Limbal niche cells can reduce the angiogenic potential of cultivated oral mucosal epithelial cells

Elevated neutrophils and reduced NK cells are associated with altered tear molecular signatures and clinical sequelae of chronic ocular Stevens-Johnson syndrome

PURPOSE

Stevens-Johnson syndrome (SJS) is characterised as an immuno-inflammatory condition with potentially blinding ocular sequelae. Therefore, we have investigated the ocular surface immune cell profile and correlated it with secreted tear molecular factors and clinical ocular sequelae in SJS patients.

METHODS

21 patients (42 eyes) with chronic ocular SJS and 16 healthy controls (20 eyes) were included in the study. Severity, types of keratopathies and ocular surface (OS) manifestations were determined. OS wash samples from study subjects were used to determine the status of 13 immune cell subsets using flow cytometry. Levels of 42 secreted immuno-inflammatory factors were measured by flow cytometry-based multiplex ELISA in tear samples.

RESULTS

Neutrophils (Total, activated), neutrophils/NK cells ratio, neutrophils/T cells ratio were significantly (p < 0.05) elevated in SJS, while, proportions of T cells and NKT cells were significantly lower in SJS patients. Positive association between neutrophils and chronic ocular surface complication score (COCS) was observed, whereas, a negative association was noted between NK cells and COCS. Tear fluid levels of IL-6, IL-8, IL-18, IFNα/β/γ, TNFα, LIF, IL-8, HGF, sTNFR-I, NGAL, Granzyme, Perforins, MMP9/TIMP1 ratio were significantly higher in SJS. Loss of Limbal niche correlated significantly with immune profile and clinical sequelae. Increased neutrophils, decreased NK cells and specific set of altered secreted immuno-inflammatory mediators including bFGF, and IL-8 were observed in SJS patients with different types of keratopathies compared to those without keratopathy.

CONCLUSION

Distinct ocular surface immune profile variations were observed to correlate with clinical stages of chronic ocular SJS. Our findings uncover novel mechanisms and potential for targeted therapy in chronic ocular SJS patients.

Enrichment, Characterization, and Proteomic Profiling of Small Extracellular Vesicles Derived from Human Limbal Mesenchymal Stromal Cells and Melanocytes

Limbal epithelial progenitor cells (LEPC) rely on their niche environment for proper functionality and self-renewal. While extracellular vesicles (EV), specifically small EVs (sEV), have been proposed to support LEPC homeostasis, data on sEV derived from limbal niche cells like limbal mesenchymal stromal cells (LMSC) remain limited, and there are no studies on sEVs from limbal melanocytes (LM). In this study, we isolated sEV from conditioned media of LMSC and LM using a combination of tangential flow filtration and size exclusion chromatography and characterized them by nanoparticle tracking analysis, transmission electron microscopy, Western blot, multiplex bead arrays, and quantitative mass spectrometry. The internalization of sEV by LEPC was studied using flow cytometry and confocal microscopy. The isolated sEVs exhibited typical EV characteristics, including cell-specific markers such as CD90 for LMSC-sEV and Melan-A for LM-sEV. Bioinformatics analysis of the proteomic data suggested a significant role of sEVs in extracellular matrix deposition, with LMSC-derived sEV containing proteins involved in collagen remodeling and cell matrix adhesion, whereas LM-sEV proteins were implicated in other cellular bioprocesses such as cellular pigmentation and development. Moreover, fluorescently labeled LMSC-sEV and LM-sEV were taken up by LEPC and localized to their perinuclear compartment. These findings provide valuable insights into the complex role of sEV from niche cells in regulating the human limbal stem cell niche.

ABCB5+ Limbal Epithelial Stem Cells Inhibit Developmental but Promote Inflammatory (Lymph) Angiogenesis While Preventing Corneal Inflammation

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.

Advancements in Ocular Regenerative Therapies

The use of stem cells (SCs) has emerged as a promising avenue in ophthalmology, offering potential therapeutic solutions for various vision impairments and degenerative eye diseases. SCs possess the unique ability to self-renew and differentiate into specialised cell types, making them valuable tools for repairing damaged tissues and restoring visual function. Stem cell-based therapies hold significant potential for addressing conditions such as age-related macular degeneration (AMD), retinitis pigmentosa (RP), corneal disorders, and optic nerve damage. Therefore, researchers have explored different sources of stem cells, including embryonic stem cells (ESC), induced pluripotent stem cells (iPSCs), and adult stem cells, for ocular tissue regeneration. Preclinical studies and early-phase clinical trials have demonstrated promising outcomes, with some patients experiencing improved vision following stem cell-based interventions. However, several challenges remain, including optimising the differentiation protocols, ensuring transplanted cells' safety and long-term viability, and developing effective delivery methods. The field of stem cell research in ophthalmology witnesses a constant influx of new reports and discoveries. To effectively navigate these tons of information, it becomes crucial to summarise and systematise these findings periodically. In light of recent discoveries, this paper demonstrates the potential applications of stem cells in ophthalmology, focusing on their use in various eye tissues, including the cornea, retina, conjunctiva, iris, trabecular meshwork, lens, ciliary body, sclera, and orbital fat.

