GTCA

# # # # Today’s post is ‘blue sky’ stuff (meaning that it is not going to be in the clinical any time soon), but it is utterly fascinating (almost sci fi) research. Scientists at Stanford University have developed a method by which they can reprogram cells to use synthetic materials (provided by the scientists themselves) to build functional artificial structures. And to add to the sci fi nature of it, they have called this approach “GTCA” (“genetically targeted chemical assembly”). In today’s post, we discuss what GTCA is, what they found in their study, and where this wondrous discovery could go next.  # # # #

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Prof Karl Deisseroth. Source: Ozy

This is Karl Deisseroth.

Looks like the mad scientist type, right? Well, remember his name because this guy is fast heading for a Nobel prize.

Possibly two.

He is the D. H. Chen Professor of Bioengineering and of Psychiatry and Behavioral Sciences at Stanford University. And he is one of the leading researchers in a field that he basically started. That field is called optogenetics (Click here to read a previous SoPD post about this topic).

Optogenetics. Source: Harvard

He also developed (along with Kwanghun Chung) a better way of visualising the brain called CLARITY.

CLARITY is a technique that transforms intact tissue (like the brain) to make it completely transparent. With a clear brain – and some additional biological techniques – an exceptionally detailed map of neuronal pathways can be generated.

For an example, watch this video:

Prof Deisseroth and colleagues are also seeking to pioneer additional areas of neuroscience, and in today’s post we will be exploring a new research report that could have important implications for Parkinson’s.

How so?

Here on the SoPD we often discuss research focused on the slowing or stopping of Parkinson’s, but often overlooked are efforts to restore and rejuvenate. Replace the lost cells and circuits that have been lost to degeneration.

At the start of this year (in the 2020 wish list post), I said that I was hoping to see “a focus on rejuvenation”.

And it is fair to say that Prof Deisseroth and colleagues appear to be trying to deliver on that particular wish.

Interesting. What have Prof Deisseroth and his team done?

In late March, as the world was waking up to the terrible potential of the developing COVID-19 situation, this report was published in the prestigious journal Science:

Title: Genetically targeted chemical assembly of functional materials in living cells, tissues, and animals
Authors: Liu J, Kim YS, Richardson CE, Tom A, Ramakrishnan C, Birey F, Katsumata T, Chen S, Wang C, Wang X, Joubert LM, Jiang Y, Wang H, Fenno LE, Tok JB, Pașca SP, Shen K, Bao Z, Deisseroth K.
Journal: Science. 2020 Mar 20;367(6484):1372-1376.
PMID: 32193327

In this study, the researchers wanted to determine whether certain cells within an “intact biological system” could be genetically encouraged to “build new physical structures with desired form and function”.

They basically wanted to know if they could “customise cells”. For example, add some new functional branches to a neuron in the brain.

Whoa! How on Earth were they planning to do that?

They wanted to design a “single-enzyme–facilitated polymerization using chemically modified monomers for which polymerization is triggered by an enzyme that can be expressed in specific cells”.

All clear?

You lost me

Which part?

After “They wanted…”

Ok, let’s start at the beginning. The researchers decided to use polymerization as their starting point.

And what is polymerization?

Polymerization a chemical process that combines monomer molecules to form a polymer. Monomers are molecules that are able to bind together and form long chains.

A good example of a monomer is glucose. It forms a polymer (starch or glycogen) when a large number of glucose molecules joined together (via glycosidic bonds).

Source: Chemistryhungergames

The researchers chose to use an electroactive polymer – meaning that the polymer would be electrically functional or conductive. For this property, they chose the electroconductive polymer polyaniline.

Another appealing and necessary feature of this polymer is that it is capable of synthesis in solutions – a necessary feature for “biological system compatibility”.

Ok, Monomers become polymers. Got it. But what about the enzyme part of “single-enzyme–facilitated polymerization”?

The “single enzyme” provides the researchers with a means of targetting the polymerization to particular cells.

And the enzyme that the researchers used in their study was APEX2.

APEX is an enzyme present in peas and soybeans, that researchers have engineered for other purposes. The re-engineered version is called APEX2 (Click here to read more about this).

APEX2 is a peroxidase, which means that it is reactive to the chemical hydrogen peroxide. It breaks down hydrogen peroxide. Interestingly, peroxidases can also catalyze the synthesis of conductive polymers in the presence of hydrogen peroxide. And this is why the researchers were interested in APEX2 – by combining APEX2, hydrogen peroxide, and the conductive polymer polyaniline, the investigators were hoping to start ‘customising’ some cells.

