Abstract
Purpose :
Corneal plasmacytoid dendritic cells (pDCs) are closely associated with corneal nerves, suggesting their potential role in neuroimmune crosstalk. We have recently demonstrated that local depletion of corneal pDCs results in decreased corneal nerve density. Herein, we aim to characterize the neurodegenerative mechanisms of corneal nerves that are observed with local pDC depletion.
Methods :
Adult BDCA2-DTR mice, which express the diphtheria toxin (DT) receptor under control of the BDCA2 promoter were used for the selective depletion of pDCs. DT (30 ng/eye) or normal saline for controls were administered subconjunctivally at day 0 and repeated every 2 days thereafter for continuous pDC depletion. At days 1 and 3, corneas were excised and underwent immunofluorescent staining for βIII-tubulin to assess corneal nerve degeneration by confocal microscopy. Nerve density was measured using NeuronJ plugin for ImageJ. Trigeminal ganglions (TGs) were excised and enzymatically digested for neuronal isolation. RNA isolated from TG neurons was used for RT-qPCR for candidate neurodegenerative markers Caspase-3, Caspase-6, DR6, JNK, Sarm-1, MycBP2, Tau, IKKβ, Calpain-1 and Calpain-2.
Results :
Local depletion of pDCs led to a degeneration of stromal and subbasal corneal nerve axons. By day 1, the corneal nerve density was significantly reduced centrally (80.1%), and peripherally (80.8%), with a greater effect at day 3 (14.6% and 15.5%) normalized to control (p < 0.01). No significant alteration of neurodegenerative markers was observed in TG on day 1, following pDC depletion. However, pDC depletion led to significant changes in TG on day 3 following pDC depletion, judged by higher levels of neurodegenerative markers Tau (4.72-fold increase in the pDC depleted group, p <0.01) and Calpain-1 (3.31-fold increase in the pDC depleted group; p <0.05). Taken together, the data suggest that the pDC depletion results in alterations to both corneal nerves as well as the TG, likely in a calpain-mediated manner.
Conclusions :
This study provides new insights into neuroimmune crosstalk, revealing the crucial role for pDCs to support neuronal health and maintenance in the cornea and TG. Depletion of pDCs led to a degeneration of the corneal nerve axons and a significant upregulation in neurodegenerative markers in the TG, which may be relevant for ocular diseases associated with nerve loss.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.