Scientists worldwide are competing to be the first to influence aging in people, an endeavor which would bring immense medical and economic advantages. This race to influence aging has now reached a fevered pitch.
Sinclair and her team used a virus to deliver three of the four Yamanaka factors into damaged retinal ganglion cells of aged mice, where it reversed shortened telomeres and rejuvenated the mice.
Epigenetics
Genes have an important impact on health and appearance, but so do other factors. Diet and exercise habits have the power to alter gene expression through epigenetics – unlike genetic mutations which directly change DNA sequence, epigenetics affects how our bodies read it instead.
Researchers are conducting extensive studies on how non-genetic factors impact an individual’s epigenetic profile – or how their genetic code is expressed – including its expression by non-genetic factors. Epigenetics was originally coined by Conrad Waddington in the 1940s to refer to molecular mechanisms that turn genotypes into phenotypes; today it more generally refers to heritable changes in gene function that do not involve DNA sequence changes.
Epigenetic mechanisms regulate access to chromatin, transcription, translation, mRNA splicing and its interactions with its targets as well as cell cycle regulation, differentiation and apoptosis – although some of these processes may be reversible while others cannot.
Some dietary habits may lead to the degradation of epigenetic marks that regulate how genes are expressed over time, leading to their expression behaving more like they’re older than they really are, leading to signs of premature aging in individuals.
Scientists have recently discovered that mammals keep a back-up copy of their youthful epigenetic profiles, which when restored can reverse age-related diseases like cancer, diabetes and Alzheimer’s. A team led by Harvard Medical School geneticist David Sinclair (not related to antiaging company Rejuvenate) demonstrated this approach with mice by administering a cocktail of chemicals which manipulate an enzyme involved in fixing DNA breaks – these mice lived 9% longer than untreated ones!
Sinclair and her team created mice engineered to experience DNA breaks three times more frequently than usual and administered their reprogramming drug; upon receiving treatment for DNA breaks faithfully repaired and epigenetic signatures returned to youthful patterns; giving the treated mice much younger appearances than untreated counterparts, while improving overall health status.
Cellular Reprogramming
Shinya Yamanaka and his Nobel Prize-winning team discovered a cocktail of proteins that reprogram adult cells into multipotent stem cells, giving rise to numerous benefits for health and disease prevention. Now, researchers are using these same tools to reverse the aging process in mice and, they hope, eventually humans. Already they’ve demonstrated they can turn back time in neuron cells, skin cells and connective tissue fibroblasts; experiments will soon extend this research onto nonhuman primates as well.
Reprogramming involves dramatic modifications to gene expression, chromatin status and other cell factors, often with long-term consequences on gene expression levels, transcription rates and down-regulation rates of age-associated genes. As a result, many cells fail to fully revert to their original state following OSKM induction; these have been labeled “partially reprogrammed.” Previously it was thought these partially reprogrammed cells had reached an irreversible point due to high reversion rates observed after its withdrawal; new research shows otherwise; cells that remain partially reprogrammed up until day 13 after OSKM induction still exhibit reduced epigenetic age, transcriptional age downregulation as well as down-regulation of age associated genes as well as more youthful genes such as collagens (see figure).
These results demonstrate that partial rejuvenation can be attained through extended reprogramming sessions. Furthermore, these results indicate it may be possible to achieve partial rejuvenation through using optimal conditions for reprogramming; specifically the use of optimal cell types like fibroblasts is necessary for successful reprogramming while small molecules to promote conversion should also be considered (see figure).
Understanding the steps and barriers associated with cell reprogramming and rejuvenation will enable strategies that could lead to clinical translation. This work will be further advanced through parallel implementation of technologies such as lineage tracing and event recording combined with longitudinal live tracking and sequencing techniques, providing enhanced temporal resolution for identifying key cell states and setting dynamic objectives that govern efficient reprogramming. Synthetic biology approaches that utilize signaling-regulatory networks can also be utilized during reprogramming to fine-tune desired outcomes (see figure). With these new tools at our fingertips, scientists will be able to better identify and target dynamic objectives behind cell reprogramming and rejuvenation processes.
