Research

Loss of Telomere Leads to p53 and Autophagy Induced Cell Death.

“autophagy-deficient cells … continued to proliferate and bypassed crisis” (2)
“In summary, cells in telomere crisis undergo cell death through autophagy, which is triggered by chromosome breakage and transduced by the cGAS–STING pathway. As cell death in crisis represents the final barrier against neoplastic transformation, a cancer therapy that involves inhibition of autophagy could be counterproductive… Moreover, cells lacking either cGAS or STING proliferated beyond crisis. “”Autophagy mediates the turnover of cytoplasmic macromolecules to support cellular homeostasis. Autophagy generally blocks apoptosis, but in specific circumstances it can lead to cell death through excessive degradation of cell constituents. The authors studied telomere crisis using human fibroblasts and epithelial cells, in which the RB and/or p53 pathways were suppressed; these cells bypassed senescence and entered replicative stress, exhibiting telomere attrition, chromosome fusions and cell death.””Telomere deprotection through TRF2 depletion was sufficient to activate autophagy independently of replicative crisis, and genetic suppression of telomere fusions in TRF2-depleted cells reduced the accumulation of cytosolic DNA and attenuated autophagy, suggesting that fusion-dependent cytosolic DNA is required for the telomeric autophagy response. ” (2)

“The cell fate of CPCs changes with age and is characterized by a switch away from proliferation and quiescence (reversible form of cell cycle arrest) towards senescence and increased basal commitment (‘irreversible’ forms of cell cycle arrest) accounting for age-associated stem cell exhaustion. Mechanistically, short telomeres activate p53 that induces autophagy and at least partially contributes to the age-associated change in cell fate. Blunting telomere shortening via overexpression of TERT-WT, silencing p53 , or treating with pharmacological inhibitors of p53 (PFT) and autophagy (3-MA, Ulk1-In, BF) selectively attenuate senescence and basal commitment and reverse cell fate of aged CPCs.” (3)

Circadian Rhythm Controls Telomeres and Telomerase Activity.

“Circadian clocks are fundamental machinery in organisms ranging from archaea to humans. Disruption of the circadian system is associated with premature aging in mice, but the molecular basis underlying this phenomenon is still unclear. In this study, we found that telomerase activity exhibits endogenous circadian rhythmicity in humans and mice. Human and mouse TERT mRNA expression oscillates with circadian rhythms and are under the control of CLOCK–BMAL1 heterodimers.

CLOCK deficiency in mice causes loss of rhythmic telomerase activities, TERT mRNA oscillation, and shortened telomere length. Physicians with regular work schedules have circadian oscillation of telomerase activity while emergency physicians working in shifts lose the circadian rhythms of telomerase activity. These findings identify the circadian rhythm as a mechanism underlying telomere and telomerase activity control that serve as interconnections between circadian systems and aging.” (4)

“Human activity is driven by NADH and ATP produced from nutrients, and the resulting NAD and AMP play a predominant role in energy regulation. Caloric restriction increases both AMP and NAD and is known to extend the healthspan (healthy lifespan) of animals. Silent information regulator T1 (SIRT1), the NAD-dependent deacetylase, attenuates telomere shortening, while peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a master modulator of gene expression, is phosphorylated by AMP kinase and deacetylated by SIRT1. Thus, PGC-1α is a key component of the circadian oscillator that integrates the mammalian clock and energy metabolism.

Reactive oxygen species produced in clock mutants result in telomere shortening. The circadian rhythms produced by clock genes and lifestyle factors are ultimately controlled by the human brain and drive homeostatic and hedonic feeding and daily activity. ” (9).

• Telomerase and TERT mRNA expressions exhibit endogenous circadian rhythm.
• Human and mouse TERT mRNA expression are under the control of CLOCK–BMAL1 heterodimers.
• CLOCK deficient mice have shortened telomere length and abnormal oscillations of telomerase activity and TERT mRNA.
• Emergency physicians working in shifts lose the circadian rhythms of telomerase activity.

What is Thymosin Beta-4?

The beta-thymosins (b-thymosins) comprise a family of structurally related, highly conserved amino acid sequences in species ranging from mammals to echinoderms. Of the 16 known family members, thymosin β4 (Tb4), thymosin β10 (Tb10), and thymosin β15 (Tb15) are found in man.Thymosin beta-4 (TB4) is a 43 amino acid, 5kDa polypeptide that is an important mediator of cell proliferation, migration, and differentiation. TB4 is the most abundant member of the β- thymosin family in mammalian tissue and is regarded as the main G-actin sequestering peptide. It is found in all tissues and cell types except red blood cells. Thymosin beta-4 is angiogenic and can promote endothelial cell migration and adhesion, and angiogenesis. TB4 also accelerates wound healing and reduces inflammation and scarring when applied in dermal wound-healing assays.

