The End of the Battle Against Diabetes?

Using Transdifferentiation of Hepatocytes Into Pancreatic Progenitors Through Overexpression of TGIF2 (Huh? Don’t worry, I’ll explain)

9 min readFeb 22, 2021

493 million adults suffer from it. That’s 1 in 11 people.

Possible complications include stroke, a coma, lower limb amputation, heart disease, kidney failure, blindness, and death.

It’s the 9th leading cause of death worldwide.

Diabetes: Types, Current Treatments & Cures?

Diabetes is a chronic, metabolic disease that is caused by high glucose levels because the beta cells in our body either can’t produce enough insulin or the insulin produced by the body isn't being used effectively by the body. Insulin is a hormone that moves and stores glucose in our cells so that it can be used for energy. Glucose in the bloodstream can be dangerous for an extended period of time because it can damage oxygen-carrying blood vessels.

Type 1 & Type 2 Diabetes: What’s the Difference?

There are two types of diabetes, type 1 and type 2.

This diagram explains how insulin is supposed to interact with glucose and move them into the cells for energy, compared to how Type 1 and Type 2 diabetes are developed and how they differ.

Type 1 diabetes affects 5–10% of all diabetic patients. It is an autoimmune disease where the immune system is attacking the body’s beta cells and slowly diminishes insulin levels. Often called juvenile diabetes, type 1 is usually diagnosed in childhood to early teens and can be influenced by factors such as genetics and environmental triggers like a virus.

Type 2 diabetes affects 90–95% of all diabetic patients. Type 2 is a result of cells not responding to insulin (insulin resistance), and the pancreas tries to make more insulin to respond to the high levels of glucose in the cells, but it can’t keep up. Also known as adult-onset diabetes, type 2 is typically a result of diet and lifestyle choices, and unlike type 1 is completely preventable.

Current Treatments for Diabetes

There are multiple treatments for diabetes, but they mainly focus on treating the symptoms instead of the root cause. The most common for both type 1 and type 2 diabetics is daily insulin injections. Through needles, pens, pumps, or other devices, diabetics must take and monitor their insulin intake to make sure that their glucose levels are in a good range. Other treatments include glucose monitoring to know when to take insulin or when glucose levels are too low or too high, and multiple medications in addition to the insulin. Diabetics also have dietary restrictions, deciding what and when they can eat.

Is There A Cure?

No. There is no cure for diabetes right now but with novel treatments for type 1 diabetes like islet cell transplantation and stem cell transplants, it looks promising.

Islet cells are clusters of different types of pancreatic cells, including insulin-producing beta cells. Islet cells are transplanted into a patient from a deceased organ donor, and while very effective have their limitations.

Potential Immune Rejection: Since the islet cells are allogenous (comes from another person), there is a chance of the immune system attacking the implanted islets and because of this, once transplanted, the patient is on a lifetime of immunosuppression drugs, putting them at risk for infections and certain cancers.
Limited Supply of Islets: One of the biggest barriers to the widespread use of islet transplants is because since they originate from deceased organ donors, there is a limited supply of donor pancreases that are viable for harvesting enough islets.

Stem Cell Transplants are also another option. Stem cells are unspecialized cells that can be turned into specialized cells, and in this case, islet cells. Stem cell transplants are a novel therapy in treating diabetes, and while they seem effective, like islet cells, they have their faults.

Immune Rejection: Like the islet cell transplant, stem cell transplants also have a chance for immune rejection because they are not from the patient. So if transplanted, the patient would probably have to be on a lifetime of immunosuppressant drugs.
Complications: Stem cells are able to divide for an extended period of time, which increases the chance of diseases like cancer. Another complication of stem cell transplantation is the potential for disease and infection.

While these two treatments are very effective in treating diabetes, they are not good enough to treat diabetes. What is good enough then?

Transdifferentiation of Hepatocytes into Pancreatic Progenitors Through The Forced Expression Of TGIF2

You probably don't understand what that sentence meant. Neither did I when I first read this research paper. Before you open a new google tab to search up all these words, I’ll save you the time and define it for you.

Transdifferentiation: When a specialized cell, such as a hepatocyte, is transformed into another specialized cell without entering a pluripotent state. Also known as lineage conversion or lineage reprogramming
Hepatocytes: Liver cells that make up about 80% of the liver.
Pancreatic Progenitors: Multipotent cells (stem cells that can give rise to a limited set of cells), that can give rise to both exocrine and endocrine pancreatic cells, including beta cells.

So now that you know what these words mean, let’s dive into the details.

Why We Use Hepatocytes

There are two main reasons why hepatocytes are used for transdifferentiation into pancreatic progenitors for diabetes.

The liver is the only organ in our body that effectively regenerates its function, so if we were to transdifferentiate some liver cells, it wouldn't impair liver function. If the liver didn't regenerate and we irreversibly turned hepatocytes into pancreatic progenitors, then it could potentially cure diabetes, but it would lead to a whole other set of problems like liver disease and eventual failure. So because the liver can regenerate, we can take some liver cells and turn them into pancreatic cells and have two functioning organs, instead of just one.
The pancreatic and liver cell lineages are very closely related. Both the liver and pancreas come from the same foregut progenitors and don't separate until late in organogenesis (embryonic organ development). They come from the same hepatopancreatic cell lineage, and there are only a handful of factors that help make the decision for a cell to continue down a liver lineage or a pancreas lineage.

