1. Telomere Length Protocol19
1. DNA isolation
Most DNA isolation methods may be used. Our Lab prefers Qiagen DNeasy Kit (#69506) for blood sources. Depending on the source of DNA, such as buccal or other sources, a different isolation method may be used.
2. Primers
All primers are diluted to a stock concentration of 100pmoles/&mu;l in PCR grade water and stored at -20 &deg;C until required. Working stocks of primers are made fresh and are stored at 20 &deg;C for a short period of time (A few months.) Standard primers were used for telomeres and &beta;-Globin, the SCG, as described in O'Callaghan et al. 20.
Primer sequences: 
Telo 1: 5'-CGGTTTGTTTGGGTTTGGGTTTGGGTT-TGGGTTTGGGTT-3'
Telo 2: 5'-GGCTTGCCTTACCCTTACCCTTACCCTTACCCTT-ACCCT-3' 
SCG 1: 5'-GCTTCTGACACAACTGTGTTCACTAGC-3' 
SCG 2: 5'-CACCAACTTCATCCACGTTC-ACC-3'
Note: Primers are diluted to a working concentration of 10pmoles/&mu;l, prior to adding to reaction mix.
3. Serial Dilution of Genomic DNA
Serial dilutions of genomic DNA for Telo and Single Copy Gene (SCG) are created to generate a standard Ct value curve for the assay. The genomic DNA used was extracted from lymphocytes from blood samples. These dilutions are created by diluting DNA with PCR grade H20 to each concentration by a factor of 1.68 to yield the two sets of serial dilutions using the same genomic DNA. The starting concentrations have been optimized based on trial and error and may need to be adjusted when using different reagents, instruments, DNA from other species, cell types, and SCG used.
Note: Serial dilution using genomic DNA are made by mixing gently and waiting at least 15 min to one hour before taking DNA for the next dilution. Each dilution requires time for genomic DNA to dissociate. For long term storage, aliquot serial dilutions into PCR strips for storage at -80 &deg;C. Each PCR strip is thawed and used once to avoid freeze thaw cycles that may damage DNA.
4. Reaction setup for RT-PCR
Instrument used: Roche480 Light Cycler
Reagent: Roche Light cycler sybr-green
Dilute test DNA samples to a final concentration of 10 ng/&mu;l. We test concentration using Nanodrop or Qubit. We further dilute the DNA from 10ng/&mu;l to final 5ng/&mu;l. We do not test concentration again.
Reaction components:
<table border="1">
 <tbody>
 <tr>
 <td fo:width="1.5in">TELO</td>
 <td fo:width="1.5in">1x</td>
 <td fo:width=".25in" rowspan="6"> </td>
 <td fo:width="1.5in">SCG</td>
 <td fo:width="1.5in">1x</td>
 </tr>
 <tr>
 <td>H20</td>
 <td>6 &mu;l</td>
 <td>H20</td>
 <td>6 &mu;l</td>
 </tr>
 <tr>
 <td>Telo 1</td>
 <td>0.2 &mu;l</td>
 <td>SCG 1</td>
 <td>0.6 &mu;l</td>
 </tr>
 <tr>
 <td>Telo 2</td>
 <td>1.8 &mu;l</td>
 <td>SCG 2</td>
 <td>1.4 &mu;l</td>
 </tr>
 <tr>
 <td>Rxn mix</td>
 <td>10 &mu;l</td>
 <td>Rxn mix</td>
 <td>10 &mu;l</td>
 </tr>
 <tr>
 <td>DNA or serial dilution</td>
 <td>2 &mu;l</td>
 <td>DNA or serial dilution</td>
 <td>2 &mu;l</td>
 </tr>
 </tbody>
</table>
Note: Master Mix is made without DNA and with an excess of 5% to 10%.
Both Telo and SCG are run together on the same plate using the following program. To test for precision, at least three replicates of each sample and control should be run. Variations in the primers used may affect the results. Our protocol has been optimized to work as follows on the Roche480 Light Cycler and our primers.
Initial denature 
10 min denature 95 &deg;C 
Cycling 
95 &deg;C 10 sec hold 
60 &deg;C 5 sec hold 
72 &deg;C 11 sec hold and single acquisition 
Repeat 45 to 55 times as required
2. Quantitative Telomerase Detection (QTD) Protocol (Based on QTD Kit by Allied Biotech, Inc. Cat. No. MT3012)
Extract Preparation
<ol>
 <li>Pellet cells or tissue.</li>
 <li>Wash once with 1x PBS.</li>
 <li>Repellet and remove 1x PBS.*</li>
 <li>Resuspend the cell pellet in 200 &mu;l of 1 x Lysis Buffer for every 105-106 cells or 40-100 mg of tissue.</li>
 <li>Incubate on ice for 30 min.</li>
 <li>Spin down the sample at 12,000 x g for 30 min at 4 &deg;C.</li>
 <li>Transfer 160 &mu;l of the supernatant into a fresh tube and determine protein concentration.</li>
 <li>Aliquot and quick-freeze the remaining extract on dry ice/ethanol, store at -80 &deg;C.</li>
</ol>
*In this condition, telomerase in frozen cells or tissues is stable for at least a year. When thawed for use, resuspend the cells immediately in 1 x Lysis Buffer.
2.1. Assay Controls
Heat inactivation control: For each sample, heat treat an additional control extract by incubating at 85 &deg;C for 10 min prior to telomerase activity assay.
Standard curve for TSR control template: Perform Quantitative Real-Time PCR using dilutions of TSR, an oligonucleotide with a similar sequence to telomere primers included with the kit to generate a standard curve.
<ol>
 <li>Prepare 1:5 serial dilutions of the stock TSR concentration (0.5 amoles/&mu;l) with Lysis Buffer</li>
 <li>Perform the telomerase detection standard assay using 1 &mu;l of each TSR dilution, including the stock concentration. These dilutions can be stored at 4 &deg;C for at least 2 weeks.</li>
</ol>
2.2. Telomerase Activity Assay using QTD Real-Time PCR
<ol>
 <li>For each sample, add the following to a PCR tube or thin-wall PCR plate (total volume 25.0 &mu;l):
 <ul>
 <li>12.5 &mu;l of 2 x QTD Premix</li>
 <li>1.0 &mu;l of Cell or Tissue Extract</li>
 <li>11.5 &mu;l of PCR Qualified Water</li>
 </ul>
 </li>
 <li>Mix thoroughly</li>
 <li>Program Real-Time PCR Detection Systems according to the below program: 
 - 25 &deg;C for 20 min (telomerase reaction) 
 - 95 &deg;C for 10 min (PCR initial activation step) 
 35-40 cycles of: 
 - 95 &deg;C for 30 sec (denaturation) 
 - 60 &deg;C for 30 sec (annealing) 
 - 72 &deg;C for 30 sec (extension)</li>
 <li>Place PCR tubes in the thermal cycler and start the cycling program.</li>
 <li>Collect the threshold cycle or CT value after cycles finish. The threshold cycle is the cycle at which a statistically significant increase of &Delta;Rn is first detected.</li>
</ol>
2.3. Data Analysis
<ol>
 <li>Generate a standard curve using the CT readings and compare telomerase activity.</li>
</ol>

