Investigating Susceptibility to Radiation-Induced Pulmonary Fibrosis

Researchers evaluated three different mouse strains with varying sensitivity to radiation lung fibrosis in an effort to uncover the underlying mechanisms.

Investigating Susceptibility to Radiation-Induced Pulmonary Fibrosis

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Radiation is an effective treatment for many types of cancer. Unfortunately, this treatment has the potential to cause long-term side effects in some patients, including the thickening or scarring of lung tissue, known as pulmonary fibrosis. Radiation-induced pulmonary fibrosis (RIPF) is a serious complication that can occur after radiation therapy and can lead to death. Predicting an individual’s risk of developing RIPF remains challenging for clinicians, as little is known about the underlying mechanisms that cause it.

“Differential susceptibility to lung injury from radiation and other toxic insults across mouse strains is well described but poorly understood.”

Previous studies in mouse models have shown that there are natural variations in susceptibility to RIPF among different strains of mice. The mechanism(s) underlying this difference in susceptibility is still unknown. In a new study, researchers Eun Joo Chung, Seokjoo Kwon, Uma Shankavaram, Ayla O. White, Shaoli Das, and Deborah E. Citrin from the National Institutes of Health’s National Cancer Institute investigated differences in macrophage function across mouse strains and their potential contribution to varied RIPF susceptibility. On September 28, 2022, their research paper was published in Aging’s Volume 14, Issue 19, entitled, “Natural variation in macrophage polarization and function impact pneumocyte senescence and susceptibility to fibrosis.”

The Study

While the precise mechanisms underlying RIPF are not fully understood, it is thought that senescent pneumocytes (or alveolar cells) play a key role. Pneumocytes are a type of cell in the lung that are essential for gas exchange. Type II pneumocytes (AECII) function as alveolar stem cells after lung injury. The researchers hypothesized that macrophages (a type of white blood cell that play an important role in immune responses) may contribute to promoting AECII senescence.

“AECII are known to be in close contact with alveolar macrophages, and, in this fashion, to contribute to lung homeostasis [11].”

The researchers hypothesized that natural variations in macrophage function contribute to differences in RIPF susceptibility. To explore their hypothesis, they evaluated three different mouse strains with varying sensitivity to radiation lung fibrosis: C57L mice (RIPF-prone), C57BL6/J mice (intermediate) and C3H/HeN mice (RIPF-resistant). Female mice (to avoid sex-based differences in results) underwent thoracic irradiation (IR). Changes in macrophages and pneumocytes were assessed.

The Results

The team found that susceptibility to radiation-induced lung injury and premature AECII senescence varied by mouse strain. Pulmonary irradiation led to varied macrophage phenotypes and accumulation in each strain. In responses to polarizing stimuli, macrophages demonstrated strain-dependent responses. M2 macrophages induced AECII senescence via NOX2-derived superoxide production in a strain-dependent manner. Finally, macrophages expressing NOX2 accumulated in fibrotic lungs after radiation.

“NOX1 and NOX2 protein were expressed at the highest levels in C57L BMDM, with intermediate expression in C57BL6/J BMDM and the lowest expression in C3H/HeN BMDM (Figure 6B).”

The researchers demonstrated that the C57L mice (the strain with the greatest sensitivity to RIPF) exhibited the greatest rate of accumulation of senescent AECII cells. At the same time, they found that the fibrosis-sensitive (C57L and C57Bl6/J) mouse strains exhibit a greater accumulation of M2 polarized macrophages than the fibrosis-resistant strain (C3H/HeN).

“However, until now, the impact of M2 polarization on AECII senescence was unexplored. In this study, we identified that M2 macrophage polarization can contribute to AECII senescence, potentially leading to a positive feedback loop that furthers pulmonary injury.”

Conclusion

This study provides new insights into the role of macrophages in RIPF susceptibility. The findings suggest that natural variations in macrophage function contribute to differences in RIPF susceptibility. The different macrophage polarization profiles across strains may contribute to their varying susceptibilities to RIPF by promoting AECII senescence. These findings may help to develop new strategies for the prevention and treatment of RIPF.

“In this study, variation in the accumulation of senescent cells across strains with varying sensitivity to fibrosis has been established. Further, strain variation in macrophage response to polarizing stimuli and capacity to produce superoxide and induce senescence in epithelial cells is described. Together, these data highlight the importance of macrophage-epithelial interactions in the context of lung fibrosis and identify NOX2 as a possible therapeutic target in radiation lung injury.”

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Aging-US: Hallmarks of Cancer and Hallmarks of Aging

“Hyperfunctional signaling directly drives age-related diseases.”

— Mikhail Blagosklonny, M.D., Ph.D.

