Scientists have discovered that a common bone hormone may ease chronic back pain by blocking the growth of pain-triggering nerves in the spine. This approach could lead to entirely new treatments that target the source of pain, not just the symptoms.
Low back pain (LBP) is one of the most widespread health issues globally, affecting people across all age groups and putting significant strain on healthcare systems. For many, the pain becomes long-lasting, disrupting work, sleep, and everyday life. In most cases, however, doctors cannot pinpoint a clear structural cause, which makes effective long-term treatment challenging.
A new study published in Volume 14 of the journal Bone Research suggests that a hormone-based treatment could help ease chronic back pain by reducing abnormal nerve growth within damaged spinal tissue. The research was led by Dr. Janet L. Crane from the Center for Musculoskeletal Research, Department of Orthopedic Surgery, Johns Hopkins University School of Medicine, United States. The findings offer new insight into how bone cells may influence pain signaling in degenerating spines.
“During spinal degeneration, pain-sensing nerves grow into regions where they normally do not exist. Our findings show that parathyroid hormone can reverse this process by activating natural signals that push these nerves away,” says Dr. Crane.
Understanding Parathyroid Hormone and Its Effects
Parathyroid hormone (PTH) is naturally produced by the parathyroid glands and plays a key role in regulating calcium levels and bone remodeling. Synthetic versions of PTH are already used to treat osteoporosis. Earlier research hinted that these treatments might also reduce bone-related pain, but the underlying biological mechanism was not well understood.
To explore this further, the research team used three mouse models that replicate common causes of spinal degeneration: natural aging, surgically induced mechanical instability, and genetic susceptibility. These models allowed scientists to study how degeneration affects both bone structure and nerve growth. The mice received daily injections of PTH for periods ranging from two weeks to two months, while control animals were given inactive solutions. Researchers then examined spinal tissue using high-resolution imaging and measured responses to pressure, heat, and movement.
Improved Spine Structure and Reduced Pain Sensitivity
After one to two months of treatment, mice treated with PTH showed clear improvements in their vertebral endplates, the thin layers that separate spinal discs from vertebrae. These structures became denser and more stable. At the same time, treated mice showed reduced sensitivity to pain, tolerated pressure better, responded more slowly to heat, and displayed increased activity compared to untreated animals.
How PTH Reduces Pain-Causing Nerve Growth
The researchers also examined nerve fibers within the spine. In damaged tissue, pain-sensing nerves often extend into areas where they do not typically belong, increasing discomfort. The study found that PTH treatment significantly reduced these abnormal nerve fibers, based on markers such as PGP9.5 and CGRP.
Further analysis revealed the underlying mechanism. PTH stimulated osteoblasts, the cells responsible for building bone, to produce a protein called Slit3. This protein acts as a guidance signal that repels growing nerve fibers, preventing them from entering sensitive regions of the spine.
Slit3 Protein and the Molecular Pathway
Laboratory experiments confirmed that Slit3 directly limits nerve growth. When nerve cells were exposed to Slit3, their extensions became shorter and less invasive. In contrast, when researchers removed Slit3 from osteoblasts in mice, PTH no longer reduced nerve growth or improved pain responses. The team also identified a regulatory protein called FoxA2 that helps trigger Slit3 production in response to PTH, offering deeper insight into how hormonal signals influence nerve behavior.
What This Means for Future Back Pain Treatments
Although these findings come from animal studies, they may help explain why some patients receiving PTH-based treatments for osteoporosis report reduced back pain. The researchers note that further studies in humans are needed before this approach can be used clinically.
“Our study suggests that PTH treatment of LBP during spinal degeneration may reduce aberrant innervation, laying the foundation for future clinical trials exploring the efficacy of PTH as a disease-modifying and pain-relief treatment for spinal degeneration,” concludes Dr. Crane.
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