Effectiveness of senolytics
A non-invasive biomarker will evaluate the effectiveness of the destruction of aged cells
Oleg Lischuk, N+1
In the future, it can be used to test the effectiveness of therapy for age-related diseases. The results of the study are published in the journal Cell Metabolism (Wiley et al., Oxylipin biosynthesis reinforces cellular senescence and allows detection of senolysis).
Replicative cell aging, or senescence, is a condition in which cells that have been subjected to metabolic stress and have accumulated irreversible damage to DNA and organelles stop dividing (as a natural defense against malignant degeneration), but do not undergo apoptosis (programmed death) for a long time. The accumulation of such cells leads to age-related deterioration of individual organs and the entire organism, since they are characterized by an aging-related secretory phenotype (SASP). It is a synthesis of numerous biologically active substances associated with embryogenesis, wound healing, inflammation and metabolic activity that negatively affect the surrounding tissue. Most of these substances have a protein nature and are relatively well studied, much less is known about the lipid metabolism of senescent cells.
Christopher Wiley from the Bakovsky Institute for Aging Research and colleagues decided to look into this issue. To do this, they evaluated the lipid profiles of cultured human fibroblasts in the state of proliferation (PRO), rest (QUI) and induced aging (SEN), as well as cells with senescence associated with mitochondrial dysfunction (MiDAS).
It turned out that in aged cells the level of biologically active oxylipins and their precursors – 20- and 22-carbon (for example, arachidonic and adrenic, respectively) polyunsaturated fatty acids (PUFA) was sharply increased. At the same time, acids with a longer carbon chain and digomoprostaglandins synthesized from them prevailed. The researchers also found a large number of other PUFA products: various variants of prostaglandins D2, E2 and F2a, as well as lecotriene B4 and related metabolites; all of them were largely oxidized to form oxylipins. The level of poorly studied 1a,1b-digomo-15-deoxy-Δ12,14-prostaglandin J2 (dh-15d-PGJ2), uncharacteristic for normal (non-aged) cells, was most strongly increased.
The molecule is dh-15d-PGJ2. Drawings from the article by Wiley et al.
The transcriptome analysis by quantitative PCR showed a corresponding increase in the expression of prostaglandin synthesis genes (PTGS2, PTGDS, PTGES and TBXAS, but not PTGIS) and leukotrienes (ALOX5, ALOX15, ALOX5AP, LTC4S and, to a lesser extent, LTA4H).
A similar pattern was observed in vivo in genetically engineered mice with doxorubicin-induced cellular aging.
Since dh-15d-PGJ2 specifically accumulates in senescent cells and is practically not secreted by them, the researchers suggested that it could serve as a marker of the death of these cells (senolysis). To test this hypothesis, the senolytic drug ABT-263 was added to the nutrient medium of various types of aged cells (SEN, MiDAS and others) and a day later, after the death of about 90 percent of the cells, a significant amount of the desired substance was observed in the medium. In a similar experiment with normal cells (QUI), this did not happen.
Turning to the in vivo study, the authors injected mice with doxorubicin and allowed the senescent cells to accumulate in their body for six weeks. After that, the animals were prescribed ABT-263 and a significant (p<0.01) increase in the concentration of dh-15d-PGJ2 in their blood plasma and urine was observed. In groups where mice were injected with either neutral phosphate-salt solution (PBS), or only doxorubicin, or only ABT-263, the levels of the studied substance in biological fluids practically did not change. This confirmed the specificity of dh-15d-PGJ2 as a marker of senolysis, which can potentially be used for non-invasive control of treatment aimed at cleansing the body of aged cells.
The researchers also clarified the biological role of dh-15d-PGJ2 as a signaling molecule. Suppression of its synthesis allowed the cells to avoid aging, continue to multiply and significantly reduce the secretion of inflammatory mediators. The addition of this substance to normal cells, on the contrary, induced their senescence by activating the RAS oncogene signaling pathway.
Biological and diagnostic role of dh-15d-PGJ2.
Despite the fact that the inevitability of aging of multicellular organisms, including humans, has been confirmed statistically and mathematically by modeling, many scientific laboratories are working to slow it down and potentially prevent it. In animal experiments, it was possible to cleanse the body of aged cells and prolong life by various methods. Among them, suppression of mitochondrial biogenesis by the appointment of rapamycin; restoration of mitochondrial chaperone proteins by metolazone; normalization of mitochondrial metabolism by nicotinamide riboside; temporary activation of factors that transform mature cells into stem cells; stimulation of apoptosis by blocking the action of transcription factor FOXO4 on antitumor protein p53 and others. In addition to the effects on senescent cells, experiments to slow the aging of the body include ovarian transplantation and blood transfusion of young animals, strict restriction of caloric intake of food, telomere lengthening by telomerases and manipulation of stem cells.
A recent study of the epigenetic "clock" revealed an interesting fact: it turned out that the embryos immediately after conception become younger, and begin to age about the 10th day after fertilization.
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