Yale researchers have discovered a potential therapy for treating a severe vascular disease that often leads to seizures and strokes.
Researchers at the Yale School of Medicine, in collaboration with pharmaceutical company Genentech, have found that the secretion of the protein angiopoietin 2, or ANGPT2, in brain endothelial cells — cells found on the inside of blood vessels and vessel walls — is implicated in cerebral cavernous malformations, a disorder that affects the central nervous system and may lead to hemorrhage, seizures and strokes. According to the study co-authors, this finding is crucial, as they can now look towards inhibiting ANGPT2 secretion as a therapeutic approach against the cavernous malformations, or CCMs. The study was published in the journal Nature on Aug. 22.
“We wanted to look at whether the CCM3 gene, when mutated, also increases [ANGPT2 secretion] and if that process has anything to do with the CCM disorder. So we performed the study and our hypothesis was correct,” medical school professor and senior author Wang Min.
Min, a professor at the School of Medicine, first became interested in this vascular disease 10 years ago, when he was invited to a conference focused on CCMs. At that time, there was no animal model for the disease, no therapy and no treatment, Min explained.
CCMs result from loss-of-function mutations, which happen when a mutation occurs in a gene, and the function that gene encodes for is subsequently lost. The loss-of-function mutations for CCMs occur in three particular genes: CCM1, CCM2 and CCM3. Min explained that genes 1 and 2 are very similar and work together. However, CCM3 is very unique, and mutations in this gene cause the most severe symptoms of the CCM disease.
“The previous two papers in Nature [on CCMs] focused on 1 and 2. Our lab is the first one to create knock-out mice with the mutated CCM3 gene,” he added.
Medical school professor and contributor to the paper Dianqing Wu’s original interest in neutrophils — a type of white blood cell important to immune system function — led him to discover an important protein kinase, a type of protein that helps regulate other protein formation through phosphorylation or the addition of a phosphate group. This protein kinase of neutrophil, which is known to interact with CCM3, regulates exocytosis, the process of secreting a cell’s contents by way of a cell vacuole, a membrane-bound organelle.
The researchers then hypothesized that the CCM3 gene was also involved in angiopoietin 2 — or ANGPT2 — exocytosis.
“Previously, in other studies, no one has ever implicated CCM3 in exocytosis or that angiopoietin 2 has played a role in this disease,” Wu said.
Min compared the role of CCM3 deficiency to a locker. With no mutation in the gene, the cell is able to prevent damage by blocking the release of proteins in endothelial cells, most notably ANGPT2. When CCM3 undergoes a loss-of-function mutation, the locker is broken and ANGPT2 is released, destabilizing the cell junctions of the vascular lining. This destabilization ultimately results in CCMs, according to the study.
Min and Wu then identified angiopoietin 2 as one of the many proteins released from the cell which plays a critical role in exhibiting symptoms of the disease. Thus, the disease’s symptoms can be significantly reduced if researchers are able to get rid of normalize the defects caused by that protein using an antibody — proteins of the immune system responsible for identifying pathogens for their eventual disposal.
Wu said they now hope to elucidate the mechanisms of a synthetic antibody produced by Genentech that serves as a neutralizing treatment, normalizing the lesions in the brain and retina caused by ANGPT2 secretion. He added that this molecular antibody, genetically engineered from human genes, is already being tested in other human diseases and can be repurposed to treat CCMs.
Though their findings provide a novel approach for treatment, the researchers said that much more preclinical testing needs to be done in studying this complex disease. The three genes that result in CCMs are similar but not identical and must be understood in more detail, they added. Min stated that one of their next goals includes building an even better in vitro knockout mice model, where the loss-of-function mutation is restricted to the brain, as in the actual disease, rather than existing globally in the body.
The researchers added that they also hope to work with Genentech to create small molecules that shrink or block the dilation of blood vessels causing the lesions.
Currently, the primary treatment option for a CCM is surgical removal, according to the National Institute of Neurological Disorders and Stroke.
Correction, Sept. 15: A previous version of this article indicated that Dr. Wu was the senior author of the paper. In fact, it was Dr. Min. It also incorrectly stated that the molecular antibody was already being used in other human diseases. They are currently being tested.