Chronic stress worsened bone loss in mice after ovary removal

In an animal experiment, researchers studied ovariectomised mice—mice whose ovaries had been removed—with osteoporosis, a condition that weakens bones. After eight weeks of chronic stress, the mice showed anxiety- and depression-like behaviour and worse osteoporosis. Bone tissue contained more cathepsin K, a protein-cutting enzyme, alongside markers of inflammation and cell death. Markers also indicated reduced autophagy, the process by which cells break down and recycle their components. E64d, an inhibitor of protein-cutting enzymes, reversed these changes.

The researchers also exposed lab-grown mouse cells resembling bone-forming cells to serum, the fluid left after blood clots, from stressed mice. This reduced cell viability, their ability to stay alive. Inhibiting cathepsin K restored autophagy and reduced cell injury. The researchers concluded that stress accelerated bone loss at least partly through cathepsin K activation and reduced autophagy.