Gene editing treats smooth muscle disease in preclinical model

Using gene editing in a preclinical model, researchers at UT Southwestern Medical Center blocked the symptoms of a rare smooth muscle disease before they developed. Their findings, published in Circulation, could eventually lead to gene therapies for this and other genetic diseases affecting smooth muscle cells.

“Gene editing has been used in other disease contexts, but its application to inherited vascular diseases, particularly targeting smooth muscle cells in vivo, is still emerging. Our approach advances the field by demonstrating functional correction in a cell type that’s notoriously difficult to target,” said Eric Olson, Ph.D., Chair and Professor of Molecular Biology and a member of the Harold C. Simmons Comprehensive Cancer Center at UT Southwestern.

Dr. Olson co-led the study with Ning Liu, Ph.D., Professor of Molecular Biology, and first author Qianqian Ding, Ph.D., postdoctoral researcher, both members of the Olson Lab.

Fewer than 1,000 people in the U.S. have multisystem smooth muscle dysfunction syndrome (MSMDS). The disease is marked by widespread disorders in smooth muscles, a type of non-striated contractile tissue found in blood vessels and various hollow organs.

Patients with MSMDS develop problems affecting the lungs, gastrointestinal system, kidneys, bladder, and eyes beginning in childhood. They are also significantly more vulnerable to aortic aneurysms and aortic dissections—medical emergencies affecting the body’s largest artery that necessitate emergency surgery to prevent sudden death.

Because MSMDS is often caused by a single nucleotide mutation—a pathological change in one “letter” of the genetic code, in this case in a gene called ACTA2—gene therapy could theoretically cure patients with this disease, Dr. Ding explained. However, no gene therapies developed thus far have successfully targeted smooth muscle tissues.

To look for a possible solution, Drs. Ding, Liu, and Olson and their colleagues used a strategy called base editing—a variation of the CRISPR gene editing method that uses targeted molecular machinery to swap one specific letter of the genetic code for another, converting a mutant gene to its healthy form.

The researchers tested this approach first in human smooth muscle cells carrying mutant ACTA2. After introducing the base editing components into mutant cells growing in petri dishes, the scientists showed that the disease-causing mutant version of ACTA2 was corrected.

This treatment resolved pathological traits seen in the mutant cells, including an inability to contract and excessive proliferation and migration.

While this gene editing strategy appeared to be successful in cells, Dr. Ding explained, applying it to whole organisms was far more challenging because the base editing machinery must be expressed specifically in smooth muscle cells.

To achieve this, they packaged them with a promoter—a DNA fragment that ensures genes are expressed in the right cell type. Mice carrying the human ACTA2 mutation responsible for MSMDS that received the base editing components three days after birth remained healthy, while untreated mice developed symptoms including enlarged bladders and kidneys, dilated small intestines, and weakened aortas.

This strategy might be effective in human patients early in their disease process—an approach the team hopes will eventually be tested in clinical trials.

They plan to investigate in future studies whether gene editing could reverse symptoms of MSMDS after they’ve developed and whether their approach could hold promise for other genetic smooth muscle diseases.

Using gene editing in a preclinical model, researchers at UT Southwestern Medical Center blocked the symptoms of a rare smooth muscle disease before they developed. Their findings, published in Circulation, could eventually lead to gene therapies for this and other genetic diseases affecting smooth muscle cells.

“Gene editing has been used in other disease contexts, but its application to inherited vascular diseases, particularly targeting smooth muscle cells in vivo, is still emerging. Our approach advances the field by demonstrating functional correction in a cell type that’s notoriously difficult to target,” said Eric Olson, Ph.D., Chair and Professor of Molecular Biology and a member of the Harold C. Simmons Comprehensive Cancer Center at UT Southwestern.

Dr. Olson co-led the study with Ning Liu, Ph.D., Professor of Molecular Biology, and first author Qianqian Ding, Ph.D., postdoctoral researcher, both members of the Olson Lab.

Fewer than 1,000 people in the U.S. have multisystem smooth muscle dysfunction syndrome (MSMDS). The disease is marked by widespread disorders in smooth muscles, a type of non-striated contractile tissue found in blood vessels and various hollow organs.

Patients with MSMDS develop problems affecting the lungs, gastrointestinal system, kidneys, bladder, and eyes beginning in childhood. They are also significantly more vulnerable to aortic aneurysms and aortic dissections—medical emergencies affecting the body’s largest artery that necessitate emergency surgery to prevent sudden death.

Because MSMDS is often caused by a single nucleotide mutation—a pathological change in one “letter” of the genetic code, in this case in a gene called ACTA2—gene therapy could theoretically cure patients with this disease, Dr. Ding explained. However, no gene therapies developed thus far have successfully targeted smooth muscle tissues.

To look for a possible solution, Drs. Ding, Liu, and Olson and their colleagues used a strategy called base editing—a variation of the CRISPR gene editing method that uses targeted molecular machinery to swap one specific letter of the genetic code for another, converting a mutant gene to its healthy form.

The researchers tested this approach first in human smooth muscle cells carrying mutant ACTA2. After introducing the base editing components into mutant cells growing in petri dishes, the scientists showed that the disease-causing mutant version of ACTA2 was corrected.

This treatment resolved pathological traits seen in the mutant cells, including an inability to contract and excessive proliferation and migration.

While this gene editing strategy appeared to be successful in cells, Dr. Ding explained, applying it to whole organisms was far more challenging because the base editing machinery must be expressed specifically in smooth muscle cells.

To achieve this, they packaged them with a promoter—a DNA fragment that ensures genes are expressed in the right cell type. Mice carrying the human ACTA2 mutation responsible for MSMDS that received the base editing components three days after birth remained healthy, while untreated mice developed symptoms including enlarged bladders and kidneys, dilated small intestines, and weakened aortas.

This strategy might be effective in human patients early in their disease process—an approach the team hopes will eventually be tested in clinical trials.

They plan to investigate in future studies whether gene editing could reverse symptoms of MSMDS after they’ve developed and whether their approach could hold promise for other genetic smooth muscle diseases.