Research and Application of Stem Cells in Eye Diseases

Limbal stem cells ( LSC , limbal stem cell )

A stem cell that mainly exists in many corneal parts such as the limbus ( Limbus ); the main feature is the high expression of P63 and the low expression of CD71 .

Retinal pigment epithelium ( RPE , retinal pigment epithelium )

Composed of a single layer of pigment epithelial cells, the arrangement is very regular. Cells are polygonal. The main feature is that ZO-1 , bestrophin, MiTF and other markers are positive; OCT4, NANOG, and SOX2 and other markers are negative.

Mesenchymal stem cells ( MSC , mesenchymal stem cells )

Mainly present in various tissues ( such as bone marrow, umbilical cord, placenta, fat and various organs, etc. ), it is a kind of adult stem cell with self-replication ability and multi-directional differentiation potential, which can develop into hard bone, cartilage, fat and other type of cells. The main feature is adherent growth; expresses CD105 , CD73 and CD90 , does not express CD45 , CD32 , CD14 or CD11b , CD79 α or CD19 and HLA-DR surface markers; MSC can differentiate into osteoblasts, adipocytes and chondrocytes in vitro cell.

Stem cells hold great promise in helping us understand and treat many diseases, injuries and other health problems. The potential for stem cell therapy is clear, and hematopoietic stem cell transplants have saved the lives of thousands of children with leukemia. Stem cell technology has also been researched and applied to eye diseases, especially in the treatment of eye diseases related to corneal injury and neurodegeneration. At the request of our friends, Mr. Bubu will give you a brief overview of the research and application status of stem cells in ophthalmic diseases.

Stem cells have been used in the clinical research of ophthalmic diseases mainly include: limbal stem cells ( limbal stem cells ), oral mucosal epithelial cells ( mucosalepithelial cells ), corneal epithelial stem cells ( corneal epithelial stem cells ) etc. Pigment epithelial cells ( ES derived RPE ), mesenchymal stem cells ( mesenchymal stem cells ) are used to treat retinopathy, and transplantation of hematopoietic stem cells and mesenchymal stem cells is used to treat some eye diseases caused by autoimmunity.

At present, the application of stem cells in ophthalmic diseases mainly focuses on the following aspects:

1Research and Application of Stem Cells in Corneal Injury

Limbal stem cell ( limbal stem cell ): a kind of stem cell that mainly exists in many corneal parts such as the corneal limbus ( Limbus ) [1] ; the main feature is high expression of P63 and low expression of CD71[2] . At present, it is mainly used to treat corneal damage caused by ocular trauma (chemical substances, burns, etc.); corneal limbal stem cell deficiency ( LSCD ); corneal clouding or whitening caused by corneal spots, etc.

Autologous corneal limbal stem cell transplantation has become a mature surgical method. Patients with unilateral corneal limbal stem cell deficiency and patients with bilateral corneal limbal stem cell slight deficiency can transplant autologous limbal stem cells or other parts (oral mucosa, etc.) to achieve eye reconstruction. Table, the purpose of restoring vision, which does not require immunosuppressants but may cause damage to the other normal eye; and for patients with severe limbal stem cell defects in both eyes, since allogeneic limbal stem cells can only be cultured and transplanted, it still needs to be solved Problems with immune rejection, immunosuppressant use.

In July 2014 , the Ophthalmology Team of Sun Yat-Sen University and American researchers published an article " WNT7A and PAX6 define corneal epithelium homeostasis and pathogenesis " [3] in the journal Nature . The research results confirmed that WNT7A and PA X6 , the key factors that regulate the differentiation of limbal stem cells, play an important role in the specialized differentiation of corneal lineage. For the first time, skin stem cells were induced to differentiate into limbal stem cells and successfully restored corneal function. Disease offers new strategies. This provides a potential resource for treating patients with limbal stem cell deficiency for repair and regeneration of the corneal surface.

In 2010 , N Engl J magazine published an article " Limbal Stem-Cell Therapy and Long-Term Corneal Regeneration " [4] , Italian researchers used the patient 's own limbal stem cells to treat corneal damage. Stem cells are extracted from the edge of foreign tissue between the white of the patient's eye and the cornea, and then implanted into the damaged part of the patient's eye after they develop into fibrous tissue. The treatment of 112 patients who were blinded by chemical burns resulted in the restoration of vision in more than three-quarters of the patients. The success rate of the first transplant using this technique is 68.2% , and the success rate of the second transplant is 75% . There are still 13.1% of the patients whose vision is partially improved, and only 10.3% of the patients whose vision cannot be improved. (Table 1. ) This study found that the proportion of P63- positive cells is important for treatment success.

