex loadings in the disc they are quite high on the one hand and we will see that in a second and you have complex loading you have compression, you have tension you certainly have mostly compression in the inner area and tension mostly in the outer area but then of course you also have areas here outer areas that also have compression and then you have also shear forces but the disc is of course made for that and if it's not degenerated it can handle it really quite well there is one case that it cannot handle so well and that is a combination of compression and shear and do you know any or does anything come to your mind that would be a combination of a movement where you have compression and also shear forces torsion, yeah so compression and torsion combined what typical daily activity could that be yeah but then you necessarily usually would lift it I don't know like this but you don't necessarily turn around yes yeah and there's one in the winter you probably might not know that depending on where you are from but in the winter there's a very typical activity not really if you think about snow shuffling that is the very typical example where discs can have a herniation quite easy on skiing of course also because you have the movement but then you don't really have the compression part so much shuffling snow and you lift the snow and it's quite heavy and then you want to throw it over your shoulder that's exactly when it happens so if you would live in an area that has quite heavy winters like I did when I was in Vermont or also Switzerland now the clinicians actually see an increase in disc herniations in the winter months when there is heavy snow because that is a very typical movement where a disc that already has a structural defect will just not withstand anymore so this is a combination of what I've just told you now and we've already said that the lumber areas they are most prone to degeneration because of the loading and because of the bad nutrition in this area and this is something that shows it to you that's the compressive strength of the spine where you can see that in the lumber area you have the highest peaks of compressive strength and we're going to see in a second what that actually does then on a pathology level now if you speak about loading of the disc there is a general misconception that loading tends to be always bad and that's of course not the case because the effects of the loading they depend very very strongly on the magnitude that apply but also the frequency then the combination of loading so the snow shuffling example for example how good or bad the tissue has been before and how good or bad the cells are to adopt to whatever you give them as a loading so this is the one that we've seen before and if you look now at discreniation and where that happens mostly then you can actually see that it is specifically the area where you have these high peaks of mechanical loading is also the areas of the spine where you see discreniation most frequently so that indicates that loading actually plays a role but it's certainly not the only aspect that plays a role in this pathology and this is a very famous study that has been done 15 years ago more than 15 years ago in Olmberg I did my PhD and up to then there was one study that looked at loads in the spine hydrostatic pressure in the spine and how high and low it would be with different activities and at that time there was a clinician a spine surgeon working at the institute and he said it would be really really important to know the loads in the spine to better tell patients what to do and what not to do so he was willing to have such a pressure sensor sticked into his disc and then he would be doing different activities which you can see here here you can see the pressure sensor in his disc so this is a very famous study because it has never done before because no one ever volunteered to really do it afterwards and before there was only an N of 1 so of course there will be quite a bit of variation between different subjects but it was still quite helpful to see how the loads differed and this is now relative to a standing position and of course then you have those cases where you lift something heavy this was in the various so people would lift a beer case because that was around it was quite heavy and you can see the pressures go up and if you look at what that is in megapascals so a real evaluation of the data quantified then this is more than 2 megapascals and that is obviously quite high loads that you can have compared to a lot of other tissues so this is something that also needs to be kept in mind when you want to go for some kind of biomaterial possibly cell seeded regenerative approach the loads will be so high that not all materials will actually be able to withstand that what is also important to know I have said before that loading is not necessarily good or bad it really depends on the conditions in which you apply like which magnitude which frequency and what has been described quite in detail over the past years is that there is some kind of safe window as we call it where you apply loading that is very physiological and that will actually be beneficial for the cells because if you take loading away the cells also don't like that because they need the cues to keep matrix production going and so on so an area somewhere between 0.3 and 1 megapascals has been described to be beneficial it will make the cells produce more matrix keep it going and so on but then if you go too high or if you go too low then it will actually be detrimental and that is something that is very very typically in kind of all tissues that you always have physiological loads that are good and then if you go hyper or hyperphysiological then it's not good anymore now if you want to analyze what loads actually do to your spine you can of course do that in humans but that's very very tricky because it cannot really control what they do every day so you would go over to in vitro studies or also animal models and these are just a few examples of how you can set an experiment