Small-Molecule Induction Promotes Corneal Endothelial Cell Differentiation From Human iPS Cells

Matrix glycosaminoglycans and proteoglycans in human cornea organoids and similarities with fetal corneal stages

PURPOSE

We developed human cornea organoids (HCOs) from induced pluripotent stem cells (iPSCs) where single-cell RNA-sequence (scRNA-seq) analysis suggested similarity with developing rather than mature human corneas. We performed immunohistology to determine the presence of corneal glycosaminoglycans as an assessment of maturity. We undertook a detailed comparison of the HCO scRNA-seq data with a recent scRNA-seq study of human fetal corneas at different stages to gauge the HCO's maturity.

METHODS

We generated HCOs from a second iPSC line, NCRM-1, to assess the reproducibility of HCO development. We stained sections from both HCO lines with Alcian blue and picrosirius red to determine deposition of sulfated glycosaminoglycans and fibrillar collagens. We immunolocalized glycosaminoglycan biosynthetic enzymes and proteoglycan core proteins. The scRNA-seq data from IMR90.4 HCOs were compared to that of fetal corneas using MetaNeighbor analysis to assess the similarity of HCOs to different stages of human corneal development.

RESULTS

The MetaNeighbor analysis suggests closer alignment of the IMR90.4 HCOs with 17-18 post-conception week fetal human corneas. HCOs from both iPSC lines deposit sulfated glycosaminoglycans and fibrillar collagens. Immunohistology showed chondroitin/dermatan sulfate (CS/DS) and keratan sulfate in the presumptive stromal and some epithelial layers. The NCRM-1-derived HCOs show increased CS/DS staining compared to the IMR90.4 derived HCOs.

CONCLUSIONS

Both HCO lines show similar developmental patterns and timeline. The NCRM-1 HCO line may have more glycosaminoglycan deposition. Overall, the glycosaminoglycan deposition pattern is consistent with an immature tissue. Optimizations based on our current findings may yield more mature stromal cells and cornea-typical proteoglycans.

Embryoid body-based differentiation of human-induced pluripotent stem cells into cells with a corneal stromal keratocyte phenotype

OBJECTIVE

The transparency of the cornea is determined by the extracellular matrix, which is secreted by corneal stromal keratocytes (CSKs). Human-induced pluripotent stem cell (hiPSC)-derived keratocytes (hiPSC-CSKs) can be used in cell-based therapy for treating corneal blindness. Our goal was to develop an effective small molecule-based technique for differentiating hiPSCs into keratocytes.

METHODS AND ANALYSIS

hiPSCs were cultured in chemically defined medium, and embryoid bodies (EBs) were generated; these EBs were induced into CSKs using keratocyte-differentiated medium. The expression of keratocyte-specific markers was assessed using quantitative RT-PCR, immunostaining and Western blotting.

RESULTS

We found that the expression of genes encoding keratocyte markers, including aldehyde dehydrogenase 1 family member A1 (ALDH1A1), lumican and keratocan, was upregulated. Immunostaining showed positive staining for ALDH1A1 and keratocan in the hiPSC-CSK samples. Similarly, western blot analysis indicated that ALDH1A1 and keratocan expression levels were significantly greater in the hiPSC-CSKs than in the control cells. In addition, hiPSC-CSKs were not transformed into fibroblasts or myofibroblasts.

CONCLUSION

We established an innovative and effective method to generate CSKs via the EB-based differentiation of hiPSCs, which might be employed for cell-based therapy of corneal stromal opacities.

Differentiation of Human Mesenchymal Stem Cells into Corneal Epithelial Cells: Current Progress

The limited availability of corneal tissue grafts poses significant challenges in the treatment of corneal blindness. Novel treatment utilizes stem cell grafts transplanted from the healthy side of the cornea to the damaged side. However, this procedure is only possible for those who have one-sided corneal blindness. Human stem cells offer promising potential for corneal tissue engineering, providing an alternative solution. Among the different types of stem cells, mesenchymal stem cells (MSCs) stand out due to their abundance and ease of isolation. Human MSCs can be derived from bone marrow, adipose, and umbilical cord tissues. Differentiating MSC toward corneal tissue can be achieved through several methods including chemical induction and co-culture with adult corneal cells such as human limbal epithelial stem cells (LESCs) and human corneal epithelial cells (hTCEpi). Adipose-derived stem cells (ADSCs) are the most common type of MSC that has been studied for corneal differentiation. Corneal epithelial cells are the most common corneal cell type targeted by researchers for corneal differentiation. Chemical induction with small molecules, especially bone morphogenetic protein 4 (BMP4), all-trans retinoic acid (ATRA), and epidermal growth factor (EGF), has gained more popularity in corneal epithelial cell differentiation. This review highlights the current progress in utilizing MSCs for corneal differentiation studies, showcasing their potential to revolutionize treatments for corneal blindness.

Focus on seed cells: stem cells in 3D bioprinting of corneal grafts

Corneal opacity is one of the leading causes of severe vision impairment. Corneal transplantation is the dominant therapy for irreversible corneal blindness. However, there is a worldwide shortage of donor grafts and consequently an urgent demand for alternatives. Three-dimensional (3D) bioprinting is an innovative additive manufacturing technology for high-resolution distribution of bioink to construct human tissues. The technology has shown great promise in the field of bone, cartilage and skin tissue construction. 3D bioprinting allows precise structural construction and functional cell printing, which makes it possible to print personalized full-thickness or lamellar corneal layers. Seed cells play an important role in producing corneal biological functions. And stem cells are potential seed cells for corneal tissue construction. In this review, the basic anatomy and physiology of the natural human cornea and the grafts for keratoplasties are introduced. Then, the applications of 3D bioprinting techniques and bioinks for corneal tissue construction and their interaction with seed cells are reviewed, and both the application and promising future of stem cells in corneal tissue engineering is discussed. Finally, the development trends requirements and challenges of using stem cells as seed cells in corneal graft construction are summarized, and future development directions are suggested.

