Scientists have discovered a hormone that stops chronic back pain

Parathyroid hormone (PTH) is produced by the parathyroid glands and is involved in regulating calcium levels and renewing bone tissue. Its synthetic analogues are already used in the treatment of osteoporosis. It was also previously suggested that such therapy may reduce bone-related pain, but the exact mechanism of this effect remained unclear.

To study this question, the scientists conducted experiments in three mouse models that mimic common causes of spinal degeneration: age-related changes, surgically induced instability and genetic predisposition. This made it possible to assess the impact of degeneration on both the condition of bone tissue and nerve growth. The animals were given PTH daily for two weeks to two months, while the control group received an inactive solution. The researchers then analyzed the spinal tissue using high-precision imaging and tested the response to pressure, heat and movement.

After one to two months of therapy, mice treated with PTH showed marked improvement in the condition of their vertebral endplates, the thin layers that separate the intervertebral discs from the vertebrae themselves. These structures have become stronger and more stable. At the same time, the animals’ sensitivity to pain decreased: they tolerated pressure better, responded more slowly to heat and were more active compared to the control group. Scientists also examined nerve fibers in the spine. When damaged, pain nerves often grow into areas where they do not belong, increasing pain. The study showed that PTH therapy significantly reduced the number of such abnormal nerve fibers, which was confirmed by the markers PGP9.5 and CGRP.

Further analysis helped to identify the mechanism of this effect. PTH stimulates osteoblasts, the cells that form bone, to produce the protein Slit3. This protein acts as a signal that “repels” growing nerve fibers and prevents them from penetrating sensitive areas of the spine.

Laboratory experiments confirmed that Slit3 indeed limits the growth of nerves: under its influence, their processes became shorter and less capable of penetrating tissue. At the same time, if Slit3 was removed from osteoblasts in mice, PTH stopped suppressing the growth of nerve fibers and did not improve pain. The scientists also discovered the FoxA2 protein, which regulates the production of Slit3 in response to PTH, which helps to better understand how hormonal signals influence the behavior of the nervous system.