Chapter 5. : Further Means for Life Extension and Healthy Aging

 There are other means, both hypothetical and proven, to extend life and to have healthy aging.
As one ages, both the efficiency and efficacy of an individuals intermediary metabolism decreases.
What are metabolism, intermediary metabolism or intermediate metabolism?

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"Metabolism (from Greek: μεταβολή metabolē, "change") is the set of life-sustaining chemical transformations within the cells of organisms. The three main purposes of metabolism are the conversion of food/fuel to energy to run cellular processes, the conversion of food/fuel to building blocks for proteins, lipids, nucleic acids, and some carbohydrates, and the elimination of nitrogenous wastes. These  enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The word metabolism can also refer to the sum of all chemical reactions that occur in living organisms, including  digestion and the transport of substances into and between different cells, in which case the set of reactions within the cells is called intermediary metabolism or intermediate metabolism.
Metabolism is usually divided into two categories:  catabolism, the breaking down of organic matter for example, the breaking down of glucose to pyruvate, by  cellular respiration, and  anabolism, the building up of components of cells such as proteins and  nucleic acids. Usually, breaking down releases  energy and building up consumes energy.
The chemical reactions of metabolism are organized into  metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, by a sequence of  enzymes. Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require  energy that will not occur by themselves, by  coupling them to  spontaneous reactions that release energy. Enzymes act as  catalysts that allow the reactions to proceed more rapidly. Enzymes also allow the regulation of metabolic pathways in response to changes in the  cell's environment or to  signals from other cells." 1.

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As enzymatic reactions are the basis of metabolism and intermediary metabolism, their degradation, efficacy, and efficiency with age must be assertively addressed in order improve both longevity and healthy aging.

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"Research has shown that natural enzyme production starts to diminish at the age of 20. Studies indicate that the body’s capacity to produce enzymes diminishes by 13% every 10 years. This means that at the age of 40 our enzyme production is 25% less than when we were a child. At the age of 70, the body seems to only produce one third of the enzymes it needs!
Researchers at the Michael Reese Hospital in Chicago found that enzyme sin the saliva, the pancreas and the blood are weaker as we age. The stomach also produces less and less hydrochloric acid, the essential acid that activates digestive enzymes in the stomach.
When the digestion of our food demands such a large production of enzymes, our reserves can empty and deplete the body’s capability of producing enzymes. À large demande of digestive enzymes depletes the metabolic enzyme production that each of the cells of your body needs to function and negatively affects the whole body." 2.

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Therefore preserving and enhancing enzyme activity and biochemical stability is both a problem and a goal which must be addressed with regard to life extension and healthy aging.


Genetic Engineering

Genetic engineering might prove to be a means to address the problem of telomere degradation along with other associated biological, biochemical, genetic, and biochemical deficits associated with the
aging process.
What is "genetic engineering"?

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"Genetic engineering, also called genetic modification, is the direct manipulation of an organism's  genes using  biotechnology. It is a set of technologies used to change the genetic makeup of cells, including the transfer of genes within and across species boundaries to produce improved or novel  organisms. New  DNA is obtained by either isolating and copying the genetic material of interest using  recombinant DNA methods or by  artificially synthesizing the DNA. A  construct is usually created and used to insert this DNA into the host organism." 3.

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Telomerase, telomeres, and other genetic entities associated with aging might be appropriately modified using recombinant DNA methods and/or by artificially synthesizing the DNA.

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"Genetic engineering is a process that alters the genetic make-up of an organism by either removing or introducing  DNA. Unlike traditionally  animal and  plant breeding, which involves doing multiple crosses and then selecting for the organism with the desired phenotype, genetic engineering takes the  gene directly from one organism and inserts it in the other. This is much faster, can be used to insert any genes from any organism (even ones from different  domains) and prevents other undesirable genes from also being added. [1]
Genetic engineering could potentially fix severe  genetic disorders in humans by replacing the defective gene with a functioning one.[2] It is an important tool in research that allows the function of specific genes to be studied. [3] Drugs, vaccines and other products have been harvested from organisms engineered to produce them. [4] Crops have been developed that aid  food security by increasing yield, nutritional value and tolerance to environmental stresses. [5]
The DNA can be introduced directly into the host organism or into a cell that is then  fused or  hybridized with the host. [6] This relies on  recombinant nucleic acid techniques to form new combinations of heritable genetic material followed by the incorporation of that material either indirectly through a  vector system or directly through  micro-injection, macro-injection or  micro-encapsulation. [7]
Genetic engineering does not normally include traditional breeding,  in vitro fertilization, induction of  polyploidy,  mutagenesis and cell fusion techniques that do not use recombinant nucleic acids or a genetically modified organism in the process. [6] However, some broad definitions of genetic engineering include  selective breeding. [7] Cloning and  stem cell research, although not considered genetic engineering, [8] are closely related and genetic engineering can be used within them. [9]  Synthetic biology is an emerging discipline that takes genetic engineering a step further by introducing artificially synthesized material into an organism." [10] 4.

