Excess Fat Disrupts Heart Cell's Energy System

A University of Iowa study has identified how excess fat in the heart, a common feature in diabetes and obesity, can harm the cells' essential ability to produce energy. Researchers believe the mechanism may contribute to the two- to five-fold increased risk of heart failure in people with diabetes.

Typical mitochondrial network (green) in two human cells. Image credit: Simon Troeder/Wikipedia (CC BY 4.0)

The heart is the most energy-hungry organ in the body. Just like a combustion engine burning fuel to power the pistons, healthy heart cells consume fuel molecules to create the necessary energy to keep the heart pumping. This essential energy production takes place inside mitochondria, the self-contained "powerplant" organelles inside cells.

Although mitochondria in a healthy heart primarily use fatty acids as fuel, they can easily adapt to use other fuel molecules as needed, including glucose, lactate, and ketone bodies. Diabetes, however, reduces the heart muscle's metabolic adaptability and causes heart cells to overuse fat as a metabolic fuel.

The study found that this cardiac lipid overload leads to numerous small, misshapen mitochondria that don't produce energy as efficiently as normal mitochondria. Previous research has suggested that problems with mitochondrial energy production may play a role in heart failure associated with diabetes.

The team used genetically modified mice that mimic the increased fatty acid uptake (lipid overload) that characterizes diabetes to investigate the consequences of cardiac lipid overload on mitochondria.

In the mouse model, lipid uptake to heart is doubled. This modest increase resulted in mitochondria that became thinner and more twisted than mitochondria in healthy heart cells.

These structural changes (almost like a noodle snaking through the heart) lead to an appearance of mitochondrial fragmentation when imaged by conventional electron microscopy.

Prolonged lipid overload leads to increased levels of damaging substances called reactive oxygen species (ROS). The excess ROS disrupts the mitochondrial network by altering the activity of several important proteins that help control the size and shape of mitochondria.

Removing the excess ROS restored normal-looking mitochondria, which worked properly, despite the lipid overload.

Surprisingly, using the same approach to remove ROS in normal heart cells led to mitochondria that were four times as large as normal, suggesting that ROS levels are inversely proportional to mitochondria size.

The findings suggest that cardiac lipid overload disrupts normal mitochondrial structure, which may impair energy production and compromise heart function. (Tasnim News Agency)

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