No conflicts of interest declared.

Telomere length provides a unique cellular marker to study the stressed and aging cell and offers insights into the mechanisms of aging. Since its role in aging had first been suggested, a multitude of studies have been done relating telomere length to age, longevity, age-related disease, cancers, and stress. For decades, the gold standard of telomere length measurements was terminal restriction fragment analysis using Southern hybridization. However, recently an affordable, quick, and easy to perform method by Cawthon has evolved. Using Quantitative Real-Time PCR, Cawthon offered a useful alternative to measure telomere length, making studies for large sample sizes possible.
Using qRT-PCR, many studies have been done to investigate the relationship between telomere length and a variety of outcomes, especially age-related diseases. More specifically, this method has allowed researchers to perform large epidemiological studies on populations that demonstrate or deny a correlation between telomere length and a variety of diseases. To name a few, ischemic heart disease 7, Alzheimer's Disease 22, osteocarcoma in females 23, lung cancer among smokers 24, familial thyroid cancer 25, diabetes 5, blood pressure 26, aging 27, and dementia 28 have been correlated with shorter telomere length, while age-related macular degeneration 7, colorectal cancer 43, and death from infectious disease, cancer, cardiac or cerebrovascular disease 44 have been shown to have no significant relationship with telomere length . Additionally, certain stresses have been shown to coincide with shorter telomere length, for example, an increased amount of inflammatory markers, TNF-&alpha; and IL-6, have been correlated with shorter telomere lengths in leukocytes 29. Also, stressful lifestyles due to time consuming work schedules, shift work, or the nature of the work, in particular a caretaker position for a chronically ill child, have been associated with differences in telomere length. This suggests that stress could cause premature aging by way of telomere shortening without sufficient recovery 30, 31. In a recent study, having fewer social relationships is also associated with shorter telomeres 32. Prevention of telomere length shortening has also been shown to correlate with healthy life choices, such as taking a daily multivitamin and not smoking 24, 33. Additionally, these studies revealed possible clinical uses for measuring telomeres, for example, as a non-invasive screening test for the possible development of cirrhosis 34. In other cases, where similar studies have shown no significant correlation (or a modest correlation) between a disease and telomere length, researchers have been encouraged to study other novel mechanisms for cellular decline and the diseased state7.
These studies have strength in numbers and have demonstrated the utility of measuring telomere length as one of the first steps in deciphering the aging process. Cawthon's qRT-PCR method was useful for this purpose because it can compare large numbers of people, requires minimal DNA, and can give reliable evidence towards a relationship between telomere length and cell health. These studies help to steer future aging research efforts to certain genes, tissues, and cellular processes.
Inevitably, after a significant difference in telomere length is noted, an explanation is queried. To answers these questions, studies on telomerase, the enzyme involved in telomere maintenance and its regulation, have been established. PCR based telomerase activity protocols have been offered, giving additional information towards: a. determining the contributions of the degradation of telomeres, and b. failure of successful telomere length maintenance by telomerase, thus providing another chapter to the story on aging as a whole, in particular cell senescence.
Although qRT-PCR detects average telomere length, and not on an individual chromosome basis, this method is a powerful tool for evidence towards how the cell reacts to aging and stress and provides a preamble to the story of how we age. Interestingly, this information has already led to telomere length measurement in the clinic for estimating biological age and will further our understanding of the aging process and inevitably lead to prevention or delay and screening of aging and age-related disease.
<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 </tr>
 <tr>
 <td>Quantitative Telomerase Detection </td>
 <td>Allied Biotech </td>
 <td>MT3012 </td>
 </tr>
 <tr>
 <td>Qiagen DNeasy Kit</td>
 <td>Qiagen</td>
 <td>69506</td>
 </tr>
 <tr>
 <td>LightCycler 480 SYBR Green I Master, Ready-to-use hot start reaction mix for SYBR Green I-based real-time PCR using the LightCycler 480 Instrument</td>
 <td>Roche Diagnostics</td>
 <td>4707516</td>
 </tr>
 </tbody>
</table>

