The human heart is one of the hardest-working organs in the body. It never takes a day off and requires a continuous supply of energy to keep beating.
To meet these enormous energy demands, heart cells mainly rely on fats as fuel.
For decades, researchers have viewed this ability to burn fat as a sign of a healthy heart.
A new study from UT Southwestern Medical Center is challenging that assumption. Researchers have discovered that when heart cells burn fat at excessively high levels, the process can actually damage the heart’s energy-producing structures and contribute to heart failure.
The findings, published in the Journal of Clinical Investigation, reveal a previously unknown connection between fat metabolism, mitochondrial health, and heart disease.
Heart failure affects millions of people around the world and remains one of the leading causes of hospitalization and death.
The condition develops when the heart can no longer pump blood effectively enough to meet the body’s needs. Common risk factors include obesity, diabetes, high blood pressure, and metabolic syndrome.
Scientists have known that the way the heart uses energy changes during heart failure. Healthy hearts primarily burn fat, while failing hearts often rely more heavily on glucose. This observation has sparked debate among researchers. Some argued that reduced fat burning contributes to disease, while others believed it might represent an adaptive response.
The new research suggests that the answer may depend on maintaining the right balance.
The investigators focused on two enzymes that normally help regulate the movement of fatty acids into mitochondria. Mitochondria are tiny structures inside cells that convert nutrients into usable energy. They are especially abundant in heart muscle because of the heart’s constant energy needs.
Using genetically engineered mice, the researchers removed these enzymes from heart cells. Without them, fatty acids entered mitochondria without proper control and were rapidly burned for energy.
At first, the change seemed likely to increase energy production. Instead, it triggered a chain reaction that ultimately damaged the heart.
The excessive fat burning consumed large amounts of linoleic acid, a fatty acid obtained from food. Linoleic acid is needed to produce cardiolipin, a specialized lipid that helps maintain the structure and function of mitochondrial membranes.
Cardiolipin acts like a support system for the machinery that generates cellular energy. Without adequate amounts of it, mitochondria struggle to function normally.
As cardiolipin levels dropped, the mitochondria became damaged and less efficient. Energy production declined, heart muscle weakened, and the mice developed enlarged hearts. Eventually, they showed signs of dilated cardiomyopathy, a serious condition in which the heart becomes stretched and weakened.
The researchers then investigated whether slowing fat entry into mitochondria could protect the heart. They used drugs that block CPT1, a protein responsible for transporting fatty acids into mitochondria.
The results depended heavily on timing. When treatment was started before heart damage appeared, the drugs successfully prevented heart failure. When treatment began after cardiomyopathy had already developed, the drugs provided little benefit.
This suggests that future therapies targeting metabolism may work best as preventive treatments rather than as treatments for advanced disease.
The findings are significant because they identify cardiolipin depletion as a possible early warning sign of heart damage. Future research may determine whether measuring cardiolipin or related molecules could help identify patients who are at risk before symptoms appear.
The study also highlights the complexity of metabolism. Earlier research from the same laboratory found that reducing the activity of these enzymes could help decrease fat accumulation in the liver.
In contrast, removing them in the heart produced harmful effects. This demonstrates that different organs can respond very differently to changes in metabolism.
According to the researchers, the goal should not be simply to increase or decrease fat burning. Instead, the heart appears to need flexibility and balance. Too little fat metabolism may be problematic, but too much can also cause harm.
In analyzing the study, one of its greatest strengths is the detailed explanation it provides for how excessive fat burning damages heart cells. The research moves beyond simple observations and identifies a specific pathway involving linoleic acid, cardiolipin, and mitochondrial dysfunction.
Because the experiments were conducted in mice, it remains uncertain whether the same process occurs in human heart disease. However, the findings fit well with existing knowledge about mitochondrial health and heart failure.
If future studies confirm the results in patients, cardiolipin could become an important target for new treatments and early detection strategies. The work also offers valuable insights into heart disease associated with obesity, diabetes, and chronic metabolic overload, conditions that continue to become more common worldwide.
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The study was published in the Journal of Clinical Investigation.