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BUFFALO, NY- May 18, 2022 – Dr. Mikhail Blagosklonny published his new review paper in Aging (Aging-US) Volume 14, Issue 9, entitled, “Hallmarks of cancer and hallmarks of aging.”

In this review, Dr. Blagosklonny expands on Gems and de Magalhães’ notion that canonic hallmarks of aging are superficial imitations of the hallmarks of cancer. He takes their work a step further and proposes the hallmarks of cancer and aging based on a hierarchical principle and the hyperfunction theory.

“Here I present the hallmarks of cancer, depicted as a circle by Hanahan and Weinberg [1], not as the circle but hierarchically, from molecular levels to the organism (Figure 1).”

Figure 1. Hierarchical representation (from molecular to organismal levels) of the original hallmarks of cancer based on Hanahan and Weinberg. See text for explanation.

Next, Dr. Blagosklonny depicts the hallmarks of aging suggested by López-Otín et al. based on the hierarchical principle. 

“This representation renders hallmarks tangible but reveals three shortcomings (Figure 2).”

Figure 2. Hierarchical representation of the hallmarks of aging based on López-Otín et al. See text for explanation.

The first shortcoming that Dr. Blagosklonny notes is the lack of hallmarks on the organismal level. The second is that the relationship between hallmarks on different levels is unclear. The third is that the inclusion of genetic instability as a hallmark is based on the theory that aging is caused by the accumulation of molecular damage. 

“The molecular damage theory was refuted by key experiments, as discussed in detail [44–51].” 

Dr. Blagosklonny then uses the hyperfunction theory to arrange the hierarchical hallmarks of aging.

“Let us depict hallmarks of aging, according to the hyperfunction theory of aging (Figure 3).”

Figure 3. Hierarchical hallmarks of aging based on hyperfunction theory, applicable to humans. Non-life-limiting hallmarks are shown in brown color. See text for explanation.

Dr. Blagosklonny continues by discussing the key to understanding aging and aging as a selective force for cancer. He concludes this review by discussing the common hallmarks of cancer, aging and cell senescence.

“In organismal aging, cancer and cellular senescence, the same key signaling pathways, such as mTOR, are involved. This is why the same drugs, such as rapamycin, can suppress all of them.”

DOI: https://doi.org/10.18632/aging.204082 

Correspondence to: Mikhail V. Blagosklonny 

Email: Blagosklonny@oncotarget.comBlagosklonny@rapalogs.com 

Keywords: oncology, carcinogenesis, geroscience, mTOR, rapamycin, hyperfunction theory

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About Aging-US:

Launched in 2009, Aging-US publishes papers of general interest and biological significance in all fields of aging research and age-related diseases, including cancer—and now, with a special focus on COVID-19 vulnerability as an age-dependent syndrome. Topics in Aging-US go beyond traditional gerontology, including, but not limited to, cellular and molecular biology, human age-related diseases, pathology in model organisms, signal transduction pathways (e.g., p53, sirtuins, and PI-3K/AKT/mTOR, among others), and approaches to modulating these signaling pathways.

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Trending With Impact: Underlying Mechanisms of Replicative Senescence

Published on the cover of Aging’s Volume 14, Issue 7, researchers conducted a new study investigating the role of IGFBP5 in replicative senescence.

cell division illustration

The Trending With Impact series highlights Aging (Aging-US) publications that attract higher visibility among readers around the world online, in the news, and on social media—beyond normal readership levels. Look for future science news about the latest trending publications here, and at Aging-US.com.

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In 1961, Leonard Hayflick and Paul Moorhead proposed a theory later named the Hayflick Limit. They discovered that a normal human cell can divide between 50 and 70 times before it can no longer proliferate and eventually dies. Researchers have since continued to explore this phenomenon and, today, this aging process is known as cellular (replicative) senescence.

“There are currently several experimental models of cellular senescence. Hayflick and Moorhead observed that primary human fibroblasts in culture exhibit a limited proliferative capacity [6]. This growth arrest during passages is called replicative senescence.”

This permanent cessation of the cell cycle is universally found in biology due to known and unknown causes, including the shortening of telomeres. While telomere shortening plays an important role, it is not the only event responsible for inducing cellular senescence. Thus, researchers have spent decades under the microscope experimenting with cellular models of replicative senescence.

In a new study released on April 4, 2022, researchers from Sapporo Medical University in Sapporo, Japan, investigated mechanisms of replicative senescence in vitro. Their trending research paper was published on the cover of Aging (Aging-US) Volume 14, Issue 7, and entitled, “Downregulation of IGFBP5 contributes to replicative senescence via ERK2 activation in mouse embryonic fibroblasts.”

