Mois : juillet 2024

Scientists have shown that prolonged, continuous expression of reprogramming factors counters cognitive decline in old rats and probably decreases their epigenetic age [1].

Reprogramming and cognitive function

Cellular reprogramming, the act of bringing differentiated cells back to a stem-like pluripotent state by expressing certain genes, has been one of the hottest subfields in longevity in recent years. Reprogramming, which can be either full or partial, also results in cellular rejuvenation.

Numerous studies have shown that reprogramming can increase healthspan and lifespan in animal models. However, in vivo reprogramming can also lead to disease and death due to harsh side effects [2]. Creating effective and safe reprogramming protocols is very much a work in progress.

One aspect that has not received a lot of attention is the impact of cellular reprogramming on age-related cognitive decline. In this new study published in GeroScience, researchers delivered viral vectors carrying the four “classic” reprogramming factors known as OSKM into the hippocampi of aged female rats. A month after the injections, the researchers ran tests to ascertain their effects on the animals’ cognitive function.

Unlike creating transgenic OSKM-expressing mice, introducing OSKM via viral vectors has a good safety profile, at least for now. As their inspiration, the authors mention “the pioneering results achieved by David Sinclair’s team employing OSK gene therapy in the retina of mice.” [3] Sinclair’s group had omitted the fourth factor, c-Myc, because of its cancer-causing (oncogenic) potential, but in this new study, the researchers used the full four-factor cocktail.

You can teach an old rat new tricks

The researchers employed the Barnes memory test to assess learning performance and spatial memory. During six acquisition training (AT) sessions, the rats were tasked with locating an escape box within two minutes, which was concealed beneath one of 20 holes around the edge of the platform.

Old untreated rats showed marked cognitive decline compared to young animals. While young animals learned the location of the escape hole quickly, and their results plateaued after three to five trials, their aged counterparts seemed to have lost this learning ability almost completely.

The OSKM-treated rats were somewhere in the middle, demonstrating notable improvement on the fifth and the sixth attempts, although still not on par with the young animals. After an improvement on AT2, the results worsened on AT3 and AT4, which the researchers do not have a definitive explanation for yet.

Steve Horvath, a renowned geroscientist currently with UCLA and Altos Labs, and the corresponding author on the study, told Lifespan.io that “there might have been a major stress response that initially negated the beneficial effects. Once the stress response subsided, the benefits became apparent. In other words, it could be a hormesis effect at the level of brain cells.”

The second lead author, Rodolfo Goya of the National University of La Plata in Argentina, suggested that the AT2 value might have been noisy and that the real statistically significant improvement in the study group occurred starting with AT5.

The expression of the OSKM genes in the dentate gyrus, a hippocampal region, was detectable for at least four weeks after the injection. According to the paper, “39 days of continuous OSKM expression induced no pathological alterations in the hippocampal parenchyma or other brain regions.”

Mild biological age decrease

The researchers then investigated whether the treatment had led to a decrease in biological age versus controls, as measured by three different epigenetic clocks. Such clocks, pioneered by Horvath himself, are based on DNA methylation patterns that are known to correlate with chronological age and mortality. According to the clocks, the treatment led to mild rejuvenation. The difference was statistically significant when a one-tailed p-value test was used – in other words, where only the possibility of the treatment lowering biological age, but not of increasing it, was considered.

“I find it very surprising that this gene therapy seems to rejuvenate both cognitive function and the methylation patterns of the hippocampus,” Horvath said. “This paper contributes to the growing body of literature suggesting that interrupted reprogramming could have beneficial effects on the brain.”

In our study, we specifically investigated the effects of OSKM gene delivery on hippocampal DNA methylation. We found suggestive evidence of epigenetic rejuvenation, corroborated by two separate epigenetic clocks designed specifically for rat and mouse brain samples. These findings align with numerous studies that have also reported signs of epigenetic rejuvenation in human and mouse cells and tissues following OSKM or OSK application. While our sample size was limited (n=8 old OSKM-treated samples versus n=6 old controls), these epigenetic clocks, trained using independent data, provide insights due to their accuracy.

Literature

[1] Horvath, S., Lacunza, E., Mallat, M. C., Portiansky, E. L., Gallardo, M. D., Brooke, R. T., … & Goya, R. G. (2024). Cognitive rejuvenation in old rats by hippocampal oskm gene therapy. GeroScience, 1-15.

