Restore age-related vision loss through epigenetic reprogramming

• The proof of concept study represents the first successful attempt to reverse the aging clock in animals through epigenetic reprogramming.
• Scientists used embryonic genes to reprogram cells in mouse retinas.
• The approach reversed the eye damage induced by glaucoma in animals.
• The approach also restored age-related vision loss in older mice.
• Working spells promise to use the same approach in other tissues, organs beyond the eyes.
• Success paves the way for the treatment of various age-related diseases in humans.

Scientists at Harvard Medical School succeeded in restoring vision in mice by going back in time to aged eye cells in the retina to regain function of juvenile genes.

The team’s work, described today (December 2, 2020) in Nature, represents the first demonstration that it is possible to safely reprogram complex tissues, such as nerve cells in the eye, at an earlier age.

In addition to resetting the aging clock of cells, researchers have successfully reversed vision loss in animals with disease mimicking human glaucoma, one of the leading causes of blindness worldwide.

The achievement represents the first successful attempt to reverse glaucoma-induced vision loss, rather than simply stopping its progression, the team said. If replicated in further studies, the approach could pave the way for therapies aimed at promoting tissue repair in various organs and reversing aging and age-related diseases in humans.

“Our study demonstrates that it is possible to safely reverse the age of complex tissues such as the retina and restore its juvenile biological function,” said lead author David Sinclair, professor of genetics at the Blavatnik Institute of Harvard Medical School, co-director of the Paul F. Glenn Center for Research in the Biology of Aging at HMS and an expert on aging.

Sinclair and colleagues warn that the results must be replicated in other studies, including in different animal models, before any human experiment. Nonetheless, they add, the results offer a proof of concept and a path to designing treatments for a range of human age-related diseases.

“If confirmed by further studies, these results could be transformative for the care of age-related vision diseases like glaucoma and for the fields of biology and medical therapeutics for the disease in general” , Sinclair said.

For their work, the team used an adeno-associated virus (AAV) as a vehicle to deliver three youth-restoring genes – Oct4, Sox2 and Klf4 – into the retina of mice – which are normally activated during embryonic development. The three genes, along with a fourth, which was not used in this work, are collectively known as the Yamanaka factors.

The treatment had multiple beneficial effects on the eye. First, it promoted nerve regeneration after optic nerve injury in mice with damaged optic nerves. Second, it reversed vision loss in animals with disease mimicking human glaucoma. And third, it reversed vision loss in aging animals without glaucoma.

The team’s approach is based on a new theory about why we age. Most cells in the body contain the same DNA molecules but have very diverse functions. To achieve this degree of specialization, these cells must read only genes specific to their type. This regulatory function is the responsibility of the epigenome, a system for activating and deactivating genes according to specific patterns without altering the underlying underlying DNA sequence of the gene.

This theory postulates that changes in the epigenome over time cause cells to read bad genes and malfunction, resulting in diseases related to aging. One of the most important changes in the epigenome is DNA methylation, a process by which methyl groups are stuck on DNA. DNA methylation patterns are established during embryonic development to produce the different types of cells. Over time, young DNA methylation patterns are lost and genes inside cells that should be turned on are turned off and vice versa, resulting in impaired cell function. Some of these DNA methylation changes are predictable and have been used to determine the biological age of a cell or tissue.

Yet whether DNA methylation results in age-related changes inside cells is unclear. In the current study, the researchers hypothesized that while DNA methylation does indeed control aging, erasing some of its fingerprints could reverse the age of cells inside living organisms and cause them to age. bring back to their earlier and younger state.

Previous work had achieved this feat in cells grown in laboratory dishes, but failed to demonstrate the effect on living organisms.

The new findings demonstrate that the approach could also be used in animals.

Overcome a big obstacle

Lead author of the study, Yuancheng Lu, a genetics researcher at HMS and a former doctoral student in Sinclair’s lab, developed gene therapy that could safely reverse the age of cells in a living animal.

Lu’s work builds on the Nobel Prize winning discovery of Shinya Yamanaka, who identified the four transcription factors, Oct4, Sox2, Klf4, c-Myc, which could erase epigenetic markers on cells and bring these cells back. in their primitive embryonic state from which they can develop into any other type of cell.

Subsequent studies, however, showed two important setbacks. First, when used in adult mice, the four Yamanaka factors could also induce tumor growth, making the approach dangerous. Second, the factors could reset the cellular state to the most primitive cellular state, thereby completely erasing a cell’s identity.

