HSCI researchers find drug that protects insulin-producing cells from stress and autoimmune attack

 

To treat type 1 diabetes, scientists have learned how to grow large volumes of insulin-producing beta cells to replace the ones destroyed by the patient’s immune system. However, those cells are also subject to attack from the immune system, so researchers are working on ways to protect them against that attack. 

In a new study, Harvard Stem Cell Institute (HSCI) researchers have identified an unusual strategy for protection. Using mouse models and human cells, they found that targeting a protein called renalase may protect beta cells against autoimmune attack by strengthening them against stress. Furthermore, an existing FDA-approved drug inhibits renalase and, in turn, increases beta cell survival.

The results, published in the journal Nature Metabolism, may lead to the development of new drugs that could help protect transplanted beta cells, or even slow the original onset of the disease.

The study joins a growing set of evidence suggesting that functional problems with beta cells themselves may help to trigger the autoimmune attack in type 1 diabetes. “You might have genes that make the beta cell a little bit dysfunctional and more prone to becoming a target of the immune system,” said Stephan Kissler, who co-led the study with Peng Yi. They are both HSCI affiliate faculty members at Joslin Diabetes Center. 

Searching the genome

To search for potential ways to protect beta cells from autoimmune attack, Kissler and Yi used an approach that inhibited genes across the genome, one at a time.

They chose a screening technique based on the CRISPR gene-editing method, applying it to a beta cell line from a mouse that models type 1 diabetes. “Whole genome CRISPR screening is a powerful tool for new target discovery and we hoped that it would help us find any mutations that protect the beta cell,” Yi said. 

The CRISPR screen for surviving beta cells produced a dozen genes of interest. The most striking was the gene for renalase, which previous research had shown is associated with type 1 diabetes.

To confirm the screen results, the researchers created mouse beta cells, some with the renalase gene functionally “knocked out” and some not. They transplanted these cells to mice with autoimmune diabetes.

Intact beta cells died off — but the renalase knock-out cells survived. “This was a very black-and-white research model,” Kissler said. “If the cells aren’t protected, they’re gone.”

Explaining the mechanism

The investigators checked to see if the cells that lacked the renalase gene provoked a diminished response from T immune cells, which are responsible for spearheading autoimmune assault. The scientists found that one type of T cell was less likely to attack these knockout cells than to attack normal beta cells.

But what was slowing this autoimmune assault? 

In earlier work to analyze beta cell survival, Yi had analyzed how the cells respond to a condition called endoplasmic reticulum (ER) stress. Now when the team tried three ways of introducing ER stress to mouse beta cells in a dish, the researchers saw that the renalase mutation was protecting against this condition.

In the next step, to see if the same mechanisms were at work in human cells, the team joined up with HSCI co-director Douglas Melton to create human beta cells for similar tests in a dish. “Again, we saw that the renalase knockout protected cells against ER stress,” Kissler said.

Targeting the protein

The functions of renalase are not well understood, but Yi and Kissler knew that the protein is an enzyme, which can be targeted by drug compounds. Furthermore, other scientists had produced a three-dimensional crystal structural map of the protein. 

Wondering if this map would give clues to uncover a compound that could target renalase, the researchers began working with Celia Schiffer of the University of Massachusetts Medical School. Structural biologists at the university’s structure-based drug design core facility noticed that renalase is very similar to another enzyme that is inhibited by existing drugs — including one drug known as pargyline that was approved by the FDA almost 60 years ago to treat hypertension.

Testing pargyline in their mouse transplant model, the researchers found that the drug protected beta cells extremely well. Studying it in the mouse beta cells themselves, the scientists demonstrated that pargyline indeed was protecting against ER stress. In experiments with human cells, pargyline also displayed a protective effect.

Kissler and Yi hope to test pargyline in a pilot clinical trial to see if it slows the progress of new onset type 1 diabetes in a small number of patients.  “Since it’s FDA-approved and the drug is safe, this would be the best approach to test if the protection we observed in mice and human cells will hold true in people,” Kissler said.  If research results continue to be positive, their next goal will be to find industry backing to develop a small molecule drug that provides even better protection than pargyline.  

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This story was originally published on the Joslin Diabetes Center website on July 27, 2020, under the title “Protecting beta cells against stress may guard against type 1 diabetes.”

Source article: Cai, E., Ishikawa, Y., Zhang, W. et al. (2020). Genome-scale in vivo CRISPR screen identifies RNLS as a target for beta cell protection in type 1 diabetes. Nature Metabolism. DOI: 10.1038/s42255-020-0254-1

The study was supported by the Harvard Stem Cell Institute, JDRF, and the National Institute of Diabetes and Digestive and Kidney Diseases.