Perineural Invasion Exhibits Traits of Neurodegeneration

Perineural invasion (PNI) frequently occurs in head and neck squamous cell carcinoma (HNSCC), which correlates with poor survival and induces intractable pain and numbness. There is no effective treatment for PNI or associated pain. To gain a better understanding of PNI at the molecular and cellular level, we produced an orthotopic, syngeneic mouse model of PNI by inoculating mouse oral cancer cells into the infraorbital nerve (ION), a nerve that is susceptible to cancer invasion in patients with HNSCC. Mice with PNI in the ION exhibited both evoked and spontaneous nociception and impaired oral function, mimicking human conditions. PNI resulted in a drastic reduction in the proportion and altered mechanical thresholds in mechanically sensitive trigeminal neurons; axon and myelin abnormalities, as well as phagocytic cells, were observed. The tumor bed is marked by CD4⁺ and CD8⁺ T cells, CD68⁺ cells, and F4/80⁺ macrophages, while CD4⁺, CD8⁺, and CD68⁺ immune cells can be found surrounding the nerve. The intraneural niche is predominantly marked by CD68 that does not overlap with F4/80 but instead overlaps with NF200 and MPZ and occasionally with DAPI, suggesting these are likely phagocytic macrophages or Schwann cells. Finally, our RNA sequencing pathway analysis in mouse and human HNSCC found perturbed pathways in neuroinflammation, mitochondrial dysfunction, and cellular metabolism. Additionally, ION-PNI exhibits nerve degenerative features with perturbed pathways that are observed in Alzheimer, Parkinson, and prion diseases. In conclusion, we report a novel, anatomically relevant in vivo model that could be used to study the cellular and molecular mechanisms of PNI-induced neuropathies. Importantly, we found that PNI resembles neurodegenerative diseases with features of altered sensory transduction and conduction, neuroinflammation, and mitochondrial dysfunction, which may underlie peripheral neuropathies, such as pain.