New Insight Into the Neuroimmune Interplay In Pseudomonas aeruginosa Keratitis

The miR-183/96/182 cluster (miR-183C) is required for normal functions of sensory neurons (SN) and various immune cells, including myeloid cells (MC). This research aims to reveal the roles of miR-183C of SN in the interplay of corneal sensory nerves (CSN) and MC during Pseudomonas aeruginosa (PA) keratitis.

Methods

Double-tracing mice with SN-specific (SNS) conditional knockout of miR-183C (CKO) and age-and sex-matched wild type (WT) controls were used. Their CSN are labeled with Red Fluorescent Protein (RFP); MC with Enhanced Green (EG)FP. The left corneas were scarified and infected with ATCC19660 PA. Corneal flatmounts were prepared at 3, 6, and 12 hours post-infection (hpi) and 1, 3, and 5 days (d)pi for confocal microscopy. Myeloperoxidase (MPO) assay and plate count were performed at 1 dpi.

Results

In WT mice, CSN began to degenerate as early as 3 hpi, starting from the fine terminal CSN in the epithelial/subepithelial layers, most prominently in the central region. By 1 dpi, CSN in the epithelium/subepithelial layer were nearly completely destroyed, while stromal nerves persisted. From 3 dpi, CSN were obliterated in both layers. In CKO vs WT mice, CNS followed a slightly slower pace of degeneration. CSN density was decreased at 3 and 6 hpi. However, at 3 dpi, residual large-diameter stromal CSN were better preserved. MC were decreased in the central cornea at 3 and 6 hpi, but increased in the periphery. Both changes were more prominent in CKO vs WT mice. At 12 hpi, densely packed MC formed a ring-shaped band circling a “dark” zone nearly devoid of MC, colocalizing with CSN most degenerated zone in the central cornea. In CKO vs WT, the ring center was larger with fewer MC. At 1 dpi, the entire cornea was filled with MC; however, MC density was lower in CKO mice. An MPO assay showed decreased neutrophils in PA-infected cornea of CKO mice. This led to a decreased severity of PA keratitis at 3 dpi.

Conclusions

This double-tracing model reveals the interplay between CSN and MC during PA keratitis with greater clarity, providing new insights into PA keratitis. CSN-imposed modulation on innate immunity is most impressive within 24 hours after infection. Functionally, the miR-183C in CSN modulates CSN density and the dynamics of MC fluxes-a neuroimmune interaction in display.