Inducible Changes to the Epigenome (ICE)
Epigenetic changes within cells control which genes are turned on or off, helping ensure each cell produces only what they require for its specific function. If too many or too few proteins are produced by a cell, disease and even death could occur; the type of protein produced also depends on where that particular cell resides within the body – for instance, one needed for bone development is not produced in muscle cells, vice versa.
Scientists have long observed epigenetic changes associated with aging in mice and humans; however, scientists could never be certain whether these epigenetic alterations caused or simply resulted from it. To solve this conundrum, Sinclair’s team created temporary cuts in laboratory mice’s DNA that mimicked low-grade breaks experienced daily by mammalian cells; then they compared these “ICE” mice against Cre control mice on epigenetic status comparison.
Researchers discovered that ICE mice were epigenetically older than Cre controls using reduced representation bisulfite sequencing to measure CpG site methylation levels as an indicator of age; they discovered that the methylation levels among ICE mice were approximately 50 percent higher than in Cre control mice.
Researchers used RNA-Seq to compare the gastrocnemius muscle cells from ICE and Cre mice. They discovered that ICE cells expressed muscle-specific markers like Col1A1, Neurod1, and Nefh at lower levels than Cre cells; this suggested they were showing symptoms similar to aged mice, such as loss of muscle stem cells and an shift toward immune-skewed gene expression profiles.
Scientists conducted an experiment to see whether reversing epigenetic changes could slow or reverse their accelerated aging, using gene therapy with Oct4, Sox2, and Klf4. These pioneer transcription factors are active in mouse embryonic stem cells and have been found to rejuvenate human muscle tissue, likening their action to rebooting a malfunctioning computer. When administered via injection into ICE mice, gene therapy reduced various biomarkers of aging significantly – much like rebooting it.
Yamanaka Factors
Ten years ago, Kyoto University biologist Shinya Yamanaka won part of the Nobel Prize for discovering four genes that could reprogram adult cells into stem cells for use as versatile replacement organs, an advancement known as cellular reprogramming that may extend animal lives–possibly even ours! Since then, tech titans and venture capitalists have invested billions into labs trying to age-reverse mice’s DNA by altering it directly.
Researchers have used an innovative reversal technique to rejuvenate neurons of adult mice, finding that rejuvenated neurons improved synaptic connections, increased metabolism and even helped protect against neurodegenerative disorders like Alzheimer’s.
To achieve this, the team injected iPS cells into mice suffering from premature-ageing diseases and observed how these reprogrammed cells accelerated muscle regeneration and reversed behavioral deficits. Furthermore, scientists also reprogrammed cells from the hippocampus–an area involved with memory and learning–which resulted in less damage during aging as well as improved synaptic connections and memory function.
Researchers were amazed to discover that genetic factors that turn adult cells into iPS cells also rewound the “transcriptional clock,” restoring normal gene expression. Juan Carlos Izpisua Belmonte of the Gene Expression Laboratory at Salk Institute for Biological Studies explains that “transcriptional clock” refers to molecular mechanisms which regulate gene activity throughout development; its levels peak early and gradually decline as cells mature.
Resetting is controlled by proteins known as coregulators. Our team found that iPS cells express several of these coregulators known to play key roles in normal developmental processes. To identify coreregulators that play a role in delaying aging, the team conducted an exhaustive examination of genomic DNA changes in iPS cells using ChIP-chip. Analysis revealed a set of genes whose expression is essential to maintaining pluripotency, with results from an earlier ChIP-chip experiment showing these same genes are also involved in reprogramming. To facilitate their work, the team then utilized a system that enabled controlled expression of individual transcription factors (Oct4, Sox2, Klf4 and c-Myc). They did this in order to generate iPS cells with specific combinations of coregulators.
