Abstract
Purpose :
The trigeminal ganglion (TG) plays a pivotal role in eye diseases like neurotrophic and herpes keratitis. Despite the development of multiple mouse models to explore TG physiology and pathology, the understanding of mouse TG anatomy remains unclear, which has impacted interpretations of many datasets. Further, the identity of cornea-innervating neurons is limited given that genomic classifications focus on the entire TG rather than corneal neurons. Therefore, we conducted an investigation aimed at clarifying TG anatomy while also classifying cornea-innervating neurons using proteomic and genomic assays.
Methods :
We examined TG anatomy in female and male C57BL/6 mice (n=20) by tracing ophthalmic, maxillary, and mandibular divisions and comparing them with human structures. We used intrastromal injections of Fast Blue or Wheat Germ Agglutinin to retrograde label cornea afferents. Back-labeled TG neurons were either handpicked and analyzed via single-cell RNAseq (Smartseq V2) or whole-mount TGs were analyzed via immunohistochemistry (IHC) study for neuropeptides (CGRP, SP), purinoceptors (P2X3), and ion channels (Trpv1).
Results :
The anatomy of the mouse TG and its associated cranial structures significantly differs from that of humans. While only the ophthalmic and maxillary divisions traverse the human orbital cavity, mice exhibit the passage of all three divisions, including the complete divisions of the ophthalmic and maxillary, and the anterior subdivision of the mandibular division. Retrograde tracing identified a corneal niche near the Sphenoid body housing 112 neurons (n=112±9). scRNAseq revealed 9 clusters of neurons with anchor genes consisting of calca, trpv1, peizo1/2, trpm8, and others. An IHC survey of the corneal neuron niche identified that 37% of neurons expressed P2X3, 58% expressed Trpv1, 21% expressed CGRP, and 22% expressed SP. Substantial overlap of markers was noted as illustrated by 55% of SP+ neurons co-expressing CGRP, 94% of CGRP+ neurons co-expressed Trpv1+, and only 40% of SP+ neurons expressed Trpv1.
Conclusions :
Our study clarifies unique mouse TG anatomy, correcting past misinterpretations. Using optimized tracing methods, we precisely located the corneal niche, characterizing its neurons via scRNA seq and IHC. These data pave the way for future investigations into corneal neuron functions and potential therapeutic targets.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.