The problem with testing rejuvenation biotechnologies in laboratory animals is that it takes them so long to get old.
It takes more than two years for the exponential age-related increase in morbidity and mortality to become obvious in well-cared-for, wild-type laboratory mice and rats of a healthy strain. For that very reason, it takes at least this much time for the long-term health effects of the cellular and molecular lesions that accumulate with age in their tissues to reveal themselves, allowing researchers to probe the relationship — and, more importantly, to test therapies that remove such damage from aging tissues, in order to restore youthful functionality to aging bodies. Feeding, housing, cleaning, and providing basic veterinary and other care to a colony of small mammals for this long is expensive, and introduces a burdensome delay between experimental conception and execution — and just as you begin to want to study the animals, the colony begins suffering from attrition. As the National Institute on Aging (NIA)’s Interventions Testing Program (ITP)‘s Dr. Richard Miller has emphasized, “the real production cost of mice rises not linearly with chronologic age, but instead in proportion to the mortality rate, i.e. as an exponential function of age [our emphasis]. If half your mice live to age 24 months, then producing a single 24 month old mouse requires you to pay someone to house two mice for 24 months, one of which has just died. If only 10% of the mice survive to age 32 months, then the real cost of each 32 month old mouse is the cost of raising 10 mice for anywhere from 18 to 32 months to get the one alive at 32 months. … The nominal cost of a 32 month old mouse (at $0.58/cage/day) is $140, but adjusting for attrition and disease gives a real cost closer to $1,400 each.”
Meanwhile, promising experiments can founder upon the sheer passage of time: ambitious and talented graduate students lose patients or move on, grants expire, priorities and incentives shift. Indeed, amongst the chief reasons for the rising use of extremely short-lived model organisms (such as the roundworm C. elegans and the fruit fly D. melanogaster) in biogerontology in the last decade or so has been that they age and die so quickly that results can be expected in days or weeks instead of years. Unfortunately, they are not often useful as models for testing rejuvenation biotechnologies, simply because the causes of their death and disease are often quite different from our own: notably, neither organism develops true cancers.
Some researchers resort to shortcuts to compress the intrinsic delay introduced by the relatively long lifespans of laboratory rodents with a variety of shortcuts, including administering toxins that add to the burden of cellular and molecular lesions characteristic of the degenerative aging process and accelerate the appearance of age-related disease, or using strains of mutant animals that putatively suffer from “accelerated aging.” Unfortunately, both of these approaches have a cart-and-horse problem: the very linkage between the pathologies observed and the intrinsic aging process has been overlaid by processes which may or may not faithfully replicate the causes or results of aging on those same pathologies. How, in other words, do researchers know that the lesions and physiological and metabolic abnormalities that their experimental designs impose are actually equivalent to the superficially-similar phenotype of a “naturally”-aging animal? Or that therapies that prevent, ameliorate, or remove and repair such induced lesions will have similar effects on an animal (or a human being) that has acquired similar-seeming lesions from quite different mechanistic origins?
Another way that researchers sometimes try to foreshorten the delay between experimental conception and execution in studies involving the degenerative aging process is to compare young-adult animals to animals that are barely weaned, instead of genuinely old animals to young-adult ones. While aging has doubtless occurred in both designs, the former type results inevitably in severe confounding between ongoing developmental changes and the stochastic process of age-related decay. Or, again, rejuvenation biotechnologies are tested in young animals that have been subjected to acute experimental insult (such as induced myocardial infarction and stroke) that mimic those that occur as a result of structural decay and metabolic disturbances in the bodies of aging organisms. Such studies deliver a single, severe, but uncomplicated strike to a body that is otherwise in the pristine structural and metabolic condition of youth; as a result, they fail to capture the myriad of ways in which the degenerative aging process both exacerbates the injury itself, and weakens the body’s regenerative response to it — both its intrinsic healing response, and the local milieu in which rejuvenation biotechnologies must act. Parabiosis experiments by Irina Conboy and others have clearly shown, for instance, how differently stem and progenitor cells behave in young and biologically aged tissues: delivering pristine stem and progenitor cells into the body of an aged animal after injury leads to a substantially poorer outcome than does providing the same cells to young animals with similar trauma. *
For all of these reasons, it is imperative to the progress of basic biogerontology and translational rejuvenation biomedicine for researchers to be able to work with genuinely aged animals and their tissues. Recognizing that imperative — and the challenges that it poses to practicing researchers — the NIA moved almost two decades ago to establish a semi-centralized system of aged rodent colonies. The colonies include the most widely-used strains of healthy, longevous rats and mice, maintained under specific pathogen-free conditions, housed according to standardized protocols, and fed standardized diets. From these colonies, NIA makes live animals, tissue, or serum samples from animals at various ages available to researchers. To investigate the effects of retarded aging, Calorie restricted (CR) and (until recently) slow-aging Ames and Snell dwarf mice of the same ages have also been raised and made available. By making such animals readily and quickly available, the NIA’s aged rodent colony system has clearly played an important role in facilitating the great expansion of biogerontology research in recent decades, generating research that was foundational to our current position at the cusp of a revolution in rejuvenation biotechnology.