This diagram explains how hepatocytes and pancreatic progenitors come from the same hepatopancreatic stem/progenitor cell. (Source)

The Deciding Factor: TGIF2

The developmental regulator TGIF2 is one of the main factors that control whether a cell will become a pancreatic cell or a liver cell. TGIF2 stands for Homeobox TG-interacting factor 2. TGIF2 expression pushes foregut progenitors towards a pancreatic cell fate and away from a hepatic cell fate. The more TGIF2 that is expressed in a foregut progenitor, the more likely it will become a pancreatic cell.

But the crazy thing is when TGIF2 is overexpressed in mature hepatocytes, the hepatocytes undergo extensive transcriptional remodelling, essentially repressing its original hepatic identity to create a pancreatic progenitor phenotype, with its properties.

How It’s Delivered In Vivo

So now that we know that we can turn hepatocytes into pancreatic progenitors using TGIF2, let’s talk about how it actually gets to the liver in vivo (in the body).

Loading the TGIF2 into the delivery mechanism (Adeno Associated Virus)

To transport the TGIF2 regulator to the liver in vivo (in the body), an adeno-associated virus (AAV), with a virus vector of 8 is used. An AAV is a non-enveloped virus that can be programmed to deliver DNA, RNA, and other biologically active materials (like TGIF2) to specific cells in the body. It is one of the most commonly used delivery systems for gene editing and delivery. An AAV8 is used in this case because it has low immunogenicity (the ability for a foreign substance to provoke an immune response in the body) and with this specific vector and type of virus, has a hepatic tropism, which targets specifically the liver and has higher liver transduction efficacy than other AAV vectors.

Once the delivery mechanism is assembled, it is inserted into the patient intravenously (through the veins), where it seeks out the liver cells and once inside the cells, expresses the TGIF2, turning the hepatocyte into a pancreatic progenitor.

And The Verdict Is…

It works!! In mice. Yeah, I know that doesn't sound as exciting as it would be if this worked in humans, but the results in mice so far have been pretty promising. Through immunofluorescence, the TGIF2-induced pancreatic progenitors (TiPP) cells have shown that pancreatic progenitor markers like PDX-1 and NKX6.1 are being produced by these newly transdifferentiated hepatocytes. Also, the TiPP cells in diabetic mice have further differentiated and acquired beta cell properties, that are able to produce insulin and glucagon, as shown by the endocrine markers.

**Image A:** An immunofluorescence image of the TiPP cells in mice. The TiPP cells in vivo of the mice are producing pancreatic progenitor markers such as PDX1 (blue), and NKX6.1 (red). **Image B:** Another immunofluorescence image of the TiPP cells producing glucagon (red) and insulin(blue) markers in vivo in mice. (Source)

And even more promising, is the fact that when the AAV-TGIF2 is injected into adult hyperglycemic Akita mice with almost 0 beta cells, the TiPP cells matured into beta cells that produced insulin. Over the course of the 8 weeks of the experiment, blood glucose levels improved.

The TiPP cells in hyperglycemic Akita mice (red trendline) are shown to have matured into insulin-producing beta cells and have lowered glucose levels in these mice over the 8 weeks of the experiment. The blue dotted line represents normoglycemia which is around 200mg per decilitre. (Source)

Key Points:

Diabetes is a chronic, metabolic disease that happens when there are high levels of glucose in the body when insulin either is not produced (Type 1 diabetes), or the body doesn't respond to the insulin as well as it should (Type 2 diabetes).
Using Regenerative Medicine, specifically the transdifferentiation of hepatocytes into pancreatic progenitors could potentially cure diabetes through overexpression of TGIF2.
Transdifferentiation: When a specialized cell is transformed into another specialized cell without entering a pluripotent state.
Hepatocytes: Liver cells
Pancreatic Progenitors: multipotent cells (stem cells that can give rise to a limited set of cells), that can give rise to both exocrine and endocrine pancreatic cells, including insulin-producing beta cells.
The liver and pancreas are closely related in lineage and the liver is the only organ in our body that effectively regenerates, making it a good candidate for transdifferentiation.
TGIF2 is a developmental regulator responsible for liver vs pancreas fate decisions in a cell.
When TGIF2 is overexpressed in hepatocytes, they undergo extensive transcriptional remodelling and become cells with a pancreatic progenitor phenotype
Delivery in vivo is through an Adeno-Associated Virus with a vector of 8 (AAV8). An AAV is used because it has a hepatic tropism (targets specifically liver cells), and has a low immune response.
Results in mice have shown that the TGIF-induced pancreatic progenitor cells (TiPP cells) show both pancreatic progenitor markers and endocrine markers such as insulin. And with adult hyperglycemic Akita mice, the TiPP cells matured into beta cells and improved blood glucose levels.

What Does This Mean For Us: Future Applications and Improvements

The transdifferentiation of hepatocytes into pancreatic progenitors to cure diabetes is a novel approach.

With more research on the intersection between medicine and technology, we could start to see newer advancements and improvements on this treatment to make it more viable for humans. An example of this is the use of nanotechnology. Using nanotechnology, we could eliminate the use of the AAV as the delivery mechanism and instead use synthetic or biological nanoparticles like nanobots and extracellular vesicles to deliver the TGIF2 regulator to the hepatocytes. This approach is better than the AAV because as more research is done, nanotechnology in medicine can evade the immune system and can release when and where we want it to go.

But as of now, this approach for treating diabetes still needs more research and trials before it can be used, but there is hope that we can eliminate diabetes as the 9th leading cause of death worldwide.

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