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Of course, research with regard to genetic engineering and synthetic biology, especially with regard to their application on human genetics and biology, must be highly regulated.

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"Critics have objected to the use of genetic engineering on several grounds, that include ethical, ecological and economic concerns. Many of these concerns involve GM crops and whether food produced from them is safe, whether it should be labeled and what impact growing them will have on the environment. These controversies have led to litigation, international trade disputes, and protests, and to restrictive regulation of commercial products in some countries. [175]
Accusations that scientists are " playing God" and other  religious issues have been ascribed to the technology from the beginning. [176] Other ethical issues raised include the  patenting of life, [177] the use of  intellectual property rights, [178] the level of labeling on products, [179] [180] control of the food supply [181] and the objectivity of the regulatory process. [182] Although doubts have been raised, [183] economically most studies have found growing GM crops to be beneficial to farmers." 5.

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Some animal species, such as some shark species, show remarkable longevity associated with the retention of those biochemical reaction mechanisms and biological constituents that progressively deteriorate in humans and which are associated with aging.
Using recombinant nucleic acids or a synthetically genetically modified replica of the same, genetic engineering could be used to prolong both the quality of and length of human life.
This might provide a very interesting and productive line of genetic engineering research.
A construct of this newly created DNA could then be inserted into the host organism (humans).
Using non-human mammalian species initially for such projects would, of course, be mandatory.

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"The DNA can be introduced directly into the host organism or into a cell that is then fused or hybridized with the host.
This relies on recombinant nucleic acid techniques to form new combinations of  heritable genetic material followed by
the incorporation of that material either indirectly through a vector system or directly through micro-injection, macro-
injection or micro-encapsulation." 6.

Artificial Means to Increase Levels of Nicotinamide Mononucleotide

"With advanced age, cell NAD+ levels plummet to near zero. Normal aging may one day be classified as “NAD+ deficiency syndrome.”Fortunately, there are proven ways to boost NAD+ levels." 7.

Therefore, given the aforementioned, artificial means might be developed to enhance the enzymatic pathways both to NAD+ biosynthesis along with the biosynthesis of NMN.
Oral ingestion of NMN supplements may prove useful.
However, the biosynthesis of NAD+, NAD+ substitutes, NAD+ precursors, and NAD+ enzymatic utilization enzymes might prove to be an appropriate approach to effectively address the metabolic and physiological aging problems associated with the severe depletion of NAD+ associated with advanced age.
Again, as stated in the previous chapter: "Oral Nicotinamide Riboside, NR, an NAD+ precursor vitamin, has "distinct and superior pharmokinetics to those of nicotinic acid and nicotinamide. We further show that single doses of 100,300, and 1,000 mg of NR produce dose-dependent increases in the blood NAD+ metabolome in the first clinical trial of NR pharmacokinetics in humans. We also report that nicotinic acid adenine dinucleotie (NAAD), which was not thought to be enroute for the conversion of NR to NAD+, is formed from NR and discover that the rise in NAAD is a highly sensitive biomarker of effective NAD+ repletion." 8.

