Project description:For decades, it has been well accepted that corneal epithelial stem cells and their immediate progeny, the early transit amplifying (eTA) cells, reside in the limbal epithelial basal layer. Activation of quiescent stem/eTA cells is required for proper re-epithelialization during wound healing. The molecular profile of activated stem/eTA cells remains unclear because of difficulties in obtaining discrete cell populations for analyses. Single cell RNA sequencing (scRNA-seq) technology can profile the transcriptome at a single cell level, providing information on how stem/eTA cell activation is regulated. Using this technology, we report that ACE2, a key component in the renin-angiotensin system (RAS), functions as a negative regulator of stem/eTA activation. Methods: Mouse corneal epithelium was exposed to 1M NaOH for 30s or mechanically removed with a diamond burr. Corneas were processed for scRNA-seq and data was analyzed using R with a Seurat package. Limbal epithelial cell proliferation was assessed using BrdU incorporation. RT-qPCR, western blotting and immunostaining were conducted to determine the change of gene expression. Results: ACE2 was predominantly expressed in the stem cell-enriched limbal basal epithelium. scRNA-seq combined with GO analysis suggested that ACE2 was involved in limbal stem/eTA cell proliferation. Interestingly, immunostaining and RT-qPCR indicated that ACE2 expression was reduced following corneal injuries. Reduction in ACE2 promoted proliferation in human limbal epithelial cell culture as well as in mouse limbal epithelium after corneal epithelial debridement. Significantly, the negative effect of ACE2 on proliferation was not reversed following treatment with the angiotensin II receptor blocker losartan, indicating that the function of ACE2 in limbal epithelium is independent of RAS. scRNA-seq also revealed that reduction of ACE2 caused activation of the TGFA/EGFR pathway, which reduced expression of Lcn2. Lcn2 is a negative regulator of proliferation in a variety of cells. Inhibition of EGFR or overexpression of Lcn2 reversed the increased proliferation in limbal epithelial cells lacking ACE2. Conclusion: Our findings strongly support the idea that in response to corneal injury, ACE2 is downregulated, which results in the activation of stem/eTA cell proliferation via a novel TGFA/EGFR/Lcn2 signaling pathway in an angiotensin-independent way.

Project description:Limbal stem cells (LSCs), known as corneal epithelial stem cells, are located at the basal epithelial layer of the corneal limbus and serve an important function in maintaining the homeostasis of the corneal epithelium. Several putative molecular markers of LSCs have been previously identified. However, the specificity of these markers remains largely controversial. To address this gap in the current understanding of LSCs, we performed a transcriptome profiling of heterogeneous corneal limbal basal cells using single-cell transcriptomics technology to identify LSCs and their exclusive markers. We isolated limbal basal cells from two young donors, constructed scRNA-seq libraries, generated RNA-sequencing data using the 10x Genomics platform, and then finally obtained the transcriptome of about 18,000 individual single-cells using Cell ranger (https://10xgenomics.com). Next, we performed quality control, filtering and data integration using Seurat package (https://satijalab.org/seurat), about 16,400 cells were retained for further downstream analysis such as dimensional reduction, unsupervised clustering, and Differentially expressed gene selection, trajectory analysis and visualization. We identified 11 unique clusters of cells assigned to a putative cell type based on published known biomarkers for differentiation, proliferation and putative epithelial stem cells. As a results, we found 2 Terminally Differentiated Cell (TDC), 3 Post-Mitotic Cell (PMC), 1 Transient Amplifying Cell (TAC), 2 Limbal Progenitor Cell (LPC), Putative Limbal Stem Cell (LSC) and 2 Melanocyte (MC) sub-cell type clusters. Furthermore, we confirmed the trajectory order of LSC differentiation for 9 clusters using Pseudotemporal and Functional PCA analysis. Lastly, we validated each assigned cell subtypes and determined their location in human corneal limbus tissue with 9 markers using RNAscope We were able to reveal the heterogeneity of corneal limbal basal epithelium by defining novel dynamic trajectories for cell types in a pseudotemporal manner. This approach allowed us to identify the distinct clusters of LSCs and progenitors with exclusively expressed markers, and might apply for translational research on regenerating a normal corneal epithelium and restoring vision.

Project description:Limbal stem cells including epithelial and stromal/Mesenchymal stem cells that contribute to sustained corneal homeostasis, maintain their ability to act as self-renewal progenitor cells by virtue of their limbal niche and intercellular communication. Extracellular vehicles (EVs), including exosomes (Exos), are important paracrine mediators through their cargo transfer for intercellular communication in various stem cell niches. Previously we have shown the differential cargos and regulatory roles of limbal stromal cell (LSC)-derived Exos, in limbal epithelial cells (LEC) in normal (N) and diabetic (DM) limbal niche. In the present study, to have a comprehensive knowledge of reciprocal LEC-LSC crosstalk, we investigated the proteomics and miRNA profile of exosomes derived from LEC and their regulatory roles in LSC in N and DM limbus. Our study showed wound healing and proliferation rates in primary N-LSC were significantly enhanced upon treatment by normal LEC-derived Exos (N-Exos), but not by diabetic Exos (DM-Exos). Further, N-Exos treated LSC showed downregulation of keratocyte markers, ALDH3A1 and lumican, but not keratocan, and upregulation of MSC markers, CD105, CD90, and CD73 compared to the DM-Exos treated LSC. Using next generation sequencing (NGS) and proteomics analysis, we revealed some miRNAs and proteins in the Exos that affect the cellular crosstalk and the function of the cornea. We also documented differences in DM vs. normal LEC-derived Exo’s cargos. Overall, DM-Exos have less effect on LSC proliferation, wound healing, and stem cell maintenance than N-Exos, likely by transferring their cargo proteins and/or regulatory miRNAs targeting cell cycle, ERK/MAPK, TGF-β, EMT, PI3K-Akt-mTOR signaling molecules. This suggests that the small RNA and protein cargo differences in DM vs. N LEC-derived Exos could contribute to the disease state. Our study revealed a complex contribution of Exos to health and diabetic state of corneal homeostasis and suggests the potential of EV therapeutics for diabetic cornea regenerative medicine

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