[2] Parras, A., Vílchez-Acosta, A., Desdín-Micó, G., Picó, S., Mrabti, C., Montenegro-Borbolla, E., … & Ocampo, A. (2023). In vivo reprogramming leads to premature death linked to hepatic and intestinal failure. Nature Aging, 3(12), 1509-1520.

[3] Lu, Y., Brommer, B., Tian, X., Krishnan, A., Meer, M., Wang, C., … & Sinclair, D. A. (2020). Reprogramming to recover youthful epigenetic information and restore vision. Nature, 588(7836), 124-129.

In Aging Cell, researchers have published new data on the relationship between senescence and the extracellular matrix in the tendons of older people.

Easy to injure, hard to heal

The researchers begin this paper by pointing out that injuries to the musculoskeletal system are responsible for over a quarter of the years that elderly people spend living with disability instead of good health [1]. A significant portion of these injuries are to the tendons; for example, over half of people over 80 have sustained injuries to the tendons of a shoulder’s rotator cuff [2]. Compounding the problem, older people have a much harder time healing from these injuries than younger people [3].

The tendons are largely composed of the extracellular matrix (ECM), which is primarily made of collagen, along with an interfascicular matrix composed of collagens and proteins [4]. Exactly how these tissues age is unclear, as data often depends on the exact age of the person and the specific tendon measured. Cross-linking of this collagen plays a significant role [5], as do age-related cellular changes: with aging, the cells in the tendons do not proliferate as well [4], which is likely to be a reason for the slower healing.

The cells responsible for tendon maintenance (tenocytes) engage in a balancing act, producing matrix metalloproteinases (MMPs) to destroy damaged matrix tissues [6] while also synthesizing proteins with which to rebuild these tissues [7]. Exercise and a lack of exercise can affect this process as well.

However, cellular senescence might put its thumb on the scale. Senescent cells secrete multiple compounds, and MMPs are among them [8]. These researchers note that because 2D models do not accurately replicate how cells interact with each other and with the matrices surrounding them, the effects of senescence on tendons have not been properly examined. For this purpose, they used a system of live tendon explants that they had used in a previous study [9].

Why young cells heal better

There were four groups of cells used in total: three of them were taken from young mice, with one group being exposed to radiation and another group being exposed to doxorubicin, both of which induce senescence. One group of young cells was not exposed to any senescence inducers, and the fourth group was from naturally aged mice.

After confirming that doxorubicin and radiation induce senescence both in tendons and in tenocytes, the researchers examined how these cells functioned by placing them in a cellular culture. This environment is devoid of stresses, so it replicates a mechanical-unloading injury. Interestingly, natural aging was less harmful in some respects than induced senescence: the cells exposed to both of these inducers lost the ability to produce common Type 1 collagen over time in this culture, and critical proteoglycans used for tissue creation were less present as well. The researchers hypothesized that this reflects senescent tendons’ inability to heal properly.

Similarly, amino acids that are part of the collagen formation process were significantly more present in the healthy young tendons than in the other three. The researchers also discovered metabolic changes in the cells, although that was outside the scope of this experiment.

Not all MMPs are the same

Some of the MMPs that the researchers measured had completely different trajectories than others. After 14 days in culture, MMP-1 was significantly less expressed in the three senescent groups and maintained in the young group. MMP-3, curiously, was increased the most in the induced-senescence groups, increasing nearly as much in the young group and only somewhat increasing in the aged roup. MMP-13, on the other hand, also increased in all groups, but by far increasing the most in the naturally aged group. These findings, in addition to findings showing that inflammatory chemicals were broadly increased in all groups, surprised the researchers, who had expected more evidence of tissue breakdown due to senescence.

These findings are explained by a lack of stress being interpreted as injury, which causes the cells to behave in a way that is similar to senescence. However, not all of these changes are the same; for example, cells responding to injury do not stop dividing as senescent cells do, and it is unclear whether or not these changes are permanent [10].

The researchers then performed a preliminary investigation with tissues under stress, comparing doxorubicin-treated young cells to untreated young cells. Amazingly, they found few differences in the performance of these tissues. Therefore, they had to conclude that the senescence-associated secretory phenotype (SASP) is either not a major part of failing tendon function under normal circumstances or affects it in a way that this study was unable to detect. While these are largely negative results, they clear an important space and encourage investigation into other areas.

