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Researchers at Northwestern University developed an experimental RNA therapy that induces white fat to burn calories through thermogenesis. When combined with the GLP-1 drug semaglutide in mouse experiments, the dual treatment amplified weight and fat loss while significantly preserving lean muscle mass, according to a study published on September 21, 2026.
While GLP-1 receptor agonists like semaglutide—found in medications such as Wegovy and Ozempic—have transformed modern obesity care by suppressing appetite and reducing body weight, they carry a notable physiological drawback. Patients frequently shed lean muscle mass alongside fat, and when they discontinue treatment, the weight they typically regain returns primarily as fat. A team of scientists led by Dr. Joseph Bass at the Northwestern University Feinberg School of Medicine set out to address this metabolic hurdle by targeting the body’s internal fat storage mechanisms.
Reprogramming Fat Cells With Targeted RNA Therapy
The experimental approach focuses on a biological pivot point: converting energy-storing white fat into energy-consuming beige fat. Beige fat is a specialized type of adipose tissue that burns energy through heat-generating processes known as thermogenesis. To unlock this process, the researchers engineered a short strand of RNA designed to silence a gene called ZFP423, which normally acts as a metabolic brake preventing white fat from transforming into calorie-burning beige tissue.
The foundational scientific inquiry originated years prior from a question regarding why eating identical calorie counts at different times of day alters weight gain. Chelsea Hepler, then a researcher in the Bass lab and now at the University of Michigan, identified a connection between the body’s internal clock and fat beiging. That work drew upon earlier findings by Rana Gupta at Duke University, who pinpointed how ZFP423 functions as a brake in the adipocyte transformation process. Partnering with Ionis Pharmaceuticals, the Northwestern team successfully built an RNA-based drug candidate to release that biological brake.
Combination Trial Results in Mice and Metabolic Improvements
Initial testing examined the RNA therapy administered alone to mice maintained on standard and high-fat diets. The treatment improved glucose tolerance and reduced body fat on high-fat diets without causing any accompanying decrease in lean mass. Buoyed by those outcomes, the investigators advanced to a combination trial pairing the RNA therapeutic with semaglutide.
The dual treatment yielded profound shifts in body composition compared with semaglutide administered on its own. Mice receiving both therapies experienced a lean mass reduction rate of just 5.5%, whereas animals treated exclusively with semaglutide suffered a 10% loss in lean mass. Furthermore, final fat mass measurements at the conclusion of the treatment period showed that combination therapy mice retained roughly 4 grams of body fat compared to nearly 8 grams for the semaglutide-only group.
Broader Scientific Landscape and Path Toward Human Trials
The Northwestern discovery arrives alongside parallel investigations seeking to protect muscle integrity during periods of intensive weight loss. Researchers at the University of California, Davis, and the Arc Institute have explored companion compounds such as prostaglandin dehydrogenase inhibitors (PGDHIs)—including an experimental agent designated as MF-300—which enhance muscle repair and stem cell proliferation following injury during semaglutide treatment. While PGDHIs target regenerative muscle capacity after damage, the Northwestern RNA therapy directly alters systemic energy expenditure by revving up thermogenesis in adipose depots.
Moving forward, the Northwestern research team is testing similar RNA therapies in human cells. Northwestern University has filed a provisional patent application listing Bass and first author Anneke Thorne as inventors. The study, detailed in the Proceedings of the National Academy of Sciences, establishes a preliminary genetic framework that could eventually redefine how clinicians manage the dual challenge of eliminating fat while defending lean tissue during metabolic therapies.