Mois : septembre 2024

In a recent study, researchers injected rats with mesenchymal stromal cells. They observed improvements in aging-related biomarkers and phenotypes in many organs [1].

The rejuvenating role of MSCs

Mesenchymal stromal cells (MSCs) can be obtained from diverse sources, including bone marrow, adipose tissue, perinatal tissue, and dental tissues [2].

MSCs have been shown to have multiple beneficial effects. Previous research has found that they can “alleviate oxidative stress and inflammatory responses, promote tissue repair, and restore proper immunological functions” [3, 4], stimulate angiogenesis [5], extend murine lifespan and healthspan, and have a protective effect against stem cell and fibroblast aging [6]. MSCs’ safety and efficacy have been shown in Phase I and II clinical trials investigating aging-related frailty [7].

Positive impact on aging biomarkers

This study aimed to comprehensively evaluate the impact of human-derived umbilical cord-derived mesenchymal stromal cells (UC-MSCs) on senescence in rats.

The researchers used ten naturally aged male rats (24 months old) and five young male rats (8 weeks old). They treated them with four weekly tail vein injections of UC-MSCs. The authors stated that they wished to have more animals in the study, but they were limited due to the scarcity of naturally aged animals.

The researchers observed a significant increase in p16, p21, SA-β-gal, and lipofuscin, which are aging-related factors and biomarkers of aging and senescence, in the heart, brain, lung, kidney, liver, spleen, intestinal tissues, and peripheral blood of aged rats. Depending on the tissue, this was observed for some or all of the markers. MSC treatment significantly reduced those markers.

The authors also measured oxidative stress markers. The levels of SOD, an enzyme that plays a role in preventing the toxic effects of free radicals, were decreased in the multiple tested organs and peripheral blood of aged rats. MSC treatment led to a significant increase in SOD levels.

Levels of MDA, a biomarker of lipid oxidative damage, significantly increased in multiple organs, brain tissue, and peripheral blood of aged rats, but MSC treatment resulted in a decrease in MDA.

The third marker, the antioxidant GSH, wasn’t consistent between different organs of aged rats. Still, the MSC treatment always increased its levels in measured tissues (but not always significantly) compared to aged controls.

The next group of measured biomarkers consisted of aging-related biomarkers related to the immune system: an antibody IgG (Immunoglobulin G) and two pro-inflammatory cytokines, IL-1β and IL-6.

The authors observed decreased levels of IgG in the brain, multiple organs, and peripheral blood of old rats compared to young rats. The difference in brain, liver, lungs, kidneys, and peripheral blood was statistically significant, and following MSC treatment, those levels increased.

In the lungs, kidneys, liver, and peripheral blood of aged rats, the researchers observed an increase in IL-1β and IL-6. MSC treatment decreased both of the cytokines in the lungs and kidneys and IL-1β in the liver.

The researchers summarize that there is an increase in aging-related factors, oxidative stress, and chronic inflammation in multiple organs of old rats. However, MSC treatment can significantly ameliorate these aging-related phenotypes.

Rejuvenating organs and the microbiome

Starting with the brain, the researchers investigated changes in two regions: the prefrontal cortex and the hippocampus. Previous research linked aging-related changes in those brain regions “to cognitive deficits, intellectual decline, sleep disorders, and circadian rhythm disruptions” [8].

The study’s authors observed aging-related phenotypes in those regions, for example, a significant decrease in the number of neurons, which was increased following MSC treatment along with improvement in other aging-related phenotypes.

Other organs also suffered from aging-related changes. Compared to young cells, aged heart cells exhibited age-related phenotypes, including accumulation of collagen fibers and increase in cellular size (hypertrophy). MSC treatment helped improve both of them.

The heart, along with the liver, also suffered from an age-related increase in the deposition of fats. Following MSC treatment, those fat depositions decreased in the old rats, suggesting that MSCs have an impact on lipid metabolism.

It is known that aging affects microbiota and that gut diversity in the elderly is lower compared to young people [9]. In this study, the researchers observed aging-related changes in the microbiomes of rats.

MSC treatment of older rats helped to increase microbial diversity and rejuvenate the microbiome towards that of younger animals. The authors suggest that such alterations might have broader effects on other organs through the modulation of amino acid and carbohydrate metabolism.

Rejuvenating the immune system

Aging is associated with the decline of the proper functioning of the immune system in a process known as immunosenescence. One of the manifestations of aging immune systems is a change in different types of immune cells, specifically ”changes in the ratio of naïve T cells and memory T cells, imbalanced CD4 + T cells and CD8 + T cells” [10].