Telomeres are repeating DNA hexamer (TTAGGG) sequences found at the ends of chromosomes. In each cell replication, these chromosome ends are shortened. If they become too short, chromosomes can undergo telomere end fusions, aberrant recombination, and degradation. Thus sufficient telomere length maintenance plays a major role in chromosome stability and cell protection 38. Telomere length maintenance is also crucial for genes found near the ends of chromosomes, since DNA replication cannot continue to the very end of chromosomes 1-2. Consequently, prevention of telomere shortening may improve cell stability.
Numerous studies have reported that telomere length is correlated with an organism's longevity and diseased state, such as in cancer 3-4, diabetes 5, and cardiovascular disease 6,7. Additionally, shortened telomeres have been associated with excessive stress or an unhealthy lifestyle 8, perhaps by promoting premature cell aging and death 9. On the other hand, some studies have found that there is no significant difference between telomere length and longevity and age related disease 39, 40, 41.
One of the cell's innate mechanisms of protection from telomere shortening is by activating its own enzyme telomerase reverse transcriptase (TERT). This enzyme and its subunit, telomerase RNA (TERC), a non-coding RNA, use the telomere as a template to add telomere repeats to chromosome ends 10. Although telomerase activity is absent from several types of cells and other mechanisms are involved in telomere length maintenance, increased telomerase activity is correlated with increased telomere length. Telomerase activation has been established as one of the mechanisms by which cells respond to damage and stress and avoid premature senescence and death. For example, longer telomeres were demonstrated in a population of Ashkenazi Jews with exceptional lifespan 11, mutations in TERC or TERT have been shown to contribute to fatal disease 12, and epigenetic regulation of telomerase has been shown to have an effect on age-related disease 13. Since its discovery, telomere length has been proposed as a biomarker for health status in various animal models as well as in humans, but these early studies were difficult to widely replicate because the method used was tedious, long and expensive. In 2002 and further tuned in 2009, Cawthon proposed and demonstrated a new, accurate, fast and simple PCR based protocol to assess telomere length and further investigate its role in various aspects of cell biology, aging and disease 19.
Choosing the correct telomere measuring method for a study is essential. Currently, there are various methods used to measure telomere length, each with its own advantages and disadvantages. Traditionally, telomere length is measured using Southern Blot analysis of terminal restriction fragments (TRFs), which involves: a. digesting the DNA with restriction enzymes that do not cut in telomere repeats in order to obtain TRFs, b. Southern Blot of these TRFs is done by determining the mean TRF length using a telomeric probe 14, 37. Although this method is highly accurate with a small coefficient of variation, is a direct measure, and can be advantageous for measuring length distribution, TRF analysis is costly, labor intensive and requires at least 3 &mu;g of DNA. This method is also insensitive to short telomeres and length determination can be confounded by subtelomeric DNA, which can be detected by the probe due the (TTAGGG)n like sequences they contain 15, 42.
Another highly accurate method in measuring telomere length is Single Telomere Elongation Length Analysis (STELA), a single molecule PCR based method that only requires a small amount of DNA. In this method, primers are made to recognize the G-rich overhang at the end of chromosomes and to bind to a unique subtelomeric sequence on one chromosome, which amplifies the telomere of a specific chromosome. The resulting amplification is then visualized by Southern Blot. This method has the advantage of being highly accurate and is able to detect short outlier telomeres 16. Unfortunately, since not all chromosomes have G-rich ends and a usable subtelomeric sequence, telomere length can only be measured on specific chromosomes and these measurements may not represent the length of all the telomeres in the cell 15.
Another method that has been practiced is the use of Peptide Nucleic Acid (PNA) probes to detect telomere length. Quantitative Florescence in situ Hybridization (Q-FISH) allows us to visualize telomeres during metaphase, where the staining of telomeres with a PNA probe in proportion to their size permits the comparison of telomeres between specific chromosomes. Although this method can also be used for cells in interphase, here the telomere length for distinct chromosomes cannot be detected, which introduces a limitation when measuring telomere length in senescent or infrequently dividing cells 17. Flow FISH instead uses flow cytometry and is currently the most sensitive method for measuring telomere length of blood cells in the clinical setting, but requires highly skilled technicians 18.
Currently, the standard method for measuring average telomere length in our lab takes advantage of the precision, sensitivity, and ease of quantitative real-time PCR. This method was made possible for measuring telomere length by the development of novel primers that avoid the synthesis of primer dimer-derived products, which would have otherwise been produced in a standard assay due to the repeating nature of telomeres. For this assay, the measurement of telomere length is represented by the T/S ratio, the telomere repeat copy number to single-copy gene number. Since there is a direct proportional relationship between the telomere length and the number of labeled telomere primers binding to the DNA during the beginning stages of PCR, the T/S ratio is directly proportional to telomere length. The T/S ratio is measured by comparing the difference in Ct, the fractional cycle number at which the sample's accumulated florescence crosses a threshold that is several standard deviations above the baseline florescence, between samples with telomere primers and SCG primers 19. This method has been criticized for its indirect measurement of telomere length, which can lead to inaccurate measurements, for example, in the case of chromosome duplications or copy number variations 15. Also, comparison between studies is often difficult, but standard oligomers have been developed to measure absolute telomere length 20. This method was furthered improved upon by Cawthon, using a monochrome multiplex qPCR assay. In this assay, the PCR was run at lower temperatures for the first few cycles to avoid primer-dimer binding and the telomere and control gene were analyzed in the same PCR tube to further avoid error. The resulting telomere length measurements strongly correlated with telomere length measured by Southern blot analysis of TRFs and had higher accuracy 15, 19, 36. At the moment, qRT-PCR is the only convenient method available for testing large sample sizes and only requires a small amount of DNA to carry out. A crucial part of this method is comprehensive quality control measures, so that when it's done properly, this method can provide valuable comparative information about telomere length. Additionally, this method had been adapted for use beyond leukocytes for measuring telomere length in a variety of different tissues 42.
Additionally, in order to further understand the biology behind telomere length maintenance and interactions between the two opposing effects (i.e. telomere shortening during replication and elongation by the telomerase enzyme), we accompanied the telomere length method with an additional assay that measures telomerase activity.
For this purpose, we used a Telomeric Repeat Amplification Protocol, an in vitro assay. Briefly, lysed, preserved, enzymatically active cells synthesized telomeric repeats onto an oligonucleotide substrate using telomerase, and the products were amplified using PCR in the presence of SYBR Green. The results were then analyzed by comparing sample and control Ct threshold values. Since telomerase is a heat-sensitive enzyme, an additional heat treated control is run alongside each sample 21.
While measuring telomere length can provide valuable insight into the possible role of telomere length in the pathophysiology of aging and disease, telomere length is not a static property and more information is needed to understand telomere function. Telomerase activity studies can add information about telomere length regulation mechanisms. For example, the controlled activation of telomerase can maintain telomere length and cell proliferation, but the uncontrolled activation of telomerase can result in cancer. These two inexpensive and straight forward methods combined provided us not only with stronger evidence towards a relationship between telomere length and cell stability, but also further insight into the possible mechanisms of telomere shortening and recovery. With these methods we hope to further elucidate the cell's response to aging and various states of cell proliferation with the ultimate goal of a better understanding of the central mechanisms of cell biology.

