With today's news, it certainly seems that senescent cell clearance has come of age as an approach to treating aging and age-related conditions. Some of the leading folk in the cellular senescence research community today published the results from a very encouraging life span study, extending life in mice via a method of removing senescent cells. This is much the same approach employed in one of the first tests of senescent cell clearance, carried out in accelerated aging mice a few years ago, but in this case normal mice were used, leaving no room to doubt the relevance of the results. The researchers have founded a new company, Unity Biotechnology, to develop therapies for the clinic based on this technology. Clearance of senescent cells has been advocated as a part of the SENS vision for the medical control of aging for more than a decade now, and it is very encouraging to see the research and development community at last coming round to this view and making tangible progress.
Senescent cells have removed themselves from the cycle of replication in reaction to cell and tissue damage, or a local tissue environment that seems likely to result in cancer. Their numbers accumulate with age. Most are destroyed by the immune system or their own programmed cell death mechanisms, but enough linger for the long term for their growing presence to be one of the contributing causes of the aging process. These cells behave badly, secreting harmful signals that degrade tissue function, generate inflammation, and alter the behavior of surrounding cells as well. Near every common age-related condition is accelerated and made worse by the presence of large numbers of senescent cells. We would be better off without them, aging would be slowed by the regular removal of these errant cells, and the therapies to make that possible are on the near horizon.
The mouse lifespan study is the important news here, as it demonstrates meaningful extension of median life span through removal of senescent cells, the first such study carried out in normal mice for this SENS-style rejuvenation technology. This sort of very direct and easily understood result has a way of waking up far more of the public than the other very convincing evidence of past years. So it looks like Oisin Biotechnology, seed funded last year by the Methuselah Foundation and SENS Research Foundation to bring a senescent cell clearance therapy to market, now has earnest competition. Insofar as the competitive urge in business and biotechnology speeds progress and produces better results, let the games begin, I say.
Researchers have made this decade's biggest breakthrough in understanding the complex world of physical aging. The researchers found that systematically removing a category of living, stagnant cells (ones which can no longer reproduce) extends the lives of otherwise normal mice by 25 percent. Better yet, scouring these cells actually pushed back the process of aging, slowing the onset of various age-related illnesses like cataracts, heart and kidney deterioration, and even tumor formation. "It's not just that we're making these mice live longer; they're actually stay healthier longer too. That's important, because if you were going to equate this to people, well, you don't want to just extend the years of life that people are miserable or hospitalized."
By rewriting a tiny portion of the mouse genetic code, the team developed a genetic line of mice with cells that could, under the right circumstances, produce a powerful protein called caspase when they start secreting p16. Caspase acts essentially as a self-destruct button; when it's manufactured in a cell, that cell rapidly dies. So what exactly are these circumstances where the p16 secreting cells start to create caspase and self-destruct? Well, only in the presence of a specific medicine the scientists could give the mice. With their highly-specific genetic tweak, the scientists had created a drug-initiated killswitch for senescent cells. In today's paper, the team reported what happened when the researchers turned on that killswitch in middle-aged mice, effectively scrubbing clean the mice of senescent cells.
Senescent cells accumulate in various tissues and organs over time, and have been speculated to have a role in ageing. To explore the physiological relevance and consequences of naturally occurring senescent cells, here we use a previously established transgene, INK-ATTAC, to induce apoptosis in p16Ink4a-expressing cells of wild-type mice by injection of AP20187 twice a week starting at one year of age. We show that AP20187 treatment extended median lifespan in both male and female mice of two distinct genetic backgrounds. The clearance of p16Ink4a-positive cells delayed tumorigenesis and attenuated age-related deterioration of several organs without apparent side effects, including kidney, heart and fat, where clearance preserved the functionality of glomeruli, cardio-protective KATP channels and adipocytes, respectively. Thus, p16Ink4a-positive cells that accumulate during adulthood negatively influence lifespan and promote age-dependent changes in several organs, and their therapeutic removal may be an attractive approach to extend healthy lifespan.
Unity will initially focus on cellular senescence, a biological mechanism theorized to be a key driver of many age-related diseases, including osteoarthritis, glaucoma and atherosclerosis. "Imagine drugs that could prevent, maybe even cure, arthritis or heart disease or loss of eyesight. It's an incredible aspiration. If we can translate this biology into medicines, our children might grow up in significantly better health as they age. There will be many obstacles to overcome, but our team is committed and inspired to achieve our mission. This has been a long journey, and we're at the point now where we can start making medicines to achieve in humans what we've achieved in mice. I can't wait to see what happens as we move into the clinic."
To close this post, and once again, I think it well worth remembering that SENS rejuvenation biotechnology advocates and supporters have been calling for exactly this approach to treating aging for more than a decade. That call was made based on the evidence arising from many fields of medical research, and from a considered perspective of aging as a process of damage accumulation, one that can be most effectively treated by repair of that damage. The presence of senescent cells is a form of damage. SENS was not so long ago derided and considered out on the fringe for putting forward that position, but for several years now it has been very clear that the SENS viewpoint was right all along. I strongly encourage anyone who remains on the fence about the validity of the SENS proposals for the treatment of aging to reexamine his or her position on the science.