So this was the “single-enzyme–facilitated polymerization” that we are talking about.

I see. What did the scientists do next?

Next the researchers genetically reprogramming rodent cells in cell culture to produce APEX2 enzyme (not something they normally do).

They then added billions of tiny polyaniline polymers to the cell culture solution, and exposed those cells to a weak concentration of hydrogen peroxide…

And guess what happened…

….

The conductive polymer started binding to the APEX2 producing cells and started forming chains. And rather quickly a mesh-like material started connecting between cells.

Artist representation of GTCA (in gold). Source: Stanford

And by electrically stimulating a neuron that was connected to other neurons by these artificial nets, the researchers were able to record signals being passed between those artificially connected neurons (a rather remarkable feat!).

That’s amazing. What did they do next?

Well, obvioursly the researchers were not satified with just one clever little party trick, so next they went looking for a nonconductive polymer, and they settled on poly(3,3′-diaminobenzidine) or PDAB.

Why did they want a nonconductive polymer?

To test whether they could control neuronal activity by the polymer that they used. Could a nonconductive polymer slow or reduce activity?

By adding PDAB (rather then polyaniline) to the cell culture solution, they found that the APEX2 producing cells exhibited significantly less electrical conductive activity.

They called this new method of customising (or augmenting) cells “GTCA” which stands for “genetically targeted chemical assembly”.

And they tested it on mouse brain slices and also on human cells in culture, and it worked in these settings as well.

But they didn’t stop there.

Huh?

Next the researchers wanted to see if this technique would work inside living organisms. For this experiment, the investigators chose C. elegans.

What are C. elegans?

Caenorhabditis elegans (or simply C. elegans) are transparent nematode – also known as roundworms. They are about 1 mm in length, and they have very well characterised nervous systems (useless pub quiz fact: C. elegans have 302 neurons and 56 glial cells in total, which communicate through approximately 6400 chemical synapses, 900 gap junctions, and 1500 neuromuscular junctions – like I said, well characterised!).

Caenorhabditis elegans – cute huh? Source: Nematode

Given their well characterised nervous systems, C. elegans provide a useful tool for studying biology. They are easy to grow/maintain, they have an overall life span of 2-3 weeks, and researchers have developed a wide range of tools that allow for genetic manipulation to address specific questions.

Prof Diesseroff and his team genetically reprogrammed different types of cells in C. elegans to produce APEX2 and then they exposed these microscopic worms to a solution of polymers and weak concentration of hydrogen peroxide.

They found that depending on what type of cells were targetted, the worms behaviour was altered (crawling faster or slower).

This is amazing. Kinda scary though. What exactly are the researchers proposing to do with this new technology?

Well, they currently have no medical applications in mind. Rather, Prof Deisseroth suggests “what we have are tools for exploration” (Source).

And obviously a lot more research and adaptation of this technology is required (like I said at the start of the post, this is REALLY blue sky stuff). But one can not help wondering how something like GTCA could be applied to neurodegenerative conditions like Parkinson’s or multiple sclerosis.

Imagine using this technology to study multiple sclerosis – a condition caused by the loss of myelin insulation around the branches of neurons (we briefly discussed MS in the previous SoPD post – click here to read that). Could demylinated neurons be rescued by the formation of replacement insulating polymers?

Likewise in Parkinson’s, if we can stop the progression of the condition, could future medicine use something like GTCA to help reconnect some of the missing circuits?

A major stumbling block for any kind of translation of this technology will be delivery – how would one get specific cells in the brain to start producing polymer meshes, while leaving others unaffected?

But hopefully further research will help elucidate this.

So what does it all mean?

Researchers have recently proposed a blending of chemistry and biology as a means of genetically targeting cells to enable them to chemically form new physical structures. And the electroconductive properties of these assemblies allows them to be functional.

At the start of the year I wrote that I was hoping to see more of “a focus on rejuvenation”. Specifically, I was wanting to see some novel approaches to replacing the cells and circuits that have been lost in Parkinson’s. Too much attention is focused solely on cell transplantation therapy.

I don’t feel like I’m going out on a limb by saying that GTCA is definitely novel, and it will be something to watch develop in future.

 

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The banner for today’s post was sourced from Stanford.