Survivors of weather-related calamities may experience premature ageing: Study

In 2017, Hurricane Maria devastated Puerto Rico. It left behind the island’s worst disaster in history. In its immediate aftermath, the hurricane killed over 3,000 people, knocked out electricity to almost all of the island’s 3.4 million population, and inflicted more than USD 100 billion in damages. But what was the long-term impact of this stress and struggle on its people’s health? Is it possible that being exposed to harsh weather occurrences may hasten the ageing process? New research on the subject has recently been published.

The findings were published in ‘Proceedings of the National Academy of Sciences.’

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“While everyone ages, we don’t all age at the same rate, and our lived experiences, both positive and negative, can influence how quickly we age. Surviving an intense incident might cause persistent inflammation and the early beginning of several age-related disorders, such as heart disease,” according to the corresponding author Noah Snyder-Mackler, an associate professor in the School of Life Sciences at Arizona State University. “However, we still don’t know exactly how these events become lodged in our bodies, resulting in detrimental health impacts that may not manifest themselves for decades after the incident occurs.”

As the ultimate toll on the survivors’ mental and physical health was still being calculated, a group of biologists led by Snyder-Mackler went to one of our closest evolutionary cousins for the first indications.

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The damage affected all of the island’s fauna, including a colony of free-roaming rhesus macaques residing on the remote Cayo Santiago island near Puerto Rico. The animals have been living on the island since 1938 when the Caribbean Primate Research Center field station was established.

Now, the ASU team, led by Snyder-Mackler and lead author Marina Watowich, a graduate student at the University of Washington and research scientist at ASU, and their collaborators at the Caribbean Primate Research Center, the University of Pennsylvania, the University of Exeter, and New York University, have published one of the first findings that natural disasters may have molecularly accelerated ageing in the monkeys’ immune systems.

As a category 4 storm, Maria wreaked havoc on Cayo Santiago’s natural ecosystem and scientific infrastructure. Surprisingly, only 2.75% of the macaque population died as a result of the storm. And there was no change in survival one year after the hurricane. Was the health of hurricane survivors harmed in any other way?

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People of the same chronological age may acquire illness at different times and in different ways. It is known that people who have had highly negative experiences are more likely to acquire heart disease and other ailments that are more frequent in older people. It is yet unknown how these negative experiences ‘get under the skin’ to induce illness. One theory is that this effect is caused by tremendous hardship ‘ageing’ the body. People’s biological ages can differ, as determined by molecular markers inscribed in our DNA, immune systems, and physiology.

“Through this study, we were able to quantify the molecular changes related with ageing, such as disruptions of protein-folding genes, increased inflammatory immune cell marker gene expression, and older biological ageing,” Watowich explained.

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The researchers discovered that the hardship caused by the hurricane may have hastened the ageing of the immune system after carefully examining the genes expressed in the macaques’ immune cells.

“On average, monkeys who survived the hurricane had immune gene expression profiles that were 2 years older or about 7-8 years of human longevity,” Watowich added.

The findings revealed that extreme weather events, which were growing more frequent and intense as a result of climate change, might have physiologically negative repercussions for people who experienced them. This was especially important considering that hurricanes and other extreme weather events are growing more powerful and prevalent as a result of climate change.

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Cayo Santiago, a 15.2-hectare island one kilometre off the southeastern coast of Puerto Rico, is home to a colony of 1,800 free-roaming rhesus macaques that have been studied for over a century.

“Cayo Santiago was the first region of Puerto Rico to be struck by Hurricane Maria, and it absorbed the full impact of the category 4 hurricane,” Snyder-Mackler explained. “The storm wrecked houses and infrastructure throughout Puerto Rico, and on Cayo Santiago, it killed much of the vegetation, as well as the water cisterns and research equipment required to keep the field station operational.”

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The rhesus macaques have many behavioural and biological characteristics with humans, including how their bodies age, yet their life is one-quarter that of ours. The scientific team recognised that by examining the macaques, they might gain estimates of ageing in years rather than decades as incomparable human research.

Marina Watowich and the rest of the researchers were able to use a collection of blood samples and a history of extensive demographic data from age-matched subgroups of the Cayo Santiago rhesus macaque community to assess how Hurricane Maria affects immune cell gene regulation and ageing.

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They discovered that 4% of genes expressed in immune cells were changed after the hurricane by undertaking a worldwide study of immune gene expression. Genes associated with inflammation had increased expression after the hurricane, while genes involved in protein translation, protein folding/refolding, the adaptive immune response, and T cells had lower expression after the hurricane.

The downregulation of so-called heat shock genes, which promote the normal operation of protein synthesis in human cells, was the most impacted, with some having two-fold reduced activity after Hurricane Maria. These genes have also been linked to heart disease and Alzheimer’s disease.

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Surprisingly, they discovered a substantial link between storm exposure and ageing effects on gene expression, with the effect of the hurricane being similar to the effect of the immune system ageing.

They looked at profiles from single-cell RNA sequencing to identify genes that are preferentially expressed in important immune cell types to determine how the hurricane may have changed levels of immune cell populations.

“Cell-specific markers of canonical pro-inflammatory immune cells, such as CD14 monocytes, were found to be more abundant in older people and those who had been affected by the hurricane. Furthermore, the expression of helper T-cell genes, which are anti-inflammatory cells, dropped in older animals and those exposed to the hurricane. This might mean that animals have increased inflammatory activity following a storm, comparable to what we find in elderly people “Snyder-Mackler stated.

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They obtained four years of data before Hurricane Maria and one year after Hurricane Maria from their long-term research, which was part of a cooperation with the Caribbean Primate Research Center, the University of Pennsylvania, the University of Exeter, and New York University. They believed that exposure to the hurricane would cause molecular alterations similar to those seen in the normal ageing process.

“Our findings imply that variations in immune cell gene expression in people exposed to a major natural catastrophe were similar in many respects to the consequences of normal ageing,” Snyder-Mackler said. “We also found signs of accelerated biological ageing in samples taken after animals were affected by Hurricane Maria,” he said.

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“Most importantly, we find a fundamental mechanism-immune cell gene regulation-that may explain how hardship, particularly in the setting of natural catastrophes, may eventually ‘get under the skin’ to promote age-related illness development and progression,” Watowich added.

Surprisingly, not all monkeys reacted the same way to the hurricane. Some monkeys’ biological ages, for example, rose faster than others. The researchers suggest that other features of the monkey’s surroundings may impact their response to hardship.

For example, much as in people, social support is an important part of being able to manage and deal with hardship. It’s likely that monkeys that had more social support after the storm were better able to overcome any negative effects. The study did have certain drawbacks, the most notable of which was the inability to compare ageing rates in the same individuals before and after the hurricane.

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They anticipated that future research would involve longer-term studies of every individual within a population to understand the interaction of biological ageing, adversity, and social structures amid a natural disaster.

Finally, they hoped that their findings will spur attempts to improve knowledge of ageing and adversity, and perhaps one day, a viable mitigation plan to reduce the toll of natural catastrophes.