Literature

[1] Briggs, A. M., Cross, M. J., Hoy, D. G., Sànchez-Riera, L., Blyth, F. M., Woolf, A. D., & March, L. (2016). Musculoskeletal health conditions represent a global threat to healthy aging: a report for the 2015 World Health Organization world report on ageing and health. The Gerontologist, 56(suppl_2), S243-S255.

[2] Teunis, T., Lubberts, B., Reilly, B. T., & Ring, D. (2014). A systematic review and pooled analysis of the prevalence of rotator cuff disease with increasing age. Journal of shoulder and elbow surgery, 23(12), 1913-1921.

[3] Ackerman, J. E., Bah, I., Jonason, J. H., Buckley, M. R., & Loiselle, A. E. (2017). Aging does not alter tendon mechanical properties during homeostasis, but does impair flexor tendon healing. Journal of Orthopaedic Research, 35(12), 2716-2724.

[4] Siadat, S. M., Zamboulis, D. E., Thorpe, C. T., Ruberti, J. W., & Connizzo, B. K. (2021). Tendon extracellular matrix assembly, maintenance and dysregulation throughout life. Progress in Heritable Soft Connective Tissue Diseases, 45-103.

[5] Couppe, C., Hansen, P., Kongsgaard, M., Kovanen, V., Suetta, C., Aagaard, P., … & Magnusson, S. P. (2009). Mechanical properties and collagen cross-linking of the patellar tendon in old and young men. Journal of applied physiology, 107(3), 880-886.

[6] Sbardella, D., R Tundo, G., Francesco Fasciglione, G., Gioia, M., Bisicchia, S., Gasbarra, E., … & Marini, S. (2014). Role of metalloproteinases in tendon pathophysiology. Mini Reviews in Medicinal Chemistry, 14(12), 978-987.

[7] Aggouras, A. N., Stowe, E. J., Mlawer, S. J., & Connizzo, B. (2024). Aged Tendons Exhibit Altered Mechanisms of Strain-Dependent Extracellular Matrix Remodeling. Journal of Biomechanical Engineering, 1-41.

[8] Coppé, J. P., Desprez, P. Y., Krtolica, A., & Campisi, J. (2010). The senescence-associated secretory phenotype: the dark side of tumor suppression. Annual review of pathology: mechanisms of disease, 5(1), 99-118.

[9] Connizzo, B. K., Piet, J. M., Shefelbine, S. J., & Grodzinsky, A. J. (2020). Age-associated changes in the response of tendon explants to stress deprivation is sex-dependent. Connective tissue research, 61(1), 48-62.

[10] Chu, X., Wen, J., & Raju, R. P. (2020). Rapid senescence‐like response after acute injury. Aging Cell, 19(9), e13201.

New research demonstrated how transitioning from a typical Western diet composed of processed foods to a whole-food diet improved cardiometabolic health and body composition and impacted gut microbiome metabolites in elderly people [1].

You are what you eat

While this study was conducted in Australia, the foods commonly consumed there are similar to common foods in the United States and many other parts of the world. As the authors noted, this Western diet is composed mostly of industrially processed foods, is high in refined sugar, salt, and saturated fat, and is low in protein and fiber. This diet is a well-known contributor to obesity, comorbidities, and increased all-cause mortality [2, 3].

On the other hand, whole-food diets and plant-derived foods have been found to positively impact health [4]. Those diets are rich in fiber, micronutrients, phytochemicals, complex carbohydrates, and plant proteins that are usually absent in Western diets.

The authors also pointed out that the quality and ratios of macronutrients are important for a healthy diet. There has also been substantial research into plant and animal protein sources and the ratios of fats, carbohydrates, and protein in various diets.

Dietary interventions in the elderly

The authors of this 4-week randomized controlled trial aimed to assess the effects of plant or animal protein sources, the fat-to-carbohydrate ratio, and the impact of transitioning from a standard Western diet to a whole-food diet, which has not been previously assessed in older individuals.

The study participants were 113 healthy individuals between the ages of 65 and 75. The participants were divided into four groups, each following a different diet: omnivorous (which includes plant and animal food) with high fat, omnivorous with high carbohydrates, semi-vegetarian with high fat, and semi-vegetarian with high carbohydrates. Access to food was not limited. Diets were carefully planned to match energy and protein concentration and followed the same menu. However, specific items were tailored to match a treatment group. Participants kept food records regarding the amount of food consumed.

