Background & Aims

Fibrous dysplasia (FD) is a rare mosaic bone disease arising from embryogenic gain-of-function mutations in GNAS and characterized by areas of abnormal fibro-osseous tissue that results in bone deformities, fractures, and pain, which can be debilitating. Clinical studies suggest the presence of both nociceptive- and neuropathic-like components of the pain phenotype in FD patients (Spencer, 2022; Golden, 2023). However, despite the detrimental impact of the pain on these patients, there is limited knowledge of the underlying mechanisms, and effective treatment options are not available. As such, there is a great need in the FD field to identify mechanisms and effective treatment options for FD pain. Therefore, the aim of this study was to identify peripheral and central nociceptive mechanisms in a translationally relevant mouse model of FD.

Methods

A mosaic-like, doxycycline-inducible transgenic mouse model (Zhao, 2018) was used in this study. A Cre-LoxP system under the Prrx1 promoter (bone marrow stromal cells) allows the expression of the causative G?sR201C mutation of FD through a tetracycline-inducible system. Male and female mice (FD and control) were given doxycycline for two and three weeks, respectively. Longitudinal x-ray imaging and end-stage histological staining of the bone confirmed FD development. Nociceptive behavior was assessed by grid hanging, burrowing, wheel running, and cage activity (Tecniplast Digital Ventilated Cages). Morphine (10mg/kg) and ibuprofen (30mg/kg) were administered to female mice before grid hanging and burrowing, respectively. Using immunohistochemistry, bones were analyzed for changes in innervation and vascularization, dorsal root ganglions (DRGs) were analyzed for evidence of nerve damage and the spinal cord (SC) was analyzed for changes in neuropeptide expression and glial cells.

Results

X-ray imaging confirmed FD model development and FD mice displayed deficits in grid hanging, burrowing, wheel running, and cage activity. Mice treated with ibuprofen maintained their burrowing behavior during the study, demonstrating significantly increased burrowing compared to the vehicle-treated mice. FD mice treated with morphine performed significantly better in grid hanging than the vehicle-treated mice on day 11, but not day 18. FD mice (male and female) ran significantly less than the control mice and were significantly less active in their cages. Histological analyses demonstrated that FD lesions in the tibio-femoral region were highly innervated (sensory and sympathetic nerve fibers) and vascularized in female and male mice. In DRGs from male mice (but not female), increased activating transcription factor-3 (ATF3) and tyrosine hydroxylase (TH) staining was observed. There was no difference in SC glial cell presence and neuropeptide expression between FD and control mice.

Conclusions

This study is the first to characterize a nociceptive phenotype in a model of FD. Grid hanging and burrowing could be reversed when analgesics were administered, demonstrating that the behavioral deficits were due, in part, to nociceptive changes. Within FD lesions, sensory and sympathetic nerve fibers and blood vessels were present, which may contribute to nociception. ATF3 and TH expression in DRGs has been associated with nerve damage – a feature of peripheral neuropathy, indicating gabapentoids as a potential treatment. There were no significant differences in SC glial cell presence and neuropeptide expression. Further studies are needed to determine the role of the central nervous system in FD pain. This study has demonstrated that nociceptive mechanisms such as nerve growth in FD lesions, nerve damage, and inflammation may contribute to FD nociception. Additionally, this model has the potential to be used to determine other mechanisms and test novel therapeutics for FD pain.

References

Zhao, X. F., et al. (2018). “Expression of an active G alpha(s) mutant in skeletal stem cells is sufficient and necessary for fibrous dysplasia initiation and maintenance.” Proceedings of the National Academy of Sciences of the United States of America 115(3): E428-E437.

Spencer, T. L., et al. (2022). “Neuropathic-like Pain in Fibrous Dysplasia/McCune-Albright Syndrome.” J Clin Endocrinol Metab 107(6): e2258-e2266.

Golden, E., et al. (2023). “Phenotyping Pain in Patients with Fibrous Dysplasia/McCune-Albright Syndrome.” J Clin Endocrinol Metab.

Presenting Author

Chelsea Hopkins

Poster Authors

Chelsea Hopkins

PhD

University of Copenhagen

Lead Author

E-mail

Anne-Marie Heegaard

University of Copenhagen

Lead Author

E-mail

Luis Fernandez de Castro

PhD

National Institutes of Health

Lead Author

E-mail

Julie Benthin

MSc

University of Copenhagen

Lead Author

E-mail

Marta Diaz-delCastillo

PhD

University of Aarhus

Lead Author

E-mail

Alison Boyce

MD

National Institutes of Health

Lead Author

E-mail

Ruth Elena Martinez Mendoza

Universidad Autónoma de Tamaulipas Reynosa

Lead Author

E-mail

Juan Antonio Vazquez Mora

MSc

Universidad Autónoma de Tamaulipas Reynosa

Lead Author

E-mail

Michael Collins

MD

National Institutes of Health

Lead Author

E-mail

Juan Miguel Jimenez Andrade

PhD

Universidad Autónoma de Tamaulipas Reynosa

Lead Author

E-mail

Topics

  • Models: Musculoskeletal