Depot- and Sex Specific Effects of the PTN/RPTPβ/ζ Axis on White Adipose Tissue Browning and Inflammatory Remodelling in Diet-Induced Obesity
This study demonstrates that genetic deletion of pleiotrophin protects against diet-induced obesity and adipose tissue dysfunction by promoting browning and reducing inflammation, whereas pharmacological inhibition of its receptor RPTPβ/ζ with MY10 exacerbates these metabolic defects in a sex- and depot-dependent manner.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Obesity is more than just a matter of weight; it is a state where the body's fat storage system becomes overwhelmed and begins to malfunction. When people or animals consume more energy than they need, fat cells grow larger and stretch beyond their comfortable limits. This expansion triggers a chronic, low-level inflammation that spreads through the body, disrupting how the body handles sugar and fuel. This condition, often called metabolic syndrome, is linked to serious health issues like type 2 diabetes and heart disease. Within the body, fat is not stored in just one uniform way. There are two main types of fat storage areas: subcutaneous fat, which sits just under the skin and generally acts as a safe buffer for excess energy, and visceral fat, which surrounds the internal organs and is much more likely to cause inflammation and metabolic trouble. Scientists have long known that the body's ability to switch between storing fat and burning it for heat is a key factor in staying healthy, but the specific molecular signals that control this switch remain a mystery.
A team of researchers at Universidad San Pablo-CEU in Spain set out to investigate one such signal: a protein called pleiotrophin. This protein is usually active during early development but is mostly quiet in adult bodies, except when the body is trying to repair tissue or grow new blood vessels. The researchers wanted to know if this protein plays a role in how fat tissue reacts to a diet high in fat, and if the answer differs between males and females. To find out, they used two different approaches. First, they studied mice that had been genetically engineered to lack the gene for pleiotrophin entirely. Second, they treated normal mice with a drug called MY10. This drug works by blocking a specific receptor on fat cells, effectively mimicking the signal that pleiotrophin would normally send. By comparing these two groups against normal mice on both standard and high-fat diets, the team could see exactly how this signaling pathway influences fat growth, inflammation, and the body's ability to burn energy.
The results revealed a clear and protective role for the absence of pleiotrophin. Mice that lacked the protein gained significantly less weight when fed a high-fat diet compared to their normal counterparts, even though they ate the same amount of food. Their fat tissue did not expand as wildly, and their fat cells remained smaller. More importantly, the fat tissue in these mice showed signs of becoming more like brown fat, a type of fat that burns energy to generate heat rather than storing it. This "browning" effect was accompanied by a rise in body temperature, suggesting these mice were burning more calories. The tissue also showed less scarring, known as fibrosis, and far fewer signs of inflammation. The immune cells that typically swarm into fat tissue during obesity were less numerous, and the tissue produced more of the chemical signals that calm inflammation rather than those that fuel it. These benefits were seen in both male and female mice, though the specific patterns of fat storage and inflammation varied between the sexes and between the fat under the skin versus the fat around the organs.
In a striking contrast, the mice treated with the drug MY10 showed the opposite effects. By blocking the receptor that pleiotrophin normally activates, the drug essentially forced the fat cells to behave as if they were receiving a constant signal to store fat and ignore the need to burn it. These mice gained more weight and accumulated more fat than the untreated mice, especially when fed a high-fat diet. Their fat cells grew larger, the tissue became more scarred, and the inflammation worsened. The drug suppressed the markers of heat production and made the fat tissue more prone to the damaging inflammation that leads to metabolic disease. This confirmed that the pathway involving pleiotrophin and its receptor acts as a switch: when the signal is absent, the body resists obesity and inflammation; when the signal is artificially boosted or mimicked, the body becomes more susceptible to the harmful effects of a high-fat diet.
The study also highlighted that the body does not respond to these signals in a uniform way. The effects depended heavily on where the fat was located and whether the animal was male or female. For instance, the subcutaneous fat under the skin showed a stronger tendency to become inflamed in response to the drug in male mice, while female mice showed a more balanced response that was only fully triggered when combined with a high-fat diet. Similarly, the visceral fat around the organs was generally more prone to inflammation and scarring than the fat under the skin. These findings suggest that any future treatments targeting this pathway would need to be carefully tailored to the specific type of fat and the sex of the patient. The researchers concluded that the pleiotrophin signaling axis is a context-dependent regulator of how fat tissue remodels itself during obesity. While removing this signal protects the body, blocking the receptor to mimic the signal makes the situation worse, indicating that the natural absence of this protein in adult fat tissue might be a crucial defense mechanism against metabolic disease.
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