In this study, the researchers observed those and other aging-related phenotype in the aged rats. Those included, reduced CD4 + T/CD8 + T ratio in peripheral blood, disordered structure of spleen, lower number of spleen cells, and higher number of apoptotic spleen cells. MSCs treatment improved those phenotypes in the aged rats.

More comprehensive, but not long-term

While the anti-aging benefits of MSCs were studied previously, the authors emphasize that their study is more comprehensive than the previous research and shows “that MSCs can modulate the entire organism’s aging process and achieve deceleration of aging through reciprocal interactions among different organs and systems.”

However, further research is needed into the molecular mechanisms of MSCs’ anti-aging action. There is also a need to assess such treatment’s long-term effects and possible side effects.

Literature

[1] Wang, L., Deng, Z., Li, Y., Wu, Y., Yao, R., Cao, Y., Wang, M., Zhou, F., Zhu, H., & Kang, H. (2024). Ameliorative effects of mesenchymal stromal cells on senescence associated phenotypes in naturally aged rats. Journal of translational medicine, 22(1), 722.

[2] Galipeau, J., & Sensébé, L. (2018). Mesenchymal Stromal Cells: Clinical Challenges and Therapeutic Opportunities. Cell stem cell, 22(6), 824–833.

[3] He, Y., Chen, D., Yang, L., Hou, Q., Ma, H., & Xu, X. (2018). The therapeutic potential of bone marrow mesenchymal stem cells in premature ovarian failure. Stem cell research & therapy, 9(1), 263.

[4] Wang, L., Li, Y., Xu, M., Deng, Z., Zhao, Y., Yang, M., Liu, Y., Yuan, R., Sun, Y., Zhang, H., Wang, H., Qian, Z., & Kang, H. (2021). Regulation of Inflammatory Cytokine Storms by Mesenchymal Stem Cells. Frontiers in immunology, 12, 726909.

[5] Xiao, X., Xu, M., Yu, H., Wang, L., Li, X., Rak, J., Wang, S., & Zhao, R. C. (2021). Mesenchymal stem cell-derived small extracellular vesicles mitigate oxidative stress-induced senescence in endothelial cells via regulation of miR-146a/Src. Signal transduction and targeted therapy, 6(1), 354.

[6] Dorronsoro, A., Santiago, F. E., Grassi, D., Zhang, T., Lai, R. C., McGowan, S. J., Angelini, L., Lavasani, M., Corbo, L., Lu, A., Brooks, R. W., Garcia-Contreras, M., Stolz, D. B., Amelio, A., Boregowda, S. V., Fallahi, M., Reich, A., Ricordi, C., Phinney, D. G., Huard, J., … Robbins, P. D. (2021). Mesenchymal stem cell-derived extracellular vesicles reduce senescence and extend health span in mouse models of aging. Aging cell, 20(4), e13337.

[7] Zhu, Y., Ge, J., Huang, C., Liu, H., & Jiang, H. (2021). Application of mesenchymal stem cell therapy for aging frailty: from mechanisms to therapeutics. Theranostics, 11(12), 5675–5685.

[8] Satoh, A., Imai, S. I., & Guarente, L. (2017). The brain, sirtuins, and ageing. Nature reviews. Neuroscience, 18(6), 362–374.

[9] Claesson, M. J., Jeffery, I. B., Conde, S., Power, S. E., O’Connor, E. M., Cusack, S., Harris, H. M., Coakley, M., Lakshminarayanan, B., O’Sullivan, O., Fitzgerald, G. F., Deane, J., O’Connor, M., Harnedy, N., O’Connor, K., O’Mahony, D., van Sinderen, D., Wallace, M., Brennan, L., Stanton, C., … O’Toole, P. W. (2012). Gut microbiota composition correlates with diet and health in the elderly. Nature, 488(7410), 178–184.

[10] Goronzy, J. J., & Weyand, C. M. (2013). Understanding immunosenescence to improve responses to vaccines. Nature immunology, 14(5), 428–436.

Scientists have compiled the most complete genome ever of the Greenland shark, an exceptionally long-lived species. Living up to 400 years probably has a lot to do with superior DNA repair mechanisms.

Methuselahs of the sea

Greenland sharks, giant, slow-moving abyss dwellers, hold the title of the longest-lived vertebrate. While estimating a wild species’ maximum lifespan is challenging, Greenland sharks are thought to live to about 400, give or take a century [1]. The closest other shark species can get to that is 100 years, which is already respectable.

