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How can we investigate Alzheimer’s Disease progression without looking inside people’s heads?

Alzheimer’s Disease is the most common form of Dementia. Around 50 million people suffer from Dementia globally, with the number projected to be 80 million people by 2030.

To date there is no known cure for Alzheimer’s Disease despite global research efforts and the development of novel therapies, such as Biogen’s Aducanumab which the FDA approved in March 2021 amid some controversy among
the scientific community.

Questions abound about the reason for the lack of progress in tackling this disease which is now a significant global economic burden estimated to have cost $818 billion USD in GDP in 2015.1 One of the open questions within the research community isabout the suitability of the research models used to explore and understand the disease and its pathology.

Historically, animal or cell models genetically engineered to recapitulate the Discovery Stems From Here disease have been used in drug discovery efforts. While these models are accessible and well-characterized, they are ultimately not human tissue. Could this be the reason for a lack of success in therapy translation from pre-clinical research to patients?

Increasingly researchers are recognizing the exciting potential of human induced pluripotent stem cells (iPSCs) as a more relevant model system for their assays.

These models have the added benefit that scientists can obtain skin tissue from patients and reprogram these cells (fibroblasts) into neurons, astrocytes, microglia or other relevant cell types to study the pathology of the disease.

To find out more about how iPSC technologies are being used in primary research into Alzheimer’s Disease, we spoke with Professor Selina Wray, Alzheimer’s Research UK Senior Research Fellow in the Department of Neurodegenerative Disease, UCL Queen Square Institute of Neurology London.

Selina Wray

Professor of Molecular Neuroscience

Alzheimer’s Research UK Senior Research Fellow

Selina Wray is a Professor of Molecular Neuroscience and Alzheimer’s Research UK Senior Research Fellow in the Department of Neurodegenerative Disease at UCL Queen Square Institute of Neurology.

Selina was awarded her PhD in 2009 from Kings College London, prior to moving to UCL Queen Square Institute of Neurology as an Alzheimer’s Research UK Junior research fellow in the group of Professor John Hardy.

Selina’s work is focused on the use of induced pluripotent stem cell (iPSC) technology to model dementia, working closely with clinical colleagues to obtain samples from participants with rare, genetic forms of dementia and using these to understand the molecular basis of Alzheimer’s Disease and Frontotemporal Dementia.

Please tell us about your research and what drives you to use iPSC models in your work?

My research is focused on understanding the very early stages of Alzheimer’s disease. Alzheimer’s disease is the most common neurodegenerative disorder. And, at the moment, there aren’t any treatments that can slow down the progression or delay the onset of disease. One of the reasons that we think that’s the case is that many of the trials have targeted the pathology of the disease.

But, the development of pathology can begin decades before symptom onset, so once the pathology is established in the brain to the extent that someone has clinical Alzheimer’s disease, there has already been substantial neuronal loss in the brain and so we need to try and intervene earlier. So, we are developing models which will let us understand the very earliest changes that are going on in the brain. Now, of course, a huge barrier to that has been that the human brain is really inaccessible during life, but thanks to the development of induced pluripotent stem cells, we’ve now been able to make models from individuals who have causative genetic mutations for Alzheimer’s disease. These mutations are very rare. Probably only <1% of the total of Alzheimer’s disease incidence is caused by mutations in this way.

But, because the pathology is very similar between the genetic and the sporadic forms, we can use information from genetic Alzheimer’s disease to understand the disease as a whole. We take fibroblasts from individuals who have familial Alzheimer’s disease. We use those to make the induced pluripotent stem cells, and then we differentiate them into cortical neurons, which is the cell type predominantly affected in the brain. Then we use them to explore and understand the molecular mechanisms of the disease in vitro.

“If you’ve got a student or postdoc who just wants to get on with doing experiments, being able to have vials of cells sent to us and know that all the quality control has already been done and that they are good cells is a huge benefit.”

Selina Wray, Professor of Molecular Neuroscience,
Alzheimer’s Research UK Senior Research Fellow

What assays do you use in your cell-based research?

We do a mixture of things; in terms of biochemical assays we do a lot of Western blotting to look for changes in protein solubility or protein post-translational modifications that are associated with disease. We also perform a lot of imaging assays. Particularly high throughput imaging using the Opera Phenix to look at things like lysosomal dysfunction and expression of synaptic proteins and whether that is altered in disease.

We’re moving more towards imaging assays because eventually we would like to develop an assay that could be used for drug screening.

One of the pathologies of Alzheimer’s disease is extracellular and, with that in mind, we’re doing a lot of ELISAs to profile what the cells are producing in the media and whether that’s different in Alzheimer’s compared to control neurons.

Why did you choose to work with Axol Biosciences?

I got to know about Censo Biotechnologies, which has recently become a part of Axol Biosciences when I was working in Edinburgh, UK. They have a lot of expertise in iPSC technologies, and we had a strength in the amount of patient material that we had available from the patient cohorts that we have back at UCL.

The appeal of working with Axol Biosciences is the quality assurance. I think one of the challenges that the field has faced is dealing with different iPSCs from multiple vendors, and the varying levels of characterization that have been done. With that in mind, it’s nice to have the reassurance that by putting it in the hands of a company where this is their expertise, there will be a stringent level of quality control that happens.

Can you tell us more about the project you worked on with Axol Biosciences?

We had an NC3Rs ‘Crack It’ grant together. This grant was designed to make human models for tau pathology, which is one of the pathological features of Alzheimer’s disease. And within that project, my lab did the neural differentiations and the characterization of the pathology.