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Again as stated in the previous chapter:"Here is a quick breakdown of the key differences between nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR):
NR is a proven form of vitamin B3, which is required to sustain healthy living. It is shown in multiple human studies to effectively increase NAD levels.
NMN is not a form of vitamin B3, and there are no clinical trials to prove it increases NAD in humans. NMN is also not the type of molecule that would ever be considered as a vitamin as it contains a phosphate, which affects its ability to enter cells.
NR is the largest is  part of NAD that can enter the cell. That is why NMN  supplements turn into NR first before that are able to make NAD.
In it supplement form, NMN must become NR first before entering the cell. Then once inside the cells, it converts back into NMN to make NAD. This is a 3-step and rather inefficient process.
NR can directly access the cell, so it only requires two steps to begin creating NAD."
NMN's only published trials are in mice and rats. NR has at least 4 published clinical trials and all of them confirm is a safe and effective way of increasing nad in people.
Despite NMN being sold as a pill to people. NMN is frequently studied through injections in rodents. In preclinical NR trials, it's most commonly added to food or water. Plus, in all of NR's published human trials it was administered in capsule form, which represents the recommended way of taking NR as a vitamin.
There are no published data to show how NMN affects human NAD levels." 9.

There are human intermediary metabolism processes, enzymatic and otherwise, which are pivotal in the ageing process. Deficits in the same can and do result in increased morbidity (illness) and mortality (death) in humans.
In this instance, as per the aforementioned, enzyme deficits increased with age.
Those particular enzymatic reactions which are rate limiting and/or critical to vital intermediary processes should be the primary focus for critical analysis for the purpose of improving the quality and quantity of the same through genetic engineering, substrate supplementation, and/or repair.
Initially, in vitro mechanisms to accomplish this goal should be attempted as models for in vitro testing.
This may prove to be a very tedious task.
Both deductive and inductive experimental processes along with trial and error methodologies associated with the same may prove useful.
Using experimental in vitro techniques which offer quick assessment, appropriate statistical quantification, appropriate specificity, and means to determine appropriate corrective measures will require very careful planning within the context of SOAP analysis (Subjective, Objective, Assessment, Plan).
Upon the determination of possible in vitro successful methodologies, initial utilization of in vivo scientific experimentation and testing, should use the same basic methodologies utilised for in vitro testing with those animal models utilized for the same selected and determined by how they can most appropriately, quickly, specifically, and validly address the conclusions and methodologies found in in vivo scientific experimentation and testing."
Human testing and experimentation should follow normal experimental guidelines based upon successful animal testing and experimentation.

Solving the End Replication Problem

What is the "End Replication Problem"?

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"Telomeres shorten in part because of the end replication problem that is exhibited during DNA replication in  eukaryotes only. Because DNA replication does not begin at either end of the DNA strand, but starts in the center, and considering that all known  DNA polymerases read the template strand in the 3' to 5' direction, one finds a leading and a lagging strand on the DNA molecule being replicated.
On the leading strand, DNA polymerase can make a complementary DNA strand without any difficulty because it reads the template strand from 3' to 5'. However, there is a problem going in the other direction on the lagging strand. To counter this, short sequences of  RNA acting as  primers attach to the lagging strand a short distance ahead of where the initiation site was. The DNA polymerase can start replication at that point and go to the end of the initiation site. This causes the formation of  Okazaki fragments. More RNA primers attach further on the DNA strand and DNA polymerase comes along and continues to make a new DNA strand.
 Eventually, the last RNA primer attaches, and DNA polymerase, RNA nuclease, and  DNA ligase come along to convert the RNA (of the primers) to DNA and to seal the gaps in between the Okazaki fragments. But, in order to change RNA to DNA, there must be another DNA strand in front of the RNA primer. This happens at all the sites of the lagging strand, but it does not happen at the end where the last RNA primer is attached. Ultimately, that RNA is destroyed by enzymes that degrade any RNA left on the DNA. Thus, a section of the telomere is lost during each cycle of replication at the 5' end of the lagging strand's daughter.
However, test-tube studies have shown that telomeres are highly susceptible to  oxidative stress. There is evidence that oxidative stress-mediated DNA damage is an important determinant of telomere shortening.  Telomere shortening due to free radicals explains the difference between the estimated loss per division because of the end-replication problem (c. 20 bp) and actual telomere shortening rates (50–100 bp), and has a greater absolute impact on telomere length than shortening caused by the end-replication problem. Population-based studies have also indicated an interaction between anti-oxidant intake and telomere length. In the Long Island Breast Cancer Study Project (LIBCSP), authors found a moderate increase in breast cancer risk among women with the shortest telomeres and lower dietary intake of beta carotene, vitamin C or E.] These results suggest that cancer risk due to telomere shortening may interact with other mechanisms of DNA damage, specifically oxidative stress.
Telomere shortening is associated with aging, mortality and aging-related diseases. In 2003, Richard Cawthon discovered that those with longer telomeres lead longer lives than those with short telomeres.  However, it is not known whether short telomeres are just a sign of cellular age or actually contribute to the aging process themselves."  10.



