A modern lifestyle often implies dietary habits that can have far-reaching consequences for human health. One of the key risk factors in this context is a high-fat diet, which not only leads to weight gain but also triggers a series of complex metabolic disorders at the cellular level. These disorders can significantly increase the risk of developing type 2 diabetes, cardiovascular diseases, and other chronic conditions that today represent a global health challenge.

At the cellular level, exposure to high fat intake initiates hundreds of changes. Recent research, such as that conducted at the Massachusetts Institute of Technology (MIT), has focused on mapping these changes, with particular emphasis on the dysregulation of metabolic enzymes directly linked to weight gain. This detailed analysis revealed how a high-fat diet affects hundreds of enzymes crucial for the metabolism of sugars, lipids, and proteins. The consequences of these disorders include increased insulin resistance, a condition in which the body's cells respond less effectively to insulin, and the accumulation of harmful molecules known as reactive oxygen species (ROS), which can cause oxidative stress and cell damage.

Interestingly, these effects were more pronounced in male subjects in experiments conducted on mice, suggesting possible sex differences in the response to metabolic stress induced by inadequate nutrition. The research team from MIT also showed that most of these harmful changes can be reversed if mice are given an antioxidant along with a high-fat diet. "Under conditions of metabolic stress, enzymes can be affected in a way that produces a more harmful state than the one that initially existed," explains Tigist Tamir, a former postdoctoral fellow at MIT and lead author of the study, who published her findings in the prestigious journal Molecular Cell. "What we showed with the antioxidant study is that you can bring them to a different state that is less dysfunctional." Forest White, a professor of biological engineering at MIT and senior author of the paper, adds that this research provides fundamental insights into the control of metabolic pathways.

Metabolic Networks and the Role of Phosphorylation

Professor White's laboratory had previously established that a high-fat diet prompts cells to activate many of the same signaling pathways associated with chronic stress. In the new study, researchers wanted to investigate in more detail the role of enzyme phosphorylation in these responses. Phosphorylation, the process of adding a phosphate group to an enzyme molecule, is a key mechanism by which cells regulate enzyme activity – they can turn them on or off. This process, controlled by enzymes called kinases, allows cells to adapt quickly to environmental changes by fine-tuning the activity of existing enzymes within the cell. Many enzymes involved in metabolism, i.e., the conversion of food into the building blocks of key molecules such as proteins, lipids, and nucleic acids, are subject to phosphorylation.

The researchers began their analysis by searching databases of human enzymes that can be phosphorylated, focusing on those involved in metabolism. They discovered that many of these metabolic enzymes belong to the oxidoreductase class, which are responsible for transferring electrons from one molecule to another. Such enzymes are essential for key metabolic reactions such as glycolysis – the breakdown of glucose into a smaller molecule called pyruvate, which is a fundamental process for energy production in the cell. Among the hundreds of identified enzymes are IDH1, which participates in the breakdown of sugars to generate energy, and AKR1C1, required for fatty acid metabolism. The researchers also found that many phosphorylated enzymes are important for managing reactive oxygen species. Although ROS are necessary for many cellular functions in small amounts, their excessive accumulation in the cell can be harmful and lead to oxidative damage.

Phosphorylation of these enzymes can make them more or less active, while they work together to respond to food intake. Most of the metabolic enzymes identified in this study are phosphorylated at sites located in regions of the enzyme important for binding to the molecules they act on (substrates) or for forming dimers – pairs of proteins that join together to form a functional enzyme. "Tigist Tamir's work has categorically shown the importance of phosphorylation in controlling flux through metabolic networks. This is fundamental knowledge arising from this systematic study she conducted, and it is something that is not classically recorded in biochemistry textbooks," White points out.

Imbalance as a Consequence of a High-Fat Diet

To investigate these effects in an animal model, the researchers compared two groups of mice: one received a high-fat diet, while the other consumed a normal, balanced diet. The results showed that, overall, the phosphorylation of metabolic enzymes in mice on a high-fat diet led to a dysfunctional state in which the cells were in redox imbalance. This means that their cells produced more reactive oxygen species than they could neutralize, leading to a condition known as oxidative stress. These mice also became overweight and developed insulin resistance, a prediabetic state.

"In the context of a continued high-fat diet, what we see is a gradual shift away from redox homeostasis towards a state that more closely resembles disease," White explains. This imbalance, where the production of harmful molecules outweighs the body's ability to remove them, is considered one of the key mechanisms by which a high-fat diet contributes to the development of chronic diseases.

Sex Differences in Metabolic Response

One of the intriguing findings of the study is that the negative effects of a high-fat diet were significantly more pronounced in male mice compared to females. Female mice showed a better ability to compensate for the high fat content in their diet by activating pathways involved in fat processing and its use for other metabolic needs. It appears that the female organism possesses more robust mechanisms for coping with increased lipid intake, which may include more efficient fat storage or faster fatty acid oxidation.

"One of the things we learned is that the overall systemic effect of these phosphorylation events led to, especially in males, an increased imbalance in redox homeostasis. They exhibited much more stress and many more phenotypes of metabolic dysfunction compared to females," says Tamir. These sex differences raise new questions about how hormonal status and genetic predispositions might influence individual susceptibility to a high-fat diet and the development of related diseases. Understanding these differences could be key to developing personalized dietary recommendations and therapies.

Antioxidant Therapy as a Potential Solution

The researchers also found that if mice on a high-fat diet were given an antioxidant called BHA (butylated hydroxyanisole), many of these harmful effects were reversed. These mice showed a significant reduction in weight gain and did not become prediabetic, unlike other mice fed the same diet without the antioxidant supplement. It appears that antioxidant treatment restores cells to a more balanced state, with a reduced number of reactive oxygen species. Additionally, metabolic enzymes showed a systemic "rewiring" and an altered phosphorylation state in these mice, indicating profound changes in cellular regulation.

"They experience a lot of metabolic dysfunction, but if you simultaneously apply something that counteracts it, then they have enough reserve to maintain some kind of normality," Tamir explains. "The study suggests that something biochemical is happening in the cells that puts them into a different state – not a normal state, but a different state where now, at the tissue and organismal level, the mice are healthier." This finding is particularly important because it suggests that interventions aimed at reducing oxidative stress can have a beneficial effect on metabolic health even in the presence of unfavorable dietary habits.

In her new laboratory at the University of North Carolina, Tamir now plans to further investigate whether antioxidant treatment can be an effective way to prevent or treat obesity-related metabolic dysfunction, and what the optimal timing for such treatment would be. Future research could also focus on identifying other antioxidant compounds, including those of natural origin, that might have similar or even more potent effects. Understanding exactly how antioxidants modulate enzyme phosphorylation and cellular signaling pathways could open doors to new therapeutic strategies for combating the obesity epidemic and its related diseases that affect millions of people worldwide.

Source: Massachusetts Institute of Technology