Scientists have been studying Greenland sharks in an attempt to understand the origins of their exceptional longevity. In a new paper, currently published as a pre-print that has not yet been peer-reviewed, a group of researchers report having compiled the most complete Greenland shark genome ever. This allowed them to make a few educated guesses.

Don’t let it break

Just like the Greenland shark itself, its genome is gigantic and full of repetitive sequences. Those account for 70% of the shark’s genome and consist mostly of retrotransposons: remnants of retroviruses that have inserted their genetic code into their hosts’ genomes over the eons of evolution. Some retrotransposons are still able to reproduce by copying themselves and inserting new copies back into the genome. Retrotransposon activity has been linked to multiple hallmarks of aging [2], and long-lived species must develop ways to mitigate it.

The researchers noticed the impressive conservation of gene order (synteny) between the Greenland shark and other shark species, such as the great white shark, even though they diverged about 250 million years ago. When we hear that sharks haven’t changed since the dawn of time, that’s what it means, genetically. “Overall, despite an evolutionary distance of several hundred million years between them,” the researchers write, “the Greenland shark and the great white shark show striking similarities in their genomic structure and organization.”

However, there still must be something in the Greenland shark’s genome that makes it live four times longer than any other shark species. Often, mechanisms that prolong lifespan involve gene duplication. For instance, elephants have several copies of the p53 gene, a crucial tumor suppressor [3].

When the researchers tested the Greenland shark’s genome for gene duplication, they found 81 genes that exist as single copies in all other members of Elasmobranch, a subclass of animals that includes sharks and rays, but have multiple copies in the Greenland shark. Those genes behave a lot like a network and, according to gene ontology analysis, are related to double-strand DNA break repair.

Interestingly, although p53 appears to act as this network’s master regulator, it exists as a single copy. However, that single p53 gene also carries a mutation specific to the Greenland shark.

“Taken together,” the authors conclude, “duplications of genes associated with DNA repair and the p53 pathway appear to distinguish the extremely long-lived Greenland shark from other Elasmobranch species, outlining the path for additional analyses and validations.”

The researchers also identified genes showing positive selection, i.e., representing significant evolutionary changes in the Greenland shark compared to closely related species. Interestingly, only eight such genes were found, which is more evidence that even relatively minor genetic changes can facilitate a massive lifespan extension.

The arms race

The authors hypothesize that what appears to be the Greenland shark’s superior DNA repair ability may have something to do with the abundance of retrotransposons in its genome. Since retrotransposons can themselves cause double-strand DNA breaks, it is possible that retrotransposon activity caused the development of highly efficient DNA repair mechanisms in sort of an arms race.

The researchers made the Greenland shark’s genome and troves of related data available to everyone via a dedicated genome browser. This means that you can try your luck in discovering other possible mechanisms that allow this amazing animal to outlive humans by a factor of four.

The expansion of retrotransposon sequences in both species contributed substantially to the increased genome sizes. In the case of the GLS, we have provided evidence that this mechanism may have contributed to the expansion of DNA repair gene sequences. Given that retrotransposons themselves are a source of double-strand breaks (Warkocki 2023), our findings suggest that the evolution of DNA repair genes and retrotransposons may be interlinked in the GLS. Specifically, retrotransposon activity may have led to the expansion of DNA repair-associated retrogenes, which, in turn, allowed for the tolerance of higher retrotransposon activity.

Literature

[1] Nielsen, J., Hedeholm, R. B., Heinemeier, J., Bushnell, P. G., Christiansen, J. S., Olsen, J., … & Steffensen, J. F. (2016). Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus). Science, 353(6300), 702-704.

[2] Gorbunova, V., Seluanov, A., Mita, P., McKerrow, W., Fenyö, D., Boeke, J. D., … & Sedivy, J. M. (2021). The role of retrotransposable elements in ageing and age-associated diseases. Nature, 596(7870), 43-53.

[3] Abegglen, L. M., Caulin, A. F., Chan, A., Lee, K., Robinson, R., Campbell, M. S., … & Schiffman, J. D. (2015). Potential mechanisms for cancer resistance in elephants and comparative cellular response to DNA damage in humans. Jama, 314(17), 1850-1860.

In a preprint published in bioRxiv, researchers have published their findings in applying an epigenetic clock to the axolotl, a salamander species that does not age like humans.