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"Lengthening

Hayflick limit is the theoretical limit to the number of times a cell may divide until the telomere becomes so short that division is inhibited and the cell enters senescence.The phenomenon of limited cellular division was first observed by  Leonard Hayflick, and is now referred to as the  Hayflick limit. Significant discoveries were subsequently made by a group of scientists organized at Geron Corporation by Geron's founder  Michael D. West that tied telomere shortening with the Hayflick limit. The cloning of the catalytic component of telomerase enabled experiments to test whether the expression of telomerase at levels sufficient to prevent telomere shortening was capable of immortalizing human cells. Telomerase was demonstrated in a 1998 publication in  Science to be capable of extending cell lifespan, and now is well-recognized as capable of immortalizing human somatic cells.
It is becoming apparent that reversing shortening of telomeres through temporary activation of telomerase may be a potent means to slow aging. The reason that this would extend human life is because it would extend the Hayflick limit. Three routes have been proposed to reverse telomere shortening: drugs, gene therapy, or metabolic suppression, so-called, torpor/hibernation. So far these ideas have not been proven in humans, but it has been demonstrated that telomere shortening is reversed in hibernation and aging is slowed (Turbill, et al. 2012   2013) and that hibernation prolongs life-span (Lyman et al. 1981). It has also been demonstrated that telomere extension has successfully reversed some signs of aging in laboratory mice  and the  nematode worm species  Caenorhabditis elegans. It has been hypothesized that longer telomeres and especially telomerase activation might cause increased cancer (e.g. Weinstein and Ciszek, 2002). However, longer telomeres might also protect against cancer, because short telomeres are associated with cancer. It has also been suggested that longer telomeres might cause increased energy consumption.
Techniques to extend telomeres could be useful for tissue engineering, because they might permit healthy, noncancerous mammalian cells to be cultured in amounts large enough to be engineering materials for biomedical repairs.
Two recent studies on long-lived  seabirds demonstrate that the role of telomeres is far from being understood. In 2003, scientists observed that the telomeres of  Leach's storm-petrel (Oceanodroma leucorhoa) seem to lengthen with chronological age, the first observed instance of such behaviour of telomeres.In 2006, Juola et al. reported that in another unrelated, long-lived seabird species, the  great frigate bird (Fregata minor), telomere length did decrease until at least c. 40 years of age (i.e. probably over the entire lifespan), but the speed of decrease slowed down massively with increasing ages, and that rates of telomere length decrease varied strongly between individual birds. They concluded that in this species (and probably in  frigate birds and their relatives in general), telomere length could not be used to determine a bird's age sufficiently well. Thus, it seems that there is much more variation in the behavior of telomere length than initially believed.
Furthermore, Gomes et al. found, in a study of the comparative biology of mammalian telomeres, that telomere length of different mammalian species correlates inversely, rather than directly, with lifespan, and they concluded that the contribution of telomere length to lifespan remains controversial. Harris et al. found little evidence that, in humans, telomere length is a significant biomarker of normal aging with respect to important cognitive and physical abilities. Gilley and Blackburn tested whether cellular senescence in  paramecium is caused by telomere shortening, and found that telomeres were not shortened during senescence." 11.

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The CRISPR technology as a means to enhance longevity and life extension

What is the CRISPR technology and how does it work?