Beta thymosins bind and sequester monomeric actin, thus preventing actin polymerization and formation of filamentous actin. Actin is a vital component of cell structure and movement. Actin is involved in many important non-muscle cellular processes, including cell locomotion, chemotaxis, phagocytosis, and cytokinesis. Of the thousands of proteins present in cells, actin makes up to 10% of the total proteins in a cell, representing a major role in the genetic makeup of the cell.

Animal studies of disease and repair when using thymosin beta-4, the major actin-sequestering molecule in mammalian cells, have provided a base for the ongoing multicenter clinical trials for wound healing, including dermal, corneal, and cardiac. TB4 has multiple biological activities, which include down-regulation of inflammatory chemokines and cytokines, and promotion of cell migration, blood vessel formation, cell survival, and stem cell maturation.

Thymosin beta-4 also inhibits inflammation, microbial growth, scar formation (by reducing the level of myofibroblasts), and apoptosis, and protects cells from cytotoxic damage, including glutamate neuronal toxicity. In addition, it binds to G-actin, blocks actin polymerization, and is released with factor X by platelets. These activities contribute to the multiple wound healing properties that have been reported in animal and human studies.

Ac-SDKP is a Peptide Fragment of Thymosin Beta 4 (TB-500)

“Tβ4 is a naturally occurring peptide consisting of 43 base pairs of amino acids and generates the N-terminal tetrapeptide AcSDKP.” (14)

Peptide Ac-SDKP was isolated from the whole Thymosin Beta 4 Peptide Sequence.

Ac-SDKP Reduced Kidney Fibrosis.

“Treatment of cultured cells with ACEi alone or in combination with AcSDKP prevented the downregulated expression of miR-29s and miR-let-7s induced by TGFβ stimulation. Interestingly, ACEi also restored miR-29 and miR-let-7 family cross-talk in endothelial cells, an effect that is shared by AcSDKP suggesting that AcSDKP may be partially involved in the anti-mesenchymal action of ACEi. The results of the present study promise to advance our understanding of how ACEi regulates antifibrotic microRNAs crosstalk and DPP-4 associated-fibrogenic processes which is a critical event in the development of diabetic kidney disease.” (14)

What are mitochondria?

Mitochondria are membrane-bound cell organelles (mitochondrion, singular) that generate most of the chemical energy needed to power the cell’s biochemical reactions. Chemical energy produced by the mitochondria is stored in a small molecule called adenosine triphosphate (ATP).Mitochondria are small, often between 0.75 and 3 micrometers and are not visible under the microscope unless they are stained.
Unlike other organelles (miniature organs within the cell), they have two membranes, an outer one and an inner one. Each membrane has different functions. Mitochondria are split into different compartments or regions, each of which carries out distinct roles.Different cell types have different numbers of mitochondria. For instance, mature red blood cells have none at all, whereas liver cells can have more than 2,000. Cells with a high demand for energy tend to have greater numbers of mitochondria. Around 40 percent of the cytoplasm in heart muscle cells is taken up by mitochondria.Although mitochondria are often drawn as oval-shaped organelles, they are constantly dividing (fission) and bonding together (fusion). So, in reality, these organelles are linked together in ever-changing networks. Also, in sperm cells, the mitochondria are spiraled in the midpiece and provide energy for tail motion.

What happens to our mitochondria as we age? How do they become dysfunctional?

Age-related changes in mitochondria are associated with decline in mitochondrial function. With advanced age, mitochondrial DNA volume, integrity and functionality decrease due to accumulation of mutations and oxidative damage induced by reactive oxygen species (ROS).

In aged subjects, mitochondria are characterized by impaired function such as lowered oxidative capacity, reduced oxidative phosphorylation, decreased ATP production, significant increase in ROS generation, and diminished antioxidant defense. Mitochondrial biogenesis declines with age due to alterations in mitochondrial dynamics and inhibition of mitophagy, an autophagy process that removes dysfunctional mitochondria.

Age-dependent abnormalities in mitochondrial quality control further weaken and impair mitochondrial function. In aged tissues, enhanced mitochondria-mediated apoptosis contributes to an increase in the percentage of apoptotic cells. However, implementation of peptides and strategies such as caloric restriction and regular physical training may delay mitochondrial aging and attenuate the age-related phenotype in humans.