Stem cell therapy for glaucoma—there is still a long way to go

Glaucoma is now the second leading reason of blindness in the world and is characterized by elevated intraocular pressure and gradual loss of vision (1).

A recently published article by Zack et al. showed us a novel way of harvesting RGC cells from embryonic stem cells. Utilization of CRIPSR-Cas9 in the experiment granted a simple, adherent cell culture protocol for differentiation of hPSCs to RGCs in vitro. CRISPR engineered ESCs showed high success rate of developing into RGCs and specific markers as well as characters of RGCs.

It seemed this novel method has provided us with a brighter beginning on the way of RGC regenerating with CRISPR technique, however, there is still a long way to go.

Firstly, CRISPR-Cas9 is still not widely used worldwide and has a lot of limitations. CRIPSR is only to be used in embryos, which brings ethical issues. Besides, success rate of inserting new gene segments into specific location in human genome by CRISPR technique is low and unstable. Thus it won’t be easy for everyone to repeat the result in the study mentioned above.

Secondly, impairment of RGCs in patients with glaucoma is different from that in patients with ocular trauma. The latter causes direct damage to optic nerve, leading to vision loss. However, glaucomatous damage of optic nerve is gradual and silent. And it’s hard to detect a clear anatomical abnormality of optic nerve in glaucoma. So re-growth of axon and redirection of axon to its original spatial position is quite hard. Without accurate localization of axon back to the central nervous system (CNS), it’s impossible for patients to regain their lost vision.

Thirdly, previous studies showed sometimes although axons grew back to their original place, they were not functional (2). No improvement in vision was observed, which means the communication between regrown axon and CNS was not successfully built. And this is the biggest obstruction we are faced with.

In a word, it’s meaningful to discover new and easier way to regenerating RGCs. But more importantly, the immortal theme about RGC regeneration is regaining function. Building up a correct anatomical structure is just the first step, and the second step needs further investigation.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned and reviewed by Section Editor Kangjun Li, PhD student (State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China).

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/aes.2017.01.07). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Quigley HA. Glaucoma. Lancet 2011;377:1367-77. [Crossref] [PubMed]
2. Lim JH, Stafford BK, Nguyen PL, et al. Neural activity promotes long-distance, target-specific regeneration of adult retinal axons. Nat Neurosci 2016;19:1073-84. [Crossref] [PubMed]