<table><tbody><tr><td>Quantitative Telomerase Detection </td><td>Allied Biotech</td><td>MT3012</td><td></td></tr><tr><td>Qiagen DNeasy Kit</td><td>Qiagen</td><td>69506</td><td></td></tr><tr><td>LightCycler 480 SYBR Green I Master, Ready-to-use hot start reaction mix for SYBR Green I-based real-time PCR using the LightCycler 480 Instrument</td><td>Roche Diagnostics</td><td>4707516</td><td></td></tr></tbody></table>

telomere length and telomerase activity; a yin and yang of cell senescence

Telomeres are repeating DNA sequences at the tip ends of the chromosomes that are diverse in length and in humans can reach a length of 15,000 base pairs. The telomere serves as a bioprotective mechanism of chromosome attrition at each cell division. At a certain length, telomeres become too short to allow replication, a process that may lead to chromosome instability or cell death. Telomere length is regulated by two opposing mechanisms: attrition and elongation. Attrition occurs as each cell divides. In contrast, elongation is partially modulated by the enzyme telomerase, which adds repeating sequences to the ends of the chromosomes. In this way, telomerase could possibly reverse an aging mechanism and rejuvenates cell viability. These are crucial elements in maintaining cell life and are used to assess cellular aging. In this manuscript we will describe an accurate, short, sophisticated and cheap method to assess telomere length in multiple tissues and species. This method takes advantage of two key elements, the tandem repeat of the telomere sequence and the sensitivity of the qRT-PCR to detect differential copy numbers of tested samples. In addition, we will describe a simple assay to assess telomerase activity as a complementary backbone test for telomere length.