up so that you can look at what mechanical loads can do to your cells and you can of course use the same principle for any other application but you need to adjust the loading type of course so this would be in vitro on cells this is a typical example of how to apply hydrostatic pressures you would have in this case collagen cells which you can see here those round diskey thingies that are seeded with cells and then you put them in bags and you put them in a water filled cylinder and then you put pressure on them or you could also go to an organ model so entire discs for example that you can put in a bioreactor which you can see here these are usually if you do cell culture studies in an incubator and then you can compress the discs over whatever periods of time there is of course always one problem, two problems on the one hand if you want to use entire organs you might be limited because you might not get any human material as entire discs so you might move to an animal model that is appropriate like a bovine model and then the other aspect of course is if you use for example the bovine model this has very huge implications because you might not get it super super clean and you might have contamination so if you want to do very long term loading studies this might be very very tricky and then there is also the possibility to do in vivo studies so this would be a rat study where compression was done actually one of my own studies when I did my postdoc in the US so this would be a rat study here is actually the rat basically and that's the end of the tail and then you surgically insert pins to which you can attach these ring shapes so this would always go through one vertebra and then in between you would have one intervertebrate disc and then you compress those two rings and thereby you can compress the intervertebrate disc in between and then you can do that for however long you want and for different magnitudes and you can see how the tissue and the cells actually respond now there is one tricky thing when you do something like this with rats has anyone ever had a rat as a pet when you were younger no? do we know what rats love to do when they don't have anything else to do or also when they have something else to do no? they will chew on everything so if you design an animal study like this we had kept it somewhat in mind but I guess not enough so you have here an air system that by air compresses these rings and that's all made up of polymers and of course the rats would love to chew on that and they can be quite flexible so you can they can grab the tail so there were two holes in here which then of course messed up the experiment you would need to repair it all the time there were two the rings and the rat because it cannot apply the compression anymore so what you end up having is an animal study where you cannot just switch it on and then leave and then come back after eight hours you need to be there watching the animals all the time and trying to keep it away from chewing and if they do then you need to repair it really quickly so that the overall study setup is still okay so if you should ever design an animal study with rats just keep it in mind that is something that will make your life so much easier especially if it's a long term study like this which was for six weeks for eight hours a day then you know how busy you're going to be entertaining the rats so the last thing I would like to mention is the difference between a symptomatic and an asymptomatic degenerative disc we've heard that a lot of you will have basically every one of you will have degeneration of the disc but not each of you will have problems so if you look at these two MRI pictures of a symptomatic and an asymptomatic disc do you see anything that you think might qualify the one as asymptomatic and the other one as asymptomatic so here you have of course the healthy ones and here you might have the degenerated or more degenerated ones anything that sticks out to you these are both cases with no real herniation just degeneration of the disc so here you would have a small bulge and here too but not really anything that would classify the herniation anything well the quite simple answer to you having no clue what I'm actually looking for is that there is no answer to that it could be in fact exactly the other way around there is no way how you could tell from an MRI picture if a degenerated disc that has no herniation it's painful or not painful which is why it makes it so difficult for the clinicians but there must be something that brings the pain of course because some have pain and some don't and this has been a very hard topic for the past years and basically what has been found is that it is in the end the level of inflammation in the tissue that makes the difference between a degenerated disc being painful and another one not being painful so the ones that are more painful or are painful have more cytokines more inflammatory mediators in the tissue and the other ones have less now if you look at inflammation you've probably had that at some point of time when you studied inflammation is normally a response to tissue damage and it's a way of trying to get rid of the tissue damage which makes sense that might still make sense in the disc but then you have one problem and the biggest problem is that you need blood vessels normally for typical inflammation and in the disc we said we don't really have blood vessels so it's kind of a strange type of inflammation it doesn't really follow the very classical rules of inflammation so normally you have blood vessels and then they become more permeable and cells of the immune system like monocytes will be able to move out from the blood vessels go into the tissue and cause an inflammation in the tissue at the side where you have a tissue damage or some foreign body material or some bacteria or whatever but disc avascular so you don't really have that and basically the answer to why is then even possible is that we're not talking about an acute inflammation we're talking about what's called a persistent