The Study

Cellular senescence is typically characterized by cell growth arrest, an increase of cells positive for SA-β -gal staining, and upregulation of p16 and p19. To begin this study, the team cultured embryonic mouse fibroblasts (MEFs) and conducted cell passages according to the 3T3 method. They found that the MEFs underwent senescence after the 5th passage (P5). The team also found that at P8, the expression of insulin-like growth factor binding protein 5 (IGFBP5) mRNA was significantly reduced when compared with that of P2 MEFs.

Next, the team performed a knockdown of IGFBP5 in the MEF cells. Results showed that IGFBP5 knockdown induced premature cellular senescence in P2 MEFs. Knockdown of IGFBP5 increased phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) but did not affect expression levels of Akt or p16 repressors. The researchers also found that supplementing the cell culture growth medium with additional exogenous IGFBP5 delayed growth arrest and reduced replicative senescence in the MEF cells.

“To examine whether activated ERK1 and ERK2 by IGFBP5 knockdown are involved in the induction of senescent phenotypes, we examined effects of knockdown of ERK1 and ERK2 using a combination with IGFBP5 siRNA in P2 MEFs.”

Upon further analysis of ERK1/2’s role in IGFBP5-knockdown cells, the team found that the silencing of ERK2, and not ERK1, blocked the increase in the number of SA-β-GAL-positive cells. ERK2 knockdown attenuated the reduction in the cell number and upregulation of p16 and p21 in IGFBP5-knockdown cells. This study provides evidence that downregulation of IGFBP5 contributes to replicative senescence via ERK2 activation in mouse embryonic fibroblasts.

Conclusion

For the first time, the role of IGFBP5 in replicative senescence was demonstrated in MEFs. Their findings suggest that ERK2 underlies cellular senescence induced by IGFBP5 downregulation. Cellular senescence appears to be a complex process with many moving parts. While more research is needed to fully understand the role of IGFBP5 in replicative senescence, this study provides new insights into the underlying mechanisms involved in this complex process.

“In conclusion, the results of the present study demonstrated that downregulation of IGFBP5 during serial passage contributes to replicative senescence via an ERK2-dependent mechanism (Figure 6). The results suggest that IGFBP5 counteracts replicative senescence in MEFs.”

Figure 6. Schematic summary of our findings. MEFs at early passage secrete certain levels of IGFBP5. Secreted IGFBP5 proteins inhibit MEK/ERK2 by attenuating their phosphorylation (P) in the neighboring cell, leading to suppression of cellular senescence. IGFBP5 secretion is decreased during serial passage, causing activation of ERK2 and cellular senescence.
Figure 6. Schematic summary of our findings. MEFs at early passage secrete certain levels of IGFBP5. Secreted IGFBP5 proteins inhibit MEK/ERK2 by attenuating their phosphorylation (P) in the neighboring cell, leading to suppression of cellular senescence. IGFBP5 secretion is decreased during serial passage, causing activation of ERK2 and cellular senescence.

Click here to read the full research paper published by Aging (Aging-US).

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Aging (Aging-US) is an open-access journal that publishes research papers bi-monthly in all fields of aging research. These papers are available at no cost to readers on Aging-us.com. Open-access journals have the power to benefit humanity from the inside out by rapidly disseminating information that may be freely shared with researchers, colleagues, family, and friends around the world.

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Trending With Impact: Radiation, Senescence and Senotherapeutics

Researchers examined the effects of thoracic radiation-induced senescent cells on tumor progression, and the role of senotherapeutics to mitigate these effects.

Radiation therapy, advanced medical linear accelerator in therapeutic oncology to treat cancer
Radiation therapy, advanced medical linear accelerator in therapeutic oncology to treat cancer

The Trending With Impact series highlights Aging (Aging-US) publications that attract higher visibility among readers around the world online, in the news, and on social media—beyond normal readership levels. Look for future science news about the latest trending publications here, and at Aging-US.com.

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Radiation therapy is a highly-efficacious inducer of cancer cell death. With this being said, radiation has also previously been shown to cause premature senescence in the lung parenchyma. Senescence in cancer cells was previously only thought of as a mechanism capable of suppressing tumor cell proliferation by halting the cell cycle. However, a growing body of evidence shows that senescent cells may play a pro-tumorigenic role in cancer.

In the tumor microenvironment, the accumulation of senescent cells can become tumorigenic due to a lack of normal tissue stem cells and due to the expression of the senescence-associated secretory phenotype (SASP). SASP expression is when senescent cells secrete high levels of inflammatory cytokines, immune modulators, growth factors, and proteases. In addition to reinforcing senescence, SASP can create a biological environment that is immuno-suppressed and tumor-permissive. Radiation-induced senescence has previously been shown to have negative impacts on cancer patients.