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"CRISPR technology is a simple yet powerful tool for editing genomes. It allows researchers to easily alter DNA sequences and modify gene function. Its many potential applications include correcting genetic defects, treating and preventing the spread of diseases and improving crops. However, its promise also raises ethical concerns.
In popular usage, "CRISPR" (pronounced "crisper") is shorthand for "CRISPR-Cas9." CRISPRs are specialized stretches of DNA. The protein Cas9 (or "CRISPR-associated") is an enzyme that acts like a pair of molecular scissors, capable of cutting strands of DNA.
CRISPR technology was adapted from the natural defense mechanisms of bacteria and archaea (the domain of single-celled microorganisms). These organisms use CRISPR-derived RNA and various Cas proteins, including Cas9, to foil attacks by viruses and other foreign bodies. They do so primarily by chopping up and destroying the DNA of a foreign invader. When these components are transferred into other, more complex, organisms, it allows for the manipulation of genes, or "editing."
Until 2017, no one really knew what this process looked like. In a paper published Nov. 10, 2017, in the journal Nature Communications, a team of researchers led by Mikihiro Shibata of Kanazawa University and Hiroshi Nishimasu of the University of Tokyo showed what it looks like when a CRISPR is in action for the very first time. [ A Breathtaking New GIF Shows CRISPR Chewing Up DNA]
CRISPR-Cas9: The key players
CRISPRs: "CRISPR" stands for "clusters of regularly interspaced short palindromic repeats." It is a specialized region of DNA with two distinct characteristics: the presence of nucleotide repeats and spacers. Repeated sequences of nucleotides — the building blocks of DNA — are distributed throughout a CRISPR region. Spacers are bits of DNA that are interspersed among these repeated sequences.
In the case of bacteria, the spacers are taken from viruses that previously attacked the organism. They serve as a bank of memories, which enables bacteria to recognize the viruses and fight off future attacks.
This was first demonstrated experimentally by Rodolphe Barrangou and a team of researchers at Danisco, a food ingredients company. In a  2007 paper published in the journal Science, the researchers used  Streptococcus thermophilus bacteria, which are commonly found in yogurt and other dairy cultures, as their model. They observed that after a virus attack, new spacers were incorporated into the CRISPR region. Moreover, the DNA sequence of these spacers was identical to parts of the virus  genome. They also manipulated the spacers by taking them out or putting in new viral DNA sequences. In this way, they were able to alter the bacteria's resistance to an attack by a specific virus. Thus, the researchers confirmed that CRISPRs play a role in regulating bacterial immunity.
CRISPR RNA (crRNA): Once a spacer is incorporated and the virus attacks again, a portion of the CRISPR is  transcribed and processed into CRISPR RNA, or "crRNA." The nucleotide sequence of the CRISPR acts as a template to produce a complementary sequence of single-stranded RNA. Each crRNA consists of a nucleotide repeat and a spacer portion, according to a 2014 review by Jennifer Doudna and Emmanuelle Charpentier, published in the journal Science.
Cas9: The Cas9 protein is an enzyme that cuts foreign DNA.
The protein typically binds to two RNA molecules: crRNA and another called tracrRNA (or "trans-activating crRNA"). The two then guide Cas9 to the target site where it will make its cut. This expanse of DNA is complementary to a 20-nucleotide stretch of the crRNA. Using two separate regions, or "domains" on its structure, Cas9 cuts both strands of the DNA double helix, making what is known as a "double-stranded break," according to the 2014 Science article.
There is a built-in safety mechanism, which ensures that Cas9 doesn't just cut anywhere in a genome. Short DNA sequences known as PAMs ("protospacer adjacent motifs") serve as tags and sit adjacent to the target DNA sequence. If the Cas9 complex doesn't see a PAM next to its target DNA sequence, it won't cut. This is one possible reason that  Cas9 doesn't ever attack the CRISPR region in bacteria, according to a 2014 review published in Nature Biotechnology.
CRISPR-Cas9 as a genome-editing tool
The genomes of various organisms encode a series of messages and instructions within their DNA sequences. Genome editing involves changing those sequences, thereby changing the messages. This can be done by inserting a cut or break in the DNA and tricking a cell's natural DNA repair mechanisms into introducing the changes one wants. CRISPR-Cas9 provides a means to do so.
In 2012, two pivotal research papers were published in the journals  Science and  PNAS, which helped transform bacterial CRISPR-Cas9 into a simple, programmable genome-editing tool.
The studies, conducted by separate groups, concluded that Cas9 could be directed to cut any region of DNA. This could be done by simply changing the nucleotide sequence of crRNA, which binds to a complementary DNA target. In the 2012 Science article, Martin Jinek and colleagues further simplified the system by fusing crRNA and tracrRNA to create a single "guide RNA." Thus, genome editing requires only two components: a guide RNA and the Cas9 protein.
"Operationally, you design a stretch of 20 [nucleotide] base pairs that match a gene that you want to edit," said  George Church, a professor of genetics at Harvard Medical School. An RNA molecule complementary to those 20 base pairs is constructed. Church emphasized the importance of making sure that the nucleotide sequence is found only in the target gene and nowhere else in the genome. "Then the RNA plus the protein [Cas9] will cut — like a pair of scissors — the DNA at that site, and ideally nowhere else," he explained.
Once the DNA is cut, the cell's natural repair mechanisms kick in and work to introduce mutations or other changes to the genome. There are two ways this can happen. According to the  Huntington's Outreach Project at Stanford (University), one repair method involves gluing the two cuts back together. This method, known as "non-homologous end joining," tends to introduce errors. Nucleotides are accidentally inserted or deleted, resulting in  mutations, which could disrupt a gene. In the second method, the break is fixed by filling in the gap with a sequence of nucleotides. In order to do so, the cell uses a short strand of DNA as a template. Scientists can supply the DNA template of their choosing, thereby writing-in any gene they want, or correcting a mutation. " 10.