More than just regeneration

Axolotls, and salamanders more generally, are well-known for their regenerative capabilities, being able to grow back lost limbs [1]. These amphibians, similarly to naked mole rats, have not been found to age the way we do: they do not decline in physical function, their regeneration continues throughout life, they live a very long time, and their lifespan curve does not look like other species’ [2]. Despite their regenerative power, they are also notably resistant to cancer, even when directly injected with carcinogens [3].

In fact, with an average lifespan of 10-13 years, which is very high for a small amphibian, the axolotl does not live as long as other salamanders. This has made it attractive as a research target, as modern transfection and genetic analysis techniques that are normally associated with murine research have been developed to work with this species [4].

While there are known pan-mammalian epigenetic clocks that work on people, mice, and naked mole rats [5], the axolotl is an amphibian, not a mammal. However, as similarities have been found between the African clawed frog (another amphibian) and mammals [6], the researchers surmised that epigenetic aging is similar enough between these species for this line of inquiry to be effective. However, unlike mammals, amphibians’ epigenetic ages do not vary considerably between tissues.

No differences between old and young

The researchers found 5,386 epigenetic CpG sites that axolotls, clawed frogs, and mammals have in common. They then attempted to use an algorithm to create a clock with these sites that works over the axolotl’s lifespan. This effort failed completely: there appeared to be no significant correlation between epigenetic age and chronological age, whether they attempted to build a single-tissue or pan-tissue clock. This was in spite of having more than a sufficient number of high-quality samples to use, and an even closer examination failed to reveal any significant differences between the methylation of a 3.55-year-old axolotl and a 9.83-year-old axolotl.

However, the axolotls did appear to be aging earlier in life, so the researchers developed a clock that was only trained on animals up to 4 years of age. This clock was able to predict ages of these salamanders within a few months. The researchers, therefore, concluded that axolotl epigenetic aging is “biphasic”: they age up to a certain point, and then they simply stop epigenetically aging to any measurable degree.

An axolotl early-life clock was also demonstrated to be compatible with epigenetic clocks for clawed frogs and people. According to this dual-species clock, very young humans had similar methylation as very young axolotls, but as the humans aged, the axolotls did not age with them.

A closer examination revealed the similarities and differences. HOX genes, which are associated with organismal development, all change methylation in the early lives of people, frogs, and axolotls, demonstrating growth. However, CpGs that were associated with an increase in mortality risk, such as cancer, simply did not exist in the axolotl clock.

Even limb regeneration did not appear to age these animals. Cutting off an axolotl’s tail six times in a row did not have any significant effects on that area’s epigenetic age, although there was a trend towards being marked as epigenetically older. On the other hand, amputating one of its limbs three times made the epigenetics of that repeatedly regrown limb younger. The researchers found that this correlated with the expression of factors that are known to affect cells at various stages of differentation, and they posit that this “dynamic regulation may be central to the epigenetic rejuvenation that takes place upon limb regeneration.”

Medical professionals, and people who have suffered severe injuries, have desired to harness the salamander’s regeneration for a long time. Now, it appears that this regeneration might also come along with significant anti-aging effects. Applying these effects to mammals, however, will require significant amounts of time and experimentation.

Literature

[1] Brockes, J. P., & Kumar, A. (2008). Comparative aspects of animal regeneration. Annual review of cell and developmental biology, 24(1), 525-549.

[2] Yun, M. H. (2021). Salamander insights into ageing and rejuvenation. Frontiers in cell and developmental biology, 9, 689062.

[3] Ingram, A. J. (1971). The reactions to carcinogens in the axolotl (Ambystoma mexicanum) in relation to the ‘regeneration field control’hypothesis. Development, 26(3), 425-441.

[4] Murawala, P., Oliveira, C. R., Okulski, H., Yun, M. H., & Tanaka, E. M. (2022). Baculovirus Production and Infection in Axolotls. In Salamanders: Methods and Protocols (pp. 369-387). New York, NY: Springer US.

[5] Lu, A. T., Fei, Z., Haghani, A., Robeck, T. R., Zoller, J. A., Li, C. Z., … & Singh, K. (2023). Universal DNA methylation age across mammalian tissues. Nature aging, 3(9), 1144-1166.

[6] Zoller, J. A., Parasyraki, E., Lu, A. T., Haghani, A., Niehrs, C., & Horvath, S. (2024). DNA methylation clocks for clawed frogs reveal evolutionary conservation of epigenetic aging. GeroScience, 46(1), 945-960.