Effects of Exosomal microRNAs on Oral Mucosal Epithelial Cells Cocultured with Limbal Niche Cells

Autologous cultivated oral mucosal epithelial transplantation (COMET) is an important method for the treatment of limbal stem cell deficiency (LSCD), but the appearance of peripheral corneal neovascularization after COMET has prevented its widespread use in clinical practice. Using limbal niche cells (LNCs) as feeders in the process of coculturing could inhibit the postoperative corneal neovascularization. However, the specific mechanism is still unclear. In this study, LNCs were used as feeder cells to alter the phenotype of cultured oral mucosal epithelial cells (COMECs) by mimicking the primitive limbal microenvironment. The high-throughput sequencing of COMECs cocultured with LNCs or 3T3 cells (named LNCs group and 3T3 groups) was performed, and differential miRNA expression was analyzed. A total of 99 known and 1 newly predicted miRNAs were significantly upregulated in the LNCs group, while 101 known and 8 newly predicted miRNAs were significantly downregulated. A total of 3000 target genes with the 60 most significantly differentially expressed miRNAs were predicted, and 7 upregulated and 7 downregulated miRNAs were ultimately screened. The supernatants obtained from both cocultures were found to be rich in exosomes, indicating that the intercellular communication between COMECs and LNCs or 3T3 cells was highly active. Furthermore, the expression levels of rno-miR-200-5p, rno-miR-204-5p, rno-miR-126a-3p, rno-miR-192-5p, rno-miR-211-5p, rno-miR-143-3p, and rno-miR-184 were significantly higher in the LNCs group compared to the 3T3 group, and the expression levels had a similar trend in exosomes. Meanwhile, sequencing of the cell lines revealed 7 miRNAs that were significantly downregulated in the LNCs group. Interestingly, in that case, rno-miR-23a-3p, rno-miR-379-5p, and rno-miR-127-5p were also significantly downregulated in the exosomes. In summary, this study suggested that signal transduction between cells mediated by exosomal miRNAs may be an important factor for the inhibition of angiogenesis by LNCs nourished COMECs.

Goals and Challenges of Stem Cell-Based Therapy for Corneal Blindness Due to Limbal Deficiency

Corneal failure is a highly prevalent cause of blindness. One special cause of corneal failure occurs due to malfunction or destruction of the limbal stem cell niche, upon which the superficial cornea depends for homeostatic maintenance and wound healing. Failure of the limbal niche is referred to as limbal stem cell deficiency. As the corneal epithelial stem cell niche is easily accessible, limbal stem cell-based therapy and regenerative medicine applied to the ocular surface are among the most highly advanced forms of this novel approach to disease therapy. However, the challenges are still great, including the development of cell-based products and understanding how they work in the patient's eye. Advances are being made at the molecular, cellular, and tissue levels to alter disease processes and to reduce or eliminate blindness. Efforts must be coordinated from the most basic research to the most clinically oriented projects so that cell-based therapies can become an integrated part of the therapeutic armamentarium to fight corneal blindness. We undoubtedly are progressing along the right path because cell-based therapy for eye diseases is one of the most successful examples of global regenerative medicine.

Subconjunctival Injection of Transdifferentiated Oral Mucosal Epithelial Cells for Limbal Stem Cell Deficiency in Rats

Rat limbal niche cells (LNCs) have been proven to induce transdifferentiation of oral mucosal epithelial cells (OMECs) into corneal epithelial-like cells termed transdifferentiated oral mucosal epithelial cells (T-OMECs). This investigation aimed to evaluate the effect of subconjunctival T-OMEC injections on alkali-induced limbal stem cell deficiency (LSCD) in rats. LNCs were cocultured with OMECs in the Transwell system to obtain T-OMECs, with NIH-3T3 cells serving as a control. Subconjunctival injection of single T-OMEC or OMEC suspension was performed immediately after corneal alkali injury. T-OMECs were prelabeled with the fluorescent dye CM-DiI in vitro and tracked in vivo. Corneal epithelial defect, opacity, and neovascularization were quantitatively analyzed. The degree of corneal epithelial defect (from day 1 onward), opacity (from day 5 onward), and neovascularization (from day 2 onward) was significantly less in the T-OMEC group than in the OMEC group. Cytokeratin 12 (CK12), pigment epithelium-derived factor, and soluble fms-like tyrosine kinase-1 were expressed at a higher rate following T-OMEC injection. Some CM-DiI-labeled cells were found to be coexpressed with CK12, Pax6, and ΔNp63α in the corneal epithelium after subconjunctival injection. Subconjunctival injection of T-OMECs prevents conjunctival invasion and maintains a normal corneal phenotype, which might be a novel strategy in the treatment of LSCD.

Ex vivo cultivated oral mucosal epithelial cell transplantation for limbal stem cell deficiency: a review

Destruction or dysfunction of limbal epithelial stem cells (LESCs) leads to unilateral or bilateral limbal stem cell deficiency (LSCD). Fifteen years have passed since the first transplantation of ex vivo cultivated oral mucosal epithelial cells (COMET) in humans in 2004, which represents the first use of a cultured non-limbal autologous cell type to treat bilateral LSCD. This review summarizes clinical outcomes from COMET studies published from 2004 to 2019 and reviews results with emphasis on the culture methods by which grafted cell sheets were prepared.