Lu and his colleagues worked around these obstacles by changing the approach slightly. They dropped the c-Myc gene and delivered only the three remaining Yamanaka genes, Oct4, Sox2, and Klf4. The modified approach was successful in reversing cellular aging without fueling tumor growth or losing its identity.

Gene therapy applied to the regeneration of the optic nerve

In the current study, the researchers targeted cells in the central nervous system, as they are the first part of the body affected by aging. After birth, the ability of the central nervous system to regenerate rapidly declines.

To test whether the regenerative ability of young animals could be passed on to adult mice, the researchers administered the altered combination of three genes via AAV into retinal ganglion cells from adult mice with optic nerve damage.

For the work, Lu and Sinclair have teamed up with Zhigang He, HMS professor of neurology and ophthalmology at Boston Children’s Hospital, who studies optic nerve and spinal cord neuroregeneration.

The treatment resulted in a doubling of the number of retinal ganglion cells surviving after the injury and a five-fold increase in nerve regrowth.

“At the start of this project, many of our colleagues said that our approach would fail or be too dangerous to use,” Lu said. “Our results suggest that this method is safe and could potentially revolutionize eye treatment and many other organs affected by aging. ”

Glaucoma reversal and age-related vision loss

Following the encouraging results in mice with optic nerve damage, the team partnered with colleagues at the Schepens Eye Research Institute at Massachusetts Eye and Ear Bruce Ksander, associate professor of ophthalmology HMS, and Meredith Gregory-Ksander, assistant professor of ophthalmology HMS. They planned two sets of experiments: one to test whether the cocktail of three genes could restore vision loss from glaucoma and another to see if the approach could reverse vision loss due to normal aging.

In a mouse model of glaucoma, the treatment led to an increase in the electrical activity of nerve cells and a noticeable increase in visual acuity, as measured by the animals’ ability to see moving vertical lines on a screen. Remarkably, he did this after the glaucoma-induced vision loss had already occurred.

“Recovery of visual function after injury has rarely been demonstrated by scientists,” Ksander said. “This new approach, which successfully reverses the multiple causes of vision loss in mice without the need for a retinal transplant, represents a new treatment modality in regenerative medicine.

The treatment also worked well in 12-month-old mice whose vision was reduced due to normal aging. After treatment of the aged mice, the gene expression patterns and electrical signals of the optic nerve cells were similar to those of the young mice and vision was restored. When the researchers analyzed the molecular changes in the treated cells, they found inverted patterns of DNA methylation – an observation suggesting that DNA methylation is not a mere marker or bystander in the process of aging, but rather an active agent that drives it.

“What this tells us is that the clock doesn’t just represent time – it’s time,” Sinclair said. “If you wind up the hands of the clock, time also goes back.”

The researchers said that if their results were confirmed in other animal work, they could start clinical trials within two years to test the approach’s effectiveness in people with glaucoma. So far, the results are encouraging, the researchers said. In the current study, a one-year full-body mouse treatment with the three-gene approach showed no negative side effects.

Reference: December 2, 2020, Nature.
DOI: 10.1038 / s41586-020-2975-4

Other authors on the paper include Benedikt Brommer, Xiao Tian, ​​Anitha Krishnan, Margarita Meer, Chen Wang, Daniel Vera, Qiurui Zeng, Doudou Yu, Michael Bonkowski, Jae-Hyun Yang, Songlin Zhou, Emma Hoffmann, Margarete Karg , Michael Schultz, Alice Kane, Noah Davidsohn, Ekaterina Korobkina, Karolina Chwalek, Luis Rajman, George Church, Konrad Hochedlinger, Vadim Gladyshev, Steve Horvath and Morgan Levine.

This work was funded in part by a seed and development grant from Harvard Medical School Epigenetics, the Glenn Foundation for Medical Research, Edward Schulak, the National Institutes of Health (grants R01AG019719, R37AG028730, R01EY026939, R01EY021526, R01AG067782, R01GM06520Y, R01AG067782, R01GM065204, R01GM065204,, R24EY028767 and R21EY030276) and the Saint-Vincent de Paul Foundation.

Relevant Disclosures: David Sinclair is a consultant, licensed patent inventor, board member and shareholder of Iduna Therapeutics, a Life Biosciences company developing epigenetic reprogramming therapies, and unpaid consultant to Zymo Research, a company of epigenetic tools. Yuancheng Lu, Luis Rajman and Steve Horvath are shareholders of Iduna Therapeutics. George Church and Noah Davidsohn are co-founders of Rejuvenate Bio.