Nicotinamide promotes the differentiation of functional corneal endothelial cells from human embryonic stem cells

Corneal transplantation represents the primary therapeutic approach for managing corneal endothelial dysfunction, but corneal donors remain scarce. Anterior chamber cell injection emerges as a highly promising alternative strategy for corneal transplantation, with pluripotent stem cells (PSC) demonstrating considerable potential as an optimal cell source. Nevertheless, only a few studies have explored the differentiation of functional corneal endothelial-like cells originating from PSC. In this investigation, a chemical-defined protocol was successfully developed for the differentiation of functional corneal endothelial-like cells derived from human embryonic stem cells (hESC). The application of nicotinamide (NAM) exhibited a remarkable capability in suppressing the fibrotic phenotype, leading to the generation of more homogeneous and well-distinctive differentiated cells. Furthermore, NAM effectively suppressed the expression of genes implicated in endothelial cell migration and extracellular matrix synthesis. Notably, NAM also facilitated the upregulation of surface marker genes specific to functional corneal endothelial cells (CEC), including CD26 (-) CD44 (-∼+-) CD105 (-) CD133 (-) CD166 (+) CD200 (-). Moreover, in vitro functional assays were performed, revealing intact barrier properties and Na+/K+-ATP pump functionality in the differentiated cells treated with NAM. Consequently, our findings provide robust evidence supporting the capacity of NAM to enhance the differentiation of functional CEC originating from hESC, offering potential seed cells for therapeutic interventions of corneal endothelial dysfunction.

Corneal Endothelial-like Cells Derived from Induced Pluripotent Stem Cells for Cell Therapy

Corneal endothelial dysfunction is one of the leading causes of corneal blindness, and the current conventional treatment option is corneal transplantation using a cadaveric donor cornea. However, there is a global shortage of suitable donor graft material, necessitating the exploration of novel therapeutic approaches. A stem cell-based regenerative medicine approach using induced pluripotent stem cells (iPSCs) offers a promising solution, as they possess self-renewal capabilities, can be derived from adult somatic cells, and can be differentiated into all cell types including corneal endothelial cells (CECs). This review discusses the progress and challenges in developing protocols to induce iPSCs into CECs, focusing on the different media formulations used to differentiate iPSCs to neural crest cells (NCCs) and subsequently to CECs, as well as the characterization methods and markers that define iPSC-derived CECs. The hurdles and solutions for the clinical application of iPSC-derived cell therapy are also addressed, including the establishment of protocols that adhere to good manufacturing practice (GMP) guidelines. The potential risks of genetic mutations in iPSC-derived CECs associated with long-term in vitro culture and the danger of potential tumorigenicity following transplantation are evaluated. In all, this review provides insights into the advancement and obstacles of using iPSC in the treatment of corneal endothelial dysfunction.

iPSC-Derived Corneal Endothelial Cells

The corneal endothelium is the innermost monolayer of the cornea that maintains corneal transparency and thickness. However, adult human corneal endothelial cells (CECs) possess limited proliferative capacity, and injuries can only be repaired by migration and enlargement of resident cells. When corneal endothelial cell density is lower than the critical level (400-500 cells/mm2) due to disease or trauma, corneal endothelial dysfunction will occur and lead to corneal edema. Corneal transplantation remains the most effective clinical treatment therapy but is limited by the global shortage of healthy corneal donors. Recently, researchers have developed several alternative strategies for the treatment of corneal endothelial disease, including the transplantation of cultured human CECs and artificial corneal endothelial replacement. Early-stage results show that these strategies can effectively resolve corneal edema and restore corneal clarity and thickness, but the long-term efficacy and safety remain to be further validated. Induced pluripotent stem cells (iPSCs) represent an ideal cell source for the treatment and drug discovery of corneal endothelial diseases, which can avoid the ethical-related and immune-related problems of human embryonic stem cells (hESCs). At present, many approaches have been developed to induce the differentiation of corneal endothelial-like cells from human induced pluripotent stem cells (hiPSCs). Their safety and efficacy for the treatment of corneal endothelial dysfunction have been confirmed in rabbit and nonhuman primate animal models. Therefore, the iPSC-derived corneal endothelial cell model may provide a novel effective platform for basic and clinical research of disease modeling, drug screening, mechanistic investigation, and toxicology testing.

Cell therapy in corneal endothelial disease

PURPOSE OF REVIEW

Endothelial keratoplasty is the current gold standard for treating corneal endothelial diseases, achieving excellent visual outcomes and rapid rehabilitation. There are, however, severe limitations to donor tissue supply and uneven access to surgical teams and facilities across the globe. Cell therapy is an exciting approach that has shown promising early results. Herein, we review the latest developments in cell therapy for corneal endothelial disease.

RECENT FINDINGS

We highlight the work of several groups that have reported successful functional outcomes of cell therapy in animal models, with the utilization of human embryonic stem cells, human-induced pluripotent stem cells and cadaveric human corneal endothelial cells (CECs) to generate populations of CECs for intracameral injection. The use of corneal endothelial progenitors, viability of cryopreserved cells and efficacy of simple noncultured cells, in treating corneal decompensation is of particular interest. Further additions to the collective understanding of CEC physiology, and the process of cultivating and administering effective cell therapy are reviewed as well.

SUMMARY

The latest developments in cell therapy for corneal endothelial disease are presented. The continuous growth in this field gives rise to the hope that a viable solution to the large numbers of corneal blind around the world will one day be reality.