An example of a telomere length qRT-PCR assay is shown in Figure 1. On the top left panel, samples labeled in red and green represent the location of the tested subjects on the 96-well plate. On the top right panel, the amplification curve is demonstrated. Each subject is tested by two assays (Telomere and Single Copy Gene), which is done in triplicates. Due to different DNA copy numbers produced in the two assays of selected individuals, the number of cycles until the florescence detection reaches its exponential curve differs between assays. In higher copy number tubes (i.e. Telomere assay), the amount of fluorescence detection reaches its exponential curve after 27 cycles. The second set of lines represents the Single Copy Gene (SCG) that has only one copy in the genome, and thus has much less copies than the telomere samples and reaches its exponential curve only after 31 cycles. The brown lines represent the standard curve that is based on a serial dilution of known sample concentrations. The bottom right panel represents the log concentration of the standard curve points (a straight line demonstrates an optimal serial dilution). This linear curve is being used to calculate the concentration of the tested tubes (bottom left panel). The qRT-PCR results, initially in Cawthon's hands 19, and repeated by us and others, have been shown to be correlated with those obtained by the terminal restriction fragment length assay. One T/S ratio unit (qRT-PCR cycles of the telomere run over qRT-PCR cycles of the SCG run) is equivalent to a mean telomere length of 4,270bp in leukocytes 42. Dividing the qRT-PCR cycles for the Telomere assay by the SCG assay in our example resulted in a ratio of 0.87, which is equivalent to an average of 3,715bp. This measurement consists of the telomere length alone and does not include subtelomeric regions.
The qRT-PCR demonstrated here involved very little sample preparation. In this example (Figure 1), qualitative as well as quantitative differences (represented by the serial dilution and the concordance between the triplicates) were observed between the two assays. The results calculated from this test show intermediate telomere length for a 65 year old subject.
An example of telomerase activity assay results and the possible relationship between telomerase activity and telomere length is demonstrated by Figure 2. Our preliminary results show that a longer telomere length may be associated with increased telomerase activity.
<img src="/files/ftp_upload/50246/50246fig1.jpg" alt="Figure 1" fo:content-width="4in" fo:src="/files/ftp_upload/50246/50246fig1highres.jpg"/> 
Figure 1. Figure 1 represents the typical output from a qRT-PCR assay for Telomere length. The upper left corner shows the samples arranged in a 96-well plate, in triplicate. The lower left corner lists the calculated concentrations and CT values for each sample, which are used to calculate the T/S values. The upper right is a graph of the amplification curve (number of cycles versus the florescence detected from CYBR green), used to visualize the results. On the bottom right, the standard curve for the Log concentration versus CT value of the serial dilution control is graphed. A straight line confirms that the serial dilution was accurately measured and loaded. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/50246/50246fig1large.jpg" target="_blank">Click here to view larger figure</a>.
<img src="/files/ftp_upload/50246/50246fig2.jpg" alt="Figure 2"/> 
Figure 2. Using preliminary results from the qRT-PCR assay for telomerase activity and telomerase length, Figure 2 shows a direct, significant relationship (p = 0.008) between the telomere length, measured by T/S ratio, and telomerase activity, measured by Ct value.

Watch this Scientific Journal Video about Telomere Length and Telomerase Activity; A Yin and Yang of Cell Senescence at JoVE.com

Telomere Length and Telomerase Activity; A Yin and Yang of Cell Senescence

An accurate, short, sophisticated and cheap method is described that assesses telomere length in multiple tissues and species using qRT-PCR. In addition, we will describe a simple assay to assess telomerase activity as a complementary backbone test for telomere length.

Telomeres  are repeating DNA sequences at the tip ends of the chromosomes that are diverse  in length and in humans can reach a length of 15,000 base ...

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46.4K Views.  Albert Einstein College of Medicine. An accurate, short, sophisticated and cheap method is described that assesses telomere length in multiple tissues and species using qRT-PCR. In addition, we will describe a simple assay to assess telomerase activity as a complementary backbone test for telomere length.

Video: Telomere Length and Telomerase Activity; A Yin and Yang of Cell Senescence

Modified Terminal Restriction Fragment Analysis for Quantifying Telomere Length Using In-gel Hybridization

There are several different techniques for measuring telomere length, each with their own advantages and disadvantages. The traditional approach, Telomere Restriction Fragment (TRF) analysis, utilizes a DNA hybridization technique whereby genomic DNA samples are digested with restriction enzymes, leaving behind telomere DNA repeats and some sub-telomeric DNA. These are separated by agarose gel electrophoresis, transferred to a filter membrane and hybridized to oligonucleotide probes tagged with either chemiluminescence or radioactivity to visualize telomere restriction fragments. This approach, while requiring a larger quantity of DNA than other techniques such as PCR, can measure the telomere length distribution of a population of cells and allows measurement expressed in absolute kilobases. This manuscript demonstrates a modified DNA hybridization procedure for determining telomere length. Genomic DNA is first digested with restriction enzymes (that do not cut telomeres) and separated by agarose gel electrophoresis. The gel is then dried and the DNA is denatured and hybridized in situ to a radiolabeled oligonucleotide probe. This in situ hybridization avoids loss of telomere DNA and improves signal intensity. Following hybridization, the gels are imaged utilizing phosphor screens and the telomere length is quantified using a graphing program. This procedure was developed by the laboratories of Drs. Woodring Wright and Jerry Shay at the University of Texas Southwestern1,2. Here, we present a detailed description of this procedure, with some modifications.

In this article, a detailed protocol for quantifying telomere length using a modified terminal restriction fragment analysis is discussed that provides fast and efficient direct measurement of telomere length. This technique can be applied to a variety of cell sources of DNA for quantifying telomere length.

