A common bone hormone used to treat osteoporosis may hold the key to stopping chronic back pain at its source by preventing pain-sensing nerves from invading damaged spinal tissue. Scientists at Johns Hopkins University discovered that parathyroid hormone (PTH) can reverse abnormal nerve growth in degenerating spines, potentially offering a disease-modifying treatment rather than just symptom relief .

What Makes This Discovery Different From Current Back Pain Treatments?

Most back pain treatments focus on managing symptoms, but this research targets the underlying biological cause. Low back pain (LBP) affects people across all age groups globally and often becomes chronic, disrupting work, sleep, and daily life. The challenge is that doctors frequently cannot pinpoint a clear structural cause, making long-term treatment difficult. This new approach changes that equation by addressing how pain actually develops in degenerating spines .

During spinal degeneration, pain-sensing nerves abnormally grow into regions where they normally do not exist.

"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," stated Dr. Janet L. Crane.

Dr. Janet L. Crane, Associate Professor of Pediatrics and Director of the Pediatric Bone Health Program, Johns Hopkins University School of Medicine

How Did Researchers Test This Hormone's Effects?

The research team, led by Dr. Crane at Johns Hopkins University School of Medicine, used three different 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 in realistic conditions .

Mice received daily injections of PTH for periods ranging from two weeks to two months, while control animals received inactive solutions. Researchers then examined spinal tissue using high-resolution imaging and measured responses to pressure, heat, and movement to assess pain sensitivity .

What Were the Key Results?

After one to two months of PTH treatment, the results were striking. Mice treated with the hormone 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 measurable improvements across multiple pain measures :

• Pressure Tolerance: Treated mice tolerated pressure better than untreated animals, indicating reduced pain sensitivity to mechanical stress.
• Heat Response: Treated mice responded more slowly to heat, suggesting decreased pain signaling in response to thermal stimuli.
• Physical Activity: Treated mice displayed increased activity compared to untreated animals, showing improved functional capacity and reduced pain-related limitations.

The most important finding involved the abnormal nerve fibers themselves. PTH treatment significantly reduced these pain-causing nerves based on specific markers such as PGP9.5 and CGRP, which are indicators of pain-sensing nerve growth .

What Is the Biological Mechanism Behind This Effect?

The researchers uncovered the precise biological pathway explaining how PTH reduces pain-causing nerve growth. 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. Laboratory experiments confirmed that Slit3 directly limits nerve growth; when nerve cells were exposed to Slit3, their extensions became shorter and less invasive .

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. When researchers removed Slit3 from osteoblasts in mice, PTH no longer reduced nerve growth or improved pain responses, confirming that Slit3 is essential to the hormone's pain-relieving effects .

How to Understand What This Means for Future Treatments

• Current Clinical Use: Synthetic versions of PTH are already approved and used to treat osteoporosis, meaning the hormone is already safe for human use and well-studied in clinical settings.
• Dual Benefit Potential: Some patients receiving PTH-based treatments for osteoporosis have reported reduced back pain, which may now be explained by this nerve-blocking mechanism discovered in the research.
• Next Steps Required: Although these findings come from animal studies, further research in humans is needed before this approach can be used clinically as a back pain treatment.

The research was published in Volume 14 of the journal Bone Research and was supported by the U.S. Department of Health and Human Services National Institute on Aging.

"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," concluded Dr. Crane.

Dr. Janet L. Crane, Associate Professor of Pediatrics, Johns Hopkins University School of Medicine

This discovery represents a significant shift in how scientists think about chronic back pain. Rather than simply masking pain signals, PTH appears to prevent the biological changes that cause pain in the first place. If human trials confirm these findings, it could offer patients a fundamentally new way to address one of the most common health problems affecting people worldwide.