“Cells that have undergone premature senescence due to stress, such as irradiation, are resistant to apoptotic cell death and effectively escape immune surveillance, resulting in their accumulation in tissue over time.”

Recently, researchers from the National Cancer Institute investigated the irradiated lung and the impact of radiation-induced senescent parenchymal cells on tumor growth. They also explored three senotherapeutics, rapamycin, INK-128 and ABT-737, for their potential to mitigate radiation-induced senescence. On February 12, 2022, the team’s priority research paper was published on the cover of Aging (Aging-US) Volume 14, Issue 3, and entitled, “Senescence-associated tumor growth is promoted by 12-Lipoxygenase.”

The Study

In this study, researchers intravenously injected melanoma cells into murine models two, four and eight weeks after daily fractions of thoracic irradiation exposure. There was also a control arm of unirradiated murine models. Tumor development was monitored by the number and size of the nodules in lung tissues. The number of cells exhibiting senescent activity was also recorded after two, four and eight weeks of thoracic irradiation. Their data demonstrated a correlation between the time points when tumors developed in the irradiated lungs and a marked accumulation of senescent cells.

“As previously described, in irradiated lungs, senescent cells increased significantly 4 and 8 weeks after IR compared to age matched unirradiated controls (Figure 1A).”

A characteristic of oncogene- and stress-induced senescence is the activation of mTOR signaling. Given this connection, the researchers conducted parallel studies evaluating senostatic agents capable of targeting the mTOR pathway, rapamycin and INK-128, and a senolytic agent to selectively eliminate senescent cells, ABT-737.  The data showed that rapamycin and INK-128 significantly reduced the number of tumor nodules in the lungs of irradiated mice compared to the controls. ABT-737 demonstrated reduced pulmonary senescence in irradiated mice.

The researchers also studied 12-Lipoxygensae (12-LOX), an enzyme that metabolizes a certain SASP molecule previously implicated in pulmonary senescence: 12(S)-HETE. 12-LOX is a known contributor to radiation-induced senescence and lung injury. The team specifically focused on the role of 12-LOX in pulmonary senescence and its impact on radiation-enhanced tumor growth. They found that inhibiting 12-LOX activity reduced radiation-induced lung senescence and mitigated radiation-enhanced tumor growth.

“Finally, we link senescence associated 12-LOX activity and production of 12(S)-HETE to the observed enhanced tumor growth after irradiation.”

Conclusion

In sum, the researchers found that radiation therapy can induce senescence in the lung parenchyma and also enhance tumor growth. The contribution of senescence in tumor progression was emphasized by the protection delivered by the mTOR-targeted senostatic and senolytic agents. This important discovery could lead to new therapies for cancer patients who are undergoing radiation therapy.

“Together, this study demonstrates the critical role of senescence in mediating radiation-enhanced tumor growth and identifies Alox12 as an important player in this phenomenon. Treatment with a senostatic agent, INK-128, identified in this study, or with agents like rapamycin and ABT-737 suggested their potential therapeutic use in alleviating radiation associated tumor growth.”

Click here to read the full priority research paper published by Aging (Aging-US).

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Aging (Aging-US) is an open-access journal that publishes research papers bi-monthly in all fields of aging research. These papers are available to read at no cost to readers on Aging-us.com. Open-access journals offer information that has the potential to benefit our societies from the inside out and may be shared with friends, neighbors, colleagues, and other researchers, far and wide.

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Trending With Impact: Therapeutic Strategy Improves Cell Senescence

In the cover paper of Aging (Aging-US) Volume 14, Issue 2, researchers discovered a potential therapeutic strategy to target senescent cells and combat aging and age-related diseases.

The Trending With Impact series highlights Aging (Aging-US) publications that attract higher visibility among readers around the world online, in the news, and on social media—beyond normal readership levels. Look for future science news about the latest trending publications here, and at Aging-US.com.

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Cellular senescence appears to be a phenomenon fundamentally ingrained within the aging process and linked to age-related diseases. Characterized broadly by permanent cessation of the cell cycle, cellular senescence may not be as permanent as once thought. 

Researchers from Incheon National University and Korea University conducted a new study exploring analogs of oxazoloquinoline and their potential to alleviate cellular senescence. Their trending research paper was published as the cover of Aging (Aging-US) Volume 14, Issue 2, and entitled, “Targeting regulation of ATP synthase 5 alpha/beta dimerization alleviates senescence.”

THE STUDY

Adenosine triphosphate (ATP) is an energy-carrying molecule found in all living cells. In order to meet the energy demands of the cell, the primary function of the mitochondria is to produce ATP. The maintenance of mitochondrial metabolism is inseparably linked with the regulation of senescence. Therefore, dysfunctional mitochondria has been considered as both a target and the cause of senescence. In addition to a marked decrease in ATP production, senescent cells also increase the expression of inflammatory cytokines, including interleukin 33, or IL-33. The researchers believe that reducing IL-33 may be a possible intervention to reduce senescence in aging patients and age-related diseases.

