Your weight hasn't budged in decades, but your waistline keeps growing. Scientists now think they know why.
Researchers at City of Hope have identified a biological trigger for age-related belly fat that goes beyond simple weight gain. Their work, published in Science, centers on a newly discovered stem cell that emerges during middle age and appears to supercharge the body's fat-cell factory.
The stakes are high. Abdominal fat accumulation is linked to slower metabolism, type 2 diabetes, heart disease, and accelerated aging. Yet the precise mechanism driving belly expansion has eluded scientists for years.
"People often lose muscle and gain body fat as they age, even when their body weight remains the same," said Qiong Wang, an associate professor of molecular and cellular endocrinology at City of Hope. "We discovered that aging triggers the arrival of a new type of adult stem cell and enhances the body's massive production of new fat cells, especially around the belly."
The conventional wisdom held that existing fat cells simply enlarge over time. But Wang's team suspected something else was happening: the body was manufacturing entirely new fat cells at an accelerated rate.
To test this, researchers transplanted stem cells called adipocyte progenitor cells (APCs) from young and old mice into a fresh group of young mice. The difference was stunning. Stem cells from older animals generated far more new fat cells than those from younger ones. The reverse transplant told the real story: young cells placed into aging mice produced relatively few new fat cells. This meant the aging itself was baked into the older stem cells.
Using single-cell RNA sequencing to examine gene activity in individual cells, the team made a critical discovery. In young mice, APCs remained relatively quiet. But by middle age, these cells ramped up dramatically and began churning out new fat cells at a much higher rate.
The research uncovered something more startling: during middle age, some APCs morphed into a newly identified stem cell population the team named committed preadipocytes, age-specific, or CP-As. These cells appeared only during aging and proved exceptionally effective at producing new fat cells.
The team then traced the molecular commands driving this transformation. They identified a critical signaling pathway called leukemia inhibitory factor receptor, or LIFR. In older mice, this pathway appeared essential for telling CP-As to multiply and become fat cells. Younger mice didn't need this signal to produce fat at all.
"The body's fat-making process is driven by LIFR," Wang explained. "Our research indicates that LIFR plays a crucial role in triggering CP-As to create new fat cells and expand belly fat in older mice."
The findings weren't confined to rodents. When the team analyzed human tissue samples using the same sequencing technique, they identified cells closely resembling CP-As, appearing in greater numbers in middle-aged individuals. These human versions also showed a strong capacity to generate new fat cells, suggesting the same biological mechanism operates in people.
The discovery opens a new avenue for treatment. Rather than simply targeting existing fat cells, future therapies could aim to block or eliminate CP-As before they accumulate. The researchers say their next steps include tracking these cells in ongoing animal studies, understanding their behavior in humans, and exploring ways to interfere with their function.
"Understanding the role of CP-As in metabolic disorders and how these cells emerge during aging could lead to new medical solutions for reducing belly fat and improving health and longevity," Wang said.
Author Jessica Williams: "This isn't just about fitting into your old jeans, it's about understanding why our bodies betray us in predictable ways as we age, and whether science can finally do something about it."
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