The Bone Matrix and the Narwhal
Inventing new ways to study osteoporosisRene Harrison
Osteoporosis is known as the “silent thief.” It slowly robs people of their bone mass and density, and there are few symptoms until a catastrophic fracture occurs. According to Osteoporosis Canada, a national charitable organization based in Toronto, these fractures are more common than heart attack, stroke and breast cancer combined. At least 33 percent of women and 20 percent of men will experience in their lifetime a fracture due to bone-wasting disease.
Bone mass is regulated by two types of cells: osteoblasts that deposit (or create) bone, and osteoclasts that dissolve (or remove) bone. When an adult is healthy, these cells work in equilibrium to maintain bone mass. However, in bone-wasting disorders like osteoporosis, either the osteoblasts make less bone, the osteoclasts remove too much bone, or both scenarios occur at once.
As cell biologists, my group at our laboratory at UTSC are focused on determining how and why bone cells go awry and cause bone loss. This is the essential puzzle that drives our work every day.
Cell biologists are ideally trained to address these problems. Our tool of choice is the microscope, as magnification of these tiny units of life is essential to studying them. However, the major barrier to our work is the bone itself. Calcified bone is impenetrable to light. The illumination from our microscopes is therefore unable to reveal the cellular changes occurring within the bone matrix.
So, how do we study bone diseases if our favourite tools won’t work? My lab is concentrating on a number of strategies. One involves in vitro analysis of bone cells. “In vitro” is just a fancy way of saying that my research group grows bone cells in a lab instead of studying them in naturally occurring bone. We are optimizing the creation of an artificial bone matrix upon which purified bone cells (osteoblasts and osteoclasts) can then be plated and studied. Unlike natural bone, this artificial matrix allows light to pass through it, enabling us to observe and study the matrix with advanced light and electron microscopy.
Another strategy we pursue involves slicing bone into ultra-thin sections. Using diamond knives, we can generate pieces of bone that are no more than 100 microns thick (each micron being one millionth of a metre) and that allow light to pass through. These bone slices are then placed atop bone cells, and our microscopes are able to reveal what’s happening.
The key to this second strategy is to use bone that is extremely smooth, so that we can easily observe the destruction, or pitting, in the bone caused by osteoclasts. It just so happens that the smoothest type of bone in existence is also one of the most precious: ivory. Sources for ivory are difficult to find, however, and often illegal—for good reason. But I have been able to use my connections in Winnipeg, where I received my undergraduate and graduate training, to get an entire ivory tusk from a “sea unicorn,” no less—a narwhal!
The Department of Fisheries and Oceans, based in Winnipeg, collects (and confiscates) ivory tusks from Canada's Far North, and in special instances it will donate these for research. The narwhal ivory tusk we were able to obtain has greatly assisted our research into bone diseases. What's more, ours became the first lab recently to send narwhal ivory into space!
Why on earth would we send bone into space, you ask? Because astronauts experience a severe form of osteoporosis called “disuse osteoporosis.” It has long been known that running and jogging are healthy for bone, and it is thought that bone cells are healthiest when mechanically stimulated. Disuse osteoporosis arises from the lack of weight-bearing activities. Patients are afflicted with disuse as they age, become less mobile or are confined to bed rest for extended periods, or when they experience microgravity (weightlessness) for prolonged periods. Space agencies are therefore very interested in understanding which bone-cell defects occur in astronauts, particularly when trying to plan long missions such as a trip to Mars. The Canadian and European space agencies decided to employ cell biologists like ourselves to get at this mystery.
My research group was awarded a contract with the Canadian Space Agency to study bone cells aboard a Russian Foton-M3 satellite. Along with two other Canadian groups, we worked at the European Space Agency in Noordvjik, Netherlands, to optimize the growth of bone cells, some of which were grown on the narwhal ivory slices, in a fully automated in vitro cell-culture apparatus. Once conditions were ideal, the Foton-M3 was launched and the cells were sent into space to experience microgravity for 14 days. At the end of the flight, a fixative was applied to the cells, which preserved their state indefinitely for later analysis back on Earth.
Our samples landed in the remote plains of Kazakhstan. We quickly set to work on determining whether the osteoblasts or osteoclasts were affected by microgravity. Using the advanced fluorescent microscopes at the Centre for the Neurobiology of Stress at UTSC, we analyzed the morphology and inner architecture of the “astronaut” cells.
We observed a large defect in osteoblasts, meaning that less bone was being manufactured in the absence of weight than we typically see here on Earth. This alone could explain the dramatic bone loss observed in disuse osteoporosis. But to our surprise, we also saw an increase in ivory resorption pits made by the osteoclasts. In other words, more bone was being dissolved in conditions of weightlessness than it is on the ground. Now we know that astronauts are actually facing a double whammy of bone-cell defects. This could explain why they lose 1 percent of their bone mass every month they are in space.
This research is just one of the many avenues of inquiry my research team at UTSC is engaged in. Our hope is that one day, we will know enough about bone-wasting disorders to help prevent, treat and cure them. Until then, we will continue to come up with new ways to study the bone matrix—and, perhaps, new reasons to send narwhal tusks into space.
Rene Harrison is an associate professor of biological sciences at UTSC.