“In this study, using in-house compound library containing 20 oxazoloquinoline analogs designed to IL-33 inhibitors [9], we aimed to identify compounds capable of ameliorating senescence.”

The researchers investigated 20 oxazoloquinoline analogs using in vitro assays of senescent human diploid fibroblasts and embryonic kidney cells. Efficacy of the candidate compounds was determined using a screening strategy to measure their capacity to increase cell number. Cell numbers were measured between zero and 20 days after compound exposure. The researchers also measured indicators including mitochondrial membrane potential, reactive oxygen species (ROS) levels and p21 expression. They found that the analog KB1541 led to the maximum cell number increase, the recovery of mitochondrial function and the alleviation of cellular senescence. The researchers suggest that KB1541 could be a promising therapeutic agent for use in aging-related diseases.

“The increase in mitochondrial cristae length by KB1541 could be explained by previous findings showing that the increase in ATP generation exerted beneficial effects in mitochondrial function including increases in calcium buffering capacity and decrease in overall ROS production [48].”

CONCLUSIONS

“Taken together, our study provides evidence that the fine-tuning of ATP synthase 5 alpha/beta dimerization by KB1541 can induce mitochondrial functional recovery, concomitant recovery of senescent phenotypes, rendering the use of KB1541 as a potentially advantageous therapeutic strategy in aging and age-related diseases.”

The authors acknowledged that further studies are needed to clarify the exact relationship between IL-33 and mitochondrial energy metabolism. Further studies are also needed to investigate whether other IL-33 inhibitors can modulate senescence by the mechanisms found in the study. This research provides valuable insight into the potential of oxazoloquinoline analogs as novel therapeutic agents for aging and age-related diseases. With further exploration, their findings could lead to new therapeutic strategies to combat aging.

“The role of IL-33 in senescence is not clearly elucidated, therefore discovery of a novel interacting partner will provide clues toward revealing its function.”

Click here to read the full research paper published by Aging (Aging-US).

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Aging (Aging-US) is an open-access journal that publishes research papers bi-monthly in all fields of aging research. These papers are available to read at no cost to readers on Aging-us.com. Open-access journals offer information that has the potential to benefit our societies from the inside out and may be shared with friends, neighbors, colleagues, and other researchers, far and wide.

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Trending With Impact: Hair Follicles May Replace Traditional Biopsies

A new device has been developed by researchers to efficiently and painlessly collect hair follicle tissue samples from laboratory mammals, and even humans.

Figure 6. Markers of senescence analysis in hair follicular cells.
Figure 6. Markers of senescence analysis in hair follicular cells.

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Laboratory mammals have impacted human-kind far beyond enhancing scientific knowledge in behavioral and environmental research. These animals have greatly contributed to human healthspan and lifespan in countless ways; from validating life-saving cancer therapies to accelerating the future of human anti-aging and longevity interventions. With respect for these salubrious animals, ethical standards (per country) require that researchers handle laboratory mammals with care, and that pain and stress are minimized. Blood and skin tissue samples (biopsies) collected from animals should be replaced whenever possible. For the researchers, this twofold invasive procedure for the animals is also time- and resource-limiting—presenting a bottleneck in the biomedical research process.

“However, we present here a simple method for obtaining biological material in the form of follicular cells from laboratory mice with sufficient quantities and quality for multiple analyses using standard modern molecular biology methods.”

In an effort to efficiently and humanely solve this ethics/logistics problem, researchers—from Palacky UniversityUniversity Hospital OlomoucDanish Cancer Society Research Center, and Karolinska Institute—developed a novel, non-invasive device that can be used to collect tissue samples from hair follicles. They tested the applications of this device and authored a research paper of the study. In December of 2021, their paper was published on the cover of Aging (Aging-US) Volume 13, Issue 23, and entitled, “An efficient, non-invasive approach for in-vivo sampling of hair follicles: design and applications in monitoring DNA damage and aging.”

“As millions of laboratory mice are routinely genotyped globally every year this approach represents a major ethical and logistic breakthrough.”

The Follicular Cells’ Collector

As opposed to traditional biopsies, hair follicle collection is a humane, easy, non-invasive, and painless method of DNA and tissue sample collection. Each hair follicle contains approximately 50 cells—of various cell types. 

“This micro-organ structure also has other advantages in biomarker studies, including suitability for investigations of circadian rhythms [57], and the presence of numerous cell types in a small area, which can be easily distinguished, such as keratinocytes, melanocytes, or perifollicular macrophages and mast cells [810].”

