The Role of Schwann Cells in Regulation of Limbal Stem Cells During Corneal Maintenance and Healing
Seyed Kaveh Mirmoeini, MD, MASc1,2, Konstantin Feinberg, PhD3, Kiana Tajdaran, MD, MASc1, Jennifer J Zhang, MD, PhD4, Tessa Gordon, PhD4 and Gregory H Borschel, MD5, (1)University of Toronto, Toronto, ON, Canada, (2)The Hospital for Sick Children, Toronto, ON, Canada, (3)Hospital for Sick Children, Toronto, ON, Canada, (4)Division of Plastic and Reconstructive Surgery, The Hospital for Sick Children, Toronto, ON, Canada, (5)Division of Plastic and Reconstructive Surgery, The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada
Background: Corneal nerves play a crucial role in maintaining corneal health, which includes regulation of activity of limbal stem cell(LSC). Their loss leads to neurotrophic keratopathy(NK), with corneal ulceration, scarring, and ultimately, blindness. Using a Transgenic mouse we have identified a highly prominent limbal presence of the nerves-ensheathing Schwann cells(SC). This finding is the base of our hypothesis that SCs, via paracrine interaction with LSC, play a key role in corneal epithelial maintenance and healing.
Aims: 1) Define the role of SCs in corneal healing 2) Determine the paracrine interaction between the limbal SCs and LSC.
Methods: 1) Local corneal ablation of SCs was induced in a genetically modified mouse where topical application of tamoxifen induced SCs apoptosis. Corneal epithelium was then removed with an Amoils brush under anesthesia and fluorescein was used to assess healing over 4 days. Topical application of the media collected from in-vitro cultured rat SCs(SCCM) was used as a gain of function control. 2) We performed single-cell expression analysis of 10,000 cells derived from dissociated rat limbus with droplet-based high throughput 10x Genomics to identify ~3000 genes. We used the data to predict possible ligand-receptor interactions between the limbal SCs and LSC.
Results: 1) Ablation of SCs impaired corneal wound healing in mouse cornea, suggesting involvement of SC in innervation-dependent corneal epithelial recovery. Topical application of SCCM was potent in mediating corneal wound healing SCs-ablated corneas. 2) Genomic analysis suggested presence of paracrine crosstalk between SCs and LSCs, and relevant downstream intracellular signaling events in LSCs. The latter included activation of Notch signaling and VEGF-mediated cell migration, and inhibition of apoptosis. Further expression analysis comparing between limbal region of healthy and wounded corneas indicated significant changes in the expression of jag1, lgals3, and ptn genes by SCs. All mentioned above genes could potentially play a role in corneal recovery.
Conclusion: Our findings i) describe the presence of a high volume of SCs at limbus, located in close spatial vicinity to LSCs, ii) demonstrate the importance of the limbal SCs for corneal epithelial recovery and iii) suggest the presence of paracrine SC-LSC interaction that may be responsible for the limbal nerves-mediated activation of LSCs during homeostasis or the epithelial recovery after injury. These findings potentially anticipate new avenues for treating NK.
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