Hidden fat inside muscles can fuel rapid aging and disease

Plenty of people are trying to shed that stubborn belly fat for beach season. However, a new study is warning about the serious health impact of another type of fat — in your muscles. Researchers in Australia have found that the makeup of our muscle fibers plays a direct role in whether we suffer from disease and unhealthy aging.

The findings, in a nutshell

Australian scientists are pointing to a surprising culprit that links muscle health with disease: a type of cell known as fibro-adipogenic progenitors (FAPs). According to the research in the journal Molecular Aspects of Medicine, these cells, hidden deep within our muscles, play a crucial role in how fat accumulates between muscle fibers. Researchers from the Victor Chang Cardiac Research Institute say FAPs influence various health conditions, from obesity to muscle degeneration.

Imagine fat cells sneaking into your muscles, disrupting their function, and leading to various health issues. This is the reality of intermuscular adipose tissue (IMAT), a type of fat that accumulates within muscles. Researchers have found that FAPs are key players in this process. While FAPs are essential for muscle repair and maintenance, they can also transform into fat cells under certain conditions, contributing to IMAT and its associated problems. This dual role of FAPs makes them both heroes and villains in the story of muscle health.

(Credit: Molecular Aspects of Medicine)

“Everyone knows the dangers of belly fat, and how a build-up fat in your cardiac arteries can cause a heart attack. But there is a type of fat that barely anyone has heard of, despite it being linked to a whole range of life-threatening diseases,” says lead author Dr. Osvaldo Contreras in the media release.

“IMAT is crucial for maintaining muscle function, but in common with other fats, too much of it can be a bad thing. Excessive IMAT deposition can trigger muscle atrophy, diminished functional capacity, inflammation, insulin resistance, cardiovascular diseases, metabolic disorders, and even accelerate the aging process.”

Methodology

To understand how FAPs contribute to IMAT, scientists examined the presence and behavior of FAPs in various muscle tissues, both healthy and diseased.
Using advanced techniques, such as single-cell RNA sequencing, the researchers could map the different states and functions of these cells.
Scientists also explored how factors like muscle injury, chronic diseases, and metabolic conditions influence FAP behavior.
By studying both animal models and human tissues, they provided a comprehensive picture of how FAPs operate.

Key Results

Under normal conditions, FAPs help maintain muscle health by supporting the growth and repair of muscle fibers.
In situations of chronic inflammation or metabolic disturbances, these cells can turn into adipocytes, the fat cells that make up IMAT.
Prolonged physical inactivity or muscle injuries can trigger FAPs to adopt a fat-storing role, leading to increased IMAT.
IMAT is not just a passive bystander; its accumulation is linked to severe health issues like insulin resistance, cardiovascular diseases, and muscle atrophy.

Study Limitations

One of the main challenges is the complexity of FAP behavior, which varies depending on the muscle type and the specific conditions affecting it.
The exact molecular pathways that govern the switch from muscle-supporting to fat-storing FAPs are still unclear.
The study authors relied on animal models to study human diseases, which may not always perfectly replicate the human condition.

Takeaways from the study

By targeting FAPs and understanding their behavior, we could develop new therapies to combat muscle degeneration, obesity, and related metabolic disorders. For example, treatments that prevent FAPs from turning into adipocytes could help maintain muscle mass and function in aging populations or individuals with chronic diseases. Additionally, enhancing the beneficial roles of FAPs could improve muscle repair and regeneration after injuries. One of the best ways to do this, according to the research team, is by exercising.

“While the importance of exercise is often emphasized, its critical role in combating frailty and a myriad of diseases is often overlooked,” adds Dr. Flores-Opazo from the Institute of Health Sciences at Universidad de O’Higgins in Chile.

“Regular exercise, including weight training, is imperative for maintaining muscle health and resilience.”

In conclusion, the discovery of the pivotal role of FAPs in muscle health opens up exciting new avenues for research and treatment. As scientists delve deeper into the mechanics of these cells, they’re moving closer to new therapies that could significantly impact public health and perhaps even slow the aging process.

StudyFinds Editor Chris Melore contributed to this report.