2Research and application of stem cells in retinal diseases

Retinal diseases are very common in clinical practice. Here Mr. Bubu mainly talks about dry age-related macular degeneration ( Dry age-related macular degeneration , AMD ) and juvenile macular dystrophy ( Stargardt disease). Both diseases are associated with degenerative changes in the retinal pigment epithelium ( RPE ). The former mainly affects the elderly, while the latter is a genetic disorder that usually presents in childhood. Both diseases can cause impairment of retinal pigment epithelium ( RPE ) function, which can lead to blindness. Retinal pigment epithelium ( retinal pigment epithelium ), is composed of a single layer of pigment epithelial cells, arranged very regularly. Cells are polygonal. The main feature is that ZO-1 , bestrophin, MiTF and other markers are positive ; OCT4, NANOG, and SOX2 and other markers are negative.

In 2010 , ACT (advanced cell technology) of the United States obtained FDA permission to use retinal pigment epithelial cells ( RPE) derived from embryonic stem cells to treat two degenerative eye diseases: dry age-related macular degeneration (Dry age-related macular degeneration , AMD ) and juvenile macular dystrophy ( Stargardt disease). This is the second clinical trial approved by the FDA involving cells derived from human embryonic stem ( hES ). In 2012 , the research institution published an article " Embryonic stem cell trials for macular degeneration: a preliminary report " in " The Lancet " [ 5] , and American researchers used human embryonic stem cells (hESC) to treat Preliminary data from two patients with different degenerative eye diseases suggest that hESC therapy is not only safe but also shows some therapeutic efficacy. hESCs _Early bone cells and nerve tissue cells were induced, and then these cells differentiated into retinal epithelial cells with a purity of more than 99% . The researchers injected about 50,000 isolated retinal epithelial cells under the retinas of two patients, an elderly woman with dry age-related macular degeneration in her 70s and a middle-aged woman. The young female patient suffered from Stargardt's disease, which caused blindness in both. After 4 months, the researchers found that the RPE had been completely replaced by the injected retinal epithelial cells, and the data confirmed that the injected cells survived and greatly improved their vision. (as in Table 2. )

3Research and Application of Stem Cells in Other Eye Diseases

As a progressive apoptosis (or death) disease of retinal ganglion cells, glaucoma theoretically has the possibility of applying cell replacement therapy, especially stem cell therapy. The possible action sites of stem cells for glaucoma should be located in the retinal ganglion cells, optic nerve head and trabecular meshwork: (1) most of the current research focuses on the replacement therapy of retinal ganglion cells, but the expected structure and function have not been obtained after transplantation. Functional repair, but also lacks the means to monitor cell proliferation and differentiation throughout the process. (2) The reconstruction of trabecular meshwork cells mainly replaces the degenerated sclera-keratocytes. (3) Stem cells may replace degenerated optic nerve cells (mainly astrocytes) or promote optic nerve myelination.

The hematopoietic and mesenchymal components in bone marrow cells contribute to the repair of damaged organs, and some people try to treat chronic glaucoma with mesenchymal stem cells. In 2013, Stem Cells published an article " Transplantation of Mesenchymal Stem Cells Promotes Tissue Regeneration in a Glaucoma Model Through Laser-Induced Paracrine Factor Secretion and Progenitor Cell Recruitment " [6]. Mesenchymal stem cells can promote glaucomatous tissue regeneration through laser-induced paracrine factor secretion and progenitor cell proliferation. Experiments have shown that mesenchymal stem cells in the bone marrow induce the regeneration of trabecular meshwork cells, and injection into the anterior chamber is more effective than hematopoietic cells in causing a decrease in intraocular pressure (IOP) (p<.001). Furthermore, mesenchymal stem cells and the factors they secrete induce reactivation of the progenitor cell pool in the ciliary body, promoting cell proliferation. Laser-induced tissue remodeling introduces mesenchymal stem cells into the damaged area according to the predetermined target, and also increases the ocular progenitor cells to a certain extent. This study confirmed that mesenchymal stem cells and their secreted components are key mediators of tissue repair in open-angle glaucoma through local neural progenitor cells.

summary

Although many documents indicate that various stem cells can be used for intraocular cell transplantation, the results are not very satisfactory. Advances in stem cell culture, purification, proliferation, directional induction, and transplantation have brought hope to some ophthalmic diseases that are difficult to treat with conventional medical methods. However, all kinds of stem cells have their unavoidable shortcomings, especially the common problem of how to differentiate into specific eye terminal cells, which has become an obstacle for stem cell transplantation to treat ophthalmic diseases in various tissues.