Understanding how the body burns fat is fundamental to grasping a wide array of metabolic functions, including body temperature regulation, weight management, energy levels, and more. Researchers have now identified a novel molecular “switch” that governs fat burning in mice. The findings of this study have been published in the journal Nature.
This research, conducted by a team of scientists from McGill University in Canada, focuses on brown adipose tissue, often referred to as brown fat. Brown fat is present in the body in smaller quantities compared to white adipose tissue. While white fat primarily serves as an energy store and is associated with excess weight and obesity, the main role of brown fat is to burn calories to generate heat.
It was recently discovered that brown fat produces heat through not one, but two distinct mechanisms: a long-established process involving the protein UCP1, and a more recently identified process known as the futile creatine cycle.
Until now, it remained unclear how this futile creatine cycle was initiated. Therefore, pinpointing the mechanism that controls it is crucial for improving health across several domains.
“For the first time, we’ve been able to pinpoint how an alternative heat-generating pathway, independent of the classic system, is activated,” explains biochemist Lawrence Kazak from McGill University. “This paves the way for understanding how various energy-expending systems work in concert to maintain optimal body temperature.”
This breakthrough resulted from a detailed examination of the brown adipose tissue of mice exposed to cold conditions, and the various chemical substances that accumulated within it.
These chemical substances were then tested on an enzyme known to play a critical role in the futile creatine cycle: tissue-nonspecific alkaline phosphatase (TNAP).
The researchers discovered that glycerol, a component of some fat molecules, could activate TNAP. Advanced 3D mapping of the enzyme revealed the precise manner in which this occurs: glycerol binds to a specific cavity within TNAP, which the researchers have termed the “glycerol pocket.”
To validate their findings, the team investigated a rare bone disorder linked to low levels of TNAP, known as hypophosphatasia. In this condition, bones fail to calcify properly, rendering them soft and weak.
They analyzed genetic data from approximately 500,000 individuals from the UK Biobank and established a correlation between mutations in the glycerol pocket and reduced bone density and diminished TNAP activity, providing further evidence that TNAP functions as a vital molecular regulator.
“This discovery,” states Mark MacKenzie, a cell biologist at McGill University, “opens doors to a new type of therapeutic approach. By enhancing TNAP enzyme activity through its glycerol pocket using naturally occurring or synthetic bioactive compounds, it could potentially augment the enzyme’s beneficial effects in patients, helping to restore insufficient bone mineralization to healthy levels.”
While it is premature to discuss specific treatments, identifying how this heat-producing pathway in brown fat is activated represents a significant advance in disease management.
Currently, enzyme replacement therapy is used to treat hypophosphatasia, but it necessitates three injections per week. The researchers hope their work may lead to the development of more easily administered medications; drug candidates are already undergoing evaluation.
And although the connection to bone health might be more direct here, this also has implications for combating obesity and diabetes, conditions where energy expenditure plays a critical role.
Previous studies have linked the futile creatine cycle to obesity in mice, though it’s important to note that these rodents possess more brown fat relative to their body size than humans do.
Future research may explore TNAP’s role in these conditions, but for now, we have new insights into a critical energy-burning mechanism: two pathways that operate in parallel yet function independently.
“Our work not only expands the conceptual framework of energy-dissipating pathways but also offers opportunities for structure-based design of TNAP activators, presenting a targeted alternative to enzyme replacement therapy for skeletal disorders,” the researchers write. “The broader implications may extend far beyond adipose and bone tissues.”
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