Two paths of aging: New insights on promoting healthspan
Master aging circuit identified
July 16, 2020
Science Daily/University of California - San Diego
Molecular biologists and bioengineers at the University of California San Diego have unraveled key mechanisms behind the mysteries of aging. They isolated two distinct paths that cells travel during aging and engineered a new way to genetically program these processes to extend lifespan.
The research is described July 17 in the journal Science.
Our lifespans as humans are determined by the aging of our individual cells. To understand whether different cells age at the same rate and by the same cause, the researchers studied aging in the budding yeast Saccharomyces cerevisiae, a tractable model for investigating mechanisms of aging, including the aging paths of skin and stem cells.
The scientists discovered that cells of the same genetic material and within the same environment can age in strikingly distinct ways, their fates unfolding through different molecular and cellular trajectories. Using microfluidics, computer modeling and other techniques, they found that about half of the cells age through a gradual decline in the stability of the nucleolus, a region of nuclear DNA where key components of protein-producing "factories" are synthesized. In contrast, the other half age due to dysfunction of their mitochondria, the energy production units of cells.
The cells embark upon either the nucleolar or mitochondrial path early in life, and follow this "aging route" throughout their entire lifespan through decline and death. At the heart of the controls the researchers found a master circuit that guides these aging processes.
"To understand how cells make these decisions, we identified the molecular processes underlying each aging route and the connections among them, revealing a molecular circuit that controls cell aging, analogous to electric circuits that control home appliances," said Nan Hao, senior author of the study and an associate professor in the Section of Molecular Biology, Division of Biological Sciences.
Having developed a new model of the aging landscape, Hao and his coauthors found they could manipulate and ultimately optimize the aging process. Computer simulations helped the researchers reprogram the master molecular circuit by modifying its DNA, allowing them to genetically create a novel aging route that features a dramatically extended lifespan.
"Our study raises the possibility of rationally designing gene or chemical-based therapies to reprogram how human cells age, with a goal of effectively delaying human aging and extending human healthspan," said Hao.
The researchers will now test their new model in more complex cells and organisms and eventually in human cells to seek similar aging routes. They also plan to test chemical techniques and evaluate how combinations of therapeutics and drug "cocktails" might guide pathways to longevity.
"Much of the work featured in this paper benefits from a strong interdisciplinary team that was assembled," said Biological Sciences Professor of Molecular Biology Lorraine Pillus, one of the study's coauthors. "One great aspect of the team is that we not only do the modeling but we then do the experimentation to determine whether the model is correct or not. These iterative processes are critical for the work that we are doing."
https://www.sciencedaily.com/releases/2020/07/200716144732.htm
A moderate dose of novel form of stress promotes longevity
July 10, 2019
Science Daily/Baylor College of Medicine
A newly described form of stress called chromatin architectural defect, or chromatin stress, triggers in cells a response that leads to a longer life. Researchers at Baylor College of Medicine and the Houston Methodist Research Institute report in the journal Science Advances that moderate chromatin stress levels set off a stress response in yeast, the tiny laboratory worm C. elegans, the fruit fly and mouse embryonic stem cells, and in yeast and C. elegans the response promotes longevity. The findings suggest that chromatin stress response and the longevity it mediates may be conserved in other organisms, opening the possibility of new ways to intervene in human aging and promote longevity.
"Chromatin stress refers to disruptions in the way DNA is packed within the nucleus of the cell," said corresponding author Dr. Weiwei Dang, assistant professor of molecular and human genetics and the Huffington Center on Aging and member of the Dan L Duncan Comprehensive Cancer Center at Baylor. "One of the factors that influences chromatin structure is proteins called histones."
In the nucleus of cells, DNA wraps itself around histone proteins forming a 'beads-on-a-string' structure called chromatin. Other proteins bind along chromatin and the structure folds further into more complicated configurations. Everything involving DNA would have to deal with this chromatin structure, Dang explained. For example, when a particular gene is expressed, certain enzymes interact with the chromatin structure to negotiate access to the gene and translate it into proteins. When chromatin stress happens, disruption of the chromatin structure can lead to unwanted changes in gene expression, such as expression of genes when they are not supposed to or lack of gene expression when it should occur.
In this study, Dang and his colleagues worked in the lab with the yeast Saccharomyces cerevisiae to investigate how the dosage of histone genes would affect longevity.
They expected that yeast genetically engineered to carry fewer copies of certain histone genes than normal or control yeast would have chromatin changes that would result in the yeast living less than controls.
"Unexpectedly, we found that yeast with fewer copies of histone genes lived longer than the controls," said first author Ruofan Yu, research assistant in molecular and human genetics in the Dang lab.
Yeast with a moderately low dose of histone genes showed a moderate reduction of histone gene expression and significant chromatin stress. Their response to chromatin disruption was changes in the activation of a number of genes that eventually promoted longevity.
In previous work Dang and colleagues had shown that in aging cells chromatin structure progressively falls apart. Histone alterations, such as a decrease in their protein levels, are a characteristic of the aging process, but the researchers showed that if they compensated for this age-related decrease in histone levels by overexpressing certain histone genes they extended the lifespan of aging yeast cells. In this study they discovered that moderately reducing the number of copies of histone genes in young yeast also promoted longevity.
"We have identified a previously unrecognized and unexpected form of stress that triggers a response that benefits the organism," Yu said. "The mechanism underlying the chromatin stress response generated by moderate reduction of histone dosage is different from the one triggered by histone overexpression we had previously described, as shown by their different profiles of protein expression responses."
Dang, Yu and their colleagues found that chromatin stress also occurs in other organisms such as the laboratory worm C. elegans, the fruit fly and mouse embryonic stem cells, and in yeast and C. elegans the chromatin stress response promotes longevity.
"Our findings suggest that the chromatin stress response may also be present in other organisms. If present in humans, it would offer new possibilities to intervene in the aging process," Dang said.
https://www.sciencedaily.com/releases/2019/07/190710193923.htm