There are several different techniques for measuring telomere length, each with their own advantages and disadvantages. The traditional approach, Telomere ...

Cancer Research

Induction and Validation of Cellular Senescence in Primary Human Cells

Cellular senescence is a state of permanent cell cycle arrest activated in response to different damaging stimuli. Activation of cellular senescence is a hallmark of various pathophysiological conditions including tumor suppression, tissue remodeling and aging. The inducers of cellular senescence in vivo are still poorly characterized. However, a number of stimuli can be used to promote cellular senescence ex vivo. Among them, most common senescence-inducers are replicative exhaustion, ionizing and non-ionizing radiation, genotoxic drugs, oxidative stress, and demethylating and acetylating agents. Here, we will provide detailed instructions on how to use these stimuli to induce fibroblasts into senescence. This protocol can easily be adapted for different types of primary cells and cell lines, including cancer cells. We also describe different methods for the validation of senescence induction. In particular, we focus on measuring the activity of the lysosomal enzyme Senescence-Associated &#946;-galactosidase (SA-&#946;-gal), the rate of DNA synthesis using 5-ethynyl-2&#39;-deoxyuridine (EdU) incorporation assay, the levels of expression of the cell cycle inhibitors p16 and p21, and the expression and secretion of members of the Senescence-Associated Secretory Phenotype (SASP). Finally, we provide example results and discuss further applications of these protocols.

Here, we discuss a series of protocols for induction and validation of cellular senescence in cultured cells. We focus on different senescence-inducing stimuli and describe the quantification of common senescence-associated markers. We provide technical details using fibroblasts as a model, but the protocols can be adapted to various cellular models.

Cellular senescence is a state of permanent cell cycle arrest activated in response to different damaging stimuli. Activation of cellular senescence is a ...

Developmental Biology

A Quantitative Measurement of Reactive Oxygen Species and Senescence-associated Secretory Phenotype in Normal Human Fibroblasts During Oncogene-induced Senescence

Cellular senescence has been considered a state of irreversible growth arrest upon exhaustion of proliferative capacity or exposure to various stresses. Recent studies have extended the role of cellular senescence to various physiological processes, including development, wound healing, immune surveillance, and age-related tissue dysfunction. Although cell cycle arrest is a critical hallmark of cellular senescence, an increased intracellular reactive oxygen species (ROS) production has also been demonstrated to play an important role in the induction of cellular senescence. In addition, recent studies revealed that senescent cells exhibit potent paracrine activities on neighboring cells and tissues through a senescence-associated secretory phenotype (SASP). The sharp increase in interest regarding therapeutic strategies against cellular senescence emphasizes the need for a precise understanding of senescence mechanisms, including intracellular ROS and the SASP. Here, we describe protocols for quantitatively assessing intracellular ROS levels during H-Ras-induced cellular senescence using ROS-sensitive fluorescent dye and flow cytometry. In addition, we introduce sensitive techniques for the analysis of the induction of mRNA expression and secretion of SASP factors. These protocols can be applied to various cellular senescence models.

Intracellular ROS has been shown to play an important role in the induction of cellular senescence. Here, we describe a sensitive assay for quantifying ROS levels during cellular senescence. We also provide protocols for assessing the senescence-associated secretory phenotype, which reportedly contributes to various age-related dysfunctions.

Cellular senescence has been considered a state of irreversible growth arrest upon exhaustion of proliferative capacity or exposure to various stresses. ...

Accurate Telomere Length Assessment in Human Population Studies

Monochrome Multiplex Quantitative PCR Telomere Length Measurement

Telomeres are ribonucleoprotein structures at the end of all eukaryotic chromosomes that protect DNA from damage and preserve chromosome stability. Telomere length (TL) has been associated with various exposures, biological processes, and health outcomes. This article describes the monochrome multiplex quantitative polymerase chain reaction (MMqPCR) assay protocol routinely conducted in our laboratory for measuring relative mean TL from human DNA. There are several different PCR-based TL measurement methods, but the specific protocol for the MMqPCR method presented in this publication is repeatable, efficient, cost-effective, and suitable&#160;for population-based studies. This detailed protocol outlines all information necessary for investigators to establish this assay in their laboratory. In addition, this protocol provides specific steps to increase the reproducibility of TL measurement by this assay, defined by the intraclass correlation coefficient (ICC) across repeated measurements of the same sample. The ICC is a critical factor in evaluating expected power for a specific study population; as such, reporting cohort-specific ICCs for any TL assay is a necessary step to enhance the overall rigor of population-based studies of TL. Example results utilizing DNA samples extracted from peripheral blood mononuclear cells demonstrate the feasibility of generating highly repeatable TL data using this MMqPCR protocol.

Author Spotlight: Exploring the Impact of Trauma on Cellular Aging

Here we present a protocol for the measurement of relative telomere length (TL) using the monochrome multiplex quantitative polymerase chain reaction (MMqPCR) assay. The MMqPCR assay is a repeatable, efficient, and cost-effective method for measuring TL from human DNA in population-based studies.

Telomeres are ribonucleoprotein structures at the end of all eukaryotic chromosomes that protect DNA from damage and preserve chromosome stability. ...