Excellent a resource as these aged animal colonies may be, however, NIA has in recent years been forced to be almost miserly in their distribution. The NIA’s fiscal and managerial resources are limited, and the demand of researchers for aged animals has chronically exceeded the organization’s ability to supply them. Originally, NIA provided aged animals to NIA and some Veterans’ Administration researchers at very low cost, and at heavily-subsidized pricing to outside researchers. But in 2006, budgetary and other constraints forced NIA to greatly restrict access to the aged rodent program, while forcing users to pay more of the true cost of raising the animals. It even considered discontinuing the CR colony altogether when the then-current cohorts expired, because the much greater longevity of these animals concomitantly increases their price over and above the dear cost of aged ad libitum-fed animals. These restrictions were loosened somewhat in 2009 — only to be re-imposed more severely than ever in the summer of 2010, when NIA stopped providing aged animals to any but NIA-funded projects. Today, access to these precious living resources is limited to projects directly related to aging and funded by either NIH or other Federal agencies, or by US nonprofit research organizations. While exceptions can be granted, standard policy is to restrict the number of animals allocated to a given grantee each month; and, as noted above, slow-aging Ames and Snell dwarf mouse colonies are being terminated. It is difficult to know how much valuable research has been delayed or abandoned over the last decade due to scientists’ sheer inability to access aged animals on a timely and cost-effective basis.
Now, a collaboration of British research organizations has come up with a completely new model to give scientists greater access to the aging animals that are the linchpin of progress in basic biogerontology and rejuvenation research.
... And A New "Prefabrication" Model
The MRC Harwell center for mouse genetics and the Centre for Integrated research into Musculoskeletal Ageing (CIMA) at the the Universities of Sheffield and Newcastle recently devised a model to get much more data out of the aged mice that are already in rodent vivaria across the UK and beyond. And with funding provided by the Wellcome Trust, the new Shared Ageing Research Models (ShARM) resource is now up and running. Headed by CIMA mesenchymal stem cell biologist Dr. Ilaria Bellantuono, ShARM uses a collaborative, decentralized, and “lean” approach to increasing scientists’ access to aging animals for biogerontology research. The approach is quite different from the system used by the NIA. Instead of providing more mice to the scientists that need them for research, ShARM gives more scientists access to the limited supply of aged animals and tissues that are already in the British and international research system, allowing them to unlock lifesaving information out of biological materials that would otherwise be lost to science.
Imagine a biogerontologist who has raised a colony of rats into senescence in order to study (for example) the relationship between age-related decline in cognitive function and associated changes in hippocampal gene expression. She runs the aged animals and young controls through a Morris water maze, and then sacrifices them to obtain brain tissue for a microarray study. Under status quo ante, two or three years’ worth of investment in those mice — and an unquantifiable amount of additional data on the impact of aging on the remainder of the aged organism — would simply go out in the biological waste material stream. But by participating in ShARM’s biorepository, the researcher can open up access for multiple additional laboratories to mine what the degenerative aging process has seared into the same animals’ otherwise-forfeited tissues and serum.
To participate in ShARM, the original researcher collects and flash-freezes multiple young-control and old animal tissues in accordance with a standardized protocol — tissues that would otherwise be so much biological waste material. A small fund is available within ShARM to award researchers whose samples meet certain minimum criteria with up to £55 per donated mouse; these monies not only defray the original researcher’s costs for raising the animals (and for then harvesting, submitting, and documenting the tissues), but incentivize donation and the taking of the care required to submit better-quality tissue samples.
These are then stored at a secure and proficient tissue bank, along with documentation of the samples’ provenance. Researchers looking to perform studies with such tissues can then browse the biorepository databases and select samples that meet their research needs. The cost to the second (and, potentially, third, fourth, or more) researcher to obtain these samples is minimal: just a small administrative fee (£35/tissue) to help ensure the sustainability of ShARM as a nonprofit organization, amounting to about a third of what live aged animals cost when purchased from the NIA even with its generous subsidy, and a much smaller fraction of what it would have cost to raise an entirely new colony of animals for each of the several studies that might now make use of the animal’s tissues.
In addition to banking tissues from already-sacrificed animals, ShARM also maintains an anonymized database of live colonies of aging animals, including information on information on rodent strain, current age, expected time of sacrifice, and husbandry. The database thus acts as matchmaker or clearing house for collaboration between researchers maintaining live colonies of aging rodents and other scientists needing bespoke or non-frozen tissue samples, or even to generate a side-project in an ongoing live animal study.
