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Corneal transparency and avascularity are essential for vision. The avascular cornea transitions into the vascularized conjunctiva at the limbus. Here, we explore a limbal stromal cell sub-population that expresses ABCB5 and has mesenchymal stem cell characteristics. Human primary corneal stromal cells were enriched for ABCB5 by using FACS sorting. ABCB5+ cells expressed the MSC markers CD90, CD73, and CD105. ABCB5+ but not ABCB5− cells from the same donor displayed evidence of pluripotency with a significantly higher colony-forming efficiency and the ability of trilineage differentiation (osteogenic, adipogenic, and chondrogenic). The ABCB5+ cell secretome demonstrated lower levels of the pro-inflammatory protein MIF (macrophage migration inhibitory factor) as well as of the pro-(lymph)angiogenic growth factors VEGFA and VEGFC, which correlated with reduced proliferation of Jurkat cells co-cultured with ABCB5+ cells and decreased proliferation of blood and lymphatic endothelial cells cultured in ABCB5+ cell-conditioned media. These data support the hypothesis that ABCB5+ limbal stromal cells are a putative MSC population with potential anti-inflammatory and anti-(lymph)angiogenic effects. The therapeutic modulation of ABCB5+ limbal stromal cells may prevent cornea neovascularization and inflammation and, if transplanted to other sites in the body, provide similar protective properties to other tissues. [ABSTRACT FROM AUTHOR]

The limbus, the vascularized junction between the cornea and conjunctiva, is thought to function as a barrier against corneal neovascularization. However, the exact mechanisms regulating this remain unknown. In this study, the limbal epithelial stem cell (LESC) marker ABCB5 was used to investigate the role of LESCs in corneal neovascularization. In an ABCB5KO model, a mild but significant increase of limbal lymphatic and blood vascular network complexity was observed in developing mice (4 weeks) but not in adult mice. Conversely, when using a cornea suture model, the WT animals exhibited a mild but significant increase in the number of lymphatic vessel sprouts compared to the ABCB5KO, suggesting a contextual anti-lymphangiogenic effect of ABCB5 on the limbal vasculature during development, but a pro-lymphangiogenic effect under inflammatory challenge in adulthood. In addition, conditioned media from ABCB5-positive cultured human limbal epithelial cells (ABCB5+) stimulated human blood and lymphatic endothelial cell proliferation and migration. Finally, a proteomic analysis demonstrated ABCB5+ cells have a pro(lymph)angiogenic as well as an anti-inflammatory profile. These data suggest a novel dual, context-dependent role of ABCB5+ LESCs, inhibiting developmental but promoting inflammatory (lymph)angiogenesis in adulthood and exerting anti-inflammatory effects. These findings are of high clinical relevance in relation to LESC therapy against blindness. [ABSTRACT FROM AUTHOR]

Current research on healthy corneal stromal cells will typically use primary cells as they are the most representative of in vivo behaviour. Primary cells are normally isolated from the limbus of discarded donor peripheral corneal tissue left over from transplantation (due to its relative abundance). Therefore, the central part of the cornea is less used in research as this tissue is usually used for transplantation. In some cases, although rare, the whole cornea, can become available for research. It is important to keep in mind that these corneas often have longer storage time, but the use of the central tissue for research is even more interesting, as knowing what cells are being transplanted into recipients would be highly relevant. To this end, stromal cells were extracted from both the limbus and central button of healthy corneas donated for research. This allowed for important comparison between central and limbal cells in culture. Of interest here was the extraction method of stromal cells from the donor tissue. The two most common methods of extraction are enzyme digestion and explant migration. However, no work has been done to understand how each method relatively affects the extracted cells. The extraction method and location from which stromal cells are harvested seems to have a significant effect on the cell adherence, survival, and gene expression of the stromal cells in culture. Enzyme digested cells showed that limbal and central cells had different gene expressions prior to culture, with gene such as ALDH3A1 being much more expressed in limbal cells. Enzyme digesting the limbal ring seems to yield the hardiest populations of stromal cells, a desirable trait in the culture of primary cells., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Keratoconus is the most common ectatic disease of the cornea. The disease is usually detected between ages 15 and 25. Incidence is estimated at one out of every 2000 individuals, with some specific ethnic groups being more at risk. Keratoconus manifests itself as a progressive stromal thinning and deformation of the corneal tissue into a conical shape. The etiology of keratoconus is uncertain, although several studies have associated the disease to environmental factors, behavioral conditions and certain genetic disorders. In an effort to better understand how the corneal stroma becomes compromised, multiple experiments have been conducted over the last few years looking at the cells themselves and the factors they produce. The secretion pathways and levels of inflammatory molecules, growth factors, digestive enzymes, and apoptotic factors are all relevant to keratoconus. This review describes the current knowledge of keratoconic pathological signaling pathways within the cornea that may help future developments in disease prevention, treatment and modeling. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc., (© 2019 Wiley Periodicals, Inc.)