Genetics

Quantifying Telomere Length Using Non-Radioactive Chemiluminescence Detection

Optimization of Performance Parameters of the TAGGG Telomere Length Assay

Telomeres are repetitive sequences which are present at chromosomal ends; their shortening is a characteristic feature of human somatic cells. Shortening occurs due to a problem with end replication and the absence of the telomerase enzyme, which is responsible for maintaining telomere length. Interestingly, telomeres also shorten in response to various internal physiological processes, like oxidative stress and inflammation, which may be impacted due to extracellular agents like pollutants, infectious agents, nutrients, or radiation. Thus, telomere length serves as an excellent biomarker of aging and various physiological health parameters. The TAGGG telomere length assay kit is used to quantify average telomere lengths using the telomere restriction fragment (TRF) assay and is highly reproducible. However, it is an expensive method, and because of this, it is not employed routinely for large sample numbers. Here, we describe a detailed protocol for an optimized and cost-effective measurement of telomere length using Southern blots or TRF analysis and non-radioactive chemiluminescence-based detection.

Author Spotlight: Optimization of Performance Parameters of the TAGGG Telomere Length Assay  

Here, we describe in detail the protocol for quantifying telomere length using non-radioactive chemiluminescent detection, with a focus on the optimization of various performance parameters of the TAGGG telomere length assay kit, such as buffer quantities and probe concentrations.

Telomeres are repetitive sequences which are present at chromosomal ends; their shortening is a characteristic feature of human somatic cells. Shortening ...

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Telomerase Activity in the Various Regions of Mouse Brain: Non-Radioactive Telomerase Repeat Amplification Protocol (TRAP) Assay

Telomerase, a ribonucleoprotein, is responsible for maintaining the telomere length and therefore promoting genomic integrity, proliferation, and lifespan. In addition, telomerase protects the mitochondria from oxidative stress and confers resistance to apoptosis, suggesting its possible importance for the surviving of non-mitotic, highly active cells such as neurons. We previously demonstrated the ability of novel telomerase activators to increase telomerase activity and expression in the various mouse brain regions and to protect motor neurons cells from oxidative stress. These results strengthen the notion that telomerase is involved in the protection of neurons from various lesions. To underline the role of telomerase in the brain, we here compare the activity of telomerase in male and female mouse brain and its dependence on age. TRAP assay is a standard method for detecting telomerase activity in various tissues or cell lines. Here we demonstrate the analysis of telomerase activity in three regions of the mouse brain by non-denaturing protein extraction using CHAPS lysis buffer followed by modification of the standard TRAP assay.
In this 2-step assay, endogenous telomerase elongates a specific telomerase substrate (TS primer) by adding TTAGGG 6 bp repeats (telomerase reaction). The telomerase reaction products are amplified by PCR reaction creating a DNA ladder of 6 bp increments. The analysis of the DNA ladder is made by 4.5% high resolution agarose gel electrophoresis followed by staining with highly sensitive nucleic acid stain.
Compared to the traditional TRAP assay that utilize 32P labeled radioactive dCTP&#39;s for DNA detection and polyacrylamide gel electrophoresis for resolving the DNA ladder, this protocol offers a non-toxic time saving TRAP assay for evaluating telomerase activity in the mouse brain, demonstrating the ability to detect differences in telomerase activity in the various female and male mouse brain region.

Telomerase Activity in the Various Regions of Mouse Brain: Non-Radioactive Telomerase Repeat Amplification Protocol TRAP Assay

Telomerase is expressed in the neonatal brain and also in distinct regions of the adult brain. We present a non-toxic time saving TRAP assay for the analysis of telomerase activity in various regions of the mouse brain and detection of differences in telomerase activity between male and female mouse brains.

Telomerase, a ribonucleoprotein, is responsible for maintaining the telomere length and therefore promoting genomic integrity, proliferation, and ...

Neuroscience

Utilizing Murine Inducible Telomerase Alleles in the Studies of Tissue Degeneration/Regeneration and Cancer

Telomere dysfunction-induced loss of genome integrity and its associated DNA damage signaling and checkpoint responses are well-established drivers that cause tissue degeneration during ageing. Cancer, with incidence rates greatly increasing with age, is characterized by short telomere lengths and high telomerase activity. To study the roles of telomere dysfunction and telomerase reactivation in ageing and cancer, the protocol shows how to generate two murine inducible telomerase knock-in alleles 4-Hydroxytamoxifen (4-OHT)-inducible TERT-Estrogen Receptor (mTERT-ER) and Lox-Stopper-LoxTERT (LSL-mTERT). The protocol describes the procedures to induce telomere dysfunction and reactivate telomerase activity in mTERT-ER and LSL-mTERT mice in vivo. The representative data show that reactivation of telomerase activity can ameliorate the tissue degenerative phenotypes induced by telomere dysfunction. In order to determine the impact of telomerase reactivation on tumorigenesis, we generated prostate tumor model G4 PB-Cre4 PtenL/L p53L/L LSL-mTERTL/L and thymic T-cell lymphoma model G4 Atm-/- mTERTER/ER. The representative data show that telomerase reactivation in the backdrop of genomic instability induced by telomere dysfunction can greatly enhance tumorigenesis. The protocol also describes the procedures used to isolate neural stem cells (NSCs) from mTERT-ER and LSL-mTERT mice and reactivate telomerase activity in NSCs in vitro. The representative data show that reactivation of telomerase can enhance the self-renewal capability and neurogenesis in vitro. Finally, the protocol describes the procedures for performing telomere FISH (Fluorescence In Situ Hybridization) on both mouse FFPE (Formalin Fixed and Paraffin Embedded) brain tissues and metaphase chromosomes of cultured cells.