ShARM is also a very open program, giving quick and inexpensive access to tissues and serum of animals that have undergone degenerative aging to any legitimate biogerontology researcher in Britain and across the world. The availability of both banked and on-demand tissue samples, and the opportunity for collaboration with principal investigators with registered live animal colonies, makes it possible to move from conceptualizing an experiment to executing it in far less time, and with far fewer logistical requirements, than had previously been possible except through informal personal networks. In our hypothetical example, the original investigator was focused on the brain, but her participation in ShARM would allow other investigators to perform studies on the histology of the same animals’ muscles and kidneys; on metabolomic or glucoregulatory changes in the serum; or on any number of additional subjects outside of the original researcher’s specialty and beyond her budget or technical capacity to investigate, or the outside investigators’ ability to support with animals of their own.
ShARM will also foster collaboration and the sharing of information and advice amongst biogerontologists working with laboratory rodents with the forthcoming rollout of MiCEPACE. In addition to creating a convenient, centralized portal for the scattered and informally-shared information and resources available elsewhere on the husbandry, lifespan, and pathology of aging mouse strains, MiCEPACE will host online discussion fora for ShARM members to share data, experience, and advice on these and other subjects across specialties and ranges of background. Sara Well, the ShARM welfare lead at MRC Harwell, elaborates:
Commonly used indicators of ill health such as reduced activity and loss of coat condition are also natural signs of stock progressing in age. We plan to have discussion boards on pathology reports, behavioural observations (such as aggression, stereopathy) and reproductive capability (timing of the end of fertility). By using standardised language and sharing welfare assessment regimes, such as cage-side observations and subsequent pathology, it will be possible to develop true indicators of welfare concerns and develop appropriate assessments. In such a way it will be possible to define justified humane endpoints for termination of experimental stock whilst preserving the best scientific outcome.
I would also add that such observations will further extend and confirm what is known about the phenotype of degenerative aging in these strains, and potentially to develop new endpoints for intervention studies.
MiCEPACE will also host forums where users can give feedback on the ShARM resources themselves. When problems or areas for improvement are widely-voiced, ShARM will establish task forces recruited from the users themselves to tackle them.
And while the specifics of its implementation have not yet been finalized, ShARM also plans to establish collaborative infrastructure for a highly innovative form of distributed research in biogerontology. As noted above, the first form of scientific collaboration enabled by ShARM will be that when one investigator performs and publishes a study of (for example) the aging mouse brain , the biorepository and live aging animal colony systems will allow other researchers to study tissues that are surplus to the original investigation but critical to their own research. But beyond this, the biorepository and live aging animal colony systems will encourage the researchers to create new research collaborations. With the resulting centralized database, researchers will be able to choose to bring their data together with findings derived by other investigators from other tissues from the same animal, so that when one researcher publishes data on a given mouse’s brain, and another on its skeletal muscles, and another on its retinas, and so on, MiCEPACE will give all of these scientists the power to bring their scattered observations together across geographical and disciplinary distances, so that with all participants’ permission they can generate a kind of “virtual aged mouse” for collaborative study.
This novel capability will allow those researchers and perhaps others to see all of the different observations that were made in a given mouse — and others from the same colony and the same laboratory — in a wider context, drawing a fuller picture of aging and of the effects of intervention, and creating the opportunity for new correlative and other discoveries to be made. There are precedents for this in the use of public health registries in epidemiological research, but if the implementation of this new system fulfills the vision behind it, this aspect of the innovation in experimental biomedical research methods will be, literally, without precedent.
Through all of these tools, ShARM is creating new efficiencies in biogerontology and rejuvenation biotechnology research, giving more scientists the opportunity to study the biological aging process and ways to intervene in the process, and maximizing the scientific value of every aging mouse in the system. Precious data that would otherwise be lost to science is reclaimed, while reducing the financial costs of the science and the number of animals required to give new biomedical insights that will save human lives and suffering, and potentially increasing the granularity of what is known about aging in individual mice to levels unreachable by individual scientists working in isolation.
We at SENS Foundation are impressed with the innovation that the ShARM collaborators have demonstrated, will look for opportunities for scientists in the SENS Research Center and SENS Foundation’s extramural scientific partners to make use of it, and encourage others to do the same. Above all, we look forward to seeing new insights on the ravages of aging revealed, and new ways to prolong, preserve, and restore youthful health developed, thanks to the tools that they have put in the scientific community’s hands.
*SENS Foundation is exploring options for research extending our understanding of both the impairment of the regenerative response to rejuvenation biotechnologies when delivered to tissues ravaged by a lifetime of unrepaired damage and (mal)adaptive metabolic compensation to same, and the potential to mitigate or reverse those impairments by repairing the underlying damage or therapeutic mimicry of the youthful local milieu.