inflammation that lasts very long so it's a chronic disease obviously and when you have chronic inflammation you can also have resident cells so the cells of the tissue itself being involved and importantly it can be triggered by different things it doesn't need to be for example infection it can also be foreign bodies immune diseases micro organisms of course as well but then there is a very important aspect in the disc which is called intrinsic stimuli so it's something that is in the tissue itself will actually cause the resident cells to make an inflammation happening and we're going to have a look at what that actually is so this little table just shows you that you have a lot of different cytokines so cytokines are inflammatory mediators in the disc described are very classical candidates like TNF-alpha and Alvan-beta IL-6 or IL-8 and this is a small figure that actually shows you that even in a normal healthy disc you have certain levels of the cytokines so this would here be the red ones Alvan-beta and TNF-alpha so you have a basic level of inflammation already going on but then when you go towards a painful degeneration or a herniation those levels then increase and this is a comparison of the cytokine levels in an asymptomatic deteriorated disc compared to an asymptomatic degenerated disc and it's basically just proving to you what I just told you that inflammation seems to play an important role and seems to be the distinguishing factor between those painful and non-painful degenerated discs now there's one thing that I would like to quickly touch on and that is neovascularization because I've told you that you have the disc and then you have basically blood vessels only here in the outer area and you also have together with the blood vessels normally nerves only in the outer area and that's a healthy tissue but then if you have a degenerated disc you have those structural defect securing like clefts and tears and you also have changes in the mechanical loading and you have less protoglycan content which actually inhibits ingroids of blood vessels and nerves so all of a sudden you have the blood vessels and the nerves growing in much more and then what also changes what we just saw is that in a normal healthy disc you have some cytokines so some of these inflammatory mediators the basal level is there but it's not really so many so the possibility that one of these will irritate one of the ingroing nerve endings is actually quite low but if you have more nerves growing in and further in and you have much more cytokines being present then the chances are that with your daily loading and the diffusion and water being pressed in and out that these cytokines come in contact with the nerves and cause pain is actually much higher and this is the basic understanding of how a disc can actually be painful at least the current stage of the knowledge and that also explains to you why a provocative discography the one where you try to detect which disc is painful and which not may cause pain because you stick your needle in and then you have fluid going in the contrast medium that you inject and it will of course also go out again and by going out it might take some of these cytokines with them and when it goes out again it will come to the nerve endings directly at that moment which is why the patients say in the moment of the injection and shortly thereafter that they have very severe pain that is very typical to what they normally have but more severe compared to what they normally experience and of course when you have this new vascularization happening then you can also have cells of the immune system going in and this is something that has been shown here so you change the entire situation but what is important to know is that the immune system that normally drive the inflammation here they just play kind of an accompanying role they help the resident cells to drive the information but the resident cells are actually the ones that play the crucial role and if you look at a herniation which is what we have also discussed before normally what happens is you press the nucleus proposes material out and then it comes in contact with the spinal nerves and it presses on the spinal nerves but it also because of this inflammatory nature irritate the nerves and that will cause pain and that is something that you can of course also simulate in animal models if you want to have a model of a discreniation you just take some nucleus proposes material out from the tail for example and then you put it artificially on the spinal nerves the dorsal root ganglia and this will cause pain sensation in the animals and you can see a picture of that here so this would be the nucleus proposes material on the spinal nerves and what is important to understand is that it's not the material that just compresses the spinal nerves that causes the problems it's not the compression per se but it is the inflammatory nature plus the compression because if you put something else on like muscle tissue for example or just the weight you're not going to have the pain development in these animals so it's a really good way of a good model of understanding what actually happens during herniation on a molecular level this is a summary of what I've just told you with the ingrowing nerve so we don't need to look at that but what I would like to super super shortly touch on is what the mechanisms are why there is an inflammation occurring because we now know yeah there are more cytokines if you have a painful disc deterioration but we don't really know why that is happening and there are actually different causes of inflammation and the ones are matrix degradation products then hyperphysiological loading can also cause inflammation genetics of course basically always plays a role in oxidative stress as well and then this is called a sterile inflammation so an inflammation that has no underlying reason is no bacterial infection but then of course you can also have bacterial contamination there is some very new data on that and then most likely we also have a lot of other