Osteoporosis directly affects more than 200 million worldwide, including one in three women and one in five men over the age of 50. Because it is a bone disease, osteoporosis is a common cause of fractures, which in turn lead to reduced mobility, independence, and overall quality of life. The economic impact of osteoporosis on patients, families, and the healthcare system exceeds $19 billion a year and is expected to surpass $25 billion the year 2025.
The current standard of care for osteoporosis is to manage symptoms and to inhibit bone resorption (breakdown) with drugs. However, these drugs are only effective in half of all patients. Additionally, because these drugs interfere with bone remodeling, they may actually contribute to the tiny cracks in the bones that compromise bone health.
Now, with a major grant from the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health, a team from the UW Institute for Stem Cell and Regenerative Medicine (ISCRM) is on a mission to confront the root cause of osteoporosis. To do that, they are focusing on the primary determinant of bone health: our own genetics.
“We want to understand the genetic risk factors for osteoporosis, to use that insight to identify new therapeutic targets,” explains Ronald Kwon, PhD, the lead investigator behind the research effort. Kwon is an Associate Professor of Orthopaedics and Sports Medicine, an ISCRM faculty member, and the Director of the Musculoskeletal Systems Biology Lab (MSBL).
Momentum for the investigation is building. Claire Watson, an acting instructor in the lab, is the lead author of a paper, published earlier this year in journal Cell Systems, that validates the screening approach used by the research team and establishes a statistical model to help the researchers identify genes that contribute to skeletal disease. The paper details the merits of CRISPR-edited zebrafish as a model to decode mutations observed in zebrafish bones.
Zebrafish, 3D Imaging, and a Full-Scale Screen
Scientists have long known that genetics have a lot to say about a person’s susceptibility to osteoporosis. Bone biologists estimate that up to 80% of bone mineral density – a key indicator for osteoporosis – is heritable, meaning the degree to which it can be statistically attributed to genetic makeup.
Over the last few decades, researchers have identified hundreds of locations in the human genome which contain genetic variants that help protect some people from osteoporosis, and make others more susceptible to this disease. These genetic variants are thought to influence the activation of specific genes that contribute to bone weakening. However, those specific genes – the true culprits – have yet to be identified. That may change soon.
Kwon and his team have spent the last several years assembling the people, partners, and technology to identify these genes, and improve the prospect of more effective treatments for millions of patients.
The first piece of the puzzle was developing the right technology. For their studies, the team uses the zebrafish, an aquatic species that shares a surprising number of genes with humans, yet reproduces and matures much more quickly. “The small size and low cast of zebrafish enable us to look at many more genes over successive generations than we would in other animals models,” says Kwon.
Several years ago, Kwon pioneered a new technique to image zebrafish skeletons. Specifically, the Kwon lab uses micro-CT technology, a 3D imaging technique, similar to a CAT scan, that allows them to see inside a solid object – like the bones in a zebrafish skeleton. Using a semi-automated process, they measure bone health characteristics, including density, length, and thickness, in multiple regions of bones simultaneously, as they search for patterns that point to proclivity for osteoporosis.
The team had the technology to image to zebrafish in incredible detail. To conduct sophisticated screens, they needed the ability to rapidly mutate the genes they were studying. That skillset arrived in 2014, when Claire Watson joined the lab, bringing with her a background in genetics and an aptitude for developing new approaches to screening and mutating genes.
Another crucial asset for the Kwon lab is the ISCRM Aquatics Core, a large zebrafish facility where much of the osteoporosis investigation will take place. “The main benefit of zebrafish is you can do high throughput biological screens to look for many things at once,” says Kwon. “Being a part of ISCRM allows us to do a full-scale study – to study the mechanisms of regeneration, and also what happens when we lose the capacity to regenerate naturally.”
“We know which genes we want to manipulate,” adds Watson. “Working with zebrafish lets us manipulate many genes at once and then see which ones give us the traits related to bone mass and density that help us understand more about the causes of osteoporosis.”
Partnerships and Funding Fuel the Future
In 2015, Dr. Kwon met Yi-Hsiang Hsu, a human geneticist at Harvard who was investigating the genetic processes that confer protection or vulnerability to osteoporosis. Hsu was able to locate an approximate location within the genome containing DNA that seemed to make people more or less susceptible to the bone disease. The partnership with Hsu gave Kwon and his team a chance to put their imaging and gene manipulation expertise to work and to gather preliminary data about the nature of osteoporosis in zebrafish.
The collaboration with Hsu also helped attract private funding. In June 2018, Kwon received the John H. Tietze Stem Cell Scientist Award. This year, the lab was awarded a five-year, $2.2M grant from the National Institutes of Health to conduct one of the largest screens ever performed for causal genes underlying genetics risk for osteoporosis.
Long term, Kwon hopes that developing a more detailed profile of the genes that code for bone mass density – where they are, and how they work – will be a stepping stone to therapies that boost bone regeneration. “Our objective now is to identify and understand the functions of the genes associated with osteoporosis and how they influence bone mass density,” says Kwon.
Research reported in this article is being supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award Number R01AR074417.