Telomere and telomerase play essential roles in ageing and tumorigenesis. The goal of this protocol is to show how to generate two murine inducible telomerase knock-in alleles and how to utilize them in the studies of tissue degeneration/regeneration and cancer.

Telomere dysfunction-induced loss of genome integrity and its associated DNA damage signaling and checkpoint responses are well-established drivers that ...

Medicine

Techniques to Induce and Quantify Cellular Senescence

In response to cellular stress or damage, proliferating cells can induce a specific program that initiates a state of long-term cell-cycle arrest, termed cellular senescence. Accumulation of senescent cells occurs with organismal aging and through continual culturing in vitro. Senescent cells influence many biological processes, including embryonic development, tissue repair and regeneration, tumor suppression, and aging. Hallmarks of senescent cells include, but are not limited to, increased senescence-associated &#946;-galactosidase activity (SA-&#946;-gal); p16INK4A, p53, and p21 levels; higher levels of DNA damage, including &#947;-H2AX; the formation of Senescence-associated Heterochromatin Foci (SAHF); and the acquisition of a Senescence-associated Secretory Phenotype (SASP), a phenomenon characterized by the secretion of a number of pro-inflammatory cytokines and signaling molecules. Here, we describe protocols for both replicative and DNA damage-induced senescence in cultured cells. In addition, we highlight techniques to monitor the senescent phenotype using several senescence-associated markers, including SA-&#946;-gal, &#947;-H2AX and SAHF staining, and to quantify protein and mRNA levels of cell cycle regulators and SASP factors. These methods can be applied to the assessment of senescence in various models and tissues.

Cellular senescence, the irreversible state of cell-cycle arrest, can be induced by various cellular stresses. Here, we describe protocols to induce cellular senescence and methods to assess markers of senescence.

In response to cellular stress or damage, proliferating cells can induce a specific program that initiates a state of long-term cell-cycle arrest, termed ...

An Introduction to Aging and Regeneration

Tissues are maintained through a balance of cellular aging and regeneration. Aging refers to the gradual loss of cellular function, and regeneration is the repair of damaged tissue generally mediated by preexisting adult or somatic stem cells. Scientists are interested in understanding the biological mechanisms behind these two complex processes. By doing so, researchers may be able to use somatic stem cells to treat degenerative diseases and develop therapies that could delay the effects of aging.
In this video, we provide a brief history of the field of aging and regeneration, touching upon observations made in ancient Greece, as well as modern-day experiments. Some of the questions being asked in this field, and the prominent methods being used by biologists to answer them, are then explored. Finally, we look at a few specific experiments being conducted in today\'s aging and regeneration research laboratories.

Aging, Regeneration and Telomerase Activity

Tissues are maintained through a balance of cellular aging and regeneration. Aging refers to the gradual loss of cellular function, and regeneration is ...

JoVE Science Education

Advanced Biology

Replicative Cell Senescence

Replicative cell senescence is a property of cells that allows them to divide a finite number of times throughout the organism&#39;s lifespan while preventing excessive proliferation. Replicative senescence is associated with the gradual loss of the telomere &#8212; short, repetitive DNA sequences found at the end of the chromosomes. Telomeres are bound by a group of proteins to form a protective cap on the ends of chromosomes. Embryonic stem cells express telomerase &#8212; an enzyme that adds the telomeric repeat sequence and enables repetitive cell division; however, in adults, telomerase is active only in the cells that need to divide regularly.
Because telomerase is inactive in most human somatic cells, the length of the telomere decreases with every cell division. After a critical length, telomere shortening leads to permanent cell cycle arrest. This mechanism is assumed to protect against cancer development by limiting the abnormal proliferation of tumors; however, a rare mutation can activate telomerase, which reconstructs the telomere region, allowing the cells to proliferate. Thus, telomerase is a perfect target for specific anticancer therapy, as most cancer cells express telomerase while normal cells do not.
The relation between telomere length and tumor formation has been experimentally verified using oncogenic mice. Oncogenic mice are mouse models that have cancer-causing genes. When such oncogenic mice are crossed with telomerase-deficient mice that lack telomerase activity, the resultant progeny mice express shorter telomeres than the oncogenic parent. These progeny mice, when interbred, generate successive generations that have progressively shorter telomeres. The frequency of tumor formation is studied by treating the progeny mice with carcinogens at every generation. As per the results, the late generation mice with shorter telomeres exhibit a reduced frequency of tumor formation compared to the early generation mice that maintain longer telomeres. This proves that limiting the replicative capacity of cells suppresses tumor formation.

Shortening of Telomere Length and Replicative Cell Senescence

Replikacyjne starzenie się komórek

Replicative cell senescence is a property of cells that allows them to divide a finite number of times throughout the organism&#39;s lifespan while ...