factors that play a role but we just don't know them yet so I will show you two or three slides and then the rest I will skip but this is quite important one of the causes of inflammation being matrix degradation products so normally you have lots of different matrix proteins in the disc these can be protoglycans can be collagen, purionic acid for example is also a very important one with a high water binding capacity or also fibronectin and then you also have enzymes of these matrix proteins normally you would replace them in the disc often they don't really get replaced but you end up with smaller fragments of these matrix proteins and this is an example of purionic acid it can be cleaved either by purionidases so very specific enzymes that cleave it or it can also be cleaved by reactive oxygen species so oxidative stress which you also know for sure can also cause that and these are two examples of a study that we actually did where we looked at what do these fragments actually do when you put them on intervertible disc cells and we could see that they upregulate a lot of the typical cytokines that you will also find to be relative in painful disc degeneration so this might be one of the underlying mechanisms and basically the same we've also been able to show that if you have very very specific fibronectin fragments relatively small fibronectin fragments they can basically do the same so this matrix fragmentation and these fragments the accumulation of these specific fragments might play a very important role but then the question of course is why do not everyone who has degeneration, who probably develops these fragments has pain then and the answer to that is not really completely known but it is probably that there are genetic polymorphisms for these matrix proteins but also for the cleaving particles and enzymes these patients some having more of these fragments and others have less of these fragments this I will skip quickly and just show you this last one with mechanical loading so we've said that mechanical loading can be good can be bad and if you have this degeneration happening it changes the overall mechanical properties of your tissue it will therefore also alter the loading that the cells actually experience and that can then again lead to degeneration in the circle and it can also in fact directly increase inflammation and this is something that I would like to show it's a whole organ experiment with entire human discs and these were loaded and they were either loaded with 5% strain this is kind of physiological or with 30% strain and you can already see from that that this is probably really quite severe loading that was put on these discs and in the end you do see an up-regulation of some of these inflammatory markers but what you also need to recognize is that it's a relatively small change you already see a kind of a two-fold not even two-fold up-regulation of these markers which is really not very pronounced and that's something that is very very typical in the discourse in a lot of other tissues that mechanical loading plays a role but it does not play the only role it can do something, it can induce inflammation but there are certain other ways like the fragments for example that will induce inflammation in a much stronger way because the disc is in effect in the end used to loading and will not respond quite extremely in any way so this I will jump over it's some pathways you might not know and want to hear about that anyways and the last thing that I would like to mention only was the one slide is that when you think about therapies then there is of course the one approach that you want to prevent degeneration that's something that a lot of people are working on not taking into account that maybe the degeneration itself is not the problem it is the cytokines of the inflammation and it's maybe better to work on the inflammation side predominantly and have the regeneration side also happening rather than doing it vice versa and just looking at trying to regenerate the disc but not taking care of potentially causing the pain and there are different ways of how you could do that you could use bioactive compounds so compounds that interfere with the inflammation and that potentially also have a regenerative potential you could also use cell therapy like stem cells for example stem cells have been shown to have an immune modulation function so they can actually reduce inflammation but then again you need to keep in mind that the disc is a very bad environment for stem cells so maybe it's not promising as you might think on the first side and then there is of course also the aspect of gene therapy where you bring in bacterial vectors where you insert specific gene sequences that when they are taken up by the cell will cause the cell to produce something and this could be for example inhibitors of the cytokines could also be growth factors that produce more matrix or a combination of these these are all approaches that you could take if you want to work on new therapies for degenerative disc disease rather than doing spinal surgeries as are mostly done nowadays and these are a few examples you can have a look at them if you want later on and with that I would actually like to close so that you can have your lunch break in time thank you very much Karin for this brilliant talk any questions yes very nice presentation and it's good to see the other picture of the of the same topic let's say so my question is regarding let's say from your point of view let's say how the use of computational models can help in the reach of an understanding of log back pain or the generation itself well I think the computational models would be great because the experiments that we do are quite tricky to do we don't have a lot of material that we get so we can only do first experiments and then we would be able to confirm something that you find out with your campaign computational models in a second set of experiments rather than we trying to find out everything with cell and organ culture experiments you don't get a lot of tissue