Our fat cells, or adipocytes, do much more than simply store excess weight. They serve as an important energy reserve for the body. Inside each adipocyte, fat is stored in the form of lipid droplets, which can be used when the body needs energy, such as between meals. To release this stored energy, the body uses a protein called HSL, which acts like a switch. When energy levels drop, hormones like adrenaline activate HSL, prompting it to release fat that is then delivered to various organs.

The Role of HSL and the Unexpected Consequences of Its Absence

One might assume that without HSL, fat would accumulate in the body as if access to energy reserves were lost. However, studies on mice and humans with mutations in the HSL gene have shown the opposite: the absence of this protein does not lead to excess fat or obesity. In fact, such individuals experience a loss of fat mass—a condition known as lipodystrophy. Although obesity and lipodystrophy seem like opposites, both problems are linked to dysfunctional fat cells and can result in metabolic disorders and cardiovascular diseases.

New Discoveries About HSL Function

To understand this unusual behavior, a team led by Dominique Langin from the University of Toulouse carefully studied where exactly HSL is located inside adipocytes. It was previously known that this protein works on the surface of lipid droplets, helping to break down stored fat. However, research has shown that HSL is also present inside the nucleus of fat cells. In the nucleus, HSL can interact with other proteins and help maintain optimal fat tissue levels and adipocyte health.

Regulation of HSL Levels and Its Importance

Scientists also discovered that the level of nuclear HSL is tightly regulated. Adrenaline, which activates HSL on lipid droplets, also promotes its exit from the nucleus—a process that naturally occurs during fasting. At the same time, obese mice show elevated levels of HSL in the nucleus, indicating a disruption in the regulatory system.

Since the 1960s, HSL has been known as an enzyme that mobilizes fat. Now it is clear that it also plays a crucial role in the nucleus of adipocytes, helping to maintain the health of fat tissue. This additional function explains why the absence of HSL leads to lipodystrophy and opens new perspectives on metabolic disorders such as obesity and related health issues.

The Relevance of This Research

This discovery comes at a critically important time: in France, every second adult is overweight or obese, and worldwide, there are about two and a half billion such people. Obesity increases the risk of developing various diseases, including diabetes and cardiovascular problems, and often reduces overall quality of life. Continuing scientific research is essential for improving prevention and supporting patients.