Endothelial-Stromal Communication in Murine and Human Corneas

Posterior Limbal Mesenchymal Stromal Cells Promote Proliferation and Stemness of Transition Zone Cells: A Novel Insight Into Corneal Endothelial Rejuvenation

Purpose

Progenitors for the corneal endothelium have been identified in the transition zone (TZ), but their cellular interactions remain undefined. Posterior limbal mesenchymal stromal cells (P-LMSCs) may support TZ cells in the posterior limbus. This study aims to characterize P-LMSCs and investigate their effects on TZ cells.

Methods

Human P-LMSCs and TZ cells were isolated by explant culture. P-LMSCs were characterized by comparing with anterior limbal mesenchymal stromal cells (A-LMSCs) using immunocytochemistry. TZ cells were cocultured with P-LMSCs in a Transwell, with TZ cell and A-LMSC coculture and TZ cells only as the control groups. The proliferation and wound healing capacity of TZ cells were assessed by EdU assay and scratch wound assay. Colony forming assay, droplet digital PCR, Western blotting, and immunocytochemistry were used to compare the stemness of TZ cells. The effect of P-LMSC conditioned medium on endothelial wound healing was evaluated in organ-cultured mouse corneas. Endothelial regeneration was measured by trypan blue staining.

Results

P-LMSCs expressed similar proteins (vimentin, Nestin, TRA-1-60, Oct3/4) as A-LMSCs. TZ cells cocultured with P-LMSCs had significantly higher proliferation, wound healing speed, and colony-forming efficiency than TZ cells only. TZ cells supported by P-LMSCs expressed higher levels of stem/progenitor markers (Nestin, Sox9, AP-2α, Pitx2) than the control groups. P-LMSC conditioned medium stimulated regeneration of mouse corneal endothelium from the TZ region.

Conclusions

The proliferation and stemness of TZ cells were enhanced by P-LMSCs in both cell and organ culture models. Our study provides an innovative strategy for corneal endothelial rejuvenation.

Composition, structure and function of the corneal stroma

No other tissue in the body depends more on the composition and organization of the extracellular matrix (ECM) for normal structure and function than the corneal stroma. The precise arrangement and orientation of collagen fibrils, lamellae and keratocytes that occurs during development and is needed in adults to maintain stromal function is dependent on the regulated interaction of multiple ECM components that contribute to attain the unique properties of the cornea: transparency, shape, mechanical strength, and avascularity. This review summarizes the contribution of different ECM components, their structure, regulation and function in modulating the properties of the corneal stroma. Fibril forming collagens (I, III, V), fibril associated collagens with interrupted triple helices (XII and XIV), network forming collagens (IV, VI and VIII) as well as small leucine-rich proteoglycans (SLRP) expressed in the stroma: decorin, biglycan, lumican, keratocan, and fibromodulin are some of the ECM components reviewed in this manuscript. There are spatial and temporal differences in the expression of these ECM components, as well as interactions among them that contribute to stromal function. Unique regions within the stroma like Bowman's layer and Descemet's layer are discussed. To define the complexity of corneal stroma composition and structure as well as the relationship to function is a daunting task. Our knowledge is expanding, and we expect that this review provides a comprehensive overview of current knowledge, definition of gaps and suggests future research directions.

Extracellular matrix: The proteins that function throughout the body

The idea and meetings that planned this issue focused on extracellular matrix (ECM) started over 4 years ago. The invitations were sent to investigators over 2 years ago and manuscripts have been submitted, reviewed, and edited since the summer and fall of 2018. Most of the manuscripts were published in early view in 2019, and we are thrilled to share the final collection. This volume contains 6 reviews, 13 original research papers, and 4 remembrances. Marion (Emmy) Gordon and I organized the articles into seven topic areas, including ECM structure, genetics, and development; cancer; vascular structures and development; inflammation and wound healing; collagen in special structures; cornea and other ocular tissues; and extracellular vesicles. Anat Rec, 2020. © 2020 American Association for Anatomy.