Researchers at McGill University have identified a molecular trigger that activates an alternative energy-burning system in brown fat, a discovery that could reshape how doctors treat bone disease.
The findings, published in Nature, center on brown fat's role in heat generation. Unlike white fat that stores calories, brown fat burns them to warm the body. Scientists knew brown fat relied on two separate pathways for this process, but the mechanism activating the second pathway remained unknown until now.
Lawrence Kazak's team found that when the body encounters cold, it breaks down stored fat and releases a molecule called glycerol. This glycerol binds to an enzyme called TNAP at a specific location the researchers call the glycerol pocket. That binding flips the switch on the alternative heat-producing system, known as the futile creatine cycle.
Kazak, an associate professor in the Department of Biochemistry, described the moment of clarity: "This is the first time we've identified how an alternative heat-producing pathway is activated, independent of the classic system."
The bone connection that changes everything
While the brown fat findings alone represent a significant advance in metabolism research, the real clinical payoff could come from bone health. The TNAP enzyme that acts as the glycerol pocket gatekeeper already plays a crucial role in bone mineralization, the process that builds and maintains skeletal strength.
Mutations that cripple TNAP activity cause hypophosphatasia, a rare genetic disorder nicknamed "soft bones." Patients face chronic fractures, persistent pain, and structural skeletal abnormalities. The condition appears with elevated frequency in parts of Canada, particularly Quebec and Manitoba.
By studying how TNAP mutations affect brown fat cells in the laboratory, the McGill researchers made an unexpected connection: the same molecular switch controlling energy-burning fat also directly influences the cells responsible for hardening and mineralizing bone tissue.
Marc McKee, a professor in the Faculty of Dental Medicine and the Faculty of Medicine and Health Sciences, grasped the implications immediately. "This finding opens the door to a new kind of treatment, where increasing the activity of the TNAP enzyme through its glycerol pocket by natural or synthetic bioactive compounds could potentially boost the beneficial actions of the enzyme in patients, to help restore deficient bone mineralization to healthy levels."
The breakthrough builds on earlier work by McKee and collaborator José-Luis Millán of the Sanford Burnham Prebys Medical Discovery Institute. Their previous research produced the first enzyme replacement therapy specifically designed for hypophosphatasia patients with defective TNAP.
The team has already identified dozens of potential drug candidates worthy of further investigation. Rather than simply replacing missing enzyme activity, these compounds could work by amplifying what little TNAP function remains, offering patients a more refined therapeutic option.
The study involved researchers from Queen Mary University of London, Northeastern University, and the Maine Health Institute for Research. Funding came from the Canadian Institutes of Health Research, the Natural Sciences and Engineering Research Council of Canada, and Quebec's health research fund.
Author Jessica Williams: "This is the kind of serendipitous discovery that makes biomedical research so compelling, where understanding heat generation in fat cells unexpectedly illuminates the path to treating childhood bone disease."
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