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The Unexpected Role of Secreted Proteases in Birth Defects

03/27/2019

A group of Cleveland Clinic researchers have identified how the proteases ADAMTS9 and ADAMTS20 contribute to embryonic development and how defects in these enzymes lead to serious birth defects.

In a preclinical study, the researchers used genetic engineering and gene editing technology to inactivate the genes that produce the proteases ADAMTS9 and ADAMTS20 (proteases are enzymes that break down other proteins). Their inactivation led to birth defects including faulty closure of the neural tube and palate and failed separation of the trachea and esophagus. The team found that that these effects were mediated by disruption of the sonic hedgehog (Shh) signaling pathway.

“Turning off” the ADAMTS9 gene inhibited Shh signaling, which, under normal conditions, helps embryonic cells to properly differentiate, explaining the observed developmental abnormalities. Shh signaling is transduced through the primary cilium—a long, antenna-like organelle that protrudes from the body of a cell and aids in extracellular sensing, signal transduction and embryonic development. Genetic mutations that alter cilia function, and the resulting clinical disorders, are called ciliopathies and are known to affect the development of many organs. Silencing ADAMTS9 with gene editing technology, and, by extension, inactivating ADAMTS9 and ADAMTS20, resulted in underdeveloped and faulty primary cilia in both preclinical models and cell culture.

Although ADAMTS9 and ADAMTS20 are extracellular enzymes—they help to break down and prevent accumulation of excess extracellular matrix—the researchers found that they can also localize and accumulate inside of the cell, in vesicles at the base of the cilium. Staining analyses revealed that ADAMTS9 and ADAMTS20 were transported into the cell through endocytic vesicles, which are like protective bubbles that help outside molecules cross the cellular membrane and enter the cell.

Very surprisingly, preventing vesicular intake of these enzymes significantly reduced cilium length. This observation, and the discovery that suppressing ADAMTS9 affects cillia development, suggests that ADAMTS9 and ADAMTS20 play an important role in ciliogenesis. While secreted proteolytic enzymes have on a few occasions been shown to have intracellular effects, to the authors’ knowledge, this is the first time that they have been implicated in organelle development, making this an exciting advance for the field of cellular biology.

In a related study, which was published in American Journal of Human Genetics, a group at Harvard Medical School, in collaboration with the Lerner research team, identified ADAMTS9 mutations in patients with ciliopathies. These findings suggest ADAMTS9 and ADAMTS20 may play an active role in inherited ciliopathies and provide an actionable pathway that may help prevent serious birth defects.

Sumeda Nandadasa, PhD, Department of Biomedical Engineering, is first author on the paper, which was published in Nature Communications and supported in part by grants from the National Heart, Lung, and Blood Institute and National Eye Institute, both parts of the National Institutes of Health, and Cleveland Clinic Pediatric Institute (Mark Lauer Pediatric Research Grant). Dr. Nandadasa is in the lab of Suneel Apte, MBBS, DPhil. Dr. Apte is an American Heart Association-Paul G. Allen Frontiers Group Distinguished Investigator, a program which also supported this research.

Photo: A 3D super-resolution confocal microscopy image showing a primary cilium in green and vesicles containing ADAMTS9 accumulating at the base of the cilium in red. Image captured at 1000x optical magnification.



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