Axol Biosciences was tasked with creating a bank of cells for those that could be used in the lab but could also potentially be used by industry partners. This meant we were all working from the same bank of cells. Both iPSCs and neural precursors had been generated according to standard operating procedures and had been characterized before the end user used them.

The overarching goal was to explore if we can replace or reduce animal usage in Alzheimer’s research with these human cell models.

How successful was the project?

It was challenging, but I think we had some really good success. We’re very early adopters of this technology and it’s clear there are some challenges in using stem cell derived models to understand diseases of neurodegeneration because iPSCs are more like fetal neurons and we’re researching diseases that don’t clinically manifest until later life.

That’s particularly true of tau pathology because tau is involved in neurodevelopment, and it’s developmentally regulated as well. But we were able to show some key biochemical signatures associated with disease could be recapitulated in our model. We were also able to show that some of the assays could be miniaturized using microfluidics devices. Our collaborators at the University of Strathclyde did that work. Miniaturizing the assays is of course appealing when you consider that it provides better value for money, making research or diagnostic assays more accessible moving forward.

What were the key benefits of outsourcing to Axol Biosciences and working with them?

It was nice to not have to do some of the quality control ourselves because, although I think it’s really important work, it’s not necessarily the most exciting bit of working with these cells.

If you’ve got a student or postdoc who just wants to get on with doing experiments, actually being able to have vials of cells sent to us and know that all the QC has already been done and that they are good cells is a huge benefit.

I think the same in terms of reprogramming the cells ourselves as well, it’s not always the best use of somebody’s time in the lab when you can outsource it and know that you’re probably getting higher quality material because of that.

How important are in vitro stem cell models for understanding and tackling neurodegenerative disease?

Particularly with Alzheimer’s disease, but also true for other neurodegenerative diseases like motor neuron disease and
Parkinson’s disease, the most used models have been in vivo animal models.

But the truth is that we’ve cured Alzheimer’s in a mouse many times and that hasn’t translated into clinical success.
So, there’s clearly a missing piece of the jigsaw puzzle. And to me, it seems very likely that it’s something specific about
the biology of human neurons that makes them selectively vulnerable.

And, of course, the challenge that we’ve had, as I mentioned earlier, is that the human brain isn’t accessible during life. So,
we’re able to look at post-mortem, but that’s a little bit like turning up at the scene of a crime and trying to piece together
a sequence of events from what evidence is left. Where the power of iPSCs lies for me is that we can follow the disease
process in real time.

We can really say, “Okay, we have these neurons, what’s the sequence of events that leads to things starting to go wrong within the cells and ultimately cumulates in disease?” And, although we’re a little way off this yet, my hope for the future is that these models will be good for personalized medicine, so we might be able to use them to say what specific treatments would work best for each individual based on their cell biology. Another way they can be used, and this is already happening in the field, is to do compound screens directly in human cells. We’re starting to bridge the gap between the relevance of the models we use and the patients themselves. I think that’s hugely powerful and important.

In your lab’s day-to-day work, what are the challenges you face and how are you overcoming them?

The ones that I spoke about so far are more broad challenges within the field. I think in our own lab, those challenges still exist, and we try to mitigate them by careful characterization of the cell lines, by bulk-buying reagents such as growth substrates for the cells – so that we’re always working with the same master stocks and that reagents are from the same batch as far as we can. And, I think by just being transparent.

I’ve just taken part in a seminar series with the British Neuroscience Association. Madeline Lancaster organized it, and it was about how do we as a field make sure that we are open about these challenges, and that helps to increase reproducibility across the field as a whole.

We’re starting to bridge the gap between the relevance of the models we use and the patients themselves. I think that’s hugely powerful and important.

Selina Wray, Professor of Molecular Neuroscience,
Alzheimer’s Research UK Senior Research Fellow

Is reproducibility a big problem within the iPSC field?

I wouldn’t say it’s a big problem. I would just say that it’s important to consider your experimental design before starting so that you do make choices such as, ‘how many control lines do I need?’ ‘How many patient lines do I need?’ ‘What is the best way to differentiate them into the cell type that I’m interested in?’ ‘What is my benchmark for QC of those differentiated cells?’ -So that you know that they’re very high quality before you do any analysis. I don’t think it’s necessarily that reproducibility is a problem.

It’s just that there are a number of considerations that you need to make before starting to ensure that your experiment is well designed.

Do you think it’s possible to achieve a clinical trial in a dishfor Alzheimer’s Disease or other forms of dementia?

I think so. There have been studies that are already published that have done drug screens within patient derived neurons. I think as a proof of concept that shows that the system is robust enough to perform those kinds of studies. As I said, we’re not there yet, but I do think that having these human models will kind of bridge the gap between in vivo and in patient studies where things haven’t translated very well in the past and, on their own, won’t be enough. But seeing that a drug works in a human neuron in a dish before it goes into a patient has got to be a good thing, I think.

References

  1. Dementia. (2021). Retrieved 22 July 2021
  2. BMJ editorial on Aducanumab
  3. Drummond, E., & Wisniewski, T. (2016). Alzheimer’s disease: experimental models and reality. Acta Neuropathologica, 133(2), 155-175. doi: 10.1007/s00401-016-1662-x
  4. Arber, C., Lovejoy, C., & Wray, S. (2017). Stem cell models of Alzheimer’s disease: progress and challenges. Alzheimer’s Research & Therapy, 9(1). doi: 0.1186/s13195-017-0268-4

Cortical neurons stained for Tbr1 and b-III tubulin
Credit: Selina Wray and Charlie Arber, UCL

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