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How can CRISPR technology increase longevity and life extension?

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"Introducing the Harvard Pioneer of  CRISPR, Dr. George Church. He is a highly distinguished professor of genetics and major figure at Harvard Medical School and in science worldwide. He is a pioneer in the area of genome engineering and the development of gene editing tools based on the CRISPR/Cas9 system (referred to as CRISPR here).
In December 2015, Dr. Church presented a talk highlighting that aging seems to be controlled to a large extent by the action of a rather small subset of your genes, and especially by master genes that control large numbers of other genes.
Your genes are areas of your DNA that determine eye color, hair color, sex, height, and other characteristics of your body. It is becoming more and more clear that genes also determine how you age.
Dr. Church described how science has now advanced to the point where the activity of your genes, whether the genes are “turned on” (expressed) or “turned off” (repressed, or down-regulated,) can increasingly be controlled, and not just in a test tube, but in whole bodies, and even in the brain.
Reducing or Reversing the Aging Process
CRISPR – Clustered Regularly Interspaced Short Palindromic Repeats
Dr. Church’s focus is on CRISPR technology, which is a relatively new and particularly powerful method for adjusting gene activity in many different ways. It can even be applied for “editing”, or changing genes, which can be used to correct deleterious mutations, or to create deliberate mutations that can have good effects (such as in knocking out the effects of pro-aging genes).
The implication is very clear: If aging is controlled by master genes, and if the activity of such genes can now be intentionally controlled, then we are beginning to approach the regulating and reversing of aging on a very fundamental level. The same technology can be applied to the correction of many diseases as well, whether age-related or not.
Dr. Church wants to make the control of aging a practical reality, and soon. In an interview with the Washington Post at the beginning of December 2015, Dr. Church said his lab is already reversing aging in mice. He has already been able to reverse aging in human cells using CRISPR technology, and expects the first clinical trials of this technology to begin within as little as one year and that human applications may only be a few years away.
As exciting as this is, it’s not the only alternative when it comes to what’s happening at the cellular level. A second technology is currently available. It focuses on telomere lengthening. Telomeres are directly related to aging." 11.

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"A simple version of the CRISPR/Cas system, CRISPR/Cas9, has been modified to edit genomes. By delivering the  Cas9 nuclease complexed with a synthetic  guide RNA (gRNA) into a cell, the cell's  genome can be cut at a desired location, allowing existing genes to be removed and/or new ones added.The Cas9-gRNA complex corresponds with the CAS III CRISPR-RNA complex in the above diagram.
 Diagram of the CRISPR prokaryotic antiviral defense mechanism. [14]CRISPR/Cas genome editing techniques have many potential applications, including medicine and crop seed enhancement. The use of CRISPR/Cas9-gRNA complex for  genome editing was the  AAAS's choice for breakthrough of the year in 2015. Bioethical concerns have been raised about the prospect of using CRISPR for  germline editing." 12.