Previously, the limitations of using hair follicles as DNA and tissue samples stemmed from ineffective technology. Many devices involved ordinary tweezers and forceps with high risks for cross-contamination. The researchers termed their novel tissue sample collection device the “follicular cells’ collector.” The follicular cells’ collector is designed with dual pipettes and utilizes a precision vacuum method of hair follicle extraction. The device can be used to comfortably collect DNA and tissue samples from laboratory mammals, and even from humans. 

“Although hair samples have been previously used for that purpose [2931], our sample collection approach may motivate researchers to use them more routinely and widely.”

The Study

To validate that these hair follicle samples contain the required genetic information necessary in most studies, researchers compared murine genotyping results of 151 tail biopsies and 151 hair samples. In order to determine the ability of these samples to detect changes in expression patterns induced by external factors, the team also observed the DNA damage response in hair follicle cells after gamma irradiation and after the topical application of chemical clastogens. Further exploring its potential application in aging research, researchers assayed expression patterns of selected markers of biological age and senescence in murine hair follicular cells. The researchers conducted many other tests and experiments using murine hair follicular cells in this study.

“The speed by which the samples can be collected and processed (e.g. by fixation) is among the biggest advantages of our solution as it can be performed within seconds. This fact limits any potential underlying cellular responses and additional DDR [DNA damage response] caused by cofounding stressing factors related to the withdrawal process [2].”

Conclusion

The researchers found that the follicular cells’ collector method of obtaining mouse hair follicular cells can be successfully used for genotyping, quantitative polymerase chain reaction testing and quantitative immunofluorescence. They also demonstrated that this method can successfully monitor quality and expression level changes of selected proteins—induced by external factors and during natural or experimentally induced aging. 

“Our results highlight the value of hair follicles as biological material for convenient in vivo sampling and processing in both translational research and routine applications, with a broad range of ethical and logistic advantages over currently used biopsy-based approaches.”

Click here to read the full research paper published by Aging (Aging-US).

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Aging (Aging-US) is an open-access journal that publishes research papers bi-monthly in all fields of aging research and other topics. These papers are available to read at no cost to readers on Aging-us.com. Open-access journals offer information that has the potential to benefit our societies from the inside out and may be shared with friends, neighbors, colleagues, and other researchers, far and wide.

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Trending With Impact: A New Marker of Aging and Cellular Senescence

Researchers from the Campisi Lab discovered new insights while investigating Cdkn1a transcript variants 1 and 2.

Embryonic stem cell colony

The Trending with Impact series highlights Aging publications that attract higher visibility among readers around the world online, in the news, and on social media—beyond normal readership levels. Look for future science news about the latest trending publications here, and at Aging-US.com.

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The phenomenon in which cells are still metabolically active but can no longer proliferate is known as cellular senescence. Cellular senescence is a normal mechanism in development and tissue homeostasis—and a hallmark of aging.

“Most of my lab works on a process called cellular senescence, which is a cellular response to stresses and damage, many of which increase with age,” Dr. Judy Campisi, Professor at the Buck Institute for Research on Aging and Senior Scientist at the Lawrence Berkeley National Lab, said in a recent Aging interview

An international team of researchers from Dr. Campisi’s lab are in search of new biological markers of cellular senescence and aging. Understanding mechanisms of aging such as senescence is key for developing new, safe interventions that may extend human life—with compounding socioeconomic and cultural impacts. Researchers from this lab come from institutions including the Buck Institute, the University of California, Berkeley’s Lawrence Berkeley National Lab, Universidad de CórdobaUniversidad MayorGeroscience Center for Brain Health and Metabolism, and Unity Biotechnology. The team published a trending 2021 paper in Aging‘s Volume 13, Issue 10, entitled, “Cdkn1a transcript variant 2 is a marker of aging and cellular senescence.” 

“Our results are, to our knowledge, the first to study Ckdn1a transcript variants in the context of aging.”

THE STUDY

There are a number of mechanisms that drive cellular senescence. Previously, mRNA and protein coding gene Cdkn1a transcript variant 1 (p21var1) has been better-studied compared to Cdkn1a transcript variant 2 (p21var2). The authors of this paper explain that this is likely because the encoded protein is identical to that encoded by variant 1, and both variants are regulated by p53. However, neither variants have ever before been studied in the context of aging. In this study, the researchers explored the expression levels of both Cdkn1a transcript variants 1 and 2 in the context of cellular senescence using several tissues from aged mice and a cell culture model of mouse cells.

“The stringent cell growth arrest associated with cellular senescence is determined, among other mechanisms, by activities of cyclin-dependent kinase inhibitor proteins p16Ink4a and p21Cip1/Waf1, encoded by the Cdkn2a and Cdkn1a loci, respectively [1].”

