Protein Revs Up Bone Stem Cells; Points Toward Future Osteoporosis Drug

Take a moment to feel your arm and wrist bones. They’re a lot more like solid rock than the soft stretchy skin that covers them. But bone is very much a living tissue continually being broken down and built back up in a process called bone remodeling. In people with osteoporosis, this balance tips toward bone breakdown leading to more porous, fragile bones with increased risk of fractures. An estimated ten million people in the U.S. have osteoporosis accounting for 1.5 million fractures annually at a cost of $17 billion in medical care, not to mention the emotional toll of these often debilitating and even life threatening injuries.

Fluorescent imaging mouse spines. Treatment with NELL-1 (right) shows greater bone formation compared to untreated mice (left). Credit: Broad Stem Cell Research Center

Fluorescent imaging of mouse spines. Treatment with NELL-1 (right) shows greater bone formation compared to untreated mice (left). Credit: Broad Stem Cell Research Center

This week a CIRM-funded research team at UCLA reported in Nature Communications that injection of a human protein called NELL-1 into the blood of mice with osteoporosis-like symptoms tipped the balance back toward bone formation. In a large animal study, delivering NELL-1 directly into the spine also led to increased bone volume. In a university press release, co-senior author Kang Ting spoke of his hopes that these results open up a new therapeutic avenue for treating osteoporosis and other ailments:

“Our end goal is really to harness the bone forming properties of NELL-1 to better treat patients with diverse causes of bone loss, from trauma in military personnel to osteoporosis from age, disease or very weak gravity, which causes bone loss in astronauts.”

In petri dish experiments leading up to these animal results, the research team showed that NELL-1 acts by increasing the specialization of mesenchymal stem cells – a type of adult stem cell found in the bone marrow and fat – into osteoblasts, the cells responsible for building new bone. At the same time, NELL-1 reduced the generation of osteoclasts, the cells responsible for the breakdown, or resorption, of bone. This dual action of NELL-1 explains how it improved the osteoporosis-like symptoms in the animals. Check out this fascinating animation for a visual description of osteoblasts and osteoclasts:

Many of the other molecules that promote bone growth aren’t as efficient as NELL-1: while they increase osteoblast numbers they also increase osteoclasts to some extent. For example, Fosamax is a drug prescribed to women with osteoporosis to help build stronger bones but long-term use has been associated with even more brittle bones and fractures. So this finding with NELL-1 sets it apart and hints at fewer side effects as a therapeutic. Still, it’s known to play a role in brain, cartilage, and blood vessel development so careful studies of non-bone effects are needed as the team pursues a road to the clinic.

For more information about CIRM-funded projects related to osteoporosis, visit our online fact sheet.

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