Nerve Associated Macrophages in the Cornea are Maintained by IL-34 and are Involved in Mechanosensation

Abstract

Purpose : Macrophages (MF) play critical roles in innate immunity but are increasingly appreciated for their roles in the maintenance of tissue physiology, particularly with respect to their interactions with nerves. Certain MF populations, including microglia in the central nervous system as well as nerve associated MF (NAM) of the sciatic nerve in the peripheral nervous system, are dependent on IL-34, the alternate ligand for colony stimulating factor 1 receptor (CSF1R), signaling through which sustains these populations locally. However, the presence of these IL-34 dependent NAM populations in the cornea and their function remains unknown. Here we leverage the unique properties of the cornea, which is imbued with the densest sensory innervation in the periphery of the body and possesses a rich network of NAMs, to investigate the functional significance of IL-34 in corneal NAM populations.

Methods : Corneas from wild type (WT) and Il34 deficient (Il34^LacZ/LacZ) age matched adult mice were dissected and stained for a combination of F480, CD206, or Iba1 and Tuj1 to label MFs and nerves, respectively. Whole mount corneas were visualized using confocal microscopy and z-stacks of the central cornea were acquired. MF counts and nerve volume were calculated by rendering the signal from z-stacks as a surface using Imaris image analysis software. Additionally, corneal mechanosensation was evaluated in WT and Il34 deficient animals using Cochet-Bonnet esthesiometry.

Results : Il34 deficient animals, as compared to WT, yielded significantly reduced MF counts in the central cornea. The central cornea showed a decreased trend in nerve volume when comparing WT to Il34 deficient mice. Moreover, Il34 deficient mice had significantly reduced corneal mechanosensation compared to WT mice.

Conclusions : Collectively, our results suggest that corneal MFs are maintained in part through IL-34 signaling, and that a reduced number of corneal NAMs is correlated with decreased corneal mechanosensation.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.