Study results showed that both variants are induced during cellular senescence. They showed that p21var1 and p21var2 are equally sensitive to transcriptional upregulation after p53 stabilization. The in vitro models also found that p21var2 is preferentially induced with age.

“In sum, p21var2 expression is consistently elevated with age, in contrast with an absence of age-related change in p21var1 levels.”

The researchers conducted further tests in vivo to examine the expression pattern of p21var2 and their results suggested that the circadian regulation of p21Cip1/Waf1 is driven solely by expression of Cdkn1a transcript variant 1. The team also induced cellular senescence in vivo with doxorubicin and ABT-263 (navitoclax) and evaluated the variants’ expression. These results confirmed their in vitro findings that p21var2 is more prone to cellular senescence than p21var1, thus making it a better marker for assessing the presence of senescent cells in vivo.

CONCLUSION

“We show that, although tissue-specific exceptions may arise, p21var2 but not p21var1 is a better candidate marker of aging and senescence in mice.”

Click here to read the full research paper, published by Aging.

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2021 Ride for Roswell
2021 Ride for Roswell

Behind the Study: Cdkn1a Transcript and Aging

Dr. Judith Campisi discusses her priority research paper published in 2021 by Aging, entitled, “Cdkn1a transcript variant 2 is a marker of aging and cellular senescence.”

Researchers explain their studies that were published in Aging

Behind the Study is a series of transcribed videos from researchers elaborating on their recent oncology-focused studies published by Aging. A new Behind the Study is released each Monday. Visit the Aging YouTube channel for more insights from outstanding authors.

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Hello, my name is Judy Campisi. I am a Professor at the Buck Institute for Research on Aging and also a Senior Scientist at the Lawrence Berkeley National Lab. And my laboratory, which is a pretty international laboratory with people from Asia and Europe, published a paper in aging, “Cdkn1a transcript variant 2 is a marker of aging and cellular senescence.”

So why do we care about this?

Well, most of my lab works on a process called cellular senescence, which is a cellular response to stresses and damage, many of which increase with age. And it’s now clear from mouse models that if you eliminate senescent cells, which increase with age, you can increase the health span of a mouse – not necessarily the lifespan, but the health span. So it becomes kind of important to have ways of identifying senescent cells in detail, and we have not been able to do that so far with absolute certainty because there frankly are no senescent-specific markers. So there are markers that are commonly expressed by senescent cells, but none of them are absolutely specific.

Figure 1. The Cdkn1a variant 2 transcript is preferentially induced during aging.
Figure 1. The Cdkn1a variant 2 transcript is preferentially induced during aging.

And so what we have done is we have looked at one of those markers, which is a gene called Cdkn1a and it codes for approaching, called P21. So everyone knows that P21 is one of those common biomarkers of aging, but it also is not necessarily strictly limited to aging. And what we’ve found is that there are two mRNAs that are made from that gene, that had been known before. We looked at these two mRNAs separately and found that one of them, which is called the variant 2, is a better marker of senescence and aging than the other mRNA. And that gives us a little bit of a edge in trying to unambiguously identify senescent cells in vivo and even in culture.

So the importance of this work is that it helps refine our ways of identifying these cells. We now know that these cells are important in aging, certainly in mice, probably in humans as well. So with this group of mine, many of which come from Spain or France or Russia, many of them contributed to refining this marker and allowing us to be able to have a better way of having some confidence that a senescent cell is indeed senescence.

And I can stop here.

Click here to read the full study published by Aging.

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Aging is an open-access journal that publishes research papers monthly in all fields of aging research and other topics. These papers are available to read at no cost to readers on Aging-us.com. Open-access journals offer information that has the potential to benefit our societies from the inside out and may be shared with friends, neighbors, colleagues, and other researchers, far and wide.

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Pressurized Oxygen Therapy Can Reverse Mechanisms of Aging

For the first time, researchers demonstrate that hyperbaric oxygen therapy can reverse the mechanisms that mark the aging process.

Oxygen molecules and erythrocytes floating in a vessel in the blood stream.
Oxygen molecules and erythrocytes floating in a vessel in the blood stream.
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Aging is the progressive loss of physiological integrity, which results in impaired functionality and increased susceptibility to diseases, and ultimately death. For the first time, researchers collaborated in an in vivo study to observe the effects of hyperbaric oxygen therapy on cellular mechanisms to reverse aging.

Researchers based out of Israel from Shamir Medical Center, Tel-Aviv University, and Bar Ilan University published a groundbreaking new paper titled, “Hyperbaric oxygen therapy increases telomere length and decreases immunosenescence in isolated blood cells : a prospective trial,” in the open access journal, Aging. The importance of this study hinges on understanding the mechanisms of aging that were evaluated by the researchers.