Major health improvements

The authors noted “improvement across all measured health domains independent of diet treatments.” They hypothesize that transitioning from a Western diet to a whole-food diet is greatly responsible for the observed improvements.

The researchers observed that participants’ total energy intake and appetite didn’t change during the study. However, the levels of FGF-21, a marker of protein appetite, were significantly changed. Reducing protein consumption by 21% increased the FGF-21 levels by 25%.

Previous research observed that lowering protein intake usually results in increasing total food intake as a compensatory mechanism, and this seems to be particularly common in environments with plenty of unhealthy food options. This study seems to agree with those observations, as the researchers observed a 5% increase in food intake. Additionally, participants with high baseline FGF-21 levels exhibited high protein appetite during the study.

Despite not observing significant changes in energy consumption, the researchers observed changes in the participants’ body composition: a 3% reduction in body weight, a 5% reduction in fat mass, and a 0.7% reduction in lean mass (including muscle mass). This modest reduction in fat-free mass didn’t affect muscle strength; on the contrary, tests on muscle function showed improvement.

The authors also note that participants lost, on average, 1.7 kilograms (3.7 pounds) in the week preceding the study. During that week, the participants were tasked with recording their normal food intakes, which served as their baselines for this study. Just the act of recording food intake may lead to weight loss, as participants unintentionally improve their diets or reduce the amount of food they eat in order to lessen the burden of recording it. If this baseline is already improved compared to participants’ actual diets, then the outcomes of the dietary intervention might be underreported. This baseline weight loss might have resulted from reduced alcohol consumption during the study.

The researchers also investigated markers of cardiometabolic health. They observed that the participants who consumed more vegetarian diets had the greatest reductions in diastolic blood pressure. They also observed some positive changes in all study groups, including systolic blood pressure; total, LDL, and HDL cholesterol; insulin level: and insulin resistance. These observations agree with previous research that links plant-based diets with better cardiometabolic health.

Treats for the gut microbiota

Food in the gut also feeds the armies of various microbes that live in the intestines. Among other factors, the numbers of various species is dependent on what they are fed, so these researchers investigated how the gut flora changed. The omnivorous, high carbohydrate group experienced the biggest change in gut microbiome diversity. However, all dietary interventions led to increased production of bacterial metabolites from the fermentation of dietary fiber, which aligns with the reported increase in fiber consumption. Those metabolites “have been associated with better health outcomes, conferring protective effects in inflammation, cancer, diabetes and cardiovascular diseases.”

The authors note that the relatively short duration of this study and the limited number of fecal samples collected for the analysis might not be sufficient to observe major changes to the gut microbiome. Other major factors impacting this microbiome were also not accounted for in this study.

In conclusion, our observational results suggest that transitioning from a “standard Australian diet” to feasible alternatives-whether moderately higher or lower in F:C [fat to carbohydrate] and predominantly plant- or animal-based can improve several health markers relevant to older age. This demonstrates that a healthy diet rich in fruit, vegetables, fibre, moderate amounts of protein, regardless of their sources, while restricting alcohol and highly processed food, can be beneficial for various health domains in older adults. Furthermore, PBD [plant-based-diet] appears to offer additional benefits for cardiometabolic health.

Literature

[1] Ribeiro, R. V., Senior, A. M., Simpson, S. J., Tan, J., Raubenheimer, D., Le Couteur, D., Macia, L., Holmes, A., Eberhard, J., O’Sullivan, J., Koay, Y. C., Kanjrawi, A., Yang, J., Kim, T., & Gosby, A. (2024). Rapid benefits in older age from transition to whole food diet regardless of protein source or fat to carbohydrate ratio: Arandomised control trial. Aging cell, e14276. Advance online publication.

[2] Ludwig, D. S., & Ebbeling, C. B. (2018). The Carbohydrate-Insulin Model of Obesity: Beyond “Calories In, Calories Out”. JAMA internal medicine, 178(8), 1098–1103.

[3] Schnabel, L., Kesse-Guyot, E., Allès, B., Touvier, M., Srour, B., Hercberg, S., Buscail, C., & Julia, C. (2019). Association Between Ultraprocessed Food Consumption and Risk of Mortality Among Middle-aged Adults in France. JAMA internal medicine, 179(4), 490–498.

[4] Song, M., Fung, T. T., Hu, F. B., Willett, W. C., Longo, V. D., Chan, A. T., & Giovannucci, E. L. (2016). Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality. JAMA internal medicine, 176(10), 1453–1463.