The human skeleton is made up of bone, cartilage, fat, nerves, blood vessels, and bone marrow. While the skeleton is usually strong and vibrant in youth, it changes considerably with age. Many people, especially women, experience demineralization of bone called osteoporosis. Most of us will suffer from painful, stiff, arthritic joints either from osteoarthritis or rheumatoid arthritis or both. While some of the diseases of bone and joints have specific treatments, none of them helps to restore bone and joints to their younger state. If one could reintroduce skeletal stem cells into the body, that could all change. Excitingly, researchers have recently isolated human skeletal stem cells from bone and other tissues.
At first glance, this breakthrough may not seem so surprising. One might wonder: didn’t we already have stem cells that form bone and cartilage? The answer is yes, but with an important caveat. Before researchers recently isolated human skeletal stem cells, the only stem cells that could be used to produce bone and cartilage were rather unpredictable. In addition to bone and cartilage, the mesenchymal stem cells that have been long used to form these tissues could also produce fat, muscle, fiberglass, blood vessel cells, and other tissues. In other words, the stem cells were broadly multipotent and, by extension, could not easily be used for a specific purpose, like mending bone or repairing an arthritic joint. That is why the recent discovery of these particular skeletal stem cells is so important.
The researchers isolated skeletal stem cells from various human tissues, mainly bone. They then used the skeletal stem cells to regrow bone and/or cartilage. Not only did the stem cells produce bone and cartilage in the first animal they tested, but they could retrieve stem cells from that animal and then cause bone to regrow in a second animal. This means that the skeletal stem cells have the capability of reproducing themselves.
The same researchers also discovered that when a skeleton is injured, such as in a bone fracture, the number of skeletal stem cells in that area increases dramatically. This makes sense since these cells are used to repair and regrow bone. It is also a promising result because it suggests that stem cells could be used to accelerate bone and joint healing in humans.
Scientists not directly involved in this research heralded this finding as “an extremely important advance.” However, they also acknowledge that more work needs to be done before skeletal stem cells can be routinely used in patients with orthopedic conditions. Nevertheless, these results are an exciting development in the field of stem cell research and orthopedics.