that you can do the experiments on very cost intensive work intensive so any help that we can get trying to figure out processes and mechanisms would help us a lot to streamline our experiments and just focus on certain aspects whereas now we're basically all over the place trying to find the mechanisms and patterns so specifically inflammatory mechanisms how we can counteract them potentially also with drugs what that might do and we could then confirm the findings that you have from your models in our cell culture experiments would be of great great help thank you very much for the presentation I've never done any modeling of spine discs so maybe the question doesn't make a lot of sense it's a curiosity when you mention the animal tests doesn't have any influence in the orientation of the fibers the fact that animals don't have the standing position how can you extrapolate those data to humans it is in fact always tricky there are a few animal models like a lot of people have started to look into that which animal model is good and which is not good and the mouse or rat model for example is not really considered very good from a mechanical point of view it's not so bad because the animals they obviously don't go upright but they use the tail to stand up so if you've ever seen a rat standing in the cage that's what they do so they put compression on the tail in this specific area next to the body the sacral area another model that is really quite good from that point of view is the cow and the cow tail normally a lot of people think that the tail is just hanging there and not really doing anything but if you have a close look at cows and what they actually do they use the tail quite a lot and that also puts loads on the tail and the cow is also a good model because the discs are relatively large quite similar to the human disc actually which is not the case for smaller animal models where diffusion is very very different and also the composition is quite similar so we have a few animal models that are not upright standing and they're still reasonable good but of course a human is a human and no other animal is that way just as a remark the main time this works maybe just as a remark thank you very much for the talk because what I really like is also something that we as engineers very often miss as a point is that you say like it's not always the most intuitive explanation which is the thing that you look at because you say like okay you would think as a mechanical engineer you would say like obviously disc degeneration that's the thing which is really important so let's study disc degeneration but if you then look at the clinic like you say so you see like hmm there's maybe patients which have really bad discs but don't feel anything so this click this link to what you really see in reality and what is the intuition that you have or even that clinicians some have I think making this link is really really important and this is one of the things that we often missing it's like are we doing the right thing that means does it fit with a lot of the data that we have and that's the thing it's like we really have to look at all the clinical data the biological data and from that always keep on asking ourselves does it make sense what we do is it the right approach I very much agree otherwise you can work for years and years and an entire PhD on something that you think is a problem and in the end in your defense you might have a clinician around and then he asks so what and then you have a real problem if you can get that answer or that question Thank you very much for your presentation I have a question for chronic low back pain in your opinion how much percent it's going to be the role of this generation and how much percent it's going to be based on the facet joint arthrosis it's really hard to say a percentage I'm not really going to do that because it's not clarified exactly how much percent is allocated to different pathologies but facet joints are certainly a problem vertebra are a problem too and the back pain is a very very typical thing also and often they come in combination which makes it so hard to say 20% are related to the disc and then 10% to facet joints we don't really have the data I don't know of any study that has a good study that has looked into it personally I think that the disc is more relevant than the facet joints but you can also ask someone else and he will tell you exactly the other way around any other question comment that's a bit related to models because this isn't what's relevant to some school so I think for example that the graph that you showed where you applied 30% strain on an vertebral disc and then you had an increase of signs of inflammation but even not two fold increase so I think this is a little bit misleading because in the end what you would have is that mechanical chronic mechanical stimulation under a certain biochemical circumstances and nutritional circumstances that will progressively make the whole system shaped by everything together mechanics biochemistry and biology towards catabolic activity or anabolic activity and I think that it's indeed where models become extremely useful in order to more mechanistically or educatedly interpret this kind of evidence so if you don't agree then you can see it I totally agree this is actually a very good point about the loading and the effects being quite small but you also need to know that other studies have shown for example that if you have inflammation happening then the cells are much more susceptible to inflammation and they will take the loading more badly than cells that are in a non-inflammatory environment it's kind of all connected which makes it very difficult for us because in our experiment we can only look at like single aspects but we've never had it all together which is why the simulation would be good because you can probably more easily incorporate different aspects and give us good indications so it's like always in biology things are quite complicated and if you do experiment it's always just a very simplified model