TrkA+ Neurons Induce Pathologic Regeneration After Soft Tissue Trauma.

Area of Science:

• Regenerative Medicine
• Orthopedics
• Neuroscience

Background:

• Heterotopic ossification (HO) is abnormal bone growth in soft tissues after trauma, causing pain and mobility loss.
• Nerve growth factor (NGF)-responsive TrkA-expressing nerves invade trauma sites, a key step for HO development.
• Understanding the role of nerve signaling in HO is crucial for developing new treatments.

Purpose of the Study:

• To investigate the effect of a partial TrkA agonist, Gambogic amide (GA), on peritendinous HO after extremity trauma.
• To explore the link between TrkA signaling, nerve invasion, and ectopic bone formation.
• To assess the potential of modulating TrkA signaling for preventing trauma-induced HO.

Main Methods:

• Mice underwent a burn/tenotomy model to induce HO, with or without systemic GA treatment.
• Injury sites were analyzed using radiographic imaging, histology, and immunohistochemistry.
• Single-cell RNA sequencing was employed to examine neurotrophin signaling activity.

Main Results:

• HO induction increased neurotrophin signaling activity and TrkA-expressing nerve invasion at injury sites.
• TrkA agonism with GA resulted in increased hyper-innervation and cartilage antigen expression.
• GA treatment led to a shift in signaling from FGF to TGFβ and ultimately increased HO formation.
• Increased hyper-innervation correlated with enhanced vascular ingrowth and HO development.

Conclusions:

• TrkA agonism exacerbates, rather than prevents, heterotopic ossification following extremity trauma.
• Injury site hyper-innervation, driven by TrkA signaling, promotes vascular ingrowth and ectopic bone formation.
• Modulating TrkA signaling by inhibition may be a promising strategy to prevent trauma-induced HO and enhance tissue regeneration.