Telomeres and their role in cellular aging, and thus the organism aging (senescence), was brought to light by the Russian biologist Aleksei Olovnikov in 1971. Olovnikov pointed out that the limit of cell replication correlated with telomeres length. Telomeres are located at the end of our chromosomes, their role is literally to protect our DNA during cell replication, to prevent loss of information or any other anomalies. Thus, the telomere can be considered as a shield that avoids poor cell replication by protecting our chromosomes. However, the telomere is shortened with each cell division, and when it reaches a critical size, the cell reaches its replicative limit and the organism ages. Their original length is genetic and therefore different for each individual. However, in 1985, Elizabeth Blackburn and Carol Greider highlight telomerase, an enzyme capable of limiting telomere shortening by synthesizing new strands of telomeric DNA. Their work was rewarded in 2009 by the Nobel Prize in Physiology or Medicine. Blackburn's work also shows that telomerase not only limits the shortening of telomeres, but also allows them to be lengthened, thereby increasing the replication potential of a cell and thus delaying aging. In addition, following numerous studies (both physiological and psychological), Blackburn and Epel show that telomerase activity and telomere length vary greatly according to many factors: physical activity, dietary habits and psychological stress (learn more about their work with their book: "The telomere effect").
Read also: Our article about the relationship between telomerase and physical activity
Studies show that sirtuin 1 (SIRT1) could play a crucial role in protecting telomeres. SIRT1 (Silent mating type Information Regulator Two homolog 1) is an NAD+ (Nicotinamide Adenine Dinucleotide) dependent deacetylase protein. It is involved in many biological processes such as inflammation, cell death and metabolism by regulating other target proteins via deacetylation (i.e. removal of an acetyl group), such as FOX01, UCP2, PGC-1α, NF-kB and p53, which increases their transcription and leads to reduced inflammation, improved glucose metabolism, regulation of insulin secretion, increased mitochondrial biogenesis and function, and involvement in cell senescence. In addition, numerous studies have already shown that there is a positive relationship between SIRT1 concentration and physical activity.
Master athletes are athletes over 35 years old. Within this category, depending on the sport, there are different sub-categories depending on the age of the athletes. These athletes are an interesting model because generally they do not present the health problems that can be found in the population of the same age but whose level of physical activity is non-existent or low. Some studies have shown that Master athletes have higher levels of SIRT1 than their sedentary counterparts. But is there a link between SIRT1 levels, insulin secretion and telomere length?
To answer this question, Brazilian researchers compared the concentrations of SIRT1, insulin and telomere length in Master athletes and their physically inactive counterparts. To do this, the researchers recruited 52 Master athletes (50.0 ± 7.3 years old) and 19 sedentary individuals (47.6 ± 8.9 years old). The Master athletes had been training continuously for at least 15 years and were competing at national or international level in athletics (21 endurance runners and 31 sprinters). Blood samples were taken for each individual.
The main results of this study show that compared to sedentary and inactive individuals, insulin concentration was significantly lower, SIRT1 concentration was significantly higher, and telomere length was significantly greater in Master athletes (see Figures below). No significant differences were observed between endurance runners and sprinters.
Master athletes had 18% less body mass and 41% less total body fat than their sedentary and inactive counterparts.
Statistical analyses showed that SIRT1 concentration was inversely correlated with insulin concentration (r = -0.38, p = 0.001) (weak correlation) and positively correlated with telomere length (r = 0.65, p = 0.001) (moderate correlation). Telomere length and insulin concentration were not correlated.
Mechanical and metabolic stimuli due to exercise induce inflammatory and oxidative responses and enhance DNA repair capacity, increase mitochondrial biogenesis and insulin sensitivity. Insulin and IGF-1 are directly associated with the mTOR pathway and inversely correlated with the AMPK pathway. AMPK and SIRT1 regulate each other and share many target molecules that are related to longevity.
Increasing SIRT1 through exercise decreases the expression of pro-inflammatory cytokines such as TNF-α and IL-6, which ultimately reduces oxidative stress. Furthermore, SIRT1 plays an important role in the regulation of insulin secretion from pancreatic β-cells. Reducing SIRT1 can lead to apoptosis (the process by which cells initiate self-destruction in response to a signal) of these cells. Increasing SIRT1 would prevent the decrease in the number of β-cells. Studies have shown that Master athletes have lower insulin resistance than their sedentary and inactive counterparts.
Concerning telomere length, the positive correlation with SIRT1 would seem to indicate a positive role of physical activity on longevity. Of course, it is possible to assume that Master athletes are genetically predisposed to physical activity. But studies have already shown the impact of physical activity on telomere length and increased SIRT1 concentration.
Moderate to intense physical activity regularly practiced over many years stimulates our antioxidant and anti-inflammatory defense systems, which are managed by, among others, SIRT1, and is associated with longer telomeres and increased insulin sensitivity. SIRT1 deacetylates FOX01, PGC-1α and NF-kB which contributes to positive effects on glucose metabolism, insulin secretion, mitochondrial function, inflammatory responses, and telomere length.
The nutritional factor, which is of primary importance when it comes to longevity, was not considered in this comparative study. It is possible to assume that Master athletes, because of their practice and lifestyle, pay more attention to their diet, especially as it will directly impact their sports performance. Numerous studies show that our food intake, quantity, quality and distribution in a day have a marked influence on the mechanisms related to longevity.
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