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"CRISPR ( /ˈkrɪspər/) is a family of DNA sequences in bacteria and archaea.[1] The sequences contain snippets of DNA from viruses that have attacked the  prokaryote. These snippets are used by the prokaryote to detect and destroy DNA from similar viruses during subsequent attacks. These sequences play a key role in a prokaryotic defense system, [] and form the basis of a technology known as CRISPR/Cas9 that effectively and specifically changes genes within organisms. CRISPR is an abbreviation of Clustered Regularly Interspaced Short Palindromic Repeats The name was minted at a time when the origin and use of the interspacing subsequences were not known. At that time the CRISPRs were described as segments of prokaryotic DNA containing short, repetitive base sequences. In a palindromic repeat, the sequence of nucleotides is the same in both directions. Each repetition is followed by short segments of  spacer DNA from previous exposures to foreign DNA (e.g., a  virus or  plasmid) Small clusters of cas (CRISPR-associated system) genes are located next to CRISPR sequences.
 CRISPR/Cas9The CRISPR/Cas system is a prokaryotic  immune system that confers resistance to foreign genetic elements such as those present within plasmids and  phages [8] that provides a form of acquired immunity. RNA harboring the spacer sequence helps Cas (CRISPR-associated) proteins recognize and cut exogenous DNA. Other RNA-guided Cas proteins cut foreign RNA. CRISPRs are found in approximately 50% of sequenced  bacterial genomes and nearly 90% of sequenced  archaea." 12.

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"A simple version of the CRISPR/Cas system, CRISPR/Cas9, has been modified to edit genomes. By delivering the  Cas9 nuclease complexed with a synthetic  guide RNA (gRNA) into a cell, the cell's genome can be cut at a desired location, allowing existing genes to be removed and/or new ones added The Cas9-gRNA complex corresponds with the CAS III CRISPR-RNA complex in the above diagram.
 Diagram of the CRISPR prokaryotic antiviral defense mechanism.CRISPR/Cas genome editing techniques have many potential applications, including medicine and crop seed enhancement. The use of CRISPR/Cas9-gRNA complex for  genome editing was the  AAAS's choice for breakthrough of the year in 2015. Bioethical concerns have been raised about the prospect of using CRISPR for germline editing." 13.

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"Cas9

Researchers studied a simpler CRISPR system from  Streptococcus pyogenes that relies on the protein  Cas9. The Cas9 endonuclease is a four-component system that includes two small RNA molecules named CRISPR RNA (crRNA) and trans-activating CRISPR RNA (tracrRNA). Jennifer Doudna and  Emmanuelle Charpentier re-engineered the Cas9 endonuclease into a more manageable two-component system by fusing the two RNA molecules into a "single-guide RNA" that, when combined with Cas9, could find and cut the DNA target specified by the guide RNA. By manipulating the nucleotide sequence of the guide RNA, the artificial Cas9 system could be programmed to target any DNA sequence for cleavage. Another group of collaborators comprising  Šikšnys together with Gasiūnas, Barrangou and Horvath showed that Cas9 from the S. thermophilus CRISPR system can also be reprogrammed to target a site of their choosing by changing the sequence of its crRNA. These advances fueled efforts to edit genomes with the modified CRISPR-Cas9 system.
 Feng Zhang's and  George Church's groups simultaneously described genome editing in human cell cultures using CRISPR-Cas9 for the first time It has since been used in a wide range of organisms, including baker's yeast ( Saccharomyces cerevisiae),the opportunistic pathogen  C. albicans,zebrafish D. rerio), fruit flies (Drosophila melanogaster), nematodes ( C. elegans), plants, mice,monkeys and human embryos." 14.

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A very interesting, well written, and informative book on the subject of the CRISPR/Cas9 system of gene editing is: " A Crack in Creation: Gene Editing and the Unthinkable Power to Control Evolution" by Jennifer A. Doudna and Samuel H. Sternberg , Houghton Mifflin Harcourt, published June 15, 2017,

One hypothetical approach to enhancing healthy aging and extending life would be for an individual to provide a body fluid and/or tissue sample. From the same, the complete genome of the individual could be mapped.  Deleterious anomalies in the same could then be identified and mapped. From this point, appropriate means to address these anomalies would be utilized including dietary, medical, biochemical, and genetic, inclusive of the CRISPR technology and related technologies
Given the aforementioned, rapid advances in the fields of life extension and healthy aging will be forthcoming fairly rapidly. The complex scientific and medical advances associated with the same are associated with complex ethical concerns especially with regard to application to the human genome.
It is imperative for the scientific and medical communities to closely monitor these scientific and medical advances so as to appropriately apply the same appropriately and ethically to the wide variety of medical problems facing humanity as well as to how to ethically advance human longevity, healthy aging, and life extension.