Aging is inevitable, but it is certainly not permanent. It may seem like aging occurs in a measured and linear fashion, day by day, week by week, and month by month, slowly leading us into our golden years. However, new research suggests that aging is more like a mosaic or patchwork quilt, stitched together from pieces of fabric by hormonal signals.
A new study published in the journal Nature Aging analyzed structural changes in dozens of human tissues and found that different parts of the body exhibit remarkably different rates of aging.
Some changes begin rapidly around age 30. Others remain relatively stable until around menopause in women. And still others seem to undergo two distinct periods of accelerated aging.
In other words, there may not be a single “aging process” occurring throughout the body. Instead, different organs or systems of the body may have their own timelines, and different organ systems may influence each other.
To understand this, a research team led by computational biologist Sanju Sinha of the Sanford Burnham Prebys Medical Research Institute in California developed a computational system called PathStAR to analyze the microscopic structure of tissue in routine pathology images.
Rather than being trained to guess a person’s chronological age, the system analyzed the physical structure of tissue changes.
The researchers applied PathStAR analysis to images of more than 25,000 postmortem tissue samples from 970 donors aged 21 to 70, covering 40 different tissue types.
“It’s a publicly available dataset used by hundreds of groups, but the molecular data is used by almost everyone,” says Sinha, referring to the Genotype-Tissue Expression project for which the samples were collected. “Tens of terabytes of image data remained virtually untouched.”
Arteries are among the most rapidly aging organs, with the most intense structural changes occurring around age 30. This is consistent with postmortem studies showing that plaque formation in arteries also increased most rapidly during this decade and then stabilized.
People whose arteries showed more accelerated structural aging also had a higher incidence of atherosclerosis (the buildup of plaque inside arteries, causing them to harden). So, while your 30s may seem a bit premature for “old age,” your arteries apparently aren’t waiting.
In women, the uterus and vagina remained relatively stable throughout early adulthood, then showed the greatest structural changes in the early to mid-50s—around the transition to menopause.
Changes included features such as tissue atrophy and thinning of the endometrium (the lining of the uterus), consistent with the effects of declining estrogen levels.
The ovaries changed again. Instead of uniform changes, ovarian tissue showed a peak in structural aging between the ages of 35 and 40 and another peak between the ages of 55 and 60, corresponding to the postmenopausal period.
The researchers were able to detect this pattern in the physical structure of the tissue, despite the fact that comparable analyses of gene expression and DNA methylation did not reproduce the same two peaks.
A similar two-stage aging pattern was also observed in other organs.
Of the fourteen other tissues for which the researchers were able to establish high-confidence aging trajectories, nine demonstrated so-called “biphasic” aging, with two periods of accelerated structural changes, typically occurring between the ages of 30 and 50.
These include organs seemingly unrelated to reproduction—the esophagus, stomach, colon, and small intestine. In men, the prostate and testicles also undergo similar aging.
Thus, it appears that these organs age synchronously, and the connections between them are not limited to adjacent organs.
People who experienced accelerated structural aging in the colon and esophagus also frequently experienced this phenomenon in the prostate, but the synchronicity of these changes appeared to be more widespread.
“More than half of the tissues we studied followed the structural aging of the ovaries,” says Sinha, “so we view the ovaries as a kind of regulator of aging throughout the body.”
Hormones may play a key role, as They enter our bodies in large quantities as signaling molecules; they are not limited to the reproductive system.
“The most dramatic decline in hormonal signaling capacity was observed in gastrointestinal tissues,” the researchers report, “consistent with the known expression of estrogen receptors throughout the gastrointestinal epithelium and their role in maintaining the mucosal barrier.”
It is therefore not surprising that the intestine ages at the same rate as the uterus or prostate.
Accelerated structural aging in these various organs shared a common characteristic: increased inflammation, along with decreased energy production, cell proliferation, and cell quality control systems.
The researchers argue that understanding how organs and systems age may ultimately change our understanding of methods to slow aging. Rather than viewing aging as a single, uniform process, it may be more beneficial to target specific organs during their periods of greatest vulnerability.
“By developing therapies aimed at protecting the reproductive system from aging, we see the potential to protect many other organs and extend overall healthy lifespan,” says Sinha.
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This study has several important caveats. First, these are postmortem samples, and a person’s cause of death can affect the age of their tissues, especially in young people.
The researchers acknowledge that changes do not always indicate aging: “Not all age-related changes imply functional decline; some may reflect adaptive remodeling or neutral variations,” they note in their paper.
Furthermore, the analysis used relatively broad age ranges, so it cannot pinpoint exactly when changes in a specific individual’s tissues begin.
However, judging by this work, it is likely that our bodies are not all controlled by the same biological clock.
There may be dozens of them, and not all of them keep the same time.
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