“At the cellular level, two key hallmarks of the aging process include telomere length (TL) shortening and cellular senescence.”

Telomere Length

Telomeres (TLs) function to protect chromosomes from DNA damage and are located at the end of the chromosome. In each instance of cell division, the telomeres shorten due to an inherent inability to fully replicate the DNA strand. Given that cells can only replicate a finite number of times before they can no longer engage in mitosis, the shortening of telomeres has been shown in adults to lead to increased rates of mortality.

Researchers in this study also provide examples of studies that are finding a number of pharmacological agents capable of reducing the shortening rate of telomeres.

“Shortened TLs can be a direct inherited trait, but several environmental factors have also been associated with shortening TL, including stress, lack of physical endurance activity, excess body mass index, smoking, chronic inflammation, vitamins deficiency, and oxidative stress [2, 8, 9].”

Cellular Senescence

The other hallmark mechanism of the aging process is cellular senescence. Previously, senescent cells have been viewed as mechanisms that protect the body against cancer through cell-cycle arrest, however, recent discoveries have found that they also have a role in processes such as development, tissue repair, aging, and age-related disorders. The phase of senescence can be triggered by telomere shortening and other non-telomeric DNA damage.

“The primary purpose of senescence is to prevent propagation of damaged cells by triggering their elimination via the immune system. The accumulation of senescent cells with aging reflects either an increase in the generation of these cells and/or a decrease in their clearance, which in turn aggravates the damage and contributes to aging [1].”

Oxidative Stress

In this well-written paper, the researchers introduce the topic by citing numerous interventional studies measuring the association between telomere length and lifestyle modifications. Studies include the measuring of diet, supplements, physical activity, stress management, and social support. However, the team found that the most common mechanism associated with telomere shortening is oxidative stress.

“Oxidative stress can occur from imbalances between the production of reactive oxygen species (ROS) and cellular scavengers.”

Previous studies indicate that telomeres are highly sensitive to oxidative DNA damage which occurs due to an excess of reactive oxygen species (ROS), or molecular oxygen by-products. The excess formation of these ROS occurs through the sequential reduction of oxygen via the addition of electrons and a lack of scavenger cells to digest excess microorganisms. This leads to the shortening of telomeres.

Hyperbaric Oxygen Therapy

Hyperbaric oxygen therapy (HBOT) has been observed to stimulate brain function and increase cognitive ability in previous studies. HBOT involves patients breathing in 100% oxygen in a pressurized chamber on a repeated basis. Being in this type of environment increases the amount of oxygen that is dissolved in the blood and tissue. Increasing oxygen levels in the body using pure oxygen on a daily basis can induce the hormesis phenomenon. This eustress type of therapy has been shown to have beneficial and positive effects on the body and mind.

“Single exposures [to HBOT] increase ROS generation acutely, triggering the antioxidant response, and with repeated exposures, the response becomes protective [13, 18].”

The Study

This study was designed to evaluate the effects of HBOT on the telomeres and concentrations of senescent cells in aging/healthy adults. Thirty-five participants living independently at 64+ years of age received HBOT exposures daily, over the course of 60 days.

Researchers collected whole blood samples prior to intervention (baseline), at the 30th and 60th session, and 1-2 weeks after the last HBOT session. They assessed the telomere lengths and senescence of peripheral blood mononuclear cells (PBMCs) in each participant’s blood sample.

Figure 3. Senescent cell changes with HBOT.
Figure 3. Senescent cell changes with HBOT.

“In this study, for the first time in humans, it was found that repeated daily HBOT sessions can increase PBMC telomere length by more than 20% in an aging population, with B cells having the most striking change. In addition, HBOT decreased the number of senescent cells by 10-37%, with T helper senescent cells being the most affected.”

Conclusion

Following HBOT, telomere lengths increased by over 20% in T helper, T cytotoxic, natural killer, and B cells. There was also a significant decrease in the number of senescent T cytotoxic and T helper cells observed in the participant blood samples, allowing for new healthy cells to regenerate.

“In conclusion, the study indicates that HBOT may induce significant senolytic effects including significantly increasing telomere length and clearance of senescent cells in the aging populations.”

Click here to read the full scientific paper, published in Aging.

Learn more about Hyperbaric Oxygen Therapy (HBOT)

Aging is an open-access journal that publishes research papers monthly in all fields of aging research and other topics. These papers are available to read at no cost to readers on Aging-us.com. Open-access journals offer information that has the potential to benefit our societies from the inside out and may be